Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| FUSE Measurements of Far-Ultraviolet Extinction. I. Galactic Sight Lines
We present extinction curves that include data down to far-ultravioletwavelengths (FUV; 1050-1200 Å) for nine Galactic sight lines. TheFUV extinction was measured using data from the Far UltravioletSpectroscopic Explorer. The sight lines were chosen for their unusualextinction properties in the infrared through the ultraviolet; that theyprobe a wide range of dust environments is evidenced by the large spreadin their measured ratios of total to selective extinction,RV=2.43-3.81. We find that extrapolation of the Fitzpatrick& Massa relationship from the ultraviolet appears to be a goodpredictor of the FUV extinction behavior. We find that predictions ofthe FUV extinction based on the Cardelli, Clayton, & Mathis (CCM)dependence on RV give mixed results. For the seven extinctioncurves well represented by CCM in the infrared through ultraviolet(x<8 μm-1), the FUV extinction is well predicted inthree sight lines, overpredicted in two sight lines, and underpredictedin two sight lines. A maximum entropy method analysis using a simplethree-component grain model shows that seven of the nine sight lines inthe study require a larger fraction of grain materials to be in dustwhen FUV extinction is included in the models. Most of the added grainmaterial is in the form of small (radii <~ 200 Å) grains.Based on observations with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer, which is operated by the Johns HopkinsUniversity under NASA contract NAS5-32985.
| B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| Envelope Ejection: An Alternative Evolutionary Process for Some Early Case B Binaries
We discuss the evolution of binaries with moderately high masses (~10-30Msolar) and with periods of ~3-300 days, corresponding mostlyto early case B. These are usually thought to evolve either byreasonably conservative Roche lobe overflow, if the initial mass ratiois fairly mild, or else by highly nonconservative common-envelopeevolution, with spiral-in to short periods (hours, typically), if theinitial mass ratio is rather extreme. We discuss here a handful ofbinaries from part of this period range (~50-250 days), which appear tohave followed a different path: we argue that they must have lost alarge proportion of initial mass (~70%-80%) but without shortening theirperiods at all. We suggest that their behavior may be due to the factthat stars of such masses, when evolved also to rather large radii, arenot far from the Humphreys-Davidson limit, where single stars lose theirenvelopes spontaneously in P Cygni winds, and so have envelopes that areonly lightly bound to the core. These envelopes therefore may berelatively easily dissipated by the perturbing effect of a companion. Inaddition, some or all of the stars considered here may have been closeto the Cepheid instability strip when they filled their Roche lobes. Oneor the other, or both, of high luminosity and Cepheid instability, incombination with an appropriately close binary companion, may beimplicated.
| 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.
| 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
| HR 4049: temporal variations in the structure of the circumstellar material
We present ultraviolet (UV) and optical spectropolarimetry of thepost-asymptotic giant branch star HR 4049 (= HD 89353). The polarizationis time-variable in both magnitude and position angle. The variations inthe polarization are tied to the orbital period and the circumstellarreddening and, in the optical, appear to arise from Rayleigh scatteringin a thin disc. However, the ultraviolet (λ <~ 3000 Å)polarization shows the signature of scattering from material in abipolar distribution. The near-UV (~ 2000-3000 Å) polarization hasapproximately the same position angle as the optical polarization andhence also arises from scattering in a disc. However, the componentperpendicular to the disc is of unknown origin. We discuss possiblesources for this component.
| Ultraviolet Interstellar Linear Polarization. V. Analysis of the Final Data Set
Using recent measurements of ultraviolet interstellar polarization, wehave examined its relationship to ultraviolet extinction and topolarization and extinction measurements in the visible and infrared.The relationship between the relative amount of ultraviolet polarizationand the parameter lambda_max, determined using only visible data, isconfirmed and strengthened, for example, by a tight correlation betweenp(6 mum^-1)/p_max and lambda^-1_max. A good fit to the wavelengthdependence of the polarization from the infrared to the ultraviolet canbe achieved with a five-parameter function combining a power law in theinfrared and a Serkowski-like function in the ultraviolet. Thepolarization efficiency (ratio of polarization to extinction) is less inthe ultraviolet than in the visual, and the ratio of these efficienciesincreases systematically with lambda^-1_max. We relate these effects tosystematic changes in the underlying aligned grain size distribution.The polarization efficiency of the grains causing the 2175 Åextinction bump along most sight lines is so (unusually) small that nostatistically significant polarization feature is detectable in thatwavelength region. Only two of 28 sight lines show a definitepolarization feature. The environments of the two bump sight lines aresimilar but not unique, and the mechanism for producing the polarizationfeature along only these two sight lines is still not known.
| 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.
| The Spectroscopic Orbit of the Evolved Binary HD 197770
We have used spectra taken between 1992 and 1997 to derive thespectroscopic orbit of the eclipsing double-lined spectroscopic binaryHD 197770. This binary has a period of 99.69 +/- 0.02 days and Kamplitudes of 31.2 +/- 0.8 and 47.1 +/- 0.4 km s^-1 for components A andB, respectively. The m sin^3 i values for A and B are 2.9 and 1.9,respectively, and are close to the actual masses because of theeclipsing nature of this binary. Both components of HD 197770 havespectral types near B2 III. This means that both components areundermassive by about a factor of 5 and, thus, are evolved stars.Additional evidence of the evolved nature of HD 197770 is found in 25,60, and 100 μm IRAS images of HD 197770. These images show twoapparent shells centered on HD 197770, a bright 60 μm shell with a28' diameter and a larger (0.8d diameter) bubble-like feature. At leastone of the components of HD 197770 is likely to be a post-asymptoticgiant branch star.
| A reliable transformation of HIPPARCOS H_p magnitudes into Johnson V and B magnitudes
A comparison of accurate UBV magnitudes, derived from numerousobservations at Hvar and SkalnatePleso, and of the mean Hipparcos \hpmagnitudes for a number of constant stars showed a very good mutualcorrespondence of these two data sets. Simple transformation formul\ae\are presented which allow calculating Johnson V and B magnitudes fromthe \hp magnitude and known B-V and U-B colours. For constant stars withwell-known values of both colours the accuracy of the transformation isclearly better than 0\m01. At the same time, the transformation is notcritically sensitive to the exact values of B-V and U-B. It isapplicable over a wide range of colours (B-V between -0\m25 and 2\m0)and works well also for reddened stars. However, since it was definedfor stars brighter than about 8\m0 and for reddenings smaller than about1\m0, its application outside these limits should be made with somecaution and further tested. Since the B-V and U-B colours are known forthe majority of brighter stars and since there are many classes ofvariable stars which do change colours only very mildly during theirlight changes (like the majority of Be stars) or for which theinstantaneous colours can be predicted or estimated from existingoptical observations, the transformations presented here may turn out tobe very useful for many researchers who need to combine Hipparcos andoptical photometry into one homogeneous data set.
| Ultraviolet Interstellar Linear Polarization. III. Features
Astro-2 has revealed a broad, weak spectral feature in the ultravioletinterstellar linear polarization for two lines of sight, confirming theoriginal detection toward HD 197770 and adding HD 147933--4. These arethe only two polarization features found in some 30 lines of sight nowobserved. Both features are centered close to 2175 Angstroms, theposition of the ubiquitous ultraviolet extinction bump. Twopossibilities are considered for the source of the polarization feature:changes in the mass distribution of the aligned silicate grainsresponsible for the continuum polarization, and alignment of the smallgraphite grains responsible for the extinction bump. While the formerapproach meets with some success for the HD 197770 feature, it is notpossible to produce a feature as clearly peaked as in HD 147933--4. Thecentral wavenumbers and widths of both polarization features correspondclosely to those of the corresponding extinction bump. Taken together,it seems the graphite grains are a more likely source of thepolarization features. Both polarization features have amplitudes thatare very small compared to the amount of excess extinction present inthe 2175 Angstroms bump, implying poor polarization efficiency. Manyother lines of sight have been observed with sufficient signal-to-noiseratios such that features should have been clearly detected if the samepolarization efficiency applied, and so real variations in the alignmentor shape of the grains responsible seem to occur from one line of sightto another. The weak alignment might be caused by unusually lowconcentrations of paramagnetic impurities in rapidly spinning smallgrains.
| Ultraviolet interstellar linear polarization. IV. Cross-calibration between the Wisconsin ultraviolet photo-polarimeter experiment and the faint object spectrograph.
The Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) and theFaint Object Spectrograph (FOS) started gathering UV spectropolarimetryin 1990. Each observed a wide range of polarimetrically interestingobjects before being retired. This paper examines the polarimetriccalibration of each instrument and compares the absolute calibrationsthrough the use of the limited sample of ``standard stars'' observed byboth instruments. In general, there is good agreement between the FOSand WUPPE results at the 2sigma statistical level. Data from eachinstrument can be compared directly on a straightforward basis.
| 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
| A unified model of interstellar dust.
We have simultaneously modeled both the interstellar extinction andpolarization (both linear and circular) on the basis of a trimodal dustmodel: large silicate core-organic refractory mantle dust particles;very small carbonaceous particles responsible for the hump extinction;and PAH's responsible for the FUV extinction. The core-mantle particleswhich are the exclusive contributor to the interstellar polarization andthe dominant contributor to the visual and NIR extinction are modeled asfinite cylinders with a Gaussian size distribution in terms of perfectspinning alignment. Results for models using infinite cylinders arepresented for comparison. Our model results are in good agreement withsuch observational constraints as the average interstellar extinctioncurve, the polarization law, the ratio of visual polarization toextinction (P/A)_v_, the scattering properties (albedos), the excess NIRpolarization over the extrapolation of the Serkowski law. The (P/A)_v_constraint imposed on other dust models (e.g., the silicate/graphitemodel, the composite dust model) leads to either a too low (P/A)_v_value (the silicate/graphite model) or instability of particle structure(the composite dust model). The cosmic abundance constraints, inparticular the evidence for lower oxygen abundance in the interstellarmedium than in the solar system and the possible interstellar C/Oratios, are discussed extensively. Considering the uncertainties in theinterstellar ``cosmic'' abundances, the C/O ratio and the interstellarnon-dust elemental abundances, although our model requires a bit morecarbon than the reference abundance, it is within the limit of anacceptable range and is a significant improvement over other models. Allthe other major reference abundance (cosmic - non-dust) constraints onO, N, Si, Mg, Fe are well satisfied.
| Ultraviolet Interstellar Linear Polarization: Initial Modeling Efforts for the Astro-2 WUPPE Data
Prior to the flight of the Wisconsin Ultraviolet Photo PolarimeterExperiment (WUPPE) on Astro-2, studies of ultraviolet (UV) interstellarlinear polarization have generally catagorized the wavelength dependencein two ways: that which agrees with an extrapolation of the SerkowskiLaw into the UV and that which has a polarization greater than theextrapolation (see Clayton et al. 1995 and references within). Only oneobject (HD 197770) had been reported to deviate from either of thesebehaviors. It is important to note that earlier work has been limited inscope primarily by the amount of data available (14 publishedsightlines). However, with the flight of Astro-2, WUPPE has tripled thenumber of UV interstellar polarization observations (Anderson et al.1995, 1996). These new data will provide a significant improvement toour ability to test interstellar dust grain models and study the effectsof sightline environments. We present the modeling results for severalWUPPE (Astro-2) sightlines, including two which clearly depart from thepreviously mentioned catagorizations: HD 147933 and HD 197770. Inaddition to "classial" grain modeling technques (series solution,Effective Medium Theory), we also employ the Maximum Entropy Method andthe Discrete Dipole Approximate. WUPPE is supported by NASA contract NAS5-26777. Anderson, C.M., Weitenbach, A.J., & Code, A.D. 1995,Proceedings of the Conference on Polarimetry in the Interstellar Medium,eds. Roberge & Whittet, Troy, NY, June 1995. Anderson, C.M. et al.1996, ApJ, submitted. Clayton, G. C. et al. 1995, ApJ, 445, 947
| Confirmation of Eclipses in HR 7940 (HD 197770), a Reddened B2 III Star
It has been confirmed that HR 7940 (HD 197770) is an eclipsing binary.The best period, using data with a 14 year baseline, is 99d76 +- 0d04with an epoch of primary minimum of JD 2441856.25 +- 0.25. Assuming thisperiod, 6 primary and 4 secondary eclipses have been observed. Theeclipse duration is <= 1d5. The primary and secondary eclipse depthsare similar (delta-V ~0.05). Better phase coverage is needed todetermine the parameters of the eclipsing binary system. However, theexisting data imply that this is not a close binary. The nature of HR7940 is of interest because the line of sight toward this star isimportant to studies of the interstellar medium. In particular, it isthought to show a polarized 2175A bump. (SECTION: Stars)
| A Catalogue of Correlations Between Eclipsing Binaries and Other Categories of Double Stars
Among the 9110 stars in The Bright Star Catalogue, there are 225eclipsing or ellipsoidal variables. A search has been made for these incatalogues of spectroscopic binaries, visual double or multiple stars,speckle interferometry, occulation binaries, and galatic clusters. Themajority of the photometric binaries are also members of groups ofhigher multiplicity. The variables are in systems ranging from one to 91stars, five on the average. 199 are either spectroscopic binaries (SB)or stars with variable radial velocity, with orbital periods known for160. Photometric periods are lacking for 48 while SB periods areavailable for 23 of these. Observers with photoelectric equipment areencouraged to plan observations to test if the SB periods are consistentwith photometric data. Observers are likewise encouraged to examinethose stars for which the photometric and SB periods appear to beinconsistent. Parallaxes are available for 86 of the stars, 41 of themindicating distances nearer than 50 parsecs.
| Ultraviolet Imaging Telescope Near-Ultraviolet Bright Object Catalog
We present a photometric catalog of 2244 objects detected by theUltraviolet Imaging Telescope in the near-ultraviolet (NUV; 1650A <λ < 2900 A) during the Astro Space Shuttle mission. Sources inthe catalog are as faint as m_nuv_ ~ 18.8, or f_nuv_ ~ 1.1 x 10^16^ ergss^-1^ cm^-2^ A^-1^, but the survey is not complete to this level.Optical catalogs were used to cross identify sources and derive NUV - Vcolors. A majority of the objects (88%) do indeed have proposed opticalidentifications from catalogs, and most are stars. Our purpose increating the catalog is to form a database useful for identifying veryblue objects and performing Galactic UV stellar population studies.
| Ultraviolet Interstellar Polarization of Galactic Starlight.I.Observations by the Wisconsin Ultraviolet Photo Polarimeter Experiment
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2726A&db_key=AST
| 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.
| Observations of diffuse interstellar bands and of interstellar polarization
Not Available
| The 72nd Name-List of Variable Stars
Not Available
| A Search for Polarization in Diffuse Interstellar Bands toward HD 197770
Spectroscopy and spectropolarimetry in the wavelength range 5600--5800 Ahave been obtained for the line of sight toward HD 197770, which has areported polarized 2175 A extinction bump. The 5780 and 5797 A diffuseinterstellar bands (DIBs) are anomalously weak (by a factor >2) withrespect to reddening, whereas the broader 5778 A band appears to beanomalously strong. None of these bands shows detectable polarization inexcess of that in the continuum; aligned classical grains cannot be thecarriers of these bands. The ratio of polarization to optical depth inthe DIBs is marginally smaller than would be expected if the DIBcarriers were the small, presumably carbonaceous, grains responsible forthe 2175 A absorption.
| The Visual and Ultraviolet Polarimetric Data of alpha Camelopardalis and kappa Cassiopeia: Evidence of Shocked Regions
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...447..889F&db_key=AST
| Ultraviolet interstellar linear polarization. 2: The wavelength dependence
We present new ultraviolet (UV) polarimetry of the well-studiedinterstellar line of sight toward HD 204827 obtained with the FaintObject Spectrograph on Hubble Space Telescope. HD 204827 is of greatinterest because the dust along this line of sight has extremely lowvalues of both lambdamax and RV. Its far-UVextinction is very large, reflecting its small RV value. Inaddition, we reexamine the entire sample of 14 interstellar lines ofsight for which there are now UV polarization data. We find that thepreviously suggested relationship between lambdamax and thewavelength dependence of the polarization in the UV is stronglysupported by the data for this larger sample including HD 204827. Sevenstars with lambdamax greater than or equal to 0.54 micronagree well with an extrapolation of the Serkowski relation into the UVwhile seven stars with lambdamax less than or equal to 0.53micron show polarization in excess of the Serkowski extrapolation(super-Serkowski). However, the division of the observed lines of sightinto Serkowski and super-Serkowski categories is artificial. In fact,the amount of polarization in the UV is correlated with a singleparameter, lambdamax. This may indicate that there is a meaninterstellar polarization law analogous to the mean interstellarextinction law of Cardelli, Calyton, & Mathis which is based onRV. The data are consistent with a linear relationshipbetween 1/lambdamax and rho(UV)/rhomax but moredata are needed to define the functional form. We suggest that theSerkowski and super-Serkowski designations be replaced by high and lowlambdamax which are more physically descriptive. At the sametime, we note that all seven super-Serkowski (low lambdamax)stars lie in a relatively small region of the sky between lII= 90 deg - 150 deg and b = -5 deg - 15 deg. These stars all lie in orbehind a spur of the local Orion spiral arm. Similarly, most of theSerkowski (high lambdamax stars lie in or near theScorpio-Centaurus OB Association. So lines of sight covering largerareas of the sky are needed to test the universality of thelambdamax/UV polarization relationship. The recent discoveryof warm dust near HD 197770 suggests the possibility that a mechanismother than the traditional alignment to the Galactic magnetic field maybe invoked to explain its 2175 A polarization bump.
| The Ultraviolet Sky as Observed by the Shuttle-Borne Ultraviolet Imaging Telescope
Analysis of 489 wide-field images obtained by the Shuttle-borneUltraviolet Imaging Telescope (UIT) has yielded positive detections ofFUV and NUV backgrounds in both the orbital daytime and nighttime skies.The daytime backgrounds can be attributed to atmospheric dayglow lineemission (in the FUV) and solar stray-light contamination (in the NUV).A few of the nighttime backgrounds (in both bands) appear to be affectedby stray light from UV-bright stars just beyond the imaged fields ofview. In both bands, the highest nighttime background levels are foundin nebular fields at low galactic latitude. The diffuse backgrounds inthese fields are probably associated with the adjoining nebulosity. Awayfrom the galactic plane, the nighttime FUV backgrounds are confused by OI nightglow emission and possible photometric errors. The more tightlyconstrained NUV intensities correlate with those predicted fromcorresponding optical measurements of the Zodiacal light, yielding aNUV/Vis "color" of 0.5 +/- 0.2 for the Zodiacal light. After subtractionof the predicted Zodiacal component, the residual NUV intensitiescorrelate with FIR measurements of the corresponding fields.Extrapolation to negligible FIR intensities yields an extragalactic NUVcomponent of 300 photon units or less. This upper limit supports the lowintensities that have been proposed in the debate over the strength andstructure of the UV background (cf. Henry, ARA&A, 29,89, 1991;Bowyer, ARA&A, 29,59 1991). Such low values reinforce thecharacterization of the ultraviolet sky as the "window" of choice in thesearch for nearby low- surface-brightness galaxies and faint primevalgalaxies much farther away.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Dust Metamorphosis in the Galaxy
Not Available
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Цефей |
| Прямое восхождение: | 20h43m13.50s |
| Склонение: | +57°06'51.0" |
| Видимая звёздная величина: | 6.32 |
| Расстояние: | 1923.077 парсек |
| Собственное движение RA: | -1.9 |
| Собственное движение Dec: | -5.1 |
| B-T magnitude: | 6.648 |
| V-T magnitude: | 6.367 |
Каталоги и обозначения:
|
INHABITED SKY
