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Mg and TiO spectral features at the near-IR: spectrophotometric index definitions and empirical calibrations
Using the near-infrared spectral stellar library of Cenarro et al., thebehaviour of the MgI line at 8807 Å and nearby TiO bands isanalyzed in terms of the effective temperature, surface gravity andmetallicity of the library stars. New spectroscopic indices for bothspectral features - namely MgI and sTiO - are defined, and theirsensitivities to different signal-to-noise ratios, spectral resolutions,flux calibrations and sky emission-line residuals are characterized. Thetwo new indices exhibit interesting properties. In particular, MgI is agood indicator of the Mg abundance, whereas sTiO is a powerfuldwarf-to-giant discriminator for cold spectral types. Empirical fittingpolynomials that reproduce the strength of the new indices as a functionof the stellar atmospheric parameters are computed, and a FORTRANroutine with the fitting function predictions is made available. Athorough study of several error sources, non-solar [Mg/Fe] ratios andtheir influence on the fitting function residuals is also presented.From this analysis, an [Mg/Fe] underabundance of ~ -0.04 is derived forthe Galactic open cluster M67.
| Membership, binarity, and rotation of red dwarfs in the nearby open cluster Coma Berenices (Melotte 111)
Context: Although several attempts have been made to identify solar-typemembers on the main sequence of the nearby open cluster Coma Berenices(Mel 111), the population of the lower main sequence is still poorlyknown. Aims: We observed 46 new candidates to search for new membersand monitored known spectroscopic-binary members to determine orbitalparameters. Methods: We obtained a total of 903 radial-velocitymeasurements of 69 solar-type stars in the field of Mel 111 with theCORAVEL spectrovelocimeter over 20 years. Results: Among the 35 starsfrom Trumpler's list, 23 are members according to their radialvelocities and photometry. We were able to confirm the membership ofonly 8 stars among the 46 candidates observed. Six double-lined and tensingle-lined spectroscopic binaries were discovered. Six only aremembers and an orbit was determined for them and for 4 double-linednon-members. The binary frequency is 22% (7/32). The cluster mean radialvelocity is +0.01 ± 0.08 km s-1 based on 28 members. Conclusions: The lower main sequence of the Coma Berenices open clusteris still rather poorly populated. The cluster size may be much largerthat usually accepted. Accordingly extensive programmes to determineprecise proper motions, radial velocities and photometry should beundertaken to identify faint cluster members outside the cluster centralarea. If a significant population of faint members cannot be identified,Coma Ber could be a prominent example of dynamical evolution leading tostar evaporation.Based on observations collected at the Haute-Provence Observatory(France). Table 1 is also available, and Full Table 8 only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/491/951
| Empirical calibration of the near-infrared Ca ii triplet - II. The stellar atmospheric parameters
We present a homogeneous set of stellar atmospheric parameters(Teff, logg, [Fe/H]) for a sample of about 700 field andcluster stars which constitute a new stellar library in the near-IRdeveloped for stellar population synthesis in this spectral region(λ8350-9020). Having compiled the available atmospheric data inthe literature for field stars, we have found systematic deviationsbetween the atmospheric parameters from different bibliographicreferences. The Soubiran, Katz & Cayrel sample of stars with verywell determined fundamental parameters has been taken as our standardreference system, and other papers have been calibrated and bootstrappedagainst it. The obtained transformations are provided in this paper.Once most of the data sets were on the same system, final parameterswere derived by performing error weighted means. Atmospheric parametersfor cluster stars have also been revised and updated according to recentmetallicity scales and colour-temperature relations.
| Lithium in the Coma Berenices open cluster
Lithium abundances, radial velocities, and rotational velocities arereported for 20 candidate F, G and K stars of the sparse Coma Berenicesopen cluster. All the stars are proper-motion selected, and our radialvelocities support the membership credentials of at least 12 of thecandidates. Combining our data with that in the literature, we have aclose-to-complete census of Li abundances for late-type stars withMV<5.8. These data show that the Li-depletion pattern inComa Ber is similar, but not identical, to that in the Hyades cluster,which has a similar age but higher metallicity. Several Coma Ber F starshave suffered significantly more Li depletion than their counterparts inthe Hyades. The G and early-K stars of Coma Ber have undergone less Lidepletion than those of the Hyades, but much more than that predicted bystandard evolutionary models featuring only convective mixing. Thisprovides strong evidence for additional mixing and Li depletionoperating in these stars during their first 400 Myr on the mainsequence, amounting to 0.3 dex at 6000 K and rising to 0.8-1.2 dex at5400 K. We find that 4 of the radial-velocity non-members are among asmall number of low-mass stars which were previously reported as part ofan extra-tidal moving group associated with the Coma Ber cluster. As aresult, we now find that the luminosity function of this moving group isindistinguishable from that of the central cluster. It is uncertainwhether there may be a significant number of stars with even lowermasses among the moving group.
| Empirical calibration of the lambda 4000 Å break
Empirical fitting functions, describing the behaviour of the lambda 4000Ä break, D4000, in terms of effective temperature,metallicity and surface gravity, are presented. For this purpose, thebreak has been measured in 392 stars from the Lick/IDS Library. We havefollowed a very detailed error treatment in the reduction and fittingprocedures, allowing for a reliable estimation of the breakuncertainties. This calibration can be easily incorporated into stellarpopulation models to provide accurate predictions of the break amplitudefor, relatively old, composite systems. Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| An astrometric catalogue for the area of Coma Berenices
A catalogue of stellar positions and proper motions down to the 14thphotographic magnitude in the area of the open cluster in Coma Berenicesis compiled from data of 12 different sources. The accuracy of theproper motion data is comparable to that of the Hipparcos Catalogue. Thecatalogue Table 5 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Rotation of late-type stars in young clusters
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| Photoelectric Studies. III. Color-Luminosity Arrays for the Coma Berenices and Ursa Major Clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1950ApJ...111..414E&db_key=AST
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