Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
High-Resolution Observations of Interstellar Ca I Absorption-Implications for Depletions and Electron Densities in Diffuse Clouds
We present high-resolution (FWHM~0.3-1.5 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar Ca Iabsorption toward 30 Galactic stars. Comparisons of the column densitiesof Ca I, Ca II, K I, and other species-for individual componentsidentified in the line profiles and also when integrated over entirelines of sight-yield information on relative electron densities anddepletions (dependent on assumptions regarding the ionizationequilibrium). There is no obvious relationship between the ratio N(CaI)/N(Ca II) [equal to ne/(Γ/αr) forphotoionization equilibrium] and the fraction of hydrogen in molecularform f(H2) (often taken to be indicative of the local densitynH). For a smaller sample of sight lines for which thethermal pressure (nHT) and local density can be estimated viaanalysis of the C I fine-structure excitation, the average electrondensity inferred from C, Na, and K (assuming photoionizationequilibrium) seems to be independent of nH andnHT. While the electron density (ne) obtained fromthe ratio N(Ca I)/N(Ca II) is often significantly higher than the valuesderived from other elements, the patterns of relative nederived from different elements show both similarities and differencesfor different lines of sight-suggesting that additional processesbesides photoionization and radiative recombination commonly andsignificantly affect the ionization balance of heavy elements in diffuseinterstellar clouds. Such additional processes may also contribute tothe (apparently) larger than expected fractional ionizations(ne/nH) found for some lines of sight withindependent determinations of nH. In general, inclusion of``grain-assisted'' recombination does reduce the inferred ne,but it does not reconcile the ne estimated from differentelements; it may, however, suggest some dependence of ne onnH. The depletion of calcium may have a much weakerdependence on density than was suggested by earlier comparisons with CHand CN. Two appendices present similar high-resolution spectra of Fe Ifor a few stars and give a compilation of column density data for Ca I,Ca II, Fe I, and S I.
| 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
| Star formation in the Cepheus Flare region - II. A-type stars associated with IRAS sources
In order to reveal the star-forming history of the molecular cloudcomplex we studied the intermediate mass stellar population in theCepheus Flare region. (Paper I dealt with the distance and the youngstellar object candidates of the region.) Correlating the IRAS PointSource Catalogue and Faint Source Catalogue positions with those of 1214B8-A8 and 1760 F0-F5 type stars brighter thanF12F25ν212ν225 ≈ 4.3, V>> 13mag and classified during an objective prism survey, weidentified 19 stars showing far-infrared excess emission in the CepheusFlare region. In addition to the 16 stars whose counterparts are givenin the IRAS catalogues, we found three more stars with infrared excessnot recognized before. In order to identify the young medium-mass starsassociated with the Cepheus Flare molecular clouds we observed theoptical spectra of the IR-excess stars, and using published opticalphotometry and the IRAS data we examined their spectral energydistributions (SEDs) and IRAS two-colour diagram. The observationsresulted in the discovery of a new Herbig Ae/Be star, BD +68°1118,coinciding with IRAS 21169+6842. More evolved HAe/Be stars may beSAO19953, BD +67°1314 and BD +69°1231, whose Hα linesshowed weak emission components. Possible β Pictoris- or Vega-typestars may be HD 203854, HD 212826 and HD 216486, whereas thefar-infrared fluxes at the positions of BD +72°1018, HD 210806 andHD 217903 can be attributed to the heating of the interstellarenvironment. We used distances and radial velocities of the starsderived from the spectroscopy and published optical photometry asindicators of their relations to the clouds. Information on theenvironment of the observed stars deduced from the diffuse interstellarband at λ6613 is briefly discussed.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Star Formation in the Cepheus Flare Molecular Clouds. I. Distance Determination and the Young Stellar Object Candidates
Results of an objective prism Schmidt survey are combined with IRASsurvey data in order to assess the star-forming activity in the CepheusFlare, a nearby giant molecular cloud complex at ~+15 deg above theGalactic equator. The distribution of absorbing matter along the line ofsight was also studied. The Wolf diagrams, displaying the cumulativedistribution of field star distance moduli, show that the interstellarmatter in this region is concentrated at three characteristic distances:200, 300, and 450 pc. The three components, though partly overlapping,can be separated along the Galactic latitude. Within the area of theCepheus Flare, distances are determined for 14 Lynds dark clouds and forsome other clouds. In order to compile a sample of young stellar object(YSO) candidates, three types of star formation signposts were searchedfor the following: 1. Prestellar cores in the IRAS 100 mu m opticaldepth image of the region, 2. Far-infrared sources representing embeddedYSOs and optically visible pre-main-sequence star candidates using IRASPoint Source Catalog, Faint Source Catalog, and calibrated IRAS detectorscans, 3. H alpha emission stars appearing on low-dispersion objectiveprism Schmidt plates as candidate pre-main-sequence stars. The IRAS 100mu m optical depth image of the region revealed 107 dense cores. Most ofthem are probably "starless" cores and, as such, potential sites offuture star formation. One hundred twenty-two IRAS point sources wereselected as probable YSOs at various evolutionary stages. An objectiveprism search for H alpha emission stars covering an area of about 150deg2 resulted in the detection of 142 H alpha emission stars. Infraredfluxes taken from the IRAS catalogs or determined from the detectorscans are listed for 95 of them. This sample is expected to consist ofmostly T Tauri stars associated with the cloud complex. Finding chartsand catalogs of the young stellar object candidates are also given.These results may serve as a basis for further dedicated studies of theregion and will be useful for comparison when star-forming activity inother cloud complexes is investigated.
| Effective temperature of detached eclipsing binaries from HIPPARCOS parallax
Effective temperatures of detached eclipsing binaries computed throughHipparcos trigonometric parallaxes are compared with the photometricdeterminations. The former are based on the values of the radius, theapparent visual magnitude and the bolometric correction of the star,whereas the latter are obtained from standard calibrations usingStromgren or Johnson colour indices. The working sample contains allwell-studied detached double-lined eclipsing binaries belonging to theHipparcos catalogue and with relative errors in the parallaxes smallerthan 20%. They cover a temperature range from 5000 K to 25000 K. A smallsystematic trend of 0.010 dex (s.d. 0.010) for T_eff <= 10000 K andof 0.015 dex (s.d. 0.060) for T_eff > 10000 K is observed between thetwo temperature determinations, that could be due to inaccuracies onphotometric effective temperatures. Based on data from the ESA Hipparcosastrometry satellite
| Star formation in L 1199
Lynds 1199 is an extended dark cloud of moderate opacity in the upperCepheus region. The B3V type star HD206135 illuminating the reflectionnebula DG 175 is associated with this cloud. In this paper the nature ofthe cloud and its associated young stellar objects is studied on thebasis of13CO data obtained with the 4 m millimeter wavetelescope of Nagoya University, photographic observations taken with the60/90 cm Schmidt telescope of Konkoly Observatory, as well as IRAS data.
| CH(+) in the interstellar medium
This paper describes observations of interstellar CH(+) along the linesof sight to O and B stars with E(B-V)s up to +1.13. Along some lines ofsight with strong detections of CH(+), we find distinct radial velocityshifts between the CH(+) lines and other neutral species, such as Ca Iand CH. The shifts are small but are predicted by shock models of CH(+)formation in which the shock is inclined with respect to the observer.We have also found no column densities exceeding approximately1013.8/sq cm. When these data are examined along with theother CH(+) data collected from the literature, the previously seentendency of CH(+) column density to increase with E(B-V) does notcontinue beyond reddenings of about +0.6. These findings offer supportto the shock model of CH(+) formation for at least some lines of sight.
| The polarized dust envelope around the red supergiant MU Cephei
A polarization map of scattered light around the red supergiant MuCephei has been developed which shows a large dust envelope with amorphology agreeing fairly well with that of its Na I emission. Astructure with two different shells lying inside and outside of about 17arcsec from the star is found along with a significant asymmetry. Thepolarization of the scattered light is not tangentially oriented, withdeviations of about 20 deg, which can be at least qualitativelyexplained by homogeneously aligned nonspherical grains. The alignment ofthe polarization suggests that it is due to the interstellar magneticfield. The colors of the polarized scattered light around Mu Cep andAlpha Ori are found to be consistently very similar with a B and Ustrikingly different from that predicted from Rayleigh scattering. Thepolarized intensity of the shells, interpreted with Mie scatteringtheory, yields dust loss rates in agreement with a rate deduced frominfrared data.
| BVR observations of polarization parameters of stars in reflection nebulas
The observed polarizations of the nuclei of reflection nebulas and fieldstars in B, V, R filters are given. A connection has been found betweenthe direction of the polarization vector, the structure of thereflection nebula, and the shape of the cloud in which the nebula issituated. The direction of the plane of polarization for stars seenthrough the filamentary structure of a nebula is the same as thedirection of the filaments. Stars situated at the edges of clouds andchannels have direction of the polarization vector the same as theapparent boundary of the cloud.
| Short-Period Variability of the Binary Star HD 206631
Not Available
| 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.
| A survey of interstellar neutral potassium. I - Abundances and physical conditions in clouds toward 188 early-type stars
Observations of interstellar absorption in the resonance doublet 7664,7698 A of neutral potassium toward 188 early-type stars at a spectralresolution of 8 km/s are reported. The 7664 A line is successfullyseparated from nearly coincident telluric O2 absorption for all but afew of the 165 stars for which K I absorption is detected, makingpossible an abundance analysis by the doublet ratio method. Therelationships between the potassium abundances and other atomicabundances, the abundance of molecular hydrogen, and interstellarreddening are investigated.
| 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.
| 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
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Cefeusz |
| Rektaszcenzió: | 21h36m57.06s |
| Deklináció: | +68°11'07.3" |
| Vizuális fényesség: | 8.259 |
| Távolság: | 1190.476 parszek |
| RA sajátmozgás: | 0.9 |
| Dec sajátmozgás: | -4 |
| B-T magnitude: | 8.452 |
| V-T magnitude: | 8.275 |
Katalógusok és elnevezések:
|
