Contents
Images
Upload your image
DSS Images Other Images
Related articles
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.
| Asteroseismology of solar-type stars with CORALIE and HARPS . I: Observations and modelling of single stars
We present here the detection and characterization of solar-likeoscillations in several targets such as beta Vir, eta Boo, delta Eri,chi Eri and the Am star HD 209625 obtained with the CORALIE and HARPSspectrographs based at the ESO La Silla Observatory. The measurement ofthe frequencies of p-mode oscillations provides an insight into theinternal structure and is nowadays the most powerful constraint on thetheory of stellar evolution.
| Kinematic structure of the corona of the Ursa Major flow found using proper motions and radial velocities of single stars
Aims.We study the kinematic structure of peripheral areas of the UrsaMajoris stream (Sirius supercluster). Methods.We use diagrams ofindividual stellar apexes developed by us and the classical technique ofproper motion diagrams generalized to a star sample distributed over thesky. Results.Out of 128 cluster members we have identified threecorona (sub)structures comprised of 13, 13 and 8 stars. Thesubstructures have a spatial extension comparable to the size of thecorona. Kinematically, these groups are distinguished by their propermotions, radial velocities and by the directions of their spatialmotion. Coordinates of their apexes significantly differ from those ofthe apexes of the stream and its nucleus. Our analysis shows that thesesubstructures do not belong to known kinematic groups, such as Hyades orCastor. We find kinematic inhomogeneity of the corona of the UMa stream.
| Spectral disentangling of the triple system DG Leo: orbits and chemical composition
DG Leo is a spectroscopic triple system composed of three stars oflate-A spectral type, one of which was suggested to be a δ Scutistar. Seven nights of observations at high spectral and hightime-resolution at the Observatoire de Haute-Provence with the ELODIEspectrograph were used to obtain the component spectra by applying aFourier transform spectral disentangling technique. Comparing these withsynthetic spectra, the stellar fundamental parameters (effectivetemperature, surface gravity, projected rotation velocity and chemicalcomposition) are derived. The inner binary consists of two Amcomponents, at least one of which is not yet rotating synchronously atthe orbital period though the orbit is a circular one. The distant thirdcomponent is confirmed to be a δ Scuti star with normal chemicalcomposition.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| 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.
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group
Utilizing Hipparcos parallaxes, original radial velocities and recentliterature values, new Ca II H and K emission measurements,literature-based abundance estimates, and updated photometry (includingrecent resolved measurements of close doubles), we revisit the UrsaMajor moving group membership status of some 220 stars to produce afinal clean list of nearly 60 assured members, based on kinematic andphotometric criteria. Scatter in the velocity dispersions and H-Rdiagram is correlated with trial activity-based membership assignments,indicating the usefulness of criteria based on photometric andchromospheric emission to examine membership. Closer inspection,however, shows that activity is considerably more robust at excludingmembership, failing to do so only for <=15% of objects, perhapsconsiderably less. Our UMa members demonstrate nonzero vertex deviationin the Bottlinger diagram, behavior seen in older and recent studies ofnearby young disk stars and perhaps related to Galactic spiralstructure. Comparison of isochrones and our final UMa group membersindicates an age of 500+/-100 Myr, some 200 Myr older than thecanonically quoted UMa age. Our UMa kinematic/photometric members' meanchromospheric emission levels, rotational velocities, and scattertherein are indistinguishable from values in the Hyades and smaller thanthose evinced by members of the younger Pleiades and M34 clusters,suggesting these characteristics decline rapidly with age over 200-500Myr. None of our UMa members demonstrate inordinately low absolutevalues of chromospheric emission, but several may show residual fluxes afactor of >=2 below a Hyades-defined lower envelope. If one defines aMaunder-like minimum in a relative sense, then the UMa results maysuggest that solar-type stars spend 10% of their entire main-sequencelives in periods of precipitously low activity, which is consistent withestimates from older field stars. As related asides, we note six evolvedstars (among our UMa nonmembers) with distinctive kinematics that liealong a 2 Gyr isochrone and appear to be late-type counterparts to diskF stars defining intermediate-age star streams in previous studies,identify a small number of potentially very young but isolated fieldstars, note that active stars (whether UMa members or not) in our samplelie very close to the solar composition zero-age main sequence, unlikeHipparcos-based positions in the H-R diagram of Pleiades dwarfs, andargue that some extant transformations of activity indices are notadequate for cool dwarfs, for which Ca II infrared triplet emissionseems to be a better proxy than Hα-based values for Ca II H and Kindices.
| 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
| 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.
| Composite Spectra. XII. μ Leonis: An Evolving Am Binary
It is shown by techniques of spectrum disentangling that both componentsof the composite-spectrum binary ο Leo (V=3.52 mag) have Amcharacteristics, even though the primary is an evolving giant(logg=3.25) with Teff~6100 K. This is believed to be thefirst isolation of such a cool Am star, and the finding challenges thetheories of diffusion, which are widely accepted as the cause ofmetallicism. The primary component of ο Leo appears to bedeficient in Ca and Sc, as are classical Am stars-though the δ Delstars which are described as evolved Am stars are not-and thereforeseems to be in a class on its own. It is suggested that the unusualstate of the primary component is attributable either to its currentstate of rapid evolution or to regular Am-star evolution that isdifficult to recognize spectroscopically. This paper describes thetechnical problems that have hitherto prevented the identification ofsuch unexpected properties in this easily observed binary, determinesthe physical parameters of the component stars, examines theirevolutionary states, and debates the possible classification of thegiant component. Future directions for this work will include detailedchemical composition analyses and an observing program designed tosearch for other cases of substantially evolved Am stars.
| 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
| Transition probabilities in Gd III
Theoretical lifetimes, calculated with inclusion of core-polarizationeffects, have been determined for five 4f76p levels of doublyionized gadolinium. They agree quite well with recent experimentalvalues measured by time-resolved laser-induced fluorescencespectroscopy. From this agreement, the accuracy of a first set of Gd IIItransition probabilities, calculated for4f75d-4f76p and 4f76s-4f76ptransitions of astrophysical interest, has been assessed.
| 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.
| Vertical Chromium Distribution in the Atmospheres of CP Stars. II. Modeling
Vertical chromium distributions in the atmospheres of several Ap and Amstars are fitted using detailed modeling of the profiles of CrII lines.The vertical distributions obtained for Ap stars are consistent withBabel's results of an investigation of Cr lines in the spectrum of theAp star 53 Cam. It is shown that the observational data cannot beinterpreted in terms of the hypothesis that microturbulent velocityvaries with depth.
| 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.
| Accuracy of radial-velocity measurements for early-type stars. II. Investigations of spectrum mismatch from high-resolution observations
The accuracy with which radial velocities of early-type stars can bemeasured is limited in practice by the existence of asymmetricaldifferences between object and template spectrum, constituting``spectrum mismatch''. Our studies of the magnitude of spectrum-mismatcherrors, commenced in Paper I (Verschueren et al. \cite{VDG99}) on thebasis of synthetic spectra having different attributes of effectivetemperature (Teff and {log g}, are continued here in acomplementary approach that employs observed spectra. From over 60de-archived observations we derive accurate wavelength scales for thespectra of 16 dwarfs of spectral types B8-F7, and examine the results ofcross-correlating the spectra against different (observed) templatespectra. We also test the effects of (a) truncating the spectra atdifferent levels below the continuum, (b) adding rotational broadeningto enforce a visual match of line-width between object and template, (c)applying rotational broadening to exacerbate a rotational mismatch, and(d) neglecting the presence of faint companion spectra. We alsocross-correlate pairs of spectra such that the differences between theirTeff are minimal. We conclude that it will be possible tomeasure radial velocities to an accuracy considerably better than 1 kms-1 for slowly-rotating stars in the range of spectral typesexamined, and a careful discussion of the nature and sources of therandom and systematic errors that become significant in work of thisnature enables us to specify conditions that are important for achievingsuch accuracy routinely. We find that both rotational broadening, andthe star-to-star variations in line strengths that are so prevelantamong A-type spectra, can give rise to more deleterious mismatch shifts(RV errors) than do differences in Teff alone, even for DeltaTeff as great as 300-400 K. By intercomparing the resultsgiven by wide regions of spectrum ( ~ 800 Å) with those obtainedby isolating small groups of features in very narrow windows ( ~ 30Å), we have been able to designate a window near lambda 4570Åthat should be particularly reliable for high-accuracy results,and we propose further studies at very high S/N ratio in that specificwindow to complement and extend the results of the present paper.
| Metal abundances of field A and Am stars
Detailed abundances of 9 field A and Am stars are derived for Mg, Ca,Sc, Cr, Fe, and Ni using high resolution spectroscopy. Most of oursample Am stars show the characteristic deficiencies of Ca and Sc on onehand, and the overabundances of the iron peak elements on the other,which is consistent with the predictions of the diffusion model for MainSequence or slightly evolved stars. There seems to be a correlationbetween abundances of Ca and Sc and the effective temperature for starsof similar age: the abundance of Ca increases with increasing masswhereas that of Sc decreases. Two of our Am stars have a differentabundance pattern: Ca is overabundant in the hot magnetic Am star o Pegand its abundance is nearly normal in the metallic giant star rho Pup.The other objects of our sample have globally a solar composition except28 And, which shows significant deficiencies for most the studiedelements. Based on observations collected at the Observatoire deHaute-Provence (France), and on data from the ESA\protect\linebreakHIPPARCOS astrometry satellite.
| 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.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Spectroscopy of Hot Stars in the Galactic Halo. III. Analysis of a Large Sample of Field Horizontal-Branch and Other A-Type Stars
We present results from an analysis of medium-resolution spectroscopyand UBV photometry for a sample of 1121 A-type stars in the halo (anddisk) of the Galaxy. A previously developed calibration technique isused to assign estimates of effective temperature, surface gravity, andstellar metal abundance, as parameterized by [Fe/H]. Radial velocitiesare reported with an accuracy of ~10 km s^-1. Distance estimates areobtained for the stars with well-determined luminosity classes. Notethat although we refer to ``A-type'' stars, which dominate the presentsample, the present data set includes roughly 100 stars of laterspectral types, as a result of the temperature range we have chosen toexplore in this paper (6000 K<=T_eff<=10,000 K). Included in thehot star sample are 444 stars we classify as field horizontal-branchstars, 416 we classify as main-sequence-gravity A-type (or slightlylater) stars (including stars that are likely members of the bluemetal-poor population, the so-called BMPs), 140 stars we classify aslikely metallic-line (Am) or peculiar (Ap) stars, and 121 stars thatcannot be unambiguously classified based on the present data.Examination of the distributions in metallicity and velocity indicatesthat the field horizontal-branch and main-sequence A-type samples arequite distinct; hence we expect only a modest amount ofcross-contamination between the subsamples. We identify 58 RR Lyraecandidates among the hot star sample, based on incompatibilities intheir photometric and spectroscopic data. There are 19 stars in thesample that have been previously classified as RR Lyrae variables, andone additional star that had been previously suggested as a variable,though not necessarily of the RR Lyrae class. There are 115 stars in thesample that were previously classified as BMPs by Preston, Beers, &Shectman, most of which fall into the main-sequence A-type category, but10 of which are found among the Am/Ap classifications. Furthermore, 53of stars previously considered to be BMPs are shown by our analysis tohave metal abundances [Fe/H]>-1, which calls their identificationwith this population somewhat into question.
| Vertical stratification of CR in the atmospheres of CP stars.
Not Available
| Elemental abundance analyses with DAO spectrograms - XX. The early A stars epsilon Serpentis, 29 Vulpeculae and sigma Aquarii
Elemental abundances of the early A stars epsilon Ser, 29 Vul and sigmaAqr are derived consistently with previous studies of this series usingspectrograms obtained with Reticon and CCD detectors. The derivedabundances confirm that epsilon Ser is a definite Am star. 29 Vul showsevidence for a weakly operating Am star phenomenon. sigma Aqr, a hot Amstar prototype, has abundances similar to those of o Peg, another classprototype.
| Far-Infrared Photometry of Circumstellar Matter Around Intermediate Mass Stars
Not Available
| 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
| Detection of atmospheric velocity fields in A-type stars
High signal-to-noise spectra with spectral resolution of more than 10(5)have been obtained of one normal B9.5V, one normal A1V, two Am stars,and two HgMn B stars having v sin i less than 6 km s(-1) . These spectraare modeled with LTE line profile synthesis to test the extent to whichthe spectrum of each star can be modeled correctly with a single set ofparameters T_e, log g, chemical abundances, v sin i, and(depth-independent) microturbulent velocity xi . The answer to thisquestion is important for abundance analysis of A and B stars; ifconventional line synthesis does not reproduce the line profilesobserved in stars of small v sin i, results obtained from such analysisare not likely to be very precise. The comparison of models withobservations is then used to search for direct evidence of atmosphericmotions, including line-strength dependent broadening, line core shape,and line asymmetries, in order to study how the microturbulence derivedfrom abundance analysis is related to more direct evidence ofatmospheric velocity fields. It is found for the three stars with 12,000>= T_e >= 10,200 K (the normal star 21 Peg and the two HgMn stars53 Tau and HD 193452) that xi is less than 1 km s(-1) , and lineprofiles are reproduced accurately by the synthesis with a single set ofparameters. The slightly cooler (T_e ~ 9800 K) star HD 72660 has only aslightly stronger surface convective layer than the hotter stars, butfor this star xi ~ 2.2 km s(-1) . Strong spectral lines all showsignificant asymmetry, with the blue line wing deeper than the red wing,and have line bisectors which have curvature towards the blue with aspan of about 0.5 to 1.0 km s(-1) . A single model fits all linessatisfactorily. The two Am stars (HD 108642 and 32 Aqr), with T_e ~ 8000K, are found to have much larger values of xi (4 to 5 km s(-1) ). Thestrong spectral lines of these two stars are extremely asymmetric, withdepressed blue wings, and the bisectors have spans of order 3 km s(-1) .No consistent fit to all lines can be found with a single model of thetype used here. It is concluded (a) that classical LTE line synthesis isable to reproduce with considerable accuracy the line profiles of late Band early A stars with T_e above about 9500 K, but that the LTE modelwith depth-independent microturbulence provides a very poorapproximation for cooler A stars, (b) that curve-of-growthmicroturbulent velocities in A stars are related to directly detectableatmospheric velocity fields, and (c) that the discrepancies betweencalculated and observed line profiles in stars with temperatures in thevicinity of 8000 K are so large that abundances derived mainly fromsaturated lines may well contain significant errors. As a by-product,laboratory gf values for Fe II between 3800 and 5300 Angstroms have beencombined to form a set of data optimized for internal consistency of thegf values. Based on observations obtained with the Canada-France-Hawaiitelescope, operated by the National Research Council of Canada, theCentre National de Recherche Scientifique of France, and the Universityof Hawaii, and with the 1.52-m telescope of the Observatoire de HauteProvence, operated by the Centre National de Recherche Scientifique ofFrance.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Wassermann |
| Right ascension: | 22h04m47.40s |
| Declination: | -00°54'24.0" |
| Apparent magnitude: | 5.3 |
| Distance: | 70.922 parsecs |
| Proper motion RA: | -19.9 |
| Proper motion Dec: | -42.5 |
| B-T magnitude: | 5.574 |
| V-T magnitude: | 5.303 |
Catalogs and designations:
|
