J/ApJ/928/20 Variable hot subdwarf from Gaia DR2 and TESS (Barlow+, 2022)
New variable hot subdwarf stars identified from anomalous Gaia flux errors,
observed by TESS, and classified via Fourier diagnostics.
Barlow B.N., Corcoran K.A., Parker I.M., Kupfer T., Nemeth P.,
Hermes J.J., Lopez I.D., Frondorf W.J., Vestal D., Holden J.
<Astrophys. J., 928, 20 (2022)>
=2022ApJ...928...20B 2022ApJ...928...20B
ADC_Keywords: Stars, subdwarf; Stars, variable; Colors; Optical;
Magnitudes, absolute
Keywords: B subdwarf stars ; Surveys ; Binary stars ; Eclipsing binary stars ;
Close binary stars ; Short period variable stars
Abstract:
Hot subdwarf stars are mostly stripped red giants that can exhibit
photometric variations due to stellar pulsations, eclipses, the
reflection effect, ellipsoidal modulation, and Doppler beaming.
Detailed studies of their light curves help constrain stellar
parameters through asteroseismological analyses or binary light-curve
modeling and generally improve our capacity to draw a statistically
meaningful picture of this enigmatic stage of stellar evolution. From
an analysis of Gaia DR2 flux errors, we have identified around
1200 candidate hot subdwarfs with inflated flux errors for their
magnitudes-a strong indicator of photometric variability. As a pilot
study, we obtained 2 minute cadence TESS Cycle 2 observations of
187 candidate hot subdwarfs with anomalous Gaia flux errors. More than
90% of our targets show significant photometric variations in their
TESS light curves. Many of the new systems found are cataclysmic
variables, but we report the discovery of several new variable hot
subdwarfs, including HW Vir binaries, reflection-effect systems,
pulsating sdBVs stars, and ellipsoidally modulated systems. We
determine atmospheric parameters for select systems using follow-up
spectroscopy from the 3m Shane telescope. Finally, we present a
Fourier diagnostic plot for classifying binary light curves using the
relative amplitudes and phases of their fundamental and harmonic
signals in their periodograms. This plot makes it possible to identify
certain types of variables efficiently, without directly investigating
their light curves, and may assist in the rapid classification of
systems observed in large photometric surveys.
Description:
All of our targets are sourced from Geier+ (2019, J/A+A/621/A38), who
compiled a catalog of 39800 confirmed and candidate hot subdwarf
stars from a variety of photometric and spectroscopic sources.
We obtained 2 minute cadence TESS Cycle 2 observations for all bright
(G<17mag), high-varindex Gaia DR2 hot subdwarfs falling in
Sectors 14-26, from 2019 July 18 through 2020 July 4. Targets were
observed whether or not they were previously known to vary. These
observations were made possible by TESS Guest Investigator (GI)
program #G022141.
All 187 observed systems are highlighted in Figure 1.
We download calibrated light curves from the Mikulski Archive for
Space Telescopes (MAST). See Section 3.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 110 1208 Known and candidate hot subdwarf stars from the
Geier+ 2019, J/A+A/621/A38 catalog with the highest
varindex values, arranged from highest to lowest
varindex values
table5.dat 104 187 Summary of results from our TESS Cycle 2 survey of
candidate variable hot subdwarf stars
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See also:
B/cb : Cataclysmic Binaries, LMXBs, and related objects (Ritter+, 2004)
II/207 : Palomar-Green catalog UV-excess stellar objects (Green+ 1986)
I/276 : Tycho Double Star Catalogue (TDSC) (Fabricius+ 2002)
V/110 : Catalog of Cataclysmic Variables (Downes+ 2001)
V/113 : Cataclysmic Binaries, LMXBs, and related objects (Ritter+, 2003)
V/123 : Catalog of Cataclysmic Variables (Downes+ 2001-2006)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
I/358 : Gaia DR3 Part 4. Variability (Gaia Collaboration, 2022)
J/ApJS/61/569 : KPD UV-excess objects (Downes+, 1986)
J/AJ/119/1901 : ROTSE all-sky surveys for variable stars (Akerlof+, 2000)
J/A+A/400/939 : Stellar parameters of 115 HQS sdB stars (Edelmann+, 2003)
J/A+A/513/A6 : NOT survey of subdwarf B stars (Ostensen+, 2010)
J/A+A/546/A69 : Orbits of visual binaries & dynamical masses (Malkov+, 2012)
J/MNRAS/427/2180 : GALEX survey subdwarf atmospheric parameters (Nemeth+, 2012)
J/MNRAS/457/3396 : New hot subdwarf stars (Perez-Fernandez+, 2016)
J/ApJ/845/171 : Rapidly pulsating sdB stars with GALEX (Boudreaux+, 2017)
J/AJ/153/204 : RR Lyrae stars from the PS1 3π survey (Sesar+, 2017)
J/ApJS/238/25 : UV var. with GALEX gPhoton archive. I. (de la Vega+, 2018)
J/AJ/156/241 : Variable stars measured by ATLAS (Heinze+, 2018)
J/MNRAS/485/3457 : Rotational modulation in TESS B stars (Balona+, 2019)
J/A+A/623/A110 : Gaia DR2. Variable stars in CMD (Gaia Collaboration+, 2019)
J/A+A/621/A38 : Gaia catalogue of hot subluminous stars (Geier+, 2019)
J/A+A/630/A80 : EREBOS project. I. (Schaffenroth+, 2019)
J/MNRAS/492/L40 : Disentangling cataclysmic var. in Gaia DR2 (Abril+, 2020)
J/ApJS/250/20 : Rot. periods in TESS objects of interest (Canto+, 2020)
J/A+A/635/A193 : Catalogue of hot subdwarf stars DR2 (Geier, 2020)
J/ApJ/912/125 : Variable white dwarfs from Gaia & ZTF phot. (Guidry+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR2 Gaia DR2 identifier
21- 49 A29 --- Alias Alternative target name
51- 63 F13.9 deg RAdeg Gaia DR2 Right Ascension (J2000)
65- 77 F13.9 deg DEdeg Gaia DR2 Declination (J2000)
79- 84 F6.3 mag Gmag [2.68/19] Gaia DR2 apparent G magnitude
86- 91 F6.3 mag GMAG [-2.3/11.8]? Gaia DR2 absolute G magnitude
93- 98 F6.3 mag BP-RP [-3.2/0.6] Gaia DR2 GBP-GRP color
100-104 F5.3 --- VG [0.028/1.2] Gaia variability metric (1)
106-110 F5.3 --- varindex [0.02/1.1] Gaia variability index (2)
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Note (1): In order to put targets on an even playing field, we normalize the
G flux errors by taking the published values from Gaia DR2 (σG),
dividing by the mean G flux (), and multiplying by the square root
of the number of G flux observations (nobs,G). This Gaia variability
metric is then described in Equation 1 by:
VG=σG/xnobs,G0.5
Note (2): We rank candidate variables based on their variability index
(varindex), which we define as their residuals after subtracting the
best-fitting exponential curve, given by:
varindex=VG-(AeβG+c)
where A=1.3466x10-8, β=0.77634, and c=0.00962. Systems with the
highest varindex values are most likely to be variable. See Section 2.
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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 --- TIC [4738707/2046417955] TESS Input Catalog ID
12- 30 I19 --- GaiaDR2 Gaia DR2 Identifier
32- 59 A28 --- Alias Alternative name for target
61- 76 F16.12 d Period [0.005/5.3]?=-99 Period of binary system or
dominant mode in multimode system
78-104 A27 --- Type Classification type
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 26-Jan-2024