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Elemental abundance analyses with DAO spectrograms. XXIX. The mercury-manganese stars 53 Tau, β Tau, γ Crv, and υ Her
We performed elemental abundances analyses of the mercury-manganese(HgMn) stars 53 Tau, β Tau, and γ Crv consistent withprevious studies of similar stars in this series. The derived v sin ivalues for the last two stars are 59 and 32 km s-1,respectively, both of which are greater than those of HgMn starspreviously studied. For 53 Tau this analysis using selected wavelengthregions replaces one performed with coadded photographic spectra. Astricter upper limit is placed on any Hg II λ3984 line. Theabundances of β Tau are usually greater than those of γ Crv.But the later star has a Hg II λ3984 line which the former lacks.Our analysis of υ Her, which was performed with spectrogramsobtained with CCD detectors, is extended by using additionalspectrograms to increase the range of wavelengths covered longward ofλ4800. Minor changes in the derived abundances result.
| 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
| STELIB: A library of stellar spectra at R ~ 2000
We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃsica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433
| 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.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| 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
| A highly sensitive search for magnetic fields in B, A and F stars
Circular spectropolarimetric observations of 74 stars were obtained inan attempt to detect magnetic fields via the longitudinal Zeeman effectin their spectral lines. The sample observed includes 22 normal B, A andF stars, four emission-line B and A stars, 25 Am stars, 10 HgMn stars,two lambda Boo stars and 11 magnetic Ap stars. Using the Least-SquaresDeconvolution multi-line analysis approach (Donati et al.\cite{donati97etal}), high precision Stokes I and V mean signatures wereextracted from each spectrum. We find absolutely no evidence formagnetic fields in the normal, Am and HgMn stars, with upper limits onlongitudinal field measurements usually considerably smaller than anypreviously obtained for these objects. We conclude that if any magneticfields exist in the photospheres of these stars, these fields are notordered as in the magnetic Ap stars, nor do they resemble the fields ofactive late-type stars. We also detect for the first time a field in theA2pSr star HD 108945 and make new precise measurements of longitudinalfields in five previously known magnetic Ap stars, but do not detectfields in five other stars classified as Ap SrCrEu. We also report newresults for several binary systems, including a new vsin i for therapidly rotating secondary of the Am-delta Del SB2 HD 110951. Based onobservations obtained using the MuSiCoS spectropolarimeter on theBernard Lyot telescope, l'Observatoire du Pic du Midi, France.
| The presence of Nd and Pr in HgMn stars
Optical region spectra for a number of upper main sequence chemicallypeculiar (CP) stars have been observed to study singly and doublyionized praseodymium and neodymium lines. In order to improve existingatomic data of these elements, laboratory measurements have been carriedout with the Lund VUV Fourier Transform Spectrometer (FTS). From thesemeasurements wavelengths and hyperfine structure (hfs) have been studiedfor selected Pr Ii, Pr Iii and Nd Iii lines of astrophysical interest.Radiative lifetimes for some excited states of Pr Ii have beendetermined with the aid of laser spectroscopy at the Lund Laser Center(LLC) and have been combined with branching fractions measured in thelaboratory to calculate gf values for some of the stronger optical linesof Pr Ii. With the aid of the derived gf values and laboratorymeasurements of the hfs, a praseodymium abundance was derived fromselected Pr Ii lines in the spectrum of the Am star 32 Aqr. Thisabundance was used to derive astrophysical gf values for selected Pr Iiilines in 32 Aqr, and these gf values were used to get a praseodymiumabundance for the HgMn star HR 7775. The praseodymium abundance in HR7775 was then utilized to derive astrophysical gf values for allobservable Pr Iii lines in this star. The neodymium abundance, derivedfrom unblended lines of Nd Ii in HR 7775, has been utilized to establishastrophysical gf values for observed Nd Iii lines in the optical regionof this star. Selected Pr Iii and Nd Iii lines have been identified andstudied in a number of HgMn stars and three hot Am stars. Thepraseodymium and neodymium abundance change rapidly from an approximate1-1.2 dex enhancement for the hot Am stars to 1.5-3 dex enhancement forthe cool HgMn stars, indicating a well-defined boundary between the hotAm and HgMn stars in the vicinity of 10 500 K. The enhancement ofpraseodymium and neodymium in Am and HgMn stars may be explained bydiffusive processes active in the stellar atmosphere, while the observeddiscontinuity might be explained by a thin hydrogen convection zonethought to be present for the Am stars, but absent in the HgMn stars.The absence of a convection zone would cause the diffused elements togather higher in the atmosphere of HgMn stars compared to Am stars, andexplain the observed increase in abundance.
| Photometric Monitoring of Bright Be Stars. IV. 1996-1999
We report long-term UBV observations of 15 bright, active Be stars,namely: X Persei, EW Canis Majoris, θ Coronae Borealis, 4 (V839)Herculis, 88 (V744) Herculis, 66 (V2048) Ophiuchi, NW Serpentis, CXDraconis, 12 (V395) Vulpeculae, 28 (V1624) Cygni, QR Vulpeculae, 59(V832) Cygni, EW Lacertae, ο Andromedae, and KX Andromedae. Theobservations were made in 1996-1999 through the Automatic PhotometricTelescope Service in Arizona and through the American Association ofVariable Star Observers (AAVSO) photoelectric photometry program andhave been added to a database extending back 20 years. We describe thestars' recent behavior and also comment on the long-term behavior ofsome of them. They vary photometrically on timescales ranging from abouta day to many years.
| The Coudé Echelle Spectrograph for the Xinglong 2.16 Telescope
A brief description of the NAO coudé echelle spectrograph mountedon the 2.16 m telescope at Xinglong station is given. This echellespectrograph is located at the coudé focus with a prism crossdisperser. The echelle image covers the spectral region from 330 to 1100nm displayed in 80 spectral orders in one exposure through two lightbeams. With a slit height of 2 mm, spectral orders are separated by 15to 23 pixels in blue region and by 7 to 19 pixels in red region.Alternatively, two additional resolution modes corresponding todifferent focal length cameras with resolving power R =16 000, 170 000in the blue beam and R = 13 000, 170 000 in the red beam could beprovided by this spectrograph. The bias, dark, wavelength calibration,flat field and science exposure are described in details. The limitingmagnitude for 1 hour exposure with an S/N ratio of 100 scales to V = 9.5in the red path and to V = 7.2 in the blue path.
| A Complete Survey of Case A Binary Evolution with Comparison to Observed Algol-type Systems
We undertake a comparison of observed Algol-type binaries with a libraryof computed Case A binary evolution tracks. The library consists of 5500binary tracks with various values of initial primary massM10, mass ratio q0, and period P0,designed to sample the phase-space of Case A binaries in the range-0.10<=logM10<=1.7. Each binary is evolved using astandard code with the assumption that both total mass and orbitalangular momentum are conserved. This code follows the evolution of bothstars to the point where contact or reverse mass transfer occurs. Theresulting binary tracks show a rich variety of behavior that we sortinto several subclasses of case A and case B. We present the results ofthis classification, the final mass ratio, and the fraction of timespent in Roche Lobe overflow for each binary system. The conservativeassumption under which we created this library is expected to hold for abroad range of binaries, where both components have spectra in the rangeG0 to B1 and luminosity classes III to V. We gather a list of relativelywell-determined, observed hot Algol-type binaries meeting thiscriterion, as well as a list of cooler Algol-type binaries, for which weexpect significant dynamo-driven mass loss and angular momentum loss. Wefit each observed binary to our library of tracks using aχ2-minimizing procedure. We find that the hot Algolsdisplay overall acceptable χ2, confirming theconservative assumption, while the cool Algols show much less acceptableχ2, suggesting the need for more free parameters, such asmass and angular momentum loss.
| Elemental abundance analyses with DAO spectrograms. XXV. The superficially normal B and A stars alpha Draconis, tau Herculis, gamma Lyrae, and HR 7926
Elemental abundances analyses of the superfically normal B and A starsalpha Dra (A0 III), tau Her (B5 IV), gamma Lyr (B9 III), and HR 7926 (B8II-III) are performed consistent with previous studies of this seriesusing spectrograms obtained with Reticon and CCD detectors. Comparisonsof the first two analyses with those of the same stars performed earlierin this series which used mostly coadded photographic plates show thegeneral consistency of the derived elemental abundances. A slightincrease in the adopted effective temperature produces a correspondingincrease in the derived abundances. In these stars the He/H ratios arefound to be close to solar. Except for gamma Lyr the metals show for themost part marginally subsolar abundance values. But this star has Al,Ca, Sc, and Sr abundances that are substantially underabundant as wellas other underabundant values. 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-strasbg.fr/cgi-bin/qcat?J/A+A/371/1078
| Elemental abundance analyses with DAO spectrograms. XXIV. The Mercury Manganese stars upsilon Her, phi Her, and HR 7018
Elemental abundances analyses are performed for the Mercury-Manganesestars upsilon Her, phi Her, and HR 7018 consistent with previous studiesof this series using spectrograms obtained with Reticon and CCDdetectors. Comparisons of the first two analyses with those performedusing coadded photographic plates show the general consistency of thederived elemental abundances. For upsilon Her and for phi Her,abundances were newly found for O, and for Al, V, Zn, and Ce,respectively. HR 7018 is discovered to be a single-lined spectroscopicbinary. Its Sc abundance is the smallest of any class member withderived abundances and its Sr abundance the largest of any known HgMnstar. A correlation analysis of the most complete abundance sets for 20HgMn stars shows that the abundances of some elements are correlatedwith one another and some are functions of the stellar effectivetemperature. Table 6 is 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/367/597
| 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
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| 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 Normal Energy Distributions in Stellar Spectra: Giants and Supergiants
We have derived the normal spectral energy distributions for thoseearly-type subgiants, giants, and supergiants that were not investigatedin our earlier studies, which were in most cases also not included inthe studies of Sviderskiene. Color indices computed using our normalenergy distributions are in good agreement with normal colors derivedfrom observations in the Vilnius photometric system. The reliability ofour distribution curves is also demonstrated by comparisons of observedand computed (W-B)-(B-V) two-color diagrams in the WBVR system. Normalcolor indices for the photometric WBVR system are derived.
| On the effective temperatures, surface gravities, and optical region fluxes of the CP stars
We determined effective temperatures and surface gravities for 17magnetic Chemically Peculiar (mCP) stars by comparing optical regionspectrophotometry and Hγ profiles with the predictions of ATLAS9model atmospheres. Although solar composition models can fit the energydistributions of the normal and many Mercury-Manganese stars, theycannot match the optical energy distributions of the mCP stars,especially the lambda 5200 broad, continuum regions. The role ofmetallicity and microturbulence to provide appropriate energydistributions which fit those observed for the mCP stars isinvestigated. Using metal-rich models with the opacity distributionfunctions for microturbulent velocities of 4 and 8 km s-1,their lambda 5200 broad, continuum features are often fit as part ofthis process. For some stars it is impossible to fit simultaneously boththis feature and the line blanketing in the Hγ region. Thissuggests that this continuum feature is produced by elements other thanthose which contribute most of the general line blanketing. A systematicdifference in the temperatures found by the photometric andspectrophotometric approaches is discovered for the hotter mCP stars. Aninvestigation of 10 Mercury-Manganese stars shows a similar effect. Thismay be due to the photospheric compositions becoming less solar withincreasing temperature.
| Oxygen 6156-8 Angstroms Triplet in Chemically Peculiar Stars of the Upper Main Sequence: Do HgMn Stars Show an Oxygen Anomaly?
An extensive spectrum-fitting analysis in the lambda ~ 6150 Angstromsregion was performed for forty late-B and A chemically peculiar (HgMn,Ap, Am, weak-lined) and normal stars of the upper main sequence, inorder to quantitatively establish the abundance of oxygen from the O I6156-8 triplet and to study its behavior/anomaly for each peculiaritygroup, where special attention was paid to HgMn-type stars. Magnetic Apvariables (Si or SrCrEu type) generally show a remarkably large oxygendepletion (by ~ -1.6 dex to ~ -0.4 dex relative to the solar abundance),and classical Am stars also show a clear underabundance (by ~ -0.6 dexon the average). In contrast, the oxygen abundance in HgMn stars,exhibiting only a mild deficiency relative to the Sun typically by ~0.3-0.4 dex, is not markedly different from the tendency of normalstars, also showing a subsolar abundance ([O/H] =~ -0.2). In view of therecent observational implication that the present solar oxygen abundanceis enriched by ~ 0.2-0.3 dex relative to the interstellar gas (fromwhich young stars are formed), and thus unsuitable for the comparisonstandard, we concluded that the extent of the average O-deficiency inHgMn stars is appreciably reduced down to only ~ 0.1-0.2 dex (i.e., notmuch different from the initial composition), which contrasts with theirwell-known drastically large N-depletion. Yet, as can be seen from thedelicate and tight O vs. Fe anticorrelation, this marginal deficiencyshould be real, and thus some physical process simultaneously producingO-depletion/Fe-enrichment must have actually worked in the atmosphere ofHgMn stars.
| Manganese abundances in mercury-manganese stars
We use exact curve-of-growth analysis and spectral synthesis to deducethe abundance of Mn from high signal-to-noise ratio visible-regionechelle spectra of selected Mn i and MnII lines in 24 HgMn stars. Theresults are compared with the Mn abundances derived from UV resonancelines by Smith & Dworetsky. We find excellent agreement for severalunblended Mn lines and confirm the temperature dependence of the Mnabundance found by Smith & Dworetsky. The MnII lines at lambdalambda 4206 and 4326 are much stronger than one would predict from themean Mn abundances. The lack of agreement is greatest for stars with thestrongest MnII lines. Using ad hoc multicomponent fits to the profilesof sharp-lined stars, we show that most of the discrepancies can beexplained by hyperfine structure that desaturates the lines, with fullwidths of the order of 0.06-0.09 A.
| Differential UBV photometry of two CP3 stars: 11 Her and 6 Her
Differential UBV photometry of two CP3 stars 11 Her and 6 Her ispresented. The effort is focused on 7832 period reported by Rakosch andFiedler (1978) for 11 Her. However, the observations from the seasonJanuary 1991 - September 1993 can not confirm suggested period.Moreover, 6 Her seems to be constant within 0.01 mag. as well.
| Abundances of the Elements in Sharp-lined Early-Type Stars from IUE High-Dispersion Spectrograms. II. The Nitrogen Deficiency in Mercury-Manganese Stars
We determine nitrogen abundances from co-added IUE high-dispersion SWPspectrograms of four HgMn stars and five normal or superficially normalmain-sequence B and A stars. We find N deficiencies in the HgMn starsgreater than previously reported (depletion factors of 135-400 relativeto the Sun). N abundance discrepancies from UV and IR studies of normalstars are discussed in light of possible non-LTE effects. Our data setfor our sample of HgMn stars (observed with a consistent strategy tomaximize the benefits of co-additions) is an improvement over the singleor few images previously used to derive N abundances for most of thesestars.
| Mercury Elemental and Isotopic Abundances in Mercury-Manganese Stars
Hg II abundances have been determined for 42 mercury-manganese (HgMn)stars by fitting synthetic spectra to observed spectra of the 3984Å Hg II line. Twenty of the stars had lines sharp enough to allowtheir Hg isotopic abundance mixes to be estimated. The Hg abundance isreported for more HgMn stars here than in any other single work. Nocorrelation was found between Hg II abundance and T_eff or the meancentral wavelength of HgMn lambda3984 stars. The mean central wavelengthof lambda3984 , an indicator of the Hg isotopic mix, is looselycorrelated with T_eff: stars with primarily heavy Hg isotopes tend to becooler, although one star, 46 Aql, has almost pure ^204Hg and T_eff inabout the middle of the temperature range for HgMn stars. We find thatthere is no evidence that any of the HgMn stars have ^196Hg or ^198Hg.For the very sharp-lined stars, the ^204Hg abundance decreases withincreasing T_eff. No correlation is seen between the mean centralwavelength and the surface gravity. No correlation was found between theprojected rotational velocity and the Hg II abundance or the centralwavelength of lambda3984, although this result may be biased by theselection of stars with low reported vsini. Hg I lambda4358 was measuredat high spectral resolution for seven HgMn stars. The isotopic shiftsare too small, and the hyperfine components are too weak to allowunambiguous isotopic abundance ratios to be found. Hg I abundancescorrelate fairly well with Hg II abundances. Some of the Hg isotopicmixtures are difficult to explain using only diffusion. HR 7245 hasapproximately equal abundances of ^199Hg, ^200Hg, ^202Hg, and ^204Hg butvery little ^201Hg, and 11 Per has Hg that is mostly ^199Hg and ^204Hg.Calculations show that hyperfine splitting of ^201Hg changes theradiative forces it feels compared with other isotopes, which may alterdiffusion of that isotope enough to explain its absence in HR 7245, butwe have found no possible explanation for the Hg isotopic mix found in11 Per. These are the first very high resolution measurements of Hg IIlambda3984 for HR 7245 and 11 Per. Although diffusion may be acting inHgMn stars, either there are one or more other mechanisms acting to helpproduce the overabundances and isotopic mixtures seen or ourunderstanding of diffusion is lacking on some important point.
| Gallium abundances in mercury-manganese stars
There is a widespread assertion in the literature that the optical Galines give much higher abundances than the UV lines. We have determinedGa abundances in HgMn stars taking the observed hyperfine structure ofthe optical Ga II lines into account. This reduces these abundances towithin 0.2 dex of the values from the resonance lines.
| 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 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
| The gallium problem in HgMn stars
Previous studies of visible-region high-excitation lines of ion{Ga}{ii}in HgMn stars have usually concluded that these lines (lambda lambda4251-4262 and lambda 6334) yield abundance estimates for gallium ~1 dexgreater than the UV resonance lines. Of the explanations proposed in theliterature, we find that the presence of hyperfine structure (hfs) inthe lines is the most likely. We analyse Lick Hamilton Echelle CCDspectra by spectrum synthesis with the code UCLSYN. Using the Bidelman& Corliss (bidelman) measurements of hfs in ion{Ga}{ii}, and thecalculations given by Lanz et al. (lanz), with the oscillator strengthsby Ryabchikova & Smirnov (rya, b), we determine a difference inabundance (visual-UV) of only 0.2 dex. Of this difference, about 0.1 dexcan be explained by the simplified approximation to the true hfs, whichcan be estimated theoretically, and the remaining 0.1 dex can probablybe accounted for by the stratification of Ga found by Smith (smith, b.,smith, d.). We conclude that the visible-region and UV abundances are inagreement within the errors of the determinations, and that the anomalypreviously found by several investigations is an artifact of thesimplified atomic line structures assumed, or results from the use ofvery different gf-values from those adopted here.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
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Membro dei seguenti gruppi:
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Osservazione e dati astrometrici
| Costellazione: | Ercole |
| Ascensione retta: | 16h02m47.90s |
| Declinazione: | +46°02'12.0" |
| Magnitudine apparente: | 4.76 |
| Distanza: | 115.207 parsec |
| Moto proprio RA: | 54 |
| Moto proprio Dec: | -63.1 |
| B-T magnitude: | 4.596 |
| V-T magnitude: | 4.694 |
Cataloghi e designazioni:
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INHABITED SKY
