내용
사진
사진 업로드
DSS Images Other Images
관련 글
The polar wind of the fast rotating Be star Achernar. VINCI/VLTI interferometric observations of an elongated polar envelope
Context: .Be stars show evidence of mass loss and circumstellarenvelopes (CSE) from UV resonance lines, near-IR excesses, and thepresence of episodic hydrogen emission lines. The geometry of theseenvelopes is still uncertain, although it is often assumed that they areformed by a disk around the stellar equator and a hot polar wind.Aims: .We probe the close environment of the fast rotating Be starAchernar at angular scales of a few milliarcseconds (mas) in theinfrared, in order to constrain the geometry of a possible polar CSE. Methods: .We obtained long-baseline interferometric observations ofAchernar with the VINCI/VLTI beam combiner in the H and K bands, usingvarious telescope configurations and baseline lengths with a wideazimuthal coverage. Results: .The observed visibility measurementsalong the polar direction are significantly lower than the visibilityfunction of the photosphere of the star alone, in particular at lowspatial frequencies. This points to the presence of an asymmetricdiffuse CSE elongated along the polar direction of the star. To ourdata, we fit a simple model consisting of two components: a 2Delliptical Gaussian superimposed on a uniform ellipse representing thedistorted photosphere of the fast rotating star. Conclusions: .Weclearly detected a CSE elongated along the polar axis of the star, aswell as rotational flattening of the stellar photosphere. For theuniform-ellipse photosphere we derive a major axis of θ_eq = 2.13± 0.05 mas and a minor axis of θ_pol = 1.51 ± 0.02mas. The relative near-IR flux measured for the CSE compared to thestellar photosphere is f = 4.7 ± 0.3%. Its angular dimensions areloosely constrained by the available data at ρ_eq = 2.7 ± 1.3mas and ρ_pol = 17.6 ± 4.9 mas. This CSE could be linked tofree-free emission from the radiative pressure driven wind originatingfrom the hot polar caps of the star.
| First results from the ESO VLTI calibrators program
The ESO Very Large Telescope Interferometer (VLTI) is one of the leadinginterferometric facilities. It is equipped with several 8.2 and 1.8 mtelescopes, a large number of baselines up to 200 m, and with severalsubsystems designed to enable high quality measurements and to improvesignificantly the limits of sensitivities currently available tolong-baseline interferometry. The full scientific potential of the VLTIcan be exploited only if a consistent set of good quality calibrators isavailable. For this, a large number of observations of potentialcalibrators have been obtained during the commissioning phase of theVLTI. These data are publicly available. We briefly describe theinterferometer, the VINCI instrument used for the observations, the dataflow from acquisition to processed results, and we present and commenton the volume of observations gathered and scrutinized. The result is alist of 191 calibrator candidates, for which a total of 12 066observations can be deemed of satisfactory quality. We present a generalstatistical analysis of this sample, using as a starting point theangular diameters previously available in the literature. We derive thegeneral characteristics of the VLTI transfer function, and its trendwith time in the period 2001 through mid-2004. A second paper will bedevoted to a detailed investigation of a selected sample, aimed atestablishing a VLTI-based homogeneous system of calibrators.
| The K-band intensity profile of R Leonis probed by VLTI/VINCI
We present near-infrared K-band interferometric measurements of the Mirastar R Leonis obtained in April 2001 and January 2002 with the VLTI, thecommissioning instrument VINCI, and the two test siderostats. Theseepochs correspond to near-maximum stellar variability phases ~0.08 and~1.02 (one cycle later), respectively. The April 2001 data cover a rangeof spatial frequencies (31 35 cycles/arcsecond) within the first lobe ofthe visibility function. These measurements indicate a center-to-limbintensity variation (CLV) that is clearly different from a uniform disk(UD) intensity profile. We show that these measured visibility valuesare consistent with predictions from recent self-excited dynamic Miramodel atmospheres that include molecular shells close tocontinuum-forming layers. We derive high-precision Rosseland diametersof 28.5 ± 0.4 mas and 26.2 ± 0.8 mas for the April 2001and January 2002 data, respectively. Together with literature estimatesof the distance and the bolometric flux, these values correspond tolinear radii of 350+50-40 R_ȯ and320+50-40 R_ȯ, and to effective temperaturesof 2930 ± 270 K and 3080 ± 310 K, respectively.Based on public commissioning data released from the ESO VLTI(www.eso.org/projects/vlti/instru/vinci/ vinci_data_sets.html)
| 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
| Dating Ptolemy's star catalogue through proper motions : the Hipparchan epoch.
Not Available
| 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).
| Photometric modelling of starspots - I. A Barnes-Evans-like surface brightness-colour relation using (Ic-K)
In the first part of this work, the empirical correlation of stellarsurface brightness FV with (Ic-K) broad-bandcolour is investigated by using a sample of stars cooler than the Sun. Abilinear correlation is found to represent well the brightness of G, Kand M giant stars. The change in slope occurs at (Ic-K)~2.1or at about the transition from K to M spectral types. The samerelationship is also investigated for dwarf stars and found to bedistinctly different from that of the giants. The dwarf star correlationdiffers by an average of -0.4 in (Ic-K) or by a maximum inFV of ~-0.1, positioning it below that of the giants, withboth trends tending towards convergence for the hotter stars in oursample. The flux distribution derived from theFV-(Ic-K) relationship for the giant stars,together with that derived from an FV-(V-K) relationship andthe blackbody flux distribution, is then utilized to compute syntheticlight V and colour (V-R)c, (V-I)c and (V-K) curvesof cool spotted stars. We investigate the effects on the amplitudes ofthe curves by using these FV-colour relations and by assumingthe effective gravity of the spots to be lower than the gravity of theunspotted photosphere. We find that the amplitudes produced by using theFV-(Ic-K) relationship are larger than thoseproduced by the other two brightness correlations, meaning smallerand/or warmer spots.
| Revision and Calibration of MK Luminosity Classes for Cool Giants by HIPPARCOS Parallaxes
The Hipparcos parallaxes of cool giants are utilized in two ways in thispaper. First, a plot of reduced parallaxes of stars brighter than 6.5,as a function of spectral type, for the first time separates members ofthe clump from stars in the main giant ridge. A slight modification ofthe MK luminosity standards has been made so that luminosity class IIIbdefines members of the clump, and nearly all of the class III stars fallwithin the main giant ridge. Second, a new calibration of MK luminosityclasses III and IIIb in terms of visual absolute magnitudes has beenmade.
| Probing the {Na} BT I D and {K} BT I lambda 7699 resonance lines sensitivity to background opacity in late-type stars
We have measured the equivalent width WK of the K i resonanceline at 7699 Angstroms for a large sample of low activity late-typestars observed with high spectral resolution and we have verified thatthe relation WK vs. Teff is monotonicallydecreasing, for both dwarf and giant stars. This behaviour is differentfrom that of the Na I D lines for stars of the same type, which showedthat the relation WNa vs. Teff has a maximum forTeff ~ 4000 K, which is better defined for giants than fordwarfs (Tripicchio et al. 1997). The fit of the observed K I equivalentwidths by means of a NLTE spectral line synthesis using conventionalbackground opacity shows that, for dwarf stars, the adopted modelsoverestimate the observed WK for temperatures <~ 4000 K.This result is similar to that discussed for the Na I D lines in ourprevious paper. On the other hand, for giant stars with Teff<~ 3800 K these models in general underestimate WK. Thediscrepancies between observed and computed WK andWNa for cool stars are much stronger than the variations dueto uncertainties in either atmospheric model or line parameters, likeeffective temperature and surface gravity, or Van der Waals broadening.For M dwarf stars, the most convincing explanation for the disagreementis the lack of atomic and molecular line opacity in the adopted models.In fact, a NLTE spectral synthesis including an additional backgroundopacity reproduces with a good level of accuracy the equivalent widths,as well as the general shape of the profiles for both the Na I D and K Ilines, in a subsample of early-M dwarfs. Based on observations collectedat the European Southern Observatory (ESO), La Silla, Chile, and at theMcDonald Observatory, Mt. Locke, Texas, USA
| Averaged energy distributions in the stellar spectra.
Not Available
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| 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.
| Systematic Errors in the FK5 Catalog as Derived from CCD Observations in the Extragalactic Reference Frame.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..850S&db_key=AST
| The NaI resonance lines as a spectroscopic test of late-type stellar atmospheres.
We have tested current models for the atmospheres (including photosphereand low chromosphere) of late-type stars using the D resonance lines ofneutral sodium as a diagnostic. To this end, we have measured theequivalent widths of the D lines for a sample of 39 dwarf and 45 giantlate-type stars observed with high spectral resolution. We constructedphotospheric models over a grid in effective temperature and surfacegravity spanning the spectral types F to M, and luminosity classes V andIII of the sample stars. The model photospheres were extended into thechromosphere by assuming a suitable scaling from the Sun, andtheoretical Nai D equivalent widths were computed over the grid ofmodels including the deviations from local thermodynamic equilibrium. Bytaking into account both the experimental errors and the possiblevariations of stellar parameters (effective temperature, surfacegravity, sodium abundance and microturbulence), the comparison betweenobserved and computed equivalent widths allows us to state that themodel atmospheres we have used can reproduce the observations for thetwo luminosity classes and for all the spectral types except for theM-type stars. We have discussed the importance of line blanketing in thespectral analysis of these stars, but at present we cannot conclude thatthis effect would reduce the discrepancy.
| The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NM
A spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%.
| 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 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
| On the spectra and photometry of M-giant stars
From a sample of 97 very bright M-giant stars in the Solarneighbourhood, high-quality "intrinsic" spectra in the spectral range380 <~ λ[nm] <~ 900 for all M-spectral subtypes of the Caseand MK classification systems are obtained. The results are fitted tophotospheric synthetic spectra in the range 99 <~ λ [nm]<=12500 in order to infer the corresponding continua. The syntheticspectra are also compared to the intrinsic spectra. The effectivetemperatures are derived and mathematical spectral classificationcriteria are found. The (UB)_j_(VRI)_c_(JHKLM)_ESO_ photometric data ofthe sample are also given. The data are available on the StrasbourgAstronomical Data Centre (CDS).
| Corrections to the right ascension to be applied to the apparent places of 1217 stars given in "The Chinese Astronomical Almanach" for the year 1984 to 1992.
Not Available
| Asymptotic giant branch stars near the sun
Available red and near-infrared photometry and apparent motions of M, S,and C asymptotic giant branch (AGB) stars in the Bright Star Catalogueare tabulated and discussed. It is shown that the red and near infraredindices normally used for late-type stars are interchangeable except forcarbon stars. The M-type giants are variable with visual amplitudegreater than 0.05 mag. The reddening-free parameter m2 from Genevaphotometry is essentially a temperature parameter for M giants, whilethe reddening-free parameter d is a sensitive detector of blue stellarcompanions. The space density of AGB stars near the sun decreases by afactor of 35 in a temperature range 3800 to 3400 K. Two of the S starsnear the sun were found to have nearly equal space motions and may becomembers of the Arcturus group.
| 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.
| JHKLM standard stars in the ESO system
A list of 199 standard stars suitable for the ESO standard photometricsystem at JHKLM is given. Faint stars (although brighter than K = 7.7)to be used on larger telescopes are included. This list is based on ananalysis of all infrared photometric observations carried out at LaSilla from 1979 until 1989 inclusive. The accuracy of the data (about0.02 mag. at J, H, K, L, and M) is similar to the one achieved at SAAOand CTIO. Comparisons with these systems, as well as with the AAO andMSSO systems, are made: it is shown that the ESO system is very close tothe other ones, with the exception of CTIOs.
| Santiago declination catalogue. II - A declination catalogue of 493 FK5 stars (equinox J2000.0)
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991A&AS...90..109C&db_key=AST
| Physical data of the fundamental stars.
Not Available
| M Giant Populations and Galactic Structure
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.247..227F&db_key=AST
| Southern JHKL standards
The basis for the current SAAO standard photometric system at JHKL isgiven. This depends on an extensive investigation involving 230 starsdistributed around the sky. The accuracy is estimated at + or - 0.02 magfor J, H and K and + or - 0.05 mag for L.
| A list of MK standard stars
Not Available
| The Perkins catalog of revised MK types for the cooler stars
A catalog is presented listing the spectral types of the G, K, M, and Sstars that have been classified at the Perkins Observatory in therevised MK system. Extensive comparisons have been made to ensureconsistency between the MK spectral types of stars in the Northern andSouthern Hemispheres. Different classification spectrograms have beengradually improved in spite of some inherent limitations. In thecatalog, the full subclasses used are the following: G0, G5, G8, K0, K1,K2, K3, K4, K5, M0, M1, M2, M3, M4, M5, M6, M7, and M8. Theirregularities are the price paid for keeping the general scheme of theoriginal Henry Draper classification.
| Stellar integrated fluxes in the wavelength range 380 NM - 900 NM derived from Johnson 13-colour photometry
Petford et al. (1988) have reported measured integrated fluxes for 216stars with a wide spread of spectral type and luminosity, and mentionedthat a cubic-spline integration over the relevant Johnson 13-colormagnitudes, converted to fluxes using Johnson's calibration, is inexcellent agreement with those measurements. In this paper a list of thefluxes derived in this way, corrected for a small dependence on B-V, isgiven for all the 1215 stars in Johnson's 1975 catalog with completeentries.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
INHABITED SKY
