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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 (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 and van Belle et al. 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:
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
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
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
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.
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
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
Note (1): Relative to the center of mass of the close pair.
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
Note (1): Computed at local midnight (7UT) on the date of observation.
Byte-by-byte Description of file: table8.dat
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
History: From electronic version of the journal
(End) Sylvain Guehenneux [CDS] 01-Mar-2017
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