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A photometric and spectroscopic study of the hottest pulsating extreme helium star, V2076 Oph (HD 160641)
We present results from a three-site photometric and high-resolutionspectroscopic campaign on the hottest known extreme helium star V2076Oph (HD 160641). A core programme of intensive observations covered twoweeks and a much lower sampling rate extended over another two months.Despite the fact that the data seem to indicate periodicity near half aday (though the light curves are clearly not formed by a singleperiodicity), conventional Fourier analysis of the data fails to revealcoherent frequencies. Furthermore, we are unable to recover frequencieswhich were apparently clear in an earlier campaign on the star. Evidenceof monotonic pulsation amplitude changes is seen at the higherfrequencies from a wavelet analysis, but more data are needed beforethis study can be extended to lower frequencies. The application oflinear stochastic differential equation (LSDE) methods indicates thatthe observed light variations could be a result of random variationsgiving the appearance of intermittent periodicity. High-resolutionspectroscopic observations were obtained during the campaign andadditional observations were made three years later. Complex lineprofile variations were observed. It is proposed that the differentbehaviour of the emission line studied may indicate it is associatedwith a stellar wind or resident circumstellar material. The frequenciesthat are extracted from the velocity data do not conform to thoseidentified in the current or previous photometric campaigns.
| High proper motion stars in Kapteyn Selected Area 94
We have applied the astrometric techniques devised by Murray foranalysis of 48-inch Schmidt photographic data to SuperCOSMOS scans of UKSchmidt plates centred on Kapteyn's Selected Area 94(α=2h 53m, δ=0°). In thispreliminary study, we combine astrometric data from four short-exposureV-band plates, taken in 1987 August (2 plates) and 1993 August (2plates), with BVRI photometry from sky-limited plate material, toidentify stars with proper motions exceeding 0.1arcsecyr-1.This paper discusses the completeness of the resulting sample andpresents spectroscopy of 30 stars with μ>0.2arcsecyr-1.Based on the latter observations and the distribution in the[HV, (V-I)] reduced proper-motion diagram, we have classifiedstars in the complete sample as candidate white dwarfs, main-sequencedwarfs and halo subdwarfs, and derived estimates of the disc and haloluminosity functions.
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