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No Fossil Disk in the T Tauri Multiple System V773 Tauri
We present new multiepoch near-infrared (NIR) and optical high angularresolution images of the V773 Tau pre-main-sequence triple system, aweak-line T Tauri star (WTTS) system in which the presence of anevolved, ``fossil'' protoplanetary disk has been inferred on the basisof a significant IR excess. Our images reveal a fourth object bound tothe system, V773 Tau D. While it is much fainter than all othercomponents at 2 μm, it is the brightest source in the system at 4.7μm. We also present medium-resolution K-band adaptive opticsspectroscopy of this object, which is featureless with the exception ofa weak Brγ emission line. Based on this spectrum and on thespectral energy distribution (SED) of the system, we show that V773 TauD is another member of the small class of ``infrared companions'' (IRCs)to T Tauri stars (TTSs). It is the least luminous, and probably theleast massive, component of the system, as opposed to most other IRCs,which suggests that numerous low-luminosity IRCs such as V773 Tau D maystill remain to be discovered. Furthermore, it is the source of thestrong IR excess in the system. We therefore reject the interpretationof this excess as the signature of a fossil (or ``passive'') disk andfurther suggest that these systems may be much less frequent thanpreviously thought. We further show that V773 Tau C is a variableclassical TTS (CTTS) and that its motion provides a well-constrainedorbital model. We show that V773 Tau D can be dynamically stable withinthis quadruple system if its orbit is highly inclined. Finally, V773 Tauis the first multiple system to display such a variety of evolutionarystates (WTTS, CTTS, IRC), which may be the consequence of the strongstar-star interactions in this compact quadruple system.
| On the relation between diffuse interstellar bands and simple molecular species
We present observations of the major diffuse interstellar bands (DIBs)at 5780 and 5797 Ä as well as literature data and our ownobservations of the violet lines of CH and CH(+) , in the lines of sighttoward some 70 stars representing various degrees of the interstellarreddening. The correlations are shown and discussed in the context ofindicators such as far-UV extinction parameters and neutral molecularabundances. The results show that the DIBs in question (lambda lambda5797 and 5780) both probably form in diffuse cloud interiors, in arelated regime where CH and H_2 form. The ratio of the two DIBscorrelates with CH abundance, confirming that the lambda 5797 carrier isfavoured in enhanced molecular gas regions over the lambda 5780 carrier.The ratio of the two DIBs correlates poorly with CH(+) abundance. Ourcompilation of observational data also suggests that the DIB ratio maybe equally useful as a cloud type indicator as is R_V, the ratio oftotal to selective extinction, and much more readily observed. Based onobservations obtained at the Russian Special Astrophysical Observatory(SAO), Terskol Observatory (TER), Canada France Hawaii Telescope (CFHT),European Southern Observatory (ESO), Observatoire de Haute-Provence(OHP)
| The diffuse interstellar bands at 5797, 6379 and 6613 Angstroms. Ionization properties of the carriers
We present a study of the behaviour and ionization properties of threenarrow Diffuse Interstellar Bands (DIBs) at lambda lambda 5797, 6379 and6613 Angstroms. In all three DIBs substructures have recently beendetected, indicating large gaseous molecular carriers. Studying DIBs inregions with drastically different physical properties in terms of UVflux and density enables us to monitor the behaviour of the carriers andhence to constrain their nature. We observed these three DIBs along 40different lines-of-sight (35 program stars and 5 standard stars)consisting of HII regions, dark clouds, molecular clouds and reflectionnebulae. The DIB variations at low reddening are explained by a newmodel of photoionization equilibrium of the DIB carriers. This modeltakes into account the penetration depth of UV ionizing photonsthroughout the cloud. The slope of the variation of DIB strength as afunction of reddening thus allows us to estimate the effectiveionization potentials of the carriers. Following this new analysis, thecarriers of the lambda 5797 and lambda 6613 Angstroms DIBs would haveionization potentials above 10eV, reminiscent of large PAHs orfullerenes which have a single positive charge. The estimated ionizationpotential (7--9eV) of the lambda 6379 Angstroms DIB seems to indicate alarge neutral carrier. Based on observations with OHP 1.93m Telescopeand Elalie spectrograph.
| 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.
| Diffuse interstellar bands in the Taurus dark clouds
This paper presents strengths and profiles of seven diffuse interstellarbands measured in a group of field stars situated behind the Taurus darkcloud complex. Comparison with the current 'band family' theories showsthat, within a single complex, the relative proportions of differentfamily carriers can vary in rather close unions: although correlationswith extinction are poor in all cases, some pairs of bands arenonetheless strongly interrelated. Band strengths relative to reddeningare investigated and found to be reasonably well fitted by a model inwhich all of the DIB production takes place in a surface layer of thecloud. These results are compared with existing data for the Rho Ophcloud. Band production efficiency varies in the same way in bothregions, falling rapidly with increasing E(B-V) to a limiting value afactor of 3-10 below the norm for the diffuse ISM. Comparison of grainproperties and the UV radiation field in the two cases shows that therelative weakness of the diffuse bands in dark clouds is driven bychanging grain properties rather than by species or other ionizedmolecules.
| Interstellar extinction in the Taurus dark clouds. II
The results of photoelectric photometry of 89 stars in the Vilniusseven-color system in the area of the Taurus dark clouds withcoordinates (1950) 4h16m-4h33m, +16 deg-+20 deg are presented.Photometric spectral types, absolute magnitudes, color excesses,interstellar extinctions and distances of the stars are determined. Thedistance of the dark nebula is found to be 140 pc and is in goodagreement with the distance determined by Straizys and Meistas (1980)for the dark nebula Khavtassi 286, 278. The average extinction in theinvestigated area is of the order of 1.4.
| The polarization of T and RY Tau.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Bika |
| Rektaszcenzió: | 04h19m30.16s |
| Deklináció: | +19°56'52.1" |
| Vizuális fényesség: | 7.857 |
| Távolság: | 257.732 parszek |
| RA sajátmozgás: | 7.3 |
| Dec sajátmozgás: | -6.6 |
| B-T magnitude: | 8.098 |
| V-T magnitude: | 7.877 |
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