J/A+A/639/L6 HERMES spectra of LS V +22 25 (Shenar+, 2020)
The "hidden" companion in LB-1 unveiled by spectral disentangling.
Shenar T., Bodensteiner J., Abdul-Masih M., Fabry M., Mahy L., Marchant P.,
Banyard G., Bowman D.M., Dsilva K., Hawcroft C., Reggiani M., Sana H.
<Astron. Astrophys. 639, L6 (2020)>
=2020A&A...639L...6S 2020A&A...639L...6S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable ; Binaries, spectroscopic ; Spectra, optical
Keywords: stars: early-type - stars: emission-line, Be -
binaries: spectroscopic - binaries: close -
stars: individual: LS V+22 25
Abstract:
The intriguing binary LS V +22 25 (LB-1) has drawn much attention
following claims of it being a single-lined spectroscopic
binary with a 79-day orbit comprising a B-type star and a ∼70M☉
black hole - the most massive stellar black hole reported to date.
Subsequent studies demonstrated a lack of evidence for a companion of
such great mass. Recent analyses have implied that the primary star is
a stripped He-rich star with peculiar sub-solar abundances of heavy
elements, such as Mg and Fe. However, the nature of the secondary,
which was proposed to be a black hole, a neutron star, or a main
sequence star, remains unknown.
Based on 26 newly acquired spectroscopic observations secured with the
HERMES and FEROS spectrographs covering the orbit of the system, we
perform an orbital analysis and spectral disentangling of LB-1 to
elucidate the nature of the system.
To derive the radial velocity semi-amplitude K2 of the secondary and
extract the spectra of the two components, we used two independent
disentangling methods: the shift-and-add technique and Fourier
disentangling with FDBinary. We used atmosphere models to constrain
the surface properties and abundances.
Our disentangling and spectral analysis shows that LB-1 contains two
components of comparable brightness in the optical. The narrow-lined
primary, which we estimate to contribute 55% in the optical, has
spectral properties that suggest that it is a stripped star: it has a
small spectroscopic mass (∼1M☉) for a B-type star and it is He-
and N-rich. Unlike previous reports, the abundances of heavy elements
are found to be solar. The 'hidden' secondary, which contributes about
45% of the optical flux, is a rapidly rotating (vsini∼300km/s) B3 V
star with a decretion disk - a Be star. As a result of its rapid
rotation and dilution, the photospheric absorption lines of the
secondary are not readily apparent in the individual observations.We
measure a semi-amplitude for this star of K2=11.2±1.0km/s and
adopting a mass of M2=72M☉ typical for B3 V stars, we derive an
orbital mass for the stripped primary of M1=1.5±0.4 M☉. The
orbital inclination of 394 implies a near-critical rotation for the Be
secondary (veq∼470km/s).
LB-1 does not contain a compact object. Instead, it is a rare Be
binary system consisting of a stripped star (the former mass donor)
and a Be star rotating at near its critical velocity (the former mass
accretor). This system is a clear example that binary interactions
play a decisive role in the production of rapid stellar rotators and
Be stars.
Description:
HERMES spectrograph, MERCATOR telescope.
24 normalised spectra of LB-1 taken between Dec 2019 and Mar 2020.
Wavelengths given in logarithm.
For extraction use: EXP(crval + [0,1,2....,naxis]*cdelt)
Objects:
----------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------
06 11 49.08 +22 49 32.7 LB-1 = LS V +22 25
----------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
list.dat 143 24 List of fits spectra
fits/* . 24 Individual fits spectra
--------------------------------------------------------------------------------
Byte-by-byte Description of file: list.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- Nx Number of pixels along X-axis
8- 33 A26 "datime" Obs.date Observation date
35- 41 F7.5 [0.1nm] bloglambda log of lower value of wavelength interval
43- 49 F7.5 [0.1nm] Bloglambda log of upper value of wavelength interval
51- 54 I4 Kibyte size Size of FITS file
56- 88 A33 --- FileName Name of FITS file, in subdirectory fits
90-143 A54 --- Title Title of the FITS file
--------------------------------------------------------------------------------
Acknowledgements:
Tomer Shenar, tomer.shenar(at)kuleuven.be
(End) Patricia Vannier [CDS] 25-Jun-2020