DOCSLIB.ORG

Catching Stellar Mergers at Work with the Very Large Telescope

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
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. in brightness at irregular intervals (De Marco et al., 2002). Two evolutionary sce- The two Very Large Telescope Interfer- narios have been suggested for produc- Observations ometer (VLTI) instruments AMBER ing an RCB star: a double-degenerate and MIDI were used to study the close merger of two white dwarfs (WD) or a VLTI observations of both targets were environment of two post-merger stellar final helium-shell flash in a planetary neb- obtained with the low spectral resolution systems: the R Coronae Borealis star ula central star. V854 Cen has a large mode of AMBER (R = 35), the three- V854 Cen and the red nova V838 Mon. hydrogen content and polycyclic aromatic telescope combiner (Petrov et al., 2007). The observations reveal the presence hydrocarbons (PAHs) detected in the The observations were performed with of flattened dusty structures in the core mid-infrared, making it an unusual mem- the 1.8-metre Auxiliary Telescopes (ATs) of both objects, which are very likely ber of its class. This star also has a fast using the compact (baseline, B ≤ 35 m) discs. This finding confirms that the wind which reaches several hundreds and long configurations (B ≤ 140 m). Full merger of two stars can lead to the for- of km s–1 (Clayton et al., 2013; Kameswara details can be found in Chesneau et al. mation of a disc. Rao & Lambert, 1993). Kameswara Rao (2014a) for V854 Cen and Chesneau et al. & Lambert (1993) provided strong argu- (2014b) for V838 Mon. Near-infrared ments that V854 Cen may be surrounded observations were obtained with AMBER, With the advent of optical interferometry, by a bipolar nebula, extending up to about similar to those for R Corona Borealis, the close environments around many 2 arcseconds, as revealed by its C II ex­­ using three ATs and the compact base- evolved stars have been resolved (see tended emission (Clayton & Ayres, 2001). lines. Mid-infrared interferometric data Chesneau, 2011). Companions encom- were also obtained for V838 Mon with the passing a large range of mass, from stel- V838 Mon is a nova-like object that two-telescope recombiner MIDI (Leinert lar objects to Jovian-mass planets, are erupted in 2002 (reaching V = 6.8; Bond et al., 2004), which had a field of view suspected to strongly influence the ejecta et al., 2003). The eruption was unlike ~ 0.3 arcseconds, identical to the near- when a low- to intermediate-mass star classical novae because the effective infrared field of view, thanks to the use of reaches the asymptotic giant branch, or temperature of the object dropped and the Unit Telescopes. even as early as the red giant branch the spectral type evolved to that of a very (de Marco, 2009). This interaction can late L-type supergiant (Loebman et al., V854 Cen was also observed with the potentially influence dramatically the fate 2014). The mid-infrared flux of V838 Mon mid-infrared imager VISIR (Lagage of the star, leading to poorly known increased by a factor of two between et al., 2004) with a pixel scale of evolutionary paths, affecting the time- 2004 and 2007, suggesting that new dust 0.075 arcseconds and field of view of scales of the different stellar evolutionary was forming in the expanding ejecta of 19.2 by 19.2 arcseconds through the stages, to the extent that the product the outbursts (Wisniewski et al., 2008). SiC filter (λ = 11.65 μm, width 2.34 μm). bears little similarity to, for example, the The expanding ejecta engulfed a com- Figure 1 displays the VISIR image, timescale and chemistry involved for panion close to the central source (Bond, showing a clearly extended nebulosity the evolution of a single, naked star 2006), seen as a faint, blue component around the central star. (Frankowski & Jorissen, 2007). in the spectrum, and Tylenda et al. (2005) argued that the pre-outburst spectral Interferometry in the near- and mid- energy distribution (SED) is well matched Modelling the visibilities infrared is the best tool with which to by a pair of early main-sequence stars probe the close environment of evolved (B3V + B1.5V or B4V + A0.5V), making The interferometer data do not directly stars. Indeed, ultra-sharp images of V838 Mon a triple system (main star + provide an image of the sources, and these environments can be made, prob- subsolar merging star + B3V companion). we used an in-house tool called fitOmatic The Messenger 158 – December 2014 35 Astronomical Science Millour F. et al., Catching Stellar Mergers at Work with the VLTI (closure phase and differential phases). In explained this way, and indeed it does. V854 Cen order to fit the interferometric data (i.e. However, such a model contains too minimise the least squares), it uses a sim- many components and can only be ulated annealing algorithm, leading to the loosely constrained. The position angle best-match solutions shown in this paper. (PA) of the outer contours of the VISIR 11.65 μm images is only marginally con- sistent with that derived with AMBER, V854 Cen so it is possible that the spatial structure The best-match model for the compact of the mass loss of V853 Cen is inhomo- array data has two components: an geneous and randomly variable. unresolved uniform disc (Θ < 2.5 milli- arcseconds [mas], star component), and N a flattened Gaussian (shell component) V838 Mon 1ǥ with a full width at half maximum (FWHM) The MIDI dispersed visibilities were E of the minor axis of 8 ± 1 mas, and major translated into the simplest possible geo- axis 11 ± 3 mas. The orientation of the metrical ad hoc model — a Gaussian Figure 1. A VISIR 11.65 μm image is shown of V854 major axis is 126 ± 29° (Chesneau et al., brightness distribution, as described in Cen with enhanced contours of the outer regions. The 2014a). The long-array data shows that Leinert et al. (2004). The resulting fits extended nebulosity can be seen in blue and purple. the star is unresolved (Θ < 1.0 mas). Fig- shown in Figure 3 depict the general ure 2 shows the fit of the AMBER data by appearance of the mid-infrared structure. (Millour et al., 2009) to fit simple geo- the geometrical model. The semimajor and semiminor axes of metric components. These fits provide the drawn ellipses represent the half- the poor man’s images displayed in this Given that the closure phase signal width at half maximum of the Gaussian. article (Figures 2 and 3), at an unmatched observed on V854 Cen is null within the The extent of that structure increases spatial resolution. The fitOmatic tool uses error bars, a companion star, if any, from a FWHM of 25 mas at 8 μm to a set of simple (uniform disc, Gaussian, would not have a flux exceeding 3 % of 70 mas at 13 μm, with a high flattening etc.) and less simple (“pinwheel”, rotating the total flux, i.e. well below the detection ratio. The major axis is oriented at a and expanding disc, etc.) chromatic limit down to a typical spatial resolution PA close to 10 ± 30°. The 2013 short- models that can be combined together to of 10 mas. A model with a fully clumped baseline AMBER visibilities are all very form more complex objects. The model is uniform shell that contained up to 30 close to unity in the band centres at matched to the data using least squares, clumps was used to determine whether 1.7 μm and 2.2 μm and are consistent with special care taken for the phases the high H-band visibilities could be with a completely unresolved object. The Figure 2. Bellow: Geometrical models from fitOmatic 1.0 1.52892 2.49122 of the environment of V854 Cen at 2.5 μm. Upper right panel: Combined H- (blue) and K- (red) band interferometric visibilities obtained with AMBER compared with the signal from the polychromatic V² 0.5 geometrical modelling.
Load more

Recommended publications
  • 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]
  • 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.
    [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]