J/ApJ/859/145 20yr obs. of the spectroscopic binary EC 20117-4014 (Otani+, 2018)
Orbital characteristics of the subdwarf-B and F V star binary
EC 20117-4014 (=V4640 Sgr).
Otani T., Oswalt T.D., Lynas-Gray A.E., Kilkenny D., Koen C., Amaral M.,
Jordan R.
<Astrophys. J., 859, 145-145 (2018)>
=2018ApJ...859..145O 2018ApJ...859..145O (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, spectroscopic; Photometry, UBV
Keywords: binaries: spectroscopic; stars: evolution;
stars: individual: EC 20117-4014; stars: oscillations; subdwarfs
Abstract:
Among the competing evolution theories for subdwarf-B (sdB) stars is
the binary evolution scenario. EC 20117-4014 (=V4640 Sgr) is a
spectroscopic binary system consisting of a pulsating sdB star and a
late F main-sequence companion; however, the period and the orbit
semimajor axes have not been precisely determined. This paper presents
orbital characteristics of the EC 20117-4014 binary system using 20
years of photometric data. Periodic observed minus calculated (O-C)
variations were detected in the two highest-amplitude pulsations
identified in the EC 20117-4014 power spectrum, indicating the binary
system's precise orbital period (P=792.3d) and the light-travel-time
amplitude (A=468.9s). This binary shows no significant orbital
eccentricity, and the upper limit of the eccentricity is 0.025 (using
3σ as an upper limit). This upper limit of the eccentricity is
the lowest among all wide sdB binaries with known orbital parameters.
This analysis indicated that the sdB is likely to have lost its
hydrogen envelope through stable Roche lobe overflow, thus supporting
hypotheses for the origin of sdB stars. In addition to those results,
the underlying pulsation period change obtained from the photometric
data was dP/dt=5.4(±0.7)x10-14d.d-1, which shows that the sdB is
just before the end of the core helium-burning phase.
Description:
The discovery observations of EC 20117-4014 were made with the 0.75
and 1.0m telescopes at the Sutherland site of the South African
Astronomical Observatory (SAAO) in 1995. Because EC 20117-4014 is
relatively bright, it was mainly monitored with the SAAO 0.5m
telescope between the discovery in 1995 and 2000.
Since 2010, EC 20117-4014 has also been monitored using the SARA-CT
0.6m telescope at the Cerro Tololo InterAmerican Observatory (CTIO)
in Chile.
The observation log is presented in Table 2.
Objects:
-------------------------------------------------------------------------
RA (ICRS) DE Designation(s) (Per)
-------------------------------------------------------------------------
20 15 04.79 -40 05 44.1 EC 20117-4014 = TYC 7952-2164-1 (P=792.3d)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 37 89 Observation log for EC 20117-4014
table4.dat 36 91 O-C data points for F1 (7.29mHz) and F2 (7.04mHz)
pulsation modes before removing the second order
polynomial fit
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See also:
VI/65 : Evolutionary models of evolved stars (Dorman+ 1993)
J/ApJ/419/596 : Pop I UV radiation models (Dorman+, 1993)
J/MNRAS/287/867 : Edinburgh-Cape Blue Object Survey. Zone 1. (Kilkenny+ 1997)
J/A+A/513/A6 : NOT survey of subdwarf B stars (Ostensen+, 2010)
J/MNRAS/427/2180 : GALEX survey subdwarf atmospheric parameters (Nemeth+, 2012)
J/A+A/576/A44 : Hot subdwarf binaries from MUCHFUSS (Kupfer+, 2015)
J/MNRAS/459/4343 : Edinburgh-Cape Blue Object Survey (Kilkenny+, 2016)
J/ApJ/832/183 : Bin. stellar evolution data for Kepler syst. (Kostov+, 2016)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 A11 "Y/M/D" Date UT date of observation
13- 23 F11.5 d Start [4869.4/12191.7] Start of run; BJD-2445000)
25- 27 F3.1 h Length [0.8/9.3] Observation length
29- 35 A7 --- Obs Observatory ("SAAO" --75 occurrences-- or
"SARA-CT" --14 occurrences)
37 I1 --- Ref [1/4]? Publications using the data (1)
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Note (1): Reference code as follows:
1 = O'Donoghue et al. 1997MNRAS.285..657O 1997MNRAS.285..657O
2 = Randall et al. 2006ApJ...648..637R 2006ApJ...648..637R
3 = Otani T. 2015, PhD thesis Florida Institute of Technology
4 = Lynas-Gray A.E. 2013ASPC..479..273L 2013ASPC..479..273L
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 12 F12.6 d Time [4869.4/12191.9] Mid-observing time;
BJD-2445000
14- 19 F6.1 s O-C(F1) [-467/470] O-C value of F1
21- 24 F4.1 s e_O-C(F1) [1.9/14.2] Uncertainty in F1
26- 31 F6.1 s O-C(F2) [-467/472]? O-C values of F2
33- 36 F4.1 s e_O-C(F2) [4.9/18.5]? Uncertainty in F2
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Jun-2019