J/ApJ/912/125 Variable white dwarfs from Gaia & ZTF photometry (Guidry+, 2021)
I spy transits and pulsations: empirical variability in white dwarfs using Gaia
and the Zwicky Transient Facility.
Guidry J.A., Vanderbosch Z.P., Hermes J.J., Barlow B.N., Lopez I.D.,
Boudreaux T.M., Corcoran K.A., Bell K.J., Montgomery M.H., Heintz T.M.,
Castanheira B.G., Reding J.S., Dunlap B.H., Winget D.E., Winget K.I.,
Kuehne J.W.
<Astrophys. J., 912, 125 (2021)>
=2021ApJ...912..125G 2021ApJ...912..125G
ADC_Keywords: Stars, white dwarf; Stars, variable; Photometry; Optical;
Effective temperatures
Keywords: White dwarf stars ; Variable stars ; Stellar pulsations ;
ZZ Ceti stars ; Transits ; Planetesimals ; Circumstellar dust ;
Transient detection ; Cataclysmic variable stars
Abstract:
We present a novel method to detect variable astrophysical objects and
transient phenomena using anomalous excess scatter in repeated
measurements from public catalogs of Gaia DR2 and Zwicky Transient
Facility (ZTF) DR3 photometry. We first provide a generalized, all-sky
proxy for variability using only Gaia DR2 photometry, calibrated to
white dwarf stars. To ensure more robust candidate detection, we
further employ a method combining Gaia with ZTF photometry and alerts.
To demonstrate its efficacy, we apply this latter technique to a
sample of roughly 12100 white dwarfs within 200pc centered on the
ZZ Ceti instability strip, where hydrogen-atmosphere white dwarfs are
known to pulsate. By inspecting the top 1% of the samples ranked by
these methods, we demonstrate that both the Gaia-only and ZTF-informed
techniques are highly effective at identifying known and new variable
white dwarfs, which we verify using follow-up, high-speed photometry.
We confirm variability in all 33 out of 33 (100%) observed white
dwarfs within our top 1% highest-ranked candidates, both inside and
outside the ZZ Ceti instability strip. In addition to dozens of new
pulsating white dwarfs, we also identify five white dwarfs highly
likely to show transiting planetary debris; if confirmed, these
systems would more than triple the number of white dwarfs known to
host transiting debris.
Description:
We selected targets for variability assessment from the Gaia DR2
catalog of white dwarf candidates
Gentile Fusillo+ (2019, J/MNRAS/482/4570), which contains 486623
objects. We restricted our sources to those within 200pc. This
resulted in a list of 46002 all-sky sources, which we use to assess
variability using Gaia DR2 data products alone, with observations
spanning 22 months from 2014 July to 2016 May. See Section 2.1.
For the 18269 objects defined in our sample centered on the ZZ Ceti
instability strip, we queried the public ZTF survey for the DR3 g and
r-band light curves. The coverage for ZTF DR3 extends from
2018-March-17 to 2019-December-31. See Section 2.2.
Our final Gaia+ZTF sample contains a total of 12073 objects.
See Section 2.3.
Over the course of two years, from 2018 October to 2020 November, we
observed 34 white dwarfs in this study from McDonald Observatory on
the 2.1m Otto Struve telescope using the ProEM Camera.
An additional eight white dwarfs were identified as variable
candidates using the global Gaia variability metric. We observed these
objects using the Small and Moderate Aperture Research Telescope
System (SMARTS) consortium 0.9m telescope at Cerro Tololo
Inter-American Observatory in 2018 May.
For some objects exhibiting variability indicative of transiting
planetary debris or other nonpulsational phenomena, we obtained
identification spectra using the second-generation Low-Resolution
Spectrograph (LRS2) on the 10.2m Hobby-Eberly Telescope (HET) at
McDonald Observatory. We used LRS2-B to observe the transiting debris
candidate ZTF J0923+4236 on 2020 November 2 with five consecutive
600s exposures in 1.7" seeing, and to obtain time-resolved
spectroscopy of the polar candidate ZTF J0146+4914 on 2020 November 7
with 13 consecutive 320s exposures in 2.1" seeing.
We also obtained follow-up observations using the DeVeny Spectrograph
mounted on the 4.3m Lowell Discovery Telescope (LDT). Observations
were carried out on 2020-November-16 with 1.7" seeing, with 6x180s
exposures of ZTFJ0328-1219 and 9x300s exposures of ZTF0347-1802.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table5.dat 92 121 Table of parameters and metrics for the combined
Gaia and ZTF top 1% (see Appendix F)
table6.dat 130 67 Pulsation spectra for newly confirmed ZZ Cetis
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See also:
I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/ApJ/730/128 : Spectroscopy of DA WD from the SDSS-DR4 (Tremblay+, 2011)
J/ApJS/204/5 : SDSS DR7 white dwarf catalog (Kleinman+, 2013)
J/ApJ/812/167 : ELM survey. VI. 11 new ELM WD binaries (Gianninas+, 2015)
J/MNRAS/446/4078 : New white dwarf stars in SDSS DR10 (Kepler+, 2015)
J/ApJ/818/L7 : High-speed phot. obs. of WD 1145+017 syst. (Gansicke+, 2016)
J/ApJ/823/49 : HST/COS observations of 7 white dwarfs (Sandhaus+, 2016)
J/ApJS/232/23 : 27 pulsating DA WDs follow-up observations (Hermes+, 2017)
J/A+A/623/A110 : Gaia DR2. Variable stars in CMD (Gaia Collaboration+, 2019)
J/MNRAS/482/4570 : Gaia DR2 white dwarf candidates (Gentile Fusillo+, 2019)
J/MNRAS/486/2169 : White dwarf and subdwarf stars in SDSS DR14 (Kepler+, 2019)
J/ApJS/249/18 : The ZTF catalog of periodic variable stars (Chen+, 2020)
J/AJ/160/252 : ZZ Ceti WDs and candidates in Gaia survey (Vincent+, 2020)
J/A+A/648/A44 : Large-amplitude variables in Gaia DR2 (Mowlavi+, 2021)
Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 A2 --- --- [WD]
4- 23 A20 --- WD Name of the source (JHHMMSS.ss+DDMMSS.ss) (1)
25- 33 F9.5 deg RAdeg Gaia DR2 right ascension (ICRS) at Ep=2015.5
35- 43 F9.5 deg DEdeg [-23.4/77.3] Gaia DR2 declination (ICRS)
at Ep=2015.5
45- 47 A3 --- Class Classification (2)
49- 54 F6.1 --- R [12.9/1616] Rank parameter (see Section 3.4)
56- 59 F4.1 --- Var1 [1.4/55] ZTF light-curve metric
(VZTF; see Section 3.2)
61- 64 F4.1 --- Var2 [0.3/46] Gaia variability metric
(VG; see Section 3.1)
66- 67 I2 --- NA [0/15] ZTF Alert variability metric (NA;
see Section 3.3)
69- 72 F4.1 mag Gmag [15/19.2] Average observed Gaia DR2
G-band magnitude
74- 78 I5 K Teff [7240/15690] Effective temperature (3)
80- 82 F3.1 [cm/s2] logg [7/9] Log of surface gravity (3)
84- 92 A9 --- Obs Observatory (4)
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Note (1): All of the object names and stellar parameters are directly sourced
from the Gentile Fusillo+ (2019, J/MNRAS/482/4570) Gaia DR2 catalog
for candidate white dwarfs.
Note (2): The key for these classifications is as follows:
ZZ = known ZZ Ceti (31 occurrences),
cZZ = new confirmed ZZ Ceti (29 occurrences),
CV = known cataclysmic variable (6 occurrences),
cCV = new confirmed cataclysmic variable (1 occurrence),
TR = known transiting debris (2 occurrences),
cTR = new candidate white dwarf with transiting debris (4 occurrences),
EB = known eclipsing binary (2 occurrences),
MS = rotational modulation due to a cool magnetic spot (1 occurrence),
V = objects whose variability has yet to be classified or confirmed
(45 occurrences).
Note (3): Teff and logg are derived from the Gaia photometry assuming a
pure hydrogen photosphere.
Note (4): Observatory as follows:
McD = the McDonald Observatory 2.1m telescope (see Appendix C)
ZTF = 8 new ZZ Cetis classified using their ZTF light curves
CTIO = the CTIO SMARTS 0.9m (see Appendix D; 1 occurrence)
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Cl Classification (1)
6- 7 A2 --- --- [WD]
9- 28 A20 --- WD Name of the source (JHHMMSS.ss+DDMMSS.ss)
30 A1 --- f_WD [d] Flag on WD (2)
32- 36 I5 K Teff [7410/12610]? Effective temperature
37 A1 --- f_Teff [*] Flag on Teff (2)
39- 41 F3.1 [cm/s2] logg [7/8.8]? Log of surface gravity
42 A1 --- f_logg [*] Flag on logg (2)
44- 49 F6.1 s WMP [353.4/3700.6]? The weighted mean pulsation
period
50 A1 --- f_WMP [D] Flag on WMP (2)
52- 130 A79 --- Per Linerly independent periods (s) /
corresponding amplitudes (%)
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Note (1): Code as follows:
McD = McDonald Observatory 2.1m pulsators (28 occurrences)
CTIO = CTIO SMARTS 0.9m pulsators (8 occurrences)
ZTF = ZTF significant periods (31 occurrences)
Note (2): Flag as follows:
d = Observed in SDSS g-band
D = The weighted mean period of pulsations is only relevant to pulsating
white dwarfs
* = The lowest-mass extremely low-mass (ELM) white dwarfs do not have
Teff and logg values in the Gentile Fusillo+ (2019, J/MNRAS/482/4570)
Gaia DR2 catalog.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 02-Nov-2022