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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
| Measuring magnetic fields of early-type stars with FORS1 at the VLT
This paper describes an experiment aimed at evaluating the capability ofthe FORS1 instrument at the VLT for measuring weak ( =~ 0.1%) Zeemancircular polarization signatures in stellar H Balmer lines. We haveobtained low-resolution polarized spectra at 3500-5800 Å of twobright A-type stars, HD 94660, and HD 96441. The former is a well knownmagnetic star, the latter an apparently non-magnetic, unpolarized starthat was observed for comparison purposes. In order to test thepossibility of performing multi-object spectropolarimetric measurements(e.g., for cluster studies), observations were taken both on-axis (i.e.,at the CCD field center) and off-axis (i.e., at the edges of the CCD).In HD 94660 (the magnetic star), we detected a clear signal of circularpolarization in all observed hydrogen Balmer lines (i.e., from Hβto the Balmer limit), with a typical peak-to-peak amplitude of about0.8%. From the analysis of Stokes V under the weak-field approximation,we have estimated a mean longitudinal field of -2085 +/- 85 G, a valuefully consistent with previous studies of this star. Notably, we foundthat at wavelengths shorter than about 4100 Å, the polarizationsignal detected off-axis is about 20-30% smaller than that detectedon-axis. No polarization due to the Zeeman effect was detected in thecomparison star HD 96441, and we estimate that the contribution due toinstrumental circular polarization is limited to the order of 0.01%.This experiment demonstrates the effectiveness of FORS1 at the VLT as atool for high-sensitivity diagnosis of the magnetic field in upper mainsequence stars, providing the potential for measuring fields in fainterand more rapidly rotating stars than has previously been possible. Basedon observations obtained at the VLT within the context of DDT266.D-5649.
| 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
| Detecting magnetic fields of upper-main-sequence stars with FORS1 at ANTU.
Not Available
| 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).
| 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
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Osservazione e dati astrometrici
| Costellazione: | Idra |
| Ascensione retta: | 11h06m38.70s |
| Declinazione: | -28°43'40.0" |
| Magnitudine apparente: | 6.77 |
| Distanza: | 197.628 parsec |
| Moto proprio RA: | -43.3 |
| Moto proprio Dec: | -29.7 |
| B-T magnitude: | 6.797 |
| V-T magnitude: | 6.749 |
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