Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Surface abundances of light elements for a large sample of early B-type stars - III. An analysis of helium lines in spectra of 102 stars
Non-local thermodynamic equilibrium analysis of He I lines in spectraof 102 B stars is implemented in order to derive the helium abundanceHe/H, the microturbulent parameter Vt and the projectedrotation velocity v sini. A simultaneous determination of He/H andVt for the stars is effected by analysing equivalent widthsof the 4471- and 4922-Å lines primarily as indicators of He/H andthe 4713-, 5016-, 5876- and 6678-Å lines primarily as indicatorsof Vt. The rotation velocities v sini are found from profilesof the same lines. It is shown that, when Vt > 7 kms-1, the Vt(He I) values determined from He Ilines are systematically overestimated as compared with theVt(OII, NII) values derived from OII and NII lines. Thisdiscrepancy is especially appreciable for hot evolved B giants withVt(He I) = 16-23 km s-1 and may indicate a failureof classical model atmospheres to represent the strong He I lines forthese stars.Two programme stars, HR 1512 and 7651, are found to be helium-weakstars. The remaining 100 stars are divided into three groups accordingto their masses M. The microturbulent parameter Vt(He I) islow for all stars of group A (M= 4.1-6.9 Msolar) and for allstars with the relative ages t/tMS < 0.8 of group B (M=7.0-11.2 Msolar). Their Vt(He I) values are withinthe 0 to 5 km s-1 range, as a rule; the mean value isVt= 1.7 km s-1. Only evolved giants of group B,which are close to the termination of the main-sequence (MS)evolutionary phase (t/tMS > 0.8), show Vt(He I)up to 11 km s-1. The helium abundance He/H is correlated withthe relative age t/tMS in both groups; the averaged He/Henhancement during the MS phase is 26 per cent. For group C, containingthe most massive stars (M= 12.4-18.8 Msolar), theVt(He I) values display a correlation with t/tMS,varying from 4 to 23 km s-1. The He/H determination for hotevolved B giants of the group with Vt(He I) > 15 kms-1 depends on a choice between the Vt(He I) andVt(OII, NII) scales. The mean He/H enrichment by 67 per centduring the MS phase is found, if the abundances He/H are based on theVt(OII, NII) scale; however, two evolved giants withespecially high v sini, HR 7446 and 7993, show the He/H enhancement byabout a factor of 2.5. When using the same Vt scale, we founda trend of He/H with projected rotational velocities v sini a largedispersion for v sini > 150 km s-1 can result fromdifferences in masses M.A comparison with the stellar model computations with rotationallyinduced mixing shows that the observed helium enrichment during the MSphase can be explained by rotation with initial velocities 250-400 kms-1. The He/H distribution on M and v sini based on theVt(OII, NII) scale seems to be in better agreement with thetheory than one based on the Vt(He I) scale. The mean valueHe/H = 0.10 derived for stars in the zero age main sequence (ZAMS)vicinity can be adopted as the typical initial helium abundance forearly B stars in the solar neighbourhood.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Variability of the He I λ5876 Å line in early type chemically peculiar stars. II
To try to understand the behavior of helium variability in ChemicallyPeculiar stars, we continued our on-going observational campaign startedby \cite{catanzaro99}. In this paper we present a new set of timeresolved spectroscopic observations of the He I 5876 Å line for asample of 10 stars in the spectral range B3 - A2 and characterized bydifferent overabundances.This line does not show variability in two stars: HD 77350 and HD175156. It shows instead an equivalent width variation in phase with theHipparcos light curve for two stars: HD 79158 and HD 196502. Antiphasevariations have been found in 4 stars of our sample, namely: HD 35502,HD 124224, HD 129174 and HD 142990. Nothing we can say about HD 115735because of the constancy of Hipparcos photometric data, while no phaserelation has been observed for HD 90044.In the text we discuss the case of HD 175156, according to photometriccalibration and our spectroscopic observations we rule out themembership of this star to the main sequence chemically peculiar stars.We confirm the results obtained in the previous paper for which phaserelations between light, spectral and magnetic variations are notdependent on stellar spectral type or peculiarity subclass.Based on observations collected at stellar station ``M. G. Fracastoro''of the Catania Astrophysical Observatory and on observations collectedat Complejo Astrónomico El Leoncito (Casleo), which is operatedunder agreement between the Consejo Nacional de InvestigationesCientifícas y Técnicas (CONICET) and the NationalUniversities of La Plata, Córdoba and San Juan.
| 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
| A study of the behaviour of the NaI/KI column density ratio in the interstellar medium using the Na ultraviolet doublet
Here we make a new study of the behaviour of the NaI/KI column densityratio in the interstellar medium, using a sample of new observations of28 stars obtained at the Nordic Optical Telescope (NOT) in 1996 and1997, and previously published observations (obtained by some of theauthors) of 21 stars. The sightlines cover a range of distances anddirections, including into the Galactic halo. We make use of newobservations of the NaI ultraviolet (UV) doublet for some 18 stars. Thisdoublet is much weaker than the NaI D doublet and so is less susceptibleto saturation effects, and it is well known that it can be used toobtain more accurate NaI column densities with a smaller error range. Wefind an average N(NaI)/N(KI) ratio from the NaI UV data of about 90,which is rather higher than that found previously by Hobbs and Lequeux.The Na UV-KI ratio shows a small increase in value with increasingcolumn density, while we also find a sample of low N(NaI)/N(KI) ratioclouds generally seen towards distant objects on high-latitudesightlines that reach into the halo, so that the ratio decreases moresharply at lower column densities. As the values of the ratio for thesehalo clouds (10-20) bracket the cosmic Na/K abundance ratio, we suggestthat these ratios result from a harder radiation field in the lowerhalo, such that the ionized fractions of NaI and KI become similar.Clearly caution needs to be applied in using any kind of `standardvalue' for the NaI/KI column density ratio.
| Surface abundances of light elements for a large sample of early B-type stars - II. Basic parameters of 107 stars
Effective temperatures Teff, surface gravities logg andinterstellar extinctions AV are found for 107 B stars.Distances d of the stars, which are based on the derivedTeff, logg and AV values, show good agreement withthose obtained from the Hipparcos parallaxes. Comparing theTeff and logg values with evolutionary computations, we infermasses, radii, luminosities, ages and relative ages of the stars.Empirical relations between the Teff and logg parameters, onthe one hand, and the photometric indices Q, [c1] and β,on the other hand, are constructed; these relations give a fast methodfor the Teff and logg estimation of early and medium B stars.Inclusion of the infrared J, H and K colours into the Teff,logg and AV determination shows that (i) the Teffand logg parameters are altered only slightly; (ii) the AVvalue is rather sensitive to these colours, so an accuracy better than0.05mag in the JHK data is necessary for precise AVevaluation.
| 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.
| Profiles of the λ6196 and λ6379 Diffuse Interstellar Bands
We have looked for rotational structure in the sharp λ6196 andλ6379 diffuse interstellar bands (DIBs) at a resolution ~120,000in seven stars where the interstellar λ7699 K I line isunresolved. The λ6196 DIB is bell-shaped with a flat core anddiffers slightly in width from star to star. It is accompanied by a weakDIB at λ6194.7, with which it does not maintain a constant depthratio. The λ6379 DIB is asymmetric with a sharp double core, butthe profile hardly varies between the stars apart from beingundetectable for HD 37061. Weak features connect it to the weakerλ6376 DIB, with which it varies in unison. Simple rotationalmodels do not fit the observed profiles of λ6196 and λ6376at all well because of more prominent branch structure in the models. Weachieve an acceptable fit by arbitrarily convolving the modeled profileswith Gaussians (0.2 to 0.3 cm-1). The Gaussians correspond toan unexpected or anomalous broadening process that cannot be explainedby the interstellar velocity distribution or the instrumentalpoint-spread function. The fits give upper limits to the ratio of therotational temperature to the moment of inertia of the molecularcarriers. If the former lies in the range 10-100 K, then the moleculesmust be large, with moments of inertia comparable with that of thefullerene C60. We present evidence that the anomalousbroadening of the rotational profiles is intramolecular in origin, butit is not easily explained by broadening processes previously invoked inconnection with the DIBs. We suggest that some other process such as azero-point vibrational isotope shift may be involved that could becharacteristic of many of the narrow bands.
| Far-Ultraviolet Spectra of B Stars near the Ecliptic
Spectra of B stars in the wavelength range of 911-1100 Å have beenobtained with the Espectrógrafo Ultravioleta de RadiaciónDifusa (EURD) spectrograph on board the Spanish satellite MINISAT-01with ~5 Å spectral resolution. International Ultraviolet Explorer(IUE) spectra of the same stars have been used to normalize Kuruczmodels to the distance, reddening, and spectral type of thecorresponding star. The comparison of eight main-sequence stars studiedin detail (α Vir, ɛ Tau, λ Tau, τ Tau, αLeo, ζ Lib, θ Oph, and σ Sgr) shows agreement withKurucz models, but observed fluxes are 10%-40% higher than the models inmost cases. The difference in flux between observations and models ishigher in the wavelength range between Lyα and Lyβ. Wesuggest that Kurucz models underestimate the far-ultraviolet (FUV) fluxof main-sequence B stars between these two Lyman lines. Computation offlux distributions of line-blanketed model atmospheres including non-LTEeffects suggests that this flux underestimate could be due to departuresfrom LTE, although other causes cannot be ruled out. We found that thecommon assumption of solar metallicity for young disk stars should bemade with care, since small deviations can have a significant impact onFUV model fluxes. Two peculiar stars (ρ Leo and ɛ Aqr) and twoemission-line stars (ɛ Cap and π Aqr) were also studied. Ofthese, only ɛ Aqr has a flux in agreement with the models. The resthave strong variability in the IUE range and/or uncertain reddening,which makes the comparison with models difficult. Based on thedevelopment and utilization of the Espectrógrafo Ultravioleta deRadiación Difusa, a collaboration of the Spanish InstitutoNacional de Técnica Aeroespacial and the Center for EUVAstrophysics, University of California, Berkeley.
| EURD: The Mission and the Stellar Absolute Fluxes of B-Type Stars
We present here stellar spectra of B stars obtained with the EURDspectrograph, one of the three instruments on board MINISAT-01. EURD isa spectrograph specially designed to detect diffuse radiation in thewavelength range between 350 and 1100 Å with 5 Å spectralresolution. EURD main scientific targets are: the spectrum ofinterstellar medium, atmospheric airglow, decaying neutrinos, Moon andearly type stars.
| Surface abundances of light elements for a large sample of early B-type stars - I. Spectral observations of 123 stars; measurements of hydrogen and helium lines; infrared photometry
High-resolution spectral observations of 123 B0-B5 stars in the mainsequence evolutionary phase were obtained at two observatories, namelythe McDonald Observatory (McDO) and the Crimean AstrophysicalObservatory (CrAO). Accurate equivalent widths W of two Balmer lines,Hβ and Hγ, and ten Hei lines were obtained for all the stars,as well as of the Heiiλ4686 line for the hottest ones. A carefulanalysis of the measured equivalent widths was performed. It is shownthat there is a very good agreement between the W values derived fromthe McDO and CrAO spectra for 14 common stars. A comparison withpublished data leads to the conclusion that the W values measuredearlier by some authors for strong Hei lines are very likely to beunderestimated. Infrared photometric observations in the J, H, and Kbands were performed for 70 programme stars. All these data will be usedin other papers: in particular for the Teff and loggdetermination and for the He, C, N and O abundance analyses.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Age variation of helium abundance in He-rich stars.
Not Available
| The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars
The HR-diagram of about 1000 Bp - Ap stars in the solar neighbourhoodhas been constructed using astrometric data from Hipparcos satellite aswell as photometric and radial velocity data. The LM method\cite{luri95,luri96} allows the use of proper motion and radial velocitydata in addition to the trigonometric parallaxes to obtain luminositycalibrations and improved distances estimates. Six types of Bp - Apstars have been examined: He-rich, He-weak, HgMn, Si, Si+ and SrCrEu.Most Bp - Ap stars lie on the main sequence occupying the whole width ofit (about 2 mag), just like normal stars in the same range of spectraltypes. Their kinematic behaviour is typical of thin disk stars youngerthan about 1 Gyr. A few stars found to be high above the galactic planeor to have a high velocity are briefly discussed. Based on data from theESA Hipparcos astrometry satellite and photometric data collected in theGeneva system at ESO, La Silla (Chile) and at Jungfraujoch andGornergrat Observatories (Switzerland). Tables 3 and 4 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://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.
| Terminal Velocities and the Bistability of Stellar Winds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...455..269L&db_key=AST
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Near-infrared spectroscopy of post-AGB stars.
The results of a medium resolution near-infrared spectral survey of 18post-AGB candidate stars are presented. Most of the stars havenear-infrared hydrogen lines in absorption, which is normal for theirspectral types. Three stars, HD 101584, HD 179821 and HD 170756 have theCO first overtone bands in emission; in two of these the emission isvariable. It is suggested that the CO emission is the result of post-AGBmass loss. HD 52961 shows the rarely occurring 3.5μm emission featureand is only the fourth object in which this feature has been detected.
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| An atlas of ultraviolet P Cygni profiles
We have selected spectra of 232 stars from the International UltravioletExplorer (IUE) archives for inclusion in an atlas intended for varioususes but tailored especially for the study of stellar winds. The atlascovers the range in spectral types from O3 to F8. The full atlas coversthe reduced and normalized high resolution spectra from the IUE long-and short-wavelength spectrographs. Here we discuss the selection of thestars and the data reduction, and we present in velocity units theprofiles of lines formed in the stellar winds. The selected lines covera wide range of ionizations, allowing a comparison of the profiles fromdifferent ions in the wind of each star and a comparison of thedifferent wind lines as a function spectral type and luminosity. We alsopresent the basic data on the program stars to facilitate study of thedependence of wind features on stellar parameters such as luminosity,temperature, escape velocity, and v sin i. We provide an overview of thecharacteristic behavior of the wind lines in the H-R diagram. Thecomplete spectra are available in digital form through the NASAAstrophysics Data System (ADS). We offer a description of the electronicdatabase that is available through the ADS and guidelines for obtainingaccess to that database.
| The local distribution of NA I interstellar gas
We present high-resolution absorption measurements (lambda/Delta lambdaapproximately 75,000) of the interstellar Na I D lines at 5890 A toward80 southern hemisphere early-type stars located in the localinterstellar medium (LISM). Combining these results with other sodiummeasurements taken from the literature, we produce galactic maps of thedistribution of neutral sodium column density for a total of 293 starsgenerally lying within approximately 250 pc of the Sun. These mapsreveal the approximate shape of the mid-plane contours of the rarefiedregion of interstellar space termed the Local Bubble. Its shape is seenas highly asymmetric, with a radius ranging from 30 to 300 pc, and withan average radius of 60 pc. Similar plots of the Galactic mid-planedistribution of sources emitting extreme ultraviolet radiation show thatthey also trace out similar contours of the Local Bubble derived from NaI absorption measurements. We conclude that the Local Bubble absorptioninterface can be represented by a hydrogen column density,NuETA = 2 x 1019 cm-2, which explainsboth the local distribution of Na I absorption and the observed galacticdistribution of extreme ultraviolet sources. The derived mid-planecontours of the Bubble generally reproduce the large-scale featurescarved out in the interstellar medium by several nearby galactic shellstructures.
| The interstellar spectrum of HD 175156
Not Available
| Mid-ultraviolet and optical photometry of helium stars
Mid-ultraviolet and optical photometric analysis of helium stars arepresented. A linear relation exists between the effective temperaturederived from model atmospheres and (1965-V)0 index. The effectivetemperatures derived from (1965-V)0 index are somewhat higher than thatof MK spectral type estimates especially for late B-type helium objects.
| Radio emission from chemically peculiar stars
In five VLA observing runs the initial survey of radio emission frommagnetic Bp-Ap stars by Drake et al. is extended to include a total of16 sources detected at 6 cm out of 61 observed, giving a detection rateof 26 percent. Of these stars, three are also detected at 2 cm, four at3.6 cm, and five at 20 cm. The 11 new stars detected as radio sourceshave spectral types B5-A0 and are He-weak and Si-strong. No classical(SrCrEu-type) Ap stars have yet been detected. The 16 detected sourcesshow a wide range of radio luminosities with the early-B He-S stars onaverage 20 times more radio luminous than the late-B He-W stars and 1000times more luminous than Theta Aurigae. Multifrequency observationsindicate flat spectra in all cases. Four stars have a detectable degreeof circular polarization at one or more frequencies. It is argued thatthe radio-emitting CP (chemically peculiar) stars form a distinct classof radio stars that differs from both the hot star wind sources and theactive late-type stars. The observed properties of radio emission fromthese stars may be understood in terms of optically thickgyrosynchrotron emission from a nonthermal distribution of electronsproduced in a current sheet far from the star. In this model theelectrons travel along magnetic fields to smaller radii and highermagnetic latitudes where they mirror and radiate microwave radiation.
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| Interstellar reddening in the Southern Hemisphere. I - The UVBY beta observations
The uvby-beta photometric data obtained from a Southern Hemisphereobservational project is presented. A uvby-beta photometric network ofnearly 3900 A and early F stars has been established with the intentthat the stars serve as 'space probes' for measurements of interstellarreddening.
| Diffuse bands and peculiar interstellar clouds
An approach to the study of the diffuse interstellar bands (DIBs) isdiscussed, and results obtained so far are presented. Emphasis is placedon lines of sight along which some components of the interstellar mediumincluding the DIBs deviate from the average behavior. The varyingintensity ratios between features belonging to different families, thelack of some of the diffuse bands along peculiar lines of sight, and theapparent absence of DIBs when the reddening is mainly due tocircumstellar matter are considered.
| On the diffuse interstellar bands around 6200 A
High-resolution, high-S/N spectra are used to study a system of threediffuse interstellar bands (DIBs) near 6200 A; the intensity ratios ofthe three bands are noted to change from one line-of-sight to another,thereby suggesting that there is a different carrier for each. Itappears that intensity-ratio changes are not accompanied byprofile-shape changes. A relation between the extinction law and thebehavior of this DIBs system is suggested.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kalkan |
| Sað Açýklýk: | 18h54m43.10s |
| Yükselim: | -15°36'11.0" |
| Görünürdeki Parlaklýk: | 5.1 |
| Uzaklýk: | 510.204 parsek |
| özdevim Sað Açýklýk: | -2.9 |
| özdevim Yükselim: | -8 |
| B-T magnitude: | 5.245 |
| V-T magnitude: | 5.103 |
Kataloglar ve belirtme:
|
