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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.
| Chandra X-Ray Observations of Young Clusters. II. Orion Flanking Fields Data
We present results of Chandra observations of two flanking fields (FFs)in Orion, outside the Orion Nebula Cluster (ONC). The observations weretaken with the ACIS-I camera with an exposure time of about 48 ks eachfield. We present a catalog of 417 sources, which includes X-rayluminosity, optical and infrared photometry, and X-ray variabilityinformation. We have found 91 variable sources, 33 of which have aflarelike light curve and 11 of which have a pattern of a steadyincrease or decrease over a 10 hr period. The optical and infraredphotometry for the stars identified as X-ray sources are consistent withmost of these objects being pre-main-sequence stars with ages youngerthan 10 Myr. We present evidence for an age difference among theX-ray-selected samples of NGC 2264, Orion FFs, and ONC, with NGC 2264being the oldest and ONC being the youngest.
| Observations of Star-Forming Regions with the Midcourse Space Experiment
We have imaged seven nearby star-forming regions, the Rosette Nebula,the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5,with the Spatial Infrared Imaging Telescope on the Midcourse SpaceExperiment (MSX) satellite at 18" resolution at 8.3, 12.1, 14.7, and21.3 μm. The large angular scale of the regions imaged (~7.2-50deg2) makes these data unique in terms of the combination ofsize and resolution. In addition to the star-forming regions, twocirrus-free fields (MSXBG 160 and MSXBG 161) and a field near the southGalactic pole (MSXBG 239) were also imaged. Point sources have beenextracted from each region, resulting in the identification over 500 newsources (i.e., no identified counterparts at other wavelengths), as wellas over 1300 with prior identifications. The extended emission from thestar-forming regions is described, and prominent structures areidentified, particularly in W3 and Orion. The Rosette Nebula isdiscussed in detail. The bulk of the mid-infrared emission is consistentwith that of photon-dominated regions, including the elephant trunkcomplex. The central clump, however, and a line of site toward thenorthern edge of the cavity show significantly redder colors than therest of the Rosette complex.
| 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
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to 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
| Broad-Band X-Ray Observations of the Orion Region with ASCA
Broad-band X-ray images and spectra of the Orion Nebula region wereobtained with the X-ray satellite ASCA. Fifty two point-like sourceswere resolved, including the Orion Trapezium. A large fraction of theoptical counterparts of the ASCA sources were classified as G--M typestars. Spectral model fits and count ratios (flux ratio between soft andbroad bands) revealed that most of the point sources exhibit ahigh-temperature plasma of { ~ }2--5 keV. Model fits of the X-rayspectra from extended regions around the Orion Nebula (M42), thereflection nebula NGC 1977, and the sky between these nebulae requiredat least two-temperature components of typically 0.7--1 keV and 3--5keV. >From selected high-flux sources, we also found that the modelof a 2-temperature thin thermal plasma is more likely than that of asingle-temperature. X-ray light curves from these sources were timevariable, but showed no large flares. We thus suggest that the hardX-rays are generated even in relatively quiescent states.
| Proper motions of stars in the region of the Orion Nebula cluster (C 0532-054).
Relative proper motions and membership probabilities for 333 starswithin an area of 1.6deg by 1.8deg centred on the Orion Nebula M 42 aredetermined using plates taken over a period of 83 years with the doubleastrograph of Shanghai Observatory (scale of 30"/mm). The plates weremeasured with the ASTROSCAN automatic plate-measuring machine of LeidenObservatory. The average proper motion accuracy obtained for stars inthe photographic magnitude range 7 to 14 is 0.3mas/yr. Errors aresomewhat larger towards fainter and brighter magnitude, but the majoritylie well below 1mas/yr. 64% of the stars have been measured successfullyon at least 13 out of 18 plates. The number of stars with membershipprobabilities higher than 0.7 is 184. It is shown by a detaileddiscussion that the proper motions and membership probabilities of thestars determined in this paper are in good agreement with the resultspresented recently by other authors. Although there is a clearconcentration in the proper motion diagram, both the remainingdispersion of the internal motions and the distribution of "members" asprojected on the sky indicate that the stars in this region are notbound as one system, but do have a common origin. A similar conclusioncan be drawn from a comparison with spectroscopic and radial velocitydata.
| 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
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| A catalog of stellar Lyman-alpha fluxes
We present a catalog of stellar Ly-alpha emission fluxes, based on newand archival images obtained with the IUE spacecraft. The catalogincludes 227 stars with detectable Ly-alpha emission fluxes, and upperlimits on the Ly-alpha emission flux for another 48 stars. Multiple fluxmeasurements are given for 52 stars. We present a model for correctingthe observed Ly-alpha flux for attenuation by the local interstellarmedium, and we apply this model to derive intrinsic Ly-alpha fluxes for149 catalog stars which are located in low H I column density directionsof the local interstellar medium. In our catalog, there are 14 late-Aand early-F stars at B-V = 0.29 or less that show detectable emission atLy-alpha. We find a linear correlation between the intrinsic Ly-alphaflux and C II 1335 A flux for stars with B-V greater than 0.60, but theA and F stars deviate from this relation in the sense that theirLy-alpha flux is too low. We also find a good correlation betweenLy-alpha strength and coronal X-ray emission. This correlation holdsover most of the H-R diagram, even for the F stars, where an X-raydeficit has previously been found relative to the transition regionlines of C II and C IV.
| Machine-readable version of the Parenago catalogue of stars in the area of the Orion nebula
Not Available
| Spectroscopic binaries in the Orion OB1 association
A radial velocity study of the brighter members of the Ori OB2association is reported. The radial velocity variables, new preliminaryorbital elements for six spectroscopic binaries, and the projected axialrotation in stars for which the orbital elements are lacking arereported. The correlation between the proportion of binaries and theaverage axial rotation for the subgroups of the association isdiscussed. It is found that the Orion main-sequence members rotate atalmost the same rate as field stars of the same types. The averageradial velocity for the whole association is 23 km/s. The percentage ofspectroscopic binaries with periods shorter than 100 days plus themagnetic Ap-Bp among the main-sequence members of the association is 32percent.
| Einstein Observatory magnitude-limited X-ray survey of late-type giant and supergiant stars
Results are presented of an extensive X-ray survey of 380 giant andsupergiant stars of spectral types from F to M, carried out with theEinstein Observatory. It was found that the observed F giants orsubgiants (slightly evolved stars with a mass M less than about 2 solarmasses) are X-ray emitters at the same level of main-sequence stars ofsimilar spectral type. The G giants show a range of emissions more than3 orders of magnitude wide; some single G giants exist with X-rayluminosities comparable to RS CVn systems, while some nearby large Ggiants have upper limits on the X-ray emission below typical solarvalues. The K giants have an observed X-ray emission level significantlylower than F and F giants. None of the 29 M giants were detected, exceptfor one spectroscopic binary.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| 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.
| Stellar integrated fluxes in the wavelength range 380 NM - 900 NM derived from Johnson 13-colour photometry
Petford et al. (1988) have reported measured integrated fluxes for 216stars with a wide spread of spectral type and luminosity, and mentionedthat a cubic-spline integration over the relevant Johnson 13-colormagnitudes, converted to fluxes using Johnson's calibration, is inexcellent agreement with those measurements. In this paper a list of thefluxes derived in this way, corrected for a small dependence on B-V, isgiven for all the 1215 stars in Johnson's 1975 catalog with completeentries.
| Zur Variabilitat einiger heisser Sterne in Orion Nebel.
Not Available
| Photometry of the MG B + MgH feature for a sample of bright stars
Measurements of the strength of the 5174 A Mg b + MgH feature arepresented for a sample of solar neighborhood stars, ranging in spectraltype from B to M. The data were obtained by the use of two 70 A FWHMinterference filters and a single-channel photometer. In agreement withprevious investigations, the absorption is seen to vary with stellartemperature and gravity. It does not appear to correlate very well withFe/H abundances determined by spectroscopic techniques, despitetheoretical expectations to the contrary. If this lack of correlation isnot merely the result of errors in the Fe/H measurements, it mayindicate that Mg/Fe variations exist among the G and K stars. Since theMg b + MgH absorption appears to correlate with other metallicityfeatures in the spectra of E galaxies, it is suggested that the metalabundance spread in such galaxies is larger than that among the solarneighborhood stars studied in this investigation.
| Photometric variations in AP stars observable at La Silla in November and December
Photometric observations of 13 Ap stars made at the European SouthernObservatory at La Silla during November 1977 and December 1978 arereported. Observations were made in the uvby with the four-channelphotometer at the 40-cm telescope in November, and with the one-channelphotometer at the 50-cm telescope in December. Light variations withperiods from 0.724 to 4.64 days are obtained for 11 of the stars,including the Hg-Mn star HR 2202, which was believed not to vary.Extremely small variations are observed in Upsilon 4 Eri, with apossible period of 0.51 days, although the two Mn components are likelyto vary independently. HR 1800 was not observed to vary over two-weekobservation period. The stars 20 Eri, HR 1194, Alpha Dor, 11 Ori and HD36916 are also noted to exhibit relatively large variations for Apstars.
| A photometric study of the Orion OB 1 association. III - Subgroup analyses
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978ApJS...36..497W&db_key=AST
| A photometric study of the Orion OB 1 association. I - Observational data.
A catalog of observational data is presented for stars in the region ofthe young stellar association Orion OB 1. Photoelectric observationsobtained in the uvby-beta and UBV systems are compiled along withprevious photoelectric and spectroscopic data for all these stars aswell as for several bright members of the association with availablephotometric indices. Mean weighted values are computed for thephotometric data and summarized in tables expected to be reasonablycomplete for association members earlier than spectral type A0.Membership criteria are derived, and qualitative membershipprobabilities summarized, for the 526 stars in the final program. Theanalytical procedures are discussed for association stars of B,intermediate, and AF types. Effects of the nebular environment andvarious calibrations of Balmer-line and four-color indices areconsidered for the determination of absolute magnitudes for the B-typestars.
| Scanner K-line photometry of Orion stars
Results are presented for two-channel scanner measurements of calciumK-line strengths in 39 Orion sword and belt stars. Values of the calciumk index and its associated standard error are given for each observedstar, and the K-line strengths are compared with those of K-linestandard stars and Hyades stars. Plots of k index againstreddening-corrected color and of k-index deviation againstmetal-strength index deviation are provided which show that the Orionsword and belt stars do not differ significantly in their calcium andmetal abundances from general field stars.
| A polarization survey of stars near the Orion Nebula
A polarization survey of over 200 young stars near the Orion Nebulaindicates that 25 percent of the sample shows linear polarizationsignificantly above the average interstellar value for this cluster.Several regions of high polarization and reddening exist in the Orioncluster, although not all the stars in these regions are highlypolarized. Position angles of polarization are not randomly distributed,which suggests that an external polarization mechanism operates for mostof the polarized stars. Polarization is always accompanied by thepresence of infrared excesses. Finally, the amounts and origins ofpolarization are considered as a function of stellar spectral type andcolor.
| 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
| 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
| Catalog of Indidual Radial Velocities, 0h-12h, Measured by Astronomers of the Mount Wilson Observatory
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...19..387A&db_key=AST
| BM Orionis, the Eclipsing Binary in the Trapezium
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969PASP...81..771H&db_key=AST
| Motions of the Bright F-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...155..701E&db_key=AST
| Studies of extremely young clusters. V. Stars in the vicinity of the Orion nebula
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...155..447W&db_key=AST
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| Takýmyýldýz: | Avci |
| Sað Açýklýk: | 05h35m39.50s |
| Yükselim: | -04°51'21.0" |
| Görünürdeki Parlaklýk: | 5.26 |
| Uzaklýk: | 113.636 parsek |
| özdevim Sað Açýklýk: | -1.5 |
| özdevim Yükselim: | 8.9 |
| B-T magnitude: | 5.539 |
| V-T magnitude: | 5.266 |
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