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Lithium abundances for early F stars: new observational constraints for the Li dilution
Aims.To investigate any correlation between Li abundances and rotationalvelocities among F-G evolved stars, we study a large sample of early Fstars from the Bright Star Catalogue (BSC), most of them classified inthe literature as giant stars.Methods.Physical parameters and Liabundances are estimated for each star, often for the first time, bycomparing observed and synthetic spectra. We analyse the position of thestars in the H-R Diagram based on Hipparcos data using stellarevolutionary tracks and we discuss their Li abundances and projectedrotational velocities.Results.Observed stars are mostly on theturnoff, with masses between 1.5 and 2.0 Mȯ. The starswith measured A(Li) abundance show high Li content, most of them withabundance near the cosmic value. The A(Li) versus V sin i diagram showsthe same trend as reported in previous studies: fast rotators (V sinigse 30 km s-1) are also stars with high Li content, whereasslow rotators present a wide range of values of A(Li), ranging from nodetected Li to the cosmic value.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Rotation in Globular Cluster stars. Turn-off and subgiant stars in NGC 104, NGC 6397 and NGC 6752
We present a derivation of upper limits to the rotation of Main Sequencestars in three globular clusters using spectra obtained during timeallocated to the ESO Large Programs 165-L0263 and 167.D-0173, with UVESat VLT2 (Kueyen). The stars analyzed in this work do not show anyevidence of high values of rotational velocities as far as the outerlayers are concerned, in particular robust estimates for the upperlimits of the values of the mean projected rotational velocities areplaced, about /line{vrot sin i} = 3.5+/- 0.2 kms-1 and about /line{vrot sin i}=4.7+/-0.2 kms-1 for, respectively, the program turn-off and subgiantstars. On the basis of statistical considerations, assuming thatinclination of the rotational axis i is randomly oriented, and that allstars within the same group rotate at the same rate, we obtain estimatesfor the values of the true rotational velocities. These values are upperlimits to the true rotational velocities if there is some star-to-starscatter in rotational or macro-turbulent velocities. The mean values ofthese upper limits for vrot for the stars of the samespectral type averaged over the three clusters are found to berespectively, /line{v}rot<=3.5+/-0.4 km s-1 and/line{v}rot<=2.6+/-1.1 km s-1. Thus, theexplanation for the large rotational velocities found for the HorizontalBranch stars must be looked for either in the rotation of the core notdetectable in the outer layers (Sills & Pinsennault \cite{sill}) orin the acquisition of angular momentum during their evolution.Based on observations collected at the European Southern Observatory,Chile.
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| UBV polarimetry of 361 A- and F-type stars in selected areas
We present simultaneous UBV linear polarization measurements for 361 A-and F-type stars with accurate colour excess and distance determination.These stars are distributed in 35 Kapteyn's Selected Areas, covering thethird and fourth quadrants of the galactic plane (|b| <= 30degr ).The obtained polarization and the known colour excess are compared. Ananalysis of the polarization distribution as a function of the stellardistance is also performed. Based on observations collected at theEuropean Southern Observatory (ESO), La Silla, Chile.
| Are metallic A-F giants evolved AM stars? Rotation and rate of binaries among giant F stars
We test the hypothesis of Berthet (1992) {be91} which foresees that Amstars become giant metallic A and F stars (defined by an enhanced valueof the blanketing parameter Delta m_2 of the Geneva photometry) whenthey evolve. If this hypothesis is right, Am and metallic A-FIII starsneed to have the same rate of binaries and a similar distribution ofvsin i. From our new spectroscopic data and from vsin i and radialvelocities in the literature, we show that it is not the case. Themetallic giant stars are often fast rotators with vsin i larger than 100kms(-1) , while the maximum rotational velocity for Am stars is about100 kms(-1) . The rate of tight binaries with periods less than 1000days is less than 30% among metallic giants, which is incompatible withthe value of 75% for Am stars - [Abt & Levy 1985] {ab85}).Therefore, the simplest way to explain the existence of giant metallic Fstars is to suggest that all normal A and early F stars might go througha short ``metallic" phase when they are finishing their life on the mainsequence. Besides, it is shown that only giant stars with spectral typecomprised between F0 and F6 may have a really enhanced Delta m_2 value,while all A-type giants seem to be normal. Based on observationscollected at Observatoire de Haute Provence (OHP), France.
| The Angular Momentum of Main Sequence Stars and Its Relation to Stellar Activity
Rotational velocities are reported for intermediate-mass main sequencestars it the field. The measurements are based on new, high S/N CCDspectra from the Coudé Feed Telescope of the Kitt Peak NationalObservatory. We analyze these rotation rates for a dependence on bothmass and age. We compare the average rotation speeds of the field starswith mean velocities for young stars in Orion, the Alpha Persei cluster,the Pleiades, and the Hyades. The average rotation speeds of stars moremassive than $\sim1.6$ \msun\experience little or no change during theevolutionary lifetimes of these stars on the zero age main sequence orwithin the main sequence band. Less massive stars in the range betwee n1.6\msun\ and 1.3\msun\ also show little decline in mean rotation ratewhile they are on the main sequence, and at most a factor of 2 decreasein velocity as they evolve off the main sequence. The {\it e}-foldingtime for the loss of angular momentum b y the latter group of stars isat least 1--2 billion years. This inferred characteristic time scale forspindown is far longer than the established rotational braking time forsolar-type stars with masses below $\sim1.3$ \msun. We conclude from acomparison of the trends in rotation with trends in chromospheric andcoronal activity that the overall decline in mean rotation speed alongthe main sequence, from $\sim2$ \msun\ down to $\sim1.3$ \msun, isimposed during the pre-main sequence phase of evolution, and that thispattern changes little thereafter while the star resides on the mainsequence. The magnetic activity implicated in the rotational spindown ofthe Sun and of similar stars during their main sequence lifetimes mus ttherefore play only a minor role in determining the rotation rates ofthe intermediate mass stars, either because a solar-like dynamo is weakor absent, or else the geometry of the magnetic field is appreciablyless effective in removing angular momentu m from these stars. (SECTION:Stars)
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| The early F-type stars - Refined classification, confrontation with Stromgren photometry, and the effects of rotation
The classification for early F-type stars in the MK spectralclassification system presented by Gray and Garrison (1987) is refined.The effect of rotation on spectral classification and ubvy-betaphotometry of early F-type stars is examined. It is found that theclassical luminosity criterion, the 4417 A/4481 A ratio givesinconsistent results. It is shown that most of the stars in the DeltaDelphini class of metallic-line stars are either normal or areindistinguishable from proto-Am stars. It is suggested that thedesignation Delta Delphini should be dropped. The classifications arecompared with Stromgren photometry. The effects of rotation on thedelta-c1 index in the early-F field dwarfs is demonstrated.
| Magnetic structure in cool stars. XV - The evolution of rotation rates and chromospheric activity of giants
For cool giants and subgiants the observed dependence of rotationalvelocity and Ca II H and K line-core emission on color B-V isinterpreted in terms of changes in the moment of inertia by stellarevolution. Modeling of the rotational velocity during the evolution ofcool giants with masses between 2.0 and 3.0 solar masses, by taking intoaccount the change in the moment of inertia and assuming rigid-bodyrotation and conservation of angular momentum, describes the observeddecrease of v sin i with B-V. The computed evolution of the rotationalvelocity, together with the empirical relation between the Ca IIline-core emission and the rotation rate, explain the observed drop inthe Ca II line-core emission for giants at B-V = about 0.95. Forsubgiants with masses of about 1.5 solar mass, the change in the momentof inertia by itself cannot explain the observed v sin i distribution:there are indications of loss of angular momentum, presumably bymagnetic braking.
| Metallicism among A and F giant stars
132 stars considered as A and F giants have been studied for theirproperties in the Geneva photometric system. It is shown that thissystem to derive the temperature, absolute magnitude and Fe/H value forstars in this part of the HR diagram. 36 percent of the stars of oursample exhibit an enhanced value Delta m2 that can be interpreted interms of Fe/H. The red limit of stars having an enhanced Fe/H value is0.225 in B2-V1 or 6500 K in Teff. This corresponds to the limit definedby Vauclair and Vauclair (1982) where the diffusion timescale is equalto the stellar lifetime and permits the assumption that the diffusion isthe process responsible for the metallicism observed in the A and Fgiants.
| Cepheids and nonvariable supergiants
Photometric parameters for Cepheids in a previous paper are adapted foruse with nonvariable supergiants of similar temperature. The closecorrelation between the abundance and luminosity parameters forclassical, short-period Cepheids (SPC) confirms the nearlydispersionless luminosity temperature relation for these variables. Theassumptions that (1) the C-type variables are transiting the Cepheidtemperature for the first time, (2) the classical SPC are mostlytransiting for the second time, and (3) the long-period Cepheids (LPC)are a mixture of stars transiting for the first to third or fourth timesare found to be consistent with the various correlations of temperatureand luminosity parameters. The nonvariable supergiants with photometricparameters similar to those for the Cepheids are found to haveluminosities consistent with their spectroscopic luminosity class. Few,if any, nonvariable supergiants have temperatures and luminositiessimilar to the LPC.
| Metal abundance and microturbulence in F0-G2 stars and the calibration of the Stromgren m1 index
The strengths of two narrow groups of metal lines are measuredphotoelectrically by means of an echelle spectrometer for 16 F0-G2 giantfield stars and for 12 Hyades main-sequence stars. A model-atmosphereanalysis of these observations and similar observations of main-sequencefield stars observed earlier results in the determination of the metalabundance for 179 stars. In addition, the microturbulence parameter isdetermined for 73 of these stars. The internal accuracy of the resultsis estimated to be plus or minus 0.08 for the logarithmicmetal-to-hydrogen ratio and plus or minus 0.2 km/sec for themicroturbulence parameter. The metal abundances are found to agree verysatisfactorily with values of the logarithmic iron-to-hydrogen ratiodetermined from classical coude spectroscopy regarding both zero pointand scale. It is found that the microturbulence parameter is a functionof the effective temperature and the surface gravity. It increases from1.2 km/sec for solar type stars to approximately 3.0 km/sec for earlyF-type giants.
| Study of the F-type 1 MK spectral types.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..637M&db_key=AST
| Rotation of evolving A and F stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&A....18..428D&db_key=AST
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| Сазвежђа: | Зец |
| Ректацензија: | 05h13m59.90s |
| Deклинација: | -14°36'24.0" |
| Apparent магнитуда: | 6.21 |
| Даљина: | 75.131 parsecs |
| Proper motion RA: | 10 |
| Proper motion Dec: | -1.7 |
| B-T magnitude: | 6.657 |
| V-T magnitude: | 6.255 |
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