J/ApJ/854/12 16yrs of radial velocity measurements of S0-2 (Chu+, 2018)
Investigating the binarity of S0-2: implications for its origins and robustness
as a probe of the laws of gravity around a supermassive black hole.
Chu D.S., Do T., Hees A., Ghez A., Naoz S., Witzel G., Sakai S.,
Chappell S., Gautam A.K., Lu J.R., Matthews K.
<Astrophys. J., 854, 12 (2018)>
=2018ApJ...854...12C 2018ApJ...854...12C
ADC_Keywords: Galactic center; Stars, early-type; Radial velocities
Keywords: Galaxy: center ; gravitation ; stars: early-type ;
techniques: high angular resolution
Abstract:
The star S0-2, which orbits the supermassive black hole (SMBH) in our
Galaxy with a period of 16 years, provides the strongest constraint on
both the mass of the SMBH and the distance to the Galactic center.
S0-2 will soon provide the first measurement of relativistic effects
near a SMBH. We report the first limits on the binarity of S0-2 from
radial velocity (RV) monitoring, which has implications for both
understanding its origin and robustness as a probe of the central
gravitational field. With 87 RV measurements, which include 12 new
observations that we present, we have the requisite data set to look
for RV variations from S0-2's orbital model. Using a Lomb-Scargle
analysis and orbit- fitting for potential binaries, we detect no RV
variation beyond S0-2's orbital motion and do not find any significant
periodic signal. The lack of a binary companion does not currently
distinguish different formation scenarios for S0-2. The upper limit on
the mass of a companion star (Mcomp) still allowed by our results
has a median upper limit of Mcomp sin i ≤1.6M☉ for periods
between 1 and 150 days, the longest period to avoid tidal break-up of
the binary. We also investigate the impact of the remaining allowed
binary system on the measurement of the relativistic redshift at
S0-2's closest approach in 2018. While binary star systems are
important to consider for this experiment, we find that plausible
binaries for S0-2 will not alter a 5σ detection of the
relativistic redshift.
Description:
This investigation includes previously reported astrometric and
spectroscopic data, as well as new spectroscopic data taken with the
W. M. Keck Observatory (WMKO) using OSIRIS between 2014 to 2016.
Objects:
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RA (ICRS) DE Designation(s)
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17 45 40.04 -29 00 28.0 S0-2 = [GKM98] S0-2
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 66 87 S0-2 radial velocity measurements - from erratum
published in 2018, ApJ, 863, 111
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See also:
J/ApJ/523/248 : Variable stars in the Galactic center (Ott+, 1999)
J/ApJ/643/1011 : Early-type stars in the center of the Galaxy (Paumard+, 2006)
J/ApJ/659/1241 : Stellar variability in Galactic Center (Rafelski+, 2007)
J/ApJ/703/1323 : Spectroscopy of stars in Galaxy's nuclear cluster (Do+ 2009)
J/ApJ/707/L114 : The orbit of S2 star around Sgr A* (Gillessen+, 2009)
J/other/Sci/337.444 : RV curves of Galactic massive O stars (Sana+, 2012)
J/ApJ/764/154 : Stellar populations in the central 0.5pc. I. (Do+, 2013)
J/ApJ/830/17 : Galactic Center secondary IR astrometric standards
(Boehle+, 2016)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 10 A10 "Y/M/D" Date UT date of the observation
12- 19 F8.2 d MJD Modified Julian Date of the observation
21- 28 F8.3 yr Epoch [2000.47/2016.52] Epoch (1)
30 A1 --- f_Epoch [f] Epoch is a VLT combined data night
32- 36 I5 km/s RVel [-1556/1192]? Observed radial velocity
38- 40 I3 km/s e_RVel [8/100] The 1σ uncertainty in RVel
42- 44 I3 km/s VLSR [-14/31]? Local Standard of Rest Velocity (2)
46- 50 I5 km/s RVlsr [-1571/1199] Local Standard of Rest radial
velocity after applying the VLSR correction
52 I1 --- r_RVel Source of RVel (3)
54- 58 I5 km/s Model [-1592/1214] Model radial velocity
60- 61 I2 km/s e_Model [3/28] The 1σ uncertainty in Model
63- 66 I4 km/s Res [-53/72] Model residual; RVlsr-Model
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Note (1): The epoch time is reported in Julian years 365.25 days since J2000.
Note (2): From rvcorrect task in IRAF, with an error less than 1km/s
(Kerr & Lynden-Bell 1986MNRAS.221.1023K 1986MNRAS.221.1023K).
Note (3): Reference as follows:
1 = This work;
2 = Boehle et al. (2016, J/ApJ/830/17);
3 = Gillessen et al. (2017, J/ApJ/837/30).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 06-Nov-2018