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The Puzzle of the Metallic Line Stars
In the puzzle of the metallic line (Am) stars, there still seem to bemissing pieces. While the ``normal'' A stars have elemental abundancesclose to solar, the classical Am stars show stronger absorption linesfor most heavy elements in their spectra. Elements with ionizationpotentials that nearly agree with those of hydrogen or helium havereduced abundances. The Ca II and Sc II lines are especially weak. TheAm stars have no ultraviolet emission lines. They are binaries that,with very few exceptions, have rotational velocities vsini lower than100 km s-1. Of the main-sequence A stars, 20% to 30% are Amstars. Here we rediscuss previous suggestions that tried to explain thepeculiar line strengths in the Am star spectra. In particular, wecompare the well-studied properties of Hyades A and Am stars in order toidentify reasons that can or cannot explain the differences. We findthat accretion of interstellar material by A stars with distortedmagnetic fields, which are weaker than those in peculiar A (Ap) stars,has the best chance of explaining the main characteristics of thepeculiar heavy-element abundances in Am star photospheres.Charge-exchange reactions also seem to be important.
| A catalog of stellar magnetic rotational phase curves
Magnetized stars usually exhibit periodic variations of the effective(longitudinal) magnetic field Be caused by their rotation. Wepresent a catalog of magnetic rotational phase curves, Be vs.the rotational phase φ, and tables of their parameters for 136stars on the main sequence and above it. Phase curves were obtained bythe least squares fitting of sine wave or double wave functions to theavailable Be measurements, which were compiled from theexisting literature. Most of the catalogued objects are chemicallypeculiar A and B type stars (127 stars). For some stars we also improvedor determined periods of their rotation. We discuss the distribution ofparameters describing magnetic rotational phase curves in our sample.All tables and Appendix A are only available in electronic form athttp://www.edpsciences.org
| The field Am and ρ Puppis-like stars: Lithium and heavier elements
With observations at the Canada-France-Hawaii telescope, photosphericabundances of two evolved field Am stars, τ UMaand HR 178, have been determined for Li, Al, Si, S,Fe, Ni, and Eu by model abundance analysis. Thanks to these newdetermined abundances and the HIPPARCOS mission, making it possible tobetter estimate the evolutionary stage of field stars, one can considerthe influence of evolution on the abundances of Am stars. No abundancetrend for Al, Si, S, and Fe is found during Main Sequence evolution, upto its very last phases. The abundance of Li is, generally, cosmic.Large Li deficiencies may be observed in the very last phases (the``hook'' region of the H-R diagram) and, too, on the red side of the Amphenomenon region where the ρ Puppis-like stars lie.Based on observations collected at the Canada-France-Hawaii telescope(Hawaii).
| The physical properties of normal A stars
Designating a star as of A-type is a result of spectral classification.After separating the peculiar stars from those deemed to be normal usingthe results of a century of stellar astrophysical wisdom, I define thephysical properties of the "normal" stars. The hotter A stars haveatmospheres almost in radiative equilibrium. In the A stars convectivemotions can be found which increase in strength as the temperaturedecreases.
| Empirically Constrained Color-Temperature Relations. II. uvby
A new grid of theoretical color indices for the Strömgren uvbyphotometric system has been derived from MARCS model atmospheres and SSGsynthetic spectra for cool dwarf and giant stars having-3.0<=[Fe/H]<=+0.5 and 3000<=Teff<=8000 K. Atwarmer temperatures (i.e., 8000-2.0. To overcome thisproblem, the theoretical indices at intermediate and high metallicitieshave been corrected using a set of color calibrations based on fieldstars having well-determined distances from Hipparcos, accurateTeff estimates from the infrared flux method, andspectroscopic [Fe/H] values. In contrast with Paper I, star clustersplayed only a minor role in this analysis in that they provided asupplementary constraint on the color corrections for cool dwarf starswith Teff<=5500 K. They were mainly used to test thecolor-Teff relations and, encouragingly, isochrones thatemploy the transformations derived in this study are able to reproducethe observed CMDs (involving u-v, v-b, and b-y colors) for a number ofopen and globular clusters (including M67, the Hyades, and 47 Tuc)rather well. Moreover, our interpretations of such data are verysimilar, if not identical, with those given in Paper I from aconsideration of BV(RI)C observations for the sameclusters-which provides a compelling argument in support of thecolor-Teff relations that are reported in both studies. Inthe present investigation, we have also analyzed the observedStrömgren photometry for the classic Population II subdwarfs,compared our ``final'' (b-y)-Teff relationship with thosederived empirically in a number of recent studies and examined in somedetail the dependence of the m1 index on [Fe/H].Based, in part, on observations made with the Nordic Optical Telescope,operated jointly on the island of La Palma by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.Based, in part, on observations obtained with the Danish 1.54 mtelescope at the European Southern Observatory, La Silla, Chile.
| 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
| Elemental abundance analyses with the EBASIM spectrograph of the 2.1-m CASLEO Observatory Telescope. I. The late B and early A stars vec xi Octantis, alpha Sextantis, and 68 Tauri
We used data from the EBASIM spectrograph of the 2.1-m CASLEO telescopeto study three rather sharp-lined late B to early A stars xi Oct (B6IV), alpha Sex (B9.5 III), and 68 Tau (A2 IV). These measurements arecompared with those from the Anglo-Austrialian Telescope for the firststar and to those from the coudé spectrograph of the 1.22-mtelescope of the Dominion Astrophysical Observatory (DAO) for the othertwo stars. The equivalent width scales of the EBASIM and the DAO dataare similar. Thus for the latter two stars the DAO data is also used inthe analyses. Both xi Oct and alpha Sex generally have abundancesclose to those of the Sun in the range of values found for other normalstars with similar effective temperatures. The abundance pattern for 68Tau is that of a metallic-lined star as is well known.Tables 5 to 7 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/406/987
| 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 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.
| IR observations of Am stars
The IR observations of chemically peculiar stars are carried out andcompared with the previous data in IR and far IR from IRAS. The fluxredistribution appears to be a common phenomenon in all the stars ofthis class. The observed energy distribution and a model fit based oneffective temperature estimates show slight excess in the IR.
| 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
| 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.
| A Study of Rare Earth Elements in the Atmospheres of Chemically Peculiar Stars. Pr III and Nd III Lines
We determine the abundances of Pr and Nd in the atmospheres of magneticand non-magnetic chemically peculiar stars from the lines of rare earthelements in the first and second ionization states. The computations forthe magnetic stars take into account the influence of the magnetic fieldon line formation. We studied the influence of errors in thestellar-atmosphere parameters and the atomic parameters of the spectrallines on the accuracy of abundance determinations. Within the derivedaccuracy, ionization equilibrium is satisfied in the atmospheres ofnon-pulsating magnetic and non-magnetic stars (so that abundancesderived separately from lines of first and second ions agree). For allthe pulsating magnetic (roAp) stars studied, the abundances derived fromlines of second ions are 1.0 to 1.7 dex higher than those derived fromfirst ions. The violation of ionization equilibrium in the atmospheresof pulsating stars is probably due to, first, considerable enrichment ofPr and Nd in the uppermost atmospheric layers, and second, a higherlocation for the layer of enhanced elemental abundance in roAp starsthan in non-pulsating stars. Two objects from the list of non-pulsatingmagnetic stars, HD 62140 and HD 115708, exhibit anomalies of their Prand Nd lines characteristic of roAp stars. The differences in the rareearth anomalies for the pulsating and non-pulsating peculiar stars canbe used as a selection criterion for candidate roAp stars.
| 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
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 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/367/297
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Elemental abundance analyses with DAO spectrograms - XXIII. The superficially normal stars 28 And (A7III) and 99 Her (F7V)
Elemental abundances of 28 And (A7III) and 99 Her (F7V), which havemodest rotational velocities, are derived in a manner consistent withprevious studies in this series of papers. The values for 28 And, aδ Scuti variable, show that it is slightly metal-poor, but not aclassical Am star. 99 Her, which is somewhat more metal-poor, has arather small microturbulence for its spectral type.
| Abundance analyses of roAp stars. VI. 10 Aql and HD 122970
In this sixth paper in a sequence on abundance analyses of roAp stars wepresent the results for two further members of this group, which arefairly similar and have only a small magnetic field. The analysis of 10Aql and HD 122970 did not require, for the first time in this long termproject, the development of tools and hence was rather straight-forward.We reanalyzed Sm, Eu and Gd in HD 203932, because better atomicparameters have become available with vald-2; and for Eu we also took\hfs effects into account. Similar to the five roAp stars analysed sofar (alpha Cir: Kupka et al. 1996, HD 203932: Gelbmann et al. 1997,gamma Equ: Ryabchikova et al. 1997a, HD 24712: Ryabchikova et al. 1997b,and HD 166473: Gelbmann et al. 2000) we find nearly solar abundances ofFe and Ni, and a definite overabundance of Cr and especially Co, withlarge overabundances of rare earth elements. This pattern seems to be acommon property of chemically peculiar (CP2, Ap) stars. HD 101065(Przybylski's star), another roAp star, has a similar peculiaritypattern, except of iron (Cowley et al. 2000) which is underabundant. 10Aql and HD 122970 provide another example for the anomalous linestrengths of the second ions of rare earth elements resulting in anabundance increase of up to 2 dex (!) compared to values obtained fromlines of the first ions. As we mentioned in an earlier paper, thisanomaly yet is not found in non-roAp and ``normal'' stars. Based onobservations obtained at Crimea and McDonald Observatories
| On the cobalt abundances of early-type stars
Photographic region high-dispersion high signal-to-noise spectra of Aand F main sequence band stars which exhibit modest rotation show Co Ilines. In the hottest of these stars, we also found weak Co II lineswhose abundances are consistent with those from Co I lines. As a classthe Am stars have cobalt abundances which are greater than solar whilethe normal stars have solar values.
| Elemental abundance analyses with DAO spectrograms - XXI. The hot metallic-lined stars 60 Leonis and 6 Lyrae
Elemental abundances of the hot metallic-lined (Am) stars 60 Leo and 6Lyr, with modest rotational velocities, are derived consistently withother studies in this series of papers. Both stars are found to show theAm phenomenon strongly, with nearly solar abundances of the lightelements, overabundances of most Fe peak elements, and considerableoverabundances of SrYZr, Ba and some rare earths. Ca is underabundant,while Sc is very underabundant.
| New 3 Micron Spectra of Young Stellar Objects with H_2O Ice Bands
We present new ground-based 3 μm spectra of 14 young stellar objectswith H_2O ice absorption bands. The broad absorption feature at 3.47μm was detected toward all objects, and its optical depth iscorrelated with the optical depth of H_2O ice, strengthening an earlierfinding. The broad absorption feature at 3.25 μm was detected towardtwo more sources, and an upper limit is given for a third source. Theoptical depths of the 3.25 μm feature obtained to date are bettercorrelated with the optical depth of the refractory silicate dust thanwith that of H_2O ice. If this trend is confirmed, this would supportour proposed identification of the feature as the C-H stretch ofaromatic hydrocarbons at low temperature. An absorption feature at 3.53μm due to solid methanol was detected for the first time toward MonR2/IRS 2, as well as toward W33A and GL 2136. The wavelengths of theCH_3OH features toward W33A, GL 2136, and NGC 7538/IRS 9 can be fittedby CH_3OH-rich ices, whereas the wavelength of the feature toward MonR2/IRS 2 suggests an H_2O-rich ice environment. Solid methanolabundances toward GL 2136, NGC 7538/IRS 9, and Mon R2/IRS 2 are 3%-5%relative to H_2O ice. There is an additional narrow absorption featurenear 3.47 μm toward W33A. For the object W51/IRS 2, spatiallyresolved spectra from 2 to 4 μm indicate that the H_2O ice is locatedpredominantly in front of the eastern component and that the H_2O iceextinction is much deeper than previously estimated. For the object RNO91, spectra from 2 to 4 μm reveal stellar (or circumstellar) CO gasabsorption and deeper H_2O ice extinction than previously estimated.
| Spectroscopy of Hot Stars in the Galactic Halo. II. The Identification and Classification of Horizontal-Branch and Other A-Type Stars
We discuss a spectroscopic and photometric technique that enables theidentification and classification of field horizontal-branch (FHB) andother A-type stars, even from relatively low signal-to-noise ratiomedium-resolution spectra. This technique makes use of broadband UBVcolors predicted from model atmosphere calculations and Balmer lineprofiles and Ca II K equivalent widths determined from synthetic spectrato estimate the physical parameters T_eff, log g, and [Fe/H] for starsin the effective temperature range 6000-10,000 K. A comparison of ourmethod with high signal-to-noise ratio spectra of standard starsindicates a scatter in the derived parameters of sigma(T_eff)=+/-250 K,sigma(log g)=+/-0.14 dex, and sigma([Fe/H])=+/-0.12 dex. This precisionallows for a separation of low surface gravity FHB and other, generallyhigher surface gravity, A-type (and somewhat later) stars. We alsodevelop a synthetic-template comparison technique, which is veryeffective in the identification of metallic-line and peculiar A-typestars. A detailed investigation of the influence of noise in the spectraon the determination of physical parameters shows that, for spectra withsignal-to-noise ratios in the range 10
| The effective temperature scale of giant stars (F0-K5). I. The effective temperature determination by means of the IRFM
We have applied the InfraRed Flux Method (IRFM) to a sample ofapproximately 500 giant stars in order to derive their effectivetemperatures with an internal mean accuracy of about 1.5% and a maximumuncertainty in the zero point of the order of 0.9%. For the applicationof the IRFM, we have used a homogeneous grid of theoretical modelatmosphere flux distributions developed by \cite[Kurucz (1993)]{K93}.The atmospheric parameters of the stars roughly cover the ranges: 3500 K<= T_eff <= 8000 K; -3.0 <= [Fe/H] <= +0.5; 0.5 <= log(g) <= 3.5. The monochromatic infrared fluxes at the continuum arebased on recent photometry with errors that satisfy the accuracyrequirements of the work. We have derived the bolometric correction ofgiant stars by using a new calibration which takes the effect ofmetallicity into account. Direct spectroscopic determinations ofmetallicity have been adopted where available, although estimates basedon photometric calibrations have been considered for some stars lackingspectroscopic ones. The adopted infrared absolute flux calibration,based on direct optical measurements of stellar angular diameters, putsthe effective temperatures determined in this work in the same scale asthose obtained by direct methods. We have derived up to fourtemperatures, TJ, TH, TK and T_{L'},for each star using the monochromatic fluxes at different infraredwavelengths in the photometric bands J, H, K and L'. They show goodconsistency over 4000 K, and there is no appreciable trend withwavelength, metallicity and/or temperature. We provide a detaileddescription of the steps followed for the application of the IRFM, aswell as the sources of error and their effect on final temperatures. Wealso provide a comparison of the results with previous work.
| Vertical stratification of CR in the atmospheres of CP stars.
Not Available
| Concerning the Reported Phase-modulated Changes in the Spectrum of 41 Sextantis
Sreedhar Rao et al. have reported that the metallic-line star 41Sextantis exhibits significant changes in the depths and equivalentwidths of its spectral lines and that these changes are coupled with theorbital motion of this spectroscopic binary. Based on their discovery,they suggest that 41 Sex is a possible evolutionary link between the Amand Ap stars. High-dispersion CCD spectra of 41 Sex, obtained in 1991with the 0.9 m feed telescope and coudé spectrograph at the KittPeak National Observatory, were measured to determine the equivalentwidths and depths of several metallic lines and the depths of Ca ii Kand H_8 as a function of orbital phase. The spectrum changes thatSreedhar Rao et al. observed could not be verified with these data.Possible explanations for this lack of confirmation might be that thestar was in a quiescent state in 1991 or that the reported changes tothe spectrum happen on a timescale much greater than the orbital period.An updated solution for the spectroscopic orbital elements is alsopresented.
| Averaged energy distributions in the stellar spectra.
Not Available
| Photometry from the HIPPARCOS Catalogue: Constant MCP Stars, Comparison and Check Stars
Photometry from the Hipparcos catalogue is used to verify the constancyof four magnetic CP stars, as well as the comparison and the check starsused for variability studies of normal and chemically peculiar B and Astars with the Four College Automated Photoelectric Telescope;variability in these stars can produce spurious results. A few of thecomparison stars are found to be variable and should be replaced forfuture differential photometric studies.
| A study of the atmosphere of the metallic-line star 15 Vul
We performed new observations of the metallic-line star 15 Vul with theechelle spectrograph of the 1-m telescope of the Special AstrophysicalObservatory. Based on measurements of the equivalent widths for morethan 600 green and yellow-red lines of 24 elements, we redetermined theatmospheric chemical composition of this star. We discuss the results ofour iron-abundance determination in the atmosphere of 15 Vul from Fe Iand Fe II lines and analyze the effect of choosing lines and of theoscillator strengths used on the determination of lg e(Fe). UsingStenflo-Lindegren's multiline technique, we diagnose a magnetic field atthe surface of 15 Vul with a complex structure. The field strength wasfound from 164 Fe I lines in the wavelength range 4300 to 6700 Angstromsto be fH = 2390 +/- 540 G. An analysis of Fe I lines with variousexcitation potentials e provides evidence that the magnetic regions onthe surface of 15 Vul are cooler than the surrounding quiet photosphere.
| 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
| Broad-band JHK(L') photometry of a sample of giants with 0.5 > [Fe/H] > -3
We present the results of a three-year campaign of broad-band photometryin the near-infrared J, H, K and L' bands for a sample of approximately250 giant stars carried out at the Observatorio del Teide (Tenerife,Spain). Transformations of the Telescopio Carlos Sanchez systeminto/from several currently used infrared systems are extended to theredward part of the colour axis. The linearity of our photometric systemin the range -3 mag [Fe/H] >-3. Data of comparable quality previouslypublished have been added to the sample in order to increase thereliability of the relations to be obtained. We also provide mean IRcolours for giant stars according to spectral type.ables 1, 2 and 3 are only available in electronic form via the CDS(anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html
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| Sað Açýklýk: | 20h01m06.10s |
| Yükselim: | +27°45'13.0" |
| Görünürdeki Parlaklýk: | 4.64 |
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