Contents
Images
Upload your image
DSS Images Other Images
Related articles
Rotational velocities of A-type stars. III. Velocity distributions
Aims.A sample of v sin i of B9 to F2-type main sequence single stars hasbeen built from highly homogeneous {v sin i} parameters determined for alarge sample cleansed of objects presenting the Am and Ap phenomenon aswell as of all known binaries. The aim is to study the distributions ofrotational velocities in the mass range of A-type stars for normalsingle objects. Methods: .Robust statistical methods are used torectify the {v sin i} distributions for the projection effect and theerror distribution. The equatorial velocity distributions are obtainedfor about 1100 stars divided in six groups defined by the spectral type,under the assumption of randomly orientated rotational axes.Results: .We show that late B and early A-type main-sequence stars havegenuine bimodal distributions of true equatorial rotational velocitiesprobably due to angular momentum loss and redistribution that the starunderwent before reaching the main sequence. A striking lack of slowrotators is noticed among intermediate and late A-type stars.Full Table [see full text] is only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/671 Appendices areonly available in electronic form at http://www.aanda.org
| Instabilities in the excitation of non-radial pulsation modes in the δ Scuti star BV Circini
High resolution spectroscopic observations obtained in 1995 of theδ Scuti star BV Circini are analyzed and the results compared withthose obtained by Mantegazza et al. (\cite{Mantegazza02}) fromspectroscopic observations in 1996 and 1998. Non-radial pulsation modesboth of low and high degree have been observed. Most of them are thesame detected in the other two campaigns, however the strongesthigh-degree one (14.62 cd-1) is different from that observedin 1996 (13.85 cd-1), which in turn is different from thatobserved in 1998 (17.28 cd-1). The 13.85 cd-1smode is the only one of these independently detected in the threeseasons, in which it kept about the same amplitude. One high-degreeretrograde mode at 1.48 cd-1s has been independently detectedin the three campaigns. The mode amplitude variations are discussed andit is shown that large variations can occur from one year to the next.The mode identifications performed on the three datasets by means of thefit of line profile variations supply results in good agreement amongthemselves. The high degree prograde modes have azimuthal orders between12 and 14, while the retrograde one is about 7. Finally the stellarpulsation spectrum as derived from all the available spectroscopic andphotometric data, and which consists of about 20 terms, is discussed.Based on observations collected at ESO-La Silla.
| 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
| Close frequency pairs in Delta Scuti stars
The majority of the well-studied delta Scuti stars shows frequency pairsin the power spectra with frequency separations less than 0.06cd-1 (0.7 mu Hz) as well as amplitude variability. We examinethe interpretation in terms of separate excited stellar pulsation modes,single modes with variable amplitudes, and observational problems. Thevariable-phase technique, which examines the phase jumps near the timesof minimum amplitude of an assumed single frequency, is applied to theextensive data of the star BI CMi, which shows some of the most extremebehavior. The following results are found for the 5 features in thepower spectrum which could be explained as single modes with variableamplitudes or as double modes: for three features it can be shown thatthese are indeed pairs of separate pulsation modes beating with eachother: at times of minimum amplitude the phase jumps are observed andboth the observed amplitude and phase variations can be predictedcorrectly by assuming two separate modes of nearly equal frequencies.Artifacts caused by observational error, insufficient frequencyresolution or variable amplitudes can be ruled out. A fourth pair has aprobable origin in two excited modes, while a 5th case is inconclusivedue to long time scales of variability and small amplitudes. Theexistence of close frequency needs to be taken into account in planningthe lengths of earth-based as well as space campaigns so that sufficientfrequency resolution is obtained. Possible reasons for the existence ofclose frequencies in delta Scuti stars are considered. They include thedense frequency spacing caused by the presence of mixed modes,rotational splitting as well as near-coincidence of the frequencies ofmodes with different l values (the so-called Small Spacing).
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| Simultaneous intensive photometry and high resolution spectroscopy of delta Scuti stars. V. The high-degree modes in the pulsational content of BV Circini
We discuss here the pulsation properties of the delta Scuti star BVCircini on the basis of data obtained during a simultaneous photometricand spectroscopic campaign in 1996 and a spectroscopic one in 1998, andtaking also advantage of the previous photometric observations by Kurtz(\cite{kur81}). Nine pulsation modes were detected from photometry andthirteen from spectroscopy; five of them are in common to bothtechniques. The spectroscopic data give ample evidence of dramaticamplitude variations in some modes, in particular the strongestspectroscopic mode in 1998 was not detectable in 1996 data. The twodominant photometric modes (6.33 and 7.89 cd-1) are observedon both seasons. The typing of the modes was performed by means of asimultaneous model fit of line profile and light variations. The 6.33cd-1 photometric term is probably the fundamental radialmode, while the 7.89 cd-1 is a nonradial mode with m!=q 0.There are six high-degree prograde modes with an azimuthal order mranging from -12 to -14, and also a retrograde mode with m ~ 7. Thesemodes combined with the identification of the 6.33 cd-1 modeallowed us to estimate i ~ 60o for the value of theinclination of the rotation axis. An accurate evaluation of the mainstellar physical parameters is also proposed as a result of thepulsational analysis. Based on observations collected at ESO-La Silla(Proposals 57.E-0162, 61.E-0120).}
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly 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
| Simultaneous intensive photometry and high resolution spectroscopy of delta Scuti stars. IV. An improved picture of the pulsational behaviour of X Caeli
The delta Scuti star X Caeli has been the target of a simultaneousphotometric (14 consecutive nights) and spectroscopic campaign (8consecutive nights). From the analysis of light curves we were able topick up 17 frequency components, most of which were already detected intwo previous campaigns. The comparison with the results of the previouscampaigns shows that while some terms are rather stable (in particularthe dominant mode at 7.39 cd-1 ) others have conspicuousamplitude variations. 14 photometric terms have been also detected inthe radial velocity curve or in the analysis of the line profilevariations. There are no spectroscopic terms without photometriccounterparts, and this means that there are no high-degree modes asobserved in other delta Scuti stars. The simultaneous fit of light andline profile variations has allowed the estimation of the inclination ofrotational axis (about 70o) and the l,m identification formany modes. In particular there is clear evidence that the two shortestperiod modes are retrograde. Rather reliable results were found for thedominant mode which has l=1, m=-1. The resulting physical parameters ofits pulsation are in good agreement with the prediction of theoreticalmodels and suggest for this star a mixing length parameter of about 0.5.Finally the fundamental stellar physical parameters and their refinementare discussed in the light of the identification of the 7.47cd-1 term as a radial mode. Based on observations collectedat European Southern Observatory(Proposal 58.E-0278)
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A catalogue of variable stars in the lower instability strip.
Identifications, positions, photometry, spectra, some pulsationalfeatures, other astrophysical parameters and literature for 302pulsating variable stars in the lower instability strip, near the ZAMS,are given. About 185 stars have near homogeneous photometric informationin the Stroemgren's uvby-β photometric system. Thiscatalogue/database covers information published until November 1993.
| δ Scuti stars: a new revised list
An extensive and up to date list of δ Sct stars is presented. Thiscatalogue is intended to be a comprehensive review of observationalcharacteristics of all the δ Sct stars known until now, includingstars contained in earlier catalogues together with other new discoveredvariables, covering information published until November 1993. Globalinformation in the form of histograms and diagrams are also shown.
| Empirical P-L-C relation for Delta Scuti stars - A catalogue
An extensive and up-to-date list of 192 Delta Scuti stars is presented.Empirical period - luminosity - color (P-L-C) relations are obtained forthe four lowest modes corresponding to radial pulsations. Agreement withpredicted values indicates that, in general, both Stroemgren photometriccalibration and pulsation theory work well for these stars.
| Contributing factors to flux changes in nonradial stellar pulsations
The factors contributing to flux changes in nonradial stellar pulsationsare investigated under conditions applicable to a variety of pulsatingstar types by examining a linearized analytic representation of observedflux changes due to nonradial pulsations with mode indices (l,m).Histograms are presented, showing as a function of l, the relativeimportance of local temperature, geometry, pressure, and limb-darkeningvariations in contributing to nonradial flux changes. A procedure forthe comparison of observational light and color data with modelpredictions on an amplitude ratio versus phase difference plane isoutlined. Application of this procedure to data on Beta Cephei, 53Persei, Delta C Scuti, rapidly oscillating Ap, Cepheid, and ZZ Cetivariables stars is shown to agree with published data on these systems.
| The 67th Name-List of Variable Stars
Not Available
| Revised list of pulsating stars with ultra-short periods
A comprehensive list of 178 known Delta Scuti and RR Lyrae-stars ispresented. Using this revised list a HR diagram for these ultra shortperiod pulsating stars is plotted and the blue and red edges of theresultant instability strip are determined. Selection effects arediscussed, and the PLC relationship of Breger (1979) is tested usingdata from this list. Stars lying outside the defined instability regionare discussed.
| IAU Archives of Unpublished Observations of Variable Stars
Not Available
| The frequency analysis of low amplitude delta Scuti stars - VII. HD 208664.
Abstract image available at:http://adsabs.harvard.edu/abs/1982MNRAS.200..497K
| A Frequency Analysis of a New Delta-Scuti Star - HD132209
Abstract image available at:http://adsabs.harvard.edu/abs/1981MNRAS.196...53K
| Information on the Photoelectric Observations of Variable Stars Deposited at Odessa-Astronomical
Not Available
| The chemical evolution of the solar neighborhood. I - A bias-free reduction technique and data sample
The possible ways of measuring the age-metallicity relation for thegalactic disk in the neighborhood of the sun are discussed. It is shownthat the use of a field star sample chosen on the basis of effectivetemperature introduces a bias which results in a monotonic increase inthe metal abundance of the disk with time. However, if theage-metallicity relation for the disk can be shown to satisfy certaincriteria, the bias introduced in such a sample can be neglected: thegalactic disk apparently satisfies the criteria. It is concluded that asample analyzed through the use of uvby and H(beta) photometry inconjunction with a self-consistent set of theoretical isochronesprovides the least biased, most accurate estimate of the age-metallicityrelation for the disk.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | コンパス座 |
| Right ascension: | 15h01m02.24s |
| Declination: | -64°34'33.8" |
| Apparent magnitude: | 6.572 |
| Distance: | 127.389 parsecs |
| Proper motion RA: | -20.2 |
| Proper motion Dec: | -65.3 |
| B-T magnitude: | 6.908 |
| V-T magnitude: | 6.6 |
Catalogs and designations:
|
