Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| Hypervelocity Stars. I. The Spectroscopic Survey
We discuss our targeted search for hypervelocity stars (HVSs), starstraveling with velocities so extreme that dynamical ejection from amassive black hole is their only suggested origin. Our survey, nowhalf-complete, has successfully identified a total of four probable HVSsplus a number of other unusual objects. Here we report the two mostrecently discovered HVSs: SDSS J110557.45+093439.5 and possibly SDSSJ113312.12+010824, traveling with Galactic rest-frame velocities atleast +508+/-12 and +418+/-10 km s-1, respectively. The otherlate B-type objects in our survey are consistent with a population ofpost-main-sequence stars or blue stragglers in the Galactic halo, withmean metallicity [Fe/H]Wk=-1.3 and velocitydispersion 108+/-5 km s-1. It is interesting to note that thevelocity distribution shows a tail of objects with large positivevelocities that may be a mix of low-velocity HVSs and high-velocityrunaway stars. Our survey also includes a number of DA white dwarfs withunusually red colors, possibly extremely low mass objects. Two of ourobjects are B supergiants in the Leo A dwarf, providing the firstspectroscopic evidence for star formation in this dwarf galaxy withinthe last ~30 Myr.
| B-type supergiants in the Small Magellanic Cloud: rotational velocities and implications for evolutionary models
High-resolution spectra for 24 SMC and Galactic B-type supergiants havebeen analysed to estimate the contributions of both macroturbulence androtation to the broadening of their metal lines. Two differentmethodologies are considered, viz. goodness-of-fit comparisons betweenobserved and theoretical line profiles and identifying zeros in theFourier transforms of the observed profiles. The advantages andlimitations of the two methods are briefly discussed with the lattertechniques being adopted for estimating projected rotational velocities(v sin i) but the former being used to estimate macroturbulentvelocities. The projected rotational velocity estimates range fromapproximately 20 to 60 km s-1, apart from one SMC supergiant,Sk 191, with a v sin i ≃ 90 km s-1. Apart from Sk 191,the distribution of projected rotational velocities as a function ofspectral type are similar in both our Galactic and SMC samples withlarger values being found at earlier spectral types. There is marginalevidence for the projected rotational velocities in the SMC being higherthan those in the Galactic targets but any differences are only of theorder of 5-10 km s-1, whilst evolutionary models predictdifferences in this effective temperature range of typically 20 to 70 kms-1. The combined sample is consistent with a linearvariation of projected rotational velocity with effective temperature,which would imply rotational velocities for supergiants of 70 kms-1 at an effective temperature of 28 000 K (approximately B0spectral type) decreasing to 32 km s-1 at 12 000 K (B8spectral type). For all targets, the macroturbulent broadening wouldappear to be consistent with a Gaussian distribution (although otherdistributions cannot be discounted) with an 1/e half-width varying fromapproximately 20 km s-1 at B8 to 60 km s-1 at B0spectral types.
| Correlation patterns between 11 diffuse interstellar bands and ultraviolet extinction
We relate the equivalent widths of 11 diffuse interstellar bands,measured in the spectra of 49 stars, to different colour excesses in theultraviolet. We find that most of the observed bands correlatepositively with the extinction in the neighbourhood of the2175-Åbump. Correlation with colour excesses in other parts of theextinction curve is more variable from one diffuse interstellar band toanother; we find that some diffuse bands (5797, 5850 and 6376 Å)correlate positively with the overall slope of the extinction curve,while others (5780 and 6284 Å) exhibit negative correlation. Wediscuss the implications of these results on the links between thediffuse interstellar band carriers and the properties of theinterstellar grains.
| Profiles of Very Weak Diffuse Interstellar Bands around 6440 Å
Profiles of very weak diffuse interstellar bands (DIBs) between 6400 and6470 Å observed with high resolution and very high S/N aredemonstrated. We show that with the increasing quality of reddenedstellar spectra, the whole spectral range is covered with weak or veryweak DIBs-at least one every 2-3 Å. We also present the details ofthe profiles of a few stronger features; the presence of substructuresresembles the profiles of strong DIBs observed in high resolution duringthe last decade and supports the hypothesis of a molecular origin of atleast a majority of DIBs.
| Large-scale wind structures in OB supergiants: a search for rotationally modulated Hα variability
We present the results of a long-term monitoring campaign of theHα line in a sample of bright OB supergiants (O7.5-B9) which aimsat detecting rotationally modulated changes potentially related to theexistence of large-scale wind structures. A total of 22 objects weremonitored during 36 nights spread over six months in 2001-2002.Coordinated broad-band photometric observations were also obtained forsome targets. Conspicuous evidence for variability in Hα is foundfor the stars displaying a feature contaminated by wind emission. Mostchanges take place on a daily time-scale, although hourly variations arealso occasionally detected. Convincing evidence for a cyclical patternof variability in Hα has been found in two stars: HD 14134 and HD42087. Periodic signals are also detected in other stars, butindependent confirmation is required. Rotational modulation is suggestedfrom the similarity between the observed recurrence time-scales (in therange 13-25 d) and estimated periods of stellar rotation. We callattention to the atypical case of HD 14134, which exhibits a clear12.8-d periodicity, both in the photometric and in the spectroscopicdata sets. This places this object among a handful of early-type starswhere one may observe a clear link between extended wind structures andphotospheric disturbances. Further modelling may test the hypothesisthat azimuthally-extended wind streams are responsible for the patternsof spectral variability in our target stars.
| 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.
| Toward an adequate method to isolate spectroscopic families of diffuse interstellar bands
We divide some of the observed diffuse interstellar bands (DIBs) intofamilies that appear to have the spectral structure of single species.Three different methods are applied to separate such families, exploringthe best approach for future investigations of this type. Starting witha statistical treatment of the data, we found that statistical methodsby themselves give insufficient results. Two other methods of dataanalysis (`averaging equivalent widths' and `investigating the figureswith arranged spectrograms') were found to be more useful as tools forfinding the spectroscopic families of DIBs. On the basis of thesemethods, we suggest some candidates as `relatives' of 5780- and5797-Å bands.
| 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.
| A Method for Simultaneous Determination of AV and R and Applications
A method for the simultaneous determination of the interstellarextinction (AV) and of the ratio of total to selectiveextinction (R), derived from the 1989 Cardelli, Clayton, & Mathisfitting of the interstellar extinction law, is presented and applied toa set of 1900 color excesses derived from observations of stars inUBVRIJHKL. The method is used to study the stability of AVand R within selected regions in Perseus, Scorpius, Monoceros, Orion,Sagittarius, Ophiuchus, Carina, and Serpens. Analysis shows that R isapproximately constant and peculiar to each sector, with mean valuesthat vary from 3.2 in Perseus to 5.6 in Ophiuchus. These results aresimilar to published values by Aiello et al., He et al., Vrba &Rydgren, O'Donnell, and Cardelli, Clayton, & Mathis.
| 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.
| 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
| The association of IRAS sources and 12CO emission in the outer Galaxy
We have revisited the question of the association of CO emission withIRAS sources in the outer Galaxy using data from the FCRAO Outer GalaxySurvey (OGS). The availability of a large-scale high-resolution COsurvey allows us to approach the question of IRAS-CO associations from anew direction - namely we examined all of the IRAS sources within theOGS region for associated molecular material. By investigating theassociation of molecular material with random lines of sight in the OGSregion we were able to construct a quantitative means to judge thelikelihood that any given IRAS-CO association is valid and todisentangle multiple emission components along the line of sight. Thepaper presents a list of all of the IRAS-CO associations in the OGSregion. We show that, within the OGS region, there is a significantincrease ( ~ 22%) in the number of probable star forming regions overprevious targeted CO surveys towards IRAS sources. As a demonstration ofthe utility of the IRAS-CO association table we present the results ofthree brief studies on candidate zone-of-avoidance galaxies with IRAScounterparts, far outer Galaxy CO clouds, and very bright CO clouds withno associated IRAS sources. We find that ~ 25% of such candidate ZOAGsare Galactic objects. We have discovered two new far outer Galaxystar-forming regions, and have discovered six bright molecular cloudsthat we believe are ideal targets for the investigation of the earlieststages of sequential star formation around HII regions. Finally, thispaper provides readers with the necessary data to compare othercatalogued data sets with the OGS data.Tables 1, 2 and A1 are only available in electronic form at the CDS viaanonymous ftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/1083
| Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
| High-resolution Keck I spectroscopy of Galactic halo post-asymptotic giant branch stars
Absolute and differential abundance analyses have been performed fromhigh-resolution, high signal-to-noise ratio optical (Keck I) spectra forthree evolved Galactic halo stars, namely PG 1704 + 222, HD 341617 andLS IV -04 01. Their derived atmospheric parameters indicate that allthree objects are undergoing a post-asymptotic giant branch (post-AGB)phase of evolution. A differential abundance analysis reveals HD 341617as having a mild carbon deficiency of 0.74 dex, possibly due to the starhaving evolved off the AGB before the onset of the third dredge-up.Although such carbon underabundances are typical of hot post-AGBobjects, the same trend is not observed in PG 1704 + 222, where thecarbon abundance is found to be consistent with those derived fornitrogen and oxygen. Hence, a dredge-up scenario need not be invoked toexplain the chemical composition of PG 1704 + 222. For LS IV -04 01 noiron deficiency is apparent relative to magnesium and silicon, and hencea gas-dust separation event in the AGB progenitor need not be invokedfor this star.
| Macroturbulent and rotational broadening in the spectra of B-type supergiants
The absorption-line spectra of early B-type supergiants show significantbroadening that implies that an additional broadening mechanism(characterized here as `macroturbulence') is present in addition torotational broadening. Using high-resolution spectra withsignal-to-noise ratios of typically 500, we have attempted to quantifythe relative contributions of rotation and macroturbulence, but evenwith data of this quality significant problems were encountered.However, for all our targets, a model where macroturbulence dominatesand rotation is negligible is acceptable; the reverse scenario leads topoor agreement between theory and observation. Additionally, there ismarginal evidence for the degree of broadening increasing with linestrength, possibly a result of the stronger lines being formed higher inthe atmosphere. Acceptable values of the projected rotational velocityare normally less than or equal to 50 km s-1, which may alsobe a typical upper limit for the rotational velocity. Our best estimatesfor the projected rotational velocity are typically 10-20 kms-1 and hence compatible with this limit. These values arecompared with those predicted by single star evolutionary models, whichare initially rapidly rotating. It is concluded that either these modelsunderestimate the rate of rotational breaking or some of the targets maybe evolving through a blue loop or are binaries.
| 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.
| 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.
| On the detection of the linear C5 molecule in the interstellar medium
An upper limit of the column density of the C5 linearmolecule in translucent interstellar clouds is estimated fromhigh-resolution (R=80000) and very high signal-to-noise ratio (~1000)echelle spectra. It is 1012cm-2 per E(B-V)=1 (twoorders of magnitude lower than that of C2).
| 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 Stars in Camelopardalis OB1: Their Distance and Evolutionary History
An investigation is undertaken of the optically identified Population Iobjects in the Cam OB1 region. From the analysis of these objects it isdetermined that the distance to the Cam OB1 stars is 975+/-90 pc. Atheoretical H-R diagram for the Cam OB1 stars reveals that starformation has been going on in the region for1×106-1×108 yr. At present, the mostactive site of star formation is Cam R1, which shows an asymmetry in thedistribution of optically identified Population I objects. The majorityof the pre-main-sequence stars lie in the northern half of theassociation, while the main-sequence stars and evolved stars lie in thesouthern half.
| A possible sets of diffuse bands originating at the same carrier
This paper discusses measurements of eight selected diffuse interstellarbands (DIBs): lambda lambda 5793, 5809, 5819, 5828, 6196, 6397, 6614 and6660 performed in high resolution, high S/N spectra of 41 reddenedstars. Central depths, considered less error-prone than equivalentwidths, are measured and mutual correlations between the selected DIBsare analyzed. Tight correlations between the DIBs: 5809, 6196, 6614 and6660 may suggest their common origin despite their widths differing by afactor of up to 2. The performed simulations prove that this fact doesnot preclude a common, molecular carrier of such features.
| 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
| Helium and Carbon Abundances in Late-B and Early-A Supergiants
The abundances of carbon and helium were determined for representativelate-B and early-A supergiants based on the C I lines (9078, 9089, 9095,9112) in the near-IR, C II lines (4267, 6151), and the He I 6678 line,in an aim to investigate the nature of the envelope-mixing in theseevolved stars based on the anomaly (if any) of these elements combinedwith that of N and O published before. It turned out that N tends toincrease with a decrease in C, showing a tendency of conserving the sumof C+N nuclei, which suggests that the anomaly of C and N may bereasonably interpreted as being due to mixing of the CN-processedmaterial. However, this increase/decrease in N/C, indicative ofdredge-up of the H-burning product, is not accompanied by anyHe-enrichment. Even surprisingly, the observed tendency is just theopposite, i.e., [He/H] appears to decrease progressively in accordancewith a lowering of [C/H]. Instead of regarding this apparentcharacteristics as being real, we tentatively speculate that someactivity-related line-weakening mechanism (e.g., irradiance of X-rays)might act on the formation of He I lines, the extent of which isindirectly related to the efficiency of envelope mixing via stellarrotation.
| 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.
| Differential O and Si Abundances in M33 Early B Supergiants
We present non-LTE analyses of four M33 early B supergiant stars andfive Galactic counterparts. This is the first time that B supergiantsbeyond the Magellanic Clouds are analyzed by means of detailed non-LTEtechniques. Among the M33 stars, new spectroscopic observations of B38(ob21-108) are presented and the object is classified as B1 Ia. Theclassification of another M33 star, B133, is changed with respect to aformer study. Equivalent widths of O and Si lines are measured for theM33 objects. Stellar temperatures, gravities, microturbulences, and Siabundances are derived for all objects using the Si ionizationequilibrium and the Balmer line wings. O abundances are then alsoderived. Important approximations made during the calculations aredescribed, and their influence on the results is analyzed (namely, weset the Lyman resonance lines in detailed balance during the calculationof the atmospheric structure for stars cooler than 20,000 K, and we setthe Si III resonance lines in detailed balance during the line formationcalculations for all models). It is found that these approximations haveno significant effect on the results at any microturbulence. We found adifference in the derived temperatures of the earlier Galactic stars ascompared to those obtained by other authors, which we attribute to thedifferent lines used for their derivation. A difference can also bepresent in the results when using the Si II/Si III and the Si III/Si IVionization equilibria. We conclude that a strict differential analysisis needed to detect abundance differences. Thus, we compare results lineby line in M33 and Galactic stars of stellar parameters as similar aspossible. Three of the four M33 stars turned out to be O deficient ascompared to their Galactic counterparts, and only one, close to thecenter of M33 (M33 1054), is found to be moderately O enriched. Fromthese differential analyses we find that our data are compatible with aradial O gradient in M33 as that derived from H II region data: weobtain -0.19+/-0.13 or -0.20+/-0.07 dex kpc-1, depending onwhether B133 is included or not. Our data are also consistent with otherpossibilities such as a steep increase of the O abundance in the innerregion (at projected distances less than 9' from the center of M33),followed by a flat O abundance profile toward the outer parts of M33. Sishows the same pattern, and it is shown that Si and O correlate well, asexpected for α-elements, supporting then the high value of the Oabundance gradient in M33 as compared to the Milky Way and other nearbyspiral galaxies. The results are compared with those of a moreapproximate technique, and it is concluded that this last can be used,attention being drawn to certain problems that are indicated. As animportant additional point, it is shown that M33 1054 is most probably asingle object, in spite of the bright absolute magnitude found in theliterature.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Multicolor Polarimetry of Selected BE Stars: 1995-1998
A new polarimeter called AnyPol has been used at Limber Observatory for4 yr to monitor annually the broadband linear polarization of a sampleof bright northern Be stars. This is the fourth report on a programstarted in 1985 at McDonald Observatory and the first one to comeentirely from the new installation. Although no variability was detectedat the 3 sigma level during the current reporting period, analysis ofthe full 13 yr data set is beginning to reveal hints of long-termvariability that may provide clues for understanding the Be phenomenon.
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 148: HR 7955
Not Available
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Giraffa |
| Ascensione retta: | 03h29m04.10s |
| Declinazione: | +59°56'25.0" |
| Magnitudine apparente: | 4.21 |
| Distanza: | 1315.789 parsec |
| Moto proprio RA: | 0 |
| Moto proprio Dec: | 0 |
| B-T magnitude: | 4.623 |
| V-T magnitude: | 4.233 |
Cataloghi e designazioni:
|
