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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
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| Search for reference A0 dwarf stars: Masses and luminosities revisited with HIPPARCOS parallaxes
Hipparcos data for 71 nearby dwarf A0 stars were combined with otherdata, in particular with high resolution spectra to establish the HRdiagram in this temperature range. Almost 30% of unknown binaries weredetected and discarded before establishing the cal M-L relation forbright A0 V field stars. The relationship derived for these single starsis compared to the classical diagram derived from eclipsing binaries.The scatter of the latter is examined and the role of gravity isdiscussed. A good agreement is found between the evolution-based surfacegravity log g_ev and the value of log g_ph obtained from photometricdata. Based on observations collected at the European SouthernObservatory (ESO), La Silla, Chile in the framework of the Key Programme5-004-43K and on data from the ESA Hipparcos astrometry satellite. TheTables 1-4 are also available electronically via anonymous ftp130.79.128.5 or via http://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
| A search for Beta Canis Majoris stars
The results of a search for southern Beta CMa stars are presented.Photoelectric photometry of thirty-one candidates shows that eight ofthese are previously unrecognized probable or certain Beta CMavariables. Four of these stars are members of the galactic cluster NGC3293. One Delta Sct variable and one eclipsing binary were discovered. Afew other stars are probably ellipsoidal variables.
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