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J/AJ/117/2308    Spectroscopy of hot stars in the halo     (Wilhelm+, 1999)
Spectroscopy of hot stars in the galactic halo. II. The identification and
classification of horizontal-branch and other A-type stars
    Wilhelm R., Beers T.C., Gray R.O.
   <Astron. J. 117, 2308 (1999)>
   =1999AJ....117.2308W
ADC_Keywords: Abundances, [Fe/H] ; Colors ; Equivalent widths ;
              Models, atmosphere ; Stars, halo ; Stars, horizontal branch
Keywords: Galaxy: halo - stars: horizontal-branch - stars: Population II


Abstract:
    We discuss a spectroscopic and photometric technique that enables the
    identification and classification of field horizontal-branch (FHB) and
    other A-type stars, even from relatively low signal-to-noise ratio
    medium-resolution spectra. This technique makes use of broadband UBV
    colors predicted from model atmosphere calculations and Balmer line
    profiles and Ca II K equivalent widths determined from synthetic
    spectra to estimate the physical parameters Teff, log(g), and [Fe/H]
    for stars in the effective temperature range 6000 - 10,000 K.

Description:
    We have computed a total of 833 synthetic spectra, using the ATLAS9
    model atmospheres from Kurucz CD-ROM 13 (R. L. Kurucz 1993, private
    communication) and the PC-based spectral synthesis routine SPECTRUM
    (Gray & Corbally 1994). The parameter space we explore covers the
    ranges 6000 K ≤ Teff ≤ 10,000 K, in increments of 250 K,
    2.0 ≤ log(g) ≤ 5.0, in increments of 0.5 dex, and
    -3.0 ≤ [Fe/H] ≤ 0.0, in increments of 0.5 dex. This range is
    set, at the cool end, by the limit at which surface gravities can be
    reliably determined from U-B colors and, at the hot end, by the point
    at which surface gravity can be used as a luminosity class indicator
    and at which the Ca II K line can be employed as a metal abundance
    estimator.

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table1.dat        74      833   Calibration grid from Kurucz model atmospheres


See also:
   J/AJ/103/267 : Spectrocopy of hot stars in galactic halo (Beers+ 1992)
   VI/39 : Model Atmospheres (Kurucz, 1979)


Byte-by-byte Description of file: table1.dat

   Bytes Format Units   Label     Explanations

   1-  5  I5    K       Temp      Effective temperature of Kurucz model
   8- 10  F3.1  [g/cm2] log(g)    Log of the surface gravity of Kurucz model
  14- 18  F5.1  [Sun]   [Fe/H]    Log of the iron abundance relative to
                                   hydrogen of Kurucz model
  22- 26  F5.2  mag     B-V       Predicted B-V from Kurucz color calibrations
  30- 34  F5.2  mag     U-B       Predicted U-B from Kurucz color calibrations
  38- 42  F5.2  0.1nm   EqWCa     Equivalent width of the Ca II K line
  46- 50  F5.2  0.1nm   EqWH4     Equivalent width of Hδ
  54- 58  F5.2  0.1nm   EqWH3     Equivalent width of Hγ
  62- 66  F5.2  0.1nm   DH4       Full width at 20% below a local continuum
                                   level of Hδ
  70- 74  F5.2  0.1nm   DH3       Full width at 20% below a local continuum
                                   level of Hγ


History:
    From AJ electronic edition

References:
  Gray, R. O., & Corbally, C. J. 1994, AJ, 107, 742 (1994AJ....107..742G)
(End)                                          Greg Schwarz [AAS]    06-Apr-2000