Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
| 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).
| Revisiting Hipparcos data for pre-main sequence stars
We cross-correlate the Herbig & Bell and Hipparcos Catalogues inorder to extract the results for young stellar objects (YSOs). Wecompare the distances of individual young stars and the distance oftheir presumably associated molecular clouds, taking into accountpost-Hipparcos distances to the relevant associations and usingHipparcos intermediate astrometric data to derive new parallaxes of thepre-main sequence stars based on their grouping. We confirm that YSOsare located in their associated clouds, as anticipated by a large bodyof work, and discuss reasons which make the individual parallaxes ofsome YSOs doubtful. We find in particular that the distance of TaurusYSOs as a group is entirely consistent with the molecular clouddistance, although Hipparcos distances of some faint Taurus-Auriga starsmust be viewed with caution. We then improve some of the solutions forthe binary and multiple pre-main sequence stars. In particular, weconfirm three new astrometric young binaries discovered by Hipparcos:RY Tau, UX Ori, and IXOph. Based on observations made with the ESA Hipparcosastrometry satellite
| 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 13CO Survey of Molecular Clouds in Gemini and Auriga
A large-scale survey for molecular clouds in 13CO(J = 1-0) was performedtoward the Gemini and Auriga regions (170 deg < l <= 196 deg and-10 deg <= b < 10 deg) with velocity coverages of -30 < VLSR< +30 km s-1 and -20 < VLSR < +40 km s-1 for 170 deg < l<= 188 deg and 188 deg < l <= 196 deg, respectively, by usingthe two 4 m millimeter-wave telescopes at Nagoya University. An area of520 deg2 was covered at an 8' grid spacing with a 2.'7 beam, and 29,250positions were observed. Significant 13CO emission (>=1.2 K km s-1 =3 sigma ) is detected at 1032 positions, and 139 distinct 13CO cloudsare identified. Physical properties such as molecular column density,size, and mass are derived for each cloud. Comparison with known H IIregions and other associated visible objects indicates that 98 of the139 clouds are located at ~2 kpc, while the rest lie at <~ 1 kpc. Thecandidates for protostars are selected from IRAS point sources and 141sources are identified as protostellar candidates associated with the13CO clouds. A statistical study of the 13CO clouds and of thecandidates for protostars shows the following results: 1. The massspectra of the 13CO clouds are well represented by a power law,Ncloud(>=Mcloud) = 1.4 x 104(Mcloud/Mȯ)-0.83 - 1.4 for theclouds at ~2 kpc and Ncloud(>=Mcloud) = 3.5 x102(Mcloud/Mȯ)-0.64 - 2.4 for the rest. 2. The line width, DeltaVcomp, and the size, R, of the 13CO clouds show a power-law relationwith an index 0.24 +/- 0.06, where the dispersion in the fitting isfairly large. 3. A virial analysis made for the 13CO clouds indicatesthat the relation between the virial mass, Mvir, and the mass measuredin 13CO, Mcloud, is aproximated well by (Mvir/Mȯ) = 2.0 x101(Mcloud/Mȯ)0.72, which suggests that smaller clouds tend to bemore weakly bound gravitationally than larger clouds or are dispersingif the external pressure is negligible. This is probably the cuase of asmall index value of the line width-size relation. 4. The luminosityfunction of the IRAS point sources associated with 13CO clouds are wellrepresented by a power law withN_⋆(>=L_⋆)=4.0x102L^{-0.29}_⋆-1.9x10 forthose at ~2 kpc and N_⋆(>=L_⋆)=2.3x10L^{-0.27}_⋆-3.2for the rest. 5. The luminosity of the most luminous IRAS point sourcein a given molecular cloud increases systematically with the mass of theassociated cloud. 6. The 13CO clouds associated with IRAS point sources,which are regarded as ongoing star-forming clouds, tend to be moremassive and larger in size and to have higher column densities thanthose without any sign of star formation. These relations are found tobe consistent with those derived in Cygnus by Dobashi, Bernard, &Fukui and in Cepheus-Cassiopeia by Yonekura et al. In order to study thestar formation activities, we studied the ratio of virial mass and themass measured in 13CO, Mvir/Mcloud, and its relation with starformation. It is clearly seen that the star-forming 13CO clouds have lowMvir/Mcloud, and all the clouds with high Mvir/Mcloud exhibit no sign ofstar formation. This suggests that star formation rarely occurs inclouds with overall kinetic energy higher than the gravitational energy.
| A Study of the Kinematics of the Local Dark Clouds
Not Available
| UBV photometry of stars whose positions are accurately known. VI
Results are presented from UBV photometric observations of 1000 stars ofthe Bright Star Catalogue and the faint extension of the FK5.Observations were carried out between July 1987 and December 1990 withthe 40-cm Cassegrain telescope of the Kvistaberg Observatory.
| 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.
| The luminosity of reflection nebulae
Consideration is given to the connection between the dispersion inHubble's relation for reflection nebulae and their morphologicalcharacteristics. Statistical estimates show that the reflection nebulaeconnected with more opaque dust-gas clouds, compared to those near lessopaque clouds, have large values of Delta-B (the measure of deviationsin Hubble's relation) and a high surface brightness. These propertiesare more pronounced in the Herbig Ae/Be stars. Stars in the nebulaeconnected with more opaque dust-gas clouds were found to exhibit excessreddening, with R above 3.1. It is concluded that the dispersion in theHubble relation is mainly due to the optical depth of the nebulae.
| MK spectral classifications for 30 faint stars in Praesepe
Faint members of the Praesepe open cluster were observed with theGarrison prime-focus spectrograph on the C. F. H. Telescope. MK spectralclassifications are presented for 30 stars from F3 V to K7 V in acentral region of the cluster. The spectra look identical to those ofthe Hyades stars in this interval. Apart from two obvious binaries and abackground star, the H-R diagram shows an extremely narrow mainsequence. This yields a distance modulus, Praesepe minus Hyades, of 3.0mag.
| 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.
| Polarization of stars in R-associations - Observational data
Polarimetric data are assembled for 95 stars that are illuminatingreflection nebulae. Most of these belong to 18 standard R-associations.The observed dependence of the percentage polarization P on wavelengthand color excess E(B-V) suggest that the unpolarized light ofR-association members may become polarized as it traverses an ensembleof dust grains aligned by a magnetic field which in some cases (Tau R2,Ori R1/R2, Sco R1, Cep R2) is intrinsic to the association. In certainR-associations the grain size is variable and the stochastic magneticfield component fluctuates on a scale of 10-30 pc.
| Molecular clouds associated with reflection nebulae. I - A survey of carbon monoxide emission
The paper presents 2.6 mm wavelength CO and (C-13)O observations of 130molecular clouds associated with reflection nebulae. Enhanced COemission was found in the vicinity of the illuminating star in abouthalf the objects studied. There is a tendency for the CO peak to beslightly displaced from the star. Many examples of peaks that appear toresult from heating of the cloud by the nearby star are found, whileothers appear to be associated with independent concentrations ofmaterial.
| Lichtelektrische Beobachtungen von 14 Ap-Sterne.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...31...83R&db_key=AST
| Pulsation in peculiar A stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..698P&db_key=AST
| Stars in reflection nebulae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..233R&db_key=AST
| A study of reflection nebulae.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..990V&db_key=AST
| Notes on Diffuse Galactic Nebulae
Not Available
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Taurus |
| Ascensió Recta: | 04h48m22.74s |
| Declinació: | +29°46'22.8" |
| Magnitud Aparent: | 7.395 |
| Distancia: | 196.078 parsecs |
| Moviment propi RA: | 5.9 |
| Moviment propi Dec: | -26.6 |
| B-T magnitude: | 7.452 |
| V-T magnitude: | 7.4 |
Catàlegs i designacions:
|
