目录
图像
上传图像
DSS Images Other Images
相关文章
On the detection of chemically peculiar stars using Δa photometry
We have summarized all Δ a measurements for galactic field stars(1474 objects) from the literature published over more than two decades.These measurements were, for the first time, compiled and homogeneouslyanalyzed. The Δ a intermediate band photometric system samples thedepth of the 5200 Å flux depression by comparing the flux at thecenter with the adjacent regions with bandwidths of 110 Å to 230Å. Because it was slightly modified over the last three decades,we checked for systematic trends for the different measurements butfound no correlations whatsoever. The Δ a photometric system ismost suitable to detecting magnetic chemically peculiar (CP) stars withhigh efficiency, but is also capable of detecting a small percentage ofnon-magnetic CP objects. Furthermore, the groups of (metal-weak)λ Bootis, as well as classical Be/shell stars, can besuccessfully investigated. In addition, we also analyzed the behaviourof supergiants (luminosity class I and II). On the basis of apparentnormal type objects, the correlation of the 3σ significance limitand the percentage of positive detection for all groups was derived. Wecompared the capability of the Δ a photometric system with theΔ (V1 - G) and Z indices of the Geneva 7-color system to detectpeculiar objects. Both photometric systems show the same efficiency forthe detection of CP and λ Bootis stars, while the indices in theGeneva system are even more efficient at detecting Be/shell objects. Onthe basis of this statistical analysis it is possible to derive theincidence of CP stars in galactic open cluster and extragalactic systemsincluding the former unknown bias of undetected objects. This isespecially important in order to make a sound statistical analysis ofthe correlation between the occurrence of these objects andastrophysical parameters such as the age, metallicity, and strength ofglobal, as well as local, magnetic fields.
| 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
| CP2 stars as viewed by the UVBY H_beta system
The aim of this work is to study the capacity of the uvby H_βsystem for detecting the chemically peculiar (CP) stars based on theeffect that peculiar features in the flux distribution have on all theStromgren-Crawford indices. Our study focuses on the classical magneticpeculiar stars (CP2), though Am stars (CP1) are also included forcomparison with cool CP2 stars. Satisfactory results were obtained forhot CP2 stars: the definition of a new index p, which is a linearcombination of uvby H_β colours, allowed us to separate a highpercentage of hot CP2 stars from normal stars. According to this newindex, 60 new CP2 candidates are proposed. The working sample wasextracted from The General Catalogue of Ap and Am stars by \cite[Rensonet al. (1991)]{ren91}. Photometric observations to enlarge the sample ofCP2 stars with complete uvby H_β photometry were carried out. Theseobservations are also reported in the present paper. The new index p isalso used to correct the reddening of early CP2 stars computed as ifthey were normal stars. Tables 2, 3 and 7 are also available inelectronic form from CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Incidence of X-ray sources among magnetic chemically peculiar stars
Cash & Snow (1982) and Golub et al. (1983) have detected X-rayemission from 3 out of 7 observed magnetic chemically peculiar (CP)stars. Although the incidence of X-ray sources apparently is very high,these authors concluded that such emission is not unquestionable becauseof the presence of a companion. To determine the incidence of X-raysources among hot CP stars, I have checked the list of B-type starsmeasured by Grillo et al. (1992) selecting 90 stars. Of the 4 magneticCP stars showing X-ray emission 3 are members of a binary system. Thusit appears that detectable X-ray emission from magnetic CP stars is notvery common and still questionable. To find out whether HD 37017presents X-ray emission (Drake et al. 1987) or not (Grillo et al. 1992),I have analyzed an HRI frame from the ROSAT satellite finding noevidence for X-ray emission at this star's position.
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| Stromgren and H-beta photometry of stars earlier than G0 in 5 areas containing high latitude molecular clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989A&AS...80..127F&db_key=AST
| 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.
| A list of candidates for high-velocity AP stars
'Reduced proper motion' is used to select from a catalog of over fifteenhundred Ap stars those that probably have a high velocity. A list of 164candidates is presented, 22 of them having very probably high velocity.Some of them could be the first specimens of late Ap stars with highvelocity. The possible relation to horizontal branch stars is alsodiscussed.
| Photoelectric photometry of peculiar and related stars. II Delta-a-photometry of 339 southern Ap-stars
Delta-a system photometry of the sample of Ap stars from Bidelman andMcConnell's (1973) catalogue is discussed. Comparing delta-ameasurements in four marginally different systems, slight modificationsof the delta-a photometric system are found to be uncritical except forthe wavelength of the depression filter g2. The reddening-free index isvery efficient for silicon and chromium stars, and the spectroscopicdetection probability for these stars decreases with decreasingtemperature. Comparison of delta-a results with the Geneva index delta(V1-G) confirms that the latter's efficiency in recognizing peculiaritydrops strongly from hot to cool Ap stars. A decrease of delta-a towardsthe hot Ap stars is found using the a vs. (u-b) diagram, implying thatb-v is an unsuitable temperature indicator for such stars. The lowaverage intrinsic variability of the delta-a in the sample, whencompared with the small variation of integrated surface magnetic fieldsin case of dipole configuration, implies that the wavelength 5200feature correlates with the surface magnetic field strength.
| Photoelectric observations of peculiar A and related stars. I - Stromgren photometry of 341 AP stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&AS...36..477V&db_key=AST
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
