J/ApJ/877/44 RV variability in SDSS dwarf carbon stars (Roulston+, 2019)
The Time-Domain Spectroscopic Survey: radial velocity variability in dwarf
carbon stars.
Roulston B.R., Green P.J., Ruan J.J., MacLeod C.L., Anderson S.F.,
Badenes C., Brownstein J.R., Schneider D.P., Stassun K.G.
<Astrophys. J., 877, 44 (2019)>
=2019ApJ...877...44R 2019ApJ...877...44R
ADC_Keywords: Stars, carbon; Stars, dwarfs; Spectra, optical; Radial velocities;
Photometry, SDSS
Keywords: binaries: general ; stars: carbon ; stars: chemically peculiar
Abstract:
Dwarf carbon (dC) stars (main-sequence stars showing carbon molecular
bands) were initially thought to be an oxymoron because only
asymptotic giant branch (AGB) stars dredge carbon into their
atmospheres. Mass transfer from a former AGB companion that has since
faded to a white dwarf seems the most likely explanation. Indeed, a
few types of giants known to show anomalous abundances- notably, the
CH, Ba and CEMP-s stars-are known to have a high binary frequency. The
dC stars may be the enhanced-abundance progenitors of most, if not all
of these systems, but this requires demonstrating a high binary
frequency for dCs. Here, for a sample of 240 dC stars targeted for
repeat spectroscopy by the SDSS-IV's Time Domain Spectroscopic Survey,
we analyze radial velocity (RV) variability to constrain the binary
frequency and orbital properties. A handful of dC systems show large
velocity variability (>100km/s). We compare the dCs to a control
sample with a similar distribution of magnitude, color, proper motion,
and parallax. Using Markov chain Monte Carlo methods, we use the
measured ΔRV distribution to estimate the binary fraction and
the separation distribution assuming both a unimodal and bimodal
distribution. We find the dC stars have an enhanced binary fraction of
95%, consistent with them being products of mass transfer. These
models result in mean separations of less than 1 au corresponding to
periods on the order of 1 yr. Our results support the conclusion that
dC stars form from close binary systems via mass transfer.
Description:
Dwarf carbon (dC) stars for this study were selected from the
Green (2013, J/ApJ/765/12) and Si+ (2014SCPMA..57..176S 2014SCPMA..57..176S) carbon star
samples.
For our current work, which aims to measure RV variability, the
primary additional selection criterion was that the selected dC stars
have more than one epoch of spectroscopy in the SDSS as of 2017
November. The majority of such objects were intentionally targeted for
a second epoch of spectroscopy with the Time Domain Spectroscopic
Survey (TDSS; Morganson+ 2015ApJ...806..244M 2015ApJ...806..244M), a subprogram of the
SDSS-IV extended Baryon Acoustic Oscillation Sky Survey (eBOSS;
Dawson+ 2016AJ....151...44D 2016AJ....151...44D) project.
The observations for this work (for both dC and control sample) are
from a combination of SDSS-I/SDSS-II and SDSS-III/SDSS-IV
spectroscopic data. SDSS-I/SDSS-II spectra were taken with the legacy
SDSS spectrograph. These data have a wavelength range of 3900-9100Å
with a resolution of R∼2000.
Our final sample contains "few-epoch spectroscopy" (FES) spectra
obtained up until 2017 October 31 and spectra from SDSS DR14
(Abolfathi+ 2018ApJS..235...42A 2018ApJS..235...42A). We visually inspected all spectral
epochs and removed any spectra that had strong broad artifacts. The
final sample for this study was 240 dCs with a total of 540 spectra
within the SDSS.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 72 240 Dwarf carbon (dC) sample properties
table2.dat 73 240 Control sample properties
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See also:
II/294 : SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+A/375/366 : Carbon stars from the Hamburg/ESO survey (Christlieb+ 2001)
J/MNRAS/330/792 : Radial velocity in Draco (Kleyna+, 2002)
J/AJ/127/2838 : Faint high-lat. carbon stars SDSS photometry (Downes+, 2004)
J/ApJ/765/12 : Carbon stars and DQ WDs from SDSS-DR7+DR8 (Green, 2013)
J/ApJ/797/21 : Carbon-enhanced metal-poor stars (Placco+, 2014)
J/other/RAA/15.1671 : New carbon stars from LAMOST survey (Si+, 2015)
J/A+A/586/A158 : Binary properties of CH and CEMP stars (Jorissen+, 2016)
J/AJ/155/252 : Astrometry & photometry of dwarf carbon stars (Harris+, 2018)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/240] Object index across dC and
control table (G1)
5- 12 F8.4 deg RAdeg Right ascension (J2000)
14- 20 F7.4 deg DEdeg [-9.3/63.8] Declination (J2000)
22- 26 F5.2 mag rmag [13.6/20.6] SDSS dereddened r band PSF (AB)
magnitude
28- 32 F5.2 mag g-r [-0.09/2.01] SDSS (g-r) color index
34- 37 I4 --- Plate1 [269/9180] SDSS plate for first epoch
39- 43 I5 --- MJD1 [51581/57693] First SDSS observing epoch
45- 47 I3 --- Fiber1 [3/861] SDSS FiberID first epoch
49- 52 I4 --- Plate2 [269/9583] SDSS plate for second epoch
54- 58 I5 --- MJD2 [51658/57933] Second SDSS observing epoch
60- 63 I4 --- Fiber2 [4/1000] SDSS FiberID for second epoch
65- 68 I4 km/s dRVel [-303/365] Radial velocity difference
between epochs
70- 72 I3 km/s e_dRVel [3/210] Error in dRVel
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/240] Object index across dC and
control table (G1)
5- 12 F8.4 deg RAdeg Right ascension (J2000)
14- 21 F8.4 deg DEdeg [-11.9/62.2] Declination (J2000)
23- 27 F5.2 mag rmag [15.9/20.3] SDSS dereddened r band PSF (AB)
magnitude
29- 32 F4.2 mag g-r [0.38/1.9] SDSS (g-r) color index
34- 37 I4 --- Plate1 [267/7275] SDSS plate for first epoch
39- 43 I5 --- MJD1 [51584/57093] First SDSS observing epoch
45- 48 I4 --- Fiber1 [2/1000] SDSS FiberID first epoch
50- 53 I4 --- Plate2 [283/8856] SDSS plate for second epoch
55- 59 I5 --- MJD2 [51660/57519] Second SDSS observing epoch
61- 64 I4 --- Fiber2 [3/1000] SDSS FiberID for second epoch
66- 69 I4 km/s dRVel [-104/108] Radial velocity difference
between epochs
71- 73 I3 km/s e_dRVel [0/308] Error in dRVel
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Global notes:
Note (G1): The index links each dC star from the dC table (Table 1) to
the matching control star in Table 2.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 20-Nov-2020