J/MNRAS/523/1297 Optical spectra of M dwarfs blue depression (Jones+, 2023)
A blue depression in the optical spectra of M dwarfs.
Jones H.R.A., Pavlenko Y., Lyubchik Y., Bessell M., Allard N.,
Pinfield D.J.
<Mon. Not. R. Astron. Soc. 523, 1297 (2023)>
=2023MNRAS.523.1297J 2023MNRAS.523.1297J (SIMBAD/NED BibCode)
ADC_Keywords: Stars, M-type ; Spectra, optical
Keywords: stars: abundances - stars: atmospheres -
stars: fundamental parameters - atomic data - line: profiles -
line: identification
Abstract:
A blue depression is found in the spectra of M dwarfs from 4000 to
4500Å. This depression shows an increase toward lower temperatures
though is particularly sensitive to gravity and metallicity. It is the
single strongest and most sensitive feature in the optical spectra of
M dwarfs. The depression appears as centred on the neutral calcium
resonance line at 4227Å and leads to nearby features being weaker
by about two orders of magnitude than predicted. We consider a variety
of possible causes for the depression including temperature, gravity,
metallicity, dust, damping constants and atmospheric stratification.
We also consider relevant molecular opacities which might be the cause
identifying AlH, SiH, and NaH in the spectral region. However, none of
these solutions are satisfactory. In the absence of a more accurate
determination of the broadening of the calcium line perturbed by
molecular hydrogen, we find a promising empirical fit using a modified
Lorentzian line profile for the calcium resonance line. Such fits
provide a simplistic line-broadening description for this calcium
resonance line and potentially other un-modelled resonance lines in
cool high pressure atmospheres. Thus we claim the most plausible cause
of the blue depression in the optical spectra of M dwarfs is a lack of
appropriate treatment of line broadening for atomic calcium. The broad
wings of the calcium resonance line develop at temperatures below
about 4000K and are analogous to the neutral sodium and potassium
features which dominate the red optical spectra of L dwarfs.
Description:
Spectra from WiFeS on ANU2.3m and ISIS on WHT.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
stars.dat 89 8 List of studied M dwarfs
sp/* . 10 Individual spectra
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Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Star name
12- 13 I2 h RAh Right ascension (J2000)
15- 16 I2 min RAm Right ascension (J2000)
18- 30 F13.10 s RAs Right ascension (J2000)
32 A1 --- DE- Declination sign (J2000)
33- 34 I2 deg DEd Declination (J2000)
36- 37 I2 arcmin DEm Declination (J2000)
39- 50 F12.9 arcsec DEs Declination (J2000)
52- 70 A19 --- FileName1 Name of the first spectrum file
in subdirectory sp
72- 89 A18 --- FileName2 Name of the second spectrum file
in subdirectory sp
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
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1- 10 F10.5 0.1nm lambda Wavelength
12- 25 E14.9 10mW/m2/nm RFlux Relative absolute flux (erg/s/cm2/Å)
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Acknowledgements:
Hugh R.A. Jones, h.r.a.jones(at)herts.ac.uk
(End) Patricia Vannier [CDS] 02-May-2023