תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Revealing the Mid-Infrared Emission Structure of IRAS 16594-4656 and IRAS 07027-7934
TIMMI2 diffraction-limited mid-infrared images of a multipolarproto-planetary nebula IRAS 16594-4656 and a young [WC] ellipticalplanetary nebula IRAS 07027-7934 are presented. Their dust shells arefor the first time resolved (only marginally in the case of IRAS07027-7934) by applying the Lucy-Richardson deconvolution algorithm tothe data, taken under exceptionally good seeing conditions (<=0.5").IRAS 16594-4656 exhibits a two-peaked morphology at 8.6, 11.5, and 11.7μm, which is mainly attributed to emission from PAHs. Ourobservations suggest that the central star is surrounded by a toroidalstructure, observed edge-on, with a radius of 0.4" (~640 AU at anassumed distance of 1.6 kpc) and with its polar axis atP.A.~80deg, coincident with the orientation defined by onlyone of the bipolar outflows identified in the HST optical images. Wesuggest that the material expelled from the central source is currentlybeing collimated in this direction and that the multiple outflowformation has not been coeval. IRAS 07027-7934 shows a bright,marginally extended emission (FWHM=0.3") in the mid-infrared with aslightly elongated shape along the north-south direction, consistentwith the morphology detected by HST in the near-infrared. Themid-infrared emission is interpreted as the result of the combinedcontribution of small, highly ionized PAHs and relatively hot dustcontinuum. We propose that IRAS 07027-7934 may have recently experienceda thermal pulse (likely at the end of the AGB) which has produced aradical change in the chemistry of its central star.Based on observations collected at the European Southern Observatory (LaSilla, Chile), on observations made with ISO, an ESA project withinstruments funded by ESA Member States (especially the PI countries:France, Germany, Netherlands, and the United Kingdom) with theparticipation of ISAS and NASA, and on observations made with theNASA/ESA Hubble Space Telescope, obtained from the data archive at theSpace Telescope Science Institute, which is operated by the Associationof Universities for Research in Astronomy (AURA), Inc., under NASAcontract NAS5-26555.
| The polar wind of the fast rotating Be star Achernar. VINCI/VLTI interferometric observations of an elongated polar envelope
Context: .Be stars show evidence of mass loss and circumstellarenvelopes (CSE) from UV resonance lines, near-IR excesses, and thepresence of episodic hydrogen emission lines. The geometry of theseenvelopes is still uncertain, although it is often assumed that they areformed by a disk around the stellar equator and a hot polar wind.Aims: .We probe the close environment of the fast rotating Be starAchernar at angular scales of a few milliarcseconds (mas) in theinfrared, in order to constrain the geometry of a possible polar CSE. Methods: .We obtained long-baseline interferometric observations ofAchernar with the VINCI/VLTI beam combiner in the H and K bands, usingvarious telescope configurations and baseline lengths with a wideazimuthal coverage. Results: .The observed visibility measurementsalong the polar direction are significantly lower than the visibilityfunction of the photosphere of the star alone, in particular at lowspatial frequencies. This points to the presence of an asymmetricdiffuse CSE elongated along the polar direction of the star. To ourdata, we fit a simple model consisting of two components: a 2Delliptical Gaussian superimposed on a uniform ellipse representing thedistorted photosphere of the fast rotating star. Conclusions: .Weclearly detected a CSE elongated along the polar axis of the star, aswell as rotational flattening of the stellar photosphere. For theuniform-ellipse photosphere we derive a major axis of θ_eq = 2.13± 0.05 mas and a minor axis of θ_pol = 1.51 ± 0.02mas. The relative near-IR flux measured for the CSE compared to thestellar photosphere is f = 4.7 ± 0.3%. Its angular dimensions areloosely constrained by the available data at ρ_eq = 2.7 ± 1.3mas and ρ_pol = 17.6 ± 4.9 mas. This CSE could be linked tofree-free emission from the radiative pressure driven wind originatingfrom the hot polar caps of the star.
| Observations and Modeling of the 2-25 μm Emission from High-Mass Protostellar Object Candidates
This is a report on detailed modeling of young high-mass protostellarcandidates during their most embedded and obscured phases. We performednarrowband mid-infrared imaging of three candidate high-massprotostellar objects in G11.94-0.62, G29.96-0.02, and G45.07+0.13 atGemini Observatory using the Thermal-Region Camera and Spectrograph(T-ReCS). The sources were imaged through up to 11 narrowband filters,sampling their SEDs over the entire 2-25 μm infrared range. For thefirst time, we have fit the observed SEDs of massive protostars withmodels that take into account departures from spherical symmetry in theinfalling envelopes. In this way, we have been able to derive from themodels the detailed physical parameters for these earliest stages ofmassive stellar life. Our detailed modeling suggests that massive starformation can proceed in a way very similar to the formation of low-massstars.
| Thermal infrared observations of the Hayabusa spacecraft target asteroid 25143 Itokawa
We obtained N- and Q-band observations of the Apollo-type asteroid25143 Itokawa during its close Earth approach in July2004 with TIMMI2 at the ESO 3.6 m telescope. Our photometricmeasurement, in combination with already published data, allowed us toderive a radiometric effective diameter of 0.32 ± 0.03 km and analbedo of 0.19+0.11-0.03 through a thermophysicalmodel. This effective diameter corresponds to a slightly asymmetricaland flattened ellipsoid of the approximate size of 520(±50)× 270(±30) × 230(±20) m, based on theKaasalainen et al. (2005, Proceedings of the 1st Hayabusa Symposium, ASPConf. Ser., submitted) shape model. Our studies show that the thermalobservations lead to size estimates which are about 15% smaller than theradar results (Ostro et al. 2005, Met. Plan. Sci., submitted), slightlyoutside the stated radar uncertainties of ±10%. We determined arather high thermal inertia of 750 J m-2 s-0.5K-1. This is an indication for a bare rock dominated surface,a thick dust regolith can be excluded as well as a metallic surface.From our data we constructed a 10.0 μm thermal lightcurve which isnicely matched in amplitude and phase by the shape and spin vectorsolution in combination with our TPM description. The assumed S-typebulk density in combination with radiometric size lead to a total massestimate of 4.5+2.0-1.8 × 1010kg.
| Gravitational-darkening of Altair from interferometry
Interferometric observations have revealed that the rapid rotator Altairis a flattened star with a non-centrally symmetric intensitydistribution. In this work we perform for the first time a physicallyconsistent analysis of all interferometric data available so far,corresponding to three different interferometers operating in severalspectral bands. These observations include new data (squaredvisibilities in the H and K bands from VLTI-VINCI) as well as previouslypublished data (squared visibilities in the K band from PTI and squaredvisibilities, triple amplitudes, and closure phases in the visiblebetween 520 nm and 850 nm from NPOI). To analyze these data we perform aχ2 minimization using an interferometry-oriented modelfor fast rotators, which includes Roche approximation, limb-darkening,and von Zeipel-like gravity-darkening. Thanks to the richinterferometric data set available and to this physical model, the mainuniqueness problems were avoided. As a result, we show that theobservations can only be explained if Altair has a gravity-darkeningcompatible with the expected value for hot stars, i.e., the von Zeipeleffect (T_eff∝ g0.25).
| First results from the ESO VLTI calibrators program
The ESO Very Large Telescope Interferometer (VLTI) is one of the leadinginterferometric facilities. It is equipped with several 8.2 and 1.8 mtelescopes, a large number of baselines up to 200 m, and with severalsubsystems designed to enable high quality measurements and to improvesignificantly the limits of sensitivities currently available tolong-baseline interferometry. The full scientific potential of the VLTIcan be exploited only if a consistent set of good quality calibrators isavailable. For this, a large number of observations of potentialcalibrators have been obtained during the commissioning phase of theVLTI. These data are publicly available. We briefly describe theinterferometer, the VINCI instrument used for the observations, the dataflow from acquisition to processed results, and we present and commenton the volume of observations gathered and scrutinized. The result is alist of 191 calibrator candidates, for which a total of 12 066observations can be deemed of satisfactory quality. We present a generalstatistical analysis of this sample, using as a starting point theangular diameters previously available in the literature. We derive thegeneral characteristics of the VLTI transfer function, and its trendwith time in the period 2001 through mid-2004. A second paper will bedevoted to a detailed investigation of a selected sample, aimed atestablishing a VLTI-based homogeneous system of calibrators.
| 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
| Subgiants as probes of galactic chemical evolution
Chemical abundances for 23 candidate subgiant stars have been derivedwith the aim at exploring their usefulness for studies of galacticchemical evolution. High-resolution spectra from ESO CAT-CES andNOT-SOFIN covered 16 different spectral regions in the visible part ofthe spectrum. Some 200 different atomic and molecular spectral lineshave been used for abundance analysis of 30 elemental species. Thewings of strong, pressure-broadened metal lines were used fordetermination of stellar surface gravities, which have been comparedwith gravities derived from HIPPARCOS parallaxes and isochronic masses.Stellar space velocities have been derived from HIPPARCOS and Simbaddata, and ages and masses were derived with recent isochrones. Only 12of the stars turned out to be subgiants, i.e. on the ``horizontal'' partof the evolutionary track between the dwarf- and the giant stages. Theabundances derived for the subgiants correspond closely to those ofdwarf stars. With the possible exceptions of lithium and carbon we findthat subgiant stars show no ``chemical'' traces of post-main-sequenceevolution and that they are therefore very useful targets for studies ofgalactic chemical evolution.Based on observations made at ESO, La Silla.Based on observations made at NOT, La Palma.Tables 1 and 2 are only available in electronic form athttp://www.edpsciences.org
| First observations with an H-band integrated optics beam combiner at the VLTI
This paper reports results obtained with the Very Large TelescopeInterferometer Commissioning Instrument (VLTI-VINCI) where the fiberinterferometric coupler MONA was temporarily replaced by an integratedoptics beam combiner (IONIC). The two-beam combiner operating in the Hatmospheric band was tested at Paranal during two weeks in July 2002.Fringes were recorded on several stars with the siderostats and the UnitTelescopes (UT). We demonstrate that integrated optics allows beamcombination with a high interferometric efficiency, stability andspatial filtering. The instrumental visibility of VLTI+IONIC is betterthan 85%, which is just 5% under the visibility of the IONIC devicealone. During this run, the flux injection in the IONIC combiner was notoptimized since we used the K-band MONA optics. However, we obtainfringes with the 35 cm siderostats on a star of magnitude mH=2.47(κ2 Scl). It allows us to extrapolate a magnitudearound mH6 with 8 m telescopes without adaptive optics and in thesame poor injection conditions.Based on observations collected at the European Southern Observatory,Paranal, Chile (public commissioning data).
| Mid-infrared emission of galactic nuclei. TIMMI2 versus ISO observations and models
We investigate the mid-infrared radiation of galaxies that are poweredby a starburst or by an AGN. For this end, we compare the spectraobtained at different spatial scales in a sample of infrared brightgalaxies. ISO observations which include emission of the nucleus as wellas most of the host galaxy are compared with TIMMI2 spectra of thenuclear region. We find that ISO spectra are generally dominated bystrong PAH bands. However, this is no longer true when inspecting themid-infrared emission of the pure nucleus. Here PAH emission is detectedin starbursts whereas it is significantly reduced or completely absentin AGNs. A physical explanation of these new observational results ispresented by examining the temperature fluctuation of a PAH afterinteraction with a photon. It turns out that the hardness of theradiation field is a key parameter for quantifying the photo-destructionof small grains. Our theoretical study predicts PAH evaporation in softX-ray environments. Radiative transfer calculations of clumpy starburstsand AGN corroborate the observational fact that PAH emission isconnected to starburst activity whereas PAHs are destroyed near an AGN.The radiative transfer models predict for starbursts a much largermid-infrared size than for AGN. This is confirmed by our TIMMI2acquisition images: We find that the mid-infrared emission of Seyfertsis dominated by a compact core while most of the starbursts arespatially resolved.Based on ESO: 68.B-0066(A) and observations with ISO, an ESA projectwith instruments funded by ESA Member States (especially the PIcountries: France, Germany, The Netherlands and the UK) with theparticipation of ISAS and NASA.}
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/413/1037
| A catalogue of calibrator stars for long baseline stellar interferometry
Long baseline stellar interferometry shares with other techniques theneed for calibrator stars in order to correct for instrumental andatmospheric effects. We present a catalogue of 374 stars carefullyselected to be used for that purpose in the near infrared. Owing toseveral convergent criteria with the work of Cohen et al.(\cite{cohen99}), this catalogue is in essence a subset of theirself-consistent all-sky network of spectro-photometric calibrator stars.For every star, we provide the angular limb-darkened diameter, uniformdisc angular diameters in the J, H and K bands, the Johnson photometryand other useful parameters. Most stars are type III giants withspectral types K or M0, magnitudes V=3-7 and K=0-3. Their angularlimb-darkened diameters range from 1 to 3 mas with a median uncertaintyas low as 1.2%. The median distance from a given point on the sky to theclosest reference is 5.2degr , whereas this distance never exceeds16.4degr for any celestial location. The catalogue is only available inelectronic form at the 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/393/183
| 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.
| On the Wilson-Bappu relationship in the Mg II k line
An investigation is carried out on the Wilson-Bappu effect in the Mg Iik line at 2796.34 Å. The work is based on a selection of 230 starsobserved by both the IUE and HIPPARCOS satellites, covering a wide rangeof spectral types (F to M) and absolute visual magnitudes (-5.4<=MV <=9.0). A semi-automatic procedure is used to measurethe line widths, which applies also in the presence of strong centralabsorption reversal. The Wilson-Bappu relationship here provided isconsidered to represent an improvement over previous recent results forthe considerably larger data sample used, as well as for a properconsideration of the measurement errors. No evidence has been found fora possible dependence of the WB effect on stellar metallicity andeffective temperature.
| 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
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Spectral Irradiance Calibration in the Infrared. X. A Self-Consistent Radiometric All-Sky Network of Absolutely Calibrated Stellar Spectra
We start from our six absolutely calibrated continuous stellar spectrafrom 1.2 to 35 μm for K0, K1.5, K3, K5, and M0 giants. These wereconstructed as far as possible from actual observed spectral fragmentstaken from the ground, the Kuiper Airborne Observatory, and the IRAS LowResolution Spectrometer, and all have a common calibration pedigree.From these we spawn 422 calibrated ``spectral templates'' for stars withspectral types in the ranges G9.5-K3.5 III and K4.5-M0.5 III. Wenormalize each template by photometry for the individual stars usingpublished and/or newly secured near- and mid-infrared photometryobtained through fully characterized, absolutely calibrated,combinations of filter passband, detector radiance response, and meanterrestrial atmospheric transmission. These templates continue ourongoing effort to provide an all-sky network of absolutely calibrated,spectrally continuous, stellar standards for general infrared usage, allwith a common, traceable calibration heritage. The wavelength coverageis ideal for calibration of many existing and proposed ground-based,airborne, and satellite sensors, particularly low- tomoderate-resolution spectrometers. We analyze the statistics of probableuncertainties, in the normalization of these templates to actualphotometry, that quantify the confidence with which we can assert thatthese templates truly represent the individual stars. Each calibratedtemplate provides an angular diameter for that star. These radiometricangular diameters compare very favorably with those directly observedacross the range from 1.6 to 21 mas.
| Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Recalibration of the Wilson-Bappu Effect Using the Singly Ionized Magnesium K Line
A new calibration of the Wilson-Bappu effect is presented using datafrom a survey of the singly ionized magnesium (Mg ii) h and k lines(near 280 nm) taken from the archives of the International UltravioletExplorer satellite. Our sample consisted of 94 stars with absolutemagnitudes derived from parallaxes reported from Hipparcos. We describethe dependencies of the base widths, peak widths, and full widths athalf-maximum (FWHM) on the fundamental stellar parameters T_eff,metallicity, log g, and activity.
| Determination of the temperatures of selected ISO flux calibration stars using the Infrared Flux Method
Effective temperatures for 420 stars with spectral types between A0 andK3, and luminosity classes between II and V, selected for a fluxcalibration of the Infrared Space Observatory, ISO, have been determinedusing the Infrared Flux Method (IRFM). The determinations are based onnarrow and wide band photometric data obtained for this purpose, andtake into account previously published narrow-band measures oftemperature. Regression coefficients are given for relations between thedetermined temperatures and the photometric parameters (B2-V1), (b-y)and (B-V), corrected for interstellar extinction through use ofHipparcos parallaxes. A correction for the effect of metallicity on thedetermination of integrated flux is proposed. The importance of aknowledge of metallicity in the representation of derived temperaturesfor Class V, IV and III stars by empirical functions is discussed andformulae given. An estimate is given for the probable error of eachtemperature determination. Based on data from the ESA HipparcosAstrometry Satellite.
| Towards a fundamental calibration of stellar parameters of A, F, G, K dwarfs and giants
I report on the implementation of the empirical surface brightnesstechnique using the near-infrared Johnson broadband { (V-K)} colour assuitable sampling observable aimed at providing accurate effectivetemperatures of 537 dwarfs and giants of A-F-G-K spectral-type selectedfor a flux calibration of the Infrared Space Observatory (ISO). Thesurface brightness-colour correlation is carefully calibrated using aset of high-precision angular diameters measured by moderninterferometry techniques. The stellar sizes predicted by thiscorrelation are then combined with the bolometric flux measurementsavailable for a subset of 327 ISO standard stars in order to determineone-dimensional { (T, V-K)} temperature scales of dwarfs and giants. Theresulting very tight relationships show an intrinsic scatter induced byobservational photometry and bolometric flux measurements well below thetarget accuracy of +/- 1 % required for temperature determinations ofthe ISO standards. Major improvements related to the actual directcalibration are the high-precision broadband { K} magnitudes obtainedfor this purpose and the use of Hipparcos parallaxes for dereddeningphotometric data. The temperature scale of F-G-K dwarfs shows thesmallest random errors closely consistent with those affecting theobservational photometry alone, indicating a negligible contributionfrom the component due to the bolometric flux measurements despite thewide range in metallicity for these stars. A more detailed analysisusing a subset of selected dwarfs with large metallicity gradientsstrongly supports the actual bolometric fluxes as being practicallyunaffected by the metallicity of field stars, in contrast with recentresults claiming somewhat significant effects. The temperature scale ofF-G-K giants is affected by random errors much larger than those ofdwarfs, indicating that most of the relevant component of the scattercomes from the bolometric flux measurements. Since the giants have smallmetallicities, only gravity effects become likely responsible for theincreased level of scatter. The empirical stellar temperatures withsmall model-dependent corrections are compared with the semiempiricaldata by the Infrared Flux Method (IRFM) using the large sample of 327comparison stars. One major achievement is that all empirical andsemiempirical temperature estimates of F-G-K giants and dwarfs are foundto be closely consistent between each other to within +/- 1 %. However,there is also evidence for somewhat significant differential effects.These include an average systematic shift of (2.33 +/- 0.13) % affectingthe A-type stars, the semiempirical estimates being too low by thisamount, and an additional component of scatter as significant as +/- 1 %affecting all the comparison stars. The systematic effect confirms theresults from other investigations and indicates that previousdiscrepancies in applying the IRFM to A-type stars are not yet removedby using new LTE line-blanketed model atmospheres along with the updatedabsolute flux calibration, whereas the additional random component isfound to disappear in a broadband version of the IRFM using an infraredreference flux derived from wide rather than narrow band photometricdata. Table 1 and 2 are only available in the electronic form of thispaper
| X-ray activity and evolutionary status of late-type giants
We study the evolution of stellar activity in a volume-limited sample ofsingle giants within 35 pc distance from the Sun as measured by theamount of soft X-ray emission. This sample of 36 stars is assumed to becomplete for absolute magnitude M_V la 3.0 and for X-ray luminositiesL_x ga 1.5 x 10(28) erg s(-1) . We use ROSAT data to determine stellaractivity, Hipparcos parallaxes to place stars into the HRD, and theempirically well tested evolutionary code by P. Eggleton (see Pols etal. 1998) together with Kurucz colour tables to derive individual massesand ages. Based on more X-ray data and much improved HR diagrampositions, we confirm the suggestion by Huensch & Schroeder (1996),that stellar activity evolution is strongly coupled to stellar mass andthat it is a very common feature among giants with M ga 1.3Msun. Most pointed ROSAT observations on the giant branch(GB) and also in the ``K giant clump'' (with masses betweeen about 1.3and 2.3 M_ȯ) resulted in detections at typically solar levels. Thisindicates that magnetic activity mostly (for M ga 1.3 Msun)even survives the He-flash and, possibly, also persists on theasymptotic giant branch. The more massive stars (ga 3 M_ȯ) showeven a larger amount of activity in their advanced evolutionary stages(blue loop giants).
| The Pulkovo spectrophotometric catalog of bright stars in the range from 320 to 1080 NM - A supplement
The Pulkovo spectrophotometric catalog was published in Baltic AstronomyVol. 5, No. 4 (1996). Here we present a supplement of the catalogcontaining the flux distribution data for 77 stars in the wavelengthrange from 320 to 735 nm. Actually, this is a direct continuation ofTable 6 of the catalog.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Stellar activity and the Wilson-Bappu relation.
The MgII h and k lines of 78 single stars observed with theInternational Ultraviolet Explorer (IUE) observatory have been analyzed.Stars of spectral classes F, G, K and M and luminosity classes I-V arerepresented in the sample. From these data it is shown that theWilson-Bappu relation for the Mg II h and k lines is fulfilled over arange of 18 magnitudes, i.e. from M_v_=+12 to M_v_=-6. The samplecontains slowly rotating stars of different activity levels and issuitable for investigations of a possible relation between line widthand stellar activity. It is found that active stars have broader linesand show a larger variation in line widths than quiet stars.Observations of the active RS CVn binary σ Gem taken at epochswhen it shows different levels of activity, clearly demonstrate linebroadening following higher activity. Possible implications of the newresults for the interpretation of the Wilson-Bappu relation are brieflydiscussed.
| 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%.
| Supermetallicity at the Quarter-Century Mark: A Conservative Statistician's Review of the Evidence
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..102..105T&db_key=AST
| ROSAT X-ray observations of a complete, volume-limited sample of late-type giants.
We have investigated a complete sample of the nearest 39 late typegiants (d<=25pc) for which we have probed the X-ray luminosityfunction with unprecedented sensitivity by deep (3...18ksec) ROSATPSPC-observations in the pointed mode, together with ROSAT All-Skysurvey (RASS) data. We confirm the X-ray dividing line for luminosityclass III giants as proposed by Haisch et al. (1991, 1992) and we findevidence, that essentially all luminosity class III giants withB-V<1.2 or spectral type
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | אינדיאני |
| התרוממות ימנית: | 20h37m34.00s |
| סירוב: | -47°17'29.0" |
| גודל גלוי: | 3.11 |
| מרחק: | 31.046 פארסק |
| תנועה נכונה: | 50.9 |
| תנועה נכונה: | 65.7 |
| B-T magnitude: | 4.368 |
| V-T magnitude: | 3.203 |
קטלוגים וכינוים:
|
INHABITED SKY
