J/A+A/650/A102 SDSS J160429.12+100002.2 spectra (Irrgang+, 2021)
A proto-helium white dwarf stripped by a substellar companion via
common-envelope ejection.
Uncovering the true nature of a candidate hypervelocity B-type star.
Irrgang A., Geier S., Heber U., Kupfer T., El-Badry K., Bloemen S.
<Astron. Astrophys. 650, A102 (2021)>
=2021A&A...650A.102I 2021A&A...650A.102I (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, spectroscopic; Stars, B-type; Stars, white dwarf ;
Spectroscopy
Keywords: binaries: close - binaries: spectroscopic - brown dwarfs -
stars: individual: SDSS J160429.12+100002.2 -
stars: chemically peculiar - white dwarfs
Abstract:
In the past, SDSS J160429.12+100002.2 was spectroscopically classified
as a blue horizontal branch (BHB) star. Assuming a luminosity that is
characteristic of BHB stars, the object's radial velocity and proper
motions from Gaia Early Data Release 3 would imply that its Galactic
rest-frame velocity exceeds its local escape velocity. Consequently,
the object would be considered a hypervelocity star, which would prove
particularly interesting because its Galactic trajectory points in our
direction. However, based on the spectroscopic analysis of follow-up
observations, we show that the object is actually a short-period
(P∼3.4h) single-lined spectroscopic binary system with a visible
B-type star (effective temperature Teff=15840±160K and surface
gravity log(g)=4.86±0.04) that is less luminous than typical BHB
stars. Accordingly, the distance of the system is lower than
originally thought, which renders its Galactic orbit bound to the
Galaxy. Nevertheless, it is still an extreme halo object on a highly
retrograde orbit. The abundances of He, C, N, O, Ne, Mg, Al, Si, S,
and Ca are subsolar by factors from 3 to more than 100, while Fe is
enriched by a factor of about 6. This peculiar chemical composition
pattern is most likely caused by atomic diffusion processes. Combining
constraints from astrometry, orbital motion, photometry, and
spectroscopy, we conclude that the visible component is an unevolved
proto-helium white dwarf with a thin hydrogen envelope that was
stripped by a substellar companion through common-envelope ejection.
Its unique configuration renders the binary system an interesting test
bed for stellar binary evolution in general and common-envelope
evolution in particular.
Description:
The fully reduced and wavelength calibrated ESI and ISIS spectra used
in the analysis. Reduced spectra from other instruments are publicly
available in their respective archives.
Objects:
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RA (2000) DE Designation(s)
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16 04 29.14 +10 00 02.5 SDSS J160429.12+100002.2 = GALEX J160429.1+100002
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 159 9 List of fits spectra
fits/* . 9 Individual fits spectra
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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- 2 I2 h RAh Right Ascension of center (J2000)
4- 5 I2 min RAm Right Ascension of center (J2000)
7- 11 F5.2 s RAs Right Ascension of center (J2000)
12 A1 --- DE- Declination sign of center (J2000)
13- 14 I2 deg DEd Declination sign of center (J2000)
16- 17 I2 arcmin DEm Declination sign of center (J2000)
19- 22 F4.1 arcsec DEs Declination sign of center (J2000)
24- 28 I5 --- Nx Number of pixels along X-axis
30- 52 A23 "datime" Obs.date Observation date
54- 61 F8.3 0.1nm blambda Lower value of wavelength interval
63- 71 F9.3 0.1nm Blambda Upper value of wavelength interval
73- 75 I3 Kibyte size Size of FITS file
77- 96 A20 --- FileName Name of FITS file, in subdirectory fits
98-159 A62 --- Title Title of the FITS file
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Acknowledgements:
Andrea Irrgang, Andreas.Irrgang(at)fau.de
(End) Patricia Vannier [CDS] 16-Apr-2021