DOCSLIB.ORG

Direct Imaging of a Massive Dust Cloud Around R Coronae Borealis⋆

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Direct Imaging of a Massive Dust Cloud Around R Coronae Borealis⋆ A&A 539, A56 (2012) Astronomy DOI: 10.1051/0004-6361/201117138 & c ESO 2012 Astrophysics Direct imaging of a massive dust cloud around R Coronae Borealis S. V. Jeffers1,M.Min1,L.B.F.M.Waters2,3,H.Canovas1, M. Rodenhuis1,M.deJuanOvelar1, A. L. Chies-Santos1, and C. U. Keller1 1 Sterrekundig Instituut Utrecht, Utrecht University, PO Box 80000, 3508 TA, Utrecht, The Netherlands e-mail: [email protected] 2 SRON, Netherlands Institute for Space Research, 3584 CA Utrecht, The Netherlands 3 Astronomical Institute “Anton Pannekoek”, University of Amsterdam, PO Box 94249, 1090 GE Amsterdam, The Netherlands Received 26 April 2011 / Accepted 16 November 2011 ABSTRACT We present recent polarimetric images of the highly variable star R CrB using ExPo and archival WFPC2 images from the HST. We observed R CrB during its current dramatic minimum where it decreased more than 9 mag due to the formation of an obscuring dust cloud. Since the dust cloud is only in the line-of-sight, it mimics a coronograph allowing the imaging of the star’s circumstellar environment. Our polarimetric observations surprisingly show another scattering dust cloud at approximately 1.3 or 2000 AU from the star. We find that to obtain a decrease in the stellar light of 9 mag and with 30% of the light being reemitted at infrared wavelengths (from R CrB’s SED) the grains in R CrB’s circumstellar environment must have a very low albedo of approximately 0.07%. We show that the properties of the dust clouds formed around R CrB are best fitted using a combination of two distinct populations of grains size. The first are the extremely small 5 nm grains, formed in the low density continuous wind, and the second population of large grains (∼0.14 μm) which are found in the ejected dust clouds. The observed scattering cloud, not only contains such large grains, but is exceptionally massive compared to the average cloud. Key words. circumstellar matter – supergiants – techniques: polarimetric – stars: individual: R Coronae Borealis 1. Introduction Feast (1979) notes that the L-band observations mirror the pul- sation frequencies of the photosphere. The cool dust shell is as- R Coronae Borealis (R CrB) stars are one of the most enigmatic sumed to be continuously replenished by randomly emitted dust classes of variable stars. They frequently show irregular declines clouds. The extinction of the ejected dust is different to that of in visual brightness of up to 9 mag due to the production of thick the ISM, with an UV absorption peak at 2500 Å as opposed dust clouds. Such minima typically last for several months with to 2175 Å. Laboratory measurements and theoretical models the exception of R CrB’s current minimum which has lasted for show that this is due to small glassy or amorphous carbon grains more than 3.5 years (since July 2007 – AAVSO). The photo- (i.e. soot) formed in a hydrogen-poor environment (Hecht et al. metric minima, caused by the obscuration of starlight by a dust 1984). cloud, are characterised by a rapid decline in brightness and a gradual return to normal brightness levels. Colour variations are The formation of dust clouds on the R CrB star RY Sgr has also present with a reddening of the star during the decline, fol- been observed by de Laverny & Mékarnia (2004) with NACO at lowed by the star becoming bluer during the phase of minimum the VLT. These observations show that the dust clouds are bright, brightness and then becoming redder during the rise to normal contributing up to 2% of the stellar flux in the infrared (L-band brightness levels. Variations in colour during a minimum have 4.05 μm), and are located in any direction at several hundred also been observed (e.g. Efimov 1988) and are attributed to pul- stellar radii from RY Sgr. de Laverny & Mékarnia (2004)also sations, which are also are present in R CrB’s light curve during note that the dust clouds might be very dense and optically thick maximum light. close to the star. Leão et al. (2007) used mid-infrared interfero- / The colour variations during obscuration can be attributed metric observation of RY Sgr, with VLTI MIDI, to show that the to the presence of a cool dust shell, which has been confirmed central star is surrounded by a circumstellar envelope with one by observations of a strong IR-excess (Kilkenny & Whittet bright dust cloud at 100 stellar radii (30 AU). This is notably the closest observed dust cloud around an R CrB star. More recently 1984; Walker 1986). The cool dust shell has a temperature of / ≈500−1000 K and L-band infrared photometric observations Bright et al. (2011)alsousedVLTIMIDI to probe the circum- show that it still emits in the infrared even when the line-of- stellar environments of RY Sgy, V CrA and V854 Cen at very / sight is obscured by a dust cloud (Feast 1986; Yudin et al. 2002). small spatial scales (50 mas 400 R). They find that their obser- vations are consistent with a scenario of random dust ejection around the star, which over time creates a halo of dust. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the The dust formation mechanism in these stars is not well un- Spanish Observatorio del Roque de los Muchachos of the Instituto de derstood. However, Crause et al. (2007) show that there is a cor- Astrofisica de Canarias. relation between the onset of brightness declines and R CrB’s Article published by EDP Sciences A56, page 1 of 8 A&A 539, A56 (2012) pulsation period, linking the expulsion of dust clouds and mass Table 1. Journal summarising ExPo and HST observations. loss to internal stellar processes. This has also been shown to occur on other R CrB-type stars such as V854 Cen (Lawson Instrument Date Filter Exp time(s) No exp et al. 1992)andRYSgr(Pugach 1977). Observations show ExPo 27 May 2010 none 0.028 4 × 1000 broad emission lines (Na D lines, Ca I H & K and 388.8 nm HST/WFPC2 14 April 2009 F555W nm 7 1 He line), as the star’s brightness decreases, indicating gas ve- F555W nm 120 4 locities of ≈200 km s−1. This is in agreement with observations F814W nm 16 1 of the He I λ10830 line, which indicate a wind with a veloc- F814W nm 160 3 ity of 200−240 km s−1 (Clayton et al. 2003). They also note that the P Cygni profile is present during both maximum light and brightness decline. For R CrB, the dust grains are assumed to be 2.2. ExPo: observations and data analysis formed away from the star, at approximately 20 R∗, because at Observations of R CrB were secured at the 4.2 m William the stellar surface the temperature greatly exceeds the grain con- Herschel Telescope on La Palma, as part of a larger observing densation temperature for carbon (Feast 1986; Fadeyev 1988). run, from 22 to 27 May 2010. To obtain an image we take typ- The dust clouds are then driven away from the star by radi- ically 4000 frames with an exposure time of 0.028 s per FLC ation pressure. An alternative model proposes that the dust is angle i.e. 0◦, 22.5◦,45◦ and 67.5◦. These observations are sum- formed close to the star and moves quickly away due to radia- marised in Table 1. A set of flat fields is taken at the beginning tion pressure (originally proposed by Payne-Gaposchkin 1963). and end of each night and a set of darks is taken at the beginning However, the conditions close to the star are far from the ther- of each observation. modynamic equilibrium necessary to form dust grains, though All of the images are dark subtracted, and corrected for flat as discussed by Clayton (1996)andDonn (1967), the condensa- fielding, bias and cosmic ray effects. Once the polarization im- tion temperature of carbon in a hydrogen deficient environment, ages are free of instrumental effects, they are carefully aligned such as on an R CrB star, is much higher than when hydrogen is and averaged. Polarised images are obtained after applying a present. double-difference approach to the two beams and alternating “A” To further understand the circumstellar environment of and “B” frames, i.e. R CrB we have used imaging polarimetry observations with ExPo, the EXtreme POlarimeter (Rodenhuis, in prep.), to detect P = 0.5(PA − PB) = 0.5((AL − AR) − (BL − BR)). (1) scattered starlight during its current minimum. This method is advantageous as starlight becomes polarised when it is scattered Special care was taken in aligning the R CrB images, since its from circumstellar dust and particularly during obscuration can polarized image shows one clear dust cloud rather than an ex- enable a detection of close-in circumstellar dust. In this paper tended polarized source such as a disk or a shell. To minimise we combine images of the dust cloud in scattered light, using guiding effects, the images were first aligned with a template. imaging polarimetry, with archival images taken by the Hubble Secondly, to minimize intensity gradient effects, the images were Space Telescope (HST) to determine the properties of the grains aligned with an accuracy of a third of a pixel. This results in the in the obscuring and scattering dust clouds. cloud structure showing more detail than using other techniques In this paper we first describe the observations of R CrB us- such as aligning the images with respect to the brightest speckle.
Load more

Recommended publications
  • Catching Stellar Mergers at Work with the Very Large Telescope
    Astronomical Science Catching Stellar Mergers at Work with the Very Large Telescope Interferometer Florentin Millour1 ing the inner hundreds of astronomical The 2002 eruption has been interpreted 1 Eric Lagadec units, exactly where discs and com- as the merger of a star of ~ 8 MA with a Orsola de Marco2 panions occur and are intimately related subsolar mass star (Tylenda & Soker, Dipankar P. K. Banerjee3 to the evolution of the stars. Interferome- 2006). Djamel Mékarnia1 try is ideally suited to resolve discs in the Alain Spang1 core of nebulae around stars of a range V838 Mon is embedded in a dense, large- Olivier Chesneau1† of masses from low to high. Here we pre- scale environment that was lit up by the sent a snapshot of two such objects — light echoes resulting from the 2002 erup- the R Coronae Borealis (RCB) star V838 tion (Bond et al., 2003), and potentially 1 Laboratoire Lagrange, UMR 7293, Univ. Cen and the eruptive variable V838 Mon contaminates observations of the central Nice Sophia-Antipolis, CNRS, Observa- — highlighting the seminal contribution star. High angular resolution studies with a toire de la Côte d’Azur, Nice, France of the astronomer Olivier Chesneau, who small field of view of a few arcseconds are 2 Department of Physics & Astronomy, passed away earlier this year. an asset in isolating the central regions Macquarie University, Sydney, Australia from the extended dusty cloud. A great 3 Astronomy & Astrophysics Division, The R Coronae Borealis stars are hydro- advantage of optical interferometry studies Physical Research Laboratory, gen-deficient carbon-rich supergiants, is thus to isolate the measurements from Navrangpura, India best known for their spectacular declines the extended environment.
    [Show full text]
  • Photometry of R Coronae Borealis Stars During the Recovery Phase of Their Declines
    CSIRO PUBLISHING www.publish.csiro.au/journals/pasa Publications of the Astronomical Society of Australia, 2003, 20, 159–164 Photometry of R Coronae Borealis Stars during the Recovery Phase of their Declines Lj. Skuljan, P. L. Cottrell, A. C. Gilmore and P. M. Kilmartin Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand [email protected] [email protected] [email protected] [email protected] Received 2002 July 22, accepted 2003 January 14 Abstract: The photometric observations (UBVRI) of nine cool R Coronae Borealis (RCB) stars have been collected at Mt John University Observatory, New Zealand, over a period of twelve years. The analysis of the magnitude–colour and colour–colour diagrams for the recovery phase demonstrates that all declines exhibit a similar asymptotic approach to their normal brightness. Declines return to maximum brightness along a line with essentially the same slope that does not depend on the star or the depth of the decline. Assuming a uniform obscuration of the photosphere by the dust cloud during the recovery phase, the extinction properties of the material were determined. The ratio of total to selective extinction (RV) for the RCB stars in our sample is in the range 2.5 to 4.6, indicating that the obscuring dust has extinction properties similar to that of the interstellar dust. Observations have been compared with the theoretical extinction curves for different sorts of grains. Keywords: stars: variables: R Coronae Borealis — methods: data analysis 1 Introduction 2 Observations The R Coronae Borealis (RCB) stars are hydrogen- The photometric observations (UBV and UBVRI) of the deficient carbon-rich supergiants, with a characteristic nine RCB stars (Table 1) have been obtained at Mt John pattern of variability.
    [Show full text]
  • HET Publication Report HET Board Meeting 3/4 December 2020 Zoom Land
    HET Publication Report HET Board Meeting 3/4 December 2020 Zoom Land 1 Executive Summary • There are now 420 peer-reviewed HET publications – Fifteen papers published in 2019 – As of 27 November, nineteen published papers in 2020 • HET papers have 29363 citations – Average of 70, median of 39 citations per paper – H-number of 90 – 81 papers have ≥ 100 citations; 175 have ≥ 50 cites • Wide angle surveys account for 26% of papers and 35% of citations. • Synoptic (e.g., planet searches) and Target of Opportunity (e.g., supernovae and γ-ray bursts) programs have produced 47% of the papers and 47% of the citations, respectively. • Listing of the HET papers (with ADS links) is given at http://personal.psu.edu/dps7/hetpapers.html 2 HET Program Classification Code TypeofProgram Examples 1 ToO Supernovae,Gamma-rayBursts 2 Synoptic Exoplanets,EclipsingBinaries 3 OneorTwoObjects HaloofNGC821 4 Narrow-angle HDF,VirgoCluster 5 Wide-angle BlazarSurvey 6 HETTechnical HETQueue 7 HETDEXTheory DarkEnergywithBAO 8 Other HETOptics Programs also broken down into “Dark Time”, “Light Time”, and “Other”. 3 Peer-reviewed Publications • There are now 420 journal papers that either use HET data or (nine cases) use the HET as the motivation for the paper (e.g., technical papers, theoretical studies). • Except for 2005, approximately 22 HET papers were published each year since 2002 through the shutdown. A record 44 papers were published in 2012. • In 2020 a total of fifteen HET papers appeared; nineteen have been published to date in 2020. • Each HET partner has published at least 14 papers using HET data. • Nineteen papers have been published from NOAO time.
    [Show full text]
  • Uv Ceti Type Variable Stars Presented in the General Catalogue of Variable Stars
    IX BULGARIAN-SERBIAN ASTRONOMICAL CONFERENCE: . ASTROINFORMATICS . Sofia, 2 – 4 July, 2014 UV CETI TYPE VARIABLE STARS PRESENTED IN THE GENERAL CATALOGUE OF VARIABLE STARS Katya Tsvetkova Institute of Mathematics and Informatics, Bulgarian Academy of Sciences Sofia, 2 – 4 July, 2014 IX BULGARIAN-SERBIAN ASTRONOMICAL CONFERENCE: . ASTROINFORMATICS . Abstract We present the place and the status of UV Ceti type variable stars in the General Catalogue of Variable Stars (GCVS4, edition April 2013) having in view the improved typological classification, which is accepted in the already prepared GCVS4.2 edition. The improved classification is based on understanding the major astrophysical reasons for variability. The distribution statistics is done on the basis of the data from the GCVS4 and addition of data from the 80th Name List of Variable Stars - altogether 47 967 variable stars with determined type of variability. The class of the eruptive variable stars includes variables showing irregular or semi-regular brightness variations as a consequence of violent processes and flares occurring in their chromospheres and coronae and accompanied by shell events or mass outflow as stellar winds and/or by interaction with the surrounding interstellar matter. In this class the type of the UV Ceti stars is referred together with the types of Irregular variables (Herbig Ae/Be stars; T Tau type stars (classical and weak- line ones), connected with diffuse nebulae, or RW Aurigae type stars without such connection; FU Orionis type; YY Orionis type; Yellow
    [Show full text]
  • Variable Star
    Variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) fluctuates. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as either: Intrinsic variables, whose luminosity actually changes; for example, because the star periodically swells and shrinks. Extrinsic variables, whose apparent changes in brightness are due to changes in the amount of their light that can reach Earth; for example, because the star has an orbiting companion that sometimes Trifid Nebula contains Cepheid variable stars eclipses it. Many, possibly most, stars have at least some variation in luminosity: the energy output of our Sun, for example, varies by about 0.1% over an 11-year solar cycle.[1] Contents Discovery Detecting variability Variable star observations Interpretation of observations Nomenclature Classification Intrinsic variable stars Pulsating variable stars Eruptive variable stars Cataclysmic or explosive variable stars Extrinsic variable stars Rotating variable stars Eclipsing binaries Planetary transits See also References External links Discovery An ancient Egyptian calendar of lucky and unlucky days composed some 3,200 years ago may be the oldest preserved historical document of the discovery of a variable star, the eclipsing binary Algol.[2][3][4] Of the modern astronomers, the first variable star was identified in 1638 when Johannes Holwarda noticed that Omicron Ceti (later named Mira) pulsated in a cycle taking 11 months; the star had previously been described as a nova by David Fabricius in 1596. This discovery, combined with supernovae observed in 1572 and 1604, proved that the starry sky was not eternally invariable as Aristotle and other ancient philosophers had taught.
    [Show full text]
  • Uva-DARE (Digital Academic Repository)
    UvA-DARE (Digital Academic Repository) Advanced evolution of helium stars and massive close binaries Habets, G.M.H.J. Publication date 1985 Link to publication Citation for published version (APA): Habets, G. M. H. J. (1985). Advanced evolution of helium stars and massive close binaries. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:28 Sep 2021 IIIA.. THE EVOLUTION OF A SINGLE AND A BINARY HELIUM STAR OF 2.5 M^ UP TO NEONN IGNITION; CASE BB MASS TRANSFER. Suanary. Thee evolution of a single helium star of 2.5 M0 is calculated from the heliumm Zero Age main sequence up to off-centre neon ignition. In the carbon- shelll burning phase the 2.5 M0 helium star becomes a red giant and possibly enterss the Cepheid pulsational instability strip.
    [Show full text]
  • Chaos, Eruptions and Root-Convergence in One-Dimensional Maps Based on Metallic-Sequence Generating Functions
    Chaos, eruptions and root-convergence in one-dimensional maps based on metallic-sequence generating functions L. Aravind 1 Introduction Over the years we have observed or encountered certain natural phenomena that are char- acterized by rare, sudden eruptive behavior occurring against a background of very low amplitude fluctuations. We first encountered this in astronomy: most remarkably, inthe constellation of Corona Borealis there are two stars that exhibit this kind of behavior albeit in opposite directions. There is T Coronae Borealis, which for most part remains fluctuat- ing rather dimly in a narrow magnitude band between 9.9 and 10.6, well below naked eye visibility, and then once in a century or so (e.g. in 1866 and 1946) explosively blazes forth at magnitude of 2-3 ( ≈ 1000× brighter) changing the shape of the visible constellation. On the other side, we have the equally charismatic R Coronae Borealis, which for most part very mildly fluctuates around the magnitude of 6 at barely naked eye visibility andthen suddenly once in several years suddenly drops to the magnitude of 14 or lower ( ≈ 1500× dimmer), beyond the reach of even a typical amateur telescope. It has become increasingly clear that versions of such behaviors are observed across the domains of science. In biology, recent studies in foraging behavior have shown that diverse animals follow a pattern of foraging movements, which are characterized by routine small movements punctuated by the rare large movements. This kind of behavior allows the escaping of local resource limitations by episodic saltations to reach distant resource-rich regions. An unrelated phenomenon, earthquakes, also displays similar behavior, where small low-magnitude tremors are punctuated by rare episodes of major earthquakes with noticeable effects.
    [Show full text]
  • Nucleosynthesis in R Coronae Borealis Stars
    Nucleosynthesis in R Coronae Borealis Stars Richard Longland Universitat Politècnica de Catalunya Grup d’Astronomia i Astrofísica June 13th, 2013 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 1 / 12 Outline 1 Introduction 2 Prior Evolution Nucleosynthesis 3 Merger Nucleosynthesis 4 Conclusions Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 2 / 12 R Coronae Borealis (HIP 77442) I Yellow supergiant stars I Sudden fading episodes up I Peculiarities discovered in 1795 to 9 magnitudes I “Reverse Nova” I No atmospheric hydrogen I Fades periodically to magnitude 14 Don’t look up! Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 3 / 12 Don’t look up! R Coronae Borealis (HIP 77442) I Yellow supergiant stars I Sudden fading episodes up I Peculiarities discovered in 1795 to 9 magnitudes I “Reverse Nova” I No atmospheric hydrogen I Fades periodically to magnitude 14 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 3 / 12 Final-Flash I Dying AGB star I Final, strong, helium-shell flash I Remaining envelope blown away I Inner-regions revealed Double Degenerate I CO + He white dwarfs merge I He white dwarf disrupted and accreted I Helium burning commences, accreted material expands R CrB stars To explain: Hydrogen deficiency C, N, O, Ne, F, Li (and others) enrichment [X] = log(X=X ) 12C/13C> 500 No known R CrB binary Jeffery, S et al. MNRAS 414 (2011) 3599 Richard Longland (UPC) RCrB Nucleosynthesis June 13th, 2013 4 / 12 R CrB stars To explain: Hydrogen deficiency C, N, O, Ne, F, Li (and others) enrichment [X] = log(X=X ) 12C/13C> 500 No known R CrB binary Final-Flash I Dying AGB star I Final, strong, helium-shell flash I Remaining envelope blown away I Inner-regions revealed Double Degenerate I CO + He white dwarfs merge I He white dwarf disrupted and accreted I Helium burning commences, accreted material expands Jeffery, S et al.
    [Show full text]
  • Variable Star Section Circular
    The British Astronomical Association VARIABLE STAR SECTION CIRCULAR 57 LIGHT CURVES MARCH 1984 Head Office: Burlington House, Piccadilly, London W1V ONL. Telephone 01-734 4145 SECTION OFFICERS: Director D.R.B. Saw, 'Uppanova', 18 Dollicott, Haddenham, Aylesbury, Bucks. HP17 8JG Tel: Haddenham (0844) 292065 Assistant Director S.R. Dunlop, 140 Stocks Lane, East Wittering, nr Chichester, West Sussex P020 8NT Tel: Bracklesham Bay (0243) 670354 Programme Secetaries: Main Secretary G.A.V. Coady, 15 Cedar Close, Market Deeping, Peterborough PE6 8BD Tel: Market Deeping (0778) 345396 Binocular Secretary M.D. Taylor, 17 Cross Lane, Wakefield, West Yorkshire WF2 8DA Tel: Wakefield (0924) 374651 Assistant J. Toone, 2 Hilton Crescent, Boothstown, Binocular Secretary Worsley, Manchester M28 4FY Tel: 061 702 8619 Eclipsing Binary J.E. Isles, Flat 5, 21 Bishops Bridge Road, Secretary London W2 6BA Tel: 01 724 2803 Nova/Supernova G.M Hurst, 1 Whernside, Manor Park, Search Secretary Wellingborough, Northants. NN8 3QQ Tel: Wellingborough (0933) 676444 Chart Secretary J. Parkinson, 28 Banks Road, Golcar, Huddersfield, West Yorkshire HD7 4LX Tel: Huddersfield (0484) 642947 CIRCULARS Charges: U.K. & Eire - £2 for Circulars and light-curves (4 issues) Other countries - £3 Payments (made out to the BAA) and material for inclusion should be sent to Storm Dunlop. CHARTS Charges: Main programme - SAE plus 20p per star (4 charts) All other programmes - SAE plus 5p per star (1 sheet) Editorial We hope that with this issue we will make up some of the leeway in publication for which we apologize (once again) to members. Although we expect to publish a further installment in our occasional series 'Atlases for Variable Star Observers', no othei material for the next issue is to hand.
    [Show full text]
  • Are the Nebulae Around R Coronae Borealis Stars Evolution Or Ejection Related? D
    YY ERI ItaLpha 90 this approach was clear. From the rnea- surements of vbiMe light curve, UV and X we know that these binaries are seats of magnetic activity. Furthermore, R is gmerally believed that high AML is con- trolling the evolution of theser binaries towards the singla-& stage, involving mass transport from the secondaty to the primary component. Nobody pres- ently understands how this mass trans- port takes place and how it is Interacting with magnetic, tidal and Corfolk forces. It can be hoped that from a better sur- vey of the brightness inhomogenelties on the surface, a better insight In the origin of Wese inhomogenehie$, and re- lated large-scale motions, can be ob- bind. Our first results ate encouraging for a further development of the applicdion of this method. However, we feel that the next step wilt most probably require the use of the 3.6-m telescope, to have the possibility of enlarging the observ- able sample and of analysing less strong (and simpler) spectral lines. hence the use of the appropriate model we have a T distribution over the sur- atmospheres. However, on a more qual- face, which implies a varim-on of the line itative ground, we know that darker equivalent width and affects the refer- Bjnnendijk L 1970, WsM In Astron. 12,217. toms correspond to colder areas; from ence values of S 0.e. the value me- Ewer M. 1981, PASP W, 528. a flrst rough estimate S - 1.83 corre- spondhg to the unperturbed photo- QronW, 0. 1976, Astm. Astrophp. sponds to 350 K above the mean and sphere).
    [Show full text]
  • Annual Report 2009 ESO
    ESO European Organisation for Astronomical Research in the Southern Hemisphere Annual Report 2009 ESO European Organisation for Astronomical Research in the Southern Hemisphere Annual Report 2009 presented to the Council by the Director General Prof. Tim de Zeeuw The European Southern Observatory ESO, the European Southern Observa­ tory, is the foremost intergovernmental astronomy organisation in Europe. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. Several other countries have expressed an interest in membership. Created in 1962, ESO carries out an am­ bitious programme focused on the de­ sign, construction and operation of power­ ful ground­based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world­ View of the La Silla Observatory from the site of the One of the most exciting features of the class observing sites in the Atacama 3.6 ­metre telescope, which ESO operates together VLT is the option to use it as a giant opti­ with the New Technology Telescope, and the MPG/ Desert region of Chile: La Silla, Paranal ESO 2.2­metre Telescope. La Silla also hosts national cal interferometer (VLT Interferometer or and Chajnantor. ESO’s first site is at telescopes, such as the Swiss 1.2­metre Leonhard VLTI). This is done by combining the light La Silla, a 2400 m high mountain 600 km Euler Telescope and the Danish 1.54­metre Teles cope.
    [Show full text]
  • The COLOUR of CREATION Observing and Astrophotography Targets “At a Glance” Guide
    The COLOUR of CREATION observing and astrophotography targets “at a glance” guide. (Naked eye, binoculars, small and “monster” scopes) Dear fellow amateur astronomer. Please note - this is a work in progress – compiled from several sources - and undoubtedly WILL contain inaccuracies. It would therefor be HIGHLY appreciated if readers would be so kind as to forward ANY corrections and/ or additions (as the document is still obviously incomplete) to: [email protected]. The document will be updated/ revised/ expanded* on a regular basis, replacing the existing document on the ASSA Pretoria website, as well as on the website: coloursofcreation.co.za . This is by no means intended to be a complete nor an exhaustive listing, but rather an “at a glance guide” (2nd column), that will hopefully assist in choosing or eliminating certain objects in a specific constellation for further research, to determine suitability for observation or astrophotography. There is NO copy right - download at will. Warm regards. JohanM. *Edition 1: June 2016 (“Pre-Karoo Star Party version”). “To me, one of the wonders and lures of astronomy is observing a galaxy… realizing you are detecting ancient photons, emitted by billions of stars, reduced to a magnitude below naked eye detection…lying at a distance beyond comprehension...” ASSA 100. (Auke Slotegraaf). Messier objects. Apparent size: degrees, arc minutes, arc seconds. Interesting info. AKA’s. Emphasis, correction. Coordinates, location. Stars, star groups, etc. Variable stars. Double stars. (Only a small number included. “Colourful Ds. descriptions” taken from the book by Sissy Haas). Carbon star. C Asterisma. (Including many “Streicher” objects, taken from Asterism.
    [Show full text]