J/ApJ/922/33 Periodic dwarf carbon stars from ZTF & Gaia (Roulston+, 2021)
Unexpected short-period variability in dwarf carbon stars from the Zwicky
Transient Facility.
Roulston B.R., Green P.J., Toonen S., Hermes J.J.
<Astrophys. J., 922, 33 (2021)>
=2021ApJ...922...33R 2021ApJ...922...33R
ADC_Keywords: Stars, carbon; Photometry, ugriz; Parallaxes, trigonometric;
Stars, distances; Stars, diameters; Stars, masses
Keywords: Carbon stars ; Chemically peculiar stars ; Close binary stars ;
Common envelope evolution ; Spectroscopy ; Period search
Abstract:
Dwarf carbon (dC) stars, main-sequence stars showing carbon molecular
bands, are enriched by mass transfer from a previous
asymptotic-giant-branch (AGB) companion, which has since evolved to a
white dwarf. While previous studies have found radial-velocity
variations for large samples of dCs, there are still relatively few dC
orbital periods in the literature and no dC eclipsing binaries have
yet been found. Here, we analyze photometric light curves from DR5 of
the Zwicky Transient Facility for a sample of 944 dC stars. From these
light curves, we identify 34 periodically variable dC stars.
Remarkably, of the periodic dCs, 82% have periods less than two days.
We also provide spectroscopic follow-up for four of these periodic
systems, measuring radial velocity variations in three of them.
Short-period dCs are almost certainly post-common-envelope binary
systems, because the periodicity is most likely related to the orbital
period, with tidally locked rotation and photometric modulation on the
dC either from spots or from ellipsoidal variations. We discuss
evolutionary scenarios that these binaries may have taken to accrete
sufficient C-rich material while avoiding truncation of the thermally
pulsing AGB phase needed to provide such material in the first place.
We compare these dCs to common-envelope models to show that dC stars
probably cannot accrete enough C-rich material during the
common-envelope phase, suggesting another mechanism like wind-Roche
lobe overflow is necessary. The periodic dCs in this paper represent a
prime sample for spectroscopic follow-up and for comparison to future
models of wind-Roche lobe overflow mass transfer.
Description:
We compiled a list of all dwarf carbons (dCs) from the current
literature. The largest contributor (747 dCs, 79%) is the
Green (2013, J/ApJ/765/12) sample of carbon stars from the SDSS. We
also selected a smaller number of dCs from
Si+ (2014, J/other/SCPMA/57.176), who found 96 new dCs using a label
propagation algorithm from SDSS DR8, and from Li+ (2018, J/ApJS/234/31),
who selected carbon stars from the Large Sky Area Multi-Object Fiber
Spectroscopic Telescope survey (LAMOST) using a machine-learning
approach. Our resulting final sample consists of 944 dCs. With our
compiled sample, to ensure that any periodic candidate was indeed a dC
star, we used Gaia EDR3 parallaxes, proper motions, and distances.
Using our list of dCs, we cross-matched our sample to the ZTF DR5. The
final sample of light curves resulted in 833 dCs with ZTF g light
curves, 867 dCs with ZTF r light curves, and 554 dCs with ZTF i light
curves. Table 2 contains the properties for this final periodic dC
sample.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 122 90 34 individual periodic dwarf carbon (dC)
light-curve properties
table5.dat 84 34 Periodic dC parallaxes, distances, and estimated
physical parameters
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
V/156 : LAMOST DR7 catalogs (Luo+, 2019)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
I/352 : Distances to 1.47 billion stars in Gaia EDR3 (Bailer-Jones+, 2021)
J/ApJS/151/387 : Near-IR spectral library of late-type stars (Ivanov+, 2004)
J/AJ/134/2340 : Membership of Praesepe & Coma Ber clusters (Kraus+, 2007)
J/ApJS/194/28 : The evolution of cataclysmic variables (Knigge+, 2011)
J/ApJ/765/12 : Carbon stars & DQ WDs from SDSS-DR7+DR8 (Green, 2013)
J/other/SCPMA/57.176 : Carbon stars & DZ white dwarfs in SDSS sp. (Si+ 2014)
J/MNRAS/446/2251 : Southern Catalina Survey type-ab RR Lyrae (Torrealba+, 2015)
J/A+A/586/A158 : Binary properties of CH and CEMP stars (Jorissen+, 2016)
J/ApJS/231/1 : Hot DA WDs grid of synthetic spectra (Levenhagen+, 2017)
J/MNRAS/479/5491 : Absolute parameters of 509 main-sequence stars (Eker+, 2018)
J/AJ/155/252 : Astrometry & phot. of dwarf carbon stars (Harris+, 2018)
J/AJ/155/225 : M dwarf stars rot. broadening measurements (Kesseli+, 2018)
J/ApJS/234/31 : Carbon stars from LAMOST using machine learning (Li+, 2018)
J/MNRAS/484/5362 : White dwarf+M dwarf binaries RVs (Ashley+, 2019)
J/A+A/626/A128 : Main-sequence and subgiant Barium stars (Escorza+, 2019)
J/AJ/157/63 : Radii for low-metallicity M-dwarf stars (Kesseli+, 2019)
J/ApJ/877/44 : RV variability in SDSS dwarf carbon stars (Roulston+, 2019)
J/ApJ/901/93 : Model atm. analysis of hot WDs from SDSS (Bedard+, 2020)
J/ApJS/249/18 : The ZTF catalog of periodic variable stars (Chen+, 2020)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/90] Running sequence number
3- 4 A2 --- u_Seq [*d ] Flag(s) on Seq (1)
6- 7 I2 h RAh Hour of right ascension (ICRS) at Epoch=2016.0
9- 10 I2 min RAm Minute of right ascension (ICRS) at Epoch=2016.0
12- 16 F5.2 s RAs Second of right ascension (ICRS) at Epoch=2016.0
18 A1 --- DE- Sign of declination (ICRS) at Epoch=2016.0
19- 20 I2 deg DEd Degree of declination (ICRS) at Epoch=2016.0
22- 23 I2 arcmin DEm Arcminute of declination (ICRS) at Epoch=2016.0
25- 29 F5.2 arcsec DEs Arcsecond of declination (ICRS) at Epoch=2016.0
31 A1 --- Filt [gri] Filter
33- 36 I4 --- N [20/1281] Ngood value
38- 39 I2 --- Nrej [0/10] Nrejects value
41- 46 F6.3 mag mag [13.5/21.1] Mean magnitude in Filt
48- 52 F5.3 mag e_mag [0.01/0.21] Uncertainty on mag
54- 62 F9.6 d Per [0.13/13.6] Best period
64- 71 F8.6 d e_Per [1e-05/0.011] Per uncertainty
73 A1 --- l_logFAP Limit flag on FAP
75- 80 F6.1 --- logFAP [-238.8/-1] log of false-alarm probability for
the period
82- 87 F6.4 mag Amp [0.004/0.5] Amplitude of variability from the
best-fit model at the period
89- 94 F6.4 mag e_Amp [0.003/0.21] Amp uncertainty
96- 106 F11.5 d t0 [58627.9/59234.5] Time of light-curve maximum
brightness
108- 114 F7.5 d e_t0 [0.00013/0.03] t0 uncertainty
116 I1 --- Nt [1/6] Number of terms in our model fit
118- 122 F5.2 --- Chi2 [0.55/20.78] Reduced χ2 of the model
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Note (1): Flag as follows:
* = light curve with no detectable variability at the given period in
this filter. The model fit for this filter is unreliable.
d = suspect periods due to having more than 1% of the periodogram above the
power needed to have log(FAP)≤-5.
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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- 2 I2 h RAh Hour of right ascension (ICRS) at Epoch=2016.0
4- 5 I2 min RAm Minute of right ascension (ICRS) at Epoch=2016.0
7- 11 F5.2 s RAs Second of right ascension (ICRS) at Epoch=2016.0
13 A1 --- DE- Sign of declination (ICRS) at Epoch=2016.0
14- 15 I2 deg DEd Degree of declination (ICRS) at Epoch=2016.0
17- 18 I2 arcmin DEm Arcminute of declination (ICRS) at Epoch=2016.0
20- 24 F5.2 arcsec DEs Arcsecond of declination (ICRS) at Epoch=2016.0
26- 30 F5.3 mas plx [0.1/9.54] Gaia EDR3 parallax
32- 36 F5.3 mas e_plx [0.015/0.4] Parallax uncertainty
38- 41 I4 pc Dist [106/4420] Distance from Bailer-Jones+ I/352
43- 45 I3 pc e_Dist [0/799] Dist uncertainty
47- 50 F4.2 mag BP-RP [0.69/2.15] Gaia EDR3 BP-RP color index
52- 56 F5.2 mag Gmag [5.67/10.38] Gaia EDR3 G-band magnitude
58- 61 F4.2 mag KMag [3.9/6.82] 2MASS absolute K band magnitude
63 A1 --- f_KMag c=KMag interpolated from Gmag
65- 68 F4.2 Msun Mass [0.25/0.9] Mass (1)
70- 74 F5.2 [10-7W] logLbol [-1.96/-0.34] Log of bolometric luminosity
in erg/s (1)
76- 79 F4.2 Rsun Rad [0.22/0.86] Radius (1)
81- 84 F4.2 --- RLFF [0.05/1.6] Roche-lobe filling factor (2)
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Note (1): We use the 2MASS absolute K magnitudes to estimate masses and
bolometric luminosities for our dCs. For the solar bolometric
luminosity, we adopt the value log10L☉=33.58.
We calculate the mass errors to be of order 0.05M☉, the
log10(Lbol/L☉) errors to be of order 0.1, and the radius
errors to be of order 0.05R☉. However, we caution that physical
parameters are derived from O-rich main-sequence models, which may not
accurately represent all dCs.
Note (2): We calculate the Roche-lobe filling factor (RLFF) under the
assumption of a 0.6M☉ WD companion.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 21-Mar-2023