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Evolution of magnetic fields in stars across the upper main sequence: I. Catalogue of magnetic field measurements with FORS 1 at the VLT
To properly understand the physics of Ap and Bp stars it is particularlyimportant to identify the origin of their magnetic fields. For that, anaccurate knowledge of the evolutionary state of stars that have ameasured magnetic field is an important diagnostic. Previous resultsbased on a small and possibly biased sample suggest that thedistribution of magnetic stars with mass below 3 M_ȯ in the H-Rdiagram differs from that of normal stars in the same mass range (Hubriget al. 2000). In contrast, higher mass magnetic Bp stars may well occupythe whole main-sequence width (Hubrig, Schöller & North 2005b).In order to rediscuss the evolutionary state of upper main sequencemagnetic stars, we define a larger and bias-free sample of Ap and Bpstars with accurate Hipparcos parallaxes and reliably determinedlongitudinal magnetic fields. We used FORS 1 at the VLT in itsspectropolarimetric mode to measure the magnetic field in chemicallypeculiar stars where it was unknown or poorly known as yet. In thisfirst paper we present our results of the mean longitudinal magneticfield measurements in 136 stars. Our sample consists of 105 Ap and Bpstars, two PGa stars, 17 HgMn stars, three normal stars, and nine SPBstars. A magnetic field was for the first time detected in 57 Ap and Bpstars, in four HgMn stars, one PGa star, one normal B-type star and fourSPB stars.
| Abundances of vanadium and bromine in 3 Centauri A. Additional odd-Z anomalies
We report abundance excesses of 1.2 and 2.6 dex, respectively, forvanadium and bromine in the hot, peculiar star 3 Cen A. Abundances forthese two odd-Z elements have not been previously reported for thisstar. Taken with previous work, they strengthen the case of the originof the abundance peculiarities by diffusion.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| Abundance anomalies in hot horizontal branch stars of the galactic globular cluster NGC 1904
We present abundance measurements, based on high-resolution opticalspectroscopic data obtained with the Ultraviolet and Visual EchelleSpectrograph mounted on Kueyen (Very Large Telescope UT2), for ten starsin the extended blue horizontal branch of the Galactic globular clusterNGC 1904 (M79). In agreement with previous findings for other clusters,we obtain normal abundances for stars cooler than T_eff 11 000 K,and largely anomalous abundances for hotter stars: large He depletions,and overabundances of Fe, Ti, Cr, P and Mn. The abundances of Mg, Si andCa are roughly normal, in the hot stars as well as in the cooler ones.This abundance pattern can be attributed to the onset of diffusion andto radiation pressure in the stable atmospheres of hot horizontal branchstars.
| Heavy Element Abundances in Late-B and Early-A Stars. I. Co-Added IUE Spectra of HgMn Stars
Very heavy elements (Pt, Au, Hg, Tl, and Bi) are found to be enhanced inthe atmospheres of the chemically peculiar stars of the upper mainsequence by up to a million times the solar system levels. Suchenhancements are believed to result from atmospheric dynamics (i.e.,diffusion) rather than scenarios that dredge up nuclear-processedmaterial to the surface or transfer processed material between binarycompanions. However, the theoretical framework needs to be furtherconstrained by observations beyond the realm of the spectral types forwhich such abundance enhancements are observed at optical wavelengths.The International Ultraviolet Explorer (IUE) satellite collected spectraof bright stars for which chemical peculiarities have been derived fromground-based data. For several elements the abundance enhancements haveonly been recently measured using Hubble Space Telescope data and havetherefore not yet been exploited in the IUE data. We have initiated aprogram to analyze IUE high-dispersion spectra to more fullycharacterize the pattern of very heavy element enhancement for manymercury-manganese (HgMn) stars and to potentially extend the spectralclass (effective temperature) boundaries over which these abundanceanomalies are known to exist. The abundances of very heavy elements inchemically normal B and A-type stars provide a base level that may becompared with the solar system abundances. These early spectral typestars may therefore reveal clues for galactic chemical evolution studiessince they were formed at a later epoch than the Sun in the history ofthe Galaxy. This first paper presents the motivation for the analyses tofollow, outlines our spectral co-addition technique for IUE spectra, anddiscusses the choice of model atmospheres and the synthetic spectrumprocedures, while initiating the study by highlighting the abundance ofgold in several HgMn stars.
| Emission lines in the optical spectrum of 3 Cen A
Previously, weak emission lines had been detected at red wavelengths inthe spectra of a limited sample of mid to late B type main sequencestars. A fuller description of the occurrence and origins of these lineshas yet to be forwarded, in part due to the lack of observationsdetailing the spectral transitions involved. To address this deficiency,we present a line list of weak emission features found in the opticaland near infrared spectral region of the chemically peculiar He-weakstar 3 Cen A (HD 120709). Nearly 350 features, mostly associated withallowed transitions from high-excitation states of first ions, arecatalogued along with identifications. Prominent among the emissionlines are the spectra P II, Mn II, Fe II, Ni II and Cu II. Emissionlines from Ca II, Si II and Hg II are also evident. Abundances aredetermined for several elements from synthetic spectrum fitting, withanomalies detected for the ions O I/II, P II/III and Si II/III. The LTEsynthetic spectrum fitting also revealed that the low excitation 4s-4ptransitions of Fe II predict an abundance that is greater than thatdetermined from higher excitation 4d-4f transitions. Several of theselatter transitions have upper energy levels that are found to beassociated with emission lines. We also present empirical considerationsfor the excitation processes leading to the weak emission lines.Based on observations obtained at the European Southern Observatory, LaSilla, Chile, No. 65.L-0316 and Paranal, Chile No. 266.D-5655.Tables 2 and 3 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/1073
| 3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp:cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/447
| 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
| Formation scenarios for the young stellar associations between galactic longitudes l = 280degr - 360degr
We investigate the spatial distribution, the space velocities and agedistribution of the pre-main sequence (PMS) stars belonging toOphiuchus, Lupus and Chamaeleon star-forming regions (SFRs), and of theyoung early-type star members of the Scorpius-Centaurus OB association.These young stellar associations extend over the galactic longituderange from 280degr to 360degr , and are at a distance interval ofaround 100 and 200 pc. This study is based on a compilation ofdistances, proper motions and radial velocities from the literature forthe kinematic properties, and of basic stellar data for the constructionof Hertzsprung-Russel diagrams. Although there was no well-known OBassociation in Chamaeleon, the distances and the proper motions of agroup of 21 B- and A-type stars, taken from the Hipparcos Catalogue,lead us to propose that they form a young association. We show that theyoung early-type stars of the OB associations and the PMS stars of theSFRs follow a similar spatial distribution, i.e., there is no separationbetween the low and the high-mass young stars. We find no difference inthe kinematics nor in the ages of these two populations studied.Considering not only the stars selected by kinematic criteria but thewhole sample of young early-type stars, the scattering of their propermotions is similar to that of the PMS stars and all the young starsexhibit a common direction of motion. The space velocities of theHipparcos PMS stars of each SFR are compatible with the mean values ofthe OB associations. The PMS stars in each SFR span a wide range of ages(from 1 to 20 Myr). The ages of the OB subgroups are 8-10 Myr for UpperScorpius (US), and 16-20 Myr for Upper Centaurus Lupus (UCL) and forLower Centaurus Crux (LCC). Thus, our results do not confirm that UCL isolder than the LCC association. Based on these results and theuncertainties associated with the age determination, we cannot say thatthere is indeed a difference in the age of the two populations. Weanalyze the different scenarios for the triggering of large-scalestar-formation that have been proposed up to now, and argue that mostprobably we are observing a spiral arm that passes close to the Sun. Thealignment of young stars and molecular clouds and the average velocityof the stars in the opposite direction to the Galactic rotation agreewith the expected behavior of star formation in nearby spiral arms.Tables 1 to 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/913
| On the elemental abundance and isotopic mixture of mercury in HgMn stars
Optical region spectra of 31 HgMn stars have been studied for theabundance and isotope mixture of mercury. In the course of theinvestigation the lines Hg I lambda 4358 and Hg Ii lambda lambda3984,6149 have been studied, with abundances established for all threelines in several HgMn stars. The mercury isotope mixture has beendetermined from high resolution spectra of the lambda 3984 line.Possible signs of an ionization anomaly have been detected by thecomparison of the abundance derived from the Hg I line and the Hg Iilines in seven of the observed HgMn stars. A possible correlation of themercury abundance with Teff has been detected. Possible signsof a weak anticorrelation of the manganese and mercury abundance in HgMnstars have been found, which could be interpreted as a sign ofinhomogeneous surface distribution of these elements. For a number ofthe HgMn stars in this study the mercury abundance and isotope mixtureare reported for the first time.
| On the relationship between the mercury-manganese stars and the metallic-lined stars
An HR diagram indicating the positions of the HgMn and the Am starsanalyzed by the senior author and his collaborators shows that thecoolest HgMn stars and the hottest Am stars are found on the samestellar evolutionary tracks and hence the former must evolve into thelater. The explanation of the dividing line between these two types ofnonmagnetic chemically peculiar stars where the Hg abundances suddenlychange their degree of overabundance is a major test of the theorieswhich try to explain the anomalous abundances of such stars. Some otherimportant relationships are found which can also serve as tests oftheories which purport to explain the properties of these stars.
| Quantitative Stellar Spectral Classification. II. Early Type Stars
The method developed by Stock & Stock (1999) for stars of spectraltypes A to K to derive absolute magnitudes and intrinsic colors from theequivalent widths of absorption lines in stellar spectra is extended toB-type stars. Spectra of this type of stars for which the Hipparcoscatalogue gives parallaxes with an error of less than 20% were observedwith the CIDA one-meter reflector equipped with a Richardsonspectrograph with a Thompson 576×384 CCD detector. The dispersionis 1.753 Å/pixel using a 600 lines/mm grating in the first order.In order to cover the spectral range 3850 Å to 5750 Å thegrating had to be used in two different positions, with an overlap inthe region from 4800 Å to 4900 Å . A total of 116 stars wasobserved, but not all with both grating positions. A total of 12measurable absorption lines were identified in the spectra and theirequivalent widths were measured. These were related to the absolutemagnitudes derived from the Hipparcos catalogue and to the intrinsiccolors (deduced from the MK spectral types) using linear and secondorder polynomials and two or three lines as independent variables. Thebest solutions were obtained with polynomials of three lines,reproducing the absolute magnitudes with an average residual of about0.40 magnitudes and the intrinsic colors with an average residual of0.016 magnitudes.
| The mass ratio distribution of B-type visual binaries in the Sco OB2 association
A sample of 115 B-type stars in the Sco OB2 association is examined forexistence of visual companions in the J and K_s bands, using the ADONISnear-infrared adaptive optics system and coronograph. Practically allthe components in the separation range 0farcs3 -6farcs4 (45-900 AU) andmagnitudes down to K = 16 were detected. The K and J - K photometry ofthe primaries and differential photometry and astrometry of the 96secondaries are presented. Ten secondaries are new physical components,as inferred from the photometric and statistical criteria, while therest of the newly detected objects are faint background stars. After asmall correction for detection incompleteness and a conversion of thefluxes into masses, an unbiased distribution of the components massratio q was derived. The power law f(q)~ q-0.5 fits theobservations well, whereas a q-1.8 distribution, whichcorresponds to a random pairing of stars, is rejected. The companionstar fraction is 0.20+/-0.04 per decade of separation which iscomparable to the highest measured binary fraction among low-mass PMSstars and ~ 1.6 times higher than the binary fraction of low-mass dwarfsin the solar neighborhood and in open clusters in the same separationrange. Based on observations collected at the European SouthernObservatory, La Silla, Chile (ESO programme 65.H-0179). Tables 1, 3 andthe full version of Table 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/382/92
| An Abundance Study in the Hg-Mn Star 46 Aquilae (HD 186122) with the SUBARU/HDS
A detailed abundance analysis has been carried out for the Hg-Mn star 46Aql using high-resolution spectra in the visual region (5100--6400Å) obtained with the High Dispersion Spectrograph of the SubaruTelescope. Our attention has been mainly focused on those elements whichhave not been analyzed previously. He, C, N, and O are underabundant,while Na shows the solar abundance. We have confirmed previouslyreported underabundances of Mg, Al, and Si, and have found anoverabundances of P (+1.5 dex) and Ti (+1.0 dex) and a significantunderabundance of S (-1.8 dex). Fe is overabundant by +0.8 +/- 0.1 dexand a microturbulent velocity of 0.3 km s-1 was found from ananalysis of the FeII lines. Among a few hundred unidentified absorptionlines, we identified lines of AsII and XeII and a very large (+4.0 dex)overabundance of Xe is obtained. We have confirmed emission lines ofMnII and TiII near 6100 Å, while those of CrII cannot have beenseen.
| The Origin of MN II Emission in the Spectra of Chemically Peculiar Stars
Emission from Mn II multiplet 13 (λλ6122-6132) in thespectrum of the 3He star 3 Centauri A and the hot, mild, HgMnstar 46 Aquilae can be naturally explained by interlocked non-LTEeffects. However, reproduction of the strength of the Mn II emission inboth stars requires vertical stratification of the manganese abundance,with manganese concentrated high in the photosphere (column mass<~10-2 g cm-2). If this formation picture iscorrect, several additional transitions of Mn II with λ>8000Å should also be present in emission in the spectrum of 3 Cen A.The wide range in the strength of Mn II multiplet 13 among uppermain-sequence stars (ranging from absorption to emission) is madepossible by the interplay in the non-LTE radiative transfer solution ofthe stellar Teff, manganese abundance, and manganesestratification profile. In particular, emission is strongly suppressedby a large manganese overabundance in the photosphere. This explains whythe hot, mild, HgMn star 46 Aql, which has only a modest manganeseenhancement, is detected in emission in Mn II multiplet 13 while otherHgMn stars of similar Teff but with large photosphericmanganese overabundances, such as κ Cancri, present Mn IImultiplet 13 in absorption.
| The interpretation of Mn II emission from late-type B stars
The photospheric Mn Ii emission lines Wahlgren & Hubrig(\cite{wh2000}) detect in the spectra of several late-type B and HgMnstars and attribute to fluorescent excitation are more naturallyexplained by interlocked non-LTE effects acting in a photosphere inwhich the manganese abundance is stratified with depth. The case isparticularly strong for HD 186122 (46 Aql) and HD 179761 both of whichrequire the manganese overabundance to be concentrated to column massesof log (m)< ~-1.5.
| 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
| Neon abundances in normal late-B and mercury-manganese stars
We make new non-local thermodynamic equilibrium calculations to deducethe abundances of neon from visible-region echelle spectra of selectedNei lines in seven normal stars and 20HgMn stars. We find that the beststrong blend-free Ne line that can be used at the lower end of theeffective temperature Teff range is λ6402, althoughseveral other potentially useful Nei lines are found in the red regionof the spectra of these stars. The mean neon abundance in the normalstars (logA=8.10) is in excellent agreement with the standard abundanceof neon (8.08). However, in HgMn stars neon is almost universallyunderabundant, ranging from marginal deficits of 0.1-0.3dex tounderabundances of an order of magnitude or more. In many cases, thelines are so weak that only upper limits can be established. The mostextreme example found is υ Her with an underabundance of at least1.5dex. These underabundances are qualitatively expected from radiativeacceleration calculations, which show that Ne has a very small radiativeacceleration in the photosphere, and that it is expected to undergogravitational settling if the mixing processes are sufficiently weak andthere is no strong stellar wind. According to theoretical predictions,the low Ne abundances place an important constraint on the intensity ofsuch stellar winds, which must be less than10-14Msolaryr-1 if they arenon-turbulent.
| The First 50 Years at Palomar, 1949-1999 Another View: Instruments, Spectroscopy and Spectrophotometry and the Infrared
We review the research on a wide variety of topics using data obtainedwith the 200-inch Hale telescope. Using state-of-the-art spectrographs,photometers, spectrometers and infrared detectors, the Palomarastronomers investigated the spectra of stars, interstellar matter, AGNsand quasars in great detail. Spectral resolutions ranged from 1000 A forbroad-band photometry to 0.04 A using interferometric techniques.
| Emission Lines in the Spectrum of the 3HE Star 3 Centauri A
Emission in the 4d-->4f transitions of Mn II (multiplet 13,λλ6122-6132), in the 4f-->6g transitions of P II, and inλ6149.5 of Hg II has been detected in the spectrum of thehelium-weak star 3 Centauri A (B5 III-IVp). Weaker emission from thesame Mn II multiplet is also seen in the hot, mild HgMn star 46 Aquilae(B9 III). It is suggested that the emission is of photospheric originand may be evidence for the stratification of manganese, phosphorus, andmercury in the photosphere of 3 Cen A and of manganese in 46 Aql.
| Moderate-Resolution Near-Infrared Spectroscopy of Cool Stars: A New K-Band Library
I present an atlas of near-infrared K-band spectra of 31 late-typegiants and supergiants and two carbon stars. The spectra were obtainedat resolving powers of 830 and 2000, and have a signal-to-noise ratio>~100. These data are complemented with results from similar existinglibraries in both K and H band, and they are used to identify varioustools useful for stellar population studies at moderate resolution. Ifocus on several of the most prominent absorption features and (1)investigate the effects of spectral resolution on measurements of theirequivalent width (EW), (2) examine the variations with stellarparameters of the EWs, and (3) construct composite indices as indicatorsof stellar parameters and of the contribution from excess continuumsources commonly found in star-forming and AGN galaxies. Among thefeatures considered, the 12CO (2,0) and 12CO (6,3)bandheads together with the Si I 1.59 μm feature, first proposed byOliva, Origlia, and coworkers, constitute the best diagnostic set forstellar spectral classification and for constraining the excesscontinuum emission. The Ca I 2.26 μm and Mg I 2.28 μm featuresoffer alternatives in the K band to the 12CO (6,3) bandheadand Si I feature.
| Emission lines in the spectra of late-B type stars
We report detections of weak emission lines in the red spectral regionof sharp-lined chemically normal and peculiar (HgMn) late-B type starsfrom high spectral resolution and high signal-to-noise data. Mostemission lines originate from high-excitation states of the ions Cr IIand Mn II, with others likely to be attributed to Ti II and Fe II. Theemission is observed to extend over the entire line profile width forrotational velocities up to 18 km s-1, implying that itoriginates within the same rotational framework as the absorption linespectrum. Within the sample no obvious correlation is noted for thepresence of emission with regard to stellar effective temperature orluminosity. A dependence upon element abundance is evident from theabsence of Mn II emission for HgMn stars for which the manganeseenhancement is greater than 1.3 dex. This trend is mildly reinforced bythe chromium emission spectrum being most developed amongst stars richerin chromium. We postulate that the Cr II and Mn II emissions in the redspectral region arise from a selective excitation process involvinghydrogen Lyalpha photon energies.
| Elemental abundance analyses with Complejo Astronomico El Leoncito REOSC echelle spectrograms. IV. Extensions of nine previous analyses
Using new CASLEO echelle spectrograms, we extended our elementalabundances of the sharp-lined Mercury-Manganese stars mu Lep, 14 Hya,kappa Cnc, HR 4487, HR 4817, 28 Her, and HR 7245, the closely relatedstar 3 Cen A, and 7 Sex an A0 V star with Population I abundances, butwith Population II star space motions. The lambda lambda 4500-6200region contains a sufficient number of lines to derive high-qualityabundances of these stars. For most stars, the new spectra provideadditional lines for the analyses which improve their quality as well ashelp fill in the periodic table. Table~5 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5)or via http://cdsweb.u-strabg.fr/Abstract.html}
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| The Scorpius OB2 Complex
The Sco OB2 complex is a member of the Local Association. Theassociation contains pre-main-sequence stars in addition to objects some3 x 10^7 yr old. If it is assumed that stars in wide binaries arecoeval, then the He-weak variables in the supercluster arepre-main-sequence, elevated above that sequence by an amount similar tothat of the 3 x 10^7 yr old, normal stars but contracting toward thesequence, not evolving from it. The apparent great depth of theassociation is probably a result of some foreground superclustermembers, superposed on Sco OB2, and a rift in the absorption cloudbetween Scorpius and Ophiuchus. The adjoining Chamaeleon complex alsoappears to be a member of the supercluster.
| 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
| Elemental abundance analyses with Complejo Astronomico EL Leoncito REOSC echelle spectrograms. III. HR 4487, 14 Hydrae, and 3 Centauri A
Using CASLEO echelle spectrograms, elemental abundances are derived forthe sharp-lined non-magnetic CP stars HR 4487, 14 Hya, and 3 Cen A. Thefirst two stars are members of the Mercury-Manganese subgroup and haveabundances which are similar to other such peculiar stars. The third isa hotter related star. The detection of Mn II lines in its spectrum addsto this relationship. Table 3 is avaible electronically vit the CDS viaanonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html.
| 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
| 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
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | קנטאור |
| התרוממות ימנית: | 13h51m49.60s |
| סירוב: | -32°59'40.0" |
| גודל גלוי: | 4.56 |
| מרחק: | 91.241 פארסק |
| תנועה נכונה: | -69.6 |
| תנועה נכונה: | -22.1 |
| B-T magnitude: | 4.342 |
| V-T magnitude: | 4.497 |
קטלוגים וכינוים:
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