Contents
Images
Upload your image
DSS Images Other Images
Related articles
Reliability Checks on the Indo-US Stellar Spectral Library Using Artificial Neural Networks and Principal Component Analysis
The Indo-US coudé feed stellar spectral library (CFLIB) madeavailable to the astronomical community recently by Valdes et al. (2004,ApJS, 152, 251) contains spectra of 1273 stars in the spectral region3460 to 9464Å at a high resolution of 1Å (FWHM) and a widerange of spectral types. Cross-checking the reliability of this databaseis an important and desirable exercise since a number of stars in thisdatabase have no known spectral types and a considerable fraction ofstars has not so complete coverage in the full wavelength region of3460-9464Å resulting in gaps ranging from a few Å to severaltens of Å. We use an automated classification scheme based onArtificial Neural Networks (ANN) to classify all 1273 stars in thedatabase. In addition, principal component analysis (PCA) is carried outto reduce the dimensionality of the data set before the spectra areclassified by the ANN. Most importantly, we have successfullydemonstrated employment of a variation of the PCA technique to restorethe missing data in a sample of 300 stars out of the CFLIB.
| A deep wide-field optical survey in the young open cluster Collinder 359
We present the first deep, optical, wide-field imaging survey of theyoung open cluster Collinder 359, complemented by near-infraredfollow-up observations. This study is part of a large programme aimed atexamining the dependence of the mass function on environment and time.We have surveyed 1.6 square degrees in the cluster, in the I and zfilters, with the CFH12K camera on the Canada-France-Hawaii 3.6-mtelescope down to completeness and detection limits in both filters of22.0 and 24.0 mag, respectively. Based on their location in the optical(I-z, I) colour-magnitude diagram, we have extracted new cluster membercandidates in Collinder 359 spanning 1.3-0.03 Mȯ,assuming an age of 60 Myr and a distance of 450 pc for the cluster. Wehave used the 2MASS database as well as our own near-infrared photometryto examine the membership status of the optically-selected clustercandidates. Comparison of the location of the most massive members inCollinder 359 in a (B-V, V) diagram with theoretical isochrones suggeststhat Collinder 359 is older than α Per but younger than thePleiades. We discuss the possible relationship between Collinder 359 andIC 4665 as both clusters harbour similar parameters, including propermotion, distance, and age.
| High-resolution spectroscopic observations of post-asymptotic giant branch candidates from the Edinburgh-Cape Survey
High spectral resolution (R~ 40000) and signal-to-noise optical spectra,obtained at the Very Large Telescope (VLT), are presented for threepost-asymptotic giant branch (AGB) candidates selected from theEdinburgh-Cape (EC) Faint Blue Object Survey. The stellar atmosphericparameters and chemical compositions, derived using sophisticatednon-local thermodynamic equilibrium calculations, reveal that EC14102-1337 and EC 20068-7324 are both in an evolved post-horizontalbranch (HB) evolutionary state. However, EC 11507-2253 is most likely apost-AGB star.
| Elements for 8 RR Lyrae Variables in Ophiuchus
Not Available
| A study of the young open cluster Collinder 359
We present the first deep, optical, wide-field imaging survey of theyoung open cluster Collinder 359, complemented by near-infraredfollow-up observations. This study is part of a large programme aimed atexamining the dependence of the mass function on environment and time.We have surveyed 1.6 square degree in the cluster in the I and z filterswith the CFH12K camera on the Canada-France-Hawaii 3.6m telescope downto completeness and detection limits in both filters of 22\fm0 and24\fm0, respectively. Based on their location in the optical (I-z,I)colour-magnitude diagram, we have extracted new cluster membercandidates in Collinder 359 spanning 1.3-0.04 Mȯ,assuming an age of 100 Myr and a distance of 450 pc for the cluster. Wehave used the 2MASS database as well as our own near-infrared photometryto confirm the membership of the optically-selected cluster candidates.Additionally, we have obtained optical spectroscopy and employedchromospheric activity as a further criterion to assess the membershipof candidates.
| INTEGRAL observations of SS433: Results of a coordinated campaign
Results of simultaneous INTEGRAL and optical observations of thegalactic microquasar SS433 in May 2003 and INTEGRAL /RXTE observationsin March 2004 are presented. Persistent precessional variability with amaximum to minimum uneclipsed hard X-ray flux ratio of 4 isdiscovered. The 18 60 keV X-ray eclipse is found to be in phase withoptical and near infrared eclipses. The orbital eclipse observed byINTEGRAL in May 2003 is at least two times deeper and apparently widerthan in the soft X-ray band. The broadband 2 100 keV X-ray spectrumsimultaneously detected by RXTE/INTEGRAL in March 2004 can be explainedby bremsstrahlung emission from optically thin thermal plasma withkT 30 keV. Optical spectroscopy with the 6-m SAO BTA telescopeconfirmed the optical companion to be an A5 A7 supergiant. For the firsttime, spectorscopic indications of a strong heating effect in theoptical star atmosphere are found. The measurements of absorption lineswhich are presumably formed on the non-illuminated side of thesupergiant yield its radial velocity semi-amplitude K_v=132± 9 kms-1. The analysis of the observed hard X-ray light curve andthe eclipse duration, combined with the spectroscopically determinedoptical star radial velocity corrected for the strong heating effect,allows us to model SS433 as a massive X-ray binary. Assuming that thehard X-ray source in SS433 is eclipsed by the donor star that exactlyfills its Roche lobe, the masses of the optical and compact componentsin SS433 are suggested to be M_v≈ 30 M_ȯ and M_x≈ 9 M_ȯ,respectively. This provides further evidence that SS433 is a massivebinary system with supercritical accretion onto a black hole.
| On the massive stellar population of the super star cluster Westerlund 1
We present new spectroscopic and photometric observations of the youngGalactic open cluster Westerlund 1 (Wd 1) that reveala unique population of massive evolved stars. We identify ~200 clustermembers and present spectroscopic classifications for ~25% of these. Wefind that all stars so classified are unambiguously post-Main Sequenceobjects, consistent with an apparent lack of an identifiable MainSequence in our photometric data to V 20. We are able to identifyrich populations of Wolf Rayet stars, OB supergiants and short livedtransitional objects. Of these, the latter group consists of both hot(Luminous Blue Variable and extreme B supergiant) and cool (YellowHypergiant and Red Supergiant) objects - we find that half the knownGalactic population of YHGs resides within Wd 1. We obtain a meanV-MV ~ 25 mag from the cluster Yellow Hypergiants, implying aMain Sequence turnoff at or below MV =-5 (O7 V or later).Based solely on the masses inferred for the 53 spectroscopicallyclassified stars, we determine an absolute minimum mass of ~1.5 ×10^3~Mȯ for Wd 1. However, considering the completephotometrically and spectroscopically selected cluster population andadopting a Kroupa IMF we infer a likely mass for Wd 1 of~10^5~Mȯ, noting that inevitable source confusion andincompleteness are likely to render this an underestimate. As such, Wd 1is the most massive compact young cluster yet identified in the LocalGroup, with a mass exceeding that of Galactic Centre clusters such asthe Arches and Quintuplet. Indeed, the luminosity, inferred mass andcompact nature of Wd 1 are comparable with those of Super Star Clusters- previously identified only in external galaxies - and is consistentwith expectations for a Globular Cluster progenitor.
| Correlations between diffuse interstellar bands and atomic lines
We present and discuss correlations between strengths of the well-known,strong interstellar atomic lines of KI and CaII, and four selected,strong unidentified diffuse interstellar bands (DIBs): 5780, 5797, 5850and 6614. In order to analyse a homogeneous sample of echellehigh-resolution spectra it has been chosen to use measurements fromTerskol Observatory in Northern Caucasus plus a selected number ofhigher resolution observations performed using other instruments. Wedemonstrate that the strength of certain DIBs correlate well withneutral potassium lines and to a much lower degree with ionized calciumlines. This fact suggests that the degree of irradiation of a cloud withUV photons, capable to ionize interstellar atoms, plays a crucial rolein the formation/maintenance of certain molecular species: possiblecarriers of DIBs.
| Anomalous dust-to-gas ratios in the Galaxy
Lines of sight with E(B-V)/N(HI) considerably smaller than the averagevalue for the solar neighbourhood have been selected from the catalogueof Diplas & Savage. In order to develop quantitative considerations,estimates of the molecular hydrogen column density were obtained usingthe relation of Savage et al. extended at E(B-V) > 0.4 with therecent data of Rachford et al. Contrary to the prevailing opinion in theliterature for sightlines with similar behaviour, we found that only 22per cent of our sample was characterized by both an average gas densitylarger than 1 cm-3 and a value of RV larger thanthat in the diffuse interstellar medium. By computing extinction models,we were able to fit the E(B-V)/N(HI) by changing the value ofRV only for some sightlines. For the remaining ones, aρd/ρH ratio different from the averageGalactic value must be invoked. The application of the Kramers-Kronigrelation to the observed extinction curves confirmed this possibility.Moreover, attempts to fit such curves with models having grain volumescorresponding to the standard ρd/ρH ratiofailed.We find a linear relation between ρd/ρHand E(B-V)/N(H) for our sightlines. The average Galactic value marks theseparation into two groups characterized by lower abundances of C and Sitrapped into the grains when E(B-V)/N(H) is smaller than the Galacticvalue, and by larger abundances when E(B-V)/N(H) is greater.
| Boebachtungen von veranderlichen Sternen am Sonneberger Feld 67 Oph.
Not Available
| The Optical Spectrum of an LBV Candidate in the Cyg OB2 Association
We have obtained the first high-spectral-resolution (R=15000 and 60000)optical spectra for the extremely luminous star No. 12, identified withthe IR source IRAS 20308+4104 in the Cyg OB2 association. We haveidentified about 200 spectral features at 4552 7939 Å, includingthe interstellar NaI, KI lines and numerous DIBs, which are thestrongest absorption lines in the spectrum, along with the HeI, CII, andSiII lines. A two-dimensional spectral classification indicates that thestar's spectral type is B5±0.5 Ia+. Our analysis of theradial-velocity pattern shows the presence of a radial-velocity gradientin the stellar atmosphere, due to the infall of matter onto the star.The strong Hα emission line displays broad Thompson wings andtime-variable core absorption, providing evidence that the stellar windis inhomogeneous, and a slightly blue-shifted P Cygni absorptionprofile. We conclude that the wind is time-variable.
| 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.
| Reanalysis of Copernicus Measurements of Interstellar Carbon Monoxide
We used archival data acquired with Copernicus to reexamine CO columndensities, as self-consistent oscillator strengths are now available.Our focus is on lines of sight containing modest amounts of molecularspecies. Our resulting column densities are small enough thatself-shielding from photodissociation does not occur in the cloudsprobed by the observations. While our sample shows that the columndensities of CO and H2 are related, no correspondence withthe CH column density is evident. The case for the CH+ columndensity is less clear. Recent chemical models for these sight linessuggest that CH is mainly a by-product of CH+ synthesis inlow-density gas. The models are most successful in reproducing theamounts of CO in the densest sight lines. Thus, much of the COabsorption must arise from denser clumps along the line of sight toaccount for the trend with H2.
| On the relation between diffuse bands and column densities of H2, CH and CO molecules
Mutual relations between column densities of H2, CH and COmolecules as well as between the latter and strengths of the major 5780and 5797 diffuse bands are presented and discussed. The CH radical seemsto be a good H2 tracer, possibly better than CO. It is alsodemonstrated that the molecular fraction of the H2 moleculeis correlated with an intensity ratio of 5797 and 5780 DIBs, suggestingthe possible formation of narrow DIB carriers in denser clouds,dominated by molecular hydrogen and reasonably shielded from ionizing UVradiation by small dust grains.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/949
| High-Resolution Observations of Interstellar Ca I Absorption-Implications for Depletions and Electron Densities in Diffuse Clouds
We present high-resolution (FWHM~0.3-1.5 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar Ca Iabsorption toward 30 Galactic stars. Comparisons of the column densitiesof Ca I, Ca II, K I, and other species-for individual componentsidentified in the line profiles and also when integrated over entirelines of sight-yield information on relative electron densities anddepletions (dependent on assumptions regarding the ionizationequilibrium). There is no obvious relationship between the ratio N(CaI)/N(Ca II) [equal to ne/(Γ/αr) forphotoionization equilibrium] and the fraction of hydrogen in molecularform f(H2) (often taken to be indicative of the local densitynH). For a smaller sample of sight lines for which thethermal pressure (nHT) and local density can be estimated viaanalysis of the C I fine-structure excitation, the average electrondensity inferred from C, Na, and K (assuming photoionizationequilibrium) seems to be independent of nH andnHT. While the electron density (ne) obtained fromthe ratio N(Ca I)/N(Ca II) is often significantly higher than the valuesderived from other elements, the patterns of relative nederived from different elements show both similarities and differencesfor different lines of sight-suggesting that additional processesbesides photoionization and radiative recombination commonly andsignificantly affect the ionization balance of heavy elements in diffuseinterstellar clouds. Such additional processes may also contribute tothe (apparently) larger than expected fractional ionizations(ne/nH) found for some lines of sight withindependent determinations of nH. In general, inclusion of``grain-assisted'' recombination does reduce the inferred ne,but it does not reconcile the ne estimated from differentelements; it may, however, suggest some dependence of ne onnH. The depletion of calcium may have a much weakerdependence on density than was suggested by earlier comparisons with CHand CN. Two appendices present similar high-resolution spectra of Fe Ifor a few stars and give a compilation of column density data for Ca I,Ca II, Fe I, and S I.
| 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.
| STELIB: A library of stellar spectra at R ~ 2000
We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃsica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| 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.
| An upper limit to the interstellar C5 abundance in translucent clouds
We have analyzed high resolution spectra of several slightly tomoderately reddened stars collected at two observatories: ESO (La Silla)and Terskol (Northern Caucasia), to estimate the abundance of theC5 molecule in the interstellar medium. We confirm thepresence of a feature near 4975 Å which appears to be a weak DIBrather than the predicted C5 band since the origin band near5109 Å remains invisible even in spectra of high signal-to-noiseratio ( ~ 2500) and spectral resolution (R ~ 220 000). This confirmsthat the C5 abundance in translucent interstellar clouds isvery low. We estimate its limit as low as 1011cm-2 in the scale E(B-V)=0.35 for ``zeta" type objects thatis two times lower than that of Maier et al. (2002). Based on datacollected at the ESO 3.6 m telescope operated on La Silla Observatory,Chile and 2-m telescope of the Terskol Observatory, Russia.
| Far-ultraviolet extinction and diffuse interstellar bands
We relate the equivalent widths of the major diffuse interstellar bands(DIBs) near 5797 and 5780Å with different colour excesses,normalized by E(B-V), which characterize the growth of interstellarextinction in different wavelength ranges. It is demonstrated that thetwo DIBs correlate best with different parts of the extinction curve,and the ratio of these diffuse bands is best correlated with thefar-ultraviolet (UV) rise. A number of peculiar lines of sight are alsofound, indicating that the carriers of some DIBs and the far-UVextinction can be separated in certain environments, e.g. towards thePer OB2 association.
| Profiles of blue and infrared diffuse interstellar bands
The paper presents a survey of profiles of reasonably strong diffuseinterstellar bands (DIBs) based on the extensive set of high-resolutionspectra acquired with the aid of echelle spectrographs installed at the2-m Terskol, 2-m Pic du Midi and 1-m SAO telescopes. The surveyeddiffuse interstellar bands cover the spectral ranges of blue andnear-infrared, i.e the DIBs not surveyed by Krełowski &Schmidt. The possible modifications caused by stellar and telluric linesare discussed. The very broad features such as 4430 are not discussedbecause the shapes of their profiles, extracted from echelle spectra,are very uncertain. The signal-to-noise (S/N) ratios of the spectra arenot high enough to enable discussion of the profiles of numerous weakinterstellar features discovered recently.
| A High-Resolution Survey of Interstellar K I Absorption
We present high-resolution (FWHM ~0.4-1.8 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar K Iabsorption toward 54 Galactic stars. These new K I spectra revealcomplex structure and narrow, closely blended components in many linesof sight. Multicomponent fits to the line profiles yield estimates forthe column densities, line widths, and velocities for 319 individualinterstellar cloud components. The median component width (FWHM) and thetrue median separation between adjacent components are both <~1.2 kms-1. The median and maximum individual component K I columndensities, about 4×1010 and 1012cm-2, correspond to individual component hydrogen columndensities of about 2×1020 and 1021cm-2 and E(B-V)~0.03 and 0.17, respectively. If T istypically ~100 K, then at least half the individual components havesubsonic internal turbulent velocities. We also reexamine therelationships between the column densities of K I, Na I, C I, Li I,Htot, H2, and CH. The four trace neutral speciesexhibit essentially linear relationships with each other over wideranges in overall column density. If C is uniformly depleted by 0.4 dex,then Li, Na, and K are each typically depleted by 0.6-0.7 dex. The totalline of sight values for N(K I) and N(Na I) show roughly quadraticdependences on N(Htot), but the relationships for theensemble of individual clouds could be significantly steeper. Thesequadratic (or steeper) dependences appear to rule out significantcontributions to the ionization from cosmic rays, X-rays, and/or chargeexchange with C II in most cases. Charge exchange with negativelycharged large molecules may often be more important than radiativerecombination in neutralizing most singly ionized atomic species in coolH I clouds, however-suggesting that the true ne,nH, and thermal pressures may be significantly smaller thanthe values estimated by considering only radiative recombination. BothN(CH) and N(H2) are nearly linearly proportional to N(K I)and N(Na I) [except for 1015cm-2<~N(H2)<~1019cm-2, over which H2 makes the transition to theself-shielded regime]. Those relationships appear also to hold for manyindividual components and component groups, suggesting thathigh-resolution spectra of K I and Na I can be very useful forinterpreting lower resolution molecular data. The scatter about allthese mean relationships is generally small (<~0.1-0.2 dex), ifcertain consistently ``discrepant'' sight lines are excluded-suggestingthat both the relative depletions and the relative ionization of Li, C,Na, and K are generally within factors of 2 of their mean values.Differences noted for sight lines in Sco-Oph, in the Pleiades, near theOrion Trapezium, and in the LMC and SMC may be due to differences in thestrength and/or shape of the ambient radiation fields, perhaps amplifiedby the effects of charge transfer with large molecules.
| The problem of C7- as source of diffuse interstellar bands revisited
We used spectra of several bright, reddened stars, most of them likelyto be obscured by individual interstellar clouds, to examine theproposition that C7- may carry several diffuseinterstellar bands (DIBs) (Tulej et al. 1998). To search for the broadfeatures of the C7- B <- X system we used lowresolution, very high S/N spectra, but even in heavily reddened objectsthe predicted bands remain undetectable. High resolution (R=80 000)spectra prove that the diffuse bands, found in close vicinity of narrowlines belonging to the A <- X system, show variable strength ratiosfrom object to object which proves that they are not of the same origin.The paper brings thus evidence that the C7-molecule does not cause any of the detected DIBs.
| 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 proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Classification and properties of UV extinction curves
The catalog of Savage et al. (\cite{ref27}) reporting colour excesses of1415 stars from ANS photometry offers the opportunity to deeplyinvestigate the characteristics of UV extinction curves which differfrom the standard extinction of the diffuse interstellar medium. To thisaim we have selected a sample of 252 curves, which have been comparedwith the relations derived by Cardelli et al. (\cite{ref4}; CCM in thefollowing) for a variety of R_V values in the range 2.4-5 and have beenclassified as normal if they fit at least one of the CCM curves oranomalous otherwise. We find that normal curves with small R_V are justas numerous as those with large R_V. The anomalous objects are arrangedinto two groups according to the strength of the bump at 0.217 mu . Fora given value of c_2 this increases along the sequence: type Aanomalous, normals and type B anomalous, suggesting that this sequenceshould correspond to an increase of the amount of small grains along thesightline. Considerations concerning the environmental characteristicsindicate that the anomalous behaviour is not necessarily tied to theexistence of dense gas clouds along the line of sight.
| 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.
| Observations of Diffuse Interstellar Bands Attributed to C-7
Recent advances in laboratory gas-phase spectroscopy of large moleculesand their ions permit a direct comparison between the diffuseinterstellar bands (DIBs) and proposed carriers. On the basis ofgas-phase data, Tulej et al. recently suggested that fiveA2Πu<--X2Πgelectronic transitions of the linear carbon-chain anionC-7 match with DIBs. We have obtainedhigh-resolution visible spectra of four reddened stars (HD 46711, HD50064, HD 183143, and Cyg OB2 12) to make a detailed comparison with theC-7 laboratory data. Our data show that three ofthe C-7 bands (000 at 6270.2Å, 310 at 6064.0 Å, and120310 at 4963.0 Å)are in good agreement with DIBs in wavelength and relative intensity. Afourth band (110 at 5612.8 Å) also agrees inintensity but is apparently off by 2 Å in wavelength. All otherlaboratory bands of C-7 are not expected to bedetectable in astronomical spectra with the current level ofsensitivity. The gas-phase spectrum of C-7 agreeswith the DIBs better than that of any previously proposed molecule.However, the question of whether C-7 is a DIBcarrier cannot be definitively answered until (1) better laboratorymeasurements confirm, refute, or explain the wavelength discrepancy forthe 110 band and/or (2) better astronomicalspectra reveal the presence or absence of otherC-7 bands. Based on observations obtained with theApache Point Observatory 3.5 m telescope, which is owned and operated bythe Astrophysical Research Consortium.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Ophiucus |
| Right ascension: | 18h00m38.70s |
| Declination: | +02°55'54.0" |
| Apparent magnitude: | 3.97 |
| Distance: | 434.783 parsecs |
| Proper motion RA: | 0 |
| Proper motion Dec: | -8.9 |
| B-T magnitude: | 3.956 |
| V-T magnitude: | 3.959 |
Catalogs and designations:
|
