目录
图像
上传图像
DSS Images Other Images
相关文章
New measurements of rotation and differential rotation in A-F stars: are there two populations of differentially rotating stars?
Context. The Sun displays differential rotation that is intimatelyconnected to the solar dynamo and hence related to solar activity, thesolar cycle, and the solar wind. Considering the detectability andhabitability of planets around other stars it is important to understandthe role of differential rotation in other stars. Aims: Wepresent projected rotational velocities and new measurements of therotational profile of some 180 nearby stars with spectral types A-F. Theresults are consolidated by a homogeneous compilation of basic stellardata from photometry and the identification of multiple stellar systems.New and previous measurements of rotation by line profile analysis arecompiled and made available. Methods: The overall broadeningprofile is derived analysing spectral line shape from hundreds ofspectral lines by the method of least-squares deconvolution, reducingspectral noise to a minimum. The effect of differential rotation on thebroadening profile is best measured in inverse wavelength space by thefirst two zeros of its Fourier transform. Results: Projectedrotational velocity vsini is measured for more than 110 of the samplestars. Rigid and differential rotation can be distinguished in 56 caseswhere vsini > 12 km s-1. We detect differential rotationrates of δΩ/Ω = 5% and more. Ten stars withsignificant differential rotation rates are identified. The line shapesof 46 stars are consistent with rigid rotation, even though differentialrotation at very low rates might still be possible in these cases. Thestrongest amount of relative differential rotation (54%) detected byline profile analysis is found among F stars. Conclusions: As ofnow, 33 differential rotators detected by line profile analysis havebeen confirmed. The frequency of differential rotators decreases towardshigh effective temperature and rapid rotation. There is evidence for twopopulations of differential rotators, one of rapidly rotating A stars atthe granulation boundary with strong horizontal shear and one of mid- tolate-F type stars with moderate rates of rotation and less shear. Thegap in between can only partly be explained by an upper bound found forthe horizontal shear of F stars. Apparently, the physical conditionschange at early-F spectral types. The range of horizontal shear observedfor mid-type F stars is reproduced by theoretical calculations whilethere seems to be a discrepancy in period dependence for late-F stars.Based on observations made with ESO Telescopes at the La Silla ParanalObservatory under programme ID's 074.D-0008 and 075.D-0340.Tables 1 and2 are available in electronic form at http://www.aanda.orgTables 1 and 2 arealso available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/542/A116
| Speckle Interferometry at SOAR in 2010 and 2011: Measures, Orbits, and Rectilinear Fits
We report on the results of speckle observations at the 4.1 m SOARtelescope in 2010 and 2011. A total of 639 objects were observed. Wegive 562 measurements of 418 resolved binaries, including 21 pairsresolved for the first time, and upper detection limits for 221unresolved stars. New orbital elements have been determined for 42physical pairs, of which 22 are first-time calculations; the rest arecorrections, sometimes substantial. Linear elements are calculated fornine apparently optical doubles. We comment on new pairs, new orbitalsolutions, and other remarkable objects.Based on observations at the SOAR telescope, NOAO proposal 2010B-0096.SOAR is operated by AURA, Inc., under contract with the National ScienceFoundation.
| Speckle Interferometry at the Blanco and SOAR Telescopes in 2008 and 2009
The results of speckle interferometric measurements of binary andmultiple stars conducted in 2008 and 2009 at the Blanco and SOAR 4 mtelescopes in Chile are presented. A total of 1898 measurements of 1189resolved pairs or sub-systems and 394 observations of 285 un-resolvedtargets are listed. We resolved for the first time 48 new pairs, 21 ofwhich are new sub-systems in close visual multiple stars. Typicalinternal measurement precision is 0.3 mas in both coordinates, typicalcompanion detection capability is ?m ~ 4.2 at 0farcs15 separation.These data were obtained with a new electron-multiplication CCD camera;data processing is described in detail, including estimation ofmagnitude difference, observational errors, detection limits, andanalysis of artifacts. We comment on some newly discovered pairs andobjects of special interest.
| A catalogue of multiplicity among bright stellar systems
We consider the multiplicity of stellar systems with (combined)magnitude brighter than 6.00 in Hipparcos magnitudes. We identify 4559such bright systems (including the Sun), and the frequencies ofmultiplicities 1, 2,..., 7 are found to be 2718, 1437, 285, 86, 20, 11and 2. We discuss the uncertainties, which are substantial. We alsoconsider the distributions of periods of orbits and suborbits. We notethat for even more restricted set of 478 systems with VH<= 4.00, the proportions of higher multiples up to sextuple areprogressively larger (213, 179, 54, 19, 8, 5), suggesting substantialincompleteness in even the reasonably well studied larger sample.This sample can be seen as relatively thoroughly studied formultiplicity, and reasonably representative of stars more massive thanthe Sun. But the restriction to VH <= 6 means that oursample contains hardly any systems where all components are low-massmain-sequence stars (K or M).Data on multiplicity are important as a constraint on (i) the starformation problem, (ii) the problem of the evolution of the Galacticstellar population and (iii) the interaction of dynamics and evolutionthrough the effect of Kozai cycles. We discuss these topics briefly.
| First Speckle Interferometry at SOAR Telescope with Electron-Multiplication CCD
A simple camera with electron-multiplication CCD, fast frame rate, and apixel scale of 15mas is described. This instrument was tested at theSOAR 4-m telescope in the speckle-interferometry regime. The data wereprocessed by the standard speckle algorithm permitting derivation ofbinary-star parameters. We observed 29 objects with separations from21mas to 1.32, mostly southern binaries with known orbits. Some pairsrequire orbit revision. Two spectroscopic binaries HIP9631 and HIP11072and the astrometric binary For are resolved for the first time, whilethree objects were unresolved.
| Ultraviolet and Optical Studies of Binaries with Luminous Cool Primaries and Hot Companions. V. The Entire IUE Sample
We have obtained or retrieved IUE spectra for over 100 middle- andlate-type giant and supergiant stars whose spectra indicate the presenceof a hot component earlier than type F2. The hot companions areclassified accurately by temperature class from their far-UV spectra.The interstellar extinction of each system and the relative luminositiesof the components are derived from analysis of the UV and opticalfluxes, using a grid of UV intrinsic colors for hot dwarfs. We find thatthere is fair agreement in general between current UV spectralclassification and ground-based hot component types, in spite of thedifficulties of assigning the latter. There are a few cases in which thecool component optical classifications disagree considerably with thetemperature classes inferred from our analysis of UV and opticalphotometry. The extinction parameter agrees moderately well with otherdeterminations of B-V color excess. Many systems are worthy of furtherstudy especially to establish their spectroscopic orbits. Further workis planned to estimate luminosities of the cool components from the dataherein; in many cases, these luminosities' accuracies should becomparable to or exceed those of the Hipparcos parallaxes.
| ICCD Speckle Observations of Binary Stars. XIII. Measurements During 1989- 1994 From the Cerro Tololo 4 M Telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..936H&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.
| ICCD speckle observations of binary stars. VIII - Measurements during 1989-1991 from the Cerro Tololo 4 M telescope
One-thousand eighty-eight observations of 947 binary star systems,observed by means of speckle interferometry with the 4 m telescope onCerro Tololo, are presented. These measurements, made during the period1989-1991, comprise the second installment of results stemming from theexpansion of our speckle program to the southern hemisphere.
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
| A narrow-band search for extraterrestrial intelligence (SETI) using the interstellar contact channel hypothesis
A search is reported for narrow spectral line emission from 176 targets(including 166 stars and seven globular clusers) at the hypothesized'interstellar communications channel' frequency of 4.462336275 GHz (= pitimes the neutral hydrogen line at 1.42 GHz) using the Parkes Radiotelescope. The frequency was Doppler corrected for the solar barycenter,target barycenter, and cosmic microwave background (CMB) referenceframes. If a 'Galactic club' of extraterrestrial civilizations exists,then the null results, down to a 3 sigma limit of 2 Jy (6 Jy in CMBframe), set an upper limit of 10 exp 8 yr on the lifetime of suchcivilizations.
| Micrometric measurements of visual binaries (5th list)
The data resulting from 596 micrometric measurements of 152 binaries areset forth which represent observations taken on the GPO astrograph(described by Scardia, 1990). The traditional declination method is usedto track star position, and some of the measurements are related toprevious work by the author (1990). The data given include O-Cmeasurements corresponding to the Worley and Heintz catalogue (1984) andother relevant data.
| Les binaires spectrales, classe particuliere d'etoiles doubles ?
Not Available
| On the (B-V) colors of the bright stars
The possible causes of the dispersion of (B-V) colors of nearby stars inthe Bright Star Catalog are investigated. The distribution of (B-V)colors is presented for the entire range of spectral classes.Explanations for the dispersion in terms of a nonuniform distribution ofinterstellar absorbing material and a variability of metallicity areaddressed. A new statistical model for reddening by interstellar dustclouds is developed. It is concluded that extinction by nonuniforminterstellar matter is an important contribution to the reddening ofnearby stars, and that a part of the dispersion of (B-V) colors of Kand, possibly, M giants may be due to some unidentified variableproperty of those stars.
| Ultraviolet and optical studies of binaries with luminous cool primaries and hot companions. III - RETICON radial velocities
Radial velocities for 72 stars, most of them known or suspected binarieswith F - K giant-supergiant primaries, are derived from Reticon spectrain the region 6005-6235 A at a scale of 7 km/s per diode.Cross-correlation of the spectra normally produces results accurate tobetter than 1.0 km/s. Eight new radial velocity variables are found (HR2786, R Pup, HR 3291, HR 4451, HD 114520, HR 5667, HR 7014, and Nu1Sgr). Improved orbits are determined for 15 known spectroscopicbinaries, and provisional orbits are obtained for seven newspectroscopic binaries.
| Erratum - Discordances Between SAO and HD Numbers for Bright Stars
Not Available
| Absolute luminosity calibration of Stroemgren's 'late group'
A statistical parallax method based on the principle of maximumlikelihood is used to calibrate absolute luminosities for samples ofcooler stars constituting the 'late group' defined by Stromgren (1966).The samples examined include 415 stars of all luminosity classes and asubset comprising 86 main-sequence stars. Linear calibration relationsinvolving the Stromgren beta, (b-y), and bracketted c1 indices arederived which yield mean absolute magnitudes with an accuracy of 0.09magnitude for the overall sample and 0.13 magnitude for themain-sequence subsample. Several second-order relations are considered,and the results are compared with Crawford's (1975) calibrations as wellas with mean absolute magnitudes obtained from trigonometric parallaxes.The possible effect of interstellar absorption on the calibrationrelations is also investigated.
| Four-colour and H BET photometry of some bright southern stars- II.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972MNRAS.160..155S&db_key=AST
| Southern Stars with Abnormal Spectra
Not Available
| New Double Stars (XIV)
Not Available
| A survey of stars with composite spectra.
Not Available
|
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:
|
INHABITED SKY
