Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Optical polarimetry of infrared excess stars
We present UBRVI polarimetry measurements for a group of 38 IRASinfrared excess stars and complement these observations with V-band datataken from the literature for 87 additional objects. After correctingthe observed values by the interstellar contribution, we find that 48%of the analyzed sample has polarization excess. In addition, thepolarization of these stars may correlate with infrared color excesses,particularly at 60 and 100 μm. We caution, however, that poor IRASdata quality at longer wavelengths affects this correlation. We analyzethe wavelength dependence of the linear polarization of 15 polarizedobjects in relation to Serkowski's empirical interstellar law. We findthat for 6 to 7 objects (depending on the interstellar model) themeasured polarization differs significantly from the empiricalinterstellar law, suggesting an intrinsic origin. We analyze thepolarimetry distribution of IRAS infrared excess objects in relation tothe Exoplanet host stars (i.e., stars associated with at least onelikely planetary mass object). The corresponding polarimetrydistributions are different within a high confidence level. Finally, wecompare the metallicity distributions of F and G IRAS infrared excess,Exoplanet host and field main sequence stars, and find that F-G IRASinfrared excess objects have metallicities quite similar (although notidentical) to field main sequence stars and significantly different fromthe Exoplanet host group.
| Decay of Planetary Debris Disks
We report new Spitzer 24 μm photometry of 76 main-sequence A-typestars. We combine these results with previously reported Spitzer 24μm data and 24 and 25 μm photometry from the Infrared SpaceObservatory and the Infrared Astronomy Satellite. The result is a sampleof 266 stars with mass close to 2.5 Msolar, all detected toat least the ~7 σ level relative to their photospheric emission.We culled ages for the entire sample from the literature and/orestimated them using the H-R diagram and isochrones; they range from 5to 850 Myr. We identified excess thermal emission using an internallyderived K-24 (or 25) μm photospheric color and then compared allstars in the sample to that color. Because we have excluded stars withstrong emission lines or extended emission (associated with nearbyinterstellar gas), these excesses are likely to be generated by debrisdisks. Younger stars in the sample exhibit excess thermal emission morefrequently and with higher fractional excess than do the older stars.However, as many as 50% of the younger stars do not show excessemission. The decline in the magnitude of excess emission, for thosestars that show it, has a roughly t0/time dependence, witht0~150 Myr. If anything, stars in binary systems (includingAlgol-type stars) and λ Boo stars show less excess emission thanthe other members of the sample. Our results indicate that (1) there issubstantial variety among debris disks, including that a significantnumber of stars emerge from the protoplanetary stage of evolution withlittle remaining disk in the 10-60 AU region and (2) in addition, it islikely that much of the dust we detect is generated episodically bycollisions of large planetesimals during the planet accretion end game,and that individual events often dominate the radiometric properties ofa debris system. This latter behavior agrees generally with what we knowabout the evolution of the solar system, and also with theoreticalmodels of planetary system formation.
| Local Interstellar Matter: The Apex Cloud
Several nearby individual low column density interstellar cloudlets havebeen identified previously on the basis of kinematical features evidentin high-resolution Ca+ observations near the Sun. One ofthese cloudlets, the ``Apex Cloud'' (AC), is within 5 pc of the Sun inthe solar apex direction. The question of which interstellar cloud willconstitute the next Galactic environment of the Sun can, in principle,be determined from cloudlet velocities. The interstellar absorptionlines toward α Cen (the nearest star) are consistent withinmeasurement uncertainties with the projected ``G'' cloud (GC) and ACvelocities, and also with the velocity of the cloud inside of the solarsystem (the local interstellar cloud [LIC]), provided a small velocitygradient is present in the LIC. The high GC column density towardα Oph compared to α Aql suggests that α Aql may beembedded in the GC so that the AC would be closer to the Sun than theGC. This scenario favors the AC as the next cloud to be encountered bythe Sun, and the AC would have a supersonic velocity with respect to theLIC. The weak feature at the AC velocity toward 36 Oph suggests that theAC cloud is either patchy or does not extend to this direction.Alternatively, if the GC is the cloud that is foreground to α Cen,the similar values for N(H0) in the GC components towardα Cen and 36 Oph indicate this cloud is entirely contained withinthe nearest ~1.3 pc, and the Ca+ GC data toward α Ophwould then imply a cloud volume density of ~5 cm-3, withdramatic consequences for the heliosphere in the near future.
| Automated spectroscopic abundances of A and F-type stars using echelle spectrographs. II. Abundances of 140 A-F stars from ELODIE
Using the method presented in Erspamer & North (\cite{erspamer},hereafter Paper I), detailed abundances of 140 stars are presented. Theuncertainties characteristic of this method are presented and discussed.In particular, we show that for a S/N ratio higher than 200, the methodis applicable to stars with a rotational velocity as high as 200 kms-1. There is no correlation between abundances and Vsin i,except a spurious one for Sr, Sc and Na which we explain by the smallnumber of lines of these elements combined with a locally biasedcontinuum. Metallic giants (Hauck \cite{hauck}) show larger abundancesthan normal giants for at least 8 elements: Al, Ca, Ti, Cr, Mn, Fe, Niand Ba. The anticorrelation for Na, Mg, Si, Ca, Fe and Ni with Vsin isuggested by Varenne & Monier (\cite{varenne99}) is not confirmed.The predictions of the Montréal models (e.g. Richard et al.\cite{richard01}) are not fulfilled in general. However, a correlationbetween left [(Fe)/(H)right ] and log g is found for stars of 1.8 to 2.0M_sun. Various possible causes are discussed, but the physical realityof this correlation seems inescapable.Based on observations collected at the 1.93 m telescope at theObservatoire de Haute-Provence (St-Michel l'Observatoire, France) andCORALIE.Based on observations collected at the Swiss 1.2 m Leonard Eulertelescopes at the European Southern Observatory (La Silla, Chile).Tables 5 and 6 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/398/1121
| The Velocity Distribution of the Nearest Interstellar Gas
The bulk flow velocity for the cluster of interstellar cloudlets within~30 pc of the Sun is determined from optical and ultraviolet absorptionline data, after omitting from the sample stars with circumstellar disksor variable emission lines and the active variable HR 1099. A total of96 velocity components toward the remaining 60 stars yield a streamingvelocity through the local standard of rest of -17.0+/-4.6 kms-1, with an upstream direction of l=2.3d, b=-5.2d (usingHipparcos values for the solar apex motion). The velocity dispersion ofthe interstellar matter (ISM) within 30 pc is consistent with that ofnearby diffuse clouds, but present statistics are inadequate todistinguish between a Gaussian or exponential distribution about thebulk flow velocity. The upstream direction of the bulk flow vectorsuggests an origin associated with the Loop I supernova remnant.Groupings of component velocities by region are seen, indicatingregional departures from the bulk flow velocity or possibly separateclouds. The absorption components from the cloudlet feeding ISM into thesolar system form one of the regional features. The nominal gradientbetween the velocities of upstream and downstream gas may be an artifactof the Sun's location near the edge of the local cloud complex. The Sunmay emerge from the surrounding gas patch within several thousand years.
| Detecting low amplitude periodicities with HIPPARCOS
The HIPPARCOS and TYCHO catalogues have proven to be a very powerfulsource for detection of variability in stars. The photometric errors forindividual measurements are typically of the order of a fewmillimagnitudes. Amplitudes for periodic variability of stars and basedon HIPPARCOS data are published which are of the same order. An examplecould be the still controversial case of ET And (Scholz et al.\cite{Sch98}; Weiss et al. \cite{Wei98}) with contradicting evidence forHIPPARCOS and ground-based observations. Another case could be the AGBstar RV Cam (Kerschbaum et al. \cite{Ker01}) with a similarcontradiction. In this paper we investigate the properties of HIPPARCOSphotometry for a set of 4863 presumably constant stars and we determinethe frequency ranges of HIPPARCOS which seem to be affected by theinstrument. Based on HI photometry and SIMBAD database interrogations.
| The Asymmetric Nebula Surrounding the Extreme Red Supergiant Vy Canis Majoris
We present HST/WFPC2 images plus ground-based infrared images andphotometry of the very luminous OH/IR star VY Canis Majoris. Our WFPC2data show a complex distribution of knots and filamentary arcs in theasymmetric reflection nebula around the obscured central star. Thereflection arcs may result from multiple, asymmetric ejection episodesdue to localized events on VY CMa's surface. Such events probablyinvolve magnetic fields and convection, by analogy with solar activity.Surface photometry indicates that the star may have experienced enhancedmass loss over the past 1000 yr. We also demonstrate that the apparentasymmetry of the nebula results from a combination of high extinctionand backscattering by dust grains. Thermal-infrared images reveal a moresymmetric distribution, elongated along a nearly east-west direction. VYCMa probably has a flattened disklike distribution of dust with anortheast-southwest polar axis and may be experiencing activityanalogous to solar prominences. The presence of an axis of symmetryraises interesting questions for a star the size of Saturn's orbit.Magnetic fields and surface activity may play an important role in VYCMa's mass-loss history. Based on observations made with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS 5-26555.
| 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
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 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/367/297
| 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
| Optical, infrared and millimetre-wave properties of Vega-like systems - IV. Observations of a new sample of candidate Vega-like sources
Photometric observations at optical and near-infrared wavelengths arepresented for members of a new sample of candidate Vega-like systems, ormain sequence stars with excess infrared emission due to circumstellardust. The observations are combined with IRAS fluxes to define thespectral energy distributions of the sources. Most of the sources showonly photospheric emission at near-IR wavelengths, indicating a lack ofhot (~1000K) dust. Mid-infrared spectra are presented for four sourcesfrom the sample. One of them, HD 150193, shows strong silicate emission,while another, HD 176363, was not detected. The spectra of two starsfrom our previous sample of Vega-like sources both show UIR-bandemission, attributed to hydrocarbon materials. Detailed comparisons ofthe optical and IRAS positions suggest that in some cases the IRASsource is not physically associated with the visible star. Alternativeassociations are suggested for several of these sources. Fractionalexcess luminosities are derived from the observed spectral energydistributions. The values found are comparable to those measuredpreviously for other Vega-like sources.
| Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,199 of the stars in Part I are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives in addition to the SI mode the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 148: HR 7955
Not Available
| Additional ultra-high-resolution observations of Ca^+ ions in the local interstellar medium
We present ultra-high-resolution (0.35 km s^-1 FWHM) observations of theinterstellar Ca K line towards seven nearby stars. The spectralresolution was sufficient to resolve the line profiles fully, therebyenabling us to detect hitherto unresolved velocity components, and toobtain accurate measurements of the velocity dispersions (b values).Absorption components with velocities similar to those expected for theLocal Interstellar Cloud (LIC) and the closely associated `G cloud' wereidentified towards six of the seven stars. However, in most cases the bvalues deduced for these components were significantly larger than theb~2.2 km s^-1 (i.e. T_k~7000 K, v_t~1 km s^-1) expected for the LIC, andit is argued that this results from the presence of additional,spectrally unresolved, components having similar velocities and physicalconditions. For two stars (delta Vel and alpha Pav) we detectinterstellar components with much smaller b values (1.1+/-0.3 and0.8+/-0.1 km s^-1, respectively) than are expected for low-densityclouds within the Local Bubble. In the case of the narrow alpha Pavcomponent, we also find an anomalously large Nai/Caii column densityratio, which is indicative of a relatively high density. Thus it ispossible that, in addition to LIC-type clouds, the local interstellarmedium contains a population of previously undetected cooler and denserinterstellar clouds.
| Candidate Main-Sequence Stars with Debris Disks: A New Sample of Vega-like Sources
Vega-like sources are main-sequence stars that exhibit IR fluxes inexcess of expectations for stellar photospheres, most likely due toreradiation of stellar emission intercepted by orbiting dust grains. Wehave identified a large sample of main-sequence stars with possibleexcess IR radiation by cross-correlating the Michigan Catalog ofTwo-dimensional Spectral Types for the HD Stars with the IRAS FaintSource Survey Catalog. Some 60 of these Vega-like sources were not foundduring previous surveys of the IRAS database, the majority of whichemployed the lower sensitivity Point Source Catalog. Here, we providedetails of our search strategy, together with a preliminary examinationof the full sample of Vega-like sources.
| A second dust episode of the Wolf-Rayet system WR 19: another long-period WC+O colliding-wind binary
We present observations of WR 19 showing an infraredexcess due to newly created dust similar to an event observed in 1988.We suggest that these episodes of dust-formation are periodic (P ~ 10yr) and related to the binary nature of the object, comparable to thecolliding-wind binary WR 140. In support of thisthesis we identified absorption lines from a companion of spectral typeO9.5-9.7. We propose monitoring the object to determine orbitalparameters, non-thermal radio emission and the accurate shape of theinfrared light-curve. Based on observations collected at the EuropeanSouthern Observatory (ESO), La Silla, Chile and the South AfricanAstronomical Observatory (SAAO)
| The absolute magnitude of the early type MK standards from HIPPARCOS parallaxes
We analyse the standards of the MK system with the help of Hipparcosparallaxes, using only stars for which the error of the absolutemagnitude is <= 0.3 mag. We find that the main sequence is a wideband and that, although in general giants and dwarfs have differentabsolute magnitudes, the separation between luminosity classes V and IIIis not clear. Furthermore, there are a number of exceptions to thestrict relation between luminosity class and absolute magnitude. Weanalyse similarly the system of standards defined by Garrison & Gray(1994) separating low and high rotational velocity standards. We findsimilar effects as in the original MK system. We propose a revision ofthe MK standards, to eliminate the most deviant cases. Based on datafrom the ESA Hipparcos astrometry satellite
| Local interstellar cloud electron density from magnesium and sodium ionization: a comparison.
The ambient interstellar plasma density (i.e. the plasma density of theinterstellar medium surrounding the Sun) directly governs the structureand the size of our heliosphere. Information on this density can bederived from the ionization states of the interstellar species which canbe detected in absorption along the paths to the nearby stars, and whichcan be shown to belong to the Local Interstellar Cloud (LIC). Echellespectra around the resonance lines of neutral and singly ionizedmagnesium have been obtained for the nearby star δ Cas with theGoddard High-Resolution Spectrograph (GHRS) on board the Hubble SpaceTelescope. While apparently a unique velocity component (a uniquecloudlet) is detected in both lines of the MgII λλ2800resonance doublet, at the expected Doppler shift for the LIC, anextremely small λλ2853 Mg line is also detected at aDoppler shift compatible with the LIC motion, allowing a measurement ofthe LIC MgII/MgI ratio, here found to be 400 (-130,+190). This ratioimplies a mean electron density of about 0.28 (-0.14, +0.34)cm^-3^ alongthis line-of-sight, if equilibrium conditions prevail, and if T=7000K,when using the most recent recombination and charge-exchange rates. ThisMgII/MgI ratio is larger than for Sirius (R=~220), which lies at 110^o^from δ Cas, providing some evidence for an ionization gradient inthe local cloud. Such an electron density implies a surprisingly largeionization degree, and the upper range of the interval is incompatiblewith the minimum size of our heliosphere. A second and independent wayto derive the electron density along the path to δ Cas uses thesimplicity of the LIC geometry in the sky region surrounding the star,which allows an estimate of the H column-density to the star, as well asprevious ground-based CaII data, and the measured NaI/CaII ratio andcalcium depletion in the LIC. The resulting most probable electrondensity at 7000K, 0.05cm^-3^, provides a new evidence for a significantionization degree of the LIC, but is a factor of four to five smallerthan the value based on magnesium. The upper limit of 0.19cm^-3^ remainsconsistent with the minimum size of our heliosphere. The existence of acommon interval to the two determinations: n_e_=0.14-0.19cm^-3^ impliesthat ionization equilibrium within the LIC is not totally precluded.However, the lack of a real convergence deserves further observations,involving other interstellar species. The common interval is compatiblewith the result of Frisch (1994Sci...265.1443F), from anomalous C and Ocosmic rays abundances, if carbon is not too much filtered at theheliospheric interface. On the other hand, the sodium-based mostprobable value is in agreement with neutral hydrogen deceleration at theheliospheric interface for the Baranov two-shocks model, as well as withthe ionization degree of hydrogen implied by local EUV sources.
| The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NM
A spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%.
| Transformations from Theoretical Hertzsprung-Russell Diagrams to Color-Magnitude Diagrams: Effective Temperatures, B-V Colors, and Bolometric Corrections
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...469..355F&db_key=AST
| The nature of the two nuclei in the young merger NGC 3256: an obscured AGN?
We present new high resolution images of the starburst galaxy NGC 3256in the near-infrared broad band continuum (JHK'L') and in the H_2_ 1-0S(1) 2.121μm, Brγ 2.165μm and [Fe II] 1.644μm lines. Theline images are dominated by a primary peak with a secondary peak to thesouth and fainter extended emission covering ~10-20arcsec^2^(~2.7-5.4kpc^2^). The Brγ , [Fe II] and radio morphology are wellcorrelated, while the H_2_ emission is least enhanced on the primarypeak, and its morphology is clearly different from the other lines.Several methods were used to estimate the effects of extinction, whichwe derive to be A_V_~2.4 and ~5.3mag (continuum), and A_V_~7.8 and~10.7mag (emission lines), towards the northern and southern peaks,respectively. The difference in these values probably reflects theuncertainty inherent in each method. Corrected for this extinction,luminosities of the peaks become approximately equal in H_2_ , whereasthe northern peak still dominates the Brγ , [Fe II] and JHK'emission. The L' band image shows two equally bright emission peaks,strongly supporting the previous radio evidence for the existence of twonuclei in this relatively recent merger. Because of the large, possiblyunderestimated extinction, the S nucleus may even be the intrinsicallybrighter nucleus; mid-infrared imaging is needed to estimate therelative luminosities. From the Brγ and [Fe II] luminosities, wederive high mass star forming rates of 1.3 and0.4Msun_yr^-1^, total star formation rates of 6.7 and1.8Msun_yr^-1^ and SN rates of 0.5 and 0.3yr^-1^, for the Nand S nucleus, respectively. Finally, we discuss evidence for andagainst the existence of a heavily obscured Seyfert nucleus in the S, assuggested by the infrared line ratios, low Brγ luminosity, shallowCO 2.3μm feature and the large unresolved soft X-ray luminosity.Near-infrared spectroscopy of coronal lines and mid-IR spectroscopy onthe S nucleus, and spatially resolved X-ray observations are needed todefinitely answer this question.
| Characteristics of Nearby Interstellar Matter
There is a warm tenuous partially ionized cloud (T~104 K,n(HI)~0.1 cm-3, n(HII)~0.22-0.44 cm-3) surroundingthe solar system which regulates the environment of the solar system,determines the structure of the heliopause region, and feeds neutralinterstellar gas into the inner solar system. The velocity (V ~ -20 kms-1 from l~335 deg, b~0 deg in the local standard of rest)and enhanced CaII and FeII abundances of this cloud suggest an origin asevaporated gas from cloud surfaces in the Scorpius-CentaurusAssociation. Although the soft X-ray emission attributed to the 'LocalBubble' is enigmatic, optical and ultraviolet data are consistent withbubble formation caused by star formation epochs in theScorpius-Centaurus Association as regulated by the nearby spiral armconfiguration. The cloud surrounding the solar system (the 'localfluff') appears to be the leading region of an expanding interstellarstructure (the 'squall line') which contains a magnetic field causingpolarization of the light of nearby stars, and also absorption featuresin nearby upwind stars. The velocity vectors of the solar system andlocal fluff are perpendicular in the local standard of rest. Combiningthis information with the low column densities seen toward Sirius in theanti-apex direction, and the assumption that the cloud velocity vectoris parallel to the surface normal, suggests that the Sun entered thelocal fluff within the historical past (less than 10,000 years ago) andis skimming the surface of the cloud. Comparison of magnesiumabsorption lines toward Sirius and anomalous cosmic-ray data suggest thelocal fluff is in ionization equilibrium. [Note that a typographicalerror on page 532 incorrectly gives the age of the squall line shell as~400,000 years; the correct age is ~4 Myrs.]
| 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.
| The determination of T_eff_ of B, A and F main sequence stars from the continuum between 3200 A and 3600 A.
A method of determination of the effective temperature of B, A and Fmain sequence stars is proposed, using the slope of the continuumbetween 3200A and 3600A. The effective temperature calibration is basedon a sample of stars with energy distributions known from UV to the red.We have determined the Balmer jump and the effective temperatures for235 main sequence stars. The temperatures found have been compared withthose derived by Underhill et al. (1979), Kontizas & Theodossiou(1980), Theodossiou (1985), Morossi & Malagnini (1985). Thecomparison showed good agreement for most of the stars in common. On theother hand, the temperatures derived from the reddening-free colourfactor QUV, from the colour index (m1965-V) and from (B-V), given inGulati et al. (1989), are systematically lower than our temperatures,however the differences are within one-sigma error.
| The position corrections of 1400 stars observed with PA II in San Juan.
Not Available
| Vilnius Photometric System - Part Two - the Bright Southern Standard Stars
Not Available
| 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.
| Second astrolabe catalogue of Santiago.
Positions for 350 FK5 and 164 FK5 Extension stars as determined with theDanjon astrolabe of Santiago and differences astrolabe-catalogue aregiven for Equinox J2000.0 and for the mean observation epoch of eachstar. The average mean error in alpha is +/-0.005s and +/-0.07" indelta. The mean epoch of observation of the catalogue is J1979.96.
| High-resolution CA II observations of the local interstellar medium
High-resolution absorption measurements of the interstellar Ca II K lineobserved toward 46 early-type stars in the local ISM (LISM) arepresented. Ca II was detected in 36 of the 46 stars with 82 individualcloud components identified. Ca II was detected to most of the starscloser than 50 pc, except in the region of the Galactic quadrant l =180-270 degrees which also contains the empty line of sight to B CMa at220 pc. The mean local standard of rest velocity of the 82 Ca IIcomponents implies that the LISM clouds are associated with the motionof the solar neighborhood and not the sun. If the present data arecombined with other nearby Ca II component velocities taken from theliterature, then a cloud centered approximately at l = 90 deg, b = -40deg moving coherently with the local interstellar wind vector issupported at a significance level of 99 percent. The Ca II data havebeen combined with Na I data for the same stars to produce a N(NaI)/N(Ca II) ratio for each identified absorption feature. This ratioplotted against the local standard of rest velocities of the cloudsshows that the Routly-Spitzer effect exists down to +/- 10 km/s, whichsupports grain desorption/destruction models that are efficient atreturning calcium to the gas phase at these low velocities.
| The NA I/Ca II ratio in the local interstellar medium
We have measured Na/Ca II column-density ratios in the localinterstellar medium (LISM) within 30 pc. Thanks to a very high spectralresolution, these ratios are those of the individual clouds we are ableto separate. Na I spectra have been corrected for telluric absorptionswith the help of synthetic spectra calculated according to each type ofobserving conditions, allowing to detect extremely low Na I quantitiesin the LISM. The warm LISM Na I/Ca II ratio is typically smaller than0.5 with an average value of 0.22. This strongly confirms the observedtendency for the ratio to decrease below 0.5 in the vicinity of the Sun(Welsh et al. 1991). In the very close gas detected betweenlII = 240 deg and lII = 50 deg, the Na I/Ca IIratio is 0.15 +/- 0.05. In the local interstellar cloud (LIC)surrounding the Sun, now clearly detected, we have derived an upperlimit of 0.2, while there are indications that this limit is very closeto the real value. The temperature of the LIC being 7000 K, this makesthe ratio very little dependent on the electron density and allows toestimate the calcium depletion found to be deltaCa = -1.6 +/-0.3. According to the depletion density relationship (Phillips et al.1984), this is a standard depletion for a approx. 0.1/cu cm densitycloud.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Vela |
| Ascensió Recta: | 10h14m44.20s |
| Declinació: | -42°07'19.0" |
| Magnitud Aparent: | 3.85 |
| Distancia: | 31.526 parsecs |
| Moviment propi RA: | -150.6 |
| Moviment propi Dec: | 50.9 |
| B-T magnitude: | 3.907 |
| V-T magnitude: | 3.836 |
Catàlegs i designacions:
|
INHABITED SKY
