Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Kinematic structure of the corona of the Ursa Major flow found using proper motions and radial velocities of single stars
Aims.We study the kinematic structure of peripheral areas of the UrsaMajoris stream (Sirius supercluster). Methods.We use diagrams ofindividual stellar apexes developed by us and the classical technique ofproper motion diagrams generalized to a star sample distributed over thesky. Results.Out of 128 cluster members we have identified threecorona (sub)structures comprised of 13, 13 and 8 stars. Thesubstructures have a spatial extension comparable to the size of thecorona. Kinematically, these groups are distinguished by their propermotions, radial velocities and by the directions of their spatialmotion. Coordinates of their apexes significantly differ from those ofthe apexes of the stream and its nucleus. Our analysis shows that thesesubstructures do not belong to known kinematic groups, such as Hyades orCastor. We find kinematic inhomogeneity of the corona of the UMa stream.
| 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.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| 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
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 136: HD 7000
Not Available
| 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.
| 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_.
| Speckle observations of visual and spectroscopic binaries. VI.
Not Available
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&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.
| The second Quito astrolabe catalogue
The paper contains 515 individual corrections {DELTA}α and 235corrections {DELTA}δ to FK5 and FK5Supp. stars and 50 correctionsto their proper motions computed from observations made with theclassical Danjon astrolabe OPL-13 at Quito Astronomical Observatory ofEcuador National Polytechnical School during a period from 1964 to 1983.These corrections cover the declination zone from -30deg to +30deg. Meanprobable errors of catalogue positions are 0.047" in αcosδand 0.054" in δ. The systematic trends of the catalogue{DELTA}αalpha_cosδ,{DELTA}αdelta_cosδ,{DELTA}δalpha_, {DELTA}δdelta_ arepresented for the observed zone.
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
| Speckle observations of visual and spectroscopic binaries. V.
Not Available
| Speckle observations of visual and spectroscopic binaries. IV
This is the fourth paper of this series giving results of speckleobservations for 22 visual and 161 spectroscopic binaries. Theobservation was carried out by using the 212 cm telescope of San PedroMartir Observatory in Mexico on 7 nights from July 20 to July 26, 1991.We obtained fringes in power spectra of 19 visual and 11 spectroscopicbinaries (6 newly resolved ones) with angular separation larger than0.06 arcsec. We introduced a new ICCD TV camera in this observation, andwere able to achieve the diffraction-limit resolution of the 212 cmtelescope.
| Speckle observations of visual and spectroscopic binaries. III
This is the third paper of this series giving results of speckleobservations carried out for seven visual and 119 spectroscopic binariesat seven nights from May 20 to May 27, 1989, and for 30 visual and 272spectroscopic binaries at 12 nights from June 11 to June 15, and fromAugust 28 to September 3, 1990, using the 212-cm telescope at San PedroMartir Observatory in Mexico. Fringes in the lower spectrum of 31 visualand spectroscopic binaries with angular separation larger than 21 arcsecare obtained. Additionally to two spectroscopic binaries, HD41116 andHD206901, named in the second paper of this series, six spectroscopicbinaries are found each of which has the third component starsurrounding two stars of spectroscopic binary having periodic variationof radial velocity.
| Speckle observations of spectroscopic binaries
Results from speckle observations of binary stars carried out between1987 and 1990 using a 212-cm telescope at the San Pedro MartirObservatory, Mexico, are presented. Fringe patterns for 21 of the 76reduced spectroscopic binaries in the Fourier domain were detected. Thespeckle observations and the astrometric observations are consistent forthe stars HD41116, HD202275, and HD206901.
| Speckle observations of visual and spectroscopic binaries.
Speckle observations performed for 16 visual and 79 spectroscopicbinaries with the 212-cm telescope at San Pedro Martir Observatory arepresented. The data were collected over a period of 20 nights, from June15 to July 11, 1987. Examples are given of the power spectra of starswith differing angular separations.
| 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.
| Transformation equations and other aids for VRI photometry
Transformations among VRI systems are commonly beset by Paschen-jumpeffects, for which fully satisfactory allowance has not previously beenmade. This paper describes two new techniques which are based on thework of Gutierrez-Moreno, and which allow fully for the effects of thePaschen jump. Values of E(V-R)/E(B-V) and E(R-I)/E(B-V) are also givenfor the Cousins system for a wide range of temperatures. These and thenew techniques contribute to a set of new transformation relations whichapply for most VRI systems; the status of the remaining systems isreviewed, and future work needed for them is described. Two majorsources of Cousins VRI data underlie the new relations; the consistencyof these sources is reviewed and found to be generally satisfactory,although more work on this question is needed. Finally, three tables oftransformed standard-star and other data are given for the Cousins andJohnson systems, and a description of ways to reproduce the latter ispresented.
| The Sirius supercluster
Photometric data on the chemical composition of 927 A stars in the UrsaMajor stream, called the Sirius supercluster, were used to estimate theage and place of formation of the objects. The stars studied are in thesolar neighborhood and have been observed to be co-moving in a velocityellipsoid with a (U, V) velocity of 10.3 km/sec and concentrated in aspatial volume less than 10 pc across. The Stromgren and Geneva systemphotometric data show that the supercluster is homogeneous in chemicalcontent, although the value of the forbidden Fe/H ratio could not beprecisely determined. The supercluster age is projected to be from260-620 Myr, with the origin having been in the Carina spiral arm of theGalaxy.
| Catalogue of the energy distribution data in spectra of stars in the uniform spectrophotometric system.
Not Available
| A Note about the Comparison Between the Old and New Slettebak Systems of Axial Rotational Velocities
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1984RMxAA...9....9G&db_key=AST
| 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.
| Synchronization in early-type spectroscopic binary stars
The rotational properties of a large sample of noneclipsing double-linedspectroscopic binaries are discussed in terms of synchronization ofaxial and orbital rotation. The data covered the spectral types OB andA04, i.e., those with full radiative envelopes. Nearly 80 systems wereinvestigated, and the periods and orbital velocities are provided. Ahigh correlation was found between the fractional radius and theoccurrence of synchronicity and pseudosynchronicity. Deviations fromsynchronous rotation were most apparent at fractional radii of 0.05 andbelow. Current theories of the synchronization time scales are noted tobe inadequate for describing the small fractional radii-lack ofsynchronism observed.
| The Sirius group as a moving supercluster
Without use of trigonometric parallaxes, the distances of some 50 brightstars have been determined on the basis of their well-determined propermotions and membership in a supercluster that includes Sirius. Theastrometric parallaxes are in excellent agreement with those obtainedfrom photometric parameters and, for the stars within 40 pc of the sun,they are also in agreement with trigonometric determinations. Thesupercluster stars are near 2.4 x 10 to the 8th yr old with (Fe/H) near-0.1. The resulting color-luminosity array confirms the expectedmain-sequence displacement for stars with a metal abundance only abouttwo thirds that of the Hyades supercluster members. The superclustercontains the UMa cluster and M39 (NGC 7092) but the former, at least,has only attracted attention because of the concentration of a fewbright (Dipper) supercluster members in Ursa Major.
| Variability of the emission-line spectra and optical continua of Seyfert galaxies. I
H-beta and O III forbidden line 4959,5007 A line strengths obtained fromnew observations of 27 broad line-emitting galaxies and six narrowline-emitting galaxies are compared with earlier measurements. It isfound that about 80% of broad line-emitting galaxies show significantchanges in their optical spectra, on time scales of less than about fiveyears. An analysis of changes in O II forbidden line/H-beta ratio for 24broad line-emitting galaxies shows that (1) changes in the H-beta fluxare correlated with changes in the optical continuum, providing evidencefor energy input into the line-emitting region by photoionization, and(2) in a number of galaxies, the structure of the broad emission linesin complex, with detailed line structure changes on time scales shorterthan about two months.
| Close binary systems before and after mass transfer. III - Spectroscopic binaries
A method is presented, for the computation of absolute dimensions fromspectroscopic data on binary systems, which has been adapted for usewith the 7th Catalogue of Batten et al. (1978) and takes into accountseveral results of close binary evolution, with emphasis on the phase ofslow mass transfer during a case B mass transfer. Among the unevolvedsystems, the mass transfer case B is found to be the most abundant typeof interaction. In the set of evolving systems, a subset of 18interacting systems was found with mass ratio near unity, the first starbeing the mass loser as well as the brightest.
| List of Estimated Angular Separations of Spectroscopic Binaries
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981A&AS...44...47H&db_key=AST
| A set of faint equatorial standard stars for BVRI photometry
BVRI photoelectric photometry is presented for 48 of Landolt's (1973)faint equatorial standard stars. The 48 stars, which have spectral typesfrom A to K and V magnitudes in the range from 8.0 to 12.0, are chosento provide two blue and two red stars in each of 12 of the equatorialselected areas studied by Landolt. The program stars were observed withan S-1 photomultiplier, with the B-V, V-R, and V-I colors transformed tothe Johnson system; they were also observed with an RCA 31034Aphotomultiplier, with the resulting V-R and V-I colors given on azero-point-adjusted instrumental system. Observations of several Mdwarfs with the two photomultipliers are also reported. Serious problemsencountered in transforming the observed V-R and V-I colors of the Mdwarfs to the Johnson system are discussed.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Kígyó |
| Rektaszcenzió: | 18h37m36.00s |
| Deklináció: | -00°18'34.0" |
| Vizuális fényesség: | 5.75 |
| Távolság: | 197.628 parszek |
| RA sajátmozgás: | 14.2 |
| Dec sajátmozgás: | -22 |
| B-T magnitude: | 5.834 |
| V-T magnitude: | 5.774 |
Katalógusok és elnevezések:
|
INHABITED SKY
