J/ApJ/941/8 Radial velocities measurements of Castor Aa and Ba (Torres+, 2022)
The orbits and dynamical masses of the Castor system.
Torres G., Schaefer G.H., Monnier J.D., Anugu N., Davies C.L., Ennis J.,
Farrington C.D., Gardner T., Klement R., Kraus S., Labdon A.,
Lanthermann C., Le Bouquin J.-B., Setterholm B.R., ten Brummelaar T.
<Astrophys. J., 941, 8 (2022)>
=2022ApJ...941....8T 2022ApJ...941....8T
ADC_Keywords: Binaries, spectroscopic; Stars, double and multiple ;
Radial velocities; Interferometry; Infrared; Spectra, optical;
Spectroscopy
Keywords: Astrometric binary stars ; Interferometric binary stars ;
Spectroscopic binary stars ; Stellar evolution ; Visual binary stars ;
Radial velocity
Abstract:
Castor is a system of six stars in which the two brighter objects,
Castor A and B, revolve around each other every ∼450yr and are both
short-period spectroscopic binaries. They are attended by the more
distant Castor C, which is also a binary. Here we report
interferometric observations with the Center for High Angular
Resolution Astronomy (CHARA) array that spatially resolve the
companions in Castor A and B for the first time. We complement these
observations with new radial velocity measurements of A and B spanning
30yr, with the Hipparcos intermediate data, and with existing
astrometric observations of the visual AB pair obtained over the past
three centuries. We perform a joint orbital solution to solve
simultaneously for the three- dimensional orbits of Castor A and B as
well as the AB orbit. We find that they are far from being coplanar:
the orbit of A is nearly at right angles (92°) relative to the
wide orbit, and that of B is inclined about 59° compared to AB. We
determine the dynamical masses of the four stars in Castor A and B to
a precision better than 1%. We also determine the radii of the primary
stars of both subsystems from their angular diameters measured with
the CHARA array, and use them together with stellar evolution models
to infer an age for the system of 290Myr. The new knowledge of the
orbits enables us to measure the slow motion of Castor C as well,
which may assist future studies of the dynamical evolution of this
remarkable sextuple system.
Description:
We begin the description of the observations for Castor with our own
interferometric and spectroscopic measurements, followed by the
extensive set of visual observations from the literature.
Interferometric observations were obtained with the Center for High
Angular Resolution Astronomy (CHARA) array operated by Georgia State
University and located at Mount Wilson Observatory in southern
California. The CHARA array consists of six 1m telescopes arranged in
a "Y" configuration with baselines ranging from 34 to 331m. In 2007,
Castor A was observed on three nights with the original version of the
Michigan InfraRed Combiner (MIRC). During these observations, MIRC
combined the light from the S1, E1, W1, and W2 telescopes and recorded
fringes in eight spectral channels in the H band. In 2021, Castor A
and B were observed on six nights using the upgraded MIRC-X instrument
using all six telescopes (S1, S2, E1, E2, W1, and W2). The two nights
in March of 2021 were obtained with the R=190 grism, and the remaining
nights in 2021 November and December were obtained with the R=50 prism
to optimize the throughput for fainter targets from other programs
observed on the same nights. In 2021 November and December, we
obtained simultaneous K-band observations using the MYSTIC
six-telescope combiner with the R=49 prism.
Observations of Castor A and B at the Center for Astrophysics (CfA)
began in January of 1993. They were made with two nearly identical
copies of the Digital Speedometer (DS) on the 1.5m Wyeth reflector at
the Oak Ridge Observatory in the town of Harvard (MA), and on the 1.5m
Tillinghast reflector at the Fred L. Whipple Observatory on Mount
Hopkins (AZ). A total of 67 spectra were obtained for Castor A with
signal-to-noise ratios at 5187Å ranging from 30 to 116 per
resolution element of 8.5km/s. For Castor B we gathered 65 spectra,
and the signal-to-noise ratios are 28-118. An additional six
observations were made of the combined light of Castor A and B, when
they could not be separated under poor seeing conditions. Those have
signal-to-noise ratios of 51-86. The last of the observations with
these instruments were gathered in May of 2009.
Starting in October of 2009, spectroscopic monitoring was continued
with the Tillinghast Reflector Echelle Spectrograph (TRES), which is a
modern bench-mounted, fiber-fed instrument on the 1.5m telescope in
Arizona. We collected 174 and 164 observations of Castor A and B,
respectively, through April of 2022. The signal-to-noise ratios at
5187Å range from 91 to 1383 for Castor A, and 78 to 1015 for Castor B
per resolution element of 6.8 km/s.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
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07 34 35.87 +31 53 17.8 Castor = * alf Gem
07 34 35.86 +31 53 17.7 Castor A = * 66 Gem A
07 34 36.10 +31 53 18.5 Castor B = * 66 Gem B
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 42 73 Radial velocity measurements for Castor A
table4.dat 41 71 Radial velocity measurements for Castor B
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See also:
B/wds : The Washington Visual Double Star Catalog (Mason+ 2001-2020)
I/149 : Fifth Fundamental Catalogue (FK5) Part I (Fricke+, 1988)
I/237 : The Washington Vis. Dbl Star Catalog, 1996.0 (Worley+, 1996)
I/239 : The Hipparcos and Tycho Catalogues (ESA 1997)
I/311 : Hipparcos, the New Reduction (van Leeuwen, 2007)
I/312 : PPMX Catalog of positions and proper motions (Roeser+ 2008)
I/322 : UCAC4 Catalogue (Zacharias+, 2012)
I/339 : Hot Stuff for One Year (HSOY) (Altmann+, 2017)
I/340 : UCAC5 Catalogue (Zacharias+ 2017)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AJ/124/1144 : Orbits of 171 single-lined sp. binaries (Latham, 2002)
J/A+A/529/A75 : Limb-darkening coefficients (Claret+, 2011)
J/MNRAS/422/2765 : Orb. motion monitoring of A-star multiples (De Rosa+ 2012)
J/BaltA/24/421 : Castor stream members compilation list (Vereshchagin+, 2015)
J/A+A/607/A124 : K-G-F dwarfs stellar granulation var. (Meunier+, 2017)
J/ApJ/844/103 : Orbit alignment in triple stars (Tokovinin, 2017)
J/AJ/153/95 : Catalog of Suspected Nearby Young Stars (Riedel+, 2017)
J/ApJ/873/69 : Radial velocities of the EB M-dwarf YYGem (Kochukhov+, 2019)
J/ApJS/254/42 : Hipparcos-Gaia (EDR3) Cat. of Accelerations (Brandt, 2021)
J/AJ/163/131 : USNO-UBAD catalog of bright stars (Munn+, 2022)
J/A+A/681/A107 : Mercator Lib. of High Res. Stellar Spectrosc. (Royer+, 2024)
J/A+A/693/A228 : CARMENES input catalog of M dwarfs. IX. (Cifuentes+, 2025)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 d HJD [49004.78/54962.61] Heliocentric Julian date;
HJD-2400000 (G1)
12- 18 F7.4 d DeltaT [-0.15/-0.10] Light travel time correction
in outer orbit
20- 25 F6.2 km/s RVel [-14.5/13.3] Radial velocity of Castor Aa
27- 30 F4.2 km/s e_RVel [0.4/3.7] Uncertainty in RVel (G2)
32- 36 F5.3 --- IPhase [0.013/0.981] Inner phase (G3)
38- 42 F5.3 --- OPhase [0.073/0.11] Outer phase (G3)
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 F10.4 d HJD [49028.75/54962.61] Heliocentric Julian date;
HJD-2400000 (G1)
12- 17 F6.4 d DeltaT [0.13/0.18] Light travel time correction
in outer orbit
19- 24 F6.2 km/s RVel [-27.8/37.6] Radial velocity of Castor Ba
26- 29 F4.2 km/s e_RVel [0.5/4] Uncertainty in RVel (G2)
31- 35 F5.3 --- IPhase [0.025/0.994] Inner phase (G3)
37- 41 F5.3 --- OPhase [0.073/0.11] Outer phase (G3)
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Global notes:
Note (G1): Observations prior to HJD 2455000 were made with the DS instrument,
and more recent ones with TRES.
Note (G2): The uncertainties have been adjusted as explained in Section 3
to be more realistic.
Note (G3): Computed using the ephemerides given in Section 3.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Katia van der Woerd [CDS] 27-Jan-2025