J/MNRAS/507/104 Ellipsoidal variables in ASAS-SN catalog (Rowan+, 2021)
High tide: A systematic search for ellipsoidal variables in ASAS-SN.
Rowan D.M., Stanek K.Z., Jayasinghe T., Kochanek C.S., Thompson T.A.,
Shappee B.J., Holoien T.W.-S., Prieto J.L.
<Mon. Not. R. Astron. Soc. 507, 104-115 (2021)>
=2021MNRAS.507..104R 2021MNRAS.507..104R (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Black holes ; Binaries, X-ray ; Stars, variable ;
X-ray sources ; Infrared ; Optical
Keywords: binaries: close - stars: variables: general
Abstract:
The majority of non-merging stellar mass black holes are discovered by
observing high energy emission from accretion processes. Here, we
pursue the large, but still mostly unstudied population of
non-interacting black holes and neutron stars by searching for the
tidally induced ellipsoidal variability of their stellar companions.
We start from a sample of about 200000 rotational variables,
semiregular variables, and eclipsing binary stars from the All-Sky
Automated Survey for Supernovae. We use a Χ2 ratio test followed
by visual inspection to identify 369 candidates for ellipsoidal
variability. We also discuss how to combine the amplitude of the
variability with mass and radius estimates for observed stars to
calculate a minimum companion mass, identifying the most promising
candidates for high mass companions.
Description:
The ASAS-SN V-band observations made between 2012 and mid 2018 have
been used to classify ∼ 426000 variable stars, including about
219000 new discoveries. Since the number of ELL variables is expected to
be small relative to other types of variability, ELLs were not
included in the random forest classification used by Jayasinghe et al.
(2019MNRAS.486.1907J 2019MNRAS.486.1907J, Cat. II/366). Some ELLs were visually identified
as a part of Pawlak et al. (2019MNRAS.487.5932P 2019MNRAS.487.5932P), but most will have
been classified as eclipsing binaries or rotational variables. We use
an analytical model to search for ELL light curves in ASAS-SN and
validate the candidates with visual inspection. In the absence of RV
measurements, we combine the ELL model with photometric estimates of
the stellar properties to derive a minimum companion mass for the ELL
candidates, (see section 2 Searching for ellipsoidal variables).
We begin with the ASAS-SN catalogue of variable stars. Since ELLs can
be confused with other variable classifications, we make a broad
selection from the catalogue in classification probability Pclass > 0.9
and period P < 0.4 days. We use the periods from Jayasinghe et al.
(2019MNRAS.486.1907J 2019MNRAS.486.1907J) to phase-fold the V-band light curves,
(see section 2.1 ASAS-SN search catalogue).
We fit each light curve with a series of analytical models to identify
the best ELL candidates. Ellipsoidal modulations have a characteristic
double-peaked structure with uneven maxima where the fractional
luminosity changes can be represented by a discrete Fourier series as
the equations 1,2,3 (section 2.2 Analytical model for ellipsoidal
modulations) shoe. We proceed to ELL candidate selection using visual
insual inpection of Χ2 Fourier fit values to light curves
allowing us to 'clean' the initial sample.
For the visual inspection, we supplement the V-band light curves with
ASAS-SN g-band light curves and TESS light curves from either the SPOC
(Caldwell et al. 2020RNAAS...4..201C 2020RNAAS...4..201C) or QLP (Huang et al.
2020RNAAS...4..204H 2020RNAAS...4..204H, 2020RNAAS...4..206H 2020RNAAS...4..206H) reduction pipelines. Before
visual inspection, we phase all light curves such that the photometric
minimum occurs at ψ=0. After visually inspecting the stars
selected by the red line in figure 2 (section 2.3 Light-curve visual
inspection). After multiple rounds of visual inspection, we identified
a total of 369 ELL candidates. ELL candidates have periods ranging
from 0.25 to 143.19 d with a median period of 9.3 d. While the sample
before visual inspection has a single peak at P ∼ 0.6 d, the final
ELL candidate distribution shows three peaks. This distribution is
consistent with the sample of OGLE ellipsoidal variables in the
Galactic bulge (Soszynski et al. 2016AcA....66..405S 2016AcA....66..405S, Cat.
J/AcA/66/405; Gomel et al. 2021MNRAS.504.5907G 2021MNRAS.504.5907G, Cat. J/MNRAS/504/5907).
Then, the table1.dat shows properties of the 369 ELL candidates used
to make the analysis and the visual inspection selections. More, the
table1.dat contains the computed masses of the ELL systems (procedure
explained in the section 2.5 Minimum companion mass).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 82 369 Properties of the 369 ELL candidates
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See also:
J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)
II/366 : ASAS-SN catalog of variable stars (Jayasinghe+, 2018-2020)
I/349 : StarHorse, Gaia DR2 photo-astrometric distances
(Anders+, 2019)
J/AcA/66/405 : Galactic bulge eclipsing & ellipsoidal binaries
(Soszynski+, 2016)
J/MNRAS/504/5907 : OGLE Bulge short-period sample (Gomel+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- ASASSN-V ASAS-SN identifier (JHHMMSS.ss+DDMMSS.s)
(asassn_name) (1)
21- 31 F11.7 d Period Period (period) (1)
33- 48 F16.8 JD Ephemeris Ephemeris for ELL analytic model
(Ephemeris) (2)
50- 55 F6.4 --- e2 ?=- The amplitude of the cos(2θ)
Fourier term (e2) (3)
57- 63 F7.2 Msun M0 ?=- The mass scale most reliably measured
by the light-curve models (M0) (4)
65- 70 F6.2 Rsun R* ?=- Radius of the luminous primary (R*) (5)
72- 75 F4.2 Msun M* ?=- Luminous star mass (ML) (5)
77- 82 F6.2 Msun Mcmin ?=- The minimum companion mass (Mcmin) (6)
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Note (1): Taken from Jayasinghe et al. (2019MNRAS.486.1907J 2019MNRAS.486.1907J, Cat. II/366).
Note (2): The ephemeris is defined for the photometric minimum at phase 0.
Note (3): The best-measured quantity related to the masses is the amplitude
of the cos(2θ) Fourier term as e2 = q*(R*/a)^3, where q is
M2/M1 the mass ratio of the secondary to the photometric primary,
R* is the radius of the luminous primary and a is the binary
semimajor axis,
(see section 2.5 Minimum companion mass).
Note (4): The mass scale most reliably measured by the light-curve models,
M0 = MT/q ; Mc = M*2 / (M0-M*),
(see section 2.5 Minimum companion mass).
Note (5): Taken from StarHorse (Anders et al., 2019A&A...628A..94A 2019A&A...628A..94A, Cat. I/349).
Note (6): We focus on a more robust lower limit on the companion mass such as
Mcmin = M*2 / M0,
(see section 2.5 Minimum companion mass).
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 02-Jul-2024