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Testing Protoplanetary Disk Alignment in Young Binaries
We present K-band (2.2 μm) imaging polarimetry that resolves 19 TTauri binary and multiple systems in the Taurus-Auriga andScorpius-Ophiuchus star-forming regions. We observed systems withprojected separations 1.5"-7.2" (~200-1000 AU) in order to determine therelative orientation of the circumstellar disks in each binary system.Scattered light from these disks is polarized, allowing us to deduce theposition angle of the disk on the sky from the position angle ofpolarization even though our observations do not resolve the disksthemselves. We detected measurable polarization (typically 0.5%-2%, withtypical uncertainty 0.1%) from both stars in 14 of the systems observed.In eight of the nine binary systems, the two stars' polarizationposition angles are within 30° of each other, inconsistent withrandom orientations. In contrast, the five triple and quadruple systemsappear to have random disk orientations when comparing the polarizationposition angles of the widest pair in the system; the close pairs areunresolved in all but one system. Our observations suggest that disks inwide (200-1000 AU) binaries are aligned with each other within<~20° but not perfectly coplanar. However, we cannot conclusivelyrule out random relative disk orientations if the observed polarizationsare significantly contaminated by interstellar polarization. Even in thepresence of interstellar polarization our observations securely excludecoplanar disks. These results provide constraints on possible binaryformation mechanisms if the observed orientations are primordial. On theother hand, models of disk-binary interactions indicate that the disksmay have had time to decrease their relative inclinations sinceformation. If the common orientation of the disks in these binaries is atracer of the binary orbital plane, then our results also havesignificance for the stability of planetary orbits, suggesting thatplanetary systems in wide binaries should be stable over 109yr timescales.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| A new optical extinction law and distance estimate for the Taurus-Auriga molecular cloud
This paper presents optical spectrophotometry of field stars projectedon the Taurus-Auriga molecular cloud. We derive extinction laws forheavily reddened stars in this sample and show that the reddening lawthrough the dark cloud is nearly identical to the standard law forlambda-lambda(3600-6100) and AV approximately less than 3mag. Our spectroscopic parallaxes suggest a distance of 140 +/- 10 pcfor the northern portion of the cloud and show no compelling evidencefor a substantial variation in distance across the leading edge of thecloud.
| Radial velocity measurements. IV - Ground-based accompaniment to the HIPPARCOS observation program
The paper presents 396 radial velocities of stars distributed in 19fields of 4 x 4 degrees. The study employs the Fehrenbach objectiveprism method and the same measuring technique used in a previous paper(Fehrenbach et al., 1987).
| A Study of Flare Stars in the Taurus Region
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| Magnetic field structure in the Taurus dark cloud
Optical and infrared polarimetry of sources in the direction of theTaurus cloud are obtained in order to study the magnetic field in thiscloud and its possible role in the cloud's evolution. Most of the starsare background giant stars whose light shines through the cloud and ispolarized by the cloud material. The transverse component of themagnetic field, as delineated by the polarization vectors, is generallyperpendicular to the galactic plane, and the stratified structure of thecloud could be due to the effect of the magnetic field during the earlystages of collapse. Three of the 13 embedded stars are stronglypolarized with position angles nearly perpendicular to those of nearbyfield stars. The polarization of these stars is most likely intrinsic,and the direction of polarization indicates that the materialsurrounding these stars may be magnetic i.e., that the magnetic field isfrozen in this material.
| Polarimetric investigation of background stars in the region of T and RY Tau
Electropolarimetric observations of 97 background stars in the TTauri/RY Tauri region, obtained with the 40-cm Cassegrain telescope ofthe Biurakan Astrophysical Observatory in December 1982, are reportedand interpreted in terms of local-magnetic-field effects oncometary-nebula bending. The data are presented in a table, and thedependence of polarization position angle on declination is establishedin a graph and attributed to a continuous variation in the direction ofthe magnetic field. From the magnitude of the effect, however, it isconcluded that the observed bending of the cometary nebulae in theregion results from the combined influence of the local magnetic momentand the magnetic moment of the star itself (as proposed by Vardanian,1983) rather than from the local moment alone.
| A search for weak H-alpha emission line pre-main-sequence stars
A spectroscopic survey of 177 stars brighter than about 12.5 in R nearfour dark clouds in an effort to find pre-main-sequence (PMS) stars withweak H-alpha emission is reported. A number of such stars have beenfound previously in X-ray images of star formation clouds. Six newcandidate PMS stars with EW (H-alpha) between 0.4 and 4.2 A, in additionto four X-ray discovered stars, are found in the L1551 and L1529 cloudsin the Taurus-Auriga complex. The total number of pre-main-sequencestars in these clouds appears to be about two times the number of strongemission line T Tauri stars.
| U, B, V, R, I stellar photometry in the field of the Taurus dark clouds
A program of photoelectric stellar photometry has been carried out inthe field of the Taurus dark clouds with a view to establishing thedistance of the clouds and the absorption law in that region of the sky.It is found that the distance of the dark clouds accompanying the Tau T1and Tau T3 associations is 132 plus or minus 10 pc. Within theabsorption region 0-4 m, the Taurus dark clouds are characterized by anearly normal absorption law (to within 5-10%). In the field of the darkclouds a group of F0-G0 stars close to the main sequence is found whosespace density is three to eight times that in the solar neighborhood.
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