Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Abundance analysis of targets for the COROT/MONS asteroseismology missions. II. Abundance analysis of the COROT main targets
One of the goals of the ground-based support program for the COROT andMONS/RÖMER satellite missions is to characterize suitable targetstars for the part of the missions dedicated to asteroseismology. Wepresent the detailed abundance analysis of nine of the potential COROTmain targets using the semi-automatic software VWA. For two additionalCOROT targets we could not perform the analysis due to the highrotational velocity of these stars. For five stars with low rotationalvelocity we have also performed abundance analysis by a classicalequivalent width method in order to test the reliability of the VWAsoftware. The agreement between the different methods is good. We findthat it is necessary to measure abundances extracted from each linerelative to the abundances found from a spectrum of the Sun in order toremove systematic errors. We have constrained the global atmosphericparameters Teff, log g, and [Fe/H] to within 70-100 K,0.1-0.2 dex, and 0.1 dex for five stars which are slow rotators (v sin i< 15 km s-1). For most of the stars we find good agreementwith the parameters found from line depth ratios, H α lines,Strömgren indices, previous spectroscopic studies, and also log gdetermined from the HIPPARCOS parallaxes. For the fast rotators (v sin i> 60 km s-1) it is not possible to constrain theatmospheric parameters.Based on observations obtained with the 193 cm telescope at Observatoirede Haute Provence, France.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| Exploration of the BaSeL stellar library for 9 F-type stars COROT potential targets. Comparisons of fundamental stellar parameter determinations
The Basel Stellar Library (BaSeL models) is constituted of the mergingof various synthetic stellar spectra libraries, with the purpose ofgiving the most comprehensive coverage of stellar parameters. It hasbeen corrected for systematic deviations detected in respect toUBVRIJHKLM photometry at solar metallicity, and can then be consideredas the state-of-the-art knowledge of the broad band content of stellarspectra. In this paper, we consider a sample of 9 F-type stars withdetailed spectroscopic analysis to investigate the Basel Stellar Libraryin two photometric systems simultaneously, Johnson (B-V, U-B) andStrömgren (b-y, m1, and c1). The samplecorresponds to potential targets of the central seismology programme ofthe COROT space experiment, which have been recently observed at OHP.The atmospheric parameters Teff, [Fe/H], and log g obtainedfrom the BaSeL models are compared with spectroscopic determinations aswell as with results of other photometric calibrations. For a carefulinterpretation of the BaSeL solutions, we computed confidence regionsaround the best chi 2-estimates and projected them onTeff-[Fe/H], Teff-log g, and log g-[Fe/H]diagrams. We first derive the 3 atmospheric parameters from the fullphotometric information available (Johnson and Strömgren data). TheBaSeL library has only been calibrated for broad band UBVRIJHKLMphotometry, and it presents therefore intrinsic limitations in respectto other photometric systems, especially with different bandwidth. Thus,using this combination (Johnson and Strömgren), BaSeL temperaturesare systematically lower ( ~ 130 K), and the discrepancy for the gravityand the metallicity can be quite large in comparison to the othermethods. To disentangle these unexpected discrepancies, we fixed thetemperatures at their spectroscopic values and studied the relativeinfluence of each colour index in the log g-[Fe/H] diagrams. We findinconsistent results between Strömgren and Johnson syntheticcolours. While the Johnson colours give impressively good log g-[Fe/H]solutions, the combination of the m1 and c1Strömgren synthetic indices does not provide reliable results. Thisis not, of course, due to any intrinsic superiority of the UBV over theStrömgren system, but to the properties of the BaSeL models.Finally, in order to simultaneously and accurately determine the stellarparameters Teff, [Fe/H] and log g, we suggest to use thecombination of the synthetic BaSeL indices B-V, U-B and b-y rather thanB-V, U-B, b-y, m1 and c1. Based on observationsmade on the 193~cm telescope at Observatoire de Haute-Provence, Franceand data from the ESA Hipparcos satellite. Figures 2-5, 7 and 8 are onlyavailable in electronic form at http://www.edpsciences.org
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.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
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| The late A-type stars - Refined MK classification, confrontation with Stromgren photometry, and the effects of rotation
The MK spectral classification for late A-type stars is refined and theeffects of rotation of spectral classification and uvby(beta) photometryfor these stars are examined. It is found that, for A3 stars, the4417/4481 A wavelength ratio produces results that are inconsistent withthe Stark broadening of the H lines. It is suggested that this ratio isnot useful as a luminosity criterion at any spectral type.Self-consistent sequences of narrow- and broadline standards areestablished. The results of the refined classification system arecompared with Stromgren photometry, showing a set of low-v sin i A-typestars with anomalously large delta(c1) indices for theirluminosity types. It is proposed that these stars are rapid rotatorsseen at fairly low inclination angles.
| A systematic search for members of the Hyades Supercluster. IV - The metallic-line stars and ultrashort-period Cepheids
Bright Star Catalog stars with beta values in the 2.70-2.88 rangecontain 127 members of the Hyades Supercluster, which have been chosenon the basis of the direction of their proper motion. Available radialvelocities confirm supercluster membership for most of these stars.Exceptional regularity is noted in the values of the pulsation constantQ computed for the ultrashort period Cepheids on the basis of knownperiods, model masses and model radii. Outside the center of the Hyadescluster, the largest concentration of supercluster stars is in a regionof 30 pc radius, between 60 and 80 pc above the sun, where 30 percent ofthe expected stars in the temperature range presently discussed aresupercluster members.
| Multicolor photometry of metallic-line stars. III. A photometric catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974RMxAA...1..175M&db_key=AST
| Variability of A and F main sequence stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....12..223J&db_key=AST
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Unicorno |
| Ascensione retta: | 06h32m23.10s |
| Declinazione: | -05°52'08.0" |
| Magnitudine apparente: | 5.6 |
| Distanza: | 43.234 parsec |
| Moto proprio RA: | -0.1 |
| Moto proprio Dec: | -41.2 |
| B-T magnitude: | 5.902 |
| V-T magnitude: | 5.63 |
Cataloghi e designazioni:
|
