Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Spectral Analysis of 4 Lacertae and ν Cephei
Elemental abundance analysis based on high S/N and high resolutionDominion Astrophysical Observatory spectrograms have been performed fortwo early type supergiants: 4 Lac (B9 Iab) and {\msf ν } Cep (A2 Ia).Lines as weak as of order 5 mÅ are employed in this study. Theprojected rotational velocities of these stars are 14 and 26 kms-1, respectively. Both stars show similar radial velocityamplitudes, macroturbulent velocities and the same general elementalabundance trends. Their He, CNO and light element abundances are solaror overabundant while the iron peak and heavy element abundances aresolar or underabundant. Detailed LTE model atmosphere abundance analysisshows that 4 Lac has nuclearly processed matter in its photosphere while{\msf ν } Cep does not.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Spectral Analyses of 4 Lacertae and ν Cephei
Not Available
| Characteristics and classification of A-type supergiants in the Small Magellanic Cloud
We address the relationship between spectral type and physicalproperties for A-type supergiants in the Small Magellanic Cloud (SMC).First, we construct a self-consistent classification scheme for Asupergiants, employing the calcium K to Hɛ line ratio as atemperature-sequence discriminant. Following the precepts of the `MKprocess', the same morphological criteria are applied to Galactic andSMC spectra, with the understanding that there may not be acorrespondence in physical properties between spectral counterparts indifferent environments. Then we discuss the temperature scale,concluding that A supergiants in the SMC are systematically cooler thantheir Galactic counterparts at the same spectral type, by up to ~10 percent. Considering the relative line strengths of Hγ and the CH Gband, we extend our study to F- and early G-type supergiants, for whichsimilar effects are found. We note the implications for analyses ofluminous extragalactic supergiants, for the flux-weightedgravity-luminosity relationship and for population synthesis studies inunresolved stellar systems.
| L' and M' standard stars for the Mauna Kea Observatories Near-Infrared system
We present L' and M' photometry, obtained at the United Kingdom InfraredTelescope (UKIRT) using the Mauna Kea Observatories Near-Infrared(MKO-NIR) filter set, for 46 and 31 standard stars, respectively. The L'standards include 25 from the in-house `UKIRT Bright Standards' withmagnitudes deriving from Elias et al. and observations at the InfraredTelescope Facility in the early 1980s, and 21 fainter stars. The M'magnitudes derive from the results of Sinton and Tittemore. We estimatethe average external error to be 0.015 mag for the bright L' standardsand 0.025 mag for the fainter L' standards, and 0.026 mag for the M'standards. The new results provide a network of homogeneously observedstandards, and establish reference stars for the MKO system, in thesebands. They also extend the available standards to magnitudes whichshould be faint enough to be accessible for observations with moderndetectors on large and very large telescopes.
| Search for magnetic fields in A-type supergiants
We have searched for magnetic signatures in A-type supergiants. Theobtained magnetic values for seven of these stars are presented here.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| High-Precision Near-Infrared Photometry of a Large Sample of Bright Stars Visible from the Northern Hemisphere
We present the results of 8 yr of infrared photometric monitoring of alarge sample of stars visible from Teide Observatory (Tenerife, CanaryIslands). The final archive is made up of 10,949 photometric measuresthrough a standard InSb single-channel photometer system, principally inJHK, although some stars have measures in L'. The core of this list ofstars is the standard-star list developed for the Carlos SánchezTelescope. A total of 298 stars have been observed on at least twooccasions on a system carefully linked to the zero point defined byVega. We present high-precision photometry for these stars. The medianuncertainty in magnitude for stars with a minimum of four observationsand thus reliable statistics ranges from 0.0038 mag in J to 0.0033 magin K. Many of these stars are faint enough to be observable with arraydetectors (42 are K>8) and thus to permit a linkage of the bright andfaint infrared photometric systems. We also present photometry of anadditional 25 stars for which the original measures are no longeravailable, plus photometry in L' and/or M of 36 stars from the mainlist. We calculate the mean infrared colors of main-sequence stars fromA0 V to K5 V and show that the locus of the H-K color is linearlycorrelated with J-H. The rms dispersion in the correlation between J-Hand H-K is 0.0073 mag. We use the relationship to interpolate colors forall subclasses from A0 V to K5 V. We find that K and M main-sequence andgiant stars can be separated on the color-color diagram withhigh-precision near-infrared photometry and thus that photometry canallow us to identify potential mistakes in luminosity classclassification.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| JHK Standards for Small Telescopes
The AAVSO Futures meeting, held in Madison, WI, in May 2001, proposedthat the AAVSO support near-infrared research with small telescopes. Aphotometer, the SSP-4, has been developed to provide J- and H-bandcapability for a reasonable cost. However, proper calibrated photometryrequires a set of standard stars. This paper describes such a set ofstars, suitable for small telescopes, and with accurate coordinates,proper motions, and high-quality magnitudes.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| H I Spectra and Column Densities toward HVC and IVC Probes
We show 21 cm line profiles in the direction of stars and extragalacticobjects, lying projected on high- and intermediate-velocity clouds (HVCsand IVCs). About half of these are from new data obtained with theEffelsberg 100 m telescope, about a quarter are extracted from theLeiden-Dwingeloo Survey (LDS), and the remaining quarter were observedwith other single-dish telescopes. H I column densities were determinedfor each HVC/IVC. Paper I of this series uses these in combination withoptical and ultraviolet high-resolution measurements to deriveabundances. Here an analysis is given of the difference and ratio of N(HI) as observed with a 9' versus a 35' beam. For HVCs and IVCs the ratioN(H I-9')/N(H I-35') lies in the range 0.2-2.5. For low-velocity gasthis ratio ranges from 0.75 to 1.3 (the observed ratio is 0.85-1.4, butit appears that the correction for stray radiation is slightly off). Thesmaller range for the low-velocity gas may be caused by confusion in theline of sight, so that a low ratio in one component can be compensatedby a high ratio in another-for 11 low-velocity clouds fitted by onecomponent the distribution of ratios has a larger dispersion. Comparisonwith higher angular resolution data is possible for 16 sight lines.Eight sight lines with H I data at 1'-2' resolution show a range of0.75-1.25 for N(H I-2')/N(H I-9'), while in eight other sight lines N(HI-Lyα)/N(H I-9') ranges from 0.74 to 0.98.
| Distances and Metallicities of High- and Intermediate-Velocity Clouds
A table is presented that summarizes published absorption linemeasurements for the high- and intermediate-velocity clouds (HVCs andIVCs). New values are derived for N(H I) in the direction of observedprobes, in order to arrive at reliable abundances and abundance limits(the H I data are described in Paper II). Distances to stellar probesare revisited and calculated consistently, in order to derive distancebrackets or limits for many of the clouds, taking care to properlyinterpret nondetections. The main conclusions are the following. (1)Absolute abundances have been measured using lines of S II, N I, and OI, with the following resulting values: ~0.1 solar for one HVC (complexC), ~0.3 solar for the Magellanic Stream, ~0.5 solar for a southern IVC,and ~solar for two northern IVCs (the IV Arch and LLIV Arch). Finally,approximate values in the range 0.5-2 solar are found for three moreIVCs. (2) Depletion patterns in IVCs are like those in warm disk or halogas. (3) Most distance limits are based on strong UV lines of C II, SiII, and Mg II, a few on Ca II. Distance limits for major HVCs aregreater than 5 kpc, while distance brackets for several IVCs are in therange 0.5-2 kpc. (4) Mass limits for major IVCs are0.5-8×105 Msolar, but for major HVCs theyare more than 106 Msolar. (5) The Ca II/H I ratiovaries by up to a factor 2-5 within a single cloud, somewhat morebetween clouds. (6) The Na I/H I ratio varies by a factor of more than10 within a cloud, and even more between clouds. Thus, Ca II can beuseful for determining both lower and upper distance limits, but Na Ionly yields upper limits.
| Thermal Infrared Imaging of the Bipolar H II Region S106
The extended infrared emission from Sharpless 106 shows complexstructure in ground-based images obtained at wavelengths from 3 to 20μm. The structure of the ionization fronts and photodissociationregions are resolved in Brα emission at 4.05 μm and emissionfrom polycyclic aromatic hydrocarbons at 3.29 μm, with the H Iemission residing interior to the hydrocarbon emission. The mid-infraredobservations at 10 to 20 μm reveal the distribution of continuumemission from warm dust in the nebula. These images have a higherspatial resolution than previous mid-infrared maps, but they supportearlier findings of a relatively constant dust color temperature of ~135K in the extended dust, excluding the dust near the self-luminoussources IRS 2 and 4. All infrared images presented here show a dark lanebisecting the nebula, which probably results from shadowing of lightfrom the central engine rather than line-of-sight extinction. If thisshadow is caused by a compact disk around IRS 4, its ionized inner edgewould be within the radio photosphere of the stellar wind at wavelengthslonger than about 1.5 cm. There appears to be a faint point source seenat near-infrared wavelengths that is coincident with the position of abright far-infrared source. This source is adjacent to some brightnear-infrared nebulosity but is not clearly detected in thermal infrareddust emission.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| The Normal Energy Distributions in Stellar Spectra: Giants and Supergiants
We have derived the normal spectral energy distributions for thoseearly-type subgiants, giants, and supergiants that were not investigatedin our earlier studies, which were in most cases also not included inthe studies of Sviderskiene. Color indices computed using our normalenergy distributions are in good agreement with normal colors derivedfrom observations in the Vilnius photometric system. The reliability ofour distribution curves is also demonstrated by comparisons of observedand computed (W-B)-(B-V) two-color diagrams in the WBVR system. Normalcolor indices for the photometric WBVR system are derived.
| Keck Mid-Infrared Imaging of QSO 2237+0305
Using the Long Wavelength Spectrometer on Keck, we have imaged thegravitationally lensed radio-quiet quasi-stellar object QSO 2237+0305 at8.9 and 11.7 μm for the first time. The mid-IR flux ratios areinconsistent with the optical flux ratios but agree with the radio fluxratios and with some published gravitational lens models. These fluxratios indicate that the IR emission is not affected by microlensing,which rules out the synchrotron emission model. The IR emission islikely produced by hot dust extended on a length scale of more than 0.03pc. The spectral energy distribution further implies a narrow range ofdust temperatures, suggesting that the dust may be located in a shellextending between ~1 and 3 pc from the nucleus and intercepting abouthalf of the QSO luminosity.
| The Near-Ultraviolet Continuum of Late-Type Stars
Analyses of the near-ultraviolet continuum of late-type stars have ledto controversial results regarding the performance of state-of-the-artmodel atmospheres. The release of the homogeneous InternationalUltraviolet Explorer (IUE) final archive and the availability of thehigh-accuracy Hipparcos parallaxes provide an opportunity to revisitthis issue, as accurate stellar distances make it possible to compareobserved absolute fluxes with the predictions of model atmospheres. Thenear-UV continuum is highly sensitive to Teff and [Fe/H], andonce the gravity is constrained from the parallax, these parameters maybe derived from the analysis of low-dispersion, long-wavelength(2000-3000 Å) IUE spectra for stars previously studied by Alonso,Arribas, & Martínez-Roger using the Infrared Flux Method(IRFM). A second comparison is carried out against the starsspectroscopically investigated by Gratton, Carretta, & Castelli. Itis shown that there is a good agreement between Teff valuesobtained from the IRFM and those from the near-UV continuum, and aremarkable correspondence between observed and synthetic fluxes forstars with 4000 K<=Teff<=6000 K of any metallicity andgravity. These facts suggest that model atmospheres provide an adequatedescription of the near-UV continuum forming region and that theopacities involved are essentially understood.
| [Fe II] Bubbles in the Young Planetary Nebula Hubble 12
We have obtained narrowband images of the young planetary nebula Hubble12 showing [Fe II] line emission in bipolar bubbles near the core.Bright [Fe II] emission is strong evidence for shocks, suggesting thepresence of a high-velocity wind emanating from the central star. Wecompare our data to previously published images of Hubble 12-findingsimilar structures in hydrogen recombination and free-free emission-andwe propose three possible interpretations of the data: that the bubblesindicate the inner shock of the fast wind, that the [Fe II] emission isevidence of the outer shock of an episodic wind, or that the emission iscooling line radiation from a photodissociation region. We argue thatthe first two interpretations are more likely, since the [Fe II]emission must be shock excited.
| Understanding A-type supergiants. I. Ultraviolet and visible spectral atlas
This paper is the first of a series whose aim is to perform a systematicstudy of A-type supergiant atmospheres and winds. Here we present aspectral atlas of 41 A-supergiants observed by us in high and mediumresolution in the visible and ultraviolet. The atlas consists ofprofiles of the Hα , Hβ , Hγ , Hdelta , Hepsilon , CaII (H and K), Na I (D1 and D2), Mg II4481, Mg II [uv1] and FeII [uv1, uv2, uv3, uv62, uv63, uv161] lines for 41 stars with spectraltypes ranging from B9 to A9 and luminosity classes Ia, Iab and Ib, andprovides the basic data for a thoughtful study of these stars. Theoverall characteristics of the sample as well as the data reductionprocedures are described. We also present some examples of spectralvariability. Figures 1-3 are only available in electronic form at thehttp://www.edpsciences.com} of A-type supergiants\fnmsep\thanks{Based onobservations made with the INT and JKT telescopes operated on the islandof La Palma by the RGO in the Spanish Observatorio del Roque de LosMuchachos of the Instituto de Astrofisica de Canarias, with the 2.2~mtelescope at Calar Alto Observatory, Spain, with the Bernard Lyot 2~mtelescope at Pic Du Midi Observatory, France and observations collectedat the European Southern Observatory at La Silla, Chile.
| Understanding A-type supergiants. II. Atmospheric parameters and rotational velocities of Galactic A-type supergiants
We present the second paper of a series whose aim is to perform a globalstudy of Galactic A-supergiants. Very little work has been carried outto determine the stellar parameters of these stars. This is illustratedwith a brief review of some previous works. In this paper we analyze thedetermination of absolute magnitudes, spectral types and atmosphericparameters using the most recent Kurucz LTE blanketed model atmospheresand we discuss the applicability of the calibrations, such as theSchmidt-Kaler's (\cite{Sch-K}) calibration. Rotation is also animportant parameter in A-supergiants but their rotational velocities arepoorly known. We have calculated projected rotational velocities fromthe Fourier analysis of the observed Mg II (4481 Ä) line. Based onobservations made with the INT and JKT telescopes operated on the islandof La Palma by the RGO in the Spanish Observatorio del Roque de LosMuchachos of the Instituto de Astrofisica de Canarias, with the 2.2mtelescope at Calar Alto Observatory, Spain, with the Bernard Lyot 2mtelescope at Pic Du Midi Observatory, France and observations collectedat the European Southern Observatory at La Silla, Chile
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Broad-band JHK(L') photometry of a sample of giants with 0.5 > [Fe/H] > -3
We present the results of a three-year campaign of broad-band photometryin the near-infrared J, H, K and L' bands for a sample of approximately250 giant stars carried out at the Observatorio del Teide (Tenerife,Spain). Transformations of the Telescopio Carlos Sanchez systeminto/from several currently used infrared systems are extended to theredward part of the colour axis. The linearity of our photometric systemin the range -3 mag [Fe/H] >-3. Data of comparable quality previouslypublished have been added to the sample in order to increase thereliability of the relations to be obtained. We also provide mean IRcolours for giant stars according to spectral type.ables 1, 2 and 3 are only available in electronic form via the CDS(anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html
| Westerbork HI observations of two High-Velocity Clouds
Westerbork HI synthesis observations are presented for the directions ofthe stars 4 Lac and HD 135485. Interstellar absorption lines at highvelocities had been reported in the UV spectrum of 4 Lac, setting anupper limit of 1.2 kpc on the distance of the associated, small HI cloud(Bates et al. 1990, 1991). The Westerbork observations show that thiscloud (l = 100() o, b = - 7() o, v_LSR +100 km s(-1) ), which must havea high velocity relative to the surrounding disk gas, consists of twosmall condensations; the observations provide constraints on their massand density, and indicate that the metallicity of this cloud is close tosolar. For HD 135485, Albert et al. (1993) had found high-velocityabsorption lines in optical spectra, but later reports indicate thatthese lines are probably circumstellar. The Westerbork observationsaround HD 135485 show that the HI found here is part of a larger HVCcomplex, Complex L, described by Wakker & van Woerden (1991). Forboth objects, the Westerbork results are compared with Jodrell Banksingle-dish observations.
| Spectroscopic and photometric investigations of MAIA candidate stars
Including our own observational material and the Hipparcos photometrydata, we investigate the radial velocity and brightness of suspectedMaia variable stars which are classified also in some examples aspeculiar stars, mainly for the existence of periodic variations withtime-scales of hours. The results lead to the following conclusions: (1)Short-term radial velocity variations have been unambiguously proved forthe A0 V star gamma CrB and the A2 III star gamma UMi. The stars pulsatein an irregular manner. Moreover, gamma CrB shows a multiperiodstructure quite similar to some of the best-studied neighbouring deltaScu stars. (2) In the Hipparcos photometry as well as in our photometricruns we find significant short- and long-term variations in the stars HD8441, 2 Lyn, theta Vir, gamma UMi, and gamma CrB. For ET And theHipparcos data confirm a short-period variation found already earlier.Furthermore, we find changes of the colour index in theta Vir and gammaCrB on a time-scale of days. (3) No proofs for the existence of aseparate class of variables, designated as Maia variables, are found. Ifthe irregular behaviour of our two best-investigated stars gamma CrB andgamma UMi is typical for pulsations in this region of theHertzsprung-Russell diagram, our observational runs are too short andthe accuracy of the measurements too low to exclude such pulsations inthe other stars, however. (4) The radial velocities of the binariesalpha Dra and ET And have been further used for a recalculation of theorbital elements. For HD 8441 and 2 Lyn we estimated the orbitalelements for the first time. (5) Zeeman observations of the stars gammaGem, theta Vir, alpha Dra, 4 Lac, and ET And give no evidence of thepresence of longitudinal magnetic field strengths larger than about 150gauss. Based on spectroscopic observations taken with the 2\,m telescopeat the Th{ü
| Diffraction-limited 76mas speckle masking observations of the core of NGC 1068 with the SAO 6m telescope
We present the first K-band bispectrum speckle interferometry of NGC1068with an angular resolution of 76mas ( ~ 5.5pc). This angular resolutionallows us to attribute the measured flux to only one of the nuclearsources seen at radio wavelengths. The observed decreasing visibilityfunction suggests that the dominant central core is probably not anunresolved point source, but slightly resolved with a FWHM diameter of ~30mas ~ 2pc for an assumed Gaussian intensity distribution. This 30masobject is possibly the nuclear torus and/or a scattering halo. Wediscuss different contributions to the observed K band flux. Between5GHz and the K-band the spectrum of this component is close to a nu(1/3) proportionality. In addition to the standard interpretation of ahot dust torus surrounding the nucleus of NGC1068, one cannot excludethe possibility that a sizeable fraction of the nuclear flux reaches usvia a scattering halo. This then would allow us to determine physicalparameters of the nuclear source. Based on data collected at the SpecialAstrophysical Observatory, Russia
| High-Velocity Clouds
High-velocity clouds (HVCs) consist of neutral hydrogen (\HI) atvelocities incompatible with a simple model of differential galacticrotation; in practice one uses {the absolue value of} VLSR {greater orequal to} 90 km/s to define HVCs. This review describes the mainfeatures of the sky and velocity distributions, as well as the availableinformation on cloud properties, small-scale structure, velocitystructure, and observations other than in 21-cm emission. We show thatHVCs contain heavy elements and that the more prominent ones are morethan 2 kpc from the Galactic plane. We evaluate the hypotheses proposedfor their origin and reject those that account for only one or a fewHVCs. At least three different hypotheses are needed: one for theMagellanic Stream and possibly related clouds, one for the Outer ArmExtension, and one (or more) for the other HVCs. We discuss the evidencefor the accretion and the fountain model but cannot rule out either one.
| Bow Shocks Around Runaway Stars.III.The High Resolution Maps
In a recent survey for bow shock structures around OB runaway starsusing the ISSA/IRAS archival data and excess maps at 60 \mum, 58candidates were found. These objects are surrounded by extended infraredemission at 60 \mum, characteristic of warm dust heated by ultravioletphotons, a signature of wind bow shocks. High resolution IRAS (HiRes)images have been produced for these 58 objects and some of thosespatially resolved are presented in this study. The images were used todistinguish between multiple confused IR sources, possible artifacts andunambiguous bow shocks, as the sources of the extended 60 \mum emission.Six new bow shocks have been identified using this method, and threehave been rejected. Twenty two of the targets, however, remain spatiallyunresolved even at the nominal HiRes resolution of ~ 1arcmin . For thelarger and better defined bow shocks some internal substructure isdiscernible. The length of these features suggest that they arise as theresult of a subtle dynamical instability. It can not be ruled out,however, that some of the bow shock morphology could be imprinted by thesurrounding medium.
| UBV photometry of Be stars at Hvar: 1972--1990
A summary of results of the systematic UBV photoelectric monitoring ofbright northern Be stars carried out at the Hvar Observatory between1972 and 1990 is presented. Altogether, 76 Be stars of all luminosityclasses were observed and 13,848 UBV measurements secured.Simultaneously, 9,648 UBV measurements of 48 check stars (most of themof early spectral types) were obtained. A careful transformation of allobservations into the standard Johnson system allowed detection andmonitoring of even very mild long-term light and colour variations ofthese objects. Almost all early-type Be stars in the sample turned outto be variable. For several stars phase-locked light variations relatedto their binary nature were established. Sudden brightenings, on a timescale of a few days, were detected for o Cas and QR Vul. Tables 2 and 3are only available in electronic form at CDS via ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Gyík |
| Rektaszcenzió: | 22h24m31.00s |
| Deklináció: | +49°28'35.0" |
| Vizuális fényesség: | 4.57 |
| Távolság: | 649.351 parszek |
| RA sajátmozgás: | -5.9 |
| Dec sajátmozgás: | -1.1 |
| B-T magnitude: | 4.65 |
| V-T magnitude: | 4.591 |
Katalógusok és elnevezések:
|
INHABITED SKY
