J/AJ/170/94 Subdwarfs candidates detected by HsdDet in SDSS DR17 (Zhang+, 2025)
Finding new hot subdwarf stars in SDSS images.
Zhang J., Bu Y., Wu H., Zhang Y., Li S., Lei Z., Yi Z., Kong X., Liu M.
<Astron. J., 170, 94 (2025)>
=2025AJ....170...94Z 2025AJ....170...94Z
ADC_Keywords: Stars, subdwarf; Effective temperatures; Models; Photometry, SDSS
Keywords: Astronomical object identification ; Astrostatistics ;
Subdwarf stars ; Astronomy data analysis
Abstract:
Hot subdwarf stars, located at the end of the blue horizontal branch,
have a burning helium core, and are crucial for studying stellar
structure. Currently, the number of known hot subdwarf star is
relatively small. Many studies apply machine learning classification
to search for hot subdwarf stars based on high quality spectra. With
the accumulated image data in the digital sky surveys, we proposed the
Hot Subdwarf Detector (HsdDet), a novel multiscale object detection
algorithm designed to directly locate hot subdwarf stars' coordinates
in Sloan Digital Sky Survey (SDSS) images. We applied the HsdDet
algorithm to some photometric images of SDSS, and detected 29,695
candidates, whose reduced proper motions are primarily concentrated
between 5 and 20mas/yr. Most of the candidates have distances of
1.5∼7.5kpc, while some candidates can be as far as 20kpc or even more.
Candidates' colors are -2.5<u-g<2.0, -3.5<g-r<2.0, -2.5<r-i<2.5, and
-3.0<i-z<3.0. We crossmatched the candidates catalog with Large Sky
Area Multi-Object Fiber Spectroscopic Telescope and obtained 3823
spectra. The confidence measures the probability of a candidate being
a hot subdwarf star. With the confidence threshold being 0.5, 263 new
hot subdwarf stars were confirmed by the spectral fitting method, and
the purity is 6.9%. When we set confidence threshold at 0.9, the
purity is 13.5%. We discussed the selection bias in the search region
and released the hot subdwarf stars catalog. These results have the
potential to expand the population of hot subdwarf stars.
Description:
For the training (see Section 3), we crossmatched the catalog from
Culpan+2022 (J/A+A/662/A40) with the Sloan Digital Sky Survey (SDSS)
DR17 (III/286) at a matching radius of 0.06' and obtained 2702 images
from the SDSS science archive server (SAS).
We applied the trained HsdDet model to SDSS DR17 (III/286). We
primarily referred the criteria used in the Sloan Extension for
Galactic Understanding and Exploration (SEGUE) to select regions with
different stellar populations. SEGUE is one of the subprojects of the
SDSS-II (Yanny+2009, J/AJ/137/4377; Frebel+2014, J/ApJ/786/74), while
SEGUE-2 is one of the subprojects of the SDSS-III (Ahn+2012, V/139;
Kirby+2013, J/ApJ/770/16). A total of 38,036 targets were detected
from 216,014 SAS images. Crossing with the hot subdwarfs catalog
provided by Culpan+2022 (J/A+A/662/A40) and SDSS DR17 within 2", we
obtained finally 29,695 hot subdwarf candidates.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 43 29695 The candidates catalog
table5.dat 64 263 New hot subdwarfs confirmed in this study
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See also:
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
III/286 : APOGEE-2 DR17 final allStar catalog (Abdurro'uf+, 2022)
VI/65 : Evolutionary models of evolved stars (Dorman+ 1993)
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
J/ApJ/419/596 : Pop I UV radiation models (Dorman+, 1993)
J/ApJ/684/1143 : BHB candidates in the Milky Way (Xue+, 2008)
J/AJ/137/4377 : List of SEGUE plate pairs (Yanny+, 2009)
J/A+A/530/A28 : Priority targets for the MUCHFUSS project (Geier+, 2011)
J/MNRAS/427/2180 : GALEX survey subdwarf atmospheric parameters (Nemeth+, 2012)
J/ApJ/770/16 : Spectroscopic members of Segue 2 galaxy (Kirby+, 2013)
J/ApJ/786/74 : EW measurements of 6 Segue 1 red giants (Frebel+, 2014)
J/ApJ/818/202 : Hot subdwarf stars in LAMOST DR1 (Luo+, 2016)
J/MNRAS/457/3396 : New hot subdwarf stars (Perez-Fernandez+, 2016)
J/A+A/600/A50 : Catalog of hot subdwarf stars (Geier+, 2017)
J/MNRAS/472/4173 : Bright white dwarfs for high-speed photometry (Raddi+, 2017)
J/A+A/616/A10 : 46 open clusters GDR2 HR diagrams (Gaia Collaboration, 2018)
J/A+A/618/A15 : Parameters of EHB stars in ω Cen (Latour+, 2018)
J/A+A/621/A38 : Gaia catalogue of hot subluminous stars (Geier+, 2019)
J/MNRAS/482/4570 : Gaia DR2 white dwarf candidates (Gentile Fusillo+, 2019)
J/ApJ/881/135 : Hot subdwarf stars from GaiaDR2 & LAMOST DR5. II. (Lei+, 2019)
J/A+A/630/A80 : EREBOS project. I. (Schaffenroth+, 2019)
J/ApJ/883/175 : 1st release of the MaNGA Stellar Library (MaStar) (Yan+, 2019)
J/A+A/635/A193 : Catalogue of hot subdwarf stars DR2 (Geier, 2020)
J/ApJ/889/117 : Hot subdwarf stars in GaiaDR2 & LAMOST DR6+7. I. (Lei+, 2020)
J/A+A/654/A107 : Catalogues of Blue Horizontal Branch Stars (Culpan+, 2021)
J/MNRAS/508/3877 : Catalogue of white dwarfs in Gaia EDR3 (Gentile+, 2021)
J/ApJS/256/28 : Hot subdwarf stars with Gaia DR2 & LAMOST DR7 (Luo+, 2021)
J/A+A/662/A40 : Hot subdwarf stars studied with Gaia (Culpan+, 2022)
J/ApJS/259/5 : Hot subdwarf candidates from LAMOST DR7 (Tan+, 2022)
J/ApJ/953/122 : Masses for hot subdwarf stars in LAMOST & Gaia (Lei+, 2023)
J/ApJ/942/109 : Hot subdwarf stars from LAMOST DR8 (Lei+, 2023)
J/ApJS/269/59 : Low-surface-bright. galaxy cand. from SDSS DR16 (Xing+, 2023)
J/A+A/686/A25 : Hot sublum. stars 500pc volume-limited sample (Dawson+, 2024)
J/A+A/684/A118 : Pulsating hot subdwarf B stars (Uzundag+, 2024)
J/A+A/691/A223 : Hot subdwarf binaries (Viscasillas Vazquez+, 2024)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID [1/29695] Running index number in the catalog
7- 14 F8.6 --- Conf [0.5/0.99] Probability source is a hot subdwarf
16- 25 F10.6 deg RAdeg Right ascension (J2000)
27- 36 F10.6 deg DEdeg Declination (J2000)
38- 43 F6.2 kpc Dist [0/157.04]? Distance computed by distance
modulus
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 10 I10 --- ObsID [2001056/1127411192] Unique ID of LAMOST
spectrum
12- 21 F10.6 deg RAdeg Right ascension (J2000)
23- 31 F9.6 deg DEdeg Declination (J2000)
33- 37 I5 K Teff [20000/55690] XTGRID derived effective
temperature
39- 43 I5 K e_Teff [76/36722] Uncertainty in Teff
45- 48 F4.2 [cm/s2] logg [5/6.3] XTGRID derived surface gravity
50- 53 F4.2 [cm/s2] e_logg [0.01/4.2] Uncertainty in logg
55- 59 F5.2 [-] [He/H] [-4.2/2.02] XTGRID derived log Helium to
Hydrogen abundance
61- 64 F4.2 [-] e_[He/H] [0/3.47] Uncertainty in [He/H]
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Robin Leichtnam [CDS] 10-Jun-2026