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A Precise Orbit Determination of χ1 Orionis from Astrometric and Radial Velocity Data
We have derived an accurate orbit of χ1 Orionis (HD39587, HIP 27913, HR 2047) by combining precise astrometric and radialvelocity data. The combined orbital analysis yields P=5156.7+/-2.5 days,K1=1.885+/-0.004 km s-1,α1=94.8+/-1.6 mas, e=0.451+/-0.003, and mass ratio(M2/M1) q=0.15+/-0.005. The mass ratio derivedhere is among the smallest well-determined ratio for a G-type dwarfprimary star. We have also obtained a parallax of χ1Orionis, 115.93+/-1.02 mas, in excellent agreement with the Hipparcosvalue.
| One milliarcsecond precision studies in the regions of Delta Equulei and Chi1 Orionis
Trigonometric parallaxes for stars in the regions of the binary starsDelta Equulei (HR 8123) and Chil Orionis (HR 2047) arederived from data collected with the Multichannel Astrometric Photometer(MAP) and the Thaw Refractor of the University of Pittsburgh's AlleghenyObservatory. The weighted mean parallax of all trigonometric studies ofdelta Equ is now +5.42 +/- 0.93 mas, corresponding to absolutemagnitudes of 3.87 +/- 0.04 and 3.95 +/- 0.04 mag, respectively, for theprimary and secondary. Using the Popper and Dworetsky orbit we find aphotocentric semimajor axis of 2.9 +/- 0.8 mas and individual masses of1.21 +/- 0.090 and 1.19 +/- 0.088 solar masses, respectively, for theprimary and secondary components. The weighted mean trigonometricparallax of all studies of the binary star Chil Ori is +111.0+/- 0.92 mas, implying an absolute visual magnitude for the dominant GOV primary of 4.63 +/- 0.018 mag. The photocentric semimajor axis,derived from a fraction of the orbit, is 96.9 +/- 5.4 mas.
| Spectroscopic parallaxes of MAP region stars from UBVRI, DDO, and uvbyH-beta photometry
This paper presents the results of spectral type and luminosityclassification of reference stars in the Allegheny Observatory MAPparallax program, using broadband and intermediate-band photometry. Inaddition to the use of UBVRI and DDO photometric systems, the uvbyH-betaphotometric system was included for classification of blue (B - V lessthan 0.6) reference stars. The stellar classifications made from thephotometry are used to determine spectroscopic parallaxes. Thespectroscopic parallaxes are used in turn to adjust the relativeparallaxes measured with the MAP to absolute parallaxes. A new methodfor dereddening stars using more than one photometric system ispresented. In the process of dereddening, visual extinctions, spectraltypes, and luminosity classes are determined, as well as a measure ofthe goodness of fit. The measure of goodness of fit quantifiesconfidence in the stellar classifications. It is found that the spectraltypes are reliable to within 2.5 spectral subclasses.
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