J/ApJ/807/23 Companions of RS CVn primaries. I. sig Gem (Roettenbacher+, 2015)
Detecting the companions and ellipsoidal variations of RS CVn primaries.
I. σ Geminorum.
Roettenbacher R.M., Monnier J.D., Henry G.W., Fekel F.C., Williamson M.H.,
Pourbaix D., Latham D.W., Latham C.A., Torres G., Baron F., Che X.,
Kraus S., Schaefer G.H., Aarnio A.N., Korhonen H., Harmon R.O.,
Brummelaar T.A.T., Sturmann J., Sturmann L., Turner N.H.
<Astrophys. J., 807, 23 (2015)>
=2015ApJ...807...23R 2015ApJ...807...23R (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Radial velocities ; Interferometry ;
Photometry, UBVRI
Keywords: binaries: close; stars: activity; stars: imaging;
stars: individual: "sigma Gem"; stars: variables: general
Abstract:
To measure the properties of both components of the RS Canum
Venaticorum binary σ Geminorum (σ Gem), we directly detect
the faint companion, measure the orbit, obtain model-independent
masses and evolutionary histories, detect ellipsoidal variations of
the primary caused by the gravity of the companion, and measure
gravity darkening. We detect the companion with interferometric
observations obtained with the Michigan InfraRed Combiner at Georgia
State University's Center for High Angular Resolution Astronomy Array
with a primary-to-secondary H-band flux ratio of 270±70. A radial
velocity curve of the companion was obtained with spectra from the
Tillinghast Reflector Echelle Spectrograph on the 1.5m Tillinghast
Reflector at Fred Lawrence Whipple Observatory. We additionally use
new observations from the Tennessee State University Automated
Spectroscopic and Photometric Telescopes (AST and APT, respectively).
From our orbit, we determine model-independent masses of the
components (M1=1.28±0.07M☉, M2=0.73±0.03M☉), and
estimate a system age of 5±1Gyr. An average of the 27 year APT light
curve of σ Gem folded over the orbital period
(P=19.6027±0.0005days) reveals a quasi-sinusoidal signature, which
has previously been attributed to active longitudes 180° apart on
the surface of σ Gem. With the component masses, diameters, and
orbit, we find that the predicted light curve for ellipsoidal
variations due to the primary star partially filling its Roche lobe
potential matches well with the observed average light curve, offering
a compelling alternative explanation to the active longitudes
hypothesis. Measuring gravity darkening from the light curve gives
β<0.1, a value slightly lower than that expected from recent
theory.
Description:
We obtained interferometric data with Georgia State University's
Center for High Angular Resolution Astronomy (CHARA) Array.
Using all six telescopes and the Michigan InfraRed Combiner (MIRC), we
obtained H-band (1.5-1.8um) data on UT 2011 November 9 and December 7,
8, 9; 2012 November 7, 8, 21, 22, 24, 25, and December 4, 5.
From 2012 October 1 to 2015 January 9, using the Tillinghast telescope
with the Tillinghast Reflector Echelle Spectrograph (TRES), we were
able to make 15 detections of the secondary spectra for the first
time. Along with 16 new primary star measurements, these new radial
velocities are presented in Table 2.
The additional radial velocity data set consists of 43 spectrograms of
the primary star of σ Gem taken between 2009 January 12 and 2014
December 1 with the Tennessee State University 2m Automatic
Spectroscopic Telescope (AST).
The differential Johnson B and V light curves cover 1987 November
21-2015 March 13 (see Table 4 and Figure 1). We used differential
photometry of σ Gem and a comparison star from the Tennessee
State University T3 0.4m Automated Photometric Telescope (APT) located
at Fairborn Observatory, Arizona.
Objects:
-------------------------------------------------------------
RA (ICRS) DE Designation(s) Period
-------------------------------------------------------------
07 43 18.73 +28 53 00.6 sig Gem = HD 62044 (P=19.6027)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 23 16 Radial velocity data of σ Gem (CfA)
table3.dat 15 43 Radial velocity data of σ Gem (AST/TSU)
table4.dat 38 3179 Johnson B and V differential magnitudes of
σ Gem from the T3 APT
table8.dat 61 90 Johnson photometric ellipsoidal variations models
of σ Gem
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See also:
B/sb9 : SB9: 9th Catalog of Spectroscopic Binary Orbits (Pourbaix+, 2004-2014)
J/A+A/562/A107 : σ Gem V-band differential light curve (Kajatkari+, 2014)
J/A+A/557/A79 : Spectra of KIC10661783 (Lehmann+, 2013)
J/other/A+ARV/17.251 : Stars observed with Doppler imaging (Strassmeier, 2009)
J/AJ/135/209 : Rotational & radial vel. of 761 HIP giants (Massarotti+, 2008)
J/AJ/130/794 : Radial velocities & BV photometry of HD 144110 (Fekel+, 2005)
J/A+A/431/773 : CHARM2, an updated of CHARM catalog (Richichi+, 2005)
J/A+A/430/303 : MgII-K fluxes in cool active & quiet stars (Cardini+, 2005)
J/A+A/391/641 : Spectroscopic study of sigma Gem from IUE (Ekmekci+, 2002)
J/ApJ/578/943 : vsini of binaries with evolved component (de Medeiros+, 2002)
J/A+AS/140/29 : Phot. monitoring of 47 late-type stars (Strassmeier+, 1999)
J/A+AS/123/209 : Radial velocity curve of Sigma Gem (Duemmler+ 1997)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 --- HJD Heliocentric Julian Date (HJD-2400000)
12- 16 F5.2 km/s RV1 [9/79.1] Primary star radial velocity (1)
18- 23 F6.2 km/s RV2 [-12.2/104.1]? Secondary star radial velocity (1)
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Note (1): Errors on the primary radial velocities are 0.84km/s. Errors
on the secondary radial velocities are 3.8km/s. These were then
scaled for our orbit fit to have a total χ2=1.00. Note these
radial velocities are on the native CfA system. We added 0.14km/s
for use in our analysis (Stefanik et al. 1999ASPC..185..354S 1999ASPC..185..354S).
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.4 --- HJD Heliocentric Julian Date (HJD-2400000)
12- 15 F4.1 km/s RV1 [8.5/78] Primary star radial velocity (1)
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Note (1): Errors on the primary radial velocities are 0.3 km/s. These data
were then scaled for our orbit fit to have a total χ2=1
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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- 10 F10.4 --- HJD Heliocentric Julian Date (HJD-2400000)
12- 17 F6.3 mag VarB [-1.2/-0.7]? ΔB: σGem-HD60318 (1)
19- 24 F6.3 mag VarV [-1.2/-0.9]? ΔV: σGem-HD60318 V (1)
26- 31 F6.3 mag ChkB [-0.8/-0.7]? ΔB: υGem-HD60318 (1)
33- 38 F6.3 mag ChkV [-1.4/-1.2]? ΔV: υGem-HD60318 (1)
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Note (1): Data null values signify differential magnitudes discarded because
internal standard deviation exceeded 0.01mag. Comparison Star
magnitudes: HD 60318, V=5.33, B-V=1.01;
υ Gem (HD 60522, 69 Gem), V=4.06, B-V=1.54
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 5 F5.3 --- Phase Orbital phase of observation (1)
7- 12 F6.3 mag Umag [-0.02/0.03] Johnson U Magnitude
14- 19 F6.3 mag Bmag [-0.02/0.02] Johnson B Magnitude
21- 26 F6.3 mag Vmag [-0.02/0.02] Johnson V Magnitude
28- 33 F6.3 mag Rmag [-0.02/0.02] Johnson R Magnitude
35- 40 F6.3 mag Imag [-0.02/0.02] Johnson I Magnitude
42- 47 F6.3 mag Jmag [-0.02/0.02] Johnson J Magnitude
49- 54 F6.3 mag Hmag [-0.02/0.02] Johnson H Magnitude
56- 61 F6.3 mag Kmag [-0.01/0.01] Johnson K Magnitude
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Note (1): Orbital phase based upon T0=2453583.98 (HJD), Porb=19.6027days.
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History:
From electronic version of the journal
References:
Roettenbacher et al. Paper II. 2015ApJ...809..159R 2015ApJ...809..159R
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 13-Nov-2015