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New runaway OB stars with HIPPARCOS
A Monte Carlo method for detection of runaway OB stars fromobservational data is proposed. 61 runaway OB star candidates have beendetected by an analysis of Hipparcos proper motions. The peculiartangential and total transverse velocities have been determined forthese stars. A list of the detected runaway star candidates ispresented. The evidence of a discrepancy between photometric andparallactic distances of runaway OB star candidates is presented.
| The spectroscopic signature of roAp stars
To reliably determine the spectroscopic signature of rapidly oscillatingchemically peculiar (roAp) stars it is also necessary to investigate asample of non pulsating chemically peculiar (noAp) as well as presumably``normal'' stars. We describe in this study the sample ofspectroscopically investigated stars and comment on the techniques usedfor the analysis. In particular we discuss ionization disequilibria ofrare earths in roAp stars that distinguish them from noAp stars. In thelight of the recently discovered pulsation of β CrB we seearguments that all magnetic CP2 stars up to a transition temperature ofabout 8100 K may be pulsating.Based on observations obtained at the European Southern Observatory (LaSilla, Chile), the Canadian-French-Hawaii telescope, the South AfricaAstronomical Observatory, The Crimean Astrophysical Observatory and onnumerous SIMBAD interrogations.
| Implementing TOPbase/Iron Project: continuous absorption from FeII
We discuss implementation of TOPbase and Iron Project opacities forstellar spectral codes. We use a technique employed by Peach, where aBoltzmann-averaged cross-section is calculated for selectedtemperatures, and the opacity obtained from double interpolation intemperature and wavelength. It is straightforward to include all levelsfor which cross-sections have been calculated. Boltzmann-averagedcross-sections for FeII show a local maximum between 1700 and 2000Å. We suggest this feature arises from 3d54snl->3d54pnl transitions within FeII. IUE spectra of iron-rich CPstars show local minima in this region. Theoretical calculations of arepresentative stellar continuum demonstrate that FeII photoionizationcontributes significantly to the observed minima.
| Vertical distribution of chromium in the atmospheres of HgMn stars
We use multiplet 30 Cr II lines in the wings of Hbeta totest the hypothesis of an anomalous concentration of Cr in the upperlayers of the atmospheres of a sample of 10 HgMn stars. These lines areat different distances from the H_beta line center and are thereforeformed at different depths in the stellar atmosphere. Except for HD49606, all HgMn stars show an increase in Cr abundance with height inthe stellar atmosphere. A similar vertical distribution of Cr, but lesspronounced, has been previously found in Am stars. In contrast, novariation of Cr abundance with the depth has been found for the normallate B-type star HD 196426 and the weak magnetic late B-type star HD168733. It is possible that in HgMn stars the vertical stratificationparameter, a, depends on T_eff, with the strongest vertical gradientbeing found in the hotter stars. No correlation was found between a andthe average stellar abundance log varepsilon (Cr/H).Based on observations obtained at the European Southern Observatory, LaSilla and Paranal, Chile (ESO programmes Nos. 62.L-0348, 65.I-0644,67.D-0579).
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| The magnetic B and A stars - their cause and cure
Not Available
| On the behavior of the Cii 4267.261, 6578.052 and 6582.882 Å lines in chemically peculiar and standard stars
With the aim of investigating the possible particular behavior of carbonin a sample of chemically peculiar stars of the main sequence withoutturning to modeling, we performed spectroscopic observations of threeimportant and usually prominent single ionized carbon lines: 4267.261,6578.052 and 6582.882 Å. In addition, we observed a large numberof standard stars in order to define a kind of normality strip, usefulfor comparing the observed trend for the peculiar stars. We paidparticular attention to the problem of the determination of fundamentalatmospheric parameters, especially for the chemically peculiar stars forwhich the abundance anomalies change the flux distribution in such a waythat the classical photometric methods to infer effective temperaturesand gravities parameter cannot be applied. Regarding CP stars, we founda normal carbon abundance in Hg-Mn, Si (with some exceptions) and Hestrong stars. He weak stars are normal too, but with a large spread outof the data around the mean value. A more complicated behavior has beennoted in the group of SrCrEu stars: four out of seven show a strongoverabundance, being the others normal.
| Measurement of lifetimes by laser-induced fluorescence and determination of transition probabilities of astrophysical interest in Nd III
Selective lifetime measurements by time-resolved laser-inducedfluorescence spectroscopy for 5 levels belonging to the 4f35dconfiguration of doubly ionized neodymium provide a first and usefulexperimental test of the relativistic Hartree-Fock calculations in thision of astrophysical interest. As a consequence, the accuracy of thetransition probabilities deduced in the present work is well assessed.These new data are expected to help astrophysicists in the future torefine the analysis of the composition of chemically peculiar starswhich frequently show large overabundances of lanthanides when comparedto the solar system standards.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Ab initio calculations of oscillator strengths and Landé factors for Nd Iii
Theoretical calculations of oscillator strengths and Landég-factors made with the Cowan code are presented for the rare-earth ionNd Iii. The emphasis is on transitions in the optical region of thespectrum. Comparisons of previous ab initio calculations of this typefor other lanthanides (e.g., La Ii, Ce Iii, and Lu Ii) with publishedexperimental and theoretical data suggest that the accuracy of thelog(gf) values for individual transitions should be about +/-0.15 dex inthe absence of significant core polarization effects; the g-factorsshould be good to better than 5%, except in a few cases where termmixing is important. Applications of the data are made in thecalculation of neodymium abundances in the atmospheres of the chemicallypeculiar stars HD 101065 (``Przybylski's star") andHD 122970.
| Do the physical properties of Ap binaries depend on their orbital elements?
We reveal sufficient evidence that the physical characteristics of Apstars are related to binarity. The Ap star peculiarity [represented bythe Δ(V1-G) value and magnetic field strength] diminishes witheccentricity, and it may also increase with orbital period(Porb). This pattern, however, does not hold for largeorbital periods. A striking gap that occurs in the orbital perioddistribution of Ap binaries at 160-600d might well mark a discontinuityin the above-mentioned behaviour. There is also an interestingindication that the Ap star eccentricities are relatively lower thanthose of corresponding B9-A2 normal binaries for Porb>10d.All this gives serious support to the pioneering idea of Abt &Snowden concerning a possible interplay between the magnetism of Apstars and their binarity. Nevertheless, we argue instead in favour ofanother mechanism, namely that it is binarity that affects magnetism andnot the opposite, and suggest the presence of a newmagnetohydrodynamical mechanism induced by the stellar companion andstretching to surprisingly large Porb.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| The electron-impact broadening effect in CP stars: the case of La II , La II i, EU II , and EU II i lines
The electron-impact widths and shifts for six Eu ii lines and widths forthree La ii , and six La ii i multiplets have been calculated by usingthe modified semiempirical method. Estimation for Stark widths of664.506 nm (Eu ii ) and 666.634 nm (Eu ii i) lines are given as well.The influence of the electron-impact mechanism on line shapes andequivalent widths in hot star atmospheres has been considered.
| On the near infrared variability of chemically peculiar stars
Some CP stars have recently been discovered by Catalano et al. to bevariable also in the near infrared, although with smaller amplitudesthan in the visible. Hence an observational campaign was started inwhich the infrared light variability of a number of CP2 and CP4 starshas been investigated at the ESO-La Silla Observatory in the bands J, H,and K. As a general result, infrared variations show the same behaviorin all three filters but amplitudes are smaller than in the visible.
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The observed periods of AP and BP stars
A catalogue of all the periods up to now proposed for the variations ofCP2, CP3, and CP4 stars is presented. The main identifiers (HD and HR),the proper name, the variable-star name, and the spectral type andpeculiarity are given for each star as far as the coordinates at 2000.0and the visual magnitude. The nature of the observed variations (light,spectrum, magnetic field, etc.) is presented in a codified way. Thecatalogue is arranged in three tables: the bulk of the data, i.e. thosereferring to CP2, CP3, and CP4 stars, are given in Table 1, while thedata concerning He-strong stars are given in Table 2 and those foreclipsing or ellipsoidal variables are collected in Table 3. Notes arealso provided at the end of each table, mainly about duplicities. Thecatalogue contains data on 364 CP stars and is updated to 1996, October31. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
| Spectropolarimetry of magnetic stars. VI. Longitudinal field, crossover and quadratic field: New measurements
New determinations of the mean longitudinal magnetic field, of thecrossover, and of the mean quadratic magnetic field of Ap stars arepresented. They are based on spectra recorded simultaneously in bothcircular polarizations at ESO with the CASPEC spectrograph fed by the3.6 m telescope. This paper discusses 95 observations of 44 stars. Amajor result of this study is the discovery that HD 137509 has apredominantly quadrupolar magnetic field, a strucuture previously foundin only a couple of stars. Improvement or revision of the determinationof the rotation period has been achieved for 3 stars. The stars studiedin this work include 14 rapidly oscillating Ap stars (for 6 of which noprevious attempt to detect a magnetic field had ever been made) and 21Ap stars with spectral lines resolved into their magnetically splitcomponents when observed at high enough dispersion in unpolarized light(for 9 of these stars, no determination of the longitudinal field hadbeen performed before). The observations discussed in this paper havebeen performed between 1989 and 1994, a period during which CASPEC andits Zeeman analyzer have progressively undergone various configurationchanges. The results reported here demonstrate that the polarimetricperformance of the instrument has remained unaltered through thesemodifications. Thanks to the latter, the achieved resolving power wasincreased, which resulted in improved magnetic measurement accuracies.Based on observations collected at the European Southern Observatory (LaSilla, Chile; ESO programmes Nos. 47.7-045 and 49.7-029).
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Far-Ultraviolet Stellar Photometry: Fields Centered on rho Ophiuchi and the Galactic Center
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..104..101S&db_key=AST
| The Lambda 6708 Feature in AP Stars
Not Available
| 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
| Magnetic moments and angular momenta of stars and planets
Using published data on magnetic fields, radii, masses, and rotation, wehave compiled a data set of magnetic moments mu and angular momenta Lfor stars and planets. In our subsample of hotter stars (classes A, B,and O), there are 171 objects. In the subsample of cooler stars (classesF, G, K, and M), there are 54 objects. We include 33 white dwarfs, ofwhich 19 are in cataclysmic variables. The pulsar subsample contains 32pulsars in binaries and 429 isolated pulsars. Som subsamples exhibitsignificant empirical correlations between log mu and log L. For the hotand cool stars, the correlations are positive. However, the hot-starcorrelation is significantly shallower than for the cool stars. In thesolar system subsample, the correlation has essentially the same slopeas for the cool stars, although the magnetic moments are two to threeorders of magnitude smaller for the solar system objects at a given Lvalue. For isolated white dwarfs, the correlations are weak or absent.Pulsars and white dwarfs in close binaries show strong negativecorrelations: the results are quantitatively consistent withmagnetically enforced synchronism with the orbital period. When weconsider the centers of gravity of the different subsamples of objects,a significant positive correlation appears between log mu and log L.
| 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.
| Spectropolarimetry of magnetic stars. V. The mean quadratic magnetic field.
Systematic determinations of the mean quadratic magnetic field of Apstars have been performed for the first time. The mean quadraticmagnetic field (or, in short, the quadratic field) is the square root ofthe sum of the mean square magnetic field modulus and of the mean squarelongitudinal magnetic field. The latter are averages over the visiblestellar disk of the square of, respectively, the modulus of the magneticfield and its component along the line of sight. These averages areweighted by the local emergent line intensities. The quadratic field isdiagnosed from the study of the magnetic broadening of the stellarspectral lines as observed in unpolarized light, through thecharacterization of the widths of the lines by the second-order momentsof their profiles (in the Stokes parameter I) about their centre. Thetheoretical basis of the interpretation of these moments in terms ofmagnetic field and the strategy followed in the analysis are presented.It is shown that this analysis yields, as a by-product, the projectedequatorial velocity v_e_sini of the studied stars. Observations of asample of 29 stars are analyzed. For 22 of them, meaningful values orupper limits of the quadratic field can be determined. The lower limitof detection of the quadratic fields, set by the spectral resolution ofthe observations, is of the order of 5 kG. The observed quadratic fieldsrange from this value up to 37 kG, in the star HD 137509. The magneticfield of this star is likely the second strongest known field in Apstars. Quadratic field values derived for stars where resolvedmagnetically split lines are observed in higher-dispersion spectra areconsistent with the values of the mean field modulus measured in thosestars from the line splitting. For the stars of the sample repeatedlyobserved through their rotation cycle, the variations of the quadraticfield are well represented by a cosine with the rotation frequency ofthe star, or by the superposition of such a cosine and of a cosine withtwice that frequency. However, it appears that it is essential to have alarge number of observations distributed sufficiently uniformly andsufficiently densely over the rotation phases to determine unambiguouslythe shape of the variations. The extrema of the quadratic field tend tooccur at phases close to those of the extrema of the longitudinal field,but in some stars, the two quantities definitely vary out of phase. Theratio between the maximum and the minimum of the quadratic field isalways smaller than 1.7.
| Spectropolarimetry of magnetic stars. IV. The crossover effect.
This paper is devoted to the study of the crossover effect in magneticAp stars. It is shown that this effect can be measured by the secondorder moment about their centre of the profiles of spectral linesrecorded in the Stokes parameter V. The interpretation of thesemeasurements in terms of magnetic field is developed. It is shown thatone can derive from them a quantity called the mean asymmetry of thelongitudinal magnetic field, which is the first moment of the componentof the magnetic field along the line of sight, about the plane definedby the line of sight and the stellar rotation axis. The consistency ofthe determination of this quantity with that of the mean longitudinalmagnetic field from measurements of wavelength shifts of lines betweenright and left circular polarization is demonstrated. This technique ofanalysis is applied to observations of a sample of 29 stars, among which10 have a detectable crossover effect. For 8 of them, the availableobservational data allow the study of the variations of the asymmetry ofthe longitudinal field with rotation phase. In most cases, thisvariation is sinusoidal and essentially symmetric about 0, and it occursin quadrature with the variation of the mean longitudinal field. A morecomplex behaviour is definitely observed in HD 147010 and HD 175362,where the variation of the asymmetry of the longitudinal field is betterrepresented by the superposition of two sinusoids, one with the rotationfrequency of the star, and the other with twice that frequency.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Some problems of non-reversive CP stars. I. Spatial distribution.
Not Available
| Spectropolarimetry of magnetic stars. III. Measurement uncertainties.
The estimation of the uncertainties affecting the determination ofvarious parameters characterizing spectral line profiles recorded inStokes I and V that are used in the diagnosis of stellar magnetic fieldsthrough the moment technique is described. Simple statisticalconsiderations are presented, to demonstrate that the errors areproperly assessed and to illustrate how their evaluation can beexploited to derive information about the physical properties of thestudied stars. It is shown that taking these uncertainties properly intoaccount allows one to achieve better determination of the meanlongitudinal magnetic field. Improved values of the latter are derivedfor observations already analysed in earlier work. The approach sketchedin this paper is intended as a basis for future studies of magneticfields of Ap stars.
| Photometric variations of AP stars
The photometric variations of seven Ap stars have been analyzed fromobservations mainly obtained in the framework of the Long-TermPhotometry of Variables project at European Southern Observatory (ESO).New values for the periods and detailed light curves in the uvby systemare provided. Alpha Scl is shown to display anomalous variations thatset it apart from the other stars.
| 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
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Dades d'Observació i Astrometria
| Constel·lació: | Sagittarius |
| Ascensió Recta: | 18h22m53.10s |
| Declinació: | -36°40'10.0" |
| Magnitud Aparent: | 5.34 |
| Distancia: | 189.753 parsecs |
| Moviment propi RA: | -2.3 |
| Moviment propi Dec: | -25.3 |
| B-T magnitude: | 5.173 |
| V-T magnitude: | 5.31 |
Catàlegs i designacions:
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