Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
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.
| The cool atmospheres of the binary brown dwarf ɛ Indi B
We have imaged ɛ Indi B, the closest brown dwarf binary known,with VISIR at the VLT in three narrow-band mid-infrared bandpasseslocated around 8.6 μm, 10.5 μm and 11.3 μm. We are able tospatially resolve both components, and determine accurate mid-infraredphotometry for both components independently. In particular, our VISIRobservations probe the NH3 feature in the atmospheres of the cooler andwarmer brown dwarfs. For the first time, we can disentangle thecontributions of the two components, and find that ɛ IndiBb isin good agreement with recent "cloud-free" atmosphere models having aneffective temperature of Teff =800 K. With an assumed age of1 Gyr for the ɛ Indi system, component Ba agrees more withTeff ≈ 1100 K rather than with Teff=1200 K, assuggested by SPITZER spectroscopic observations of the combinedɛ Indi B system (Roellig et al. 2004). Even higher effectivetemperatures appear inconsistent with our absolute photometry, as theywould imply an unphysical small size of the brown dwarf ɛIndiBa.Based on observations collected with the ESO VLT, Paranal, Chile,program 60.A-9245(A).
| 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
| 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 Parsec-Scale Flow Associated with the IRAS 16547-4247 Radio Jet
IRAS 16547-4247 is the most luminous (6.2×104Lsolar) embedded young stellar object known to harbor athermal radio jet. We report the discovery using the Very LargeTelescope Infrared Spectrometer and Array Camera of a chain ofH2 2.12 μm emission knots that trace a collimated flowextending over 1.5 pc. The alignment of the H2 flow and thecentral location of the radio jet imply that these phenomena areintimately linked. We have also detected an isolated unresolved 12 μminfrared source toward the radio jet using TIMMI2. Our findings affirmthat IRAS 16547-4247 is excited by a single O-type star that is drivinga collimated jet. We argue that the accretion mechanism that producesjets in low-mass star formation also operates in the higher mass regime.
| The mineralogy, geometry and mass-loss history of IRAS 16342-3814
We present the 2-200 mu m Infrared Space Observatory (ISO) spectrum and3.8-20 mu m ISAAC and TIMMI2 images of the extreme OH/IR star IRAS16342-3814. Amorphous silicate absorption features are seen at 10 and 20mu m, together with crystalline silicate absorption features up toalmost 45 mu m. No other OH/IR star is known to have crystallinesilicate features in absorption up to these wavelengths. This suggeststhat IRAS 16342-3814 must have, or recently had, an extremely highmass-loss rate. Indeed, preliminary radiative transfer calculationssuggest that the mass-loss rate may be as large as 10-3Msun yr-1. The 3.8 mu m ISAAC image shows abipolar reflection nebula with a dark equatorial waist or torus, similarto that seen in optical images taken with the Hubble Space Telescope(HST). The position angle of the nebula decreases significantly withincreasing wavelength, suggesting that the dominant source of emissionchanges from scattering to thermal emission. Still, even up to 20 mu mthe nebula is oriented approximately along the major axis of the nebulaseen in the HST and ISAAC images, suggesting that the torus must be verycold, in agreement with the very red ISO spectrum. The 20 mu m imageshows a roughly spherically symmetric extended halo, approximately 6''in diameter, which is probably due to a previous phase of mass-loss onthe AGB, suggesting a transition from a (more) spherically symmetric toa (more) axial symmetric form of mass-loss at the end of the AGB. Usinga simple model, we estimate the maximum dust particle sizes in the torusand in the reflection nebula to be 1.3 and 0.09 mu m respectively. Thesize of the particles in the torus is large compared to typical ISMvalues, but in agreement with high mass-loss rate objects like AFGL 4106and HD161796. We discuss the possible reason for the difference inparticle size between the torus and the reflection nebula.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands and the UK) with the participation of ISAS and NASA. The SWSis a joint project of SRON and MPE. Also based on observations obtainedat the European Southern Observatory (ESO).
| 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.
| 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.
| HR 2875 - Spectroscopic discovery of the first B star + white dwarf binary
We report the discovery, in an Extreme Ultraviolet Explorer (EUVE)shortwavelength spectrum, of an unresolved hot white dwarf companion tothe 5th magnitude B5Vp star HR 2875. This is the first time that anoninteracting white dwarf + B star binary has been discovered;previously, the earliest type of star known with a white dwarf companionwas Sirius (A1V). As the white dwarf must have evolved from amain-sequence progenitor with a mass greater than that of a B5V star(6.0 solar masses or greater), this places a lower limit on the maximummass for white dwarf progenitors, with important implications for ourknowledge of the initial-final mass relation. Assuming a pure-hydrogenatmospheric composition, we constrain the temperature of the white dwarfto be between 39,000 and 49,000 K. We also argue that this degeneratestar is likely to have a mass significantly greater than the mean massfor white dwarf stars (0.55 solar mass). Finally, we suggest that otherbright B stars (e.g., Theta Hya) detected in the extreme ultravioletsurveys of the ROSAT Wide Field Camera and EUVE may also be hiding hotwhite dwarf companions.
| 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
| 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.
| 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.
| Stellar integrated fluxes in the wavelength range 380 NM - 900 NM derived from Johnson 13-colour photometry
Petford et al. (1988) have reported measured integrated fluxes for 216stars with a wide spread of spectral type and luminosity, and mentionedthat a cubic-spline integration over the relevant Johnson 13-colormagnitudes, converted to fluxes using Johnson's calibration, is inexcellent agreement with those measurements. In this paper a list of thefluxes derived in this way, corrected for a small dependence on B-V, isgiven for all the 1215 stars in Johnson's 1975 catalog with completeentries.
| Luminosity and velocity distributions of high-luminosity red stars. IV. The G-type giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974PASP...86..129E&db_key=AST
| Results of an infrared stellar survey.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..431P&db_key=AST
| The radial velocities of 185 stars observed at the Cape.
Not Available
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Corona Austral |
| Ascensión Recta: | 19h10m01.70s |
| Declinación: | -39°20'27.0" |
| Magnitud Aparente: | 4.11 |
| Distancia: | 155.763 parsecs |
| Movimiento Propio en Ascensión Recta: | 6.3 |
| Movimiento Propio en Declinación: | -36 |
| B-T magnitude: | 5.622 |
| V-T magnitude: | 4.227 |
Catálogos y designaciones:
|
