J/A+A/708/A115 Hot subdwarf stars from the Hamburg Quasar Survey (Heber+, 2026)
Hot subdwarf stars from the Hamburg Quasar Survey.
Heber U., Kufleitner L., Dorsch M., Latour M., Dawson H., Mattig F.,
Geier S.
<Astron. Astrophys. 708, A115 (2026)>
=2026A&A...708A.115H 2026A&A...708A.115H (SIMBAD/NED BibCode)
ADC_Keywords: Stars, horizontal branch ; Effective temperatures ; Abundances ;
Optical
Keywords: stars: abundances - stars: atmospheres - stars: evolution -
Hertzsprung-Russell and C-M diagrams - stars: horizontal branch -
subdwarf
Abstract:
Hot subluminous stars (subdwarf B&O, sdB, sdO) are evolved low mass
stars originating from red giants that lost their envelope almost
entirely. The multitude of observed phenomena imply that several
pathways may form hot subdwarfs, most involving close binary channels.
The Hamburg Quasar Survey (HQS) has led to the discovery of many faint
blue stars, including hot subdwarf stars. Many of the HQS-sdB stars
have been studied in detail, but analyses of the helium-rich sdOB and
sdO stars are lacking. The recent development of model spectra
calculated from model atmopheres in local thermodynamic equilibrium
(LTE) allowing for non-LTE departures (hybrid LTE/NLTE model spectra,
the 2nd generation Bamberg model grids) enables us to improve the
spectroscopic analyses of sdB stars as well as of the previously
unstudied sdO stars allowing precise atmospheric parameters to be
derived, while consistently accounting for parameter correlations and
systematic uncertainties. The Gaia mission provided astrometric data
of unprecedented quality, which allow fundamental stellar parameters
to be derived from atmospheric parameters via parallax measurements.
We used spectral energy distributions to identify composite-colour sdB
binaries and present the result of detailed spectroscopic analyses of
122 non-composite subdwarfs from the HQS to identify potential
evolutionary pathways. Comparison to evolutionary tracks both in the
Kiel (Teff-logg) and the physical Hertzsprung-Russell (Teff-logL)
diagram finds the location of the sdB stars on the extreme horizontal
branch (EHB). Their derived mass distribution and median mass of 0.45
Msun are consistent with the canonical EHB mass. We revisited the
sample of known pulsating HQS-sdB stars and find no significant
differences between their mass distributions and those of sdB stars
that do not pulsate. The helium-rich sdOB and sdO stars are found near
the helium main sequence (He-MS). The derived mass distribution of the
extremely He-rich subdwarfs is broader (0.48 to 1.05M☉) and
peaks at a median of 0.70M☉, significantly larger than those of
the hydrogen-rich stars. Intermediate He-rich subdwarfs are also He-MS
stars, but of lower mass (0.55M☉) than the extremely He-rich
subdwarfs. This strongly supports the merger scenario for the origin
of He-rich sdO stars, in which two helium white dwarfs merge following
orbital decay driven by gravitational-wave emission, producing a
He-rich sdO or sdOB star. Comparing results from similar studies, we
speculate that older populations produce more massive helium white
dwarfs mergers.
Description:
Table D.1 and D.2 include the atmospheric parameters (Teff, logg, log
N(He)/N(H)) obtained from the spectral fit, with their statistical
uncertainties. The resulting solid angle (theta) and interstellar
reddening (E44-55) obtained from the SED fit are included. Table D.1
also lists the stellar parameters (radius,luminosity, and mass)
derived using the Gaia parallaxes. Stars with parallaxes of
insufficient quality are treated in Table D.2, which does not allow
for the determination of stellar parameters. Additional information as
presented in the paper are also included, such as the effect of
metallicity and Teff-logg correlation. Comments on observed spectral
material and marking pulsating stars are also given. Please refer to
the paper for additional information.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tabled1.dat 261 103 Atmospheric and stellar parameters for 103 hot
subdwarf stars with parallax uncertainties
better than 25%
tabled2.dat 204 12 Atmospheric parameters for 12 hot subdwarf stars
with parallax uncertainties larger than 25%
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See also:
J/A+AS/134/483 : The Hamburg Quasar Survey. III. (Hagen+ 1999)
J/A+A/400/939 : Stellar parameters of 115 HQS sdB stars (Edelmann+, 2003)
Byte-by-byte Description of file: tabled1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Name HQS name (Name)
13- 21 F9.5 deg RAdeg Right ascension (J2000) (ra)
23- 30 F8.5 deg DEdeg Declination (J2000) (dec)
32- 50 I19 --- GaiaDR3 Gaia DR3 number (gaia)
52- 59 A8 --- Class Spectral class (Class)
61- 65 I5 K Teff Effective temperature (Teff)
67- 70 I4 K E_Teff Upper uncertainty on Teff (e_Teff)
72- 75 I4 K e_Teff Lower uncertainty on Teff (e_Teff)
77- 81 F5.3 [cm/s2] logg Surface gravity (g) in log (logg)
83- 87 F5.3 [cm/s2] E_logg Upper uncertainty on logg (elogghi)
89- 93 F5.3 [cm/s2] e_logg Lower uncertainty on logg (elogglo)
95-100 F6.3 --- logn(He/H) Helium abundance as log (N(He)/N(H)
(logn(He/H))
102-106 F5.3 --- E_logn(He/H) Upper uncertainty on the helium
abundance (elogn(He/H)hi)
108-112 F5.3 --- e_logn(He/H) Lower uncertainty on the helium
abundance (elogn(He/H)lo)
114-120 F7.5 % teffdiffsz Impact of metallicity on Teff in
percent (s. Sect. 3.2)
(teffdiffsz)
122-128 F7.5 --- loggdiffsz Impact of metallicity on logg
(s. Sect. 3.2) (loggdiffsz)
130-136 F7.5 --- logn(He/H)diffsz Impact of metallicity on He/H
(s. Sect. 3.2) (logn(He/H)diffsz)
138-143 F6.3 --- CorrCoeff Teff-logg correlation coefficient
(s. Sect. 3.1) (corr_coeff)
145-150 F6.4 Rsun R Stellar Radius (R)
152-157 F6.4 Rsun E_R Upper uncertainty on Radius (eRhi)
159-164 F6.4 Rsun e_R Lower uncertainty on Radius (eRlo)
166-170 F5.1 Lsun L Stellar luminosity (L)
172-176 F5.1 Lsun E_L Upper uncertainty on luminosity
(eLhi)
178-182 F5.1 Lsun e_L Lower uncertainty on luminosity
(eLlo)
184-188 F5.3 Msun M Stellar mass (M)
190-194 F5.3 Msun E_M Upper uncertainty on mass (eMhi)
196-200 F5.3 Msun e_M Lower uncertainty on mass (eMlo)
202-206 F5.3 mas plx Gaia parallax corrected for
zero-point offset (parallax)
208-212 F5.3 mas e_plx Uncertainty of Gaia parallax
(e_parallax)
214-218 F5.3 mag E(44-55) Reddening (E(44-55)) from the SED
fit (E(44-55))
220-224 F5.3 mag E_E(44-55) Upper uncertainty on E(44-55)
(eE(44-55)hi)
226-230 F5.3 mag e_E(44-55) Lower uncertainty on E(44-55)
(eE(44-55)lo)
232-239 F8.4 [rad] logtheta Angular diameter as log(theta)
(logtheta)
241-246 F6.4 [rad] E_logtheta Upper uncertainty on log(theta)
(elogthetahi)
248-253 F6.4 [rad] e_logtheta Lower uncertainty on log(theta)
(elogthetalo)
255-261 A7 --- Comment Comments (comment) (1)
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Note (1): Spectra used: DSAZ spectra (see also 2003A&A...400..939E 2003A&A...400..939E) as follows:
T = 3.5m Twin
C = 2.2m CAFOS
B = 3.5m B&C (used for comparison only)
C2 = 2.2m, Cassegrain spectrograph (used for comparison only);
ESO spectra used
U = UVES$@$VLT; other spectra
L = LAMOST
S = SDSS
AM = AM-BOK (Latour et al., 2026A&A...705A.248L 2026A&A...705A.248L)
additional information:
P = Pulsator
R = Reflection effect binary
N = no IR (H-band) photometry
2 = sdOB+WD P=0.933d, 2014A&A...562A..95G 2014A&A...562A..95G: binaries with known orbit
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Byte-by-byte Description of file: tabled2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- Name HQS name (Name)
13- 21 F9.5 deg RAdeg Right ascension (J2000) (ra)
23- 30 F8.5 deg DEdeg Declination (J2000) (dec)
32- 50 I19 --- GaiaDR3 Gaia DR3 number (gaia)
52- 59 A8 --- Class Spectral class (Class)
61- 65 I5 K Teff Effective temperature (Teff)
67- 69 I3 K E_Teff Upper uncertainty on Teff (eTeffhi)
71- 73 I3 K e_Teff Lower uncertainty on Teff (eTefflo)
75- 79 F5.3 [cm/s2] logg Surface gravity (g) in log (logg)
81- 85 F5.3 [cm/s2] E_logg Upper uncertainty on logg (elogghi)
87- 91 F5.3 [cm/s2] e_logg Lower uncertainty on logg (elogglo)
93- 98 F6.3 --- logn(He/H) Helium abundance as log (N(He)/N(H)
(logn(He/H))
100-104 F5.3 --- E_logn(He/H) Upper uncertainty on the helium
abundance (elogn(He/H)hi)
106-110 F5.3 --- e_logn(He/H) Lower uncertainty on the helium
abundance (elogn(He/H)lo)
112-118 E7.6 % teffdiffsz Impact of metallicity on Teff in
percent (s. Sect. 3.2)
(teffdiffsz)
120-126 F7.5 --- loggdiffsz Impact of metallicity on log g
(s. Sect. 3.2) (loggdiffsz)
128-134 F7.5 --- logn(He/H)diffsz Impact of metallicity on He/H
(s. Sect. 3.2) (logn(He/H)diffsz)
136-141 F6.3 --- CorrCoeff Teff-logg correlation coefficient
(s. Sect. 3.1) (corr_coeff)
143-148 F6.3 mas plx ? Gaia parallax corrected for
zero-point offset (parallax)
150-155 F6.3 mas e_plx ? Uncertainty of Gaia parallax
(e_parallax)
157-161 F5.3 mag E(44-55) Reddening (E(44-55)) from the SED fit
(E(44-55))
163-167 F5.3 mag E_E(44-55) Upper uncertainty on E(44-55)
(eE(44-55)hi)
169-173 F5.3 mag e_E(44-55) Lower uncertainty on E(44-55)
(eE(44-55)lo)
175-182 F8.4 [rad] logtheta Angular diameter as log(theta)
(logtheta)
184-189 F6.4 [rad] E_logtheta Upper uncertainty on log(theta)
(elogthetahi)
191-196 F6.4 [rad] e_logtheta Lower uncertainty on log(theta)
(elogthetalo)
198-204 A7 --- Comment Comments (comment) (1)
--------------------------------------------------------------------------------
Note (1): Spectra used: DSAZ spectra (see also Edelmann et al.
2003A&A...400..939E 2003A&A...400..939E) as follows:
T = 3.5m Twin
C = 2.2m CAFOS
B = 3.5m B&C (used for comparison only)
C2 = 2.2m, Cassegrain spectrograph (used for comparison only);
other spectra:
L = LAMOST
S = SDSS
AM = AM-BOK (Latour et al., 2026A&A...705A.248L 2026A&A...705A.248L)
additional information:
P = Pulsator
R = Reflection effect binary
N = no IR (H-band) photometry
1 = sdOB+WD P=0.2d, (2014ASPC..481..293K 2014ASPC..481..293K)
2 = Outlier
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Acknowledgements:
Ulrich Heber, ulrich.heber(at)fau.de
(End) Patricia Vannier [CDS] 04-Mar-2026