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Download Article (PDF) Baltic Astronomy, vol. 6, 499-572, 1997. CLASSIFICATION OF POPULATION II STARS IN THE VILNIUS PHOTOMETRIC SYSTEM. II. RESULTS A. Bartkevicius1 and R. Lazauskaite1 '2 1 Institute of Theoretical Physics and Astronomy, Gostauto 12, Vilnius 2600, Lithuania 2 Department of Theoretical Physics, Vilnius Pedagogical University, Studenty. 39, Vilnius 2340, Lithuania Received April 20, 1997. Abstract. The results of photometric classification of 848 true and suspected Population II stars, some of which were found to be- long to Population I, are presented. The stars were classified using a new calibration described in Paper I (Bartkevicius & Lazauskaite 1996). We combine these results with our results from Paper I and discuss in greater detail the following groups of stars: UU Herculis-type stars and other high-galactic-latitude supergiants, field red horizontal-branch stars, metal-deficient visual binaries, metal- deficient subgiants, stars from the Catalogue of Metal-deficient F-M Stars Classified Photometrically (MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs (Bartkevicius 1994a). It is confirmed that high galactic latitude supergiants from the Bartaya (1979) catalog are giants or even dwarfs. Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as field RHB stars, appear to be ordinary giants according to our classification. Some of the visual binaries studied can be considered as physical pairs. Quite a large fraction of stars from the MDPH catalog are found to have solar metallicity. A number of new possible UU Herculis-type stars, RHB stars and metal-deficient subgiants are identified. Key words: techniques: photometric - stars: fundamental para- meters (classification) - stars: Population II 500 A. Bartkevicius and R. Lazauskaite 1. INTRODUCTION Although Population II stars are rare in the solar neighborhood, they play an important role in different branches of astronomy due to their unique characteristics - they are the oldest stars in the Galaxy and, consequently, exhibit metal-deficiency, high velocities and spend most of their life in the galactic halo. Despite a long history of investigation of the stellar content of our Galaxy, a generally accepted definition of stellar populations does not exist (Majewski 1993, King 1995). In this paper, as in our previous papers (Bartkevicius 1994b, Bartkevicius & Lazauskaite 1996, hereafter Paper I) we use the term Population II for stars with metallicity [Fe/H]< —0.5 and a total space velocity (or its radial or tangential components) >100 km s-1. It is obvious that we admit to our Population II sample not only extreme Population II (halo) stars, but also intermediate Population II (thick disk, partly old disk) stars. In this paper we present the results of three-dimensional classifi- cation in the Vilnius photometric system of 848 known or suspected Population II stars and some Population I stars (visual binaries, su- pergiants, etc.) necessary for comparison with Population II stars. For the classification we use the methods described in Paper I of this series. Combining the results of classification from this paper and the results of the reclassification of 809 standard stars from Pa- per I (this brings to 1657 the number of stars classified in a unique scheme), we discuss the following groups of Population II stars: UU Herculis-type stars, field RHB stars, visual binaries, metal-deficient subgiants, stars from the MDPH catalog (Bartkevicius 1993) and the HIPPARCOS program stars (Bartkevicius 1994a). 2. PREVIOUS RESULTS OF CLASSIFICATION The development of methods for identification and classification of Population II stars in the Vilnius photometric system is briefly described in Paper I. Here we discuss applications of these methods for the determination of the main astrophysical parameters of Pop- ulation II stars. Bartkevicius & Sperauskas (1983) have classified 312 stars, among which a number of new giants and subdwarfs with high metal deficiency were identified. Twelve stars were suspected of being metal-deficient subgiants. It was estimated that about 20 % of high proper motion {¡JL > 0. 26 yr-1) stars are giants or subgiants. Classification of Population II stars 501 Bartkevicius & Tautvaisiene (1987) have made a three-dimen- sional classification of 78 known metal-deficient giants. Bartasiute (1989) has presented the results of classification of 343 stars in an area of 900 square degrees near the South Galactic Pole. Among the stars studied, 35 subdwarfs were identified. Also, the amount of interstellar reddening in this region was investigated. Bartasiute (1993) in her thesis has presented the results of clas- sification of 1189 stars. A majority of these stars are metal-deficient. The results of classification were combined with proper motion and radial velocity data, and space velocities and galactic orbits were calculated for these stars. On the basis of these data, a detailed analysis of stellar populations was carried out. Straizys et al. (1981) detected eight stars suspected of belonging to the red horizontal-branch stars. Recently, Tautvaisiene (1996a) has investigated 13 red horizontal-branch candidates identified by Rose (1985). She determined their spectral types, metallicities, abso- lute magnitudes, eifective temperatures and surface gravities. From a comparison of the observational HR diagram with isochrones, an age of 10-12 Gyr was obtained for these stars. Tautvaisiene (1987) also has calculated Te and log g for 110 metal-deficient giants from color indices in the Vilnius system and compared Te, log g plots with evolutionary tracks and isochrones. Bartkevicius et al. (1992) have classified in the Vilnius system 117 known and suspected Population II supergiants and related stars. Sperauskas (1987) has presented the photometric classification of 32 B and A stars suspected to belong to the blue horizontal- branch on the grounds of intermediate and low dispersion spectra or photometric color indices of various photometric systems. And, at last, in Paper I we presented the classification of 809 standard stars used for establishing new classification methods for Population II stars in the Vilnius photometric system. 3. OBSERVATIONS AND SELECTION OF STARS According to sources of the observed color indices, the stars in- vestigated in this paper can be divided into two groups: (1) stars observed within several special programs of investiga- tion of Population II stars (see Subsection 3.1), (2) stars selected according to some criteria (see Subsection 3.3) from the General Photometric Catalog of Stars Observed in the Vil- nius Photometric System (Straizys & Kazlauskas 1993). 502 A. Bartkevicius and R. Lazauskaite 3.1. Programs of investigation of Population II stars Since 1986, several long-term programs of the photometric in- vestigation of Population II stars in the Vilnius system have been started. Some of the investigations described in Section 2 have also been continued. Some stars are included in two or more programs. Below we list the programs and the groups of stars included: 1. Stars with known trigonometric parallaxes, absolute magni- tudes My and metallicities [Fe/H]; 2. HIPPARCOS program stars (Bartkevicius 1994a); 3. Eggen's halo and old disk moving group members (see Eggen 1996): stars from the Arcturus, a Puppis, Kapteyn and Groom- bridge 1830 moving groups; 4. Known and suspected UU Herculis-type stars, supergiants at high galactic latitudes, supergiants of normal chemical composition; 5. Field red horizontal-branch (RHB) candidates; 6. Metal-deficient subgiants; 7. Metal-deficient F-M stars classified spectroscopically from the MDSP catalog (Bartkevicius 1980) and its supplement MDSPS1 (Bartkevicius 1984) and stars from the Catalog of Metal-deficient F-M Stars Classified Photometrically (MDPH; Bartkevicius 1993); 8. Population II visual and spectral binaries; 9. Population II radial velocity program stars (Bartkevicius & Sperauskas 1990); 10. Some peculiar and astrophysically interesting stars. Not all of these programs have been completed at the present time. A detailed description of the programs related directly to the subject of the present study and a discussion of the results obtained will be presented in Section 6. 3.2. Observations Photoelectric observations in the Vilnius photometric system were done with the 63 cm telescope of the Moletai Observatory (Lithuania), the 48 cm telescope of the Vilnius University and 1 m telescope of the Institute of Theoretical Physics and Astronomy, the two latter telescopes being located at the Maidanak Observa- tory in Uzbekistan. At our request, 10 stars were observed by K. Zdanavicius with the 61 cm telescope of the Mount John Obser- vatory, New Zealand. The time of observations, the telescopes used Classification of Population II stars 503 Table 1. Observing runs and references to the published results. No. Run Observatory, Publication telescope 1. March-May 1986 Moletai, 63 cm Tautvaisiene (1996a) 2. July 1986 Maidanak, 48 cm Lazauskaite & Tautvaisiene (1990) 3. April-May 1987 Moletai, 63 cm This paper 4. August 1987 Maidanak, 48 cm Lazauskaite & Tautvaisiene (1990) 5. August 1988 Maidanak, 1 m Lazauskaite & Tautvaisiene (1990) 6. October 1988 Maidanak, 1 m Lazauskaite & Tautvaisiene (1990) 7. May 1991 Maidanak, 1 m Lazauskaite (1992) 8. October 1991 Maidanak, 1 m Lazauskaite (1992) 9. October-December 1991 Mt. John, 63 cm Zdanavicius et al. (1995) and references to the published observational data are presented in Table 1. The Moletai Observatory measurements were
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