J/AJ/152/213 Interferometry and spectroscopy of sigma Orionis (Schaefer+, 2016)
Orbits, distance, and stellar masses of the massive triple star σ Orionis.
Schaefer G.H., Hummel C.A., Gies D.R., Zavala R.T., Monnier J.D.,
Walter F.M., Turner N.H., Baron F., ten Brummelaar T., Che X.,
Farrington C.D., Kraus S., Sturmann J., Sturmann L.
<Astron. J., 152, 213-213 (2016)>
=2016AJ....152..213S 2016AJ....152..213S (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, spectroscopic ; Interferometry ; Radial velocities
Keywords: binaries: spectroscopic - binaries: visual -
stars: fundamental parameters - stars: individual: * sig Ori -
techniques: interferometric
Abstract:
We present interferometric observations of the σ Orionis triple
system using the CHARA Array, NPOI, and VLTI. Using these
measurements, we spatially resolve the orbit of the close
spectroscopic binary (Aa,Ab) for the first time and present a revised
orbit for the wide pair (A,B). Combining the visual orbits with
previously published radial velocity measurements and new radial
velocities measured at CTIO, we derive dynamical masses for the three
massive stars in the system of MAa=16.99±0.20M☉,
MAb=12.81±0.18M☉, and MB=11.5±1.2M☉. The inner and
outer orbits in the triple are not coplanar, with a relative
inclination of 120°-127°. The orbital parallax provides a
precise distance of 387.5±1.3pc to the system. This is a significant
improvement over previous estimates of the distance to the young
σ Orionis cluster.
Description:
Interferometric data on the σ Orionis triple system were
collected between 2010 and 2013 at the CHARA Array located on Mount
Wilson, California. The array has six 1m telescopes arranged in a Y
configuration with baselines ranging from 34 to 331m. here are two
telescopes in each arm, labeled as E (East), W (West), and S (South).
We used the Michigan Infrared Combiner (MIRC) to combine the light
from three to six telescopes simultaneously. All data were collected
after the photometric channels were installed in MIRC; the photometric
channels measure the amount of light received from each telescope
during the observations to improve the calibration. We used the low
spectral resolution prism (R∼42) to disperse the fringes across eight
spectral channels in the H band (λ=1.5-1.8µm).
Navy Prototype Optical Interferometer (NPOI) observations of σ
Orionis were collected over a period from 2000 to 2013. Initially, the
observations were obtained with the 3-beam combiner, and then,
starting in 2002, with the 6-beam hybrid combiner. The NPOI beam
combiners disperse the light and record the visibility spectra from
550 to 850 nm in 16 spectral channels. In total, some 59 nights of
observations were executed, of which 26 nights were of good quality.
The calibrators were selected from a list of single stars maintained
at NPOI with diameters estimated from V and (V-K) using the surface
brightness relation published by Mozurkewich et al.
2003AJ....126.2502M 2003AJ....126.2502M and van Belle et al. 2009MNRAS.394.1925V 2009MNRAS.394.1925V. The
information for all of the calibrators is given in Table5.
We obtained new spectroscopic radial velocity measurements of σ
Orionis Aa,Ab using the 1.5m telescope at Cerro Tololo Inter-American
Observatory (CTIO). We obtained 40 observations on 29 nights using the
Fiber Echelle (FE) Spectrograph
(http://www.ctio.noao.edu/~atokovin/echelle/FECH-overview.html)
(R=25000, λ=4800-7000Å) between UT 2008 September 23 and
2009 February 21. Additional observations were obtained using the
Chiron fiber-fed echelle spectrometer equipped with an image slicer
(R=78000, λ=4550-8800Å) on 10 nights between UT 2012
November 4 and 2013 February 2 and 11 nights between UT 2016 January
21 and March 27. The Chiron observations were concentrated near the
periastron passage of the close pair. The median radial velocities of
σ Ori Aa and Ab, measured from the selected spectral lines, are
presented in Table8.
Objects:
------------------------------------------------------------
RA (ICRS) DE Designation(s) (Period)
------------------------------------------------------------
05 38 44.78 -02 36 00.1 * sig Ori = HD 37468 (P=58402d)
------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 99 9 Positions of σ Orionis Aa,Ab measured
with CHARA Michigan Infrared Combiner (MIRC)
table5.dat 48 33 Navy Prototype Optical Interferometer (NPOI)
calibrators
table6.dat 67 25 Navy Prototype Optical Interferometer (NPOI)
positions for σ Orionis A,B
table7.dat 65 17 Navy Prototype Optical Interferometer (NPOI)
positions for σ Orionis Aa,Ab
table8.dat 60 61 Cerro Tololo Inter-American Observatory (CTIO)
radial velocities measured for σ Orionis
Aa,Ab
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See also:
J/AJ/150/100 : WISE YSO candidates near sig and lam Ori (Koenig+, 2015)
J/AJ/149/26 : Massive binary stars from an HST/FGS survey (Aldoretta+, 2015)
J/ApJ/754/30 : VISTA photometry of σ Ori cluster (Pena Ramirez+, 2012)
J/ApJ/743/64 : Deep infrared photometry of σ Ori cluster (Bejar+, 2011)
J/ApJ/688/362 : Disks around brown dwarfs in sig Ori cluster (Luhman+, 2008)
J/A+A/488/167 : Low-mass stars in σ Ori and λ Ori (Sacco+, 2008)
J/A+A/478/667 : The Mayrit catalogue (Caballero, 2008)
J/A+A/466/917 : Brightest stars of sigma Orionis cluster (Caballero+, 2007)
J/ApJ/662/1067 : Sptizer observations of sigma Orionis (Hernandez+, 2007)
J/AJ/128/2316 : BVRIJHKs photometry in sigma Ori cluster (Sherry+, 2004)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 "Y:M:D" Date UT date of the Michigan Infrared Combiner (MIRC)
observation obtained at the CHARA Array
13- 21 F9.3 d HJD Median Heliocentric Julian Date for the time
of observation (HJD-2400000)
23- 28 F6.4 mas Sep [1/7.4] Separation ρ
30- 36 F7.3 deg PA [74.5/250.4] Position Angle θ (measured
east of north)
38- 43 F6.4 mas emaj [0.0046/0.32] Semimajor axis of the error
ellipse σmaj (1)
45- 50 F6.4 mas emin [0.0019/0.053] Semiminor axis of the error
ellipse σmin (1)
52- 57 F6.2 deg ePA [41.1/175.7] Position angle of the major axis
of the error ellipse
59- 64 F6.4 --- fAa [0.41/0.6] Fractional flux contribution for Aa
component
66- 71 F6.4 --- e_fAa [0.0024/0.05] Error in fAa
73- 78 F6.4 --- fAb [0.19/0.39] Fractional flux contribution for Ab
component
80- 85 F6.4 --- e_fAb [0.002/0.045] Error in fAb
87- 92 F6.4 --- fB [0.09/0.35] Fractional flux contribution for B
component
94- 99 F6.4 --- e_fB [0.003/0.07] Error in fB
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Note (1): The size of the major and minor axes of the error ellipse for the
binary positions have been scaled by a factor of 2.24 to force
χ2ν=1 for an orbit fit to only the MIRC derived positions.
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 A2 --- --- [HD]
4- 9 I6 --- HD [886/222603] HD identification number
11- 20 A10 --- SpT Spectral type
21- 24 F4.2 mag Vmag [1.7/5.12] V-band magnitude
26- 30 F5.2 mag V-K [-0.94/1.31] The V-K color index
32- 35 F4.2 mag E(B-V) [0/0.17] The (B-V) color excess
37- 40 F4.2 mas Diam [0.32/1.01] Angular diameter θV-K
corrected for extinction
42- 45 F4.2 --- V2min [0.45/1] Minimum estimated calibrator visibility
V2min based on θV-K
47- 48 I2 --- Nn [1/16] Number of nights
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Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 "Y:M:D" Date UT date of the observation
13- 21 F9.4 yr Year Julian year at 7UT on the date of observation
23- 26 I4 --- Nv [30/1479] Number of measured visibilities
28- 33 F6.2 mas Sep [254.39/260.14] Derived separation ρ (1)
35- 40 F6.2 deg PA [84.17/109.8] Position Angle θ
42- 45 F4.2 mas emaj [0.59/7.59] Semimajor axis of the uncertainty
ellipse σmaj
47- 50 F4.2 mas emin [0.4/2.25] Semiminor axis of the uncertainty
ellipse σmin
52- 56 F5.1 deg ePA [7.4/175.3] Position angle of the major axis
of the uncertainty ellipse
58- 62 F5.2 mas O-Cr [-1.7/3.9] Deviation of the fitted relative binary
position from the model values (O-C)ρ
64- 67 F4.1 deg O-Ct [-1.6/1] Deviation of the fitted relative binary
position from the model values (O-C)θ
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Note (1): Relative to the center of mass of the close pair.
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Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 "Y:M:D" Date UT date of the observation
13- 20 F8.2 yr HJD Heliocentric Julian Date (HJD-2400000) (1)
22- 25 I4 --- Nv [75/1479] Number of measured visibilities
27- 30 F4.2 mas Sep [0.49/7.4] Derived separation ρ
32- 37 F6.2 deg PA [123.7/326.3] Position Angle θ
39- 42 F4.2 mas emaj [0.08/0.9] Semimajor axis of the uncertainty
ellipse σmaj
44- 47 F4.2 mas emin [0.06/0.26] Semiminor axis of the uncertainty
ellipse σmin
49- 53 F5.1 deg ePA [0.1/179.4] Position angle of the major axis
of the uncertainty ellipse
55- 59 F5.2 mas O-Cr [-0.6/1] Deviation of the fitted relative binary
position from the model values (O-C)ρ
61- 65 F5.1 deg O-Ct [-34/9.8] Deviation of the fitted relative binary
position from the model values (O-C)θ
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Note (1): Computed at local midnight (7UT) on the date of observation.
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 "Y:M:D" Date UT date
13- 21 F9.3 d HJD Heliocentric Julian Date (HJD-2400000)
23- 27 F5.3 --- Phase [0/1] Orbital phase
29- 34 F6.2 km/s RVAa [-87.9/59.3] Radial velocity for Aa component
36- 39 F4.1 km/s e_RVAa [2.6/50.6] Error in RVAa
41- 45 F5.1 km/s RVAb [13.3/204] Radial velocity for Ab component
47- 50 F4.1 km/s e_RVAb [1.8/17] Error in RVAb
52- 55 F4.1 km/s O-CAa [-6/24.1] The radial velocity residual for
Aa component
57- 60 F4.1 km/s O-CAb [-6.7/8.4] The radial velocity residual for
Ab component
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History:
From electronic version of the journal
(End) Sylvain Guehenneux [CDS] 01-Mar-2017