J/A+A/585/A145 LX Cyg optical, NIR and MIR spectra (Uttenthaler+, 2016)
LX Cygni: A carbon star is born.
Uttenthaler S., Meingast S., Lebzelter T., Aringer B., Joyce R.R.,
Hinkle K., Guzman-Ramirez L., Greimel R.
<Astron. Astrophys. 585, A145 (2016)>
=2016A&A...585A.145U 2016A&A...585A.145U (SIMBAD/NED BibCode)
ADC_Keywords: Stars, carbon ; Spectroscopy
Keywords: stars: AGB and post-AGB - stars: evolution - stars: carbon -
stars: individual: LX Cygni
Abstract:
The Mira variable LX Cygni (LX Cyg) showed a dramatic increase of its
pulsation period in the recent decades and appears to undergo an
important transition in its evolution.
We aim at investigating the spectral type evolution of this star over
the recent decades as well as during one pulsation cycle in more
detail and discuss it in connection with the period evolution.
We present optical, near- and mid-infrared low-resolution as well as
optical high-resolution spectra to determine the current spectral
type. The optical spectrum of LX Cyg has been followed for more than
one pulsation cycle. Recent spectra are compared to archival spectra
to trace the spectral type evolution and a Spitzer mid-IR spectrum is
analysed for the presence of molecular and dust features. Furthermore,
the current pulsation period is derived from AAVSO data.
It is found that the spectral type of LX Cyg changed from S to C
sometime between 1975 and 2008. Currently, the spectral type C is
stable during a pulsation cycle. It is shown that spectral features
typical of C-type stars are present in its spectrum from ∼0.5 to
14µm. An emission feature at 10.7µm is attributed to SiC grains.
The pulsation period of LX Cyg has increased from ∼460d to ∼580d
within only 20 years, and is stable now.
We conclude that the change in spectral type and the increase in
pulsation period happened simultaneously and are causally connected.
Both a recent thermal pulse (TP) and a simple surface temperature
decrease appear unlikely to explain the observations. We therefore
suggest that the underlying mechanism is related to a recent third
dredge-up mixing event that brought up carbon from the interior of the
star, i.e. that a genuine abundance change happened. We propose that
LX Cyg is a rare transition type object that is uniquely suited to
study the transformation from oxygen- to carbon-rich stars in detail.
Description:
Spectra of LX Cygni obtained with various spectrographs at various
observatories, at various wavelengths and spectral resolutions. The
flux is in arbitrary units, except for the Spitzer spectrum, where the
flux is given in Jansky. For details on the observations, see Section
2 of the paper. The data are stored in a two-column array containing
the wavelength and the flux, except for the Hermes/Mercator spectra,
where the wavelength scale is stored in the fits header. No correction
for telluric absorption has been applied.
Objects:
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RA (2000) DE Designation(s)
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21 55 57.03 +48 20 52.6 LX Cyg = V* LX Cyg
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 185 14 List of fits spectra
fits/* . 14 Individual fits spectra
sp/* . 14 Individual spectra in ascii format
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 26 A26 --- Obs.Date Observation date
(YYYY-DD-MMThh:mm:ss.ssssss)
28- 35 F8.2 01.nm blambda Lower limit of wavelength interval
37- 45 F9.2 01.nm Blambda Upper limit of wavelength interval
46- 55 F10.6 0.1nm dlambda Spectral resolution
57- 60 I4 Kibyte size Size of the fits files
62-107 A46 --- FileName Name of the spectrum file in
subdirectory fits
109-185 A77 --- Title Title of the file
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Acknowledgements:
Stefan Uttenthaler, stefan.uttenthaler(at)univie.ac.at
(End) Patricia Vannier [CDS] 23-Nov-2015