Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
On-line database of photometric observations of magnetic chemically peculiar stars
We present our extensive project of the On-line database ofphotometric observations of magnetic chemically peculiar stars tocollect published data of photometric observations of magneticchemically peculiar (mCP) stars in the optical and near IR regions. Nowthe nascent database contains more than 107 000 photometric measurementsof 102 mCP stars and will be continually supplemented with published ornew photometric data on these and about 150 additional mCP stars. Thisreport describes the structure and organization of the database.Moreover, for the all included data we estimated the error ofmeasurements and the effective amplitudes of the light curves.
| Elemental Abundance Studies of CP Stars. The Silicon Stars HD 87240 and HD 96729
We compared elemental abundances of field and open cluster Ap Si stars.In particular, an analysis of the Ap Si stars HD 87240 and HD 96729 ispresented using an ATLAS9 model atmosphere and observational materialtaken with a REOSC echelle spectrograph attached to the Jorge Sahade2.15 m telescope at CASLEO. These chemically peculiar (CP) stars belongto the southern hemisphere open clusters NGC 3114 and NGC 3532,respectively. For HD 87240 and HD 96729, C is mostly solar, Mg and S areslightly underabundant, Si and Ca are overabundant by factors between1--10. Heavier elements are all overabundant, TiCrFe by factors of 10, SrYZr by factors between 100--1000 and rare earths by factors of 1000 or more.
| Temperature Behavior of Elemental Abundances in the Atmospheres of Magnetic Peculiar Stars
We analyze the temperature dependence of the abundances of the chemicalelements Si, Ca, Cr, and Fe in the atmospheres of normal, metallic-line(Am), magnetic peculiar (Ap), and pulsating magnetic peculiar (roAp)stars in the range 6000 15000 K. The Cr and Fe abundances in theatmospheres of Ap stars increase rapidly as the temperature rises from6000 to 9000 10000 K. Subsequently, the Cr abundance decreases to valuesthat exceed the solar abundance by an order of magnitude, while the Feabundance remains enhanced by approximately +1.0 dex compared to thesolar value. The temperature dependence of the abundances of theseelements in the atmospheres of normal and Am stars is similar in shape,but its maximum is several orders of magnitude lower than that observedfor Ap stars. In the range 6000 9500 K, the observed temperaturedependences for Ap stars are satisfactorily described in terms ofelement diffusion under the combined action of gravitational settlingand radiative acceleration. It may well be that diffusion also takesplace in the atmospheres of normal stars, but its efficiency is very lowdue to the presence of microturbulence. We show that the magnetic fieldhas virtually no effect on the Cr and Fe diffusion in Ap stars in therange of effective temperatures 6000 9500 K. The Ca abundance and itsvariation in the atmospheres of Ap stars can also be explained in termsof the diffusion model if we assume the existence of a stellar wind witha variable moderate rate of (2 4) × 10- 15 M ȯ yr-1.
| uvby FCAPT photometry of the mCP stars HR 2258, MW Vul, and HR 9017 and the HgMn star 46 ρ Aqr
Differential Strömgren uvby observations from the Four CollegeAutomated Photoelectric Telescope are presented for the magnetic CP(mCP) stars HR 2258, MW Vul, and HR 9017 and the HgMn star 46 ρ Aqr.A period for HR 2258 of 15.0313 days satisfactorily phases photometryover a 30 year time span. Recent observations of MW Vul agree in phasingwith those taken 13 years ago, but the amplitudes in u, v, b, and y aregreater and the light curves have changed shape especially in thefalling branch. This type of behavior has not been seen before in anyslowly rotating mCP star. It is a signature of the precession of therotational axis which brings different parts of the surface into view. Aperiod of 0.92738 days is found for HR 9017 which is similar to thatderived by Winzer. Changes in the v-c values between observations takenin the Spring and Fall of 2003 for 46 ρ Aqr may be due to itscompanion.Tables 2-4 and 6 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/429/317
| Spectral Classification of Stars in A Supplement to the Bright Star Catalogue
MK spectral types are given for about 584 stars in A Supplement to theBright Star Catalogue. These are compared with Hipparcos parallaxes tocheck the reliability of those classifications. The estimated errors are+/-1.2 subtypes, and 10% of the luminosity classes may be wrong.
| Line Identification of the Si Star HD 87240
Line identifications are presented for the peculiar Apstar HD7240(δ = - 59° 51' 00.1'') in the spectral region λλ3710-5520. This object is a member of the southern open cluster NGC114.Comparison of this object with other field silicon stars shows that itshares many of their line anomalies.
| Abundance determinations with Blackwell diagrams
We have performed an elemental abundance analysis for Sirius, Vega, andthree peculiar silicon stars: HD 43819, HD 192913 and HD 133029 usingBlackwell diagrams and observational data taken from the literature. Wehave compared our results with previous abundance and microturbulencevelocity determinations to check the validity of Blackwell diagramsapplied to CP stars. We found a very good agreement.
| Abundance Analysis of the Silicon Star HR 6958
The elemental composition of the chemically peculiar star HR6958 hasbeen studied with emphasis on doubly ionized rare earths. A visualregion spectrum taken with the ELODIE spectrograph at the Haute-ProvenceObservatory was analyzed. A total of 40 elements including Pr III , Nd III , Tb III , Dy III , Ho III , and Er III were identified andtheir abundances computed. He is deficient by over 1dex with respect tothe Sun; the light elements (C-Ca), except for Si, have solarabundances; the iron group elements (Sc-Fe) are overabundant by 1 dex to2dex, with Ti and Cr highly overabundant; and the lanthanide rare earthsare overabundant by 3dex to 4dex. This abundance pattern with Hedeficient, Si, Ti, Cr, Sr, and Pr overabundant indicates that HR6958 isa member of Si stars.
| 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
| Radiative lifetime and oscillator strength determinations in Sm III
Radiative lifetimes of 6 levels belonging to the4f5(6Hdeg,6Fdeg)5d configuration of Sm III have beenmeasured for the first time using a time-resolved laser-inducedfluorescence technique. Experimental data have been compared withsemi-empirical calculations. The agreement is excellent for 4 levelswith 6Fdeg as a parent term. Larger discrepancies(53 and 37%) are observed for 2 levels with 6Hdegand 6Fdeg, respectively, as a parent term and areexplainable by strong mixing and cancellation effects occurring in theline strength calculations which are responsible of ``instabilities''occurring in the lifetimes considered as a function of J value withinthe term. Branching ratios for the lines depopulating the levels ofinterest have been measured by Fourier transform spectroscopy. A firstset of oscillator strengths has been deduced for this ion.
| Core-polarization effects in doubly ionized cerium (Ce III) for transitions of astrophysical interest
The importance of core-polarization effects on oscillator strengthdetermination in Ce III is emphasized. The inclusion of these effects inrelativistic Hartree-Fock (HFR) calculations leads to theoreticallifetime values for some 4f6p levels of this ion in close agreement withrecent time-resolved laser-induced fluorescence measurements. These newatomic data, the most accurate to date, have allowed the refinement ofthe stellar abundance determination of cerium in the chemically peculiarstar HD 192913, but have not altered in a drastic way the conclusionsderived in recent analyses regarding the overabundance of this element.
| Multiplicity among chemically peculiar stars. II. Cool magnetic Ap stars
We present new orbits for sixteen Ap spectroscopic binaries, four ofwhich might in fact be Am stars, and give their orbital elements. Fourof them are SB2 systems: HD 5550, HD 22128, HD 56495 and HD 98088. Thetwelve other stars are: HD 9996, HD 12288, HD 40711, HD 54908, HD 65339,HD 73709, HD 105680, HD 138426, HD 184471, HD 188854, HD 200405 and HD216533. Rough estimates of the individual masses of the components of HD65339 (53 Cam) are given, combining our radial velocities with theresults of speckle interferometry and with Hipparcos parallaxes.Considering the mass functions of 74 spectroscopic binaries from thiswork and from the literature, we conclude that the distribution of themass ratio is the same for cool Ap stars and for normal G dwarfs.Therefore, the only differences between binaries with normal stars andthose hosting an Ap star lie in the period distribution: except for thecase of HD 200405, all orbital periods are longer than (or equal to) 3days. A consequence of this peculiar distribution is a deficit of nulleccentricities. There is no indication that the secondary has a specialnature, like e.g. a white dwarf. Based on observations collected at theObservatoire de Haute-Provence (CNRS), France.Tables 1 to 3 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/394/151Appendix B is only available in electronic form athttp://www.edpsciences.org
| Elemental abundance study of the CP star HD 206653
An analysis of the abundances of the Silicon star HD 206653 is presentedusing an ATLAS9 model atmosphere and observational material taken with aREOSC echelle spectrograph attached to the Jorge Sahade 2.15 m telescopeat CASLEO. The light elements are solar or deficient except siliconwhich is overabundant by a factor of 5. The iron peak elements are alloverabundant by factors between 10 and 50. Sr and Y are around 1000times the solar values. Among the Rare Earths only Ce and Eu areidentified; both are overabundant by large factors.
| Experimental and theoretical studies of DyIII: radiative lifetimes and oscillator strengths of astrophysical interest
The lifetimes of three short-lived levels belonging to the4f96p configuration and of two long-lived levels of the4f95d configuration of DyIII have been measured for the firsttime using time-resolved laser-induced fluorescence techniques. They arein good agreement with theoretical values calculated within theframework of a pseudo-relativistic configuration interactionapproximation. Using the experimental lifetimes and the theoreticalbranching fractions, a first set of transition probabilities ofastrophysical interest has been obtained for DyIII.
| Measurement of lifetimes by laser-induced fluorescence and determination of transition probabilities of astrophysical interest in Nd III
Selective lifetime measurements by time-resolved laser-inducedfluorescence spectroscopy for 5 levels belonging to the 4f35dconfiguration of doubly ionized neodymium provide a first and usefulexperimental test of the relativistic Hartree-Fock calculations in thision of astrophysical interest. As a consequence, the accuracy of thetransition probabilities deduced in the present work is well assessed.These new data are expected to help astrophysicists in the future torefine the analysis of the composition of chemically peculiar starswhich frequently show large overabundances of lanthanides when comparedto the solar system standards.
| Radiative lifetime measurements and oscillator strengths of astrophysical interest in Ho III
Radiative lifetimes of three long-lived levels belonging to the4f105d configuration of Ho III have been measured, for thefirst time, using the time-resolved laser-induced fluorescencetechnique. A good agreement between the experimental lifetimes andtheoretical results obtained within a multiconfigurationalpseudo-relativistic Hartree-Fock (HFR) approach includingcore-polarization (CP) effects is observed provided an adequate scalingfactor is applied to the <4f|r|5d> transition matrix element. Fromthe comparison theory-experiment, it has been possible to assess thereliability of the oscillator strengths of the 4f-5d transitions ofastrophysical interest, particularly for the lines depopulating thelevels considered in the present work. The present results fill in a gapconcerning the f-values of doubly ionized holmium and are needed for aquantitative evaluation of the holmium abundance in some peculiar stars.
| On the Periods of the Magnetic CP Stars
An HR diagram annotated to show several ranges of photometericallydetermined periods has been constructed for the magnetic CP stars whoseperiods have been determined by the author and his collaborators. Thedistribution of periods reflects both the initial conditions as well asthe subsequent stellar histories. Since the stellar magnetic field doesnot penetrate the convective core, eventually a shear zone near thecore-radiative envelope boundary may develop which produces turbulenceand modifies the field. Many, but not all, of the most rapidly rotatingmCP stars are close to the ZAMS and some of the least rapidly rotatingmCP stars are the furthest from the ZAMS.
| Elemental abundance studies of CP stars. III. The magnetic CP stars alpha Scl and HD 170973
Fine analyses of the magnetic CP stars alpha Scl and HD 170973 arepresented using ATLAS9 model atmospheres which have same bulkmetallicity as the deduced abundances. The light elements are mostlysolar except for silicon, and all the heavier elements except nickel inHD 170973, which is solar, are greatly overabundant. The iron peakelements are typically 10 times overabundant, Sr is of order of 1000times solar, Y and Zr are of order of 100 times solar. The rare earthsare 1000 or more times overabundant.
| Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
A selection criterion based on the relative strength of the largestpeaks in the amplitude spectra, and an information criterion are used incombination to search for multiperiodicities in Hipparcos epochphotometry. The method is applied to all stars which have beenclassified as variable in the Hipparcos catalogue: periodic, unsolvedand microvariables. Results are assessed critically: although there aremany problems arising from aliasing, there are also a number ofinteresting frequency combinations which deserve further investigation.One such result is the possible occurrence of multiple periods of theorder of a day in a few early A-type stars. The Hipparcos catalogue alsocontains a number of these stars with single periodicities: such starswith no obvious variability classifications are listed, and informationabout their properties (e.g., radial velocity variations) discussed.These stars may constitute a new class of pulsators.
| Ab initio calculations of oscillator strengths and Landé factors for Nd Iii
Theoretical calculations of oscillator strengths and Landég-factors made with the Cowan code are presented for the rare-earth ionNd Iii. The emphasis is on transitions in the optical region of thespectrum. Comparisons of previous ab initio calculations of this typefor other lanthanides (e.g., La Ii, Ce Iii, and Lu Ii) with publishedexperimental and theoretical data suggest that the accuracy of thelog(gf) values for individual transitions should be about +/-0.15 dex inthe absence of significant core polarization effects; the g-factorsshould be good to better than 5%, except in a few cases where termmixing is important. Applications of the data are made in thecalculation of neodymium abundances in the atmospheres of the chemicallypeculiar stars HD 101065 (``Przybylski's star") andHD 122970.
| The electron-impact broadening effect in CP stars: the case of La II , La II i, EU II , and EU II i lines
The electron-impact widths and shifts for six Eu ii lines and widths forthree La ii , and six La ii i multiplets have been calculated by usingthe modified semiempirical method. Estimation for Stark widths of664.506 nm (Eu ii ) and 666.634 nm (Eu ii i) lines are given as well.The influence of the electron-impact mechanism on line shapes andequivalent widths in hot star atmospheres has been considered.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| Elemental abundance studies of CP stars. II. The silicon stars HD 133029 and HD 192913
Fine analyses of the silicon stars HD 133029 and HD 192913 are presentedusing ATLAS9 model atmospheres whose predictions fit the optical regionspectrophotometry and Hγ profiles and have the same bulkmetallicity as the deduced abundances. Both are very He poor stars. Thelight elements are mostly solar except for silicon, and all the heavierelements, except nickel in HD 133029 which is solar, are greatlyoverabundant. The iron peak elements are typically 10 timesoverabundant. SrYZr are of order of 100 times solar. The rare earths are1000 or more times overabundant. Table~4 is is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| 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 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.
| 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.
| Oscillator strength calculations in CE III: application to HD 200311
We have calculated oscillator strengths for the Ce III spectrum usingthe atomic structure code of R. D. Cowan. The results are used todetermine the cerium abundance in the silicon star HD 200311. From thedominant ion (Ce^++), we find an excess of 5 dex. We find very goodagreement with the abundance obtained from Ce II lines. Whileuncertainties remain with the oscillator strengths, it is no longerpossible to assume that underionization could explain the extraordinaryabundance excess of the lanthanide cerium in this hot, magnetic,chemically peculiar star.
| 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.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Volpetta |
| Ascensione retta: | 20h16m27.20s |
| Declinazione: | +27°46'33.9" |
| Magnitudine apparente: | 6.64 |
| Distanza: | 432.9 parsec |
| Moto proprio RA: | 6.9 |
| Moto proprio Dec: | 4.9 |
| B-T magnitude: | 6.573 |
| V-T magnitude: | 6.635 |
Cataloghi e designazioni:
|
INHABITED SKY
