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Dynamical Masses for Low-Mass Pre-Main-Sequence Stars: A Preliminary Physical Orbit for HD 98800 B
We report on Keck Interferometer observations of the double-lined binary(B) component of the quadruple pre-main-sequence (PMS) system HD 98800.With these interferometric observations, combined with astrometricmeasurements made by the Hubble Space Telescope (HST) Fine GuidanceSensors (FGS) and published radial velocity observations, we haveestimated preliminary visual and physical orbits of the HD 98800 Bsubsystem. Our orbit model calls for an inclination of 66.8d+/-3.2d andallows us to infer the masses and luminosities of the individualcomponents. In particular we find component masses of 0.699+/-0.064 and0.582+/-0.051 Msolar for the Ba (primary) and Bb (secondary)components, respectively. Spectral energy distribution (SED) modeling ofthe B subsystem suggests that the B circumstellar material is a sourceof extinction along the line of sight to the B components. This seems tocorroborate a conjecture by Tokovinin that the B subsystem is viewedthrough circumbinary material, but it raises important questions aboutthe morphology of that circumbinary material. Our modeling of thesubsystem component SEDs finds temperatures and luminosities inagreement with previous studies, and coupled with the component massestimates allows for comparison with PMS models in the low-mass regimewith few empirical constraints. Solar abundance models seem tounderpredict the inferred component temperatures and luminosities, whileassuming slightly subsolar abundances brings the models and observationsinto better agreement. The current preliminary orbit does not yet placesignificant constraints on existing PMS stellar models, but prospectsfor additional observations improving the orbit model and componentparameters are very good.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
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