J/AJ/109/1797 H-Alpha Measurements for Cool Giants (Eaton 1995)
H-Alpha Measurements for Cool Giants
Eaton J.A.
<Astron. J. 109, 1797 (1995)>
=1995AJ....109.1797E 1995AJ....109.1797E
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:
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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 --- nEWFeI *[T] Possible telluric line contamination
84-89 F6.3 0.1nm EW_CaI []? Equivalent width of Ca I lambda 6572
90 A1 --- nEWCaI *[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 nEWFeI, nEWCaI:
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
(End) [CDS] 11-Jul-1995