J/MNRAS/489/1556 K2 observations of binaries PHL 457 and EQ Psc (Baran+, 2019)
K2 observations of the sdBV + dM/bd binaries PHL 457 and EQ Psc.
Baran A.S., Telting J.H., Jeffery C.S., Ostensen R.H., Vos J., Reed M.D.,
Vuckovic M.
<Mon. Not. R. Astron. Soc., 489, 1556-1571 (2019)>
=2019MNRAS.489.1556B 2019MNRAS.489.1556B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Binaries, orbits ; Stars, subdwarf ;
Stars, variable ; Radial velocities ; Effective temperatures ;
Spectra, optical
Keywords: binaries: general - stars: individual (PHL 457, EQ Psc) -
stars: oscillations (including pulsations)
Abstract:
We present an analysis of two pulsating subdwarf B stars PHL 457 and
EQ Psc observed during the K2 mission. The K2 light curves of both
stars show variation consistent with irradiation of a cooler companion
by the hot subdwarf. They also show higher frequency oscillations
consistent with pulsation. Using new spectroscopic data, we measured
the radial velocity, effective temperature, surface gravity, and
helium abundance of both hot subdwarfs as a function of orbital phase.
We confirm the previously published spectroscopic orbit of PHL 457,
and present the first spectroscopic orbit of EQ Psc. The orbital
periods are 0.313 and 0.801d, respectively. For EQ Psc, we find a
strong correlation between Teff and orbital phase, due to
contribution of light from the irradiated companion. We calculated
amplitude spectra, identified significant pulsation frequencies, and
searched for multiplets and asymptotic period spacings. By means of
multiplets and period spacing, we identified the degrees of several
pulsation modes in each star. The g-mode multiplets indicate
subsynchronous core rotation with periods of 4.6d (PHL 457) and 9.4d
(EQ Psc). We made spectral energy distribution (SED) fits of PHL 457
and EQ Psc using available broad-band photometry and Gaia data. While
the SED of PHL 457 shows no evidence of a cool companion, the SED for
EQ Psc clearly shows an infrared (IR) access consistent with a
secondary with a temperature of about 6800K and a radius of
0.23R☉. This is the first detection of an IR access in any
sdB+dM binary.
Description:
PHL 457 and EQ Psc were observed by the Kepler spacecraft during the
K2 phase of its mission. The observations of both stars were taken in
Campaign 12, which started on 2016 December 15 and finished on 2017
March 4. We downloaded all available data from the 'Barbara A.
Mikulski Archive for Space Telescopes' (archive.stsci.edu). We used
the short-cadence (SC) data, sampled at almost 1min time resolution,
since they allow us to reasonably sample the orbital flux variation,
and to sample an amplitude spectrum beyond the g-mode region, which
means that both g- and p-mode regions are covered.
Also, low-resolution (R=2000) spectra have been collected using the
2.56m Nordic Optical Telescope with Alhambra Faint Object Spectrograph
and Camera (ALFOSC), grism number 18 and a 0.5arcsec slit. The
resulting resolution is 2.2Å. We secured 12 spectra of PHL 457
(2018 June 5-November 30) and 24 of EQ Psc (2016 June 25-2017 January
24) using this setup. For PHL 457, exposure times were 300s, yielding
S/N∼100-176. For EQ Psc, exposure times ranged from 300 to 600s with
S/N∼67-136.
Radial velocities (RVs) were derived with the FXCOR package in IRAF.
We used the Hβ, H{gamma|, Hδ, Hζ, and Hη lines to
determine the RVs, and used a spectral model fit as an RV template.
Observing logs and measured RVs are given in Tables 1 and 2.
Objects:
----------------------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------------------
23 19 24.42 -08 52 37.9 GD1110 = 2MASS J23192442-0852379 = PHL 457
23 34 34.63 -01 19 36.9 V*EQPsc = 2MASS J23343462-0119370
----------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 34 12 The ALFOSC RV data of PHL 457
table2.dat 41 39 The RV data of EQ Psc
table3.dat 22 1 Results of a circular orbital fit after folding
the RVs of PHL 457 to orbital phase
table4.dat 49 2 The results of the SED fit for PHL 457, based
on a Gaia distance of 577±21pc and extinction
E(B-V)=0.023+0.016-0.023
table5.dat 58 60 Frequency list of PHL 457 obtained with
pre-whitening
table6.dat 54 1 Results of a circular orbital fit to the RVs of
EQ PSc
table7.dat 79 2 Results of the SED fit for EQ Psc based on a
Gaia distance 489±25pc and extinction
E(B-V)=0.034+0-0.031
table8.dat 55 104 Frequency list of EQ Psc obtained with
pre-whitening
table9.dat 75 17 sdB stars with orbital and rotation periods
estimated
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 F15.7 d BJD Barycentric Julian Date
17- 20 F4.1 km/s RV ALFOSC Radial velocity
22- 24 F3.1 km/s e_RV Error on RV
26- 30 F5.1 --- S/N Signal to noise ratio
32- 34 I3 s texp Exposure time
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 13 F13.5 d BJD Barycentric Julian Date
15- 19 F5.1 km/s RV Radial velocity (1)
21- 24 F4.1 km/s e_RV Error on RV
26- 30 F5.1 --- S/N Signal to noise ratio
32- 34 I3 s texp Exposure time
36- 41 A6 --- Inst [ALFOSC MagE] Instrument used to obtain RV
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Note (1): The MagE velocities have been shifted by +23.68km/s to match those of
ALFOSC
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 F4.1 km/s gamma Systemic velocity
6- 8 F3.1 km/s e_gamma Error on gamma
10- 13 F4.1 km/s RV Radial velocity
15- 17 F3.1 km/s e_RV Error on RV
19- 22 F4.2 km/s rmsRV rms uncertainty on RV
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Fit Type of the fit (Free or Fixed) (1)
7- 11 I5 K Teff Effective temperature
13- 15 I3 K e_Teff Error on Teff
17- 20 F4.2 Rsun Rad Radius
22- 25 F4.2 Rsun e_Rad Error on Rad
27- 30 F4.1 Lsun Lstar Luminosity
32- 34 F3.1 Lsun e_Lstar Error on Lstar
36- 39 F4.2 Msun Mstar Star mass (2)
41- 44 F4.2 Msun e_Mstar Error on Mstar
46- 49 F4.2 --- chi2 Reduced chi-squared of the fit
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Note (1): In the "Free" fit, Teff is allowed to vary. In the "Fixed" fit, it is
fixed to the spectroscopic value
Note (2): The mass is determined from the radius of the SED fit and the surface
gravity of the spectroscopic fit
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- fID Frequency ID (1)
6- 15 F10.5 uHz freq Frequency
17- 23 F7.5 uHz e_freq Error on freq
25- 35 F11.5 s Period Period
37- 43 F7.5 s e_Period Error on Period
45- 50 F6.1 --- S/N Signal to noise ratio
52- 53 I2 --- n-n0 ? n value relative to an arbitrary zero-point
n0
55 I1 --- l ? Degree of the mode
57- 58 I2 --- m ? Azimuthal order of the mode
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Note (1): We recovered 58 frequencies; most of them located in the g-mode
region, and only five in the p-mode region. Two additional frequencies
corresponding to the binary orbital frequency and its first harmonic
are included (fbin, fhar).
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Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 F4.1 km/s gamma System velocity
6- 8 F3.1 km/s e_gamma Error on gamma
10- 13 F4.1 km/s RV Radial velocity
15- 17 F3.1 km/s e_RV Error on RV
19- 26 F8.6 d Period Orbital period
28- 35 F8.6 d e_Period Error on Period
37- 43 F7.3 d T0 Reference epoch (BJD-2457000.0)
45- 49 F5.3 d e_T0 Error on T0
51- 54 F4.2 km/s rmsRV rms uncertainty on RV
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Fit Type of the fit (Free or Fixed) (1)
7- 11 I5 K Teff1 Effective temperature of the hot component
13- 16 I4 K e_Teff1 Error on Teff1
18- 21 F4.2 Rsun Rad1 Radius of the hot component
23- 26 F4.2 Rsun e_Rad1 Error on Rad1
28- 31 F4.1 Lsun Lstar1 Luminosity of the hot component
33- 35 F3.1 Lsun e_Lstar1 Error on Lstar1
37- 40 F4.2 Msun Mstar1 Star mass (2)
42- 45 F4.2 Msun e_Mstar1 Error on Mstar1
47- 50 I4 K Teff2 Effective temperature of the cool component
52- 54 I3 K e_Teff2 Error on Teff2
56- 59 F4.2 Rsun Rad2 Radius of the cool component
61- 64 F4.2 Rsun e_Rad2 Error on Rad2
66- 69 F4.2 Lsun Lstar2 Luminosity of the cool component
71- 74 F4.2 Lsun e_Lstar2 Error on Lstar2
76- 79 F4.2 --- chi2 Reduced chi-squared of the fit
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Note (1): In the "Free" fit, Teff1 is allowed to vary. In the "Fixed" fit, it
is fixed to the spectroscopic value
Note (2): The mass is determined from the radius of the SED fit and the surface
gravity of the spectroscopic fit
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table8.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- fID Frequency ID (1)
6- 15 F10.5 uHz freq Frequency
17- 23 F7.5 uHz e_freq ? Error on freq
25- 35 F11.5 s Period Period
37- 43 F7.5 s e_Period ? Error on Period
45- 50 F6.1 --- S/N Signal to noise ratio
52 I1 --- l ? Degree of the mode
54- 55 I2 --- m ? Azimuthal order of the mode
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Note (1): We recovered 102 frequencies including the binary frequency and its
first harmonic
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Byte-by-byte Description of file: table9.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- Rot Rotation type (Core rotation or Surface
rotation)
18- 31 A14 --- Name Star name
33- 34 I2 --- r_Name Reference for Name (1)
36- 41 F6.3 d Porb Orbital period
43 A1 --- l_Prot Limit flag on Prot
45- 50 F6.3 d Prot Rotation period
52- 57 A6 % e_Prot Error on Prot
59- 60 A2 --- Comp [dM WD] Companion type (M dwarf or White
dwarf)
62- 75 A14 --- Method Features used to estimate the rotation period
(g modes or Spectral lines)
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Note (1): References as follows:
1 = This paper
2 = Baran & Winans (2012AcA....62..343B 2012AcA....62..343B)
3 = Reed et al. (2016MNRAS.458.1417R 2016MNRAS.458.1417R)
4 = Baran et al. (2016A&A...585A..66B 2016A&A...585A..66B)
5 = Reed et al. (2018MNRAS.474.5186R 2018MNRAS.474.5186R)
6 = Ostensen et al. (2014A&A...569A..15O 2014A&A...569A..15O, Cat. J/A+A/569/A15)
7 = Telting et al. (2012A&A...544A...1T 2012A&A...544A...1T)
8 = Telting et al. (2014A&A...570A.129T 2014A&A...570A.129T)
9 = Vennes et al. (2012ApJ...759L..25V 2012ApJ...759L..25V)
10 = Schaffenroth et al. (2014A&A...570A..70S 2014A&A...570A..70S)
11 = Vuckovic et al. (2009A&A...505..239V 2009A&A...505..239V)
12 = unpublished
13 = Vuckovic et al. (2016A&A...586A.146V 2016A&A...586A.146V)
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 03-Jan-2023