0 5 O 0 5 O C s n O M O O. O O O O O O O O O O. d d d d d d d d d d. O O O O O O O O O O. 0 > O M O « t - ( O O O O r H. c s - ^ - v c o p O c ^ c ^ r t r i r Ù.
Baltic Astronomy,
vol. 5, 1-82, 1996.
C L A S S I F I C A T I O N O F P O P U L A T I O N II S T A R S I N T H E V I L N I U S P H O T O M E T R I C S Y S T E M . I. M E T H O D S
A. Bartkevicius 1 and R. Lazauskaite 1 ' 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 February 7, 1996. Abstract. The methods used for classification of Population II stars in the Vilnius photometric system are described. An extensive set of standards with known astrophysical parameters compiled from the literature sources is given. These standard stars are classified in the Vilnius photometric system using the methods described. The accuracy of classification is evaluated by a comparison of the astrophysical parameters derived from the Vilnius photometric system with those estimated from spectroscopic studies as well as from photometric data in other systems. For dwarfs and subdwarfs, we find a satisfactory agreement between our reddenings and those estimated in the uvby/3 system. The standard deviation of [Fe/H] determined in the Vilnius system is about 0.2 dex. The absolute magnitude for dwarfs and subdwarfs is estimated with an accuracy of (60 - 100) km s~K Thus, we included into our set b o t h halo and thick disk (intermediate Population II) stars. Our preliminary set of Population II s t a n d a r d stars was described by Bartkevicius & Lazauskaite (1993). Later on, these stand a r d s were critically analyzed once more, and now the set contains a total of 809 stars of different types (827 records including variable stars in different phases). T h e groups of s t a n d a r d stars are listed in Table 1. To recognize normal stars in a sample of unknown stars, we included into our set not only Population II stars b u t also dwarfs, giants, subgiants and supergiants with normal chemical composition. A Bootis-type stars are Population I stars, however, they were included into our set due to their metal deficiency. W h i t e dwarfs were Unauthenticated Download Date | 3/23/17 2:05 AM
4
A. Bartkevicius and R. Lazauskaite
also included with the purpose of separating t h e m from s d O - B a n d s d F - G stars. T h e mean values of astrophysical parameters of s t a n d a r d stars, which were derived as described below, are presented in Table 6. It contains star name, intrinsic color index (Y—V)o, color excess EY-V> metallicity, absolute magnitude, spectral type, group m e m b e r s h i p a n d six intrinsic color indices. In the notes after the Table, information a b o u t variability, duplicity and membership in moving groups is presented. Abbreviations used in these notes are explained in Table 7. W h e n compiling astrophysical parameters of s t a n d a r d stars, much attention was given to their absolute magnitudes. T h e My values were compiled from the literature or estimated by us as described by Bartkevicius & Lazauskaite (1993). T h e individual values of My were averaged with the weights inversely proportional to t h e square of their errors. For averaging, we used only those My values which were consistent within 2 magnitudes. Color excesses EB-V or EY-v for s t a n d a r d stars were obtained f r o m different sources. For a part of stars, their reddenings were est i m a t e d by Bartkevicius &; Sperauskas (1983), Bartkevicius & Tautvaisiene (1987) and Bartasiute (1989). Color excesses of t h e remaining stars were obtained using estimations of interstellar reddening of different authors, among them, the maps of EG-y constructed by Burstein & Heiles (1982) from H I distribution and deep galaxy counts. In the final stage of this work, for calculation of reddening we used t h e program kindly supplied us by Dr. David Burstein. Stars with unknown reddening were classified in the Vilnius p h o t o m e t r i c system by the m e t h o d of comparison of reddening-free Q - p a r a m e t e r s of t h e s t a n d a r d and the program stars. Color exesses derived in different ways were averaged with equal weights. If, however, one source gave a clearly discrepant value, it was eliminated f r o m t h e average. In addition, it was assumed t h a t stars within 50 pc are u n r e d d e n e d by interstellar m a t t e r . Since in most cases reddening of the s t a n d a r d stars is small (Fig. 1), the errors of EY-y values are not significant in determination of the intrinsic color indices. T h e metallicities were taken from the Catalogue of t h e m e a n [Fe/H], Teff and log g compiled by Bartkevicius &: Lazauskaite (1995). In t h e case of [Fe/H] derived from high-resolution spectra, t h e values in Table 6 are given to two decimal places. T h e remaining metallicities are derived from the medium-resolution spectra or were estim a t e d in the Vilnius photometric system. Unauthenticated Download Date | 3/23/17 2:05 AM
Classification of Population II Stars
5
Table 1. Groups of standard stars No. Group
Abbreviation
1.
Dwarfs ( [ F e / H ] > - 0 . 2 ;
2.
Dwarfs with moderate metal deficiency
3.
Subdwarfs ( - 0 . 6 > [ F e / H ] > - 1 . 3 ;
SD
98
4.
SDEXTR
66
5.
Extreme metal-deficient subdwarfs ([Fe/H]< —1.3; My >4.0) Giants ([Fe/H]> —0.3; Mv[Fe/H]>—0.6;
(—0.3>[Fe/H]> —1.3;
Mv>4.0)
D
N
MDD
159
85
Mv>4.0) Mv>4.0)
Mv[Fe/H]>-1.3; 2.0 _ CO co V o •Ö ,-s c« bO b0 — os ' b ^ OS fc; > r-T i-H 0 3 o « H § s e i "cö O O S ^ >»2 c c J 3 C 3 X5 3
Q
Q
>
Q
Q
o
Q
¿
o Q
o
