J/A+A/676/A81 Be stars in the exofield of CoRoT. III. (Zorec+, 2023)
Study of a sample of faint Be stars in the exofield of CoRoT.
III. Global spectroscopic characterization and astrophysical parameters of
the central stars.
Zorec J., Hubert A.M., Martayan C., Fremat Y.
<Astron. Astrophys. 676, A81 (2023)>
=2023A&A...676A..81Z 2023A&A...676A..81Z (SIMBAD/NED BibCode)
ADC_Keywords: Stars, Be ; Effective temperatures ; Stars, masses ; Stars, ages ;
Rotational velocities ; Optical
Keywords: stars: early-type - stars: emission-line, Be -
stars: fundamental parameters - stars: oscillations
Abstract:
The search and interpretation of non-radial pulsations from Be star
light curves observed with the CoRoT satellite requires to obtain high
quality stellar astrophysical parameters.
The present work is devoted to the spectroscopic study of a sample of
faint Be stars observed by CoRoT in the fourth Long Run (LRA02).
Astrophysical parameters are determined from spectra in the
λλ4000-4500Å wavelength domain observed with the
VLT/FLAMES instruments at ESO. Spectra were fitted with models of
stellar atmospheres using our GIRFIT package. Spectra obtained in the
λλ6400-7200Å wavelength domain enabled to identify or
confirm the Be star candidates.
The apparent parameters (Teff, logg, Vsini) of a set of 19 B and Be
stars were corrected for the effects induced by the rapid rotation.
They enabled to determine: i) stellar masses which are in agreement
with those measured in detached binary systems; ii) spectroscopic
distances that agree with the GAIA parallaxes; iii)
centrifugal/gravity ∼0.6-0.7 equatorial force ratios which indicate
that our Be stars are under-critical rotators. The study of the Balmer
Halpha, Hgamma and Hdelta emission lines produced: 1) extents of the
circumstellar disc (CD) emitting regions that agree with the
interferometric inferences in other Be stars; 2) R-dependent exponents
n(R)=ln[rho(R)/rho☉]/ln(R☉/R) of the CD radial density
distributions; 3) CD base densities rho☉ similar to those
inferred in recent studies.
The Hγ and Hδ emission lines are formed in CD layers which
are close to the central star. These lines produced a different value
of the exponent n(R) than assumed for Hα. Further detailed
studies of Hγ and Hδ emission lines could reveal the
physical properties of regions where probably originate the viscous
transport of angular momentum to the remaining CD regions. The
under-critical rotation of Be stars suggests that their huge discrete
mass-ejections and concomitant non-radial pulsations might have a
common origin in stellar envelope regions that become unstable to
convection due to rotation. If proven that the studied Be stars are
products of binary mass transfer phases, the errors induced on the
estimated Teff by the presence of stripped sub-dwarf O/B companions
will probably not exceed their present uncertainties.
Description:
Table D.1 contains averaged parent-nonrotating-counterpart (pnrc)
astrophysical parameters of the studied Be stars: Teff (effective
temperature), logg (surface gravity), Vsin i (projected rotational
velocity), logL/L☉ (bolometric luminosity in solar units),
M/M☉, (stellar mass in solar units), Vc (equatorial linear
critical velocity), t/tMS (fractional age, tMS is the time spent by
the star in the main sequence phase), age, nu (rotational frequency),
with the respective 1sigma standard deviations. All parameters are
corrected for rotational effects assuming different ratios
W=Ω/Ωc of angular velocities (Ωc is the critical
angular velocity of the rigidly rotating object).
Table D.2 contains modes of distributions of
parent-nonrotating-counterpart (pnrc) astrophysical parameters of the
studied Be stars: Teff (effective temperature), logg (surface
gravity), Vsini (projected rotational velocity), logL/L☉
(bolometric luminosity in solar units), M/M☉, (stellar mass in
solar units), Vc (equatorial linear critical velocity), t/tMS
(fractional age, tMS is the time spent by the star in the main
sequence phase), age, nu (rotational frequency), with the respective
1sigma standard deviations. All parameters are corrected for
rotational effects assuming different ratios W=Ω/Ωc of
angular velocities (Ωc is the critical angular velocity of the
rigidly rotating object).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tabled1.dat 114 114 Averaged parent-non-rotating-counterpart (pnrc)
astrophysical parameters of the studied
B and Be stars
tabled2.dat 114 114 Modes of distributions of
parent-non-rotating-counterpart (pnrc)
astrophysical parameters of the studied
B and Be stars
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See also:
J/A+A/613/A70 : Be stars in the exofield of CoRoT. II. (Semaan+, 2018)
Byte-by-byte Description of file: tabled1.dat tabled2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 F6.3 --- W Value of the angular velocity ratio for
the calculated rotational effects (1)
9- 10 I2 --- Star [1/19] Star number, within the W value
12- 16 I5 K Teff Parent-non-rotating-counterpart (pnrc)
effective temperature
18- 21 I4 K e_Teff Standard deviation of Teff
23- 26 F4.2 [cm/s2] logg Parent-non-rotating-counterpart (pnrc)
surface gravity
28- 31 F4.2 [cm/s2] e_logg Standard deviation of logg
33- 35 I3 km/s vsini Projected rotational velocity
37- 38 I2 km/s e_vsini Standard deviation of the rotational velocity
40- 44 F5.3 [Lsun] logL Parent-non-rotating-counterpart (pnrc)
bolometric luminosity
46- 50 F5.3 [Lsun] e_logL Standard deviation of the bolometric luminosity
52- 56 F5.2 Msun M Parent-non-rotating-counterpart (pnrc)
stellar mass
58- 61 F4.2 Msun e_M Standard deviation of the stellar mass
63- 65 I3 km/s Vc Equatorial linear critical velocity
67- 68 I2 km/s e_Vc Standard deviation of the critical velocity
70- 71 I2 deg i Inclination angle
73- 74 I2 deg e_i Standard deviation of the inclination angle
76- 80 F5.3 --- t/tMS Fractional stellar age
82- 86 F5.3 --- e_t/tMS Standard deviation of the fractional age
88- 95 E8.3 yr t Stellar age
97-104 E8.3 yr e_t Standard deviation of the stellar age
106-109 F4.2 c/d nu Rotational frequency (cycle/day)
111-114 F4.2 c/d e_nu Standard deviation of the rotational frequency
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Note (1): Value of the angular velocity ratio are
0.70, 0.80, 0.90, 0.99, 0.999 and 1.00.
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Acknowledgements:
Juan Zorec, zorec(at)iap.fr
References:
Semaan et al., Paper I 2013A&A...551A.130S 2013A&A...551A.130S
Semaan et al., Paper II 2018A&A...613A..70S 2018A&A...613A..70S, Cat. J/A+A/613/A70
(End) Patricia Vannier [CDS] 15-Jun-2023