Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| Broken symmetry: The structure of the dust envelope of IRC +10216
We present polarimetric, coronagraphic near-infrared images of thereflection nebula surrounding the carbon star IRC +10216. These imagesdemonstrate convincingly that the dust envelope is not sphericallysymmetric. In unocculted images at J (1.25 micrometers) and in occultedimages at H (1.65 micrometers) and K (2.2 micrometers), the nebulaappears elongated, with major axis lying at position angle approximately20 deg. The position angle of elongation is the same as that previouslydetermined from near-infrared speckle interferometry for the innerapproximately 1 sec of the envelope. The elliptical symmetry of the Jpolarimetric map offers additional evidence of the axial symmetry of theenvelope and indicates that the equatorial plane of IRC +10216 liesperpendicular to the major axis of the nebula. The polarization map alsoindicates that the source of illumination -- presumably the stellarphotosphere or hot dust located very near the photosphere -- is directlydetected at wavelengths as short as approximately 1 micrometers. We findthat the density distribution of grains in the polar regions is roughlyn varies as r-2 and estimate that the scattering dust masswithin 12 sec in radius of the central star is approximately 5 x10-6 solar masses. These results support a model in which theenvelope of IRC +10216 is weakly bipolar and is viewed at anintermediate inclination angle such that we have a direct line of sightto the central star. The axisymmetric near-infrared intensity andpolarization morphologies are best understood in terms of enhanced massloss in the equatorial plane. An examination of previous near-infraredand millimeter-wave mapping observations supports this hypothesis. Theseobservations make clear that axisymmetric structure can be wellestablished before an intermediate-mass star leaves the asymptotic giantbranch. It is possible that the dust envelope of IRC +10216 presents anearly manifestation of the more profound bipolar structure thatcharacterizes highly evolved preplanetary nebulae.
| A multicolor survey of absolute proper motions: galactic structure and kinematics in the direction of the galactic center at intermediate latitude.
Bienayme et al. (1992) have published a magnitude-limited sample ofproper motions for stars at the intermediate galactic latitude (l=3deg,b=47deg; α_1950_=15h18m, δ_1950_=+02d16') for a 2 squaredegree field. In their study there was a lack of an accurate absoluteastrometric reference due to very small number of galaxies orextragalactic objects in the field. However, since Bienayme et al.paper, more deep photographic plates and CCD standards have beenobtained. Here we have derived a new photographic photometry and propermotions for ~20000 stars with completeness to V~18 in the same directionfor a 15.5 square degree field. The combination of four glass copies ofthe Palomar Observatory Sky Survey (i.e. POSS 1402 E&O and POSS 1429E&O) has been used as a first epoch for proper motion determination.The random error of the proper motions is approximately 0.3"/century toV~17. The photometric accuracy ranges between 0.07 to 0.10 in the V, Band U bands. We stress the importance of the magnitude and color effectsin astrometric surveys of field stars. Using color-magnitude diagrams ofa few cluster member stars, a new distance of 6.9+/-0.5kpc is derivedfor M5 and 20.3+/-0.8kpc for Pal 5 globular clusters. This is in goodagreement with other determinations. We have analyzed the components ofU+W and V galactic space motions resulting from the accurate propermotions survey. No dependence with z distance is found in the asymmetricdrift of the thick disk population. New estimates of the parameters ofthe velocity ellipsoid have been derived for the thin disk, thick diskand halo populations of the Galaxy.
| Near-infrared, polarimetric imaging of the bipolar lobes of GSS 30 - Protostellar infall and/or outflow?
The morphology noted in the present 1.65 and 2.2 micron polarimetricimages of the bipolar reflection nebula GSS 30 is consistent with thatexpected for protostellar infall and/or outflow, and the polarizationmaps suggest that the scattering orbital depth is larger along the limbsand the neck of the nebula than along the polar axis. Interpreting thelobes as cavities formed by polar outflows leads to the suggestion thatthe outflow is characterized by temporal variability in either mass-lossrate or outflow velocity, on time scales of less than several hundredyears.
| JHK infrared standard stars and absolute calibration of the San Pedro Martir Observatory (OAN) photometric system
A set of reliable standard stars for the JHK photometric system of theSan Pedro Martir National Observatory (OAN) is presented. Meanextinction coefficients for the near-IR of this site are first reportedhere; effective wavelengths and flux calibration from observations ofVega are derived for the various bandpasses. Comparison with otherwidely used photometric systems is presented and, finally,transformation equations to CIT, AAO, ESO, and Johnson's systems arederived.
| Globular cluster distances from the RR Lyrae log(period)-infrared magnitude relation
The present determinations of log(period)-2.2 micron IR relationship forRR Lyr stars in eight clusters indicate no sign of scatter in therelation apart from observational error. It is suggested that veryaccurate relative distances, insensitive to both reddening errors andthe effects of metallicity, are obtainable, although mass differencesbetween variables in different clusters may still introduce relativedistance uncertainties. A comparison of the absolute calibration of Kmagnitudes of two field stars obtained with an IR-flux method form ofthe Baade-Wesselink analysis to three other sets of distancemeasurements shows good agreement with those of Richer and Fahlman(1987).
| An atlas of stellar spectra between 2.00 and 2.45 microns
Spectra between 2.00 and 2.45 microns, with a resolution of about 0.02micron are presented for a sample of 73 stars. These stars include asupergiant, giants, dwarfs and subdwarfs, and have a range in chemicalabundance from about -2 to +0.5 dex.
| The cool components of symbiotic stars. II - Infrared photometry
This paper reports IR photometry for a sample of symbiotic binaries andK-M comparison stars. Measured CO absorption-band strengths of the coolcomponents in symbiotic stars generally are comparable to those ofsingle red giant and bright giant stars, but it is difficult todetermine the luminosity classes of these objects from their photometricCO indices. The 12-micron excesses observed in symbiotics require theircool components to lose mass more rapidly than do single red giantstars. Thus, mass-loss rates derived for red giants in close binarysystems may not be accurate estimates for mass loss in single redgiants.
| Recent star formation in interacting galaxies. I - Evidence from JHKL photometry
A survey has been carried out using JHKL photometry to investigaterecent star formation in interacting galaxies. The objective was to lookfor a K-L excess produced by 'warm' dust heated by a putative burst ofstar formation. K-L excesses are found suggesting that interactionsinduce starbursts with an efficiency approaching 100 percent. Theappearance of these inferred starbursts in interacting systems ofdifferent morphological types is qualitatively consistent with dynamicalstudies of galaxy interactions. However, the common occurrence of suchstarbursts shows that interactions have implications for theastrophysics of galaxies well beyond purely morphological effects.
| Infrared standard stars
The results of an observational program aimed at setting up a network offaint near-infrared standards of sufficient accuracy are reported. Thenetwork covers both northern and southern hemispheres and includesstandards red enough to provide at least a limited check on colortransformations. The standards are set up at J (1.2 micron), H (1.6micron), K (2.2 microns), and L (3.5 microns), and their H2O and COmolecular absorption indices are determined. The problem of colortransformations between observatories is discussed briefly. Allmagnitudes presented are transformed to the natural system defined bythe CIT observations.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Kígyó |
| Rektaszcenzió: | 15h25m01.30s |
| Deklináció: | +01°30'34.9" |
| Vizuális fényesség: | 8.475 |
| Távolság: | 192.308 parszek |
| RA sajátmozgás: | 2.5 |
| Dec sajátmozgás: | -6.8 |
| B-T magnitude: | 10.52 |
| V-T magnitude: | 8.644 |
Katalógusok és elnevezések:
|
