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|An empirical temperature calibration for the Δ a photometric system . I. The B-type stars|
We establish an empirical effective temperature calibration of mainsequence, luminosity class V to III B-type stars for the Δ aphotometric system which was originally developed to detect magneticchemically peculiar objects of the upper main sequence (early B-type toearly F-type) at 5200 Å. However, this system provides the index(g_1-y) which shows an excellent correlation with (B-V) as well as (b-y)and can be used as an indicator of the effective temperature. This issupplemented by a very accurate color-magnitude diagram, y or V versus(g_1-y), which can be used, for example, to determine the reddening,distance and age of an open cluster. This makes the Δ aphotometric system an excellent tool to investigate theHertzsprung-Russell-Diagram (HRD) in more detail. Using thereddening-free parameters and already established calibrations withinthe Strömgren uvbyβ, Geneva 7-color and Johnson UBV systems, apolynomial fit of third degree for the averaged effective temperaturesto the individual (g_1-y)0 values was derived. For thispurpose, data from the literature as well as new observations were takenresulting in 225 suitable bright normal B-type objects. The statisticalmean of the error for this sample is 238 K which is sufficient toinvestigate the HRD of distant galactic open clusters as well asextragalactic aggregates in the future.
|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 220.127.116.11 orhttp://cdsweb.u-strasbg.fr/Abstract.html
|Discovery and analysis of Gamma Doradus type pulsations in the F0 IV star HR 2740=QW PUP|
We present multisite photometric observations of the F0 IV star HR2740=QW Pup that reveal it to be a Gamma Dor type variable pulsatingwith four frequencies: 1.0434, 0.9951, 1.1088 and 0.9019/d. These datawere obtained over a time baseline spanning from January 14 to February11, 1997. The 1.0434/d term dominates in amplitude (10 mmag) over theother three (each less than 5 mmag); the light curve comprising thesefour frequencies seems to be very stable and no residual power is leftin the power spectrum. During the analysis particular attention was paidto methodological aspects, which cannot be neglected considering theproximity of the frequencies to 1/d. Physical parameters were alsoderived for all the well-known Gamma Dor stars, confirming that thisclass is very homogenous. In the framework of the campaign, two Ap starswere also observed. The photometric differences between these rotatingvariables and HR 2740 are emphasized, corroborating the pulsationalnature of the Gamma Dor stars. It is further demonstrated that therotational splitting cannot be a suitable explanation of the observedfrequency content of HR 2740.
|Behaviour of the HeI 587.6, 667.8, 706.5 and 728.1nm lines in B-type stars. On the helium stratification in the atmosphere of magnetic helium peculiar stars.|
High resolution spectra of the HeI587.6, 667.8 706.5 and 728.1nm lineshave been obtained to test the prediction (notably by Vauclair et al.1991) that helium abundance should decrease with depth in helium richstars and increase in helium weak stars. A sample of B-type mainsequence stars, with expected solar abundances and non stratifiedatmospheres, have also been observed in order to compare the behaviourof the selected lines with the chemically peculiar case and with theory.We found significant discrepancies with theory for the lines HeI 706.5.and 728.1nm, and, in order to outline differences between 'normal' and'peculiar' stars, we have adopted an empirical correction to the Lorentzbroadening parameter in the Voigt profile, under the assumption of LTE.This parameter is derived from the imposition of a satisfactory fit withobservations for the relation equivalent width vs. effective temperaturefor normal B stars. For helium rich stars we confirm Vauclair et al.(1991) predictions that helium abundance decreases with depth. However,we found that helium abundance decreases with depth in helium weak starstoo, which contradicts Vauclair et al. (1991) predictions. For somepeculiar stars, the inferred helium abundance is in disagreement withthe peculiarity class reported in the General Catalogue of Ap and Amstars (Renson et al. 1991).
|The ROSAT all-sky survey catalogue of optically bright OB-type stars.|
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
|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.
|An IRAS survey of main sequence B, A, and F stars|
Results are presented of an IRAS survey of main-sequence B, A, and Fstars, based on three primary sources as a data base: theBernacca-Perinotto Catalog of Stellar Rotational Velocities, theMichigan Spectral Catalog, and the Bright Star Catalog. The stars in thedata base are divided into four categories: (1) main-sequence singlestars, (2) main-sequence close binary stars, (3) spectrally peculiarstars such as Am, Ap, Fm, and Fp stars, and (4) subgiants. It is foundthat about 20 percent of main-sequence single stars show an IR colorexcess in at least one of the 12, 25, or 60 micron IRAS bands, while theother three groups do not show any statistically significant percentageof IR color excess stars. It is also found that stars with large (v sini) values are more likely to show color excesses at IRAS wavelengthsthan stars with small (v sin i) values.
|Photometric variability of some CP stars|
The photometric data relative to twenty-three southern CP stars havebeen re-analyzed. New or improved parameters of the lightcurves arepresented for eleven of them.
|A study of visual double stars with early type primaries. IV Astrophysical data|
Astrophysical parameters (MK class, color excess, absolute magnitude,distance, effective temperature, mass, and age) are derived fromcalibrations of the uvby-beta indices for the members of 253 doublestars with O or B type primaries and faint secondaries. The photometricspectral classification is compared to the MK classes, and the agreementis very good. The derived data together with spectroscopic and JHKL dataare used for deciding which pairs are likely to be physical and whichare optical, and it is shown that 98 (34 percent) of the secondaries arelikely to be members of physical systems. For 90 percent of the physicalpairs the projected separation between the components is less than25,000 AU. A majority of the physical secondaries are late-type stars,and 50 percent of them are contracting towards the zero-agemain-sequence. Also presented are new uvby-beta data for 43 secondariesand a computer program for determining astrophysical parameters fromuvby-beta data.
|The local system of early type stars - Spatial extent and kinematics|
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
|The A0 stars|
A photometric grid, standardized on MK spectral standards, has been usedto compare spectral types and luminosity classes obtainedphotometrically with those in two extensive spectral surveys coveringthe entire sky. Major discrepancies include the spectroscopicclassification of B9.5, which may indicate an otherwise unrecognizedspectral peculiarity, a different A0/A1 spectral type boundary in thetwo samples involved, the well-known misclassification of weak heliumstars, and an appreciable percentage of stars which are called dwarfsspectroscopically but are of higher photometric luminosity. The spacemotion vectors of these stars for which radial velocities are available,and excluding the minimum of 25 percent that are spectroscopic binarieswithout orbital elements, show structure in their distribution in the(U, V)-plane, with members of the Local Association and the Hyades andSirius superclusters forming obvious concentrations. The members of theLocal Association in the samples are mainly old (more than 200 millionyears) mode A stars, although a few much younger stars are included. Themembers of the Hyades and Sirius superclusters contain many bluestragglers, including several peculiar stars of the Hg, Mn, and Sivarieties.
|A study of visual double stars with early type primaries. II - Photometric results|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983A&AS...51..161L&db_key=AST
|A study of visual double stars with early type primaries. I - Spectroscopic results|
Attention is given to spectral peculiarities found in data on thespectral classes of 486 stars in 254 visual doublet or multiplet systemswith O or B type primaries, in order to isolate a group of very youngstars that may serve for the study of early stellar evolutioncharacteristics. It is noted that the material contains a substantialfraction of secondaries that are likely to be physical, and that severalof these may be in the premain-sequence phase of stellar evolution, orhave reached the zero-age main sequence.
|A photoelectric investigation of light variability in AP stars|
A study of the light variability of a number of peculiar A stars, mainlyin Stromgren colors u and v and in peculiarity index Delta-a, leads tothe proposal of the following light variability periods: (1) HD 5601,1.11 days; (2) HD 19712, 2.19 days; (3) HD 30849, 15.86 days; (4) HD38823, 8.64 days; (5) HD 53116, 11.98 or 18.10 days; (6) HD 56022, 0.92days; and (7) HD 81009, 33.97 days. In addition, evidence is given forvariability of HD 94660 on a time scale on the order of months or years,and it is shown that the rotation period proposed by Borra andLandstreet (1980) for HD 25267 is not supported by the light variationsobserved. The character of Delta-a variability is discussed.
|Uvby-Beta Photometry of Equatorial and Southern Bright Stars - Part Two|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&AS...42..311H&db_key=AST
|Is star formation bimodal ? II. The nearest early-type stars.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..187E&db_key=AST
|Spectral classification from the ultraviolet line features of S2/68 spectra. II - Late B-type stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...30...71C&db_key=AST
|UVBY BET photometry of equatorial and southern bright stars.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...27...47H&db_key=AST
|Photometrie ubvy de quelques etoiles Ap.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976A&AS...25..143H&db_key=AST
|Ubvy photometry of some southern field stars.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&AS...22..323H&db_key=AST
|Four-colour and H-beta photometry for bright stars in the southern hemisphere.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..624C&db_key=AST
|Radial velocities of 200 southern B stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965MNRAS.130..281B&db_key=AST
|BVRI Photoelectric Photometry for 275 Stars located between -25° y -50° Fotometría Fotoeléctrica en BVRI para 275 estrellas comprendidas en su mayoría entre -25° y -50°|
BYRI photometry in Johnson's system was done for 275 stars the mayority ofwhich are comprised between -25° and -50°. Due to systematicvariations in V magnitude in R. A. of the order of 0.2 magnitude it wasdecided to use in the present work V magnitudes of the Catalogue of theRoyal Observatory, Cape of Good Hope, South Africa. The colours presentedhere, should permit to have an homogeneous R and I Systems of photometryfor both the Northern and Southern sky, complete to the fifth magnitude, anup to -50° in declination
|Photoelectric Observations of HH Pup|
|On the individual parallaxes of the brighter galactic helium stars in the southern hemisphere, together with considerations on the parallax of stars in general.|