Publications (23)36.28 Total impact
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Article: Large-scale environments of binary AGB stars probed by Herschel. I. Morphology statistics and case studies of R Aquarii and W Aquilae
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ABSTRACT: The Mass loss of Evolved StarS (MESS) sample offers a selection of 78 Asymptotic Giant Branch (AGB) stars and Red Supergiants (RSGs) observed with the PACS photometer on-board Herschel at 70 and 160 {\mu}m. For most of these objects, the dusty AGB wind differs from spherical symmetry and the wind shape can be subdivided into four classes. In the present paper we concentrate on the influence of a companion on the morphology of the stellar wind. Literature was searched to find binaries in the MESS sample and these are subsequently linked to their wind-morphology class to assert that the binaries are not distributed equally among the classes. In the second part of the paper we concentrate on the circumstellar environment of the two prominent objects R Aqr and W Aql. Each shows a characteristic signature of a companion interaction with the stellar wind. For the symbiotic star R Aqr, PACS revealed two perfectly opposing arms which in part reflect the previously observed ring-shaped nebula in the optical. However, from the far-IR there is evidence that the emitting region is elliptical rather than circular. The outline of the wind of W Aql seems to follow a large Archimedean spiral formed by the orbit of the companion but also shows strong indications of an interaction with the interstellar medium. The nature of the companion of W Aql was investigated and the magnitude of the orbital period supports the size of the spiral outline.åp. 01/2013; 549:A69. -
Article: Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS
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ABSTRACT: We present new Herschel/PACS images at 70, 100, and 160 micron of the well-known, nearby, carbon-rich asymptotic giant branch star IRC+10216 revealing multiple dust shells in its circumstellar envelope. For the first time, dust shells (or arcs) are detected until 320 arcsec. The almost spherical shells are non-concentric and have an angular extent between 40 deg and 200 deg. The shells have a typical width of 5 arcsec - 8 arcsec, and the shell separation varies in the range of 10 arcsec - 35 arcsec, corresponding to 500-1700 yr. Local density variations within one arc are visible. The shell/intershell density contrast is typically 4, and the arcs contain some 50% more dust mass than the smooth envelope. The observed (nested) arcs record the mass-loss history over the past 16 000 yr, but Rayleigh-Taylor and Kelvin-Helmholtz instabilities in the turbulent astropause and astrosheath will erase any signature of the mass-loss history for at least the first 200 000 yr of mass loss. Accounting for the bowshock structure, the envelope mass around IRC+10216 contains >2Msun of gas and dust mass. It is argued that the origin of the shells is related to non-isotropic mass-loss events and clumpy dust formation.10/2012; -
Conference Proceeding: Headwind: The AGB-ISM Frontier
Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants; 09/2011 -
Conference Proceeding: TX Psc and X Her: Two Cases of Stellar Wind-ISM Interaction
Why Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants; 09/2011 -
Article: X Herculis and TX Piscium: two cases of ISM interaction with stellar winds observed by Herschel
åp. 08/2011; 532:A135. -
Conference Proceeding: Results from the Herschel Key Program MESS
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ABSTRACT: MESS (Mass loss of Evolved StarS) is a Herschel Guaranteed Time Key Program that will image about 100, and do spectroscopy of about 50, post-main-sequence objects of all flavours: AGB stars, post-AGB stars, planetary nebulae, luminous blue variables, Wolf-Rayet stars, and supernova remnants. In this review the implementation and current status of MESS is outlined, and first results are presented.Why Galaxies Care about AGB Stars II: Shining Examples and Common InhabitantsWhy Galaxies Care about AGB Stars II: Shining Examples and Common Inhabitants; 01/2011 -
Article: MESS (Mass-loss of Evolved StarS), a Herschel Key Program
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ABSTRACT: MESS (Mass-loss of Evolved StarS) is a Guaranteed Time Key Program that uses the PACS and SPIRE instruments on board the Herschel Space Observatory to observe a representative sample of evolved stars, that include asymptotic giant branch (AGB) and post-AGB stars, planetary nebulae and red supergiants, as well as luminous blue variables, Wolf-Rayet stars and supernova remnants. In total, of order 150 objects are observed in imaging and about 50 objects in spectroscopy. This paper describes the target selection and target list, and the observing strategy. Key science projects are described, and illustrated using results obtained during Herschel's science demonstration phase. Aperture photometry is given for the 70 AGB and post-AGB stars observed up to October 17, 2010, which constitutes the largest single uniform database of far-IR and sub-mm fluxes for late-type stars. Comment: A&A accepted12/2010; -
Article: Detection of the 69 {\mu}m band of crystalline forsterite in the Herschel MESS-program
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ABSTRACT: In this article we present the detection of the 69 {\mu}m band of the crystalline olivine forsterite within the MESS key program of Herschel. We determine the temperature of the forsterite grains by fitting the 69 {\mu}m band. Comment: Conference proceedings: "Why Galaxies Care About AGB Stars 2", Vienna 201011/2010; -
Article: Warm water vapour in the sooty outflow from a luminous carbon star.
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ABSTRACT: The detection of circumstellar water vapour around the ageing carbon star IRC +10216 challenged the current understanding of chemistry in old stars, because water was predicted to be almost absent in carbon-rich stars. Several explanations for the water were postulated, including the vaporization of icy bodies (comets or dwarf planets) in orbit around the star, grain surface reactions, and photochemistry in the outer circumstellar envelope. With a single water line detected so far from this one carbon-rich evolved star, it is difficult to discriminate between the different mechanisms proposed. Here we report the detection of dozens of water vapour lines in the far-infrared and sub-millimetre spectrum of IRC +10216 using the Herschel satellite. This includes some high-excitation lines with energies corresponding to approximately 1,000 K, which can be explained only if water is present in the warm inner sooty region of the envelope. A plausible explanation for the warm water appears to be the penetration of ultraviolet photons deep into a clumpy circumstellar envelope. This mechanism also triggers the formation of other molecules, such as ammonia, whose observed abundances are much higher than hitherto predicted.Nature 09/2010; 467(7311):64-7. · 36.28 Impact Factor -
Article: Silicon in the dust formation zone of IRC +10216 as observed with PACS and SPIRE on board Herschel
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ABSTRACT: The interstellar medium is enriched primarily by matter ejected from evolved low and intermediate mass stars. The outflows from these stars create a circumstellar envelope in which a rich gas-phase and dust-nucleation chemistry takes place. We observed the nearest carbon-rich evolved star, IRC+10216, using the PACS (55-210 {\mu}m) and SPIRE (194-672 {\mu}m) spectrometers on board Herschel. We find several tens of lines from SiS and SiO, including lines from the v=1 vibrational level. For SiS these transitions range up to J=124-123, corresponding to energies around 6700K, while the highest detectable transition is J=90-89 for SiO, which corresponds to an energy around 8400K. Both species trace the dust formation zone of IRC+10216, and the broad energy ranges involved in their detected transitions permit us to derive the physical properties of the gas and the particular zone in which each species has been formed. This allows us to check the accuracy of chemical thermodynamical equilibrium models and the suggested depletion of SiS and SiO due to accretion onto dust grains. Comment: 5 pages, 3 figures, 7 pages in online appendix, Astronomy & Astrophysics in press05/2010; -
Article: Detection of anhydrous hydrochloric acid, HCl, in IRC+10216 with the Herschel SPIRE and PACS spectrometers
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ABSTRACT: We report on the detection of anhydrous hydrochloric acid (hydrogen chlorine, HCl) in the carbon-rich star IRC+10216 using the spectroscopic facilities onboard the Herschel satellite. Lines from J=1-0 up to J=7-6 have been detected. From the observed intensities, we conclude that HCl is produced in the innermost layers of the circumstellar envelope with an abundance relative to H2 of 5x10^-8 and extends until the molecules reach its photodissociation zone. Upper limits to the column densities of AlH, MgH, CaH, CuH, KH, NaH, FeH, and other diatomic hydrides have also been obtained. Comment: Accepted for publication in Astronomy and Astrophysics (Herschel special issue)05/2010; -
Article: The detached dust shells of AQ And, U Ant, and TT Cyg
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ABSTRACT: Detached circumstellar dust shells are detected around three carbon variables using Herschel-PACS. Two of them are already known on the basis of their thermal CO emission and two are visible as extensions in IRAS imaging data. By model fits to the new data sets, physical sizes, expansion timescales, dust temperatures, and more are deduced. A comparison with existing molecular CO material shows a high degree of correlation for TT Cyg and U Ant but a few distinct differences with other observables are also found. Comment: Letter accepted for publication on the A&A Herschel Special Issue05/2010; -
Article: Herschel PACS and SPIRE imaging of CW Leo
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ABSTRACT: Herschel PACS and SPIRE images have been obtained over a 30'x30' area around the well-known carbon star CW Leo (IRC +10 216). An extended structure is found in an incomplete arc of ~22' diameter, which is cospatial with the termination shock due to interaction with the interstellar medium (ISM) as defined by Sahai & Chronopoulos from ultraviolet GALEX images. Fluxes are derived in the 70, 160, 250, 350, and 550 um bands in the region where the interaction with the ISM takes place, and this can be fitted with a modified black body with a temperature of 25+-3 K. Using the published proper motion and radial velocity for the star, we derive a heliocentric space motion of 25.1 km/s. Using the PACS and SPIRE data and the analytical formula of the bow shock structure, we infer a de-projected standoff distance of the bow shock of R0 = (8.0+-0.3)x10^17 cm. We also derive a relative velocity of the star with respect to the ISM of (106.6+-8.7)/sqrt(n_ISM) km/s, where n_ISM is the number density of the local ISM. Comment: Letter accepted for the Herschel A&A special issue05/2010; -
Article: AGB Stars in Globular Clusters
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ABSTRACT: From our study of AGB stars in globular clusters we present here three results: (1) Period-luminosity relations derived for the long-period variables in four clusters show a similar splitting into two sequences but also differ in the maximum luminosity reached. (2) C/O ratios measured in O-rich AGB stars in NGC 1846 prove the increase of C/O with luminosity, but also reveal exceptions to the general trend. (3) AGB stars in 47 Tuc reveal a remarkable change of mid-infrared dust features as the stars evolve up the AGB.10/2007; 378:105. -
Article: Der historische Buchbestand der Universitatssternwarte Wien. Ein illustrierter Katalog. Teil 2: 18. Jahrhundert
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ABSTRACT: On the occasion of the 250th anniversary of Vienna University Observatory, the authors present the second and final part of a catalogue that lists those Observatory library holdings which were published before 1800. While Part I presented 167 items published before 1700 (see my review in JAD 11,4), PART II lists 317 items published between 1700 and 1799. The book has a brief introduction that informs about the scope of the catalogue, the history of the Observatory and its library, and the development of the book holdings based on publication date. This is followed by the actual catalogue of 317 entries, where one page is assigned to a given book, arranged in chronological order (and followed by an author index), and finally a list of notes to some of the more important books, and those having a special relation to Vienna Observatory, is given. A book entry contains the name of the author in a modern version and the year of publication. Then follow the title (short as well as extended version), author, place of issue, publisher, language, number or pages and book size, bibliographic information in several catalogues (like Lalande's Bibliographie astronomique of 1803, or J.C. Poggendorff's Biographisch-literarisches Handworterbuch (written incorrectly Poggendorf in the catalogue, but not in the bibliography), and the catalogue number in the Observatory library. In addition, one, two, three (or rarely more) illustrations from the book are shown - at least the title page of each volume can be inspected. As already done in the previous review, the reviewer could not refrain from identifying acquisition (or registration) stamps on the title pages. Often one notes the old, almost rectangular rubber stamp Observatorium Universitatis Vindobonensis C: R: , which seems to belong to the era of Maximilian Hell and his successors. It was replaced by a plain stamp K.K. Universitats-Sternwarte Wien , covering the era 1867-1918. This was replaced by a round stamp showing a single-headed eagle in the centre, surrounded by the text Universitats-Sternwarte Wien , and obviously used after 1918. Finally, there is one book (J. Cassini, Tabulae Planetarum, 1764) which carries a stamp where the eagle has exchanged its hammer and sickle by a swastika, thus dating the acquisition to the time of 1938-45. The editors note that there are no indications of a previous owner. The first three types of stamps are also found on title pages of the books printed before 1700 (again, the reader is referred to my review in JAD 11,4). According to the cursory census, 219 books published between 1700 and 1799 carry the rectangular, 38 the plain Kakanian , and 21 the round stamp; there are about 30 books without such a stamp. Some of the rectangular books also carry a handwritten note that they belonged to the Jesuit College. Again, 4 of the post-1918 books also carry a rubber-stamped inscription Vermachtnis Rudolf Konig . Another major inheritage happened in the era 1867-1918: Several books carry a seal and the note Bibl.^a Coll. Lewenburg Schol. Piar. Vienna or Convictus Loevenburgici Scholarum Piarum . The majority (78%) of 18th century books was acquired by the Vienna observatory before 1867, 14% before the end of the monarchy, and 8% thereafter; for the pre-18th century books, the percentages are 58%, 29% and 13%. Thus, 18th century books were often acquired by the observatory library immediately after publication, while apparently a major percentage of 16th and 17th century books was integrated into the library in the early decades of the New University Observatory , i.e. after 1874. I wish to draw attention to a few omissions, errors or confusions. Usually, in each entry the author's lifespan is given. There are a few omissions in the case of well-known authors - e.g. with Boskovic, where, however, the life dates are given in the commentary section. The dates of Francois Noel are wrong, they should be 1651-1729; Wenceslaus Johann Gustav Karsten lived from 1732-1787. The first names of Johann Hieronymus Schroeter are consistently, but wrongly given in the catalogue as Johann Heinrich. The Institutions astronomiques of 1746 are attributed to Pierre-Charles Le Monnier, but are just an updated translation of John Keill's Introductio ad veram astronomiam, seu lectiones astronomicae habitae in schola astronomica Academiae Oxoniensis of 1718. To conclude this (incomplete) list of errata: The book Apostata Copernicanus, issued in Brno in 1790, inscribed at mentem R. P. Joannis Bap. Riccioli S.J. celeberrimi olim Philosophi & Astronomi institutum has, of course, not Riccioli as its author, but at most as its dedication bearer. Summing up: More than the on-line version (http://www.univie.ac.at/hwastro/), this fine catalogue of old astronomical books offers many opportunities to the reader to start his or her own inquiries into various historical issues. It is warmly recommended to astronomical libraries and serious students in the history of astronomy.Journal of Astronomical Data. 11/2006; 12:7. -
Article: Detection of anhydrous hydrochloric acid, HCl, in IRC+10216 with the Herschel SPIRE and PACS spectrometers Detection of HCI in IRC+10216
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Article: Silicon in the dust formation zone of IRC+10216
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Article: The detached dust shells of AQ Andromedae, U Antliae, and TT Cygni
http://dx.doi.org/10.1051/0004-6361/201014633. -
Article: Herschel PACS and SPIRE imaging of CW Leonis
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Article: PACS and SPIRE spectroscopy of the red supergiant VY CMa
http://dx.doi.org/10.1051/0004-6361/201014641.
Top co-authors
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Institutions
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2010
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KU Leuven
Leuven, VLG, Belgium
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2007
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University of Vienna
Vienna, Vienna, Austria
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