Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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.
| Spectroscopic orbits of potential interferometric binaries
We are obtaining high-resolution, red-wavelength spectra at McDonald andKitt Peak National Observatory to improve the orbits of knownspectroscopic binaries that are potential targets for ground-basedoptical interferometers. The combination of such observations willproduce three-dimensional orbits from which very accurate masses andorbital parallaxes can be obtained for double-lined systems. Thisspectroscopic program will be expanded and placed on the menu of the 2meter Automatic Spectroscopic Telescope of Tennessee State Universityonce it commences routine operation.
| Magnetic activity of six young solar analogues I. Starspot cycles from long-term photometry
A long-term photometric monitoring of a selected sample of solaranalogues has been carried out since early nineties as part of The Sunin time project, which is aimed at a multiwavelength study of stars withsolar-like global properties, but with different ages and thus atdifferent stages of their evolution. The extended time sequence ofground-based observations collected over more than a decade as part ofthis program has revealed the existence of starspot cycles. Also fromthese data it is possible to investigate surface differential rotationof the stars. In this paper we present the photometry collected to dateand report on cycles search for a selected subsample of five youngsingle G0-G5V stars with ages between =~ 130 Myr and 700 Myr:EK Dra, pi 1 UMa, HNPeg, k1 Cet and BE Cet.Also we include in this study the Pleiades-age ( =~ 130 Myr) K0V starDX Leo (HD 82443). All the cited stars show activitycycles whose period is, furthermore, the first determined fromphotometric data. They are compared to those activity cycles derivedfrom CaII H&K emission fluxes and differences are discussed. All thecycle periods, except for EK Dra, fit well the empirical relations withglobal stellar parameters derived from larger stellar samples. Thefollowing results are also inferred from the present study: i) thefastest rotating stars tend to have longer cycles; ii) the range in theobserved cycle lengths seems to converge with stellar age from a maximumdispersion around the Pleiades' age towards the solar cycle value at theSun's age; iii) the overall short- and long-term photometric variabilityincreases with inverse Rossby number with very high correlation degree,indicating that the level of magnetic activity at least in photosphereis still controlled by the stellar rotation even on the longest timescales; iiii) the increase with inverse Rossby number of the long-termoverall photometric variability seems to level off at the highestrotation rate, which may be interpreted as due to a saturation in thelevel of photospheric magnetic activity around the activity maximum.
| Activity cycle and surface differential rotation of the single Pleiades star HD 82443 (DX Leo)
The results of a long-term photometric monitoring of the young Pleiadesmoving group member HD 82443 are presented. A sequence of fifteenoptical light curves obtained from 1989 to 1998 confirms the presence ofa rotational modulation with a mean period of 5.377 days attributable tocool photospheric spots. The Maximum Entropy and the Tikhonovregularization criteria have been applied to compute maps of thephotospheric spot pattern. They show that the total spotted area issubject to cyclic changes as large as ~ 10% of the star's surface with amean period of 3.89 yr. The seasonal photometric period shows variationscorrelated with the phase of the activity cycle, which can beinterpreted as the result of a migration of the starspots in latitudeover a differentially rotating star. The dependence of the photometricperiod on the cycle phase is opposite that of the Sun and similar tothose observed in HD 114710 and HD 10476. A lower limit for theamplitude of the differential rotation in latitude can be estimated tobe (Delta Omega )/(Omega ) =~ 0.04. Nearly simultaneous UV observationsobtained in 1991 show the presence of chromospheric and transitionregion plages which do not seem to be in close spatial association withthe photospheric spots.
| Delta a and Stroemgren photometry of stars in the Renson-catalogue of AP and AM stars
We have observed 131 stars of \cite[Renson's (1991)]{re91} catalogue ofAp and Am stars both in the Stroemgren & Maitzen's (1976) Delta asystem as a contribution to the photometric studies of the lambda 5200broad band flux depression feature in chemically peculiar stars. Withfew exceptions the probability grouping of Renson for membership in theCP2 group of peculiar stars is nicely reflected by peculiar values ofDelta a. Comparison with already available Delta a values yieldsslightly larger values due to a minor shift in the filter g_1 samplingthe depression. As found by \cite[Maitzen & Vogt (1983)]{ma83} theGeneva system peculiarity parameters correlate well with Delta a. Thisstudy demonstrates the advantageous performance of a photoelectricphotometer with a rapidly rotating filter wheel moving in a stop and gomode. Tables 3 and 4 are also available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On the nature of the AM phenomenon or on a stabilization and the tidal mixing in binaries. II. Metallicity and pseudo-synchronization.
We reveal sufficient evidences that for Am binaries the metallicitymight depend on their orbital periods, P_orb_, rather than on vsini. Inparticular, δm_1_ index seems to decrease with increasing orbitalperiod up to at least P_orb_=~50d, probably even up to P_orb_=~200d.This gives further support to our "tidal mixing + stabilization"hypothesis formulated in Part I. Moreover, while the most metallic Amstars seem to have rather large periods the slowest rotators are foundto exhibit substantially shorter P_orb_. A questioning eye is thus caston the generally adopted view that Am peculiarity is caused by asuppressed rotationally induced mixing in slowly rotating `single'stars. The observed anticorrelation between rotation and metallicity mayhave also other than the `textbook' explanation, namely being the resultof the correlation between metallicity and orbital period, as themajority of Am binaries are possibly synchronized. We further argue thatthere is a tendency in Am binaries towards pseudo-synchronization up toP_orb_=~35d. This has, however, no serious impact on our conclusionsfrom Part I; on the contrary, they still hold even if this effect istaken into account.
| Starspots on the Young Single K0V Star HD 82443
Not Available
| On the nature of the AM phenomenon or on a stabilization and the tidal mixing in binaries. I. Orbital periods and rotation.
The paper casts a questioning eye on the unique role of the diffusiveparticle transport mechanism in explaining the Am phenomenon and arguesthat the so-called tidal effects might be of great importance incontrolling diffusion processes. A short period cutoff at =~1.2d as wellas a 180-800d gap were found in the orbital period distribution (OPD) ofAm binaries. The existence of the former can be ascribed to the state ofthe primaries with the almost-filled Roche lobes. The latter couldresult from the combined effects of the diffusion, tidal mixing andstabilization processes. Because the tidal mixing might surpassdiffusion in the binaries with the orbital periods P_orb_ less thanseveral hundred days and might thus sustain the He convection zone,which would otherwise disappear, no Am stars should lie below thisboundary. The fact that they are nevertheless seen there implies theexistence of some stabilization mechanism (as, e.g., that recentlyproposed by Tassoul & Tassoul 1992) for the binaries with orbitalperiods less than 180d. Further evidence is given to the fact that theOPD for the Am and the normal binaries with an A4-F1 primary arecomplementary to each other, from which it stems that Am stars are closeto the main sequence. There are, however, indications that they haveslightly larger radii (2.1-3 Rsun_) than expected for theirspectral type. The generally accepted rotational velocity cutoff at=~100km/s is shown to be of little value when applied on Am binaries ashere it is not a single quantity but, in fact, a function of P_orb_whose shape is strikingly similar to that of the curves of constantmetallicity as ascertained from observations. This also leads to thewell known overlap in rotational velocities of the normal and Am starsfor 402.5d.We have exploited this empirical cutoff function to calibrate thecorresponding turbulent diffusion coefficient associated with tidalmixing, having found out that the computed form of the lines of constantturbulence fits qualitatively the empirical shape of the curves ofconstant metallicity. As for larger orbital periods(20d55km/s found by Burkhart(1979) would then be nothing but a manifestation of insufficientlypopulated corresponding area of larger P_orb_.
| 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.
| MK morphology of AM stars
We present the results of an analysis of the spectra obtained for asample of 27 Am stars. We find evidence for the presence of groups amongthese stars and argue that all Am stars exhibit a pseudoluminosityeffect.
| The period distribution of unevolved close binary systems
Period distributions have been examined for various spectral types ofabout 600 (eclipsing and spectroscopic) close binaries, which are likelyto be substantially unevolved. The comparison with the previouscorresponding analyses of extensive (but heterogeneous) binary samplesallows a clarification of the extent of the evolutionary andobservational selection effects. Remarkably, this analysis reveals agreat deficiency of short period binaries (with periods corresponding tocase A mass transfer) in the whole spectral range. For the late spectraltypes, this result may be connected with postformation angular momentumloss caused by stellar wind magnetic braking; at least for the late Band A spectral range, a ready interpretation of this finding is thatclose binaries of corresponding periods and spectral types are rarelyformed.
| Statistics of categorized eclipsing binary systems Lightcurve shapes, periods, and spectral types
The statistics of the light curve morphologies, eclipse depths, orbitalperiods, and spectral types of about 1000 eclipsing binary systems areexamined, after attempting to subdivide these binaries into variousbasic evolutionary categories. The applicability of statisticalcriteria, based on light curve morphologies and eclipse depths, for thecategorization of eclipsing binaries has been found more limited thanpreviously believed. In particular, EW-type light curves turn out to begood indicators of contact systems (though not conversely), while EA-and EB-type light curves have little physical significance. Moreover,the study reveals a strong deficit of short-period noncontact systems inthe whole spectral range, together with an underabundance of early-typecontact binaries (compared with the number of late-type contact pairs).Interestingly, the distribution of evolved Algol-type systems isshifted, on average, to periods longer than those of unevolved detachedsystems in the OB and early A spectral range (and to shorter periods inthe F spectral range).
| Seventh catalogue of the orbital elements of spectroscopic binary systems.
Not Available
| Binaires spectroscopiques-13e catalogue complementaire.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...27...55P&db_key=AST
| UVBY BET photometry of equatorial and southern bright stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...27...47H&db_key=AST
| UBV RI Observations of Miscellaneous Stars
Not Available
| A Possible Eclipse in HD 82191
Not Available
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Aslan |
| Sað Açýklýk: | 09h31m17.39s |
| Yükselim: | +27°23'14.1" |
| Görünürdeki Parlaklýk: | 6.625 |
| Uzaklýk: | 140.647 parsek |
| özdevim Sað Açýklýk: | -31.6 |
| özdevim Yükselim: | -24.7 |
| B-T magnitude: | 6.729 |
| V-T magnitude: | 6.634 |
Kataloglar ve belirtme:
|
