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Chemical composition of semi-regular variable giants
Aims.The aim of this work was to derive chemical abundances in 5 starsthat were previously reported to be SRd variable stars from the halopopulation, and, in particular, to check if manganese does showsignificant underabundance in our program stars similar to that of TYVir, first detected by Luck & Bond. Methods: Elemental abundanceshave been found through the LTE and NLTE analyses, applied tohigh-resolution (R˜50 000) spectra. Results: We have derived theabundances of 18 chemical elements in RX Vir, AB Leo, CK Vir, SV UMa,and TY Vir, and made the following conclusions. Conclusions: .RX Vir isa typical solar-like star. Its classification as a halo population SRdvariable star should be ruled out. The remaining four stars of ourprogram have chemical composition and fundamental parameters thatconfirm their status as metal-deficient halo giants. All studied SRdgiants have relative-to-solar elemental abundances typical of the fieldhalo stars of metallicity -1.8. There is only one exception, which isthe relative manganese abundance. All SRd program stars show uniform[Mn/Fe] ratios that are typical of the stars with metallicity [Fe/H]≈ -3.5. The reason for such a low manganese abundance in these starsis unknown.Based on observations obtained at the Canada-France-Hawaii Telescope(CFHT), which is operated by the National Research Council of Canada,the Institute National des Sciences de l'Univers of the Centre Nationalde la Recherche Scientifique of France, and the University of Hawaii.
| 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.
| 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.
| Aufsuchkarten fur intrinsic Variable Stars in Brno.
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| The Chemical Compositions of the SRD Variable Stars. II. WY Andromedae, VW Eridani, and UW Librae
Chemical compositions are derived from high-resolution spectra for threestars classed as SRd variables in the General Catalogue of VariableStars. These stars are shown to be metal-poor supergiants: WY And with[Fe/H]=-1.0, VW Eri with [Fe/H]=-1.8, and UW Lib with [Fe/H]=-1.2. Theircompositions are identical to within the measurement errors to thecompositions of subdwarfs, subgiants, and less evolved giants of thesame [Fe/H]. The stars are at the tip of the first giant branch or inthe early stages of evolution along the asymptotic giant branch (AGB).There is no convincing evidence that these SRd variables areexperiencing thermal pulsing and the third dredge-up on the AGB. The SRdvariables appear to be at the cool limit of the sequence of RV Taurivariables.
| The Chemical Compositions of the SRd Variable Stars. I. XY Aquarii, RX Cephei, AB Leonis, and SV Ursae Majoris
Chemical compositions are derived from high-resolution spectra for fourstars classed as SRd variables in the General Catalogue of VariableStars. Two stars-XY Aquarii and RX Cephei-are of solar metallicity andmost likely not variable stars. Their spectroscopic effectivetemperatures and surface gravities correspond to the spectral types G0 Vfor XY Aqr and G8 III for RX Cep. Two stars are undisputed variables andshown here to be metal-poor supergiants: AB Leonis with [Fe/H] ~=-1.6and SV Ursae Majoris with [Fe/H] ~=-1.4. The metallicities and highradial velocities show them to be halo stars.
| Professional-amateur collaboration in variable star research: V. Observations of yellow semi-regular variables
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| /V - R/ observations and effective temperatures for extremely metal-deficient red giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983PASP...95...27S&db_key=AST
| Abundances in 11 field stars with large metal deficiencies
Equivalent widths from high dispersion spectra in the red region areused to derive abundances of elements from oxygen to barium in 11weak-lined stars. Values of Fe/H from 1/10 to 1/200 of the solar valueare found. The ratio of oxygen-to-iron is found to vary from one toabout five times the solar value. Calcium and titanium are found to bedeficient in most of these metal-poor stars, confirming an odd-eveneffect among Si, Ca, Sc, and Ti that has been recognized in othersamples of metal-deficient stars. It is found that barium shows anover-deficiency in stars with Fe/H ratio lower than -1.5, as seen inother metal-poor field stars but not in the globular clusters M15 andM92 with similarly large iron deficiencies. Since s-process productionof barium probably occurs in stars of intermediate mass, withmain-sequence lifetimes of 10 to the 8th to 10 to the 9th yr, thisindicates that the barium-deficient halo stars may be older than theglobular clusters with normal Ba/Fe ratios.
| Extremely metal-deficient red giants. I - A new objective-prism, photometric, and radial-velocity survey
Results of an extensive objective-prism survey to detect extremelymetal-deficient red giants and a subsequent investigation of thephotometric and radial velocity properties of the newly discovered starsare presented. The 132 red giants with Fe/H abundance ratios less thanor equal to -1.5 discovered in the present objective-prism survey on a10-deg prism down to B magnitudes of 11.5, and by previousobjective-prism and other surveys, are listed, together with results ofradial velocity and photometric measurements. Examination of theStromgren m1 index calibrated against high-resolution spectroscopicdeterminations of the Fe-H abundance ratio indicates that population IIIfield giants with abundance ratios less than -3 are extremely rare. TheStromgren c1 index is used as an indicator of surface gravity andanomalous CH strengths, resulting in the identification of field redhorizontal-branch stars, field asymptotic-branch giants and subgiants.Radial velocities obtained for about half the stars reveal thatessentially all of them have halo motions, and that the incidence ofspectroscopic binaries is very low.
| Photoelectric observations of the SRD variable CK Vir.
Not Available
| CK Virginis - a semi-irregular variable.
Not Available
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