J/A+A/705/A248 Arizona-Montreal survey of hot subdwarf stars (Latour+, 2026)
The Arizona-Montreal Spectroscopic Survey of hot subluminous stars.
Latour M., Green E.M., Dorsch M., Van Grootel V., Chayer P., Charpinet S.,
Heber U., Randall S.K., Ma X.-Y.
<Astron. Astrophys. 705, A248 (2026)>
=2026A&A...705A.248L 2026A&A...705A.248L (SIMBAD/NED BibCode)
ADC_Keywords: Stars, subdwarf ; Stars, masses ; HR diagrams ; Stars, faint blue;
Effective temperatures ; Spectroscopy ; Stars, fundamental ;
Stars, horizontal branch
Keywords: stars: atmospheres - stars: fundamental parameters -
Hertzsprung-Russell and C-M diagrams - stars: horizontal branch -
subdwarfs
Abstract:
Hot subdwarf B (sdB) and O (sdO) type stars are evolved helium-burning
objects that lost their hydrogen envelope before the
helium flash when their progenitors were close to the tip of the red
giant branch. They populate the extreme horizontal branch (EHB) in the
Hertzsprung-Russel diagram (HRD). The mass distribution of canonical
hot subdwarfs is expected to peak at the core mass required for helium
ignition under degenerate conditions, in the 0.45 to 0.5M☉ range.
However, non-degenerate helium ignition from intermediate-mass
progenitor and non-canonical pathways, such as the merger of helium
white dwarfs and delayed helium flashes, are also expected to
contribute to the hot subdwarf population.
Using the high-quality, homogeneous spectra of 336 hot subluminous
star candidates from the Arizona-Montreal Spectroscopic Survey, we
aim to improve our understanding of the atmospheric and stellar
properties of hot subdwarf stars. Our focus is on the mass
distribution of the different types of hot subdwarfs and their
connections to the various formation scenarios.
We used large grids of model atmospheres to fit the observed spectra
and derived their atmospheric parameters: effective temperature
(Teff), surface gravity, and helium abundance. The model grids were
further utilized to fit the spectral energy distribution of each star
and the Gaia parallax was used to compute the stellar parameters
radius, luminosity, and mass.
Our spectroscopic sample mostly consists of H-rich sdBs and sdOs, but
also contains 41 He-rich sdOs. Additionally, the sample includes 11
intermediate-helium stars and 19 horizontal branch objects with
Teff≳14kK. We detected the presence of helium stratification in six
sdB stars with T eff around 30kK, making them good candidates for also
showing 3 He enrichment in their atmospheres. Our sdB distribution
along the EHB shows a gap near 33kK, visible in both the Kiel
(logg-Teff ) diagram and HRD, corroborating previous observations and
predictions. The mass distributions of H-rich sdBs and sdOs are
similar and centered around 0.47M☉, consistent with the
canonical formation scenario of helium ignition under degenerate
conditions. Among the H-rich hot subdwarfs, we found no difference
between the mass distributions of close binaries and apparently single
stars. The He-sdOs have a significantly wider mass distribution than
their H-rich counterparts, with an average mass of about 0.78M☉.
In the HRD, the He-sdOs lie on the theoretical helium main sequence
for masses between 0.6 and 1M☉. This strongly favors a merger
origin for these He-rich objects. We identified a small number of
candidate low-mass (<0.45M☉) sdBs located below the EHB that
might have originated from more massive progenitors. These low-mass
sdBs preferentially show low helium abundances. Finally, we identified
more than 80 pulsating stars in our sample and find these to fall into
well-defined p- and g-mode instability regions.
Description:
Table D.1 includes the atmospheric parameters (Teff, logg, log
N(He)/N(H)) obtained from the spectral fit of the Bok spectra, with
their statistical uncertainties. The resulting solid angle (theta) and
reddening (E44-55) obtained from the SED fit are included along with
the stellar parameters (radius,luminosity, and mass) derived using the
Gaia parallaxes. Additional information as presented in the paper are
also included, about the presence of IR-excess (Sect. 4.1.2),
pulsations (Sect. 5.4), close-binary properties (Sect. 5.2), and
underluminous sdBs (Sect. 5.3). Please refer to the paper for
additional information. For the He-sdOs, we also include the masses
obtained from projecting their position in the HRD onto the Zero Age
Helium Main Sequence (ZAHeMS) of Paczynski (1971, Acta Astron., 21, 1).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tabled1.dat 296 330 Properties of the stars in the Bok sample
sp/* . 335 *Individual spectra
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Note on sp/*: spectra of all the stars in tabled1.dat plus
those of FBS0132+370, KPD0311+4801, PG1348+369, PG1544+488, PG1704+222.
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RA (2000) DE Designation(s) (FileName)
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01 35 23.98 +37 20 28.2 FBS0132+370 FBS0132+370.txt
03 14 45.91 +48 12 05.8 KPD0311+4801 KPD0311+4801.txt
13 50 52.78 +36 42 02.1 PG1348+369 PG1348+369.txt
15 46 11.69 +48 38 37.2 PG1544+488 PG1544+488.txt
17 06 46.16 +22 05 52.0 PG1704+222 PG1704+222.txt
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See also:
J/A+A/684/A118 : Pulsating hot subdwarf B stars (Uzundag+, 2024)
Byte-by-byte Description of file: tabled1.dat
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Bytes Format Units Label Explanations
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1- 27 A27 --- Name Star name
29- 37 F9.5 deg RAdeg Right ascension (J2000)
39- 47 F9.5 deg DEdeg Declination (J2000)
49- 58 I10 --- TIC TESS Input Catalog number
60- 75 A16 --- spectra Filename of the spectrum ascii file
in subdirectory sp
77- 81 F5.3 --- RUWE RUWE value from Gaia EDR3
83- 88 F6.3 mas plx Parallax value from Gaia EDR3
90- 95 F6.4 mas e_plx Parallax error from Gaia EDR3
97-104 A8 --- SpType Spectral type as defined in the paper
106-110 I5 K Teff Effective temperature
112-115 I4 K E_Teff Upper uncertainty on Teff
117-120 I4 K e_Teff Lower uncertainty on Teff
122-126 F5.3 [cm/s2] logg Surface gravity (g) in log
128-132 F5.3 [cm/s2] E_logg Upper uncertainty on logg
134-138 F5.3 [cm/s2] e_logg Lower uncertainty on logg
140-145 F6.3 --- logHe Helium abundance as log (N(He)/N(H)
147-151 F5.3 --- E_logHe Upper uncertainty on the helium abundance
153-157 F5.3 --- e_logHe Lower uncertainty on the helium abundance
159-164 A6 --- grid Model grid used for the spectral fit
166-173 F8.4 Rsun logtheta Solid angle θ (2*R/D) in log
175-180 F6.4 Rsun e_logtheta Lower uncertainty on log(theta)
182-187 F6.4 Rsun E_logtheta Upper uncertainty on log(theta)
189-193 F5.3 mag E(44-55) Reddening (E(44-55)) from the SED fit
195-199 F5.3 mag e_E(44-55) Lower uncertainty on E(44-55)
201-205 F5.3 mag E_E(44-55) Upper uncertainty on E(44-55)
207-212 F6.4 Rsun Radius Stellar Radius
214-219 F6.4 Rsun e_Radius Lower uncertainty on Radius
221-226 F6.4 Rsun E_Radius Upper uncertainty on Radius
228-234 F7.1 Lsun Lum Stellar luminosity
236-241 F6.1 Lsun e_Lum Lower uncertainty on Lum
243-248 F6.1 Lsun E_Lum Upper uncertainty on Lum
250-254 F5.2 Msun Mass Stellar mass
256-259 F4.2 Msun e_Mass Lower uncertainty on Mass
261-264 F4.2 Msun E_Mass Upper uncertainty on Mass
266 A1 --- SEDbinary [01] SED binary code (1)
268 A1 --- SEDgood [01] SED good code (2)
270-272 A3 --- pulsation Pulsation properties (3)
274-279 A6 --- binarity Binary properties (Sect.5.4) (4)
281 I1 --- bEHB [0/1] 1 if the star is below the EHB
(Sect.5.3)
283-286 F4.2 Msun Mhems ? Mass obtained from the ZAHeMS in the HRD
288-291 F4.2 Msun e_Mhems ? Lower uncertainty on Mhems
293-296 F4.2 Msun E_Mhems ? Upper uncertainty on Mhems
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Note (1): SED binary code as follows:
1 = if the SED was fitted as a binary
0 = if the SED was fitted as a single star
Note (2): SED good code as follows:
1 = if the SED fit was good
0 = if the SED fit was bad (Sect.4.2.1)
Note (3): Pulsation properties code as follows:
no = no pulsation detected
p = p-mode pulsator
g = g-mode pulsator
h = hybrid (p- and g-modes) pulsator
yes = pulsating star with an unclear type of pulsations
blank = No information on pulsations
Note (4): Close-binary categories as described in Sect.5.4
We note that stars with IR-excess from the SED fit (SED_binary=1)
were not investigated for the presence of a close companion.
Code as follows:
sd+MS = star with a low-mass main sequence companion
sd+WD = star with a WD companion
binary = star likely to be a binary from radial velocity variations,
but the companion type is unknown
single = star without significant radial velocity variations or
without information on RVs.
blank = Star not investigated for the presence of a close companion.
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Byte-by-byte Description of file: sp/*
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Bytes Format Units Label Explanations
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1- 7 F7.2 0.1nm lambda Wavelength
9- 20 E12.6 10mW/m2/nm Flux Flux (in erg/cm2/s/Å unit)
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Acknowledgements:
Marilyn Latour, marilyn.latour(at)uni-goettingen.de
(End) Patricia Vannier [CDS] 12-Nov-2025