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J/AJ/109/1797     H-Alpha Measurements for Cool Giants (Eaton 1995)
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H-Alpha Measurements for Cool Giants
     Eaton J.A.
    <Astron. J. 109, 1797 (1995)>
    =1995AJ....109.1797E
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ADC_Keywords: Stars, giant ; Equivalent widths

Abstract:
    The H-alpha line in a cool star is usually an indication of the
    conditions in its chromosphere. I have collected H-alpha spectra of
    many northern G-M stars, which show how the strength and shape of the
    H-alpha line change with spectral type. These observations detect
    surprisingly little variation in absorption-line depth (Rc ~ 0.23 +/-
    0.08), linewidth (FWHD ~ 1.44 +/- 0.22 A), or equivalent width (EW ~
    1.12 +/- 0.17 A) among G5-M5 III giants. Lines in the more luminous
    stars tend to be broader and stronger by 30%-40% than in the Class III
    giants, while the H-alpha absorption tends to weaken among the cooler
    M giants. Velocities of H-alpha and nearby photospheric lines are the
    same to within 1.4 +/- 4.4 km/s for the whole group. To interpret
    these observations, I have calculated H-alpha profiles, Ly-alpha
    strengths and [C II] strengths for a series of model chromospheres
    representing a cool giant star like Alpha Tau. Results are sensitive
    to the mass of the chromosphere, to chromospheric temperature, to
    clumping of the gas, and to the assumed physics of line formation. The
    ubiquitous nature of H-alpha in cool giants and the great depth of
    observed lines argue that chromospheres of giants cover their stellar
    disks uniformly and are homogeneous on a large scale. This is quite
    different from conditions on a small scale: To obtain a high enough
    electron density with the theoretical models, both to explain the
    excitation of hydrogen and possibly also to give the observed [C II]
    multiplet ratios, the gas is probably clumped. The 6540-6580 A spectra
    of 240 stars are plotted in an Appendix, which identifies the date of
    observation and marks positions of strong telluric lines on each
    spectrum. Section 2 assesses the effects of telluric lines and
    estimates that the strength of scattered light is ~5% of the continuum
    in these spectra. Table 1 gives the measurements of H-alpha as well as
    equivalent widths of two prominent photospheric lines, Fe I lambda
    6546 and Ca I lambda 6572, which strengthen with advancing spectral
    type.


File Summary:
--------------------------------------------------------------------------------
 FileName    Lrecl    Records   Explanations
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ReadMe          80          .   This file
table1.dat      90        254   Measurements of H-alpha in Red Giants
table1.tex     101        395   TeX version of table1.tex
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Byte-by-byte Description of file: table1.dat
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   Bytes Format  Units       Label      Explanations
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   1- 8   A8     ---         Star       Bright Star <V/50> (HR) star number
  10-21   A12    ---         Name       Other name
  23      A1     ---         Note      *[ab] Table note letter
  25-36   A12    ---         Sp         Spectral type
  37-42   F6.2   mag         Vmag       []? V magnitude
  43-48   F6.2   mag         B-V        []? B-V magnitude
  49-55   F7.3   ---         Rc         []? Residual intensity of H-alpha line
  57      A1     ---         l_FWHD     [<] FWHD limiting character
  58-61   F4.2   0.1nm       FWHD       []? Full-width of H-alpha at half-depth
  63      A1     ---         l_EW       [<] EW limiting character
  64-69   F6.3   0.1nm       EW         []? Equivalent width of H-alpha
  70-75   F6.1   km/s        dRV        []? Diff. in radial velocity between
                                            H-alpha and strong metallic lines
  76-82   F7.3   0.1nm       EW_FeI     []? Equivalent width of Fe I lambda 6546
  83      A1     ---         n_EW_FeI  *[T] Possible telluric line contamination
  84-89   F6.3   0.1nm       EW_CaI     []? Equivalent width of Ca I lambda 6572
  90      A1     ---         n_EW_CaI  *[T] Possible telluric line contamination
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Note on Note:
  a. Observed with Kitt Peak coude feed telescope only
  b. from Kurucz et al. 1984, Solar Flux Atlas from 296 to 1300 nm

Note on n_EW_FeI, n_EW_CaI:
  A "T" indicates that the equivalent widths possibly are contaminated
  by telluric absorption lines.  See the printed paper, section 2 for
  a discussion of the analysis for marking the equivalent widths as
  possibly contaminated.
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Origin: AAS CD-ROM series, Volume 4, 1995         Lee Brotzman [ADS] 04-May-1995
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(End)                                                         [CDS]  11-Jul-1995