Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
High-Resolution Infrared Spectroscopy of the Brown Dwarf ɛ Indi Ba
We report on the analysis of high-resolution infrared spectra of thenewly discovered brown dwarf ɛ Ind Ba. This is the closest knownbrown dwarf to the solar system, with a distance of 3.626 pc. Spectracovering the ranges of λλ2.308-2.317 μm andλλ1.553-1.559 μm were observed at a resolution ofλ/Δλ=R=50,000. The physical parameters of effectivetemperature and surface gravity are derived for ɛ Ind Ba bycomparison with model spectra calculated from atmospheres computed usingunified cloudy models. The results are Teff=1500+/-100 K,logg=5.2+/-0.3 (in units of cm s-2), placing it in thecritical boundary between the late L and early T dwarfs. The highspectral resolution also allows us to measure an accurate projectedrotational velocity, with vsini=28+/-3 km s-1. Combined witha published luminosity for ɛ Ind Ba [withlog(L/Lsolar)=-4.71], the derived parameters result in a``spectroscopic'' mass estimate of ~30MJ, a radius of ~0.062Rsolar, and a maximum rotational period of ~3.0 hr. Acompilation and comparison of effective temperatures derived fromspectroscopy using model atmospheres versus those derived fromluminosities and theoretical Mbol-radius relations reveal asystematic disagreement in the Teff scale. The source of thisdisagreement is unknown.Based on observations obtained at the Gemini Observatory, which isoperated by the Association of Universities for Research in Astronomy,Inc., under a cooperative agreement with the NSF on behalf of the Geminipartnership: the National Science Foundation (United States), theParticle Physics and Astronomy Research Council (United Kingdom), theNational Research Council (Canada), CONICYT (Chile), the AustralianResearch Council (Australia), CNPq (Brazil), and CONICRT (Argentina).
| The Black Hole Masses and Host Galaxies of BL Lacertae Objects
We have measured the central stellar velocity dispersion in the hostgalaxies of 11 BL Lac objects with redshifts z<=0.125. The range ofvelocity dispersions, ~170-370 km s-1, is similar to that ofnearby radio galaxies. Using the correlation between stellar velocitydispersion and black hole mass defined for nearby galaxies, we deriveestimates of the black hole masses in the range107.9-109.2 Msolar. We do not find anysignificant difference between the black hole masses inhigh-frequency-peaked and low-frequency-peaked BL Lac objects. Combiningthe velocity dispersions with previously measured host galaxy structuralparameters, we find that the host galaxies lie on the fundamental planeof elliptical galaxies. This supports the conclusions of imaging studiesthat the majority of BL Lac hosts are normal giant elliptical galaxies.
| Extent of Excess Far-Infrared Emission around Luminosity Class III Stars
With the Infrared Space Observatory, we conducted 3×3 pixelimaging photometry of 12 luminosity class III stars, which werepreviously presumed to have dust particles around them, at far-infraredwavelengths (60 and 90 μm). Eleven out of 12 targets show a peak ofexcess (above photosphere) far-infrared emission at the location of thestar, implying that the dust particles are truly associated with stars.To estimate the size of the excess emission source, the flux ratio ofcenter to boundary pixels of the 3×3 array was examined. Theradius of the dust emission is found to be ~3000 to ~10,000 AU for athin shell distribution and ~5000 to ~25,000 AU for a uniformdistribution. We consider three models for the origin of the dust:disintegration of comets, sporadic dust ejection from the star, andemission from nearby interstellar cirrus. The data seem to rule out thefirst model (as far as the ``Kuiper belt-like'' particles are assumed tobe large blackbody grains) but do not enable us to choose between theother two models.
| 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
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,199 of the stars in Part I are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives in addition to the SI mode the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
| Comparison of the ACRS and PPM Catalogs with the FK5 in the Southern Hemisphere
A comparison of the Astrographical Catalog of Reference Stars (ACRS) andthe Positions and Proper Motions Catalog (PPM) with the FK5 in thesouthern hemisphere, is presented. To this aim, the positions of FK5stars uniformly spread over the celestial sphere were astrographicallytaken. These positions were reduced in the ACRS and PPM systems and thencompared with those from the FK5 for the epoch of observation. The (FK5- ACRS) and (FK5 - PPM) systematic differences thus obtained, in thedeclination range from -30o down to the South Pole, for themean epoch of 1994.50, are shown.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| Giants with infrared excess.
We have correlated optical and infrared catalogs in order to extract alarge sample of luminosity class III stars with known infrared fluxdensities. For a non-negligible fraction of G and K giants, afar-infrared excess emission was found, starting beyond 25μm. Anexplanation in terms of present-day mass loss thus becomes unlikely,since the dust should then be warmer and the excess emission less far inthe infrared. We believe that the far-infrared excesses of theseobjects, most likely first-ascent giants, are related to the Vegaphenomenon. The dusty disks around these stars, gradually cooled downduring their main-sequence phase, could be reheated once the star leavesthe main sequence and enters the luminous post-main-sequence phase. Thefairly large sample we constructed enables us to derive an estimationfor the occurrence of excesses. This fraction of G or K giants withfar-infrared excess appears to be distinctly smaller than amongmain-sequence stars. Since the higher radiation field of giants couldlead to a larger evaporation rate of the circumstellar debris, this factdoes not conflict with our hypothesis.
| The Stellar Content of Star Stream I
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1615E&db_key=AST
| Luminosity Class III Stars with Excess Far-Infrared Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...446L..79Z&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.
| Santiago Fundamental Catalogue - A catalogue of 1105 FK5 stars (equinox J2000.0)
The positions in right ascension and declination of 1105 FK5 stars,observed with a Meridian Circle during the period 1979 to 1991, aregiven. The average mean square error of a position, for the wholecatalog, is +/- 0.009 s in right ascension and +/- 0.10 arcsec indeclination. The mean epoch of the catalog is 1983.148.
| Physical data of the fundamental stars.
Not Available
| Santiago declination catalogue - A declination catalogue of 412 FK4 stars (equinox 1950.0)
This catalog contains the positions in declination, of 412 FK4 stars.The observations were carried out with the Repsold Meridian Circle atCerro Calan National Astronomical Observatory, during the period1963-1968. The average mean square error of one observation (for thewhole catalog) is + or - 0.13 arcsec. The mean epoch of observation ofthe catalog is 1965.75.
| IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
| Local photometric standards for CaII emission stars
UBV data are given for 108 stars which are suitable local standards for52 stars with strong Ca2 emissions. An additional eight stars wererejected as possible standards because of suspected variability.
| The dynamics of the giant dumbell galaxy IC 2082.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981MNRAS.195P..15C&db_key=AST
| Narrow-Band and Broad-Band Photometry of Red Stars. III. Southern Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJ...161..199E&db_key=AST
| Polarization measurements and magnetic field structure within the magellanic clouds.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&A.....6..294S&db_key=AST
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Masa |
| Sað Açýklýk: | 04h55m11.20s |
| Yükselim: | -74°56'13.0" |
| Görünürdeki Parlaklýk: | 5.47 |
| Uzaklýk: | 218.341 parsek |
| özdevim Sað Açýklýk: | 27.8 |
| özdevim Yükselim: | 61.9 |
| B-T magnitude: | 7.448 |
| V-T magnitude: | 5.63 |
Kataloglar ve belirtme:
|
INHABITED SKY
