Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
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
| 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
| Lithium in the Super-Beryllium-rich HG-MN Stars HR 6158 and HR 8915
The chemically peculiar stars that inhabit the upper main sequenceexhibit very extreme enhancements and deficiencies of several elements.In all likelihood, the primary cause of these anomalies is radiativelydriven diffusion, although other mechanisms may also be important-suchas mass loss and various kinds of mixing. Only by examining as manyelements as possible will a cohesive theory explaining these abundanceoddities materialize. To this end, we present high-resolution(R~62,500), high signal-to-noise ratio (S/N pixel^-1~120) observationsof the 6708 Å Li I resonance doublet in a pair of Hg-Mn stars. Norecord of a lithium detection has been found for this type of chemicallypeculiar star. The atmospheres of the two program stars (HR 6158=28Her=HD 149212; HR 8915=69 Peg=HD 220933) contain an inordinate amount ofberyllium (Be) in fact, the Be abundances in these stars are among thehighest known. While the LTE concentration of Be is several thousandtimes larger than cosmic [A(Be)_i~1.27] in both stars, lithium (Li) isdetected in neither HR 6158 nor HR 8915. The calculated 3 sigma (99%confidence level) upper limits place the maximum Li enhancements at 50times and 80 times cosmic [A(Li)_i~3.23] for HR 6158 and HR 8915,respectively, or ~100 times smaller than the Be overabundances. These Liupper limits, which argue against a ``nucleosynthesis'' origin for theBe surfeit, provide yet another means of constraining the physicalprocess (or processes) responsible for the Hg-Mn phenomenon in some Astars.
| 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.
| 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.
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The observed periods of AP and BP stars
A catalogue of all the periods up to now proposed for the variations ofCP2, CP3, and CP4 stars is presented. The main identifiers (HD and HR),the proper name, the variable-star name, and the spectral type andpeculiarity are given for each star as far as the coordinates at 2000.0and the visual magnitude. The nature of the observed variations (light,spectrum, magnetic field, etc.) is presented in a codified way. Thecatalogue is arranged in three tables: the bulk of the data, i.e. thosereferring to CP2, CP3, and CP4 stars, are given in Table 1, while thedata concerning He-strong stars are given in Table 2 and those foreclipsing or ellipsoidal variables are collected in Table 3. Notes arealso provided at the end of each table, mainly about duplicities. Thecatalogue contains data on 364 CP stars and is updated to 1996, October31. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
| The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars
The HR-diagram of about 1000 Bp - Ap stars in the solar neighbourhoodhas been constructed using astrometric data from Hipparcos satellite aswell as photometric and radial velocity data. The LM method\cite{luri95,luri96} allows the use of proper motion and radial velocitydata in addition to the trigonometric parallaxes to obtain luminositycalibrations and improved distances estimates. Six types of Bp - Apstars have been examined: He-rich, He-weak, HgMn, Si, Si+ and SrCrEu.Most Bp - Ap stars lie on the main sequence occupying the whole width ofit (about 2 mag), just like normal stars in the same range of spectraltypes. Their kinematic behaviour is typical of thin disk stars youngerthan about 1 Gyr. A few stars found to be high above the galactic planeor to have a high velocity are briefly discussed. Based on data from theESA Hipparcos astrometry satellite and photometric data collected in theGeneva system at ESO, La Silla (Chile) and at Jungfraujoch andGornergrat Observatories (Switzerland). Tables 3 and 4 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| UVBY photometry of the magnetic chemically peculiar stars HD 11187, HD 15144, 20 Eridani and HR 8933 and the early F star HD 14940.
Four College Automated Photoelectric Telescope differential Stroemgrenuvby photometric observations of four magnetic chemically peculiar starsare presented. One of our comparison stars was also found to bevariable. Observations of the sharp-lined Si star HD 11187 are bestdescribed as representing a constant star. HD 15144 was also constantphotometrically. However, its comparison star HD 14940 is definitelyvariable. But we were not able to find a period. It may be a δ Scustar. Our observations of 20 Eri and the uvby values of Renson &Manfroid show definite differences in the shapes of the light curvewhich suggest that this star may be undergoing a precession of itsrotational axis. When we refined the period by using the minima we finda value of 1.92893 days. We refined Winzer's period of the relativelylarge amplitude variable HR 8933 to 2.86031 days. In v and b there aredefinite indications of a weak sub-maximum within the broad minimum.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Effective temperature of AP and AM stars from Geneva photometry
The determination of the effective temperature of different kinds ofchemically peculiar stars from Geneva photometry is rediscussed. Wepropose an improved method of determining T(eff) of Ap stars fromGeneva's reddening-free X and Y parameters or from the B2-G index. Theeffect of duplicity on the determination of T(eff) of Am stars isdiscussed.
| Amplitude variability of Tau Pegasi and the nature of singly-periodic Delta Scuti stars
Previously unavailable photometric data from the McDonald Observatoryare presented and analyzed. A frequency and amplitude analysis of thesedata, combined with other available measurements, are provided. Thepulsation modes are determined, and the results are integrated into thegeneral picture of Delta-Scuti stars. Tau-Peg = HR 8880 shows a dominantpulsation frequency of 18.4052 cycles/d with an amplitude changingslowly from 0.005 mag (or less) to 0.012 mag over 13 years. This isaccompanied by smooth changes in phase, suggesting small period changes.The variations in amplitude and phasing are similar to those recentlydiscovered in other nonradially pulsating delta-Scuti stars. The modeidentification and the observed amplitude variability show that Tau-Pegis a typical nonradially pulsating Delta-Scuti star with fast rotation.This star shows that for small amplitudes the detection of only a singlefrequency is not an indication of radial pulsation. This is in contrastto the results found for large-amplitude Delta-Scuti stars which areradial pulsators.
| Carbon, nitrogen, and oxygen abundances in the chemically peculiar stars of the upper main sequence
Low-noise, high-resolution Reticon spectra are used to obtain C, N, andO abundances for chemically peculiar stars with surface temperaturesbetween 7,000 and 15,000 K. The analysis includes C I, C II, N I, and OI lines for 13 Am and related stars, nine Hg-Mn stars, 15 magnetic Apstars, and five standard stars. The C and O abundances show a roughlymonotonic increase with surface temperature. The C and O results are ingeneral agreement with radiative diffusion theory. The N abundances,however, show that N is slightly deficient in cool nonmagnetic stars andvery deficient above 10,000 K in nonmagnetic stars. The results for Ndisagree with simple diffusion predictions, suggesting that a moredetailed model is needed for partially ionized N near the stellarsurface.
| Spectrum variability of some selected bright CP stars on the main sequence
The initial findings of a survey for spectrum variations in selected CPstars is reported. It is found that almost all observedmercury-manganese stars are spectrum variables. The implications ofchemical anomalies in these stars are briefly discussed. In particular,arguments are advanced against the general assumption that CP3 stars arenonmagnetic. The observed low rotational velocities of the CP3 stars areinterpreted as rotational braking by magnetic fields mostly in thepre-main-sequence stage of evolution of these objects. The hypothesis isadvanced that high resolution spectroscopic observations of such starswould exhibit Zeeman-broadening in lines that vary in strength and arealso sensitive to the magnetic field.
| Statistical Investigation of Chemically Peculiar Stars - Part One - the Stars with Known Periods
Not Available
| A catalogue of Fe/H determinations, 1984 edition
The present version of the Cayrel de Strobel et al. (1981) catalog ofFe/H abundance ratio determinations contains 1921 values for 1035 stars,which represents an augmentation over the previous publication of 48 and47 percent, respectively. In addition, the literature search conductedis complete up to December, 1983. Stellar metal abundance, effectivetemperature, spectroscopic gravity, spectral type, and photometricindices are covered.
| Evidence of decay of the magnetic fields of AP stars
Data obtained in the Geneva photometric system (Rufener, 1981) andappropriate calibrations of this system in terms of surface magneticfield and gravity are used to provide, on the basis of 708 field andcluster Ap stars, observational evidence that these stars undergo decayof their magnetic field on an evolutionary timescale. Justifications aregiven for the application of a photometric gravity calibration topeculiar stars. The dependence of the photometrically estimated surfacemagnetic field on gravity is found to differ markedly from availabletheoretical calculations. HgMn stars are found to show the same trend,strengthening the impression that they might be slightly magnetic.He-weak stars do not.
| Radial velocities of northern Mercury stars
About 200 radial velocities of 96 bright northern Hg-Mn or candidateHg-Mn stars are presented. Past and present data have been reexaminedfor periodic variability in cases that were neither previously known tobe binaries with well determined orbits nor were considered to haveconstant velocity. One definite new orbit was found (that of HR 3361)and several possible orbital solutions are given.
| Catalog of observed periods for the AP stars
A preliminary catalog of the Ap stars, taken in the broad sense toinclude many Bp stars, is presented. The HD and HR numbers,variable-star names, spectral types, and proposed periods are listed;the nature of the periodic variability is indicated; and references tothe observations are provided. Companion stars, confirmed spectroscopicbinaries, and anomalies are mentioned in notes.
| Beryllium abundances in Hg-Mn stars
The Hg-Mn stars show anomalous line strengths of many chemical elementsincluding Be. The Be II resonance doublet has been observed at 3130,3131 A at 6.7 A/mm in 43 Hg-Mn stars and 10 normal stars in the sametemperature range with the coude spectrograph of the 2.24 m Universityof Hawaii telescope at Mauna Kea. Measured equivalent widths of the twolines and/or the blend of the doublet have been compared with thepredictions from (1) LTE model atmospheres and (2) non-LTE lineformation in non-LTE model atmospheres. Overabundances of factors of20-20,000 relative to solar have been found for 75 percent of the Hg-Mnstars. The 25 percent with little or no Be are typically among thecooler Hg-Mn stars, but for the stars with Be excesses, there is onlymarginal evidence for a correlation of the size of the overabundance andtemperature. It is suggested that diffusion driven by radiation pressureis responsible for the observed Be abundance anomalies.
| Photometric properties of AP stars in the Geneva system
An examination of the properties in some photometric diagrams of morethan 600 Ap stars measured in the Geneva photometric system confirm thatthe Balmer discontinuity is smaller than for normal stars, along withthe link between a proposed peculiarity parameter and both rotationalvelocity and effective magnetic field. It is shown that the peculiarityparameter is sensitive to interstellar reddening, and it is foundthrough examination of the standard deviations for visual magnitudesthat cool CP 2 stars without Eu peculiarity have the greatestamplitudes. Rapid rotators have a mild peculiarity, while positivecorrelation exists for Si and SrCr stars.
| A catalogue and bibliography of Mn-Hg stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981A&AS...44..137S&db_key=AST
| The absolute magnitude of the Hg-Mn stars
The absolute magnitude of the Hg-Mn stars has been determined usingstatistical, photometric, spectroscopic, and cluster parallaxes. Theresults of all four procedures are in excellent agreement and give anaverage absolute magnitude of 0.6m plus or minus 0.4m, which locatesthese objects above the main sequence, in agreement with spectroscopicresults.
| Surface gravity of Mn-Hg stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979PASJ...31..473T&db_key=AST
| Chemical abundances in Hg-Mn stars
An abundance analysis has been conducted of 21 elements in 21 Hg-Mn, twoSi-Cr, and six normal stars using model atmospheres and high-dispersionspectroscopy in the visible and UV. Manganese line strengths implyabundances that correlate well with stellar effective temperature.Within the studied sample of Hg-Mn stars there appears to be nocorrelation of abundances of any element with projected rotationalvelocity. Abundances in several Hg-Mn stars show patterns that areprobably consistent with diffusion but difficult to reconcile withequilibrium nucleosynthesis. In general, no combination of gross stellarphysical parameters is sufficient to characterize the patterns of linestrengths observed in Hg-Mb Hg-Mn stars.
| 63rd Name-List of Variable Stars
Not Available
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Pegasus |
| Ascensió Recta: | 23h27m40.40s |
| Declinació: | +25°10'02.0" |
| Magnitud Aparent: | 5.98 |
| Distancia: | 112.486 parsecs |
| Moviment propi RA: | 27.2 |
| Moviment propi Dec: | -35 |
| B-T magnitude: | 5.899 |
| V-T magnitude: | 5.968 |
Catàlegs i designacions:
|
INHABITED SKY
