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A Detailed Far-Ultraviolet Spectral Atlas of Main-Sequence B Stars
We have constructed a detailed spectral atlas covering the wavelengthregion 930-1225 Å for 10 sharp-lined B0-B9 stars near the mainsequence. Most of the spectra we assembled are from the archives of theFar Ultraviolet Spectroscopic Explorer satellite, but for nine stars,wavelength coverage above 1188 Å was taken from high-resolutionInternational Ultraviolet Explorer or echelle Hubble SpaceTelescope/Space Telescope Imaging Spectrograph spectra. To represent thetenth star at type B0.2 V, we used the Copernicus atlas of ? Sco. Wemade extensive line identifications in the region 949-1225 Å ofall atomic features having published oscillator strengths at types B0,B2, and B8. These are provided as a supplementary dataproduct—hence the term detailed atlas. Our list of found featurestotals 2288, 1612, and 2469 lines, respectively. We were able toidentify 92%, 98%, and 98% of these features with known atomictransitions with varying degrees of certainty in these spectra. Theremaining lines do not have published oscillator strengths. Photosphericlines account for 94%, 87%, and 91%, respectively, of all ouridentifications, with the remainder being due to interstellar (usuallymolecular H2) lines. We also discuss the numbers of lineswith respect to the distributions of various ions for these three moststudied spectral subtypes. A table is also given of 162 least blendedlines that can be used as possible diagnostics of physical conditions inB star atmospheres.
| The qWR star HD 45166. II. Fundamental stellar parameters and evidence of a latitude-dependent wind
Context: The enigmatic object HD 45166 is a qWR star in a binary systemwith an orbital period of 1.596 day, and presents a rich emission-linespectrum in addition to absorption lines from the companion star (B7 V).As the system inclination is very small (i=0.77° ±0.09°), HD 45166 is an ideal laboratory for wind-structure studies.Aims: The goal of the present paper is to determine thefundamental stellar and wind parameters of the qWR star. Methods:A radiative transfer model for the wind and photosphere of the qWR starwas calculated using the non-LTE code CMFGEN. The wind asymmetry wasalso analyzed using a recently-developed version of CMFGEN to computethe emerging spectrum in two-dimensional geometry. The temporal-variancespectrum (TVS) was calculated to study the line-profile variations. Results: Abundances and stellar and wind parameters of the qWR starwere obtained. The qWR star has an effective temperature of T_eff = 50000 ± 2000 K, a luminosity of log (L/ {L}?) =3.75 ± 0.08, and a corresponding photospheric radius of R_phot =1.00 {R}?. The star is helium-rich (N(H)/N(He) = 2.0),while the CNO abundances are anomalous when compared either to solarvalues, to planetary nebulae, or to WR stars. The mass-loss rate isdot{M}= 2.2 × 10-7 {M}?yr-1, and the wind terminal velocity isv?=425 km s-1. The comparison between theobserved line profiles and models computed under differentlatitude-dependent wind densities strongly suggests the presence of anoblate wind density enhancement, with a density contrast of at least 8:1from equator to pole. If a high velocity polar wind is present ( 1200 kms-1), the minimum density contrast is reduced to 4:1. Conclusions: The wind parameters determined are unusual when comparedto O-type stars or to typical WR stars. While for WR starsv?/v_esc > 1.5, in the case of HD 45166 it is muchsmaller (v?/v_esc = 0.32). In addition, the efficiencyof momentum transfer is ?=0.74, which is at least 4 times smallerthan in a typical WR. We find evidence for the presence of a windcompression zone, since the equatorial wind density is significantlyhigher than the polar wind. The TVS supports the presence of such alatitude-dependent wind and a variable absorption/scattering gas nearthe equator.Based on observations made with the 1.52 m ESO telescope at La Silla,Chile.Appendices A and B are only available in electronic form athttp://www.aanda.org
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars
The HR-diagram of about 1000 Bp - Ap stars in the solar neighbourhoodhas been constructed using astrometric data from Hipparcos satellite aswell as photometric and radial velocity data. The LM method\cite{luri95,luri96} allows the use of proper motion and radial velocitydata in addition to the trigonometric parallaxes to obtain luminositycalibrations and improved distances estimates. Six types of Bp - Apstars have been examined: He-rich, He-weak, HgMn, Si, Si+ and SrCrEu.Most Bp - Ap stars lie on the main sequence occupying the whole width ofit (about 2 mag), just like normal stars in the same range of spectraltypes. Their kinematic behaviour is typical of thin disk stars youngerthan about 1 Gyr. A few stars found to be high above the galactic planeor to have a high velocity are briefly discussed. Based on data from theESA Hipparcos astrometry satellite and photometric data collected in theGeneva system at ESO, La Silla (Chile) and at Jungfraujoch andGornergrat Observatories (Switzerland). Tables 3 and 4 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Radial velocities and axial rotation for a sample of chemically peculiar stars.
As part of a systematic project we have determined radial velocities andprojected rotational velocities for a sample of 186 chemically peculiarstars which have been observed by the Hipparcos' satellite. The purposeis to provide necessary data to study the space velocities of peculiarstars.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Mid-ultraviolet and optical photometry of helium stars
Mid-ultraviolet and optical photometric analysis of helium stars arepresented. A linear relation exists between the effective temperaturederived from model atmospheres and (1965-V)0 index. The effectivetemperatures derived from (1965-V)0 index are somewhat higher than thatof MK spectral type estimates especially for late B-type helium objects.
| Search for Beta Cephei stars south of declination -20 deg. I - Incidence of light variability among early B giants and subgiants: Summer objects
Not Available
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Membro dei seguenti gruppi:
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Osservazione e dati astrometrici
| Costellazione: | Carena |
| Ascensione retta: | 07h42m23.78s |
| Declinazione: | -56°08'45.7" |
| Magnitudine apparente: | 7.243 |
| Distanza: | 235.294 parsec |
| Moto proprio RA: | -12.9 |
| Moto proprio Dec: | 7.9 |
| B-T magnitude: | 7.156 |
| V-T magnitude: | 7.236 |
Cataloghi e designazioni:
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