HIPPARCHOSHIPPARCHOS The Hellenic Astronomical Society Newsletter Volume 2, Issue 1
Society News Astronomy News Venus Express Greece & ESA Chaotic Sculpting of the Solar System Skinakas micro-variability observations of BL Lac objects Relativistic AGN Jets Ματιές στο Σύμπαν των Carolyn Collins Petersen και John C. Brandt
Μόλις κυκλοφόρησε!
224 έγχρωμες σελίδες Διαστάσεις: 24,5 X 28,5 cm Πολυτελής, δερματόδετη έκδοση με χρυσοτυπία Λιανική τιμή: 43,89 € *
“Αυτό που είναι ακατάληπτο σχετικά με το σύμπαν είναι ότι θα έπρεπε να είναι πέρα για πέρα καταληπτό” Albert Einstein
όλις κυκλοφόρησε από τις εκδόσεις «ΠΛΑΝΗΤΑΡΙΟ παραίτητο για όσους επιθυμούν να κατανοήσουν και να Θεσσαλονίκης» το φημισμένο βιβλίο “VISIONS εκτιμήσουν το σύμπαν, αυτό το βιβλίο συμπληρώνει την Μ OF THE COSMOS” (Cambridge University Press), Α επιτυχία του προηγούμενου έργου των συγγραφέων, μεταφρασμένο στα ελληνικά, με τίτλο «ΜΑΤΙΕΣ ΣΤΟ ΣΥΜΠΑΝ». Αυτό “Hubble Vision”, που έγινε διεθνές best seller και κέρδισε επαίνους το εντυπωσιακά εικονογραφημένο βιβλίο είναι ένας κατανοητός από όλο τον κόσμο. οδηγός για την αστρονομική εξερεύνηση, μέσα από τα μάτια των τηλεσκοπίων. Περιλαμβάνοντας τις πιο εκπληκτικές εικόνες που Περιεχόμενα: 1. Μάτια στραμμένα στον ουρανό, 2. Τηλεσκόπια: ελήφθησαν από τα μεγαλύτερα αστεροσκοπεία και από διαστημικές Χρονομηχανές πολλαπλών συχνοτήτων, 3. Πλανήτες σε ένα pixel, αποστολές, παρουσιάζει ένα θαυμάσιο πορτρέτο της ομορφιάς του 4. Οι ζωές των αστέρων, 5. Γαλαξίες: Ιστορίες αστρικών πόλεων, σύμπαντος. Το συνοδευτικό κείμενο είναι ένας προσιτός οδηγός στην 6. Το σύμπαν στο παρελθόν και στο μέλλον, 7. Αστρονομική επιστήμη που κρύβεται πίσω από τις εικόνες, με σαφείς επεξηγήσεις παρατήρηση: Η επόμενη γενιά. όλων των κύριων αστρονομικών θεμάτων. *Στις τιμές περιλαμβάνεται Φ.Π.Α.. Δεν περιλαμβάνονται έξοδα απ οστολής.
Μια πολυτελής έκδοση, μια άριστη επιλογή δώρου!
ÔÇËÅÓÊÏÐÉÁ - ÅÊÐÁÉÄÅÕÔÉÊÁ ÌÅÓÁ - ÅÊÄÏÓÅÉÓ ΄Εκθεση, πληροφορίες, παραγγελίες, Πολυτεχνείου 45 (ËáäÜäéêá), 4ος όροφ., Èåóóáëïíßêç, δωρεάν αποστολή διαφημιστικού υλικού: Τηλ.: 2310/533 902, 541 826, FAX: 2310/550 672 e-mail: [email protected] www.astronomy.gr HIPPARCHOS | Volume 2, Issue 1 3 Contents Contents
SALT : First Light ...... 8 1000th Comet ...... 8 World Year of Physics 2005 ...... 9 Astronomy Books...... 21 Cover Story: Since March 2005 Greece is the16th full ESA Member State. This FEATURES HIPPARCHOSHIPPARCHOS new development provides unique op- Greece and ESA by K.. Tsinganos...... 10 portunities to Greek Astronomers to Hipparchos publishes review papers, participate in the exploration of space Research Production of … news and comments on topics of inter- (page 10). by M. Plionis...... 30 est to astronomers, including matters concerning members of the Hellenic REVIEWS Astronomical Society The chaotic “sculpturing” of the Solar Contents System, by K.. Tsiganis ...... 17 Skinakas micro-variability observations Editor: Kostas Kokkotas SOCIETY NEWS of BL Lac objects, by I. Papadakis...... 22 Message from the President…...... 3 Department of Physics, Relativistic AGN Jets Aristotle University of Thessaloniki, … and the Descartes Prize goes to Pulse by N. Vlahakis ...... 26 Thessaloniki 54124, Greece. and J.H. Seiradakis ...... 5 Tel: +30-2310-998185 CONFERENCES Fax: +30-2310-995384 Members in new positions...... 5 Close Binaries in the 21st Century Email: [email protected] by P. G. Niarchos...... 32 NEWS Venus Express ...... 6 ISHEPAC 2005 Editorial Advisors by T. Petkou...... 33 •V. Chamandaris (Crete) Worlds without End...... 7 •D. Hatzidimitriou (Crete) 7th International Conference of the Hel- LBT : First Light ...... 7 •M. Plionis (Athens) lenic Astronomical Society •J.H. Seiradakis (Thessaloniki) Comet 9P/Tempel I...... 8 by D. Hatzidimitriou ...... 34 •N.K. Stergioulas (Thessaloniki) •K. Tsiganos (Athens)
Printed by ZITI Publications • www.ziti.gr Message from the President
t is really a long time since we com- color. So, Manolis got the journal from I municated through this column and eight pages to sixteen and now Kos- Editorial help is badly many historical events for Hel.A.S. and tas from sixteen to thirty two! This is a needed! the Hellenic Astronomy in general hap- great progress just in the time interval pened in this interval. of a very few years only. It is tempting In relation to this journal of our Soci- to imagine that one or two more edi- Please volunteer, feed us with ety, it is already known to you that Kon- tor’s changes will lead “Hipparchos” to information related to your Insti- stantinos Kokkotas, Associate Professor a full fledged astronomical journal!. Ko- tute or with exciting news from of the Aristotelian University of Thes- stas went also forward by adding some your field of research saloniki and a member of the Council pages with ads in order to cover some of Hel.A.S. since the 2004 election, suc- of the cost the extra pages will bring. ceeded Dr. Manolis Plionis as the Editor At this point I take the opportunity to of “Hipparchos”. The first issue is now in express our sincere thanks to Manolis your hands. As you can see, Kostas de- Plionis, who was instrumental in elevat- cided and passed through the Council ing the “Hipparchos” status, adding color the change of the format of our journal, pages for the first time and publishing his as well as the increase of the number inspiring (and sometimes controversial) of pages to thirty two, some of them in editorials. Also, we thank him for not
HIPPARCHOS | Volume 2, Issue 1 3 Message from the President (continued)
dropping everything in Kostas lap, but and Thessaloniki (November 7th) with the Institute of Space and Applications staying and helping him with the details the Secretary of the Special ESA-Greece and Remote Sensing of the National Ob- during the transition time. Task Force, J. Pedro V. Poiares Baptista. servatory of Athens. Substitute members As for Hel.A.S. the great event of the On the other hand we all have to try are also Prof. J. Papamastorakis (Univer- past semester was the 7th Meeting of hard in order to persuade the Greek sity of Crete), Dr. Helen Dara (Research our Society in Lixouri, Kefallinia from Government to allocate some funds Center for Astronomy and Applied September 8th to 11th, 2005. It was re- for the ESA PRODEX program, which Mathematics of the Academy of Athens), ally a superb meeting in a marvellous is- can be of great importance for the par- Prof. S. Avgoloupis (University of Thessa- land. The head of the Local Organizing ticipation of our community to nation- loniki), Prof. M. Kafatos (George Mason Committee was Dr. Nikos Solomos, who ally funded payloads on space missions. University, U.S.A.), and Prof. A. Nindos did an excellent job and made us in the For this purpose, a letter composed by (University of Ioannina). There is a two Council of Hel.A.S. feel proud for our the Councils of the previous GNCA and year term for this Committee and we all meeting. There is an item in this issue by Hel.A.S. in a special joint meeting, has hope that our presence will benefit the Prof. Despina Hatzidimitriou with more been addressed to the General Secre- Greek astronomy. details of this meeting. Meanwhile, as you tary of Research and Technology, Prof. J. The new GNCA, in its first meet- have probably heard via our e-newslet- Tsoukalas. At the moment, however, the ing, named Prof. J. Seiradakis and Prof. ter, which is sent to all of you by our financial situation of the Ministry does N. Kylafis the official representatives in Secretary Dr. K. Tsinganos, Fr. George not allow the Secretary to put even the the OPTICON network and Dr. Nikos Anagnostopoulos, Associate Profes- minimum amount required. Another di- Prantzos, as the new Greek representa- sor at the Demokritos’ University of rection we should pay attention is train- tive to the Board of Astronomy and As- Thrace, has accepted the proposition of ing of young Greek scientists in space trophysics, since Prof. J. Ventura did not the Council to be the head of the Lo- science. In that direction, ESA has the want to continue the fine job he did in cal Organizing Committee for the next Young Graduate Trainee allowing young this Board. (8th), Conference of our Society, which men and women to obtain valuable ex- Meanwhile, January is almost here and, is to be held somewhere in Thrace. We perience at various ESA establishments as you know, in this month we shall start all feel very pleased, since the places of (see the article on Greece/ESA). At the looking for candidates for President and our Panhellenic Meetings keep spreading same time, Prof. K. Tsinganos has been members of the Council of our Society. all over Greece. trying hard to persuade the Foundation I hope that we shall have enough can- The big event in this year for Hellen- of Hellenic State Fellowships IKY to add didates of men and women wanted to ic Astronomy was Greece’s official par- new space-science oriented fellowships work harder than we did. ticipation in the European Space Agency in their predoctoral program in 2006 With my sincere wishes for a Happy (ESA). Although cooperation between and also start a new program for train- and Productive New Year ESA and the Hellenic National Space ing at ESA. Committee began in the early 1990s, it Finally, in the beginning of November, Paul G. Laskarides was only the 16th of March 2005 when Prof. I. Tsoukalas, named the new Na- the official announcement was made to tional Greek Committee for Astronomy, the ESA Council by the chairman of the the official body that advises the Greek ESA Council that Greece became the Government on issues of Astronomy. 16th ESA member state. Prof. K. Tsinga- The Chairman of the previous Commit- nos, the national delegate to the ESA’s tee, the term of which expired on Sep- Science Programme Committee gives tember 8th, 2005, Prof. J. Seiradakis, asked us a detailed account of the workings the General Secretary not to be named of ESA, its science programs and oppor- again Chairman, but he accepted to be tunities for Hellenic scientists, in a de- a member in the new Committee. The tailed article in this issue. Now the Hel- good thing for our Society is that the lenic delegates in the various boards and elected Chairman of the Hellenic Astro- councils of ESA work full time to assure nomical Society is the new Chairman of as many advantages for Greece as pos- this Committee. This is a great achieve- sible and to inform their colleagues in ment for our Society and we all hope Greece of the opportunities ESA offers that this is not a simple coincidence and to Greek space science, astronomy and that in the future our Chairman will be related industry. This was the reason that always present in this Committee. The we included a special session with prom- other members, except me and John, inent invited speakers during our 7th As- are the eminent Academician, Dr. Sta- tronomical Meeting in Kefallinia, And, al- matis Krimigis (as Vice-Chairman), Prof. so for the organization of two special N. Kylafis of the University of Crete and workshops in Athens (October 31st) Dr. J. Daglis, recently elected Director of
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 4 5 ...and the Descartes Prize goes to Pulse and J.H.Seiradakis
ohn H. Seiradakis is one of the The collaboration used the telescopes Jmain researchers of the PULSE at Jodrell Bank, Effelsberg, Westerbork collaboration which has been award- and Bologna. ed the Descartes Prize in Research. The pulsar network was initiated in
The Descartes Prizes have been cre- 1995 with a grant from the European SOCIETY NEWS ated by the European Commission with Union with the aim of creating a team the aim to encourage and reward excel- who could undertake large scale re- lence in Scientific and Technological col- search projects that were otherwise too laborative research and Communication big to be undertaken by the individual in any field of science. groups on their own. It was led by Prof. On December 2 , 2005 the winners re- R. Wielebinski of the MPIfR in Bonn. The ceived the prestigious Prize from the EU work of the Manchester group, the larg- Commissioner for Science and Research, est in the collaboration, is largely funded Janez Potocnik at a high level ceremony by the United Kingdom’s Particle Physics in London. This year the 1,000,000 Eu- and Astronomy Research Council. PULSE has enabled the setting up of ros Descartes Research Prize was shared The group’s crowning achievement has a unified data format for the easy ex- between five pan-European teams who been the discovery and follow-up obser- change of pulsar data and has designed achieved major scientific breakthroughs vations, made in collaboration with Aus- and performed unique experiments to in key European research areas. Among tralian astronomers, of the first known understand pulsars. Ten years on, the them was Professor John Seiradakis double pulsar. Studies of the double pul- teams are world leaders and their re- from the Aristotle University of sar have enabled them to make the most search achievements cover a wide field, Thessaloniki. The PULSE collabora- accurate confirmation yet of Albert Ein- not only in studying the extreme phys- tion, awarded the Descartes Prize for stein’s general theory of relativity - the ics of the pulsars themselves, but also in demonstrating the impact of European theory of gravity which supplemented using them as probes of the interstel- pulsar science on modern physics. that of Isaac Newton. “Rarely does a sin- lar medium through which their sig- Members of the PULSE collabora- gle class of object lend itself to high-preci- nals pass. tion are between the pulsar groups at sion experiments in so many domains of Professor Lyne underlines the impor- the University of Manchester’s Jodrell modern and fundamental physics”, enthus- tance of the collaboration: “Our work in- Bank Observatory, the Max Planck In- es Dr Michael Kramer of the University creases mankind’s knowledge of some of stitute for Radioastronomy in Germany, of Manchester. the fundamental laws that govern the uni- ASTRON in the Netherlands, the INAF The importance of the collabora- verse. These results are not only of interest Astronomical Observatory of Cagliari in tion was emphasized by Professor John to today’s scientific professionals. They also Italy and the Aristotle University of Seiradakis of the Aristotle University help to interest young people in astronomy, Thessaloniki in Greece. of Thessaloniki: “The bringing together of physics and basic research, forming an im- The success of PULSE was possi- groups across Europe has enabled us to ben- portant foundation for a society increasingly ble because of the unique position of efit from collaborative instrumentation and based on science and technology.” Europe having the largest number of software effort, the sharing of expertise and 100m-class radiotelescopes required to training opportunities and the co-ordination of Congratulations John observe the weak signals from pulsars. observing programmes.” Members in new positions
Dr. Ioannis A. Daglis was recently select- (the other two being the Astronomy ted to them. ed by a special committee as the new Working Group (AWG) and the Funda- Dr. Vassilios Chamandaris has been Director of the Institute for Space Ap- mental Physics Advisory Group (FPAG)). recently appointed as the new Editor plications & Remote Sensing of the Na- These advisory groups act as mediators of the European Astronomical Society tional Observatory of Athens. The Direc- between the scientific community and Newsletter. Vasilis is replacing Dr. Mary tor position has a 5-years term. ESA. The three advisory groups are Kontizas who served for many years as Dr. Ioannis A. Daglis has been invited each composed of ten to fifteen scien- the Editor of the Newsletter. to become a member of ESA’s Solar Sys- tists with expertise in the specific disci- Prof. Stamatis Krimitzis has recent- tem Working Group (SSWG) for a pe- pline covered by the group. The groups ly become member of the Academy of riod of three years (2006 to 2008). SS- meet at the request of the Director of Athens. WG is one of the three scientific adviso- the Scientific Programme and issue rec- ry groups for ESA’s Science Programme ommendations on the matters submit-
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 4 5 Venus Express en route to probe the planet’s hidden mysteries
n the 9th of November 2005, the O European spacecraft Venus Ex- press lift-off from the Baikonur Cosmo- drome in Kazahkstan and was successful- ly placed into a trajectory that will take it on its journey from Earth towards its destination of the planet Venus, which it will reach next April. An initial Fre- gat upper-stage ignition took place nine minutes into the flight, manoeuvring the spacecraft into a low-earth parking orbit. A second firing, one hour and 22 minutes later, boosted the spacecraft to pursue its interplanetary trajectory. The 1240 kg mass spacecraft Venus Express is cur- rently distancing itself from Earth at full speed, heading on its five-month, 350 mil- lion kilometre journey inside our Solar System. Contact with Venus Express was established by ESA’s European Space Op- erations Centre (ESOC) at Darmstadt, Germany approximately two hours af- The Venus Express spacecraft ter lift-off. The spacecraft has correct- ly oriented itself in relation to the sun To resist this greater gravitational pull, ter environment, notably by entirely re- and has deployed its solar arrays. All on- the spacecraft will have to ignite its main designing the thermal insulation. board systems are operating perfectly engine for 53 minutes in order to achieve Whereas Mars Express sought to and the orbiter is communicating with 1.3 km/se cond deceleration and place it- retain heat to enable its electronics to the Earth via its low-gain antenna while self into a highly elliptical orbit around the function properly, Venus Express will in in a few days, it will establish communica- planet. Most of its 570 kg of propellant contrast be aiming for maximum heat tions using its high-gain antenna. will be used for this manoeuvre. dissipation in order to stay cool. Venus Express will eventually manoeu- A second engine firing will be neces- The solar arrays on Venus Express vre itself into orbit around Venus in or- sary in order to reach final operational have been completely redesigned. They der to perform a detailed study of the orbit: a polar elliptical orbit with 12-hour are shorter and are interspersed with structure, chemistry and dynamics of crossings. This will enable the probe to aluminium strips to help reject some so- the planet’s atmosphere, which is char- make approaches to within 250 km of lar flux to protect the spacecraft from acterised by extremely high tempera- the planet’s surface and withdraw to dis- temperatures topping 250 °C. tures, very high atmospheric pressure, tances of up to 66 000 km, so as to carry It has even been necessary to pro- a huge ‘greenhouse effect’ and as-yet in- out close-up observations and also get tect the rear of the solar arrays – which explicable ‘super-rotation’ which means an overall perspective. normally remain in shadow – in order that it speeds around the planet in just to counter heat from solar radiation re- four days. Twin sister of Mars Express flected by the planet’s atmosphere. The European spacecraft will also be Venus Express largely re-uses the ar- the first orbiter to probe the planet’s chitecture developed for Mars Express. An atmosphere of mystery surface while exploiting the ‘visibility This has reduced manufacturing cycles Following on from the twenty or so windows’ recently discovered in the in- and halved the mission cost, while still American and Soviet missions to the frared waveband. targeting the same scientific goals. Final- planet carried out since 1962, Venus Ex- ly approved in late 2002, Venus Express press will endeavour to answer many of Full speed ahead for Venus was thereby developed fast, indeed in the questions raised by previous mis- When making its closest approach, Ve- record time, to be ready for its 2005 sions but so far left unanswered. nus Express will face far tougher condi- launch window. It will focus on the characteristics of tions than those encountered by Mars However, Venusian environmental con- the atmosphere, its circulation, structure Express on nearing the Red Planet. For ditions are very different to those en- and composition in relation to altitude, while Venus’s size is indeed similar to that countered around Mars. Solar flux is four and its interactions with the planet’s sur- of Earth, its mass is 7.6 times that of Mars, times higher and it has been necessary to face and with the solar wind at altitude. with gravitational attraction to match. adapt the spacecraft design to this hot- To perform these studies, it has seven Continued in page 33
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 6 7 Worlds without End
ot one but three new large and are around the size of Pluto or larg- axis, and rotating with a four hour pe- Nbodies have been recently dis- er. So far, the names Santa, Eas terbunny riod — astonishingly fast. It even has a covered beyond Neptune. Together and Xena are as informal as they sound, moon, inevitably known as Rudolph. they are changing the way that as- the IAU knows them as 2003EL61, The third new object, named be- tronomers understand the earlier “005FY9 and 2003UB313 res pectively. cause it was discovered in the spring of and present solar system. The sizes of these bodies are not this year, appears to have a methane sur- This three bodies were discovered yet well known, but estimates based on face making it the such Kuiper Belt ob- using the 48-inch Samuel Oschin Tele- their orbits and reflectivity suggest ob- ject. scope at the Palomar Observatory by jects that are possibly bigger than Pluto, The team hopes to get better esti- a team of astronomers from California Xena is probably similar to Pluto with a mates of their size by compatring their Institute of Technology, the Gemini Ob- surface covered in methane ice, leading optical appearences, which gives a lower servatory and Yale University lead by to suggestions that it should be consid- limit on size, with the infrared signature Mike Brown of Caltech. ered the tenth planet. obtained from Spitzer Space Telescope These new bodies are all part of the Santa is a cigar-shaped body, about to set an upper limit (Astronomy & Geo- Kuiper Belt, orbiting beyond Neptune, the diameter of Pluto along its longer physics, October 2005)
Large Binocular Telescope (LBT): First Light
he Large Binocular Telescope The LBT’s first light images were tak- a state-of-the-art camera known as the T (LBT) partners in USA, Italy and en on 12 October 2005. The target was Large Binocular Camera (LBC), which is Germany announced that they achieved an edge-on spiral galaxy (type Sb) in the mounted high above the primary mirror “First Light” on Oct. 12, 2005. Excep- constellation of Andromeda known as at the telescope’s prime focus. Designed tional images were obtained with one NGC891. This galaxy lies at a distance by the Italian partners in the project, the of the telescope’s two primary mirrors of 24 million lys. NGC891 is of particular LBC acts like a superb digital camera. Its in place and are being released on http: interest because the galaxy-wide burst of large array of CCD detectors is fed by //www.lbto.org. star formation inferred from X-ray emis- a sophisticated six-lens optical system. This milestone marks the dawn of a sion is stirring up the gas and dust in its Scientists can obtain very deep images new era in observing the Universe. Up- disk, resulting in filaments of obscuring over a large field of view, which is im- on completion the LBT will peer deeper dust extending vertically for hundreds portant since the processes of star for- into space than ever before, and with ten of light years. mation and faint galaxy evolution can be times the clarity of the Hubble Space Tel- The images were captured through observed with unmatched efficiency. escope. With unparalleled observational capability, astronomers will be able to view planets in distant solar systems, and detect and measure objects dating back to the beginning of time. Located on Mount Graham in south- eastern Arizona, the $120 million (USD) LBT is a marvel of modern technology. It uses two massive 8.4m diameter primary mirrors mounted side-by-side to produce a collecting area equivalent to an 11.8m circular aperture. Furthermore, the inter- ferometric combination of the light paths of the two primary mirrors will provide a resolution of a 22.8m telescope. The “honeycomb” structured primary mirrors are unique in that they are light- er in weight than conventional solid-glass mirrors. The second primary mirror was recently transported from the Univer- sity of Arizona to Mount Graham and has been installed. By fall 2006, the LBT will be fully operational with both of its The “First Light” image at LBT was obtained on the night of 12 October 2005 (UT). The tar- enormous eyes wide open. get was the NGC891 edge-on spiral galaxy (type Sb) in the constellation of Andromeda.
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 6 7 Comet Dusty Bunny: Tempel 1 proves to be a ball of fluff
n the course of the Space Age, plan- half of water. The body must be riddled unexpectedly complex history of chemi- I ets have gone from astronomical with voids. So much fine dust flew out cal reactions. Humans have always found objects—wandering specks in the night that it could not have been created by comets mysterious, and seeing them up sky—to geological ones: full-fledged the impact itself but rather must have al- close has done nothing to change that. worlds you could imagine yourself walk- ready been sitting on the surface. A lack (Scientific American, November 2005) ing on. In the 1990s asteroids made the of big pieces suggest that the comet has same transition. And now it is comets’ no outer crust. Along with other data, turn, as exemplified by July’s (deliberate) these results indicate that Tempel 1 is crash of the Deep Impact probe into the not a compacted snowball, as many had nucleus of Comet Tempel 1. In Septem- conjectured, but a loose, powdery fluff ber researchers announced a batch of ball—an agglomerate of primordial dust findings at an American Astronomical that came together at low speeds and Society meeting in Cambridge, England. gently clung like dust bunnies under a The impact threw up a cone of dusty bed. If other comets are like this, landing debris some 500 meters high; it ex- on one – as ESA’s Rosetta mission plans tended right from the surface, indicat- to do in 2014—could be tricky. Comet 9P/Tempel 1 was discovered on ing that the cometary material put up Despite its flimsiness, Tempel 1 has an April 3, 1867 by E.W.L. Tempel of Mar- no significant resistance to the projec- almost planetlike surface, covered with seille, France. The comet was then 9th tile. The flight path of debris particles re- what appear to be impact craters (the magnitude and calculations revealed that vealed the strength of the comet’s grav- first ever observed on a comet), cliffs, and has an orbital period of 5.5 years and a ity, hence its density—on average, about distinct layers. The composition hints at an perihelion distance of roughly 1.5 AUs.
First light for SALT
frica’s giant eye on the sky - the capabilities of this new and powerful ob- A South African Large Telescope - servatory. It is hoped that access to such released its first light images on Sep- an instrument in Africa will boost astro- tember 1st . nomical research among local scientists. The largest telescope in the south- Its global position between comparable ern hemisphere, SALT, is now at com- telescopes in Chile and Australia will al- missioning stage in its superb dark skies low continuous observation of objects skies location on the edge of the Ka- such as supernovae in the southern lahari desert. The telescope has a mir- hemisphere. The project has already ful- The South African Large Telescope (SALT), ror 10m by 11m made up of 91 hexago- filled one of its aims, however. It was in- near Sutherland, South Africa. The cali- bration tower (left) contains an inter- nal segments. Instruments, including the tended as a showcase for South African ferometer for alignment of 91 panels of Prime Focus Imaging Spectrograph, will scientists and engineers, and has been the 10-meter-wide segmented mirror. The be installed and tested over the coming completed on time and to the original dome roof rotates for viewing, and has an weeks of commissioning, building up the $20million budget. 11-meter hexagonal openable panel.
SOHO’s 1000th comet found by a high-school teacher
he 999th and 1000th comet dis- wife Rosy and my son Kevin to compensate T covered from SOHO (Solar and for the time that I have taken from them Heliospheric Observatory) data, Tony to search for SOHO comets” Many comet Sacramento, a high-school teacher from discoveries have been by amateurs using San Costantino di Briatico, Calabria, It- SOHO images on the internet, and SO- aly, found two comets in the same SO- HO comet hunters come from all over HO image. He is an astrophysics gradu- the world. ate of Bologna University, and said : “I SOHO spacecraft is history’s greatest am very happy for this special experience comet hunter, it has accounted for ap- that is possible thanks to the SOHO satel- proximately one-half of all comet discov- lite and NASA-ESA collaboration. I want to eries with computed orbits in the history dedicate the SOHO 1000th comet to my of astronomy.
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 8 9 WORLD YEAR OF PHYSICS 2005
he General Assembly of the United Na- Winner of 1999, presented a public in Thessaloniki T tions, the Unesco and the International lecture on “Spacetime, Particles and Union of Pure and Applied Physics have de- Forces, 100 Years After Einstein”. The clared the year 2005 as the World Year lecture was attended by more than of Physics. The international celebration 800 people in the main lecture hall of coincides with the 100th anniversary of the Aristotle University of Thessalo- the “miraculous year” 1905, when Albert niki on 11/10/05. Einstein initiated on the the greatest • Seminar: “The Historic Voyager 1 and scientific revolutions by publishing five 2 Missions and the Crossing of the papers containing three ground braking Heliosphere’s Termination Shock” , discoveries. He proved the particle na- Prof. S. Krimigis (Academy of Athens, ture of light, he calculated the true di- Johns Hopkins University), 11/11/05. mensions of molecules and explained their random walk and he formulated • Seminar: “Quantum Mechanis is… the special theory of relativity, which Here”, S. Trachanas (Fundation of Re- lead to the most famous equation of all search and Technology - Hellas), 29/ representatives of the Union of Hel- times, E=mc2. For this reason, the year 11/05. lenic Physicists and representatives of 2005 is also celebrated as the Einstein private enterprises, 9/12/05. • Two-day Workshop: “Research in the Year 2005. Physics Department” with presenta- • Public Lecture: “The Constancy of The Department of Physics of the Ar- tions by all research groups in the De- the Speed of Light and Curved Space- istotle University of Thessaloniki (AUTh) partment, 6-7/12/05. times”, Prof. G. Schaefer (U. of Jena), participated in the international celebra- co-organized with the Goethe Insti- tion of the World Year of Physics and Ein- • Workshop: “Physics and the Other tute of Thessaloniki, 15/12/2005 stein Year by organizing a large number Sciences: AUTh 2005-2015”, with • Workshop: “Cosmology and Gravi- of events, which aimed at making more participation of the Heads and mem- tational Physics”, international scien- accessible to the academic community bers of several other Departments of tific workshop on new developments and the general public the important AUTh and of CERTH, 8/12/05. in Relativistic Cosmology and Gravity, discoveries of the 20th century, which • Workshop: “Physics and Technology: with participation of invited speakers was characterized as the century of Greece 2005-2015”, with participa- and speakers from AUTh, 15-16/12/05. Physics. These discoveries did not only tion of Heads of other Physics De- change our view of the Universe, but al- partments in Greece, of the research More information on the above events so brought significant improvements to center “Democritus”, of the National can be found on the web page of the the quality of everyday life. Observatory in Athens, representa- Physics Department: The events organized by the Depart- http://www.physics.auth.gr/ tives of GSRT and of the National ment of Physics included: Council on Research and Technology, Nick Stergioulas • Seminar “Neutrino and Astrophysics”, Prof. G. Gounaris (AUTh), 30/3/05. • Public Lecture: “The Life and Death of Stars”, Prof. N. Kylafis (U. of Crete), 19/4/05 • “Open Doors” two-day event, 30/9- 1/10/2005, during which dozens of school classes and the general public visited all of the research and teach- ing laboratories of the Department of Physics. In parallel, an open discussion about “Physics Jobs in the 21st Cen- tury” was organized, during which a one-hour movie with this theme was shown (an internal production of the Department of Physics made specially for the World Year of Physics). • Main Celebration Event of the World Year of Physics, in which Prof. Gerard Professor Gerard `t Hooft lecturing in the main lecture hall of the Aristotle University of `t Hooft (U. of Utrecht), Nobel Prize Thessaloniki
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 8 9 The Hellenic participation in the European Space Agency (ESA) by Kanaris Tsinganos, University of Athens, Delegate to the ESA/SPC
1. Greece and ESA formally applied to join ESA. Subsequent negotiations were followed in the sum- ESA was formed in 1975 and has cur- mer of 2004 by the signing of an agree- rently 17 Member States: Austria, Bel- ment on accession to the ESA Conven- gium, Denmark, Finland, France, Ger- tion by Jean-Jacques Dordain, ESA Direc- many, Greece, Ireland, Italy, Luxembourg, tor General on behalf of ESA, and by D. the Netherlands, Norway, Portugal, Spain, Sioufas, the Greek Minister for Devel- Sweden, Switzerland and the United opment and the Secretary General for Kingdom. Canada, Hungary and the Research and Technology Prof. I. Tsouka- Czech Republic also participate in some las, on behalf of the Greek Government. projects under cooperation agreements. Greece already participates in ESA’s tel- As it can be seen from this list, not all ecommunication and technology activi- member countries of the European Un- ties, and the Global Monitoring for Envi- ion are members of ESA and not all ESA ronment and Security Initiative. Follow- develop satellite-based technologies Member States are members of the EU. ing the ratification of the ESA Conven- and services, and to promote European ESA is an entirely independent organi- tion by the Greek Parliament, Greece industries. ESA also works closely with zation although it maintains close ties has now become ESA’s 16th Member space organizations outside Europe to with the EU through an ESA/EU Frame- State. The official announcement was share the benefits of space with the work Agreement. The two organizations made to the ESA Council on the 16th of whole of mankind. share a joint European strategy for space March 2005 by the chairman of the ESA ESA’s headquarters are in Paris where and together are developing a European Council. Now, with the deposition of its policies and programmes are decided space policy. instrument of ratification of the Conven- upon. In addition, ESA also has several Cooperation between ESA and the tion for the establishment of ESA with centers in a number of European coun- Hellenic National Space Committee the French Government on 9 March tries, each of which has different respon- began in the early 1990s and in 1994 2005, Greece become the 16th full ESA sibilities. Greece signed its first cooperation Member State. • ESTEC, the European Space Research agreement with ESA. This led to regular ESA’s job is to draw up the European and Technology Centre, the design hub exchange of information, the award of space programme and carry it through. for most ESA spacecraft and technolo- fellowships, joint symposia, mutual ac- The Agency’s projects are designed to gy development, situated in Noordwijk, cess to databases and laboratories, and find out more about the Earth, its im- the Netherlands. studies on joint projects in fields of mu- mediate space environment, the solar • ESOC, the European Space Opera- tual interest. In September 2003 Greece system and the Universe, as well as to tions Centre, responsible for control- ling ESA satellites in orbit situated in Darmstadt, Germany. • EAC, the European Astronauts Cen- tre, training astronauts for future mis- sions situated in Cologne, Germany. • ESRIN, the ESA Centre for Earth Ob- servation, based in Frascati, near Rome in Italy. Its responsibilities include col- lecting, storing and distributing Earth Observation satellite data to ESA’s partners, and acting as the Agency’s in- formation technology centre In addition, ESA has liaison offices in Belgium, the United States and Rus- sia; a launch base in French Guiana; and ground and tracking stations in various areas of the world. In February 2005 the total number of staff working for ESA numbered approximately 1907. These The “First Light” image at LBT was obtained on the night of 12 October 2005 (UT). The tar- highly qualified people come from all get was the NGC891 edge-on spiral galaxy (type Sb) in the constellation of Andromeda. Member States and include scientists,
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 10 11 engineers, information technology spe- rector General. Thus, ESA’s activities are cialists and administrative personnel. divided into nine Directorates, each head- Presently there are only a very few ed by a Director who reports directly to staff members of Greek origin work- the Director General. These are: ing in ESA. • Science Programmes • Earth Observation Pro- grammes • Technical and Quality Manage- HIPPARCOS ment • Launcher Programmes to the Science Programme Committee (SPC). Each Member State is also rep- • Human Spaceflight, Micro- resented on the SPC with one vote, re- gravity and Exploration Pro- gardless of its size or financial contribu- GIOTTO/HALLEY grammes tion. The Hellenic Delegate in the SPC is ESA’s mandatory activities (space • Resources Management the author of this article with Advisers science programmes and the general Dr. V. Tritakis and Prof. Th. Karakostas. • External Relations budget) are funded by a financial con- tribution from all the Agency’s Member • EU and Industrial Programmes States, calculated in accordance with • Operations and Infrastructure each country’s gross national product. The Greek contribution without ad- 2. The Science Programme of justments is presently 1.57%. In addi- tion, ESA conducts a number of option- ESA al programmes. Individual countries de- The Science Programme is the on- cide in which optional programme they ly mandatory element of the ESA pro- wish to participate and the amount they gramme, and is therefore both a flagship wish to contribute. and a symbol for the Agency. It enhances ISO ESA’s total budget for 2005 is 2977 European capability in space science and million EURO. The agency operates on applications, builds European industrial the basis of geographical return, i.e. it in- technical capacity, and brings together (a) Early ESA missions vests in each Member State, through in- European national space programmes. In the early period of ESA, 1968-1985, dustrial contracts for space programmes, ESA staff and contractors assemble and some 15 European spacecraft were an amount more or less equivalent to test new ESA scientific spacecraft at the launched on scientific missions to study each country’s contribution. The man- European Space Research and Technol- a vast array of disciplines: datory contribution from all member ogy Centre (ESTEC), Noordwijk (The • Cosmic rays and solar X-rays (ESRO 1B states is 371 million Euros, i.e., every Netherlands). These will then be oper- & 2B) - 1 Oct 1969 and 17 May 1968 citizen of an ESA Member State pays ated from ESA’s European Space Op- • Ionosphere and aurora (ESRO 1A) - 3 about one Euro per year. Thus the to- erations Centre (ESOC) at Darmstadt Oct 1968 tal European per capita investment in in Germany. At ESA headquarters, the • Solar wind (HEOS-1) - 5 Dec 1968 space is rather small. On average, every Director of Science oversees policy and citizen of an ESA Member State pays, in the overall shape of the science pro- • Polar magnetosphere (HEOS-2) - 31 taxes for a total expenditure on space, gramme. ESA Science staff are also de- Jan 1972 about the same as the price of a cinema ployed elsewhere, for example in Spain, • UV astronomy (TD-1) - 11 March 1972 ticket. In the United States, investment Germany, and the United States. • Ionosphere and solar particles (ESRO- in civilian space activities is almost four The present Director of Science (Pro- 4) - Nov 1972 times as much. grammes) is Prof. David Southwood. The • Gamma ray astronomy (COS-B) - 9 The ESA Council is the Agency’s gov- scientific community is represented by Aug 1975 erning body and provides the basic policy three working groups : The Solar System • Magnetosphere (GEOS-1 & 2) - 20 Aug guidelines within which the Agency de- Working Group, the Astronomy Working 1977 and 14 Jul 1978 velops the European space programme. Group and the Fundamental Physics Ad- Each Member State is represented on visory Group. Recently Dr. I. Daglis was • Magnetosphere and sun-Earth relations the Council and has one vote, regardless invited to become a member of ESA’s (ISEE-2) - 23 Oct 1977 of its size or financial contribution. The Solar System Working Group for a pe- • Ultraviolet astronomy (IUE) - 26 Jan Agency is headed by a Director General riod of three years (2006 to 2008). The 1978 who is elected by the Council every four recommendations of these three groups • Cosmic x-rays (Exosat) - 26 May 1983 years. The present Director General of are finalized by the Space Science Advi- ESA is Jean-Jacques Dordain. sory Committee, currently chaired by More recently, the ESA Giotto probe Each individual research sector has its Prof. G. Bignami, which submits the sci- (launched in 1985) became the first own Directorate that reports to the Di- entific proposals for their final approval spacecraft ever to meet two comets,
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 10 11 Cassini/Huygens (1997) also in col- HST Cassini/Huygens laboration with NASA is already in the Saturnian system. It will orbit Saturn for four years, making an extensive survey of the ringed planet and its moons. The ESA Huygens probe landed in January 2005 on the surface of Titan, Saturn’s largest moon. Data from Cassini and Huygens are offering us clues about how life be- gan on Earth. XMM-Newton (1999), the biggest science satellite ever built in Europe
solar wind affects our planet in three di- mensions. The solar wind can damage communications satellites and power Halley (1986) and Grigg-Skjellerup, stations on Earth. The original operation (1992). Between 1989 (when it was life-time of the Cluster mission ran from launched) and 1993 the Hipparcos sat- February 2001 to December 2005. How- ellite collected data on the positions and ever, in February 2005, ESA approved a movements of a million stars with the mission extension from December 2005 respective catalogues published in 1997. to December 2009. The infrared space observatory (ISO) Mars Express (2003), Venus Express was launched in 1995 and concluded Ulysses (2005) and SMART-1, (2003) are the its operation in 1998, giving the first de- tailed view and spectra of infrared ce- with its telescope mirrors are the most lestial objects. sensitive ever developed in the world, is detecting more X-ray sources than (b) ESA missions in operation. any previous satellite and is helping to There are 15 ESA missions in opera- solve many cosmic mysteries of the vio- tion today. The Hubble Space Telescope lent Universe, from what happens in and (1990), a long-term, space-based ob- around black holes to the formation of servatory whose observations are car- galaxies in the early Universe. It is de- Newton XMM ried out in visible, infrared and ultra- signed and built to return data for at violet light. In many ways Hubble has least a decade. first missions to our neighbouring plan- revolutionised modern astronomy, not The second high-energy observatory ets and the moon. The SMART-1 mis- only by being an efficient tool for mak- is Integral (2002), observing a cosmos, sion in orbit around the Moon has had ing new discoveries, but also by driving its scientific lifetime extended by ingen- astronomical research in general. ious use of its solar-electric propulsion Ulysses(1990) developed in collabo- system (or ‘ion engine’). ration with NASA is the first mission to Finally, Rosetta, (2004) is the first mis- study the environment of space above sion ever to land on a comet and follow and below the poles of the Sun. Its data it in its orbit around the Sun. ESA’s Ro- have given scientists their first look at setta spacecraft will be the first to un- the variable effect that the Sun has on dertake the long-term exploration of a the space around it. SoHO comet at close quarters. It comprises a The solar observatory SoHO (1995) Cluster stationed 1.5 million kilometres away full of violent phenomena and extreme from the Earth, constantly watches the energy in the Á-rays. Sun, returning spectacular pictures and The mission Cluster (2000) is a col- data of the storms that rage across its lection of four spacecrafts flying in for- surface. SOHO’s studies range from the mation around Earth. They, in combina- Sun’s hot interior, through its visible sur- tion with the Double – Star (2003/2004) face and stormy atmosphere, and out to developed in collaboration with China, distant regions where the wind from the give us a stereoscopic view of the terres- Sun battles with a breeze of atoms com- trial magnetosphere and its interaction ing from among the stars. The SOHO with the solar wind and relay the most mission is a joint ESA/NASA project. detailed ever information about how the
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 12 13 large orbiter, which is designed to oper- Finally, in cooperation with NASA the For this new Cosmic Vision pro- ate for a decade at large distances from James Webb Space Telescope (2014) will gramme, the scientific community was the Sun, and a small lander. Each of these follow the legacy of the Hubble Space called upon to express its new ideas carries a large complement of scientific Telescope. In fundamental physics, LISA in April 2004 and did so by submitting experiments designed to complete the Pathfinder (2009) will test the technol- more than 150 such novel ideas. ESA’s most detailed study of a comet ever at- ogy of the following three LISA (2014) scientific advisory committees and tempted. After entering orbit around satellites which will be aiming at the de- working groups made a preliminary se- Comet 67P/Churyumov-Gerasimenko tection of the much awaited gravitation- lection of themes, which were discussed al waves. in a open Workshop in Paris in Septem- ber 2004 attended by about 400 mem- 3. The future science pro- bers of the scientific and industrial com- gram of ESA: Cosmic Vi- munities. After an iteration with the Sci- sion (2015-25) ence Programme Committee (SPC) and Space science is playing a prominent its national delegations, the finally select- role in Europe’s space programme. It ed themes are addressing the following has been the core of European co-op- 4 questions: Integral eration and success in space since the (a) What are the conditions for early 1960s. As ESA turns thirty years planet formation and the emer- in 2014, the spacecraft will release a old, it continues a tradition of innovative gence of life? small lander onto the icy nucleus, then thinking and long-term perspectives that spend the next two years orbiting the comet as it heads towards the Sun. On Planck the way to Comet Churyumov-Gerasi- menko, Rosetta will receive gravity as- sists from Earth and Mars, and fly past main belt asteroids. (c) ESA Missions under develop- ment Rosetta Today, several ESA missions are under development. They are going to further form the basis for ESA’s scientific pro- explore our Solar System, observe sev- gramme. The Horizon 2000 long-term eral interesting astrophysical objects and plan for space science, formulated 20 also test fundamental physical laws. Thus, years ago (1984), is almost completed. Its Venus Express (2005) is already head- successor, Horizon 2000+, approved ten ing towards Venus. BepiColombo (2015) years ago, comes now to fruition with a will explore the closer to the Sun planet wealth of scientific satellites and space From gas and dust to stars and Mercury, while the similar Solar Orbit- telescopes in orbit producing great re- planets: Map the birth of stars and er (2015) will approach our Sun several sults. In the first years of this new millen- planets by peering into the highly ob- solar radii to get a close up view of its nium, ESA is building its future in space scured cocoons where they form. hot corona. science based on a ‘Cosmic Vision’. This From exo-planets to biomarkers: In Astrophysics, Herschel (2007) is a is a way of looking ahead, building on a Search for planets around stars other grand infrared observatory following solid past, and working today to over- than the Sun, looking for biomarkers in the successful infrared space observa- come the scientific, intellectual and tech- their atmospheres, and image them. tory ISO while its twin Planck (2007) nological challenges of tomorrow. Life and habitability in the Solar system: Explore in situ the surface and Mars Express Herschel subsurface of the solid bodies in the so- lar Systems most likely to host-or have hosted-life. Explore the environmental conditions that makes life possible. Candidate Projects are a Near – In-
LISA Pathfinder
has been planned to study the cosmic background radiation following the suc- cessful WMAP. GAIA (2012) is power- ful astrometric satellite able to map one billion of stars in six dimensions and de- cipher the history of the entire Galaxy.
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 12 13 Explore the limits of contempo- rary physics: Use the stable and weight- less environment of space to search for tiny deviations from the standard model of fundamental interactions. The gravitational wave Universe: Make a key step toward detecting the gravitational radiation background gen- erated at the Big Bang. Matter under extreme condi- tions: Probe gravity theory in the very strong field environment of black holes and other compact objects, and the state of matter at supra-nuclear energies in ESA is designing missions to detect habit- neutron stars. able planets across a wide range of stellar Candidate Projects are a Fundamental types (Credits: ESA). Physics Explorer Series, Large-Aperture X-ray Observatory, Deep Space Gravity the very first gravitationally-bound struc- Probe, Gravitational Wave Cosmic Sur- tures that were assembled in the Uni- veyor, Space Detector for Ultra-High– verse-precursors to today’s galaxies, Energy Cosmic Rays. groups and clusters of galaxies-and trace their evolution to the current epoch. (d) How did the Universe originate The evolving violent Universe: and what is it made of? Trace the formation and evolution of The early Universe: Define the physi- the supermassive black holes at galaxy cal processes that led to the inflationary centres - in relation to galaxy and star First colour view of Titan’s surface (Cred- phase in the early Universe, during which formation – and the life cycles in matter its: ESA). a drastic expansion supposedly took in the Universe along its history. place. Investigate the nature and origin Candidate Projects are a Large-Ap- frared Nulling Interferometer, Mars of the Dark Energy that is accelerating erture X-ray Observatory, Wide-Field Landers and Mars Sample Return, Far- the expansion of the Universe. Optical-Infrared Imager, All-sky Cos- Infrared Observatory, Solar Polar Or- The Universe taking shape: Find mic Microwave Background Polarisation biter, Terrestrial Planet Astrometric Surveyor, Europa Landers, Large Optical Interferometer. (b) How does the Solar System work? From the Sun to the edge of the Solar System: Study the plasma and magnetic field environment around the Earth and around Jupiter, over the Sun’s poles, and out to the Heliopause where the solar wind meets the interstellar medium. The giant planets and their en- vironments: In situ studies of Jupiter, its atmosphere, internal structure and satellites Asteroids and other small bod- ies: Obtain direct laboratory informa- tion by analysing samples from a Near- Earth Object. Candidate Projects are an Earth Mag- netospheric Swarm, Solar Polar Orbiter, Jupiter Exploration Programme, Europa Lander, Orbiter and Jupiter probes, Near – Earth Object Sample Return, Interstel- lar Heliopause Probe. LISA will be the first space-based mission to attempt the detection of gravitational waves. (c) What are the fundamental These are ripples in space that are emitted by exotic objects such as black holes (Cred- physical laws of the Universe? its: ESA).
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 14 15 Within the Horizon 2000+ programme there is still time for Hellenic scientists to participate in the preparation of several space missions. Such examples are the Herschel/Planck Observatory (launch in 2007, with involvement in the data anal- ysis from one of its three instruments SPIRE, HIFI, PACS, for more information contact V. Charmandaris, Un. of Crete). The mission BepiColombo to the planet Mercury (launch in 2015, for more infor- mation contact I. Daglis NOA/ISARS), the astrometric satellite GAIA (launch 2011, for more information contact P. Niarchos or M. Kontizas, Un. of Athens), the mission Solar Orbiter (launch in 2015, for more information contact K. Tsinganos, Un. of Athens) and also the gravitational waves space interferometer LISA (launch 2014, The science program of ESA (Credits: ESA). for more information contact K. Kokko- tas, AUTH). Mapper, Far-Infrared Observatory, Gravi- Europe or when a second source would tational Wave Cosmic Surveyor, Gamma- be an asset), provide the resources to (c) Predoctoral ESA young graduate Ray Imaging Observatory . enable Greek industry/institutes to en- trainees (YGT) ter normal ESA procurement and finally 4. Opportunities for ESA re- ESA’s Young Graduate Trainee (YGT) foster the establishment of strong and programme(2) offers recently graduated lated science/technology long-term relations between Greek men and women, a one-year non-re- work for Hellenic researchers companies and well-established Euro- newable training contract designed to pean space firms. The deadline for the give valuable working experience and (a) The first Call for Ideas for Hel- submission is 06/01/2006. to prepare them for future employment lenic participation to ESA pro- (b) Involvement in future Space mis- in the space industry and/or research. grammes. Applicants should have just completed, sions within Horizon 2000+ The Accession Agreement of Greece or be in their final year, of a higher edu- and ESA specifies transitional meas- ures that will apply during a period of six years, starting from the date of ac- cession (i.e., from 2005 to 2010). The transitional measures aim at adapting Greece’s industry to the Agency re- quirements. An ESA-Greece Task Force was set-up in September 2005 which has a programmatic role and advises the Director General of ESA on the imple- mentation of the transitional measures. Representatives from both ESA and the Hellenic Republic compose this Task Force. In the frame of these transitional measures contracts will be placed with Greek firms, institutions and universities. For this purpose the ESA-Greece Task Force has issued a first Call for Ideas (1). The proposal which the Greek commu- nity is invited to submit is a relatively simple one with a suggested overall max- imum length of only 2-3 pages. The sub- mitted ideas should cover activities that have a future potential in the frame of ESA activities or programmes (no “sin- gle-shot” activities will be considered), address specific niche markets (no com- Overall view of the history of the Universe according to the Big Bang model petitive products available elsewhere in (Credits: ESA).
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 14 15 cation course typically at Masters level closely connected to space activities. In convince ESA to issue an announcement and probably in a technical or scientific the internal fellowship programme, fel- for the employment of Greek software discipline at a university or equivalent lows carry out their research topic un- engineers in the upcoming (2007) ESA institute. They should be fluent in either der the supervision of one or more ex- “cornerstone” Herschel/Planck ob- English or French. Contracts are for one perienced scientists or engineers, in one servatory (see Dec. 2005 issue of the year and non-renewable. ESA will pro- of ESA’s establishments. Interested candi- HelAS electronic newsletter). Similarly, vide a monthly salary. In 2003 the basic dates should submit the application form Hellenic participation is needed at the net salary for a single YGT ranged from that is available online. There is no spe- level of PI or Co-I in specific mission in- 1930 to 2333 Euros per month, depend- cific closing date and applications may be struments, or in the direct involvement ing on the establishment, including ex- submitted at any time during the year. In for the analysis of related observations, patriation allowance. Also, a monthly the external fellowship programme, the in the upcoming ESA programmes. Final- expatriation allowance for those not fellows work in a university, research in- ly, we should encourage Hellenic young resident in the country to which they stitute or laboratory on a research topic researchers to apply for the various ESA are assigned, plus an installation allow- related to the research activities of the related fellowships in order to get train- ance upon arrival, travel expenses at the Agency. The application should be sent ing and serve as links between ESA and beginning and end of the contract and directly to the relevant national delega- the academic, research, industrial and health cover under ESA’s Social Security tion, who will forward it to ESA, by 31 technological sectors of Greece. All in scheme. Towards the end of the train- March for the June selection and by 30 all, it remains to be seen if the adventure ing period, trainees are asked to submit September for the December selection. of the Hellenic scientific and technologi- a report on their activities and accom- cal community in European space activi- (e) IKY fellowships for Space Physics plishments achieved during the year. ties - something dated back thousands IKY will start in the year 2006 new of years in mythology with the story of (d) Postdoctoral ESA research fel- predoctoral fellowships for studies in the Daedalus and Icarus - will be fruitful and lowships area of Space Physics, within the known worth of our expectations. ESA’s postdoctoral research fellow- frame of fellowships in Astronomy, As- ship programmes(1) aim to offer young trophysics, Relativity, Physics, etc. (1) http://www.astro.auth.gr/elaset/esa/ (2) http://www.esa.int/SPECIALS/Careers_ scientists the possibility of carrying out 5. Epilogue at_ESA/ research in a variety of disciplines relat- (3) http://www.esa.int/SPECIALS/Careers_at_ ed to space science, space applications We hope that our scientific communi- ESA/SEM19DXO4HD or space technology. The Agency has an ty will be mobilized to take soon advan- internal and an external fellowship pro- tage of the Hellenic participation to the gramme, both for two years, with no Science programmes of ESA. The first possibility of an extension. ESA hosts ap- indication of such a mobilization will proximately 20 external and 30 internal be our response to the Call for Ideas. fellowships at any given time. Applicants Secondly, we need to pursue a direct in- must have recently attained their doctor- volvement in several ESA missions under ate or be close to successfully complet- development (Herschel/Planck, JWST, ing studies in space science, space ap- GAIA, BepiColombo, Solar Orbiter and plications or techniques, or other fields LISA). As an example, we succeeded to
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 16 17 The chaotic “sculpting” of the Solar System by Kleomenis Tsiganis, Depertment of Physics, University of Thessaloniki
ABSTRACT tion; this is why we usually refer to them orbits, and (ii) the scattered disc, with he orbits of the large celestial bodies as ice giants (see [6]). bodies on highly eccentric and inclined T in our Solar System are stable for very According to the theory described (w.r.t. the mid-plane of the system) or- long times, as can be shown by numerical above, giant planets form on circular bits. Several models have been proposed simulation. This gives the erroneous impres- and co-planar orbits in the mid-plane to explain the depletion of this external sion of perpetual stability of the system. It is of the disc, within 1-10 My (the typi- disc, mostly related to collisional grinding only when we study the orbital distribution cal lifetime of a circumstellar gas disc). (see [12] and references therein). How- of the numerous minor bodies in the Solar However, our Giant planets follow orbits ever, if we assume that, at those times, System that we discover the rich variety of with eccentricities e~5-10% and mutual the giant planets had already settled on complex dynamical processes that have in inclinations i~2-3 degrees. These values, their final orbits (with orbital radii at 5.2, fact shaped our system. During the last dec- although small compared to extra-solar 9.5, 19.2 and 30.1 AU), then the mass de- ade, enormous progress has been made, in planets[7], are by no means negligible. pletion and dynamical structure of the understanding the evolution of the system It has been shown that, during the gas- Kuiper belt cannot be explained. over the last ~3.9 Gy. However, it also be- dominated phase, the eccentricity of a came clear that, in order to unveil its behav- Jupiter-sized planet cannot grow be- iour during the first ~700 million years of its yond a few times 10-3, unless very “well- lifetime, we have to find convincing explana- tuned” conditions are met [8]-[9]. Thus, tions for observations that appear as details the current values of the planetary or- of its dynamical architecture. In the follow- bital elements are most likely the result ing we are going to show how the two best- of some physical process that took place known – and up to now unexplained – ob- after the gas was gone, when the system servations in the Solar System, namely (i) the consisted of the Sun, the giant planets heavily cratered surface of the Moon and (ii) and a debris disc of planetesimals, em- the elliptic (and not circular) motion of the bryos and dust, possibly extending up to planets, lead us to the discovery of the cha- >50 AU away from the Sun. otic sculpting of the Solar System [1]-[3]. (d) Terrestrial planets begun to form Figure 1: Compiled lunar data, show- ing the inferred rate of bombardment close to the Sun, by the process de- 1. Early stages of evolution of the Moon vs. time (from C. Koeberl’s scribed in (b) (see [5],[10]). web-site). The newly-born Sun was surrounded According to the minimum mass so- by a disc of (mainly) gas and dust. The lar nebula model (see [10]), the asteroid It was already suggested in the late 60’s sedimentation of dust grains in the mid- belt (2-4 AU) was ~1,000 times more [4] that Uranus and Neptune must have plane of the disc marked the beginning of massive, at the epoch of terrestrial plan- formed much closer to the Sun than are planetary formation. A review of planet et formation, than at present (~5x10- currently observed, in order for their 3 formation theories is beyond the scopes ME). Numerical simulations indeed formation time to be shorter than the of this paper. Hence, we will only briefly show that strong perturbations, exert- lifetime of the gas disc, and subsequently present the currently accepted scenario ed by the giant planets on embryos at (somehow) moved outwards. In the fol- for the formation of our Solar System. In ~2-4 AU, prohibited the formation of lowing we are going to show how the in- chronological order, the different forma- large bodies in this region [11]. Moreo- teraction of the giant planets with the ex- tion stages are: ver, embryos were scattering away plane- ternal disc forces the former to migrate. (a) Dust grains started to accumulate, tesimals so efficiently that the primordial Let us now describe an observational forming ~1 km-sized bodies, known as asteroid belt was depleted by a factor of “detail”, whose origin dates back to the planetesimals[4]. ~200. (keep in mind that we are a factor early phases of Solar System evolution. (b) Planetesimals accumulated to of ~5-10 short!). As can be seen during most nights of the form lunar-sized objects, called plan- In the meantime, a dynamically “cold” year, the surface of the Moon is covered etary embryos, which in turn collided and massive disc of planetesimals (~30- with large lava-filled basins and numer- with each other to form the solid cores 50 ME within a ~20-30 AU-wide ring) ex- ous small craters, which are the result of (~3-15 Earth masses, ME) of the Giant isted beyond the orbits of the ice giants; an intense bombardment of the Moon by planets (Jupiter, Saturn, Uranus and Nep- the progenitor of the Kuiper belt. Today’s small bodies. When the first lunar sam- tune) [4]-[5]. Kuiper belt is estimated to be nearly as ples were analyzed, things became more (c) Jupiter and Saturn evolved to gas massive as the asteroid belt. Moreover, it complex. The values of the sample ages giants, by accreting gas envelopes that has a two-component dynamical struc- of the large basins formed a tight clus- later on collapsed on the cores. Uranus ture (see [12]): (i) the classical belt, with tering around 3.9 Gy, suggesting a heavy and Neptune have a gas-poor composi- bodies on nearly co-planar and circular bombardment of the Moon ~600 My af-
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 16 17 the two bodies give zero net displace- ment, unless (i) the kick is so strong that the particle is ejected from the system on a hyperbolic orbit, in which case the planet moves inwards, or (ii) the particle encounters one of the inner planets. In the latter case, the particle escapes the influence of the outer planet, whose or- bital radius is slightly increased. The above scheme can be generalized for the four giant planets of the Solar Sys- tem. In this chain, the innermost planet (Jupiter) is far more massive than the out- ermost one. Numerical simulations [17] show that most disc particles approach Jupiter, after being “kicked“ by Neptune, Uranus and Saturn. Thus, after wandering around the inner Solar System for some time, and provided that they don’t hit a planet (or the Moon), they are ejected on hyperbolic orbits by Jupiter. Consequent- ly, Neptune, Uranus and Saturn move out- wards, while Jupiter moves inwards. Of course, the more massive planets (Jupi- ter and Saturn) are displaced much less than the ice giants; the orbital radii of the first two change by a few tenths of an AU, while the ones of the ice giants may change by several AU. A simulation of this process is shown in Fig. (2). Six snapshots of the evolution of the system are shown, in which the red points denote the four giant planets and the blue dots are disc particles. In this simulation a disc of 35 ME was used, Figure 2: Snapshots from an N-body simulation of the migration of the outer planets. All extending up to 30 AU. The planets were bodies are projected on the (a,e) plane, where a is the semi-major axis and e the eccen- tricity of the orbit. started within 20 AU from the Sun. As shown in the plots, the planets deplete ter its formation, with a duration of only discussion it is evident that the solution the disc within 100 My and reach sta- a few tens of Mys: the Late Heavy Bom- to this problem must be related to inter- ble orbits with approximately the same bardment (LHB [13]-[15], see Fig. 1). We action of the giant planets with the ex- values of semi-major axis as observed note that an alternative scenario sup- ternal, massive, planetesimals disc. today. The remnants of the disc have ports the continuous heavy bombard- an orbital distribution that is similar to ment of the Moon. Several theoretical 2. Planitesimal – the one of the current trans-neptunian models were proposed to explain the driven migration population. Indeed, as was first shown in LHB, but all of them turned out to vio- Let us go back to the beginning of the [18], planetesimal-driven migration can late some important observational con- gas-free era and assume that Uranus and explain the final semi-major axes of the straint (see related references in [3]). Neptune were formed closer to the Sun planetary orbits and the orbits of the From the dynamical point of view, the than they are today (say, within 20-25 AU) plutinos – Pluto and ~7% of Kuiper belt “continuous bombardment” theory, al- and the external disc extended up to 40- objects – which are trapped in a 2:3 or- though easier to understand, does not 50 AU. Fernandez & Ip [16] were the first bital resonance with Neptune. seem probable. If we take into account to point out that the exchange of angular There are, however, two major prob- the depletion of the asteroid belt dur- momentum between the planets and the lems with this “smooth” migration mod- ing terrestrial planet formation, we find disc particles would force the planets to el. First, migration ends too soon (~100 that there are not enough projectiles to migrate. Roughly speaking, when a disc My from the formation of the planets) to sustain the necessary mass flux on the particle approaches the outermost plan- explain the LHB. Second, the final values Moon for 600 My. This in turn means that et, it receives a “kick” that decreases (or of eccentricity and mutual inclination of we need to find (i) the source and (ii) increases) the semi-major axis of its or- the planets are almost zero. Note that, the dynamical mechanisms responsible bit. Consequently, the planet must move in the experiment shown in Fig. (2), we for the delay, onset and short duration outwards (or inwards) by a very small even “cheated”, by initially setting the of a “cataclysmic” LHB. From the above amount. Repeated encounters between planets on eccentric orbits. Their ec-
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 18 19 centricities were in fact damped dur- planets were packed within 15 AU ing migration, due to a well-known phe- from the Sun. We tested this hy- nomenon in galactic dynamics: the small pothesis by numerical integrations, particles exert dynamical friction on the in which we found that compact planets, circularising their orbits (see al- systems are indeed stable, provid- so [10]). Thus, some excitation mecha- ed that the interplanetary distances nism, not present in this model, must are not smaller than ~3 AU. have acted during planetary migration; An initially compact configura- otherwise the planets would end up on tion of the planets evolves in a qual- circular and co-planar orbits. itatively different way, with respect to an initially well-spread one. Dur- 3. Planetary excitation and the ing migration, a pair of planets will late heavy bombardment have to pass temporarily through a There are several unknown parame- first-order (i.e. the strongest pos- ters that enter a simulation of planet mi- sible) resonance, where the ratio of gration. The most important ones are (i) their orbital frequencies is nearly the initial conditions for the planets, and constant and equal to a fraction (ii) the total mass, surface density profile, of small integers, say 1:2 or 2:3. and outer edge of the disc. Recent results Repeated resonant conjunctions suggest that the mass of the disc was be- increase the eccentricity of both tween 35 and 50 ME, and its outer edge orbits. In a well-spread system the was located at ~30-35 AU. For a more ex- planets are far enough from each tended and more massive disc, Neptune other to avoid the relevant reso- would not stop at 30 AU (see [19])! nances. For example, if Jupiter is at Figure 4: (a) Evolution of the planetary orbits in There are no constraints a priori for 5.5 AU, its 1:2 resonance with Sat- a 1.2 Gy simulation. At ~880 My Jupiter and Sat- the initial orbital radii of the giant planets. urn is at 8.73 AU, as given by Ke- urn cross the 1:2 resonance and develop eccen- Up to now, the usual assumption was a pler’s 3rd law. Thus, given their rela- tric orbits. The planets engage in a short phase (~2 My) of mutual encounters, during which their well-spread planetary system, with Jupiter tive migration, the planets can nev- eccentricities and mutual inclinations grow. Disc- starting at ~5.5 AU and Neptune at ~23 er be in a 1:2 resonance, if Saturn particles are ejected throughout the Solar System AU. It is true that, if we assume the initial starts at a>8.73 AU. and 9x1021 g of comet material hit the Moon planetary orbits to be as eccentric as to- We did several numerical ex- within 50 My. Asteroids contribute to the LHB by day, a more “compact” system would tend periments, changing the initial con- almost the same amount (~3-8 x1021 g). The sys- to be strongly unstable. However, for ini- figuration of the planets, in order tem slowly relaxes, due to dynamical friction, and the planets achieve their final orbits. tially circular orbits, the system could be to study all possible resonance stable for billions of years, even if the crossings. Indeed we found that this mechanism always ex- the four giant planets had already gravi- cites the eccentricities of tationally eroded the inner part of the the respective pair of plan- massive disc. This implies a very low flux ets. However, we found that of disc particles, driving planet migration. the 1:2 resonance between Hence, for a realistic planets-disc configu- Jupiter and Saturn also has a ration, as suggested by the results shown dramatic effect on the whole in Fig. 3(a), planetary migration would system. Thus, we focused our have been so slow that the crossing of study on compact systems, the 1:2 Jupiter-Saturn resonance would in which Saturn was initially have been delayed by several hundreds of placed closer to Jupiter than My (Fig. 3b). Then, curiously enough, the their 1:2 resonance. resonance-crossing epoch could coincide Before proceeding with with the LHB epoch! these numerical experiments, After producing these encouraging we had to consider another results, we performed a series of ~50 important dynamical process. N-body simulations, in which we moni- A compact planetary system tored the evolution of the system, until strongly modifies the surface the depletion of the disc and the end of planetary migration (typically ~1 Gy). In Figure 3: (a) Dynamical lifetime of disc particles, in a typi- density profile of the disc. As each simulation the initial positions of cal compact system of planets (triangles). Only particles shown in Fig. 3(a), the dy- starting ~2 AU away from Neptune remain in the system namical lifetime of disc par- the planets were varied, with Saturn be- until the beginning of the gas-free era. (b) The time of reso- ticles in the interplanetary ing always set interior to the 1:2 reso- nance crossing for Jupiter and Saturn, as a function of the zone is smaller than the life- nance with Jupiter and the initial inter- inner edge of the disc. For an external disc of particles, as time of the gas disc. Thus, at planetary distances being set between suggested in panel (a), the onset of instability is delayed the beginning of the gas-free 2.5 and 6 AU. The disc was represented by hundreds of My. era, the compact system of by 1,000-10,000 equal-mass particles, its
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 18 19 total mass was varied between 35 and 50 ME, and its inner edge was set 1.5-2.5 AU away from the orbit of Neptune. In these runs, the resonance-crossing time varied from ~100 My to 1.2 Gy. The typical evolution of the planetary system in our runs is shown in Fig. 4(a), where the perihelion (q) and aphelion distances (Q) of each planet are given as functions of time. The difference Q- q is proportional to the eccentricity of the orbit. Figure 4(b) shows the cumula- tive mass flux of disc particles that hit the Moon, during the same time interval. As shown in the plot, planet migration is very slow for ~880 My, as a result of the small amount of disc particles on planet-cross- ing orbits. At this point Jupiter and Saturn cross their 1:2 resonance and their orbits become eccentric. The orbits of Uranus and Neptune are then strongly perturbed, due to the small interplanetary distanc- es. In fact their eccentricities grow so much that the orbits of the planets be- gin to cross, and the planets suffer close encounters with each other. The system is thus lead to a short period (~2 My) of chaotic frenzy, during which repeated two- or even three-body encounters in- crease the eccentricities and mutual incli- nations of the planetary orbits. In 1/3 of our runs, the instability grew so strong that one of the ice giants was ejected from the system, by encounter- ing Jupiter. However, in 2/3 of our runs Figure 5: Comparison between our “synthetic” final planetary systems and the real Solar (let us call them “successful runs”), the System data. The red symbols refer class-A runs, while the blue symbols refer to class-B planetary system eventually became runs. All final planetary systems are similar to the Solar System, but class-B runs match stable, due to the action of the massive amazingly well. disc; Uranus and Neptune were forced to penetrate the outer parts of the disc, ly observed. Our runs can be divided in the asteroid belt, by including in some where dynamical friction reduced their two classes: (i) runs in which only two- reference simulations 1,000 massless eccentricities and put an end to this body encounters among the ice giants asteroids, with an initial orbital distri- planetary billiards. At the same time, disc were recorded (class-A), and (ii) runs in bution as predicted in [11]. We found particles were forced to “fly” all over the which triple encounters between Saturn, that their orbits became unstable, due Solar System. As shown in Fig. 4(b), the Uranus and Neptune took place (class- to resonance sweeping: the continuous amount of comets hitting the Moon in- B). For each class we computed the mean displacement of resonances throughout creased abruptly at the resonance cross- and standard deviation of the final values the belt, as a result of the migration of ing epoch, and ~8.4x1021 g of mass ac- of (a,e,i) for all planets. As shown in Fig. Jupiter and Saturn. In fact, our asteroid creted on the Moon within 50 My. (5), both types of evolution produce sys- belt lost ~90% of its mass; we seem to The above numbers agree well with the tems, which are very similar to the Solar have found the missing depletion factor, time-delay, intensity (estimates give ~6 System. However, the triple-encounters discussed in the introduction. This proc- x1021 g of projectile mass [20]) and du- scenario seems to provide a much better ess supplies another 3-8 x1021 g of as- ration of the LHB. We emphasize that the match to Solar System data: the current- teroid-type “bombs” on the Moon. This same series of events occurred in all our ly observed values of (a,e,i) of all Giant result is consistent with recent geo- successful simulations, since the mecha- planets fall within one standard deviation chemical evidence, concerning the com- nisms responsible for the onset and sup- from the mean values of class-B runs. position of projectiles that formed the pression of the instability are both deter- Let us not forget that, in the beginning large lunar basins (see [14]-[15]). ministic and generic to the system. of the LHB, the inner Solar System con- At the end of each successful run, the tained an asteroid belt ~10 times more 4. Conclusions – Discussion four giant planets were found to follow massive than today. We simulated the ef- Our chaotic migration model naturally orbits, very similar to the ones current- fect of our chaotic migration model on predicts a cataclysmic bombardment of
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 20 21 the Moon, reproducing quite well cur- was the existence of Trojan asteroids; a oids who where ejected from all over the rent estimates of the time-delay, duration, group of bodies that nearly share the same main belt, by a size-independent mecha- intensity and projectile composition of the orbit as Jupiter, but lead or trail the planet nism. The most likely mechanism (at that bombardment. However, what is most by ~60 degrees in longitude. Up to now epoch) is resonance sweeping, due to important is that this model explains, there was no model explaining the orbital the late migration of the outer planets, for the first time, the orbital architec- distribution of Trojans, in particular their as Strom et al. concluded. ture of the outer Solar System. nearly homogeneous distribution of orbit- Although our model is certainly physi- al inclinations between 0 and 40 degrees. REFERENCES cally plausible, there is of course no guar- We performed a series of simulations, in [ 1] Tsiganis K. et al., 2005, Nature 435, 459. antee that these events actually took which we found that primordial Trojans [ 2] Morbidelli A. et al., 2005, Nature 435, 462. place. However, there are a number of were driven away from Jupiter’s co-orbital [ 3] Gomes R. et al., 2005, Nature 435, 466. points that strongly favour our model. zones, during the chaotic evolution phase [ 4] Safronov V.S. 1969, Moscow: Nauka To begin with, this model does not in- of the system. However, at the same time, [ 5] Chambers J.E. and Wetherill G.W., 1998, Ica- volve “exotic” perturbations (e.g. passing outer-disc particles were constantly flying rus 136, 204. stars or rogue planets), of the system. All through the co-orbital regions, temporar- [ 6] Pollack J.B. et al., 1996, Icarus 124, 62. mechanisms involved are generic to plan- ily replenishing them. As the planets were [7] http://cfa-www.harvard.edu/planets etary systems. The only critical assump- moving towards a stable configuration, [ 8] Papaloizou J.C.B. et al., 2001, A&A 366, 263. tion of our model is that Saturn was some of these particles got permanently [ 9] Goldreich P. & Sari R., 2003, ApJ 585, 1024. formed interior to the location of its 1:2 trapped in the Trojan region. We found a [10] Kokubo E. & Ida S., 2002, ApJ 581, 666. resonance with Jupiter (i.e. ~0.5 AU clos- total mass of trapped particles between [11] Petit J., et al. 2001, Icarus 153, 338. -6 -5 er to the Sun than usually assumed). 4x10 and 3x10 ME. Recent observations [12] Tsiganis K., 2005, in IAU Colloquium No 196 We find no contradiction between estimate the total mass of Trojans to be - Transits of Venus: New views of the Solar System -5 and the Galaxy”, D.W Kurtz and G.E. Bromage our model and observations. In fact we ~10 ME. Moreover, the orbital distribu- seem to explain more than we asked for. tion of our trapped Trojans was very simi- (eds), Cambridge University Press, p. 209. In particular: lar to the observed one. Hence, our model [13] Hartmann W.K. et al., 2000, In: Origin of the (a) At the LHB epoch, collisions is the first to explain the origin and orbital Earth and Moon (Canup R. & Richter K., eds), Un. among asteroids must have been so fre- distribution of Jupiter Trojans. of Arizona Press, p. 493. quent that a great number of fragment Recent results seem to provide solid [14] Kring D.A. & Cohen B.A., 2002, JGR 107, 4. clusters (called “families”) must have back-up to our model. Marchis et al. [23] [15] Tagle R., 2005, Lunar Planet. Sci. Conf. XXXVI, been formed. Yet, there are no families calculated the density of the binary Tro- abstr. 2008. known, with ages greater than 3.8 Gy jan Patroclus, finding an average bulk den- [16] Fernandez J.A. & Ip W., 1984, Icarus 58, 109. [21]. Our model takes care of this prob- sity of 0.8, a number much smaller than [17] Hahn J. & Malhotra R., 1999, AJ 117, 3041. lem, since the “shaking” of the asteroid any known asteroid and similar only to [18] Malhotra R., 1993, Nature 365, 819. belt during the chaotic phase is so strong, the ones found for distant Kuiper-belt [19] Gomes R. et al, 2004, Icarus 170, 492. that no compact family would survive. objects. This astonishing result supports [20] Levison H.F. et al., 2001, Icarus 151, 286. (b) According to our simulations, the our claim that Trojans and Kuiper-belt [21] Bottke W. et al., 2005, Icarus (in press). amount of water accreted by the Earth objects have, in fact, a common origin. [22] Morbidelli A. et al., 2000, Meteor. Plan. Sci. 35, 1309. during the LHB (i.e. comets) is ~8 x1022 Finally, analyzing the size distributions of [23] Marchis F. et al., 2005, AAS DPS Meeting ab- g, i.e. 6% of the ocean mass. Measure- projectiles responsible for both ‘LHB’ and stract #37, #14.07. ments of the heavy-to-normal (D/H) ra- ‘younger’ (age < 3.8 Gy) craters, Strom et [24] Strom R.G. et al, 2005, Science 309, 1847. tio of ocean water indeed suggest a 5% al. [24] found that the latter ones corre- upper bound for the cometary contribu- spond to Near Earth Asteroids, while the Dr. Tsiganis has been recently elected tion to the Earth’s water budget [22]. former ones to Main-belt asteroids. Thus Lecturer in the Department of Physics at (c) An important test for our model large ‘LHB’ craters were formed by aster- the Aristotle U. of Thessaloniki. ISHEPAC 2005 he 2nd International School of High and 6 foreign scientist (R. Woodard, P. who are in their first years of their Ph.D. T Energy Physics and Cosmology was West, V. Mukhanov, J. Peacock, K. Narain, studies. At the same time, the wide pro- organized in Heraklion, from the 4th of C. Angelantonj). The last two weeks of gram of the school together with the September to the 27th of October 2005. the school, the students have had the high level profile of the lectures attracts The school was attended by a total of 25 opportunity to attend the pedagogical the interest of many postgraduate stu- postgraduate students, 7 of which were lectures and research seminars of the dents from outside Greece. The De- from Greek Universities. The school pro- 1st Young Researchers Workshop of the partment of Physics at the University of gram included lectures in Quantum Field Research and Training Network (RTN) Crete intents to organize ISHEPAC on Theory, General Relativity and Gravita- “SUPERSTRINGS”, which was also or- a yearly basis, and to broaden its scope tion, Particle Phenomenology, String The- ganized by the University of Crete. to include, together with High Energy ory and Cosmology. A total of 13 lec- The aim of ISHEPAC is to cover the Physics and Cosmology, also Astropar- tures contributes, 7 of them Greek (K. teaching needs of Greek postgraduate ticle physics and related matters. Kokkotas, A. Lahanas, A. Petkou, K. Skend- student in the areas of High Energy Phys- Tassos Petkou eris, M.Spiropulu, K. Tamvakis, N. Tsamis) ics and Cosmology, in particular those University of Crete
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 20 21 Skinakas micro-variability observations of BL Lac objects by Iossif Papadakis, Department of Physics, University of Crete
1. Introduction stars”. For example, DuPuy et al. (1969) Stalin et al. (2005), who have studied the detected optical variations of the order micro-variability properties of radio and Lac objects (BL Lacs) consti- of 0.3 mag day-1 in BL Lac itself (i.e. the X-ray selected BL Lacs, EGRET and radio- BL tute a class of Active Galactic prototype for this class of active galax- core dominated blazars, respectively. Nuclei whose optical spectra usually do ies), while Racine (1970) reported “optical The observed flux variations in bla- not exhibit strong emission or absorp- fluctuations by 0.1 mag over a few hours” zars have been explained in a variety of tion lines. They show high polarization, from the same “strange” object. ways: shocks traveling down the jet (e.g. continuum variability at all wavelengths The intense, long term (i.e. on time Marscher 1996), changes in the Dop- at which they have been observed, from scales of days/months/years) optical vari- pler factor due to geometrical reasons X-rays to radio, and superluminal mo- ations of BL Lacs is well established, doc- (e.g. Dreissigacker & Camenzind 1996), tion of radio components. Together umented and studied in the last thirty and gravitational microlensing (e.g. Sch- with the flat-spectrum radio quasars years (see for example the work of Car- neider & Weiss 1987). Variability studies are known as “blazars”. ini et al. 1992, Maesano et al. 1997, Webb are a powerful tool to investigate blazar Although the details of their emis- et al. 1998, and Fan et al. 2001 in the case emission and to discriminate among the sion mechanism are still under debate, of BL Lac). During the last few years, bla- various theoretical interpretations that the commonly accepted paradigm as- zar optical variability studies have result- have been proposed so far, especially if sumes the presence of a central black ed in excellent quality light curves (both the observations are done in a continu- hole fed by an accretion disc, and that in terms of length and dense sampling) as ous way and simultaneously at different of a plasma jet which is responsible for optical observers set up collaborations wave bands. At the very least, micro-vari- the non-thermal emission. In order to to make their observational effort more ability studies raise the question of what explain several observational pieces of efficient. One of those collaborations is is the smallest variability time scale, and evidence, the emitted radiation from the “Whole Earth Blazar Telescope” hence, of how small the size of the emit- the jet is assumed to be relativistically (WEBT), an international organization ting region is. beamed toward us. that includes about 30 observatories all Their overall spectral energy distribu- over the world (Skinakas observatory is 3. Skinakas observations tion shows two distinct components in one of them). The main aim of this or- of BL Lacs the ν-νF representation. The “low”-en- ν ganization is to obtain accurate and con- The Skinakas Observatory is located ergy emission, from the radio band to tinuous optical monitoring of a source in the Ida mountain in Central Crete at X-rays, peaking usually between mm and during time-limited campaigns (lasting an altitude of 1750m. It is a collaborative the UV band, is believed to be synchro- from a few days to several weeks), often project of the University of Crete, the tron radiation produced by ultra-relativ- simultaneously with satellite observa- Foundation for Research and Technolo- istic electrons in the jet. The higher en- tions in X- and γ-rays, and ground-based gy-Hellas, and the Max-Planck-Institut für ergy emission, up to γ-rays, usually peaks observations in the radio band and at Extraterestrische Physik, in Garching, Ger- between GeV-TeV, respectively. Its origin TeV energies. The results from the few many. It hosts a 0.3 m, Flat-Field, telescope, is less clearly established. The most wide- campaigns that have already been organ- and a 1.3 m, Ritchey-Cretien, telescope. ly accepted scenario regards these high ized are very encouraging (see e.g. http: The 1.3 m telescope is ideal for mi- energy photons as inversely Compton- //www.to.astro.it/blazars/webt/). cro-variability studies of BL Lacs. Since ized soft photons off the energetic elec- One of the most impressive properties most of them are usually quite bright (~ trons. The source of the soft source radi- of blazars is the detection of the so called 13-15 mag in the optical band), it is pos- ation is unclear. The seed photons could “intra-night optical variations” or “optical sible to obtain accurate measurements be those produced by the synchrotron micro-variability” (i.e. brightness changes (i.e. with an accuracy as good as ~ 0.01 process itself, or could be produced out by 10-20% on time scales as short as a mag) within 1-5 minutes. In this way, one of the jet, either in the accretion disc or fraction of an hour) in a large number can obtain light curves which are dense in the broad line region. of these sources. The systematic study (i.e. with a typical point separation of no 2. Optical variability of these variations started in the late more than ~ 10-15 minutes, depending of BL Lacs eighties by Miller and coworkers (Miller on the number of filters used). In the pe- et al. 1989, Carini et al. 1991). Since then, riod between the years 2001-2004, sys- Large amplitude, fast optical variations micro-variability studies have been per- tematic observations of a few BL Lacs, of a few BL Lac objects were detected formed by many groups. As an example over a large number of nights, and in var- from the early days of their discovery, we mention the work of Heidt & Wagn- ious filters, took place in the Observato- when they were still classified as “variable er (1996,1998), Romero et al. (2002), and ry. In total, we observed 9 BL Lac objects
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 22 23 over more than 50 nights using various optical filters (mainly B and I, but also V and R in some cases as well). All the objects are radio-selected BL Lacs chosen from the 1 Jy sample using the following criteria: a) average R-band magnitude > 16.5 mag b) variability am- plitude > 15% (as estimated by Heidt & Wagner, 1996) and c) declination > 0. The first criterion was imposed so that the peak of the emitted power in all ob- jects is at mm/infrared (IR)/optical wave- lengths. As a result, the optical emission corresponds to the emission from the most energetic, synchrotron emitting electrons in the jet. The second crite- rion was chosen in order to maximize the probability of detecting micro-var- iations during the observations, while the restriction in studying objects in the northern hemisphere was necessary for the acquisition of the longest possible light curves each night. Figure 1: The B, R and I-band light curves of BL Lac during the 1999 and 2001 Skinakas observations. Errors are also plotted but are smaller than the size of the light curve points. 4. Data reduction and the re- Time is measured in hours from 20:00 UT on July 5, 2001, for the 2001 observations, and sulting light curves from 19:00 UT on July 28, 1999 for the 1999 observations. The small filled squares at the bottom of the figure show the B band light curve of the comparison star B (for clarity Up to date we have studied the light reasons, the light curve is shifted from a mean of ~ 7 mJy to 5 mJy). curves of 4 BL Lac objects, namely BL Lac itself, S5 0954+658, S5 2007+777 and 3C 371 (Papadakis et al. 2003, Papadakis We observe significant intra-night var- 1% in the case of BL Lac, S4 0954+658, S5 et al. 2004, and Xilouris et al. 2006). In all iations during almost all nights. Two exam- 2007+777 and 3C 371, respectively. cases, the observations were carried out ples are shown in Figures 1 and 2. In the with a CCD camera using a 1024x1024 first Figure, we show the light curves of 5. Data analysis and results SITe chip with a 24 μm2 pixel size (cor- BL Lac (a bright and highly variable object) responding to 0.5” on the sky). The ex- while in Figure 2 we show the light curves Compared to most of the previous mi- posure time varied between 30 sec for resulted from the 2004 observations of cro-variability blazer studies, the big ad- the I-band observations of BL Lac and 9 S5 2007+777 (a less variable object). In vantage of the Skinakas observations is min for the B-band observations of S5 both cases, we also plot the B-band light the availability of simultaneous light curves 2007+777. The total number of frames curves of a comparison star. While these in more than one optical bands. This is a we have obtained is 899, 914 and 217 in are virtually “flat”, significant variations crucial factor, necessary to understand the the B, I and R-bands, respectively, over 33 can be observed in the light curves of the basic characteristics of the intra-night var- nights. During the observations, the see- two objects. In the case of BL Lac, we ob- iations in these objects. The main results ing varied between ~1’’-1.5’’. serve smooth variations which last for a from our analysis so far are as follows: In Standard image processing (bias sub- few hours, while in the case S5 2007+777, all four objects, the variability amplitude traction and flat fielding using twilight-sky similar amplitude smooth variations are increases toward higher frequencies, i.e. exposures) was applied to all frames using observed on time scales of ~a day. from the I to the B-band light curves. For the standard IRAF routines. In all cases, ap- A useful measure of the amplitude of example, in the case of BL Lac, frms de- erture photometry by integrating counts the observed variations is the so-called creases from ~6.5% in the B, to ~5.5% and within a circular aperture (of various ra- ~5% in the R and I-band light curves, re- “fractional variability amplitude”, frms, dii, depending on the seeing) centered on which is defined as: spectively. By fitting the light curves with the objects. Instrumental magnitudes were simple linear or exponential functions, we f = (σ2–σ2 )1/2/
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 22 23 because the B light curve may have start- ed to decay while I is still rising. Note that Figure 2: B and I band light curves for the S5 the “B/I vs B+I” plot cannot be fitted well 2007+777 during the by a simple linear function. Instead, a loop- 2004 Skinakas observa- like structure, which evolves in the clock- tions. Time is measured wise direction, appears. in hours from 18:12 UT As an example of how well the varia- on August 03, 2004. The tions in the different bands are correlated, empty circles at the bot- tom of the plot show the in Figure 4 we show the cross-correlation B-band light curve of function (CCF) between the B and I-band the comparison star 3. light curves during the 1999 and 2001 ob- For clarity reasons, the servations of BL Lac (shown in Figure 1). standard star light curve In these plots, a positive lag means that the is shifted to the mean B leads the I-band variations. The CCFs flux level of zero mJy. show large maxima (~1) at around zero lag. These results imply that the B and I- band light curves are highly correlated, as expected from their good visual agree- ment (see Figure 1), and the delay be- B and I-band light curves. We find spectral but in a rather complicated way, as the tween them is less than ~5 minutes. The variations associated with the observed bottom panel in the same Figure demon- only case where we do find evidence for flux variations. In general, we observe the strates. In this panel, we plot the B/I ratio a delay between the variations in the two usual “harder when brighter/softer when as a function of the total (i.e. B+I) source bands is during the July 5, 2001 observa- fainter” behaviour. However, the relation flux. In the first part of the observations, tions, where the I-band is delayed by ~ 15 between flux and spectral index is not as the flux decays, the B/I ratio decreases min, with respect to the B-band light curve linear in most cases. Instead, we have de- (since the flux is decaying faster in the B (this result is significant at the 95% level). tected loop like patterns in the “spectral than the I-band). As the flux subsequently In any case, most of the CCFs appear to slope vs flux” plane which evolve in the rises again, the flux ratio increases as well by asymmetric, in the sense that, on time clockwise or anti-clockwise direction. In (because B is rising faster than I). Only scales longer than ~0.5 hours, the corre- all cases, the observed variations in the during the last night of the observations lation at positive lags is larger than that different bands are well correlated, with the flux ratio appears to decrease again, at negative lags. This result suggests that no detectable delays. As an example of the spectral vari- ations that we have detected and the different variability rates in the flux decaying/rising parts of the light curves, in Figure 3 we present our results during the 2004 observations of 3C 371. In the upper panel we show the B and I-band light curves normalized to their mean (filled and open squares, respectively). It is obvious that the min/max variabil- ity amplitude is larger in the B-band. In the same panel, the solid and dashed lines correspond to best-fitting model curves which describe rather well the flux evo- lution in the two bands. The model fitting results show that the B-band flux decays and rises faster than the I-band flux. Fur- thermore, there seems to be a ~ 10-12 hrs delay between the B and I light curves at minimum (with the B-band leading). The middle panel in the same Figure shows the B/I flux ratio light curve (which is repre- sentative of the spectral slope in the op- Figure 3: (I) B and I-band light curves of 3C 371 in 2004 (filled and open squares, respective- tical band). As a result of the differences ly). They are binned using bins of size 1.5 hrs, and are normalized to their average flux level. between the B and I- band flux rise/decay (II) In the middle panel we plot their ratio B/I. (III) The B/I vs the B+I flux plot. The open and time scales, this ratio is variable, implying filled squares in this panel indicate the periods when the source flux decreases and increas- significant spectral variations during the es, respectively. The data of the first day of observations (28 July 2004) are market with the observations. These variations are corre- respective date. The solid line which connects the points aims at indicating the spectral evo- lution during the following nights until August the 2nd (last day of observations). lated with the associated flux variations,
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 24 25 the variability components with periods caused by microlensing effects. synchrotron radiation. In this case, the longer than 0.5 hours in the B-band lead The only notable exception is the important time scales which govern the the respective components in the I-band variability behaviour of S4 0954+658 spectral evolution of the flaring events light curves. during two nights in April 2001 when are the acceleration, cooling, escape and we observed a flare-like event which light travel time scales. 6. Discussion was symmetric (i.e. equal rise and decay The fact that we observe flaring events The results from the analysis of the time scales) and evolved with no spec- which last for different periods, even for Skinakas BL Lac observations demon- tral variations (i.e. same variability am- the same object, suggests that different strate that one can constrain the mecha- plitude in all bands). Raiteri et al. (1999) regions/parts of the jet contribute to the nism that causes the observed variations have found that the long term optical optical emission in BL Lac objects (as- in these objects, provided that the light variations in this source are also achro- suming that the difference in time scales curves at hand are long, dense and cov- matic. Obviously, changes of the jet ori- reflects differences in the size of the er more than one bands. To this end, we entation with respect to the observer’s emitting region). In other words, there briefly investigate below some conse- line of sight is a major cause for the ob- does not seem to exist a “smallest” char- quences of our results. served long and short term variations acteristic time scale, which could be used The continuum emission in blazers is in this source. to determine the typical size of the opti- believed to arise from a relativistic jet However, this was an isolated event. cal emitting region in these objects. Fur- oriented close to the observer, i.e. the Most of the observed flux and spectral thermore, the rich phenomenology that emitted radiation is highly beamed in the optical intra-night variations that we we observe regarding the differences in forward direction. One possible mecha- have observed are similar to the X-ray the flux rising/decaying time scales be- nism that can explain the observed vari- variability properties of well studied ob- tween different bands and the loop-like ations is if the optical emission is pro- jects like Mkn 421 (e.g. Brinkmann et al, structures in the “spectral slope vs flux” duced in discrete blobs moving along 2005; 2003) and PKS 2155-30 (e.g Zhang plots, suggests that the assumed pertur- magnetic fields and the viewing angle (i.e. et al. 2002). The peak of the synchrotron bations do not affect the particles in the the angle between the blob velocity vec- emission in these objects is located in jet in the same way. However, the qual- tor and the line of sight) varies with time. the UV/X-ray band. Therefore, the X-ray ity of the light curves we have obtained In this case the beaming or Doppler fac- band corresponds to frequencies that are allow us to identify possible physical tor should vary accordingly and, since located around/above the peak of their mechanisms which operate each time. the observed flux depends on this, view- spectral energy distribution, just like the For example, the fact that the B-band ing angle variations can result in flux vari- optical band for the four radio-selected decays faster than the I-band flux during ations. For example, a change of less than BL Lacs observed from Skinakas. The fast the first part of the 3C 371 2004 obser- 0.5 degrees can explain variations of the X-ray variations in Mkn 421 and PKS vations that we show in Figure 4 could order of 20% (Ghisellini et al. 1997). In 2155-30 are thought to be a direct result be explained by the cooling of the emit- this case, we would expect the variations of the acceleration/cooling mechanism ting particles due to synchrotron and to be “achromatic”. The same holds true of relativistic electrons which represent self-Compton radiative losses. For a par- in the case when the observed variations the highest tail of the synchrotron com- ticle of energy γmc2, emitting at an ob- are caused by gravitational microlensing. ponent. It is natural then to assume that 2 served frequency of ν0~γ , the cooling Since in most cases we observe significant the observed optical micro-variations in -0.5 time is ~ν0 . The ratio of the B and spectral variations, correlated with the as- the 4 BL Lac objects that we have studied I-band median frequencies is ~1.8, imply- sociated flux variations, we conclude that are also caused by a perturbation which -0.5 ing that tcool,B/ttcool,I~(νΒ/νΙ) ~0.7. This value is close to the ratio of the decaying B and I-band time scales that we have es- timated from the light curves. During the subsequent flux rising parts of the light curves, we observe the flux increasing first in the B and then in the I-band. This is expected in the case when the source is injected with particles at high energies for a period longer than the light crossing time of the source. In this case, the emis- sion starts increasing at high energies for as long the injection continues and the emitting volume increases accordingly. The particles start emitting at lower fre- quencies only after some time equal to the cooling time scale, hence the delay in the increase of the flux in the I-band. Our results demonstrate that well sampled, intra-night, multi-band optical theFigure fast 4: variations Cross-correlation in these objectsfunctions do between not theactivates B and I banda region light incurves the duringjet, filled the with observations of BL Lac objects, whose have1999 a and geometric 2001 BL originLac observations and/or are shown not in Figureenergetic 1. particles which emit through peak of the emitted power is at IR/
Continued in page 31
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 24 25 Relativistic AGN Jets by Nectarios Vlahakis Department of Physics , University of Athens
ABSTRACT ets in active galactic nuclei are colli- J mated, relativistic flows that emanate from accretion disks around supermas- sive black holes. Electromagnetic stress- es are the most plausible candidate for extracting energy from the source and converting it into outflow kinetic ener- gy. Questions that need to be answered in order for these processes to be well understood are: Can we explain parsec- scale accelerations that the observations infer? How the conditions near the disk are related to the terminal Lorentz fac- tor of the jet and what is the asymptotic value of the Poynting-to-matter energy flux ratio? Can we model the apparent kinematics of the observed jet compo- nents? I present solutions of the ideal magnetohydrodynamic equations that help to shed light on these questions. 1. Introduction The commonly accepted interpreta- tion of AGN jets is that they represent relativistic flows ejected from the vicin- ity of supermassive black holes and pow- ered by energy released by accretion in an underlying disk. These jets consist of Figure 1: Total intensity images of 3C345 - Top left: VSOP observations at 6cm resolve the various components that follow curved nuclear region into several components. Right: VSOP observations trace the evolution of apparent trajectories and exhibit appar- the inner jet components at a resolution of 350μas. The ellipses are the modelfit compo- ent superluminal motions, a manifesta- nents. Bottom left: 3mm image of 3C345 with a resolution of 70μas along jet direction. tion of their relativistic velocities (see From Klare et al (2001). figure 1 for the jet in the quasar 3C345). There is growing evidence that these tion up to γ≥10 must take at least 103 is of the order of the sonic distance, cer- components undergo extended (par- Schwarzschild radii. They also argue that tainly much smaller than pc-scales where sec-scale) acceleration. For example the electron/positron kinetic energy the acceleration is inferred from the ob- Unwin et al (1997) deduced a change in (estimated from the emissivity of blazar servations, since the sonic surface is lo- the bulk Lorentz factor of the C7 com- events), is too small to support the en- cated close to the event horizon of the ponent in 3C345, from γ~5 to γ~10 over ergetics of blazars and of radio lobes in central black-hole. Alternatively, a pos- a deprojected distance range of ~3-20 pc quasars. Thus, the dynamics of AGN jets sible heating source makes γ∞>>1 pos- (they also infer a decrease in the Dop- is likely dominated by protons rather sible (e.g., Meliani et al 2004). It is, how- pler factor from 12 to 4 and an increase than leptons. ever, unclear how such a heating source in the angle between the velocity of the Extended acceleration is unlikely to would be established in a natural way component and the line of sight from 2 be driven hydrodynamically in a proton- on pc-scales. o to 10 during the same period). Sikora electron outflow. If Ti is the initial tem- The most likely alternative is mag- et al (2005) give a more general argu- perature, energy conservation implies netic driving, which is considered in the ment related to the extended accelera- that pure-hydrodynamic driving gives following. 2 tion: If the bulk flow near the disk is suf- Lorentz factors γ∞~kBTi/mpc , which is AGN jets are also well collimated; e.g., ficiently fast (γ≥5) it would Comptonize of order unity even if the temperature in the galaxy M87, the jet is seen opening photons coming from the disk, produc- is as high as 1012K. widely in its formation region, at an an- ing bulk-Compton features. The absence In addition, the distance on which the gle of about 60o nearest the black hole, of such features indicate that accelera- Lorentz factor attains its terminal value but is squeezed down to only 6o at 100
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 26 27 An alternative numerical approach is to solve the time-dependent problem (which is hyperbolic in time) and ex- pect to reach a steady-state. Although there has been significant progress over the last years in doing so for studying nonrelativistic flows, all existing codes fail to simulate relativistic magnetohy- drodynamic disk-driven flows for more than a few rotational periods. On top of that, it is not always clear how the issue of the boundary conditions is handled. Besides fully numerical methods, there have also been suggested semi-analytical ones. These are basically a way to sepa- rate the two independent variables in the poloidal plane (z,v), and reduce the system to ordinary differential equations. There are two families of such models: the θ self-similar, appropriate for the de- scription of coronal outflows near the rotation axis, and the r self-similar for outflows associated with disks (see the review article by Tsinganos 2002). Li et al (1992) and Contopoulos (1994) found independently an r self- similar relativistic model, which was fur- Figure 2: The jet in the galaxy M87. The very central region is seen in the top panel, and the ther generalized including thermal ef- jet at larger spatial scales in the bottom. The arrow in the top panel indicates the direc- fects and applied to γ-ray burst jets by tion of the 20” jet (kpc-scale jet), while the dashed lines indicate the position angles of the limb-brightened structure within 1 mas (subpc-scale) of the core. The maximum resolution Vlahakis & Königl (2003), and to AGN (~0.1mas) corresponds to 0.01pc, or 30 Schwarzschild radii. This is the highest resolution jets by Vlahakis & Königl (2004). yet obtained on a nucleus of an active galaxy. From Biretta et al (2002). I’ll present in the following a typical so- lution obtained using this model, showing Schwarzschild radii (see figure 2). The jet equation: one along the flow (which gives that many of the observable characteris- opening angle continues to decrease at the velocity for a given shape of the flow) tics of AGN jets can be explained. larger distances. Magnetic self-collima- and one in the perpendicular direction 2.1 Acceleration tion has long been thought to be the with respect to the flow (the so-called underlying mechanism for the observed transfield equation that determines the As discussed in the introduction, the jet shape. shape of the flow and the magnetic field most likely acceleration mechanism for Summarizing, as far as the dynamics distribution). These two equations are AGN outflows is that they are driven of AGN jets are concerned, we need to coupled because not only the velocity magnetically. Thus, we are interested in explain extended (pc-scale) acceleration, depends on the shape of the flow and examining Poynting flux-dominated flows collimation and the observed jet kine- the magnetic field distribution, but also at the neighborhood of the accretion matics by using MHD modeling. inertial forces that are present in the disk, meaning that the electromagnetic 2. Magnetohydrodynamic transfield equation affect the shape of part of the total energy-to-mass flux ra- the magnetic fieldlines. Despite the fact tio is much larger that the matter part. (MHD) modeling that the remaining equations are only In general, there are three accelera- The dynamics of astrophysical outflows two, of which one is algebraic, the sys- tion mechanisms. may be described to zeroth order by the tem remains highly intractable. The rea- i) Thermal acceleration: This is due to set of steady, ideal magnetohydrodynam- son is that the problem remains two-di- the expansion of the flow under its own ic equations. These consist of Maxwell’s mensional (with independent variables pressure (or enthalpy) gradient. Remem- and Ohm’s equations, mass conservation, say the z and v cylindrical coordinates bering that the thermal acceleration is a entropy equation (with possible heating which define the so-called poloidal plane) result of a De-Laval nozzle coming from mechanisms included) and the momen- and the resulting partial differential equa- the interplay between gravity (that ini- tum equation. Due to the axisymmetric tion is of mixed type, i.e., changes from tially confines the flow) and pressure nature of jets, which means that there is elliptic to hyperbolic in unknown a-pri- gradients (that expands the flow) we an ignorable coordinate, the above sys- ori surfaces. Due to this fact, it is beyond conclude that thermal acceleration is al- tem can be partially integrated to yield the capability of existing numerical codes most complete at distances where the several constants of motion (e.g., Ts- to solve this highly nonlinear problem, outflow speed reaches the local sound inganos 1982). The remaining equations and no numerical solution has been ob- speed which is of the order of the es- are two components of the momentum tained so far. cape speed from the central gravitational
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 26 27 gradient is negligible even for initial tem- peratures of the order of 1010K (as in this particular solution; see figure 3c). The magnetocentrifugal mechanism is the dominant one very close to the disk and remains finite as long as the rotation speed is non-negligible. However, the magnetic acceleration rapidly takes over. The result of the acceleration is shown Figure 3: Various quan- in figure 3a. It is seen that the Lorentz tities as functions of factor increases monotonically with dis- the dimensionless cylin- drical distance v from tance. The upper curve in figure 3a indi- the axis of rotation, in cates that the Lorentz factor increases a r self-similar solution. due to a decreasing Poynting-to-mass flux The cylindrical distance ratio: the Poynting flux is converted into is normalized using the matter kinetic-energy flux. Note that the Alfvénic distance v . A sum of these two quantities is a constant (a): Lorentz factor and of motion (a result of the total energy- Poynting-to-matter en- to-mass flux ratio conservation). ergy flux ratio. If μ is the initial Poynting-to-mass flux (b): Velocity compo- ratio (over c2), and since the flow initially nents Vz, Vv,, Vj in cy- lindrical coordinates. is Poynting-flux-dominated, this number (c)Temperature. μ gives also the maximum Lorentz fac- (d) Magnetic field com- tor that the flow can achieve (in the case ponents Bz, Bv,, Bj in cy- where the whole Poynting flux is trans- lindrical coordinates. ferred to matter). Asymptotically the From Vlahakis & Königl Lorentz factor is ~μ/2, or, equivalently, (2004). the flow reaches a rough equipartition between Poynting and kinetic energy fluxes. In other words, the efficiency of the magnetic acceleration in this particu- potential. This happens very close to the from Poynting flux to kinetic energy flux. lar solution is ~50%. black hole and cannot be connected to The maximum Lorentz factor that this pc-scale accelerations, unless there is an mechanism can give is the initial ratio of 2.2 Collimation extended heating distribution. the Poynting flux over the mass flux (over In order to examine the collimation 2 ii) Magnetocentrifugal acceleration: c ). However, it is an important question if process we need to think which are the This is the result of the centrifugal force, this mechanism continues to operate until forces acting on the plasma in the trans- and can be interpreted in the «bead on the whole energy initially deposited in the field direction (i.e., perpendicular to the a rotating wire» picture (Blandford & magnetic field is transferred to the mat- flow). Besides the pressure gradient com- Payne 1982). The magnetic field lines act ter, or stops at some distance resulting ponent (which is not expected to be im- like rotating rigid wires and the plasma in some finite Poynting-to-matter energy portant for Poynting-dominated flows), as beads moving along them. If the angle flux ratio. In other words, it is important there are two forces of electromagnetic between the wires and the axis of ro- to know what the efficiency of this accel- nature. The magnetic force (the compo- tation is sufficiently large, the centrifu- eration mechanism is, and how the condi- nent of the JxB force) is responsible for gal force overtakes the gravitational pull tions near the disk affect this result. the well known and understood self-col- causing acceleration. The main ingredi- Figure 4 shows the various forces ac- limation process in nonrelativistic flows. ent of this mechanism is the rotation of celerating the jet. The thermal pressure The same force is of course present in the roots of the wires and the termi- nal speed that gives is of the order of the Keplerian velocities of the under- lying disk. However, in relativistic flows this mechanism cannot play an impor- tant role. This is because the non-negli- gible rotation that would be required in this case would constrain the maximum value of the poloidal speed (since their vector sum cannot exceed the speed of light). iii). Magnetic acceleration: This is sim- ply the result of the JxB Lorentz force; Figure 4: Various forces acting on the plasma along its motion, as functions of distance. its work describes the transformation
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 28 29 Note that the collimation and accel- eration processes shown in figure 3 are found self-consistently by solving the two coupled components of the mo- mentum equation, along and perpendic- ular to the flow direction. 2.3 Apparent kinematics The components of AGN jets follow curved (helical) trajectories over the years. Their apparent velocity, as well as their intensity, depends on two quanti- ties: the Lorentz factor and the angle Figure 5: The 3D fieldline (thin) and streamline (thick) shape for the presented model. All between the velocity of the component distances are in units of vA. and the line of sight. There have been various efforts to explain the apparent relativistic flows as well. The important relativistic jets could be collimated by an jet kinematics: as Kelvin-Helmholtz insta- difference between these two categories outer nonrelativistic magnetized wind. In bilities (Hardee & Walker 2005), or due is the appearance of the electric force. this scenario, the self-collimation works to source precession (Lobanov & Ro- The electric field is comparable with the in the outer wind, and the wind itself land 2005). However, since a MHD out- magnetic field for V≈c, since from Ohm’s forces the inner highly relativistic flow to flow – being rotating – naturally follows law E≈(V/c)B. Moreover, it is always act- collimate (see also Gracia et al 2005 for a helical path (see figure 5) it may explain ing against the collimating magnetic force. an application to the jet in M87). (or at least play some partial role to) the Thus, we expect the collimation to be However, if the flow starts with γ»1 observed kinematics. In order to explore much more difficult to achieve for ex- there is a possibility that the main part this possibility I used the self-similar so- tremely relativistic flows (Bogovalov & Ts- of the collimation happens at relatively lution presented in the previous parts inganos 1999). The magnetic and electric small values of γ. This is seen in the pre- of the article. forces almost cancel each other. Their dif- sented solution. Figure 3b shows the ve- Suppose that the angle between the ference, which is much smaller than each locity components. At the origin of the line of sight and the axis of the jet is of the two terms, equals the inertia force jet the two poloidal components Vz and θobs. Assuming that each observed plas- in the transfield direction. Quantitatively, Vy are comparable, meaning that the an- ma component corresponds to ejection this can be written as R=γ2v, where R is gle between the flow motion and the axis from a localized region of the disk (char- o the curvature radius of the streamlines of rotation is 45 . Following the ratio of acterized by an angle φo on the disk- (e.g., Bogovalov 2001): it is much more these two components from figure 3b and plane and the distance from the center, difficult to change the shape of a relativis- looking also the Lorentz factor evolution or equivalently the Alfvénic distance of tic flow because it has higher inertia. from figure 3a, we see that the collimation the field-line that is rooted at this re- The above reasoning led Bogovalov & is indeed almost complete for relatively gion), one can easily project the plasma Tsinganos (2002) to suggest that highly small values of γ. trajectory on the plane perpendicular to the line of sight, as well as to find Dop- pler factors and apparent speeds. As a test for the model we tried to fit the trajectory, Doppler factor and an- gle between velocity and line of sight, as they were inferred from observations by Unwin et al (1997). o o For θobs=9 and φo=180 the mod- el successfully explains the Unwin et al (1997) results (Vlahakis, Marin, & Königl to be submitted). Between the years 1992- 1993 the Doppler factor decreases from 12 to 4 and the viewing angle increases from 2o to 10o during the same period. Figure 5: The 3D field- 2.4 Polarization maps line (thin) and Another manifestation of magnetic streamline (thick) shape driving is the observed polarization in for the pre- radio maps of AGN jets. Fractional polar- sented model. ization of a few tens percent are typical All distances in pc-scale jets, supporting the existence are in units of a dominant large-scale magnetic field of vA. component. In addition, the observed Continued in page 33
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 28 29 Research Production of the Hellenic Astronomy, Astrophysics and Space-Science Sector by Manolis Plionis (IAA, NOA)
im: This brief note is intended to affiliation. Also there are two Spyrou, N. the ~1.4σ level (assuming Poisson statis- Ainform the members of the Hel- (a) of the Univ. of Thessaloniki, section tics), since the standard deviation of the lenic Astronomy/ Astrophysics and of Astronomy, Astrophysics & Celestial mean is ~0.22. Space Science community of some indi- Mechanics and (b) of the University of The results presented can be appre- ces regarding the research productivity Surrey, School of Electronics, Comput- ciated if compared with those of other of the Astronomy & Astrophysics sector ing and Mathematics. developed countries with similar GDP (Departments and Institutes) in Greece. • I have taken into account the specific per capita (or more appropriately with Its intension is to explore, without pre- year in which new staff members have a similar fraction of the GDP invested in tending to exhaust the theme, only the joined the different departments. pure research), an analysis which is out research output and not the overall sci- • I have excluded from the listed “ref- of the scope of this brief presentation. entific contribution (being educational, public outreach, services, or other) of Table 1 the different departments and Institutes. Period Staff Refereed Publications Citations Citation The final and most important aim is to Publications /staff /paper fortify the Hellenic Astronomical com- munity with data and possible arguments 1999-2001 74 288 3.9 2325 8.1 in the onset of the difficult struggle to convince the Greek government for the 2002-2004 80 337 4.2 need to participate in the European Southern Observatory (ESO). Study set-up: I have used the NASA ereed” articles some erroneous ADS However, we do present here (Table ADS system to retrieve relevant infor- entries (eg. erratums, book reviews by 2) a crude comparison with the scientif- mation regarding the research produc- other authors which are attributed to ic production of the Concilio Nacional tion of Greek Astronomy-Astrophys- the editor of the book or conference de le Ricerce (CNR-Italy), of the Cen- ics Institutions using the Astronomy/ proceedings, etc.) tre National de la Recherche Scienti- Planetary, Instrumentation and Physics/ • In order to take into account the fique (CNRS-France), of the Consejo Geophysics databases. I have counted time lag between publication and first ci- Superior de Investigaciones Cientificas all the refereed publications, character- tations, I present citations (counted the (CSIC-Spain) and finally of the Max-Plank ized as such by the ADS, and independ- first week or so of 2005) only for arti- (Germany) for roughly the same period ent of the journal impact factor by using the corresponding ADS filter for two 3- Table 2 year periods (1999-2001 and 2002- 2004). Furthermore: CNR-Italy CNRS-France CSIC-Spain Max-Plank Greece • The publications were selected so 4.1 4.2 5.7 6.9 4.2 that at least one of the authors has an academic position (lecturer and above for the universities, researcher D for the cles published between 1999 and 2001. (2001-2002). These data have been bor- research institutes). I have not counted I caution that the citations listed in ADS rowed from a similar study of the CNR, papers of affiliated members or students for articles published in physics journals published in early 2004. of the corresponding institutions if they are incomplete. Furthermore, I made no Note that the above European es- had no staff member as a co-author. The attempt to exclude auto-citations. timates are derived from all the natu- names of the academic staff considered in Results: The main results of this anal- ral science subjects and not only from this study can be found in the appendix. ysis can be found in Table 1, where we Astronomy/Astrophysics and Space Sci- • I have attempted to avoid double en- present the number of refereed publica- ences. It is evident that to a first order tries and verify that names were correct- tions and the mean publication number Greek Astronomy compares quite well ly used (to avoid counting papers of sci- per staff member for the two 3-year pe- with that of at least some European entists having the same or similar names riod over all Institutions (see the appen- countries. but belonging to different institutions). dix). Furthermore, for the 1st period we Appendix I note a few examples: there are two present also the total number of cita- Anastasiadis, A. (a) Aristotelis – Univ. of tions (including self-citations) counted The staff members considered in the Thessaloniki and (b) Anastasios - NOA- up to the 31/12/2004. It can be seen above analysis are: Space, which are not distinguished by the that there is a small increase of the mean • Academy of Athens: Contopoulos, ADS, and thus it was necessary to check publication per staff member in the sec- G., Dara, Efthimiopoulos, Patsis, Tri- the corresponding abstracts to verify the ond period, a result which is significant at takis, Voglis, Zachariadis, Petropoulos
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 30 31 radakis, Spyrou, Stergioulas, Varvoglis, (Efthimiopoulos in the second period • University of Ioannina: Alissandrakis, Vlahos, Voyatzis. only). Krommydas, Nindos, Tsikoudi (Nindos only in the second period) • University of Thrace (Laborato- • University of Athens: Antonopoulou, ry of Electromagnetic theory): Anag- Apostolatos, Danezis, Deligiannis, Ioan- • NOA-IAA: Boumis, Dapergolas, Geor- nostopoulos, Diamantidis, Pavlos, Rigas, nou, Konstantopoulos, Kontiza, Laska- gantopoulos, Goudis, Kontizas, Plionis, Sarafopoulos, Sarris. rides, Mastichiadis, Moussas, Niarchos, Sinachopoulos,, Xilouris (Boumis and Papagiannopoulos, Papaelias, Papathana- Xilouris in the 2nd period only) It is possible that I have accidental- soglou, Pinotsis, Preka-Papadema, Rovi- ly omitted some colleagues from the • NOA-Space: Anastasiadis, Belehaki, this-Livaniou, Sakellariadou, Stathopoul above lists (new staff members etc), a Daglis, Harlaftis, Tsiropoula ou,Theodossiou, Tsamparlis, Tsinganos, possibility that would not change signifi- Vlachakis (Vlachakis in the second pe- • University of Patras: Zafeiropoulos, cantly the results presented previously. riod only). Flogaiti, Gerogiannis, Antonakopoulos. I repeat that in all of the above statis- tics I have considered on an equal basis • University of Crete: Hadjidimitriou, • Aristotle University of Thessalo- all refereed journals, considered as such Haldoupis, Kylafis, Papamastorakis, Pa- niki: Avgoloupis, Caranicolas, Grigore- by the ADS. padakis, Reig, Vardavas, Ventura (Reig in lis, Hadjidemetriou, Ichtiaroglou, Kok- the 2nd period only). kotas, Meletlidou, Papadopoulos, Sei-
Skinakas micro-variability observations of BL Lac objects (continued from page 25)
optical wavelengths, can offer us clues munity in general. Fan,.., Qian,.., Tao,. 2001, A&A, 369, 758 on the acceleration and cooling mecha- Acknowledgments: This article is based Ghisellini, G. et al. 1997, A&A, 327, 61 nism of the energetic particles in the jet. on work that has been done in collabora- Heidt,., Wagner,.. 1996, A&A, 305, 42 In order to advance our knowledge in tion with P. Boumis, V. Samaritakis, E. Xil- Heidt,., Wagner,.. 1998, A&A, 329, 853 this field we need a much larger number ouris, A. Dapergolas and I. Alikakis. Final- Maesano,., Montagni,., Massaro,., Nesci,. 1997, of light curves with a dense sampling pat- ly, it would not be possible to complete A&AS, 122, 267 tern (no more than a few minutes) and the blazar’s optical variability monitoring Marscher, A.P. 1996, PASPC, 110, 248 in more than one bands, for a represent- project without the support and encour- Miller,.., Carini,.., Goodrich,.D. 1989, Nature, 337, 627 ative sample of BL Lacs. In this way, we agement of J. Papamastorakis, the director Papadakis,.., Boumis,., Samaritakis,., Papamasto- will be able to study, in a statistical way, of the Skinakas Observatory. rakis,. 2003, A&A, 397, 565 variability time scales, the cross-correla- References Papadakis,.., Samaritakis,., Boumis,., Papamasto- tion between the different bands, and the Brinkmann,., Papadakis,I.., Raeth,. 2005, A&A, rakis,. 2004, A&A, 426, 437 spectral evolution during flaring events. 443, 397 Raiteri, C.M. et al. 1999, A&A, 352, 19 This will allow us to understand their Brinkmann,., Papadakis,.E., den,..., Haberl,. 2003, Racine, R. 1970, ApJ, 159, 99L “typical” or “average” variability proper- A&A, 402, 929 Romero,.., Cellone,.., Combi,.A., Andruchow,. 2002, ties, and subsequently constrain physical Carini,.., Miller,.., Noble,.C., Sadun,... 1991, AJ, 101, A&A, 390, 431 models. Such light curves can result from 1196 Schneider,., Weiss,. 1987, 171, 49 dedicated, monitoring observations with Carini,.., Miller,.., Noble,.., Goodrich,.. 1992, AJ, Stalin,.., Gupta,.., Gopal-Krishna,-K; Wiita,.J.; Sagar,., medium size (i.e. 0.5-1 m) “robotic” tel- 104, 15 2005, MNRAS, 356, 607 escopes. Since there are quite a few tel- Dreissigacker,., Camenzind,. 1996, PASPC, 110, Webb, J. R., et al. 1998, AJ, 115, 2244 escopes of this size in Greece, this can 337 Xilouris, E.M. et al, 2006, A&A in press, (astro-ph/ be a promising field of research for the DuPuy, D., Schmitt,., McClure,., van,S., Racine,. 1969, 0511130) Greek observational astronomical com- ApJ, 156, 135L Zhang, Y.H. et al. 2002, ApJ, 572, 762
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• The arrival of the Cassini spacecraft • Detection of infrared radiation di- 2005 at Saturn and the successful landing rectly from an exoplanet (March of the Huygens probe on the moon 2005) ccording to the Physics News, the Titan (January 2005) • Geoneutrinos observed (July 2005) ABulletin of the American Institute • the biggest burst of light ever re- • Short gamma ray bursts identified of Physics, among the top physics sto- corded from outside the solar sys- as coming from in-spiraling neutron ries for 2005, we found five related to tem, from a soft gamma repeater stars (October 2005) astronomy: (February 2005)
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 30 31 Close Binaries in the 21st Century: New Opportunities and Challenges
The idea to organize a conference on Close Binaries in Greece was con- ceived a few years ago and the first plans were set up during the VIth Pacific Rim Conference on Stellar Astrophysics held in Xian, China, July 11-17, 2002. Af- ter many discussions, the decision to or- ganize the conference in 2005 was made in the summer of 2004 and the four or- ganizers were A. Gimenez, E. Guinan, P. Niarchos and S. Rucinski. Chairman of the LOC was P. Niarchos, who under- took the main responsibility of the or- ganization of the conference. The con- ference was supported by the Com- mission 42 ofIAU, the European Space Agency (ESA), the National and Kapo- distrian University of Athens, the Min- istry of Education and Religion Affairs, the University of Aegean, the Hellenic Astronomical Society, the Municipality of Ermoupolis, the Alpha Bank and the Figure 4: Various forces acting on the plasma along its motion, as functions of distance. PLAISIO Computers A.E.B.E. Scientific Rationale: Surveys of stars structure and stellar evolution. In special lanic Clouds (LMC and SMC). A new sur- in the Galaxy consistently show that cases, selected eclipsing binaries in near- vey planned during the next decade will most stars (>60%) are members of bi- by galaxies are being used as “standard most likely find >5-10 millionadditional nary and multiple star systems. It is cru- candles” to secure accurate distances to EBs. These surveys perform photometry, cial to determine the properties of these clusters and to the Local Group of Gal- but not spectroscopy, which provides the binary systems so that we can better axies. This results in a better calibration radial velocities of the two stars. Surveys understand the galaxies whose lumi- of the extragalactic distance scale and of M31 and M33 carried out by three nous matter consists mostly of stars in establishing an accurate zero point of groups (e.g. the DIRECT Program) are which are members of binary systems. the Hubble constant H0. discovering many additional EBs and ex- Moreover, the evolution of binary stars More recently a new class of eclips- pect > 1 million new EBs over the next is also responsible for a large number ing binaries was discovered in which the decade; radial velocities of a very small of astrophysically diverse and energetic eclipses are produced by the transit of a subset of these systems (and EBs in the phenomena that include X-ray binaries giant exosolar planet of a solar-type pri- LMC) are being obtained to determine (with black hole or neutron star com- mary star (e.g. HD 209458). Many more the physical properties of the stars and ponents), cataclysmic variables and no- of these eclipsing binary planet/star sys- their distances. The upcoming European vae (with white dwarf components), and tems are expected to be discovered COROT mission and the NASA space some types of supernovae (e.g.-SN Ia). within the next several years.These open mission “Kepler”, which are both de- From the vantage point of the observ- a new important window of opportunity signed to detect transit eclipses of stars er, a tiny fraction (0.2-0.3%) of all binary to study the properties (mass, diameter, by terrestrial-size planets (i.e. eclipsing stars are favourably aligned in space, al- albedo, atmosphere, etc.)of planets out- binary planet/star systems), will also de- lowing the observer to see the mutual side our solar system. These are exciting liver thousands of new galactic EBs with eclipses of the component stars; these binary systems with great potential that exquisitely precise (micromag) photom- systems are Eclipsing Binary (EB) stars. are just beginning to be explored. etry. Later into the future, the enor- The study of EBs over the last century, A major revolution in the study of mouslyESA space mission GAIA should with increasingly better data and analy- close binaries has taken place over the deliver ~ 8 million new EBs, an estimated ses with more sophisticated computer last decade.Very large surveys (e.g. MA- ~100,000 of which will have radial ve- codes, has led to accurate determina- CHO, EROS, OGLE and others), which locities, calibrated colours, and paral- tions of the basic astrophysical data on repeatedly photometrically monitor the laxes. Therefore, in the next decade or stars - such as masses, diameters, lumi- brightness of stars, can now detect about so there will be hundreds of thousands nosities, along with crucial information over 20,000 EBs, mostly in the galactic new EBs and several hundred eclipsing about stellar atmospheres and internal bulge and in the Large and Small Magel- planet/star binaries.
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 32 33 Programme Topics • New and Improved Tools for Analyz- it was an important event for the com- ing Light and Radial Velocity Observa- munity of binary stars astrophysics. All • Recent Developments in Close Bina- tions the participants were absolutely satisfied ry Star Research (Non-Degenerate • Future expectations: Impact of New from the scientific program, the organi- Stars) Instrumentation and Technologies zation, the hospitality and the beauty of • Formation and Evolution of Close Bi- on Close Binary Star/ Exoplanet Re- Syros and Greece. Those contributions naries: Star + Star Systems and Planet search to the conference which will pass the + Star Systems Conference activities refereeing process, will be published in • Binary Stars as Astrophysics Labora- the journal Astrophysics and Space Sci- tories A total number of 110 participants ence. The web site of the conference is: • Binaries in Clusters and Nearby Gal- from 34 countries attended the meet- axies ing. There were 9 invited lectures, 37 http://www.phys.uoa.gr/CB_Greece05 • Binary Star - Planet Systems: New De- contributed talks and 65 poster pres- P. G. Niarchos velopments and New Things learned entations. The conference was very suc- • Recent Developments in Close Bina- cessful with regards to both the scientific National and Kapodistrian University of Athens ries with Degenerate Components part and the organization. Undoubtedly
Venus Express… (continued from page 6)
instruments on board: three are flight- seek to detect molecules of water, oxy- magnetometer will study the magnetic spare units of instruments already flown gen and sulphuric compounds thought to field generated by the plasma. on Mars Express, two are from comet- be present in the atmosphere. The VMC camera will monitor the chaser Rosetta and two were designed The VIRTIS spectrometer will map planet in four wavelengths, notably ex- specifically for this mission. the various layers of the atmosphere ploiting one of the ‘infrared windows’ The PFS high-resolution spectrometer and conduct multi-wavelength cloud revealed in 1990 by the Galileo space- will measure atmospheric temperature observation in order to provide images craft (when flying by Venus en route for and composition at varying altitudes. It of atmospheric dynamics. Jupiter), making it possible to penetrate will also measure surface temperature Assisted by a magnetometer, the AS- cloud cover through to the surface. The and search for signs of current volcan- PERA 4 instrument will analyse interac- camera will also be used to monitor ic activity. tion between the upper atmosphere and atmospheric dynamics, notably to ob- The SPICAV/SOIR infrared and ultra- the solar wind in the absence of mag- serve the double atmospheri vortex at violet spectrometer and the VeRa instru- netospheric protection such as that sur- the poles, the origin of which still re- ment will also probe the atmosphere, ob- rounding Earth (for Venus had no mag- mains a mystery. serving stellar occultation and detecting netic field). It will analyse the plasma radio signals; the former will in particular generated by such interaction, while the
Relativistic AGN Jets… (continued from page 29)
electric field polarization vectors and Bogovalov, S. V. 2001, A&A, 371, 1155 Sikora, M., Begelman, M. C., Madejski, G. M., the Faraday rotation measure gradients Bogovalov, S., & Tsinganos, K. 1999, MN- & Lasota, J-P. 2005, ApJ, 625, 72 across the jet, support the existence RAS, 305, 211 Tsinganos, K. 1982, ApJ, 252, 775 of helical magnetic fields with strong Bogovalov, S., & Tsinganos, K. 2002, MN- Tsinganos, K. 2002, Hipparchos, vol. 1, is- transverse (azimuthal) component (e.g., RAS, 337, 553 sue 11 Gabuzda et al 2004). This is consistent Contopoulos, J. 1994, ApJ, 432, 508 Unwin, S. C., Wehrle, A. E., Lobanov, A. P., with the MHD picture, since the field is Gabuzda, D. C., Murray, E., & Cronin, P. 2004, Zensus, J. A., Madejski, G. M., Aller, M. F., naturally helical (see figure 5) and the MNRAS, 351, L89 & Aller, H. D. 1997, ApJ, 480, 596 azimuthal (Bj) component is dominant Gracia, J, Tsinganos, K., & Bogovalov, S. V. Vlahakis, N., & Königl, A. 2003, ApJ, 596, beyond the Alfvénic distance (see figure 2005, A&A, 442, L7 1080 3d). This is another connection between Hardee, P. E., & Walker, R. C. 2005, ASP Con- Vlahakis, N., & Königl, A. 2004, ApJ, 605, models and observations that definitely ference Series, 340, 92 656 need to be examined more closely (Vla- Klare, J., Zensus, J. A., Krichbaum, T. P., Loba- hakis, Marin, & Königl in preparation). nov, A. P., & Ros, E. 2001, IAUS, 205, 130 References Li, Z-Y., Chiueh, T., & Begelman, M. C. 1992, Editorial help is badly needed! ApJ, 394, 459 Please volunteer, feed us with in- Biretta, J. A., Junor, W., & Livio, M. 2002, Ne- Lobanov, A. P. & Roland, J. 2005, A&A, 431, formation related to your Institute wAR, 46, 239 831 or with exciting news from your Blandford, R. D., & Payne, D. G. 1982, MN- Meliani, Z., Sauty, C., Tsinganos, K., & Vlahakis, field of research RAS, 199, 883 N. 2004, A&A, 425, 773
HIPPARCHOS | Volume 2, Issue 1 HIPPARCHOS | Volume 2, Issue 1 32 33 th International Conference 7 of the Hellenic Astronomical Society by D. Xatzidimitriou
he 7th biannual International Con- T ference of the Hellenic Astronomi- cal Society, entitled “Recent Advances in Astronomy & Astrophysics”, took place in September, 8-11, 2005, in Lixourion, Kefallinia. The Scientific Organizing Committee (SOC) of the 7th HelAS conference was chaired by Prof. P.G. Laskarides (Univer- sity of Athens) and included H. Dara (Academy of Athens), J. G eorgantopou- los (National Observatory of Athens), V. Geroyiannis (University of Patras), E. Harlaftis (National Observatory of Ath- ens), J. Hadjidemetriou (University of Thessaloniki), D. Hatzidimitriou (Univer- sity of Crete), K.D. Kokkotas (University of Thessaloniki), N. Kylafis (University of sessions,well as two special meetings/ (6) Prof. James Truran Jr., Department of Crete), X. Moussas (University of Ath- moderated discussions, open to all in- Astronomy & Astrophysics, Universityof ens), P. Niarchos (University of Athens), terested participants. Chicago, USA)”Nucleosynthesis, Chal- S. Papadakis (University of Crete), J.D. S. The scientific sessions of the confer- lenges and New Developments”. Persides (University of Thessaloniki), J.H. ence were devoted to: (1) Sun, Planets & The 7th Hel.A.S. conference was spon- Seiradakis (University of Thessaloniki), N. Interplanetary Medium, (2) Our Galaxy: sored by the “Alexander S. Onassis” H. Solomos (Hellenic Naval Academy), E. Stars, Clusters, Interstellar Medium,(3) Foundation, the Hellenic Astronomical Theodossiou (University of Athens), Ch. Extragalactic Astrophysics, (4) Theoret- Society, the Municipality of Lixourion- Tomboulides (MNE & RA) and K. Tsinga- ical Insights in Dynamical Astronomy, Pali, the Hellenic Tourism Organization, nos (University of Athens). Relativity and Cosmology,(5) Instru- the Hellenic National Committee for As- The Local Organizing Committee mentation & Methods of Astronomical tronomy, the EUDOXOS National Ob- (LOC) consisted of N. Solomos [Chair] Observations,and (6) History and Edu- servatory of Education, the Technologi- (Hellenic Naval Academy & “EUDOXOS” cation in Astronomy. cal Educational Institute of Ionian Islands, National Observatory of Education), G. The special meetings were focussed on the Prefecture of Kefallinia and Ithaki and Fanourakis (NRCPS “DEMOKRITOS” discussions on the future of astronomy in the Hellenic Naval Academy. & NOE “EUDOXOS”), A. Heilaris (Hel- Greece and on the prospects of the Greek On September 9th, the General As- lenic Navy & Hellenic Naval Academy), V. participation to the European Space Agen- sembly of the HEL.A.S. was held. The Sec- Kokalis (NOE “EUDOXOS”), O. Malan- cy, with representatives from ESA, NASA retary of the Hel.A.S., Prof. K. Tsinganos, draki (National Observatory of Athens), and the Greece/ESA Task Force. summarised the current situation within D. Patrikios (NOE “EUDOXOS”) and A. The distinguished invited speakers of the Society. Sixteen new members were Zachariadou (NRCPS “DEMOKRITOS” the conference presented excellent re- elected, thus raising to 274 the number & NOE “EUDOXOS”). Thanks to the ef- view talks on a wide range of subjects. (1) of Hel.A.S. members. Progress on the forts of the LOC, the local organisation Dr Athena Coustenis (LESIA, Observa- preparation of the new Who-is-who of the conference was excellent. toire de Paris, Meudon, France) spoke in Greek Astronomy was presented by The conference was attended by over on”The Cassini/Huygensto Saturn/ Titan”, the Chairman Prof. Laskarides. A small 160 participants from Greece and abroad (2) Prof. Mike Edmunds (Head of School number of amendments to the found- and was deemed to be a great success, of Physics and Astronomy, University- ing chart of the Society were also ap- both from the point of view of organi- Wales, UK), on “The Antikythera Mech- proved by the Assembly. Finally, the es- sation and of the quality of the scientific anism”, (3). Attilio Ferrari (Dipartimento tablishment of the Harlaftis Travel Fund contributions of the participants. diFisica Generale, Universita di Torino, Fi- was announced. The aim of the fund is to Opening remarks were addressed by sica Spaziale, Italy) on “Astrophysical”, (4) support young astronomers to visit In- the Hel.A.S. chairman Prof. P. Laskaridis, Prof. Keith Horne, (Head of Astronomy, ternational Observational Facilities. by the member of the Academy of Athens School ofPhysics & Astronomy,of St. An- More details on the 7th Hel.A.S. Prof. G. Contopoulos, by the Mayor of Lix- drews, UK) on “ExtraSolar Planets” (Emil- conference and its scientific agenda ourion and other local representatives. ios Harlaftis Lecture), (5) Prof. Eric Priest can be found on its web site: http:// The scientific agenda of the confer- (Fellow of the Royal Society, University of comas.interzone.gr/cgi/article.cgi. ence contained, parallel and poster St.Andrews, UK) on “Our Enigmatic Sun”,
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