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Observations of Binary Stars with the Differential Speckle Survey Instrument. III. Measures below the Diffraction Limit of the WIYN Telescope
In this paper, we study the ability of CCD- andelectron-multiplying-CCD-based speckle imaging to obtain reliableastrometry and photometry of binary stars below the diffraction limit ofthe WIYN 3.5 m Telescope. We present a total of 120 measures of binarystars, 75 of which are below the diffraction limit. The measures aredivided into two groups that have different measurement accuracy andprecision. The first group is composed of standard speckle observations,that is, a sequence of speckle images taken in a single filter, whilethe second group consists of paired observations where the twoobservations are taken on the same observing run and in differentfilters. The more recent paired observations were taken simultaneouslywith the Differential Speckle Survey Instrument, which is a two-channelspeckle imaging system. In comparing our results to the ephemerispositions of binaries with known orbits, we find that pairedobservations provide the opportunity to identify cases of systematicerror in separation below the diffraction limit and after removing thesefrom consideration, we obtain a linear measurement uncertainty of 3-4mas. However, if observations are unpaired or if two observations takenin the same filter are paired, it becomes harder to identify cases ofsystematic error, presumably because the largest source of this error isresidual atmospheric dispersion, which is color dependent. Whenobservations are unpaired, we find that it is unwise to reportseparations below approximately 20 mas, as these are most susceptible tothis effect. Using the final results obtained, we are able to update twoolder orbits in the literature and present preliminary orbits for threesystems that were discovered by Hipparcos.The WIYN Observatory is a joint facility of the University ofWisconsin-Madison, Indiana University, Yale University, and the NationalOptical Astronomy Observatories.
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
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