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A&A 470, 1201–1214 (2007) Astronomy DOI: 10.1051/0004-6361:20077571 & c ESO 2007 Astrophysics VSOP: the variable star one-shot project I. Project presentation and first data release T. H. Dall1,C.Foellmi2, J. Pritchard3, G. Lo Curto4, C. Allende Prieto5,H.Bruntt6,P.J.Amado7, T. Arentoft8, M. Baes9, E. Depagne4,10, M. Fernandez11,V.Ivanov4, L. Koesterke5, L. Monaco4, K. O’Brien4, L. M. Sarro12,I.Saviane4, J. Scharwächter4, L. Schmidtobreick4, O. Schütz4,A.Seifahrt13, F. Selman4, M. Stefanon4, and M. Sterzik4 1 Gemini Observatory, 670 N. A’ohoku Pl., Hilo, HI 96720, USA e-mail: [email protected] 2 Laboratoire d’AstrOphysique de Grenoble, 414 rue de la Piscine, 38400 Saint-Martin d’Hères, France 3 European Southern Observatory, Karl Schwarzschild-Str. 2, 85748 Garching bei München, Germany 4 European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago, Chile 5 McDonald Observatory and Department of Astronomy, The University of Texas, Austin, TX 78712-1083, USA 6 School of Physics A28, University of Sydney, 2006 NSW, Australia 7 Universidad de Granada-IAA(CSIC), PO Box 3004, 18080 Granada, Spain 8 Department of Physics and Astronomy, University of Aarhus, 8000 Aarhus C, Denmark 9 Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281 S9, 9000 Gent, Belgium 10 Pontificia Universidad Catolica de Chile, Vicuna Mackenna 4860, Santiago de Chile, Chile 11 Instituto de Astrofísica de Andalucía, Camino Bajo de Huétor 50, 18008 Granada, Spain 12 Department of Artificial Intelligence, ETSI Informática, Juan del Rosal 16, 28040 Madrid, Spain 13 Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergässchen 2, 07745 Jena, Germany Received 29 March 2007 / Accepted 28 May 2007 ABSTRACT Context. About 500 new variable stars enter the General Catalogue of Variable Stars (GCVS) every year. Most of them however lack spectroscopic observations, which remains critical for a correct assignement of the variability type and for the understanding of the object. Aims. The Variable Star One-shot Project (VSOP) is aimed at (1) providing the variability type and spectral type of all unstudied variable stars, (2) process, publish, and make the data available as automatically as possible, and (3) generate serendipitous discov- eries. This first paper describes the project itself, the acquisition of the data, the dataflow, the spectroscopic analysis and the on-line availability of the fully calibrated and reduced data. We also present the results on the 221 stars observed during the first semester of the project. Methods. We used the high-resolution echelle spectrographs HARPS and FEROS in the ESO La Silla Observatory (Chile) to survey known variable stars. Once reduced by the dedicated pipelines, the radial velocities are determined from cross correlation with syn- thetic template spectra, and the spectral types are determined by an automatic minimum distance matching to synthetic spectra, with traditional manual spectral typing cross-checks. The variability types are determined by manually evaluating the available light curves and the spectroscopy. In the future, a new automatic classifier, currently being developed by members of the VSOP team, based on these spectroscopic data and on the photometric classifier developed for the COROT and Gaia space missions, will be used. Results. We confirm or revise spectral types of 221 variable stars from the GCVS. We identify 26 previously unknown multiple sys- tems, among them several visual binaries with spectroscopic binary individual components. We present new individual results for the multiple systems V349 Vel and BC Gru, for the composite spectrum star V4385 Sgr, for the T Tauri star V1045 Sco, and for DM Boo which we re-classify as a BY Draconis variable. The complete data release can be accessed via the VSOP web site. Key words. stars: variables: general – stars: fundamental parameters – methods: observational – astronomical data bases: miscellaneous 1. Introduction around 500 per year; actually 1700 between the Namelists 77 (Kazarovets et al. 2003) and 78 (Kazarovets et al. 2006). The There are more than 38 000 known variable stars listed in the true number of new variables is higher though, and this in- latest edition of the General Catalog of Variable Stars (GCVS; completeness of the GCVS will likely increase in the coming Kholopov et al. 1998). Almost 4000 of these have no spec- decade due to the large surveys that will be performed with tral type assigned and nearly 2000 are listed with an uncertain both ground-based and space-based telescopes. About half of the variability type, often because of lack of spectroscopic charac- newly identified GCVS variables have unknown variability type terisation. The rate of inclusion of new variables is currently and most of them have no published spectral type. Moreover, many (even “firm”) variables have disagreeing designations be- Based on data obtained at the La Silla Observatory, European ff ff Southern Observatory, under program ID 077.D-0085. tween di erent authors and even between di erent catalogs, Article published by EDP Sciences and available at http://www.aanda.org or http://dx.doi.org/10.1051/0004-6361:20077571 1202 T. H. Dall et al.: VSOP I. First data release e.g. there are frequent disagreements between the SIMBAD 2. to process, publish, and make the data available as automat- database and GCVS. In addition, binarity is rarely detectable ically as possible, facilitating additional science; unquestionably by photometric data alone. Finally, many desig- 3. to generate serendipitous discoveries that will fuel future nations are taken at face value without questioning the reliabil- research. ity. This unreliability is a major obstruction to many individual studies, and would often require only one “snapshot” spectrum In addition, due to its beginnings as a proposal for an observatory to achieve a major improvement. Of course, single shot spectra project, VSOP has been designed with a view to both science and would not always be able to reveal binarity or transient phenom- observatory efficiency. ena. Recent examples of the misidentification of variables, where 2.1. Science efficiency the designation was based solely on photometric light curve ap- pearance, and subsequently corrected by taking one single snap- A stellar spectrum is a rich source of information. Often, how- shot spectrum, include: ever, only certain aspects of the object under study is of interest FH Leo, that was long thought to be the only known cat- to the scientist conducting the study. One main goal of VSOP aclysmic variable (CV) to form part of a binary system, being is to revise spectral and variability types, but there are certainly designated as a nova-like variable by Kazarovets et al. (2003) many other scientifically interesting studies one could perform based on an outburst observed by the Hipparcos satellite. High- using our data. We choose, rather than to sit on the data until resolution FEROS spectroscopy allowed us to refute the classi- we may find time for additional studies, to make the data easily fication and show that the stars are normal F8 and G0 dwarfs available to the general community, in the hope that somebody (Dall et al. 2005), and that the outburst cannot possibly be due else will be able to do additional science with the data. This way, to an accretion disk, but rather to a superflare or to erroneous the science output is maximised. Hipparcos measurements, or due to a CV “hidden” in the light Another aspect that contributes to the science efficiency, is of the two normal stars (Vogt 2006). serendipity. The VSOP observations are targeting poorly stud- ied variable stars, many of which are exhibiting poorly studied XY Pic was included in a study of statistical properties of 1 W UMa type variables (active, very fast rotating contact bina- phenomena. We thus expect to obtain by chance data that either ries) by Selam (2004), who concluded that it was among the merit follow-up in-depth studies, or sheds light on some hith- most active stars of the sample, based on a fit of its Hipparcos erto obscured phenomenon. Much of this work may naturally be ffi light curve, using synthetic light curves based on physical pa- done by groups not a liated with VSOP. rameters. FEROS spectra of XY Pic allowed us to show that the star is a rather slowly rotating F3 giant, with no measurable chro- 2.2. Observatory efficiency mospheric activity (Dall 2005), and is likely a δ Scuti pulsator. This example shows, that even a high-quality light curve analy- VSOP was originally conceived as an ESO observatory project, sis can result in wrong conclusions about the nature of an object aimed at providing observations with loose weather and pointing without spectroscopic confirmation. constraints, with the aim of increasing observing efficiency dur- TV Ret was long thought to be a CV due to an outburst ob- ing periods when other programmes with stronger constraints served photometrically in 1977. A single low resolution spec- on airmass, seeing, and/or transparency cannot be carried out. trum, revealed the object to be a compact emission line galaxy Given the all-sky coverage, the loose constraints, and the large at z ∼ 0.1, possibly hosting an extremely bright supernova as the scope of the project, VSOP is an excellent example of a perfect cause of the outburst (Schmidtobreick et al. 2007). filler programme, which will be extended to other observatories The above examples illustrate the need for snapshot spectra, in the near future. and shows that the vast collection of poorly studied variable stars contains many errors in terms of variability type designation, 2.3. VSOP vs. other surveys which may in many cases “cover up” some potentially interest- ing physical phenomena under a wrong and seemingly dull label. The most extensive spectroscopic survey to date, is the Sloan In this paper we describe a new large project, the Variable Stars Digital Sky survey (SDSS; York et al.