J/ApJ/948/94 Binary stars from long-term obs. of the Gal. center (Chu+, 2023)
Evidence of a decreased binary fraction for massive stars within 20 milliparsecs
of the supermassive black hole at the Galactic center.
Chu D.S., Do T., Ghez A., Gautam A.K., Ciurlo A., O'neil K.K.,
Hosek M.W.J., Hees A., Naoz S., Sakai S., Lu J.R., Chen Z., Bentley R.O.,
Becklin E.E., Matthews K.
<Astrophys. J., 948, 94 (2023)>
=2023ApJ...948...94C 2023ApJ...948...94C
ADC_Keywords: Galactic center; Binaries, spectroscopic; Spectra, infrared;
Radial velocities; Spectral types; Stars, masses
Keywords: Galactic center ; Infrared spectroscopy ; Adaptive optics ;
Binary stars
Abstract:
We present the results of the first systematic search for
spectroscopic binaries within the central 2x3arcsec2 around the
supermassive black hole at the center of the Milky Way galaxy. This
survey is based primarily on over a decade of adaptive optics-fed
integral-field spectroscopy (R∼4000), obtained as part of the Galactic
Center Orbits Initiative at Keck Observatory, and it has a limiting
K'-band magnitude of 15.8, which is at least 4mag deeper than previous
spectroscopic searches for binaries at larger radii within the central
nuclear star cluster. From this primary data set, over 600 new radial
velocities are extracted and reported, increasing by a factor of 3 the
number of such measurements. We find no significant periodic signals
in our sample of 28 stars, of which 16 are massive, young
(main-sequence B) stars and 12 are low-mass, old (M and K giant)
stars. Using Monte Carlo simulations, we derive upper limits on the
intrinsic binary star fraction for the young star population at 47%
(at 95% confidence) located ∼20mpc from the black hole. The young star
binary fraction is significantly lower than that observed in the field
(70%). This result is consistent with a scenario in which the central
supermassive black hole drives nearby stellar binaries to merge or be
disrupted, and it may have important implications for the production
of gravitational waves and hypervelocity stars.
Description:
In this work, we use the Galactic Center Orbits Initiative (GCOI;
PI Ghez, W. M. Keck Observatory 1995--present) long-term monitoring
of this region with W. M. Keck Observatory to conduct a systematic
search for binary stars using radial velocities of the S-stars.
A final sample of 28 stars, of which 16 are early-type stars and
12 are late-type stars (see Table 2), has been selected according to
the criteria detailed in Section 2.
The majority of the observations (spanning 2005-2018) were taken with
the OSIRIS spectrograph (R∼4000) on the W. M. Keck 10m Telescope using
the laser guide star adaptive optics (LGSAO) system. 45 data sets were
taken in the 35mas pixel scale and through the Kn3 (2.121-2.229um)
filter, which covers the Brγ absorption line (λ=2.166um)
for the young stars and Na for the old stars. 13 data sets were taken
in the 20mas pixel scale and/or through the broader Kbb filter
(1.965-2.381um).
We also include a number of previously published data sets taken with
other instruments, including Gemini North NIFS (R∼5000).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 74 60 Summary of spectroscopic observations with new
radial velocities
table2.dat 74 28 S-star RV sample (final sample; see Section 2)
table3.dat 42 18 Polynomial fit results
table4.dat 78 970 Radial velocities and residuals
table5.dat 39 28 Companion star search results
table6.dat 54 34 Excluded stars
table7.dat 38 28 Companion mass limits
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See also:
J/ApJ/523/248 : Variable stars in the Galactic center (Ott+, 1999)
J/ApJ/659/1241 : Stellar variability in Galactic Center (Rafelski+, 2007)
J/ApJS/190/1 : A survey of stellar families (Raghavan+, 2010)
J/A+A/511/A18 : NIR observations of stars near SgrA* (Schoedel+, 2010)
J/other/Sci/337.444 : RV curves of Galactic massive O stars (Sana+, 2012)
J/ApJ/830/17 : Gal. Center secondary IR astrometric standards (Boehle+, 2016)
J/ApJ/837/30 : 25yrs obs. of stellar orbits in the GC (Gillessen+, 2017)
J/ApJ/854/12 : 16yrs of radial velocity measurements of S0-2 (Chu+, 2018)
J/ApJ/871/103 : Catalog of 563 stars in the Galactic Center (Gautam+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 "Y/M/D" Date Date of observation (UT)
12 I1 --- r_Date [1/4]? Reference on Date (1)
14- 21 F8.2 d MJD [53554.5/58341.4] Modified Julian Date
23- 30 F8.3 yr Epoch [2005.5/2018.61] Epoch of observation
32- 37 A6 --- Inst Instrument ("OSIRIS" or "NIFS")
39- 40 I2 --- Nfr Number of frames combined
42 A1 --- --- [x]
44- 46 I3 s tInt Exposure time of each frame
48- 50 A3 --- Filt Filter
52- 59 A8 mas Scale Pixel scale used
61- 63 I3 km/s FWHM [56/115]? Full Width at Half Maximum of
reference star
65 I1 --- r_FWHM [5/9]? Reference on FWHM (2)
67- 69 I3 --- S/N [13/121] Spectral signal-to-noise ratio of
reference star
71 I1 --- r_S/N [5/9]? Reference on S/N (2)
73- 74 I2 --- New [1/24] New radial velocity measurements
reported in this work (3)
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Note (1): These observations, where noted, were first reported for studies
of S0-2 alone in the reference as follows:
1 = Ghez et al. (2008ApJ...689.1044G 2008ApJ...689.1044G),
2 = Boehle et al. (2016, J/ApJ/830/17),
3 = Chu et al. (2018, J/ApJ/854/12),
4 = Do et al. (2019Sci...365..664D 2019Sci...365..664D).
Note (2): The reported values are assessed on S0-2 unless otherwise noted as
follows:
5 = S1-15
6 = S0-14
7 = S1-13
8 = S0-3
9 = S0-12
All stars used for characterization have K'mag of 13.5-14.5.
Note (3): This includes only RVs for the final sample.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Star Star name
7- 10 F4.1 mag Kmag [12.4/16] Magnitude in K' band
12- 16 A5 --- SpT Spectral Type
18- 22 F5.2 arcsec dRA [-1.4/0.6] Projected offset in Right
Ascension from SgrA*
24- 29 F6.3 arcsec dDE [-0.97/0.8] Projected offset in Declination
from SgrA*
31- 35 F5.3 arcsec R2D [0.048/1.51] Projected offset (depth) from
SgrA*
37- 39 I3 --- Nrv [7/115] Total number of Radial Velocity
points used
41- 45 F5.1 km/s sigRV [2.6/200] Median radial velocity uncertainty
47- 48 I2 yr RVBase [10/18] Baseline of radial velocity
measurements
50- 59 A10 --- RVMeth Method for subtracting Long-term Trend
61- 67 F7.3 mpc amaj [4.8/163] Semimajor Axis estimate (1)
69- 74 F6.3 mpc e_amaj [0.02/33]? Uncertainty in amaj (1)
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Note (1): Values without uncertainties come from averaging comparably
large separations.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Star Star name
7- 15 F9.4 yr t0 [2011.8/2014.5] t0 Epoch from polynomial fit
17- 22 F6.1 km/s vz0 [-749.1/183] constant velocity offset
24- 28 F5.2 km/s e_vz0 [0.4/10.6]? Uncertainty in vz0
30- 33 F4.2 km/s/yr az [0.3/9.3] acceleration parameter (1)
35- 38 F4.2 km/s/yr e_az [0.12]? Uncertainty in az (1)
40- 42 F3.1 --- chi2 [1/6.8] Reduced χ^2 of fit
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Note (1): Values without uncertainties are 3σ limits.
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [0/969] Sequential identifier
5- 15 F11.6 yr Year [2000.4/2018.8] Julian Year
17- 28 F12.6 d MJD [51718.5/58377.3] Modified Julian Date
(JD-2400000.5)
30- 41 F12.6 km/s RV [-1830/4017] radial velocity corrected to
local standard of rest
43- 52 F10.6 km/s e_RV [2/473] Uncertainty in vz
54- 60 F7.2 km/s Res [-256/360] Residual
62- 66 A5 --- Star Star name
68- 78 A11 --- r_RV Reference for RV if noted (1)
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Note (1): References, if noted as follows:
Do19 = Do+ 2019Sci...365..664D 2019Sci...365..664D
Gillessen17 = Gillessen+ 2017ApJ...837...30G 2017ApJ...837...30G
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Star Star Name
7- 11 A5 --- SpT Spectral Type
13- 17 F5.2 % LS [56/99.8] Lomb-Scargle model amplitude
significance (2)
19- 24 F6.2 % MC [64/100] Monte Carlo simulation significance (2)
26- 30 F5.2 % BS [4.47/99.94] Bootstrap False Alarm Significance
(2)
32- 33 A2 --- Comp Has Detected Companion?
35- 39 F5.2 km/s K [3/90.4] K velocity amplitude limit
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Note (2): For the period with maximum Lomb-Scargle power
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Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- Star Star Name
9- 13 F5.2 mag Kpmag [9.9/16] Magnitude in K' band
15- 21 A7 --- SpT Spectral Type
23- 27 F5.2 arcsec dRA [-1.7/1.11] Projected offset in Right
Ascension from SgrA*
29- 33 F5.2 arcsec dDE [-1.1/1.1] Projected offset in Declination
from SgrA*
35- 38 F4.2 arcsec R2D [0.2/1.7] Projected offset (depth) from SgrA*
40- 54 A15 --- Reason Exclusion Reason
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Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Star Star Name
7- 11 F5.2 mag Kpmag [12.48/15.9] Mean Magnitude in K' band
13- 17 A5 --- SpT Spectral Type
19- 22 F4.1 Msun MassIso [1.2/20.2] Mass from the isochrone
24- 27 F4.2 Msun Mcomp [0.1/6] Upper limit on companion mass
29- 33 F5.3 --- LimMRatio [0.06/0.7] Upper limit on the mass ratio
35- 38 F4.1 Msun MEqual [1.2/16.7] Mass of equal mass Binary (3)
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Note (3): Mass of each component of an equal mass binary system that would
emit same flux as the star's photometry.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-May-2025