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Ýlgili Makaleler
Dust Processing in Disks around T Tauri Stars
The 8-14 μm emission spectra of 12 T Tauri stars in the Taurus/Aurigadark clouds and in the TW Hydrae association obtained with the InfraredSpectrograph (IRS) on board Spitzer are analyzed. Assuming that the 10μm features originate from silicate grains in the optically thinsurface layers of T Tauri disks, the 8-14 μm dust emissivity for eachobject is derived from its Spitzer spectrum. The emissivities are fitwith the opacities of laboratory analogs of cosmic dust. The fitsinclude small nonspherical grains of amorphous silicates (pyroxene andolivine), crystalline silicates (forsterite and pyroxene), and quartz,together with large fluffy amorphous silicate grains. A wide range inthe fraction of crystalline silicate grains, as well as large silicategrains among these stars, are found. The dust in the transitional-diskobjects CoKu Tau/4, GM Aur, and DM Tau has the simplest form ofsilicates, with almost no hint of crystalline components and modestamounts of large grains. This indicates that the dust grains in theseobjects have been modified little from their origin in the interstellarmedium. Other stars show various amounts of crystalline silicates,similar to the wide dispersion of the degree of crystallinity reportedfor Herbig Ae/Be stars of mass <2.5 Msolar. Late spectraltype, low-mass stars can have significant fractions of crystallinesilicate grains. Higher quartz mass fractions often accompany lowamorphous olivine to amorphous pyroxene ratios. Lower contrast of the 10μm feature accompanies greater crystallinity.
| Mid-Infrared Properties of Low-Metallicity Blue Compact Dwarf Galaxies from the Spitzer Infrared Spectrograph
We present a Spitzer-based mid-infrared (MIR) study of a large sample ofblue compact dwarfs (BCDs) using the Infrared Spectrograph (IRS),including the first MIR spectrum of I Zw 18, the archetype for the BCDclass and among the most metal-poor galaxies known. We show the spectraof polycyclic aromatic hydrocarbon (PAH) emission in a low-metallicityenvironment. We find that the equivalent widths (EWs) of PAHs at 6.2,7.7, 8.6, and 11.2 μm are generally weaker in BCDs than in typicalstarburst galaxies and that the fine-structure line ratio, [Ne III]/[NeII], has a weak anticorrelation with the PAH EW. A much strongeranticorrelation is shown between the PAH EW and the product of the [NeIII]/[Ne II] ratio and the UV luminosity density divided by themetallicity. We conclude that the PAH EW in metal-poor high-excitationenvironments is determined by a combination of PAH formation anddestruction effects.
| Silicate Emission in the Spitzer IRS Spectrum of FSC 10214+4724
We present the first mid-infrared (MIR) spectrum of the z=2.2856ultraluminous infrared galaxy FSC 10214+4724, obtained with the InfraredSpectrograph (IRS) on board the Spitzer Space Telescope. The spectrumspans a rest-wavelength range of 2.3-11.5 μm, covering a number ofkey diagnostic emission and absorption features. The most prominentfeature in the IRS spectrum is the silicate emission at rest-frame ~10μm. We also detect an unresolved emission line at a rest wavelengthof 7.65 μm that we identify with [Ne VI], and a slightly resolvedfeature at 5.6 μm identified as a blend of [Mg VII] and [Mg V]. Thereare no strong PAH emission features in the FSC 10214+4724 spectrum. Weplace a limit of 0.1 μm on the equivalent width of 6.2 μm PAHemission but see no evidence of a corresponding 7.7 μm feature.Semiempirical fits to the spectral energy distribution suggest that ~45%of the bolometric luminosity arises from cold (~50 K) dust, half arisesfrom warm (190 K) dust, and the remainder, ~5%, originates from hot(~640 K) dust. The hot dust is required to fit the blue end of the steepMIR spectrum. The combination of a red continuum, strong silicateemission, little or no PAH emission, and no silicate absorption makesFSC 10214+4724 unlike most other ULIRGs or AGNs observed thus far withthe IRS. These apparently contradictory properties may be explained byan AGN that is highly magnified by the lens, masking a (dominant)overlying starburst with unusually weak PAH emission.
| Polycyclic Aromatic Hydrocarbons Orbiting HD 233517, an Evolved Oxygen-rich Red Giant
We report spectra obtained with the Spitzer Space Telescope in theλ = 5-35 μm range of HD 233517, an evolved K2 III giant withcircumstellar dust. For λ > 13 μm, the flux is a smoothcontinuum that varies approximately as ν-5/3. For λ< 13 μm, although the star is oxygen-rich, PAH features producedby carbon-rich species at 6.3, 8.2, 11.3, and 12.7 μm are detectedalong with likely broad silicate emission near 20 μm. These resultscan be explained if there is a passive, flared disk orbiting HD 233517.Our data support the hypothesis that organic molecules in orbiting disksmay be synthesized in situ as well as having been incorporated from theinterstellar medium.Based on observations with the NASA Spitzer Space Telescope, which isoperated by the California Institute of Technology for NASA.
| Computed Hβ indices from ATLAS9 model atmospheres
Aims.Grids of Hβ indices based on updated (new-ODF) ATLAS9 modelatmospheres were computed for solar and scaled solar metallicities[+0.5], [+0.2], [0.0], [ -0.5] , [ -1.0] , [ -1.5] , [ -2.0] , [ -2.5]and for α enhanced compositions [+0.5a], [0.0a], [ -0.5a] , [-1.0a] , [ -1.5a] , [ -2.0a] , [ -2.5a] , and [ -4.0a] . Methods:.Indices for T_eff > 5000 K were computed with the same methods asdescribed by Lester et al. (1986, LGK86) except for a differentnormalization of the computed natural system to the standard system.LGK86 used special ODFs to compute the fluxes. For T_eff ≤ 5000 K wecomputed the fluxes using the synthetic spectrum method. In order toassess the accuracy of the computed indices comparisons were made withthe indices computed by Smalley & Dworetsky (1995, A&A, 293,446, MD95) and with the empirical relations T_eff-Hβ given byAlonso et al. (1996, A&A, 313, 873) for several metallicities.Furthermore, for cool stars, temperatures inferred from the computedindices were compared with those of the fundamental stars listed byMD95. The same kind of comparison was made between gravities for B-typestars. Results: .The temperatures from the computed indices are ingood agreement, within the error limits, with the literature values for4750 K ≤ T_eff ≤ 8000 K, while the gravities agree for T_eff> 9000 K. The computed Hβ indices for the Sun and for Procyonare very close to the observed values. The comparison between theobserved and computed Hβ indices as function of the observedHβ has shown a very small trend which almost completely disappearswhen only stars hotter than 10 000 K are considered. The trend due tothe cool stars is probably related with the low accuracy of thefundamental T_eff which are affected by large errors for most of thestars.
| Mid-Infrared Spectra of Classical AGNs Observed with the Spitzer Space Telescope
Full low-resolution (65
| Disks in Transition in the Taurus Population: Spitzer IRS Spectra of GM Aurigae and DM Tauri
We present Spitzer Infrared Spectrograph (IRS) observations of twoobjects of the Taurus population that show unambiguous signs of clearingin their inner disks. In one of the objects, DM Tau, the outer disk istruncated at 3 AU; this object is akin to another recently reported inTaurus, CoKu Tau/4, in that the inner disk region is free of small dust.Unlike CoKu Tau/4, however, this star is still accreting, so opticallythin gas should still remain in the inner disk region. The other object,GM Aur, also accreting, has ~0.02 lunar masses of small dust in theinner disk region within ~5 AU, consistent with previous reports.However, the IRS spectrum clearly shows that the optically thick outerdisk has an inner truncation at a much larger radius than previouslysuggested, ~24 AU. These observations provide strong evidence for thepresence of gaps in protoplanetary disks.
| The Accretion Disk of the Lithium-depleted Young Binary St 34
We present the infrared spectrum of the young binary system St 34obtained with the Infrared Spectrograph (IRS) on the Spitzer SpaceTelescope. The IRS spectrum clearly shows excess dust emission,consistent with the suggestion of White & Hillenbrand that St 34 isaccreting from a circumbinary disk. The disk emission of St 34 is low incomparison with the levels observed in typical T Tauri stars; silicatefeatures at ~10 and 20 μm are much weaker than typically seen in TTauri stars; and excess emission is nearly absent at the shortestwavelengths observed (~5 μm). These features of the infrared spectrumsuggest substantial grain growth (to eliminate silicate features) andpossible settling of dust to the disk midplane (to reduce the continuumexcess emission levels), along with a relatively evacuated inner disk,as expected due to gravitational perturbations by the binary system.Although the position of St 34 in the H-R diagram suggests an age of8+/-3 Myr, assuming that it lies at the distance of the Taurus-Aurigamolecular clouds, White & Hillenbrand could not detect any Li Iabsorption, which would indicate a Li depletion age of roughly 25 Myr ormore. We suggest that St 34 is closer than the Taurus clouds by ~ 30-40pc and has an age roughly consistent with Li depletion models. Such anadvanced age would make St 34 the oldest known low-masspre-main-sequence object with a dusty accretion disk. The persistence ofoptically thick dust emission well outside the binary orbit may indicatea failure to make giant planets that could effectively remove dustparticles.
| Colors of Classical T Tauri Stars in Taurus Derived from Spitzer Infrared Spectrograph Spectra: Indication of Dust Settling
We analyzed Spitzer Infrared Spectrograph data of a representativesample of classical T Tauri stars in the Taurus star-forming region bycomputing color indices in wave bands that characterize the continuumemission from dust in circumstellar disks. We compared these indices tothose derived from a grid of accretion disk models with varyinginclination angles, mass accretion rates, and amounts of dust settling.We conclude that most T Tauri stars in our sample have experienced somedegree of dust settling and grain growth in their disks, indicating diskevolution.
| Spitzer IRS Spectra of Young Stars Near the Hydrogen-burning Mass Limit
We present Spitzer Infrared Spectrograph measurements for two youngstars near the hydrogen-burning mass limit in the Taurus star-formingregion. While one of the objects, V410 X-ray 3, displays no mid-infraredexcess, the other one, V410 Anon 13, shows a clear excess at wavelengthslongward of 10 μm, indicative of a circumstellar disk. Moreover, thedisk surrounding V410 Anon 13 is reminiscent of flared accretion disksaround classical T Tauri stars; small dust grains in the diskphotosphere generate the broad 10 μm silicate emission feature, whosestructure suggests the presence of crystalline components. Thisdemonstrates that very low mass objects, like their more massivecounterparts, experience dust processing in their disks.
| 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.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is 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/431/773
| A 2dF survey of the Small Magellanic Cloud
We present a catalogue of new spectral types for hot, luminous stars inthe Small Magellanic Cloud (SMC). The catalogue contains 4161 objects,giving an order-of-magnitude increase in the number of SMC stars withpublished spectroscopic classifications. The targets are primarily B-and A-type stars (2862 and 853 objects respectively), with oneWolf-Rayet, 139 O-type and 306 FG stars, sampling the main sequence to~mid-B. The selection and classification criteria are described, andobjects of particular interest are discussed, including UV-selectedtargets from the Ultraviolet Imaging Telescope (UIT) experiment, Be andB[e] stars, `anomalous A supergiants' and composite-spectrum systems. Weexamine the incidence of Balmer-line emission, and the relationshipbetween Hγ equivalent width and absolute magnitude for BA stars.
| Mid-infrared Spectra of Class I Protostars in Taurus
We present Spitzer Space Telescope Infrared Spectrograph observations inthe 5.3-20 μm range of five young stellar objects in Taurus that haveClass I continuum spectral energy distributions(λFλαλn,n>=0), oftentaken to represent the youngest stellar objects in this star formationregion. The spectra include a rich collection of broad absorptionfeatures that we identify with amorphous silicates and various ices,notably those of carbon dioxide and water. We show that the absorptionfeatures are produced mainly in the envelopes of these systems. Theapparent depths of silicate and 15.2 μm CO2 ice featuresvary among the objects in a manner that is consistent with a variationof inclination with respect to the line of sight, contribution to thesilicate features from material throughout the envelopes, and an originfor the CO2 ice feature in the outer parts of the envelope.Thus, these features provide new and useful constraints on models of thephysical structure of Class I protostars.
| Methane Abundance Variations toward the Massive Protostar NGC 7538 IRS 9
Absorption and emission lines originating from the ν3 CHstretching manifold of gas-phase CH4 were discovered in thehigh-resolution (R=25,000) infrared L-band spectrum along the line ofsight toward NGC 7538 IRS 9. These observations provide a diagnostic ofthe complex dynamics and chemistry in a massive star-forming region. Theline shapes resemble P Cygni profiles with the absorption and emissioncomponents shifted by ~7 km s-1 with respect to the systemicvelocity. Similar velocity components were observed in CO at 4.7 μm,but in contrast to CH4, the CO shows deep absorption due to ahigh-velocity outflow as well as absorption at the systemic velocity dueto the cold outer envelope. It is concluded that the gas-phaseCH4 abundance varies by an order of magnitude in this line ofsight: it is low in the envelope and the outflow(X[CH4]<0.4×10-6) and at least a factorof 10 larger in the central core. The discovery of solid CH4in independent ground- and space-based data sets shows that methane isnearly entirely frozen onto grains in the envelope. It thus appears thatCH4 is formed by grain surface reactions, evaporates into thegas phase in the warm inner regions of protostellar cores, and isefficiently destroyed in shocks related to outflows.Some of the data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, theNetherlands, and the United Kingdom), and with the participation of ISASand NASA.
| Characteristics and classification of A-type supergiants in the Small Magellanic Cloud
We address the relationship between spectral type and physicalproperties for A-type supergiants in the Small Magellanic Cloud (SMC).First, we construct a self-consistent classification scheme for Asupergiants, employing the calcium K to Hɛ line ratio as atemperature-sequence discriminant. Following the precepts of the `MKprocess', the same morphological criteria are applied to Galactic andSMC spectra, with the understanding that there may not be acorrespondence in physical properties between spectral counterparts indifferent environments. Then we discuss the temperature scale,concluding that A supergiants in the SMC are systematically cooler thantheir Galactic counterparts at the same spectral type, by up to ~10 percent. Considering the relative line strengths of Hγ and the CH Gband, we extend our study to F- and early G-type supergiants, for whichsimilar effects are found. We note the implications for analyses ofluminous extragalactic supergiants, for the flux-weightedgravity-luminosity relationship and for population synthesis studies inunresolved stellar systems.
| High-Precision Near-Infrared Photometry of a Large Sample of Bright Stars Visible from the Northern Hemisphere
We present the results of 8 yr of infrared photometric monitoring of alarge sample of stars visible from Teide Observatory (Tenerife, CanaryIslands). The final archive is made up of 10,949 photometric measuresthrough a standard InSb single-channel photometer system, principally inJHK, although some stars have measures in L'. The core of this list ofstars is the standard-star list developed for the Carlos SánchezTelescope. A total of 298 stars have been observed on at least twooccasions on a system carefully linked to the zero point defined byVega. We present high-precision photometry for these stars. The medianuncertainty in magnitude for stars with a minimum of four observationsand thus reliable statistics ranges from 0.0038 mag in J to 0.0033 magin K. Many of these stars are faint enough to be observable with arraydetectors (42 are K>8) and thus to permit a linkage of the bright andfaint infrared photometric systems. We also present photometry of anadditional 25 stars for which the original measures are no longeravailable, plus photometry in L' and/or M of 36 stars from the mainlist. We calculate the mean infrared colors of main-sequence stars fromA0 V to K5 V and show that the locus of the H-K color is linearlycorrelated with J-H. The rms dispersion in the correlation between J-Hand H-K is 0.0073 mag. We use the relationship to interpolate colors forall subclasses from A0 V to K5 V. We find that K and M main-sequence andgiant stars can be separated on the color-color diagram withhigh-precision near-infrared photometry and thus that photometry canallow us to identify potential mistakes in luminosity classclassification.
| 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
| High-Resolution 4.7 Micron Keck/NIRSPEC Spectra of Protostars. II. Detection of the 13CO Isotope in Icy Grain Mantles
The high-resolution (R=25,000) infrared M-band spectrum of the massiveprotostar NGC 7538 IRS 9 shows a narrow absorption feature at 4.779μm (2092.3 cm-1) that we attribute to the vibrationalstretching mode of the 13CO isotope in pure CO icy grainmantles. This is the first detection of 13CO in icy grainmantles in the interstellar medium. The 13CO band is a factorof 2.3 narrower than the apolar component of the 12CO band.With this in mind, we discuss the mechanisms that broaden solid-stateabsorption bands. It is shown that ellipsoidally shaped pure CO grainsfit the bands of both isotopes at the same time. Slightly worse butstill reasonable fits are also obtained by CO embedded inN2-rich ices and thermally processed O2-rich ices.In addition, we report new insights into the nature and evolution ofinterstellar CO ices by comparing the very high resolutionmulticomponent solid 12CO spectrum of NGC 7538 IRS 9 withthat of the previously studied low-mass source L1489 IRS. The narrowabsorption of apolar CO ices is present in both spectra but muchstronger in NGC 7538 IRS 9. It is superposed on a smooth broadabsorption feature well fitted by a combination of CO2 andH2O-rich laboratory CO ices. The abundances of the latter twoices, scaled to the total H2O ice column, are the same inboth sources. We thus suggest that thermal processing manifests itselfas evaporation of apolar ices only and not the formation ofCO2 or polar ices. Finally, the decomposition of the12CO band is used to derive the12CO/13CO abundance ratio in apolar ices. A ratioof 12CO/13CO=71+/-15 (3 σ) is deduced, ingood agreement with gas-phase CO studies (~77) and the solid12CO2/13CO2 ratio of 80+/-11found in the same line of sight. The implications for the chemical pathalong which CO2 is formed are discussed. The data presentedherein were obtained at the W. M. Keck Observatory, which is operated asa scientific partnership among the California Institute of Technology,the University of California, and the National Aeronautics and SpaceAdministration. The observatory was made possible by the generousfinancial support of the W. M. Keck Foundation.
| 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.
| Magnetic survey of bright northern main sequence stars
The first results of a systematic search for magnetic fields in thebrightest upper main sequence (MS) stars are presented. The main goal isto survey the stars with about the same detection limit and to improveexisting statistics of their magnetism. The target list contains 57upper MS stars and represents well B0.5-F9 stars. High-resolution Zeemanspectra were obtained for 30 stars of the list. The accuracy of themagnetic field measurements ranges from 20 to 300 G depending mainly onspectral class. In the majority of studied stars we did not detectmagnetic fields. In some stars we suspect the presence of a weakmagnetic field. These are the best candidates for more extensivestudies. A particular case is the star chi Dra where we probablydetected the global magnetic field. The longitudinal field strength isB_l= -54+/-12 G. Further observations of this star are needed to confirmthe detection and to ascertain if the magnetic field is variable withthe period of rotation. Based on observations collected at the 1 mtelescope of the Special Astrophysical Observatory (Nizhnij Arkhyz,Russia).
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is 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/386/492, and from theauthors on CD-Rom.
| V, I_C Observations of the Variable Antipin V71
We present VI_C CCD photometry of the variable Antipin V71 stated asfast variable of unknown type by the discoverer.
| Diameters of δ Cephei and η Aquilae Measured with the Navy Prototype Optical Interferometer
We have measured the diameters of the Cepheid variables δ Cephei(18 nights) and η Aquilae (11 nights) with the Navy PrototypeOptical Interferometer. The primary results of these observations arethe mean angular diameters <θLD> of theseCepheids: 1.520+/-0.014 milliseconds of arc (mas) for δ Cep and1.69+/-0.04 mas for η Aql. We also report limb-darkened diametersfor the check stars in this program: for β Lac,θLD=1.909+/-0.011 mas and for 12 Aql,θLD=2.418+/-0.010 mas. When combined with radiusestimates from period-radius relations in the literature, the Cepheidangular diameters suggest distances slightly smaller than, but stillconsistent with, the Hipparcos distances. Pulsations are weakly detectedat a level of ~1.5 to 2 σ for both Cepheids.
| 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
| The Three-dimensional Structure of the Warm Local Interstellar Medium. II. The Colorado Model of the Local Interstellar Cloud
In this second paper in a series on the structure of the localinterstellar medium (LISM), we construct a three-dimensional model ofthe local interstellar cloud (LIC) based on Hubble Space Telescope(HST), Extreme Ultraviolet Explorer (EUVE), and ground-based Ca IIspectra. Starting with hydrogen column densities derived from deuteriumcolumn densities measured with the Goddard High Resolution Spectrographinstrument on HST for 16 lines of sight to nearby stars, we derive amodel consisting of the sum of nine spherical harmonics that best fitthe data. We then rederive the model by including the lines of sight tothree hot white dwarfs observed by EUVE and 13 lines of sight with Ca IIcolumn densities at the projected LIC velocity. The LIC model is clearlynot a long thin filamentary structure like optical images of someinterstellar clouds (e.g., reflection nebulae in the Pleiades), butneither is it spherical in shape. As seen from the north Galactic pole,the LIC is egg-shaped with an axis of symmetry that points in thedirection l~315deg. Since the direction of the center of theScorpius-Centaurus association is l=320deg, the shape of theLIC could be determined by the flow of hot gas from Sco-Cen. The modelshows that the Sun is located just inside the LIC in the direction ofthe Galactic center and toward the north Galactic pole. The absence ofMg II absorption at the LIC velocity toward α Cen indicates thatthe distance to the edge of the LIC in this direction is <=0.05 pcand the Sun should cross the boundary between the LIC and the Galactic(G) cloud in less than 3000 yr. We estimate that the volume of the LICis about 93 pc3 and its mass is about 0.32 Msolar.The physical parameters and hydrogen column density of the LIC areroughly consistent with theoretical models of the warm interstellarmedium that assume pressure and ionization equilibrium. However, theempirical hydrogen ionization of the LIC is much higher and the gastemperature lower than the theoretical models predict. Therefore, theionization is likely due to shock activity from a nearby supernova thathas not yet reached equilibrium. The higher ionization increases the gascooling, which can explain why the gas is 2400 K cooler than theionization equilibrium models predict. Computed and observedtemperatures are in agreement for a model with the observed LIC electrondensity. Based on observations with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555.
| Infrared Space Observatory Photometric Search of Main-Sequence Stars for Vega-Type Systems
We obtained 3.6-20 μm photometry of 38 bright [IRAS F_nu(12μm)>0.7 Jy] main-sequence stars with the Infrared SpaceObservatory (ISO). Observations were conducted with the ISOPHOTinstrument, in the single-pointing photometry mode, through filters at3.6, 11.5, and 20.0 mum. We searched for excess (Vega-type) emissionfrom dust at temperatures >~100 K, located at ~1-60 AU from thestars. We thus sampled dust at warm, terrestrial material temperaturesand at cool (~100 K) temperatures of possible Kuiper Belt-type regionsin these systems. We detected 20 μm excesses from ~14% of oursources, but we did not detect 11.5 μm excesses from any of them. Wepresent single-temperature blackbody models of the location and densityof dust emission around 10 stars, two of them (29 Cyg and Gl 816) withexcesses newly reported here. We make a thorough comparison of ISO andIRAS data on our target stars and propose a new calibration procedurefor ISOPHOT staring measurements at 3.6, 11.5, and 20 mum.
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| Takýmyýldýz: | Kertenkele |
| Sað Açýklýk: | 22h31m17.50s |
| Yükselim: | +50°16'57.0" |
| Görünürdeki Parlaklýk: | 3.77 |
| Uzaklýk: | 31.387 parsek |
| özdevim Sað Açýklýk: | 0 |
| özdevim Yükselim: | 0 |
| B-T magnitude: | 3.784 |
| V-T magnitude: | 3.758 |
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