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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).
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A comprehensive variability study of the enigmatic WN8 stars - Final results
As a conclusion of our all-sky variability survey of the 'enigmatic'variable WN8 stars, we have carried out coordinated multisitephotometric and spectroscopic observations of WN8 stars in 1989 and1994-1995. We confirm the leading role of the stellar core inrestructuring the whole wind. This emerges as a statistical trend: thehigher the level of the continuum (i.e., core) light variations, thehigher the variability of the P Cygni edges of the optical emissionlines. However, the form of the correlation between the light andprofile variations is generally different for each individual star. Thehigh level of activity of WN8 stars may be supported/induced bypulsational instability.
| The enigmatic WN8 stars: Intensive photometry of four southern stars on time scales from 30 min to 3 months
We present the first results of an extensive photometric study of themost intrinsically variable Wolf-Rayet (WR) stars: the WN8 subclass.Some 375 individual differential observations of WR16 and WR40 wereobtained over a contiguous interval of approximately 3 months in anarrow visual continuum bandpass. Over the same interval, we obtainedroughly 200 broadband V observations of the fainter WN8 stars WR66 andWR82. All four WN8 stars show significant random variability on timescales of hour to approximately a day -- probably related to thestochastic formation, propagation, and decay of emitting/scatteringinhomogeneities in the winds. Unlike for WR66 and WR82, the photometricbehavior of WR16 and WR40 is more deterministic with approximately twopossible periods in the range approximately 2-30 days -- possiblyrelated to some kind of Luminous Blue Variable (LBV), binary, orrotation phenomenon. In addition, WR82 shows a possible secular declineduring the 3 months and WR66 reveals a clear periodicity of 3.51 h. Thisshort period may be related to nonradial pulsations or a spiral-inbinary process invoking a low-mass, compact companion as seen in themassive x-ray binary Cyg X-3, a WN7 + c system of period 4.8 h.
| Longterm Photometry of Variables at ESO - Part Two - the Second Data Catalogue 1986-1990
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...79S&db_key=AST
| Photometric monitoring of O-type stars
A photometric survey of 16 bright O-type stars was conducted in order todetermine the incidence of low-order nonradial pulsation or othervariability among them. For each star, several observations wereobtained per night so that periodicities as short as one hour can bedetected. The results show that microvariability with a time-scale ofthe order of days is present in all the O supergiants and in somedwarfs. Except for Zeta Oph, no periodicity characteristic of nonradialpulsation could be found in any of the stars. However, high-order modeswould not have been detected. One O-type star is a previously unknowneclipsing binary. In the process of this study, two new B-type eclipsingbinaries were discovered.
| A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
| WR 22 is an Eclipsing Binary Star
Not Available
| Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
| 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.
| Analysis of the photometric variability of WR40
New photometric data on the star WR40 are presented and, together withdata already published, are analyzed in a detailed and homogeneousmanner in order to investigate the variability of the star. Goodevidence is presented for the existence of a periodicity P = 6.250 + or- 0.078 day with a semiamplitude of 0.010 mag in the Stromgren b filter.Only part of the 0.1 mag peak-to-peak variation of the star can beexplained in this way and other interesting features of the variabilityare outlined. The physical origin of the periodicity is discussed.
| Precision photometric monitoring of southern variable Wolf-Rayet stars with a comment on the overall continuum variability of WR stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987AJ.....94.1008L&db_key=AST
| A high precision photometric investigation of the micro-variations of Wolf-Rayet stars
VBLUW photometric observations of seven WR stars, obtained with standarddeviation less than about 0.002 mag using the 90-cm Dutch telescope atESO during March-April 1986, are reported. The observation anddata-reduction techniques are discussed, and the results are presentedin extensive tables and graphs and characterized in detail. Some of thelight and color variations are tentatively attributed totemperature-induced changes in the continuum emission (e.g., nonuniformillumination of the pseudophotosphere due to dynamical inhomogeneitiessuch as temporarily hotter eddies or blobs). Particular attention isgiven to the contrast between the strong W-band (323.6-nm) excesspresently observed in WR 6 (EZ CMa) and the FUV deficiency observed byvan der Hucht et al. in 1974-1976; an explanation based on increasedouter-envelope transparency is proposed.
| Polarization measurements of 313 nearby stars
The linear polarization of 313 low galactic latitude stars has beenmeasured. With few exceptions all program stars have a spectral typelater than B9 and are within 600 parsec of the sun. 181 stars aresituated at the southern sky and 132 at the northern sky.
| A sample of old-disk-population red giants.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88..426E&db_key=AST
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