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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.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| The Chemical Compositions of the SRD Variable Stars. III. KK Aquilae, AG Aurigae, Z Aurigae, W Leo Minoris, and WW Tauri
Chemical compositions are derived from high-resolution spectra for fivefield SRd variables. These supergiants not previously analyzed are shownto be metal poor: KK Aql with [Fe/H]=-1.2, AG Aur with [Fe/H]=-1.8, ZAur with [Fe/H]=-1.4, W LMi with [Fe/H]=-1.1, and WW Tau with[Fe/H]=-1.1. Their compositions are, except for two anomalies, identicalto within the measurement errors to the compositions of subdwarfs,subgiants, and less evolved giants of the same [Fe/H]. One anomaly is ans-process enrichment for KK Aql, the first such enrichment reported foran SRd variable. The second and more remarkable anomaly is a stronglithium enrichment for W LMi, also a first for field SRd variables. TheLi I λ6707 profile is not simply that of a photospheric line butincludes strong absorption from redshifted gas, suggesting, perhaps,that lithium enrichment results from accretion of Li-rich gas. Thispotential clue to lithium enrichment is discussed in light of variousproposals for lithium synthesis in evolved stars.
| 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.
| IRAS Detections of Metal-poor Red Giants
A number of relatively bright metal-poor red giants from the HD and BDcatalogs are found to have been detected by the IRAS satellite. Data forthese stars have been retrieved from the IRAS Point Source Catalog (PSC)and/or the Faint Source Catalog (FSC). The majority of metal-poor giantsin these samples fall along relatively well-defined sequences in plotsof V-[12] versus B-V and V-I; for these stars, the 12 μm fluxdetected is presumed to arise from the photosphere. Only a subset ofstars detected at 12 μm were detected at 25 μm these are displayedin a plot of [12]-[25] versus V-[12]. There are a small number of giantsthat exhibit notable 12 and/or 25 μm excesses relative to the meansequences defined by the bulk of the sample. Those stars with the mostunambiguous evidence for infrared excesses are variable stars, eitherlong-period or semiregular variables or RV Tauri stars. As such, thosestars exhibiting infrared excesses in the metal-poor giant sample arelikely in the asymptotic giant branch (AGB) or post-AGB phase ofevolution. There is no clear evidence for nonvariable first-ascent redgiants having been detected among the infrared-excess stars. In fact,some metal-poor red giants known to exhibit outflows in theirchromospheres do not show infrared excesses. A Population II starascending the red giant branch for the first time appears to have toolow a mass-loss rate to be recognizable as an infrared-excess star inthe IRAS PSC or FSC.
| The kinematics of halo red giants
The present 337 radial velocities were obtained with typical accuraciesof 0.7 cm km/sec for 85 metal-poor field red giants, selected from thekinematically unbiased samples of Bond (1980) and Bidelman and MacConnel(1973). The multiply-observed stars suggest the field halo binaryfraction exceeds 10 percent. Using these velocities and those publishedby others, a sample of 174 red giants with Fe/H of not more than -1.5 isobtained. Their mean motion with respect to the local standard of restis -206 + or - 23 km/sec, and the velocity dispersions are sigma (R) of154 + or - 18 km/sec, sigma(theta) of 102 + or - 27 km/sec, andsigma(phi) of 107 + or - 15 km/sec. Using photometrically derivedabsolute magnitudes and published proper motions, orbital eccentricitiesare computed for 72 stars not already considered in a similar study ofsouthern stars by Norris et al. (1985). A few stars with e of less than0.4 are found.
| /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
| 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.
| Some variables of spectral type K
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973PASP...85...42E&db_key=AST
| On the Interpretation of the Motions of the Mira Variables
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| Spectra of Ninety-four Variable Stars
Not Available
| 316 neue Veränderlilche
Not Available
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Eridanus |
| Ascensió Recta: | 03h21m29.99s |
| Declinació: | -21°27'26.8" |
| Magnitud Aparent: | 9.234 |
| Moviment propi RA: | 27.5 |
| Moviment propi Dec: | -3.9 |
| B-T magnitude: | 11.183 |
| V-T magnitude: | 9.395 |
Catàlegs i designacions:
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