J/ApJ/921/41 Interferometric & AO imaging data of α Oph (Gardner+, 2021)
Establishing α Oph as a prototype rotator: precision orbit with new Keck,
CHARA, and RV observations.
Gardner T., Monnier J.D., Fekel F.C., Williamson M., Baron F., Hinkley S.,
Ireland M., Kraus A.L., Kraus S., Roettenbacher R.M., Schaefer G.,
Sturmann J., Sturmann L., ten Brummelaar T.
<Astrophys. J., 921, 41 (2021)>
=2021ApJ...921...41G 2021ApJ...921...41G
ADC_Keywords: Spectra, optical; Radial velocities; Stars, double and multiple;
Interferometry; Infrared sources
Keywords: Binary stars ; Interferometric binary stars ; Visual binary stars ;
Stellar rotation ; Stellar properties ; Spectroscopic binary stars ;
Radial velocity
Abstract:
Alpha Ophiuchi (Rasalhague) is a nearby rapidly rotating A5IV star
that has been imaged by infrared interferometry. α Oph is also
part of a known binary system, with a companion semimajor axis of
∼430mas and a high eccentricity of 0.92. The binary companion provides
the unique opportunity to measure the dynamical mass to compare with
the results of rapid rotator evolution models. The lack of data near
periastron passage limited the precision of mass measurements in
previous work. We add new interferometric data from the MIRC combiner
at the CHARA Array as well as new Keck adaptive optics imaging data
with NIRC2, including epochs taken near periastron passage. We also
obtained new radial velocities of both components at Fairborn
Observatory. Our updated combined orbit for the system drastically
reduces the errors of the orbital elements and allows for precise
measurement of the primary star mass at the few percent level. Our
resulting primary star mass of 2.20±0.06M☉ agrees well with
predictions from imaging results and matches evolution models with
rotation when plotting on a Hertzsprung-Russell diagram. However, to
truly distinguish between nonrotating and rotating evolution models
for this system, we need ∼1% errors on mass, which might be achieved
once the distance is known to higher precision in future Gaia
releases. We find that the secondary mass of 0.824±0.023M☉ is
slightly underluminous when compared to stellar evolution models. We
show that α Oph is a useful reference source for programs that
need ±1mas astrometry.
Description:
We obtained two previously unpublished epochs of α Oph near
periastron in 2012 using the high angular resolution of the Michigan
Infra-Red Combiner (MIRC). MIRC is a H-band combiner of six 1m
telescopes at the Georgia State University Center for High Angular
Resolution Astronomy (CHARA) Array. The CHARA Array is an
optical/near-IR interferometer with baselines up to 330m.
The α Oph system was observed with the Keck II adaptive optics
system and the facility AO imager NIRC2 in six previously unpublished
epochs obtained between 2002 March 27 and 2014 June 10.
Results from the two MIRC epochs, along with the rest of the
astrometry data, are presented in Table 1.
Between 2011 and 2020 we obtained 145 new radial velocity (RV) data
points for the primary component of α Oph and 107 RVs for the
secondary. This period covers two periastron passages of α Oph.
These data were taken with the Tennessee State University 2m Automated
Spectroscopic Telescope (AST) and its echelle spectrograph at the
Fairborn Observatory in southeast Arizona. The spectra have a
resolution of 0.24Å, corresponding to a resolving power of 25000 at
6000Å, and cover a wavelength range from 3800 to 8260Å.
Objects:
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RA (ICRS) DE Designation(s) (Period)
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17 34 56.06 +12 33 36.1 alf Oph = WDS J17349+1234AB (P=3139.7)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 61 8 α Oph astrometry
table2.dat 22 145 α Oph radial velocities
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See also:
I/311 : Hipparcos, the New Reduction (van Leeuwen, 2007)
J/A+AS/107/365 : Dwarfs and subdwarfs IR photometry (Alonso+, 1994)
J/A+A/393/897 : Rotational velocities of A-type stars II. (Royer+, 2002)
J/ApJ/725/331 : Astrometry in the Galactic Center (Yelda+, 2010)
J/A+A/537/A146 : Stellar models with rotation, 0.8<M<120 (Ekstrom+, 2012)
J/other/A+ARV/20.51 : Rapidly rotating stars (Van Belle, 2012)
J/AJ/145/111 : RVs of five spectroscopic binaries (Fekel+, 2013)
J/AJ/152/8 : Impact of stellar mult. on planetary systems I. (Kraus+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 "Y/M/D" Date Date of observation (UT)
13- 23 F11.3 d JD Julian Date
25- 30 F6.2 mas Sep [20.7/641.6] Mean separation
32- 35 F4.2 mas e_Sep [0.05/2.9] Sep uncertainty
37- 42 F6.2 deg PA [36.5/302.95] Position angle
44- 47 F4.2 deg e_PA [0.03/2.3] PA uncertainty
49- 61 A13 --- Inst Instrument
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliocentric Julian Date
14- 17 F4.1 km/s RVelA [4.9/33.5] Primary radial velocity (1)
19- 22 I4 km/s RVelB [-52/20]? Secondary radial velocity (2)
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Note (1): Errors on primary are 1.4km/s.
Note (2): Errors on secondary are 2km/s.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Feb-2023