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The Asymmetric Explosion of Type Ia Supernovae as Seen from Near-Infrared Observations
We present near-infrared spectra of late-phase (>200 days) Type Iasupernovae (SNe Ia) taken at the Subaru Telescope. The [Fe II] line ofSN 2003hv shows a clear flat-topped feature, while that of SN 2005Wshows a less prominent flatness. In addition, a large shift in theirline center, varying from -3000 to 1000 km s-1 with respectto the host galaxies, is seen. Such a shift suggests the occurrence ofan off-center, nonspherical explosion in the central region and providesimportant, new constraints on the explosion models of SNe Ia.Based on data collected at Subaru Telescope, which is operated by theNational Astronomical Observatory of Japan.
| Subaru K-Band Spectroscopy of Low-Mass Protostars in Taurus
We present K-band spectra of five Class I objects in the Taurusmolecular cloud. The high-sensitivity and high-spatial resolutionobservations using the Subaru Telescope enabled us to detect theemission lines of Brγ and H2 in four and two objects,respectively, and photospheric absorption lines in two objects. From theabsorption lines, the effective temperature, stellar luminosity, and theamount of veiling were estimated for the two objects (IRAS 04016+2610and IRAS 04248+2612). We conclude that the amount of circumstellaremission is much higher in IRAS 04016 (rK=7-10) than IRAS04248 (rK~2), while the stellar properties are similarbetween the two objects. Apart from the stellar spectra, the nebularspectra were obtained for IRAS 04016 and IRAS 04248. The reflectionnebulae of the Class I objects were verified from a spectroscopicviewpoint for the first time: we found that the nebular spectra areexplained as the scattered light from the central young stellar objectswith the difference of the line-of-sight extinction between the star andnebula, ΔAV~2-9 mag.Based on data collected at the Subaru Telescope, which is operated bythe National Astronomical Observatory of Japan.
| Near-Infrared Spectroscopy of Very Low-Luminosity Young Stellar Objects in the Taurus Molecular Cloud
We carried out near-infrared spectroscopic observations of 23 verylow-luminosity young stellar object (YSO) candidates and 5 of theircompanions in Heiles Cloud 2, one of the densest parts of the Taurusmolecular cloud. Twelve objects were confirmed to be YSOs by theBγ feature. The effective temperatures of the YSOs and of thecompanions are estimated from the 2.26 - μm feature, the 2.21 - μmfeature, and the H2O band strengths. Detailed comparisons ofour photometric and spectroscopic observations with evolutionary trackson the HR diagram suggest some objects to be very low-mass YSOs.
| Interstellar Extinction and Polarization in the Taurus Dark Clouds: The Optical Properties of Dust near the Diffuse/Dense Cloud Interface
Observations of interstellar linear polarization in the spectral range0.35-2.2 μm are presented for several stars reddened by dust in theTaurus region. Combined with a previously published study by Whittet etal., these results represent the most comprehensive data set availableon the spectral dependence of interstellar polarization in this nearbydark cloud (a total of 27 sight lines). Extinction data for these andother reddened stars in Taurus are assembled for the same spectralrange, combining published photometry and spectral classifications withphotometry from the Two Micron All Sky Survey. The polarization andextinction curves are characterized in terms of the parametersλmax (the wavelength of maximum polarization) andRV (the ratio of total to selective extinction),respectively. The data are used to investigate in detail the question ofwhether the optical properties of the dust change systematically as afunction of environment, considering stars observed throughprogressively more opaque (and thus progressively denser) regions of thecloud. At low visual extinctions (03, real changes in grainproperties occur, characterized by observed RVvalues in the range 3.5-4.0. A simple model for the development ofRV with AV suggests thatRV may approach values of 4.5 or more in thedensest regions of the cloud. The transition between ``normal''extinction and ``dense cloud'' extinction occurs at AV~3.2, avalue coincident with the threshold extinction above whichH2O-ice is detected on grains within the cloud. Changes inRV are thus either a direct consequence ofmantle growth or occur under closely similar physical conditions. Dustin Taurus appears to be in a different evolutionary state compared withother nearby dark clouds, such as ρ Oph, in which coagulation is thedominant physical process.
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| A Near-Infrared Search for Companions around Very Low Luminosity Young Stellar Objects in Taurus
We have carried out a near-infrared search for companions around 23 verylow luminosity young stellar objects (YSOs) in the Taurus molecularcloud. After sophisticated photometry and analysis, five extremely lowluminosity YSO (ELL-YSO) candidate companions were identified by boththeir near-infrared colors and proximity to the primary (separation lessthan 6"). They show infrared excess, as do ordinary YSOs. Their absoluteJ-band magnitudes range from 9 to 12 mag. The masses of these companionsare estimated from their J-band luminosities, which use recentevolutionary tracks for very low mass objects. It is found that all areyoung brown dwarf candidates. The Ks-band magnitude difference betweenthe ELL-YSO candidate companions and their primaries ranges from 2 to 6mag, significantly larger than observed in T Tauri binaries. It issuggested that the companions are formed by the fragmentation of a diskaround the primary. The binary frequency is 22^+9_-10% for systems witha period ranging between 10^7-10^8 days. This frequency is consistentwith that of T Tauri stars, but it is significantly higher than that oflow-mass main-sequence stars.
| Near-Infrared Imaging Polarimetry of Embedded Young Stars in the Taurus-Auriga Molecular Cloud
We describe near-infrared (JHK) imaging polarimetry of 21 embeddedprotostars in the Taurus-Auriga molecular cloud. These objects displayextended, highly polarized reflection nebulae with V-shaped, unipolar,and bipolar morphologies. Most sources have PK ~ 5%-20% in an 8"aperture; a few objects have PK <~ 5%. The polarization increasestoward shorter wavelengths and is generally aligned perpendicular to thelong axis of the reflection nebula. We develop an analytic scatteringmodel for the near-IR colors and polarizations of embedded protostars.Our Taurus data require visual extinctions, AV ~ 25-60 mag, comparableto those predicted for models of collapsing clouds. The ratio ofscattered flux to intrinsic source flux ranges from Fs/F0 ~ 0.001 at1.25 mu m to Fs/F0 ~ 0.015 at 3.5 mu m. These results indicate that theobserved ratio of scattered light to direct (extincted) light increasesfrom Fs/Fd ~ 0.1 at 3.5 mu m to Fs/Fd ~ 25 at 1.25 mu m. Our datafurther require intrinsic colors of 0.6 <~ J-H <~ 0.9, 0.3 <~H-K <~ 0.6, and 0.4 <~ K-L <~ 1.2 for the central sources ofTaurus protostars. We adopt the Terebey, Shu, & Cassen solution foran infalling, rotating protostellar cloud and use a two dimensionalMonte Carlo radiative transfer code to model the near-IR polarizationdata for this sample. Our results indicate envelope parameters inagreement with previous estimates from broadband spectral energydistributions and near-IR images. We estimate infall rates, M dot~(2-5)x10^{-6} Mȯ yr-1; centrifugal radii, Rc ~ 10-50 AU; andopening angles of the bipolar cavity, theta h ~ 10 deg-20 deg, for atypical object. Standard grain parameters can explain the near-IR colorsand polarizations of Taurus protostars. The polarization maps show thatTaurus grains have a high maximum polarization at K, Pmax,K >~ 80%.The large image sizes of this sample further imply a high K-band albedo,omega K ~ 0.3-0.4. Model polarization maps indicate that the size of the"polarization disk" increases with the size of the instrumentalpoint-spread function. Relating the morphology of polarization vectorsto disk or envelope properties thus requires some care and a goodunderstanding of the characteristics of the instrument.
| 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.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| 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.
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| An IRAS survey of the Taurus-Auriga molecular cloud
IRAS data are used to search for young premain-sequence stars notpreviously associated with molecular cloud cores in the Taurus-Aurigaregion. NIR photometry and optical spectroscopy suggest that many of theobjects are young stars. The sample includes six new embedded sourceswith luminosities comparable to that of the average T Tauri star,suggesting that surveys for premain-sequence stars in the cloud areessentially complete for luminosities greater than 0.5 solarluminosities. A disagreement is found between accretion rates derivedfrom the duration of the embedded phase and those derived from thebolometric luminosity. It is found that this disagreement may bereconciled if a star accretes most of its mass in a time that is shortcompared to the duration of the embedded phase or if the ages of T Tauristars have been underestimated.
| UBV photometry of stars whose positions are accurately known. IV
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...68..211O&db_key=AST
| 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.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Bika |
| Rektaszcenzió: | 04h18m27.84s |
| Deklináció: | +25°00'14.1" |
| Vizuális fényesség: | 8.526 |
| Távolság: | 250.627 parszek |
| RA sajátmozgás: | 2.7 |
| Dec sajátmozgás: | -4.3 |
| B-T magnitude: | 9.19 |
| V-T magnitude: | 8.581 |
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