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Hipparcos and MAP Studies of the Triple Star π Cephei
We reexamine the visual and radial velocity data for the π Cepheitriple star system and derive the masses of the three components. Ourstudy is based upon the analysis of Hipparcos Intermediate AstrometricData (IAD) measurements obtained with the red light Thaw refractor'sMultichannel Astrometric Photometer (Thaw/MAP) and positions obtainedfrom photographic plates acquired with the Thaw refractor's originalphotographic objective. The weighted mean parallax of the star system isnow 13.8+/-0.41 mas, corresponding to a distance modulus of4.30+/-0.065, yielding absolute visual magnitudes of 0.24+/-0.065 and2.50+/-0.070 for the A and B components, respectively, and a totalsystem mass of 8.81+/-0.87 Msolar. The 58 yr span of theplate collection makes possible the first detection of the photocentricmotion caused by the 160 yr orbit of π Cep A/B yielding masses of6.88+/-0.69 Msolar and 1.93+/-0.23 Msolar,respectively, for the central spectroscopic giant binary star and thelate A secondary component. Although of shorter time span, the higherprecision of the IAD and Thaw/MAP data allow the first detection of theastrometric motion caused by the spectroscopic companion of the Acomponent. A comparison of the astrometric, spectroscopic, andphotometric studies of the π Cep suggests that the spectroscopicbinary is composed of a pair of red giants with similar masses,Aa=3.63+/-0.53 Msolar, Ab=3.27+/-0.48 Msolar, anda red magnitude difference of approximately 1.7 mag. The importance oflong-term astrometric coverage is pointed out by the fact that themotion of both the A/B system and Aa/Ab system were missed during thecompilation of the Hipparcos catalog and are only revealed in those dataafter their detection in the MAP/Thaw measurements.
| 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.
| Photographic magnitudes of stars brighter than 7m.75 between +75° and +80° declination (Errata: 11 270)
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