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The Taiwan-American Occultation Survey Project Stellar Variability. I. Detection of Low-Amplitude ? Scuti Stars
We analyzed data accumulated during 2005 and 2006 by the Taiwan-AmericanOccultation Survey (TAOS) in order to detect short-period variable stars(periods of lsim1 hr) such as ? Scuti. TAOS is designed for thedetection of stellar occultation by small-size Kuiper Belt Objects andis operating four 50 cm telescopes at an effective cadence of 5 Hz. Thefour telescopes simultaneously monitor the same patch of the sky inorder to reduce false positives. To detect short-period variables, weused the fast Fourier transform algorithm (FFT) in as much as the datapoints in TAOS light curves are evenly spaced. Using FFT, we found 41short-period variables with amplitudes smaller than a few hundredths ofa magnitude and periods of about an hour, which suggest that they arelow-amplitude ? Scuti stars. The light curves of TAOS ?Scuti stars are accessible online at the Time Series Center Web site (http://timemachine.iic.harvard.edu).
| HD 173977: An ellipsoidal δ Scuti star variable
We present spectroscopic and photometric observations of the starHD 173977. It appears that the star is part of adouble line binary system, with a period of 1.801 d, corresponding totwice the period of the photometric variations. Hence the star is anellipsoidal variable. The system is probably synchronized. The physicalparameters of both components were derived through two independantmethods, one based on evolutionary tracks, the other being the result ofthe behaviour of light curves in a close binary system. After removingthe ellipsoidal variations, 3 frequencies are detected in thephotometric data: 8.56, 14.51 and 16.42 d-1, while 2additional frequencies are also possible: 10.96 and 12.11d-1. In accordance with its position in the HR diagram, theprimary component of HD 173977 should be consideredas a δ Scuti star and no longer as a γ Doradus star. Inaddition, HD 173844, used as a check star, is discovered variable with a15.79 d-1 frequency and is classified as a δ Scutistar.Based on observations obtained at the Observatoire de Haute-Provence.Spectroscopic and photometric data are only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/247
| Multi-site, multi-technique survey of γ Doradus candidates. I. Spectroscopic results for 59 stars
We present the first results of a 2-year high-resolution spectroscopycampaign of 59 candidate γ Doradus stars which were mainlydiscovered from the HIPPARCOS astrometric mission. More than 60% of thestars present line profile variations which can be interpreted as due topulsation related to γ Doradus stars. For all stars we alsoderived the projected rotation velocity (up to more than 200 kms-1). The amplitude ratios 2K/Δ m for the mainHIPPARCOS frequency are in the range 35-96 kms-1,mag-1. About 50% of the candidates arepossible members of binary systems, with 20 stars being confirmedγ Doradus. At least 6 stars present composite spectra, and in allbut one case (for which only one spectrum could be obtained), the narrowcomponent shows line profile variations, pointing towards anuncomfortable situation if this narrow component originates from a shellsurrounding the star. This paper is the first of a series concerningmode identification using both photometric and spectroscopic methods forthe confirmed γ Doradus stars of the present sample.Partially based on observations obtained at the Observatoire deHaute-Provence.
| Spectroscopy of Early F Stars: γ Doradus Candidates and Possible Metallic Shell Stars
We obtained high-resolution spectroscopic observations of 34 γDoradus candidates. From the red-wavelength spectra, we determinedspectral classes, radial velocities, and projected rotationalvelocities. The spectra of seven late A or early F stars show metalliclines that have composite profiles consisting of a narrow component nearthe center of a broad line, indicating that they may be shell stars orbinaries. Several stars, including HD 152896, HD 173977, HD 175337, andHD 195068/9, show large line profile asymmetries. Two stars, HD 11443(=α Trianguli) and HD 149420, are ellipsoidal variables and notγ Doradus stars. The percentage of binary systems in our samplemay be as high as 74%.
| The domain of γ Doradus variables in the Hertzsprung-Russell diagram
70 new γ Doradus candidates were identified from Hipparcosphotometry, which represents more than a doubling of the presently knownnumber. Selecting the objects with good evidence for multiperiodicity,it is found that these stars, together with bona fide members of theclass, occupy a well-defined region in a colour-magnitude diagram. Thisdomain corresponds to a range of 7200-7700K on the zero-age mainsequence (ZAMS) and 6900-7500K one magnitude above it, which partlyoverlaps with the instability strip of δ Scuti stars. For thefirst time, γ Doradus stars can be discussed as a group. They canbe found over a significant fraction of the main sequence lifetimes forobjects in the relevant temperature range. An upper limit on the surfacemetallicity of γ Doradus stars is apparent, which may guide thesearch for their pulsation driving mechanism. The importance of possibleobjects exhibiting both γ Doradus and δ Scuti-typepulsations is discussed.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
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