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Photometric Analysis of Two Candidate Pulsating Early Stars
Both HD199122 and HD213617 are found to be periodic with frequencieswithin the characteristic range of g-mode pulsation for either theSlowly Pulsating B Stars (SPBs) or the Gamma Doradus stars. We beganobserving HD199122 as a SPB based on its appearance in the list of suchstars found through Hipparcos data examination by Koen (MNRAS, 321, 44,2001). However, as noted by Koen, its reported spectral type A2 is latefor an SPB. Based on published photometric indices, he suggests that itsspectral type is closer to B7 and thus it is likely to be a SPB. UsingStromgren uvby photometry, we have examined over 600 differentialmeasures of this star. We find two clear frequencies of f1 = 0.80209 c/dand f2 = 0.82444 c/d, which is within the characteristic range forg-mode pulsation of hotter main sequence stars. Our data suggests thepossible presence of a third frequency, but confirmation is pending moredata analysis. A preliminary analysis of Hipparcos satellite data for HD213617 proposes a frequency of 0.55672 c/d (Handler, G.MNRAS 309,L19-L23,1999). However, Castellano (private communication) has found aperiod closer to 0.8 c/d from his analysis of the Hipparcos data. Sincethis star is an early F type, confirmation of this pulsational valuecould classify this star as a Gamma Doradus variable. We are presentlyobtaining observations for both subjects and will continue analysis asdata arrives. Observations of HD213617 were begun as part of a summerproject as part of the NASA Academy at Ames. This work has beensupported by South Carolina Space Grant and NSF grant AST-0071260 to theCollege of Charleston,.
| Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
A selection criterion based on the relative strength of the largestpeaks in the amplitude spectra, and an information criterion are used incombination to search for multiperiodicities in Hipparcos epochphotometry. The method is applied to all stars which have beenclassified as variable in the Hipparcos catalogue: periodic, unsolvedand microvariables. Results are assessed critically: although there aremany problems arising from aliasing, there are also a number ofinteresting frequency combinations which deserve further investigation.One such result is the possible occurrence of multiple periods of theorder of a day in a few early A-type stars. The Hipparcos catalogue alsocontains a number of these stars with single periodicities: such starswith no obvious variability classifications are listed, and informationabout their properties (e.g., radial velocity variations) discussed.These stars may constitute a new class of pulsators.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| UvbyHbeta_ photometry of main sequence A type stars.
We present Stroemgren uvby and Hbeta_ photometry for a set of575 northern main sequence A type stars, most of them belonging to theHipparcos Input Catalogue, with V from 5mag to 10mag and with knownradial velocities. These observations enlarge the catalogue we began tocompile some years ago to more than 1500 stars. Our catalogue includeskinematic and astrophysical data for each star. Our future goal is toperform an accurate analysis of the kinematical behaviour of these starsin the solar neighbourhood.
| Interstellar extinction in the vicinity of the North America and Pelican Nebulae. II
The results of photoelectric photometry of 564 stars in the Vilniusseven-color system in three areas near the North America and PelicanNebulae are given. Photometric spectral types, absolute magnitudes,color excesses, interstellar extinction,s and distances to the stars aredetermined. We find that the dark cloud separating both nebulae is at580 pc distance. A number of stars immersed in the dark cloud have beenfound. It seems that the dark cloud extends south down to 40 degdeclination. The area southwest of alpha Cygni in the declination zones42 deg and 43 deg is comparatively transparent at least up to 1 kpc.
| Radial velocity measurements. II - Ground-based observations of the program stars for the HIPPARCOS satellite
New radial velocities for 446 stars of magnitude 9.0 or brighter in 1616-sq-deg fields of the Northern Hemisphere are determined by automaticPDS measurement of 80-A/mm-dispersion spectra obtained at theObservatoire de Haute Provence using a 17-cm-diameter objective prism.The fields were selected to provide data for the input catalog of theESA Hipparcos astrometric satellite. The measurement techniques andprecision are discussed, and the results are presented in extensivetables and graphs.
| The S201 far-ultraviolet imaging survey. II - A field in Cygnus
Far-ultraviolet imagery of a region in Cygnus, a 20 deg diameter fieldcentered near (1950) R. A. 21 h 31.2 m decl. +37 deg 25 arcmin, wasobtained by the S201 far-ultraviolet camera during the Apollo 16mission. In a 10 minute exposure covering the 1250-1600 A wavelengthrange (effective wavelength 1400 A), 730 star images can be detected,corresponding to a limiting ultraviolet magnitude of about m (1400) =10. Assuming nominal interstellar extinction values in this region nearthe galactic plane, this result corresponds to the detection of A0 Vstars to a distance of 300 pc and of B0 V stars to 1500 pc.Uncertainties in spectral classification and interstellar extinction forindividual objects are probably more significant than calibration ormeasurement errors. Most of the objects detected are identified withstars in the Smithsonian Astrophysical Observatory Star Catalog (1966),or the Catalog of Stellar Identifications (1979) or both, but 87 objectsremain unidentified (or are identified with late-type stars).
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