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Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
The sub-arcsecond dusty environment of Eta Carinae
The core of the nebula surrounding Eta Carinae has been observed withthe VLT Adaptive Optics system NACO and with the interferometerVLTI/MIDI to constrain spatially and spectrally the warm dustyenvironment and the central object. In particular, narrow-band images at3.74 μm and 4.05 μm reveal the butterfly shaped dusty environmentclose to the central star with unprecedented spatial resolution. A voidwhose radius corresponds to the expected sublimation radius has beendiscovered around the central source. Fringes have been obtained in theMid-IR which reveal a correlated flux of about 100 Jy situated 0.3arcsec south-east of the photocenter of the nebula at 8.7 μm, whichcorresponds with the location of the star as seen in other wavelengths.This correlated flux is partly attributed to the central object, andthese observations provide an upper limit for the SED of the centralsource from 2.2 μm to 13.5 μm. Moreover, we have been able tospectrally disperse the signal from the nebula itself at PA = 318degree, i.e. in the direction of the bipolar nebula (~310°) withinthe MIDI field of view of 3 arcsec. A large amount of corundum (Al2O3)is discovered, peaking at 0.6 arcsec-1.2 arcsec south-east from thestar, whereas the dust content of the Weigelt blobs is dominated bysilicates. We discuss the mechanisms of dust formation which are closelyrelated to the geometry of this Butterfly nebulae.
| 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.
| Mid-infrared interferometry of the Mira variable RR Sco with the VLTI MIDI instrument
We present the results of the first mid-infrared interferometricobservations of the Mira variable RR Sco with the MID-infraredInterferometer (MIDI) coupled to the European Southern Observatory's(ESO) Very Large Telescope Interferometer (VLTI), together with K-bandobservations using VLTI VINCI. The observations were carried out in June2003, when the variability phase of the object was 0.6, using two unittelescopes (UT1 and UT3), as part of the Science Demonstration Time(SDT) program of the instrument. Projected baseline lengths ranged from73 to 102 m, and a spectral resolution of 30 was employed in theobservations, which enabled us to obtain the wavelength dependence ofthe visibility in the region between 8 and 13 μm. The uniform-diskdiameter was found to be 18 mas between 8 and 10 μm, while itgradually increases at wavelengths longer than 10 μm to reach 24 masat 13 μm. The uniform-disk diameter between 8 and 13 μm issignificantly larger than the K-band uniform-disk diameter of 10.2± 0.5 mas measured using VLTI VINCI with projected baselinelengths of 15-16 m, three weeks after the MIDI observations. Our modelcalculations show that optically thick emission from a warm molecularenvelope consisting of H2O and SiO can cause the apparent mid-infrared diameter to be much larger than the continuum diameter. Wefind that the warm molecular envelope model extending to 2.3R\star with a temperature of 1400 K and column densitiesof H2O and SiO of 3 × 1021 cm-2and 1 × 1020 cm-2, respectively, canreproduce the observed uniform-disk diameters between 8 and 10 μm.The observed increase of the uniform-disk diameter longward of 10 μmcan be explained by an optically thin dust shell consisting of silicateand corundum grains. The inner radius of the optically thin dust shellis derived to be 7-8 R\star with a temperature of 700 K,and the optical depth at 10 μm is found to be 0.025.Based on observations made with the Very Large Telescope Interferometerof the European Southern Observatory.
| Constraining the Lifetime of Circumstellar Disks in the Terrestrial Planet Zone: A Mid-Infrared Survey of the 30 Myr old Tucana-Horologium Association
We have conducted an N-band survey of 14 young stars in the ~30 Myr oldTucana-Horologium association to search for evidence of warm,circumstellar dust disks. Using the MIRAC-BLINC camera on the Magellan I(Baade) 6.5 m telescope, we find that none of the stars have astatistically significant N-band excess compared to the predictedstellar photospheric flux. Using three different sets of assumptions,this null result rules out the existence of the following around thesepost-T Tauri stars: (1) optically thick disks with inner hole radii of<~0.1 AU, (2) optically thin disks with masses of less than10-6 M⊕ (in ~1 μm sized grains) within<~10 AU of these stars, and (3) scaled-up analogs of the solar systemzodiacal dust cloud with more than 4000 times the emitting area. Oursurvey was sensitive to dust disks in the terrestrial planet zone withfractional luminosity oflog(Ldust/L*)~10-2.9, yet none werefound. Combined with results from previous surveys, these data suggestthat circumstellar dust disks become so optically thin as to beundetectable at N band before age ~20 Myr. We also present N-bandphotometry for several members of other young associations and asubsample of targets that will be observed with the Spitzer SpaceTelescope by the Formation and Evolution of Planetary Systems LegacyScience Program. Finally, we present an absolute calibration ofMIRAC-BLINC for four filters (L, N, 11.6, and Qs) on theCohen-Walker-Witteborn system.
| Globular Cluster Formation in M82
We present high-resolution mid-infrared (mid-IR 11.7 and 17.65 μm)maps of the central 400 pc region of the starburst galaxy M82. Sevenstar-forming clusters are identified, which together provide ~15% of thetotal mid-IR luminosity of the galaxy. We find that these young stellarclusters have inferred masses and sizes comparable to globular clusters.At least 20% of the star formation in M82 is found to occur in superstar clusters.
| Mid-infrared sizes of circumstellar disks around Herbig Ae/Be stars measured with MIDI on the VLTI
We present the first long baseline mid-infrared interferometricobservations of the circumstellar disks surrounding Herbig Ae/Be stars.The observations were obtained using the mid-infrared interferometricinstrument MIDI at the European Southern Observatory (ESO) Very LargeTelescope Interferometer VLTI on Cerro Paranal. The 102 m baseline givenby the telescopes UT1 and UT3 was employed, which provides a maximumfull spatial resolution of 20 milli-arcsec (mas) at a wavelength of 10μm. The interferometric signal was spectrally dispersed at aresolution of 30, giving spectrally resolved visibility information from8 μm to 13.5 μm. We observed seven nearby Herbig Ae/Be stars andresolved all objects. The warm dust disk of HD 100546 could even beresolved in single-telescope imaging. Characteristic dimensions of theemitting regions at 10 μm are found to be from 1 AU to 10 AU. The 10μm sizes of our sample stars correlate with the slope of the 10-25μm infrared spectrum in the sense that the reddest objects are thelargest ones. Such a correlation would be consistent with a differentgeometry in terms of flaring or flat (self-shadowed) disks for sourceswith strong or moderate mid-infrared excess, respectively. We comparethe observed spectrally resolved visibilities with predictions based onexisting models of passive centrally irradiated hydrostatic disks madeto fit the SEDs of the observed stars. We find broad qualitativeagreement of the spectral shape of visibilities corresponding to thesemodels with our observations. Quantitatively, there are discrepanciesthat show the need for a next step in modelling of circumstellar disks,satisfying both the spatial constraints such as are now available fromthe MIDI observations and the flux constraints from the SEDs in aconsistent way.Based on observations made with the Very Large Telescope Interferometerat Paranal Observatory.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Infrared Colors and Variability of Evolved Stars from COBE DIRBE Data
For a complete 12 μm flux-limited sample of 207 IRAS sources(F12>=150 Jy, |b|>=5deg), the majority ofwhich are AGB stars (~87%), we have extracted light curves in seveninfrared bands between 1.25 and 60 μm using the database of theDiffuse Infrared Background Experiment (DIRBE) instrument on the CosmicBackground Explorer (COBE) satellite. Using previous infrared surveys,we filtered these light curves to remove data points affected by nearbycompanions and obtained time-averaged flux densities and infraredcolors, as well as estimates of their variability at each wavelength. Inthe time-averaged DIRBE color-color plots, we find clear segregation ofsemiregulars, Mira variables, carbon stars, OH/IR stars, and red giantswithout circumstellar dust (i.e., V-[12]<5) and with little or novisual variation (ΔV<0.1 mag). The DIRBE 1.25-25 μm colorsbecome progressively redder and the variability in the DIRBE databaseincreases along the oxygen-rich sequence nondusty slightly varying redgiants-->SRb/Lb-->SRa-->Mira-->OH/IR and the carbon-richSRb/Lb-->Mira sequence. This supports previous assertions that theseare evolutionary sequences involving the continued production andejection of dust. The carbon stars are redder than their oxygen-richcounterparts for the same variability type, except in theF12/F25 ratio, where they are bluer. Of the 28sources in the sample not previous noted to be variable, 18 are clearlyvariable in the DIRBE data, with amplitudes of variation of ~0.9 mag at4.9 μm and ~0.6 mag at 12 μm, consistent with them being verydusty Mira-like variables. We also present individual DIRBE light curvesof a few selected stars. The DIRBE light curves of the semiregularvariable L2 Pup are particularly remarkable. The maxima at1.25, 2.2, and 3.5 μm occur 10-20 days before those at 4.9 and 12μm, and, at 4.9 and 12 μm, another maximum is seen between the twonear-infrared maxima.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable 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/qcat?J/A+A/397/997
| Discovery of an Extremely Red Object in the Field of HD 155826
We have discovered an extremely red object, LSF 1, located 7" southwest(P.A. 217°) of the bright spectroscopic binary system HD 155826.Originally reported by IRAS as one source detected at 12-60 μm, andfound as a single 6-25 μm source of similar flux in the MidcourseSpace Experiment Galactic plane survey, two bright point sources werefound in arcsecond resolution infrared images obtained with the MIRLINcamera at the Infrared Telescope Facility and confirmed by the LongWavelength Spectrometer camera on Keck I. While HD 155826 itself waseasily detected in all the broadband and narrowband filters from 0.9 to12 μm that we used, the new counterpart, LSF 1, is only visible at 10μm. In Gunn z, J, H, and K', the upper limit to the new object'smagnitude is ~14. The detection of the new bright IR source explains theconfusing [K]-[N] IRAS colors that originally implied that HD 155826 wasa possible Vega-like system. The ``anomalous long-wavelength emission''is found to arise entirely from the new source. Without mid-IR extensionor excess long-wavelength emission, HD 155826 should no longer beclassified as a Vega-like system. We suspect LSF 1 to be either a highlyreddened carbon star or a Class II YSO, with no association with thehigh proper motion HD 155826 system.
| High mass Class I sources in M 17
The region of M 17 has been imaged at 10.5 and 20.0 mr um with thegroundbased infrared camera MANIAC. In addition to a prominent diffuseemission bar (4\farcm5x0\farcm 3) extending southeast to northwest atthe interface between the H Ii region and the southwestern molecularcloud, the mosaic of 133 single frames at each wavelength revealed 22compact sources. One of these sources is the Kleinmann-Wright-Object andanother was previously identified as the ultra-compact H Ii region M17-UC1. Combining the N-band and Q-band data with near infrared datayielded spectral energy distributions that classifies all sources to beof Class I. The observed luminosities were between 55 and 4775 L_sun,which suggests that these sources represent the youngest generation ofmassive early type stars in M 17 and are surrounded by relics of theirprotostellar clouds. The morphology of the 10.5 and 20.0 mr um emissiontowards some of the sources reveals flattened structures and may be thefirst evidence of the presence of circumstellar disks around massivestars.
| Long period variable stars: galactic populations and infrared luminosity calibrations
In this paper HIPPARCOS astrometric and kinematic data are used tocalibrate both infrared luminosities and kinematical parameters of LongPeriod Variable stars (LPVs). Individual absolute K and IRAS 12 and 25luminosities of 800 LPVs are determined and made available in electronicform. The estimated mean kinematics is analyzed in terms of galacticpopulations. LPVs are found to belong to galactic populations rangingfrom the thin disk to the extended disk. An age range and a lower limitof the initial mass is given for stars of each population. A differenceof 1.3 mag in K for the upper limit of the Asymptotic Giant Branch isfound between the disk and old disk galactic populations, confirming itsdependence on the mass in the main sequence. LPVs with a thin envelopeare distinguished using the estimated mean IRAS luminosities. The levelof attraction (in the classification sense) of each group for the usualclassifying parameters of LPVs (variability and spectral types) isexamined. Table 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/374/968 or via ASTRIDdatabase (http://astrid.graal.univ-montp2.fr).
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Optical, infrared and millimetre-wave properties of Vega-like systems - IV. Observations of a new sample of candidate Vega-like sources
Photometric observations at optical and near-infrared wavelengths arepresented for members of a new sample of candidate Vega-like systems, ormain sequence stars with excess infrared emission due to circumstellardust. The observations are combined with IRAS fluxes to define thespectral energy distributions of the sources. Most of the sources showonly photospheric emission at near-IR wavelengths, indicating a lack ofhot (~1000K) dust. Mid-infrared spectra are presented for four sourcesfrom the sample. One of them, HD 150193, shows strong silicate emission,while another, HD 176363, was not detected. The spectra of two starsfrom our previous sample of Vega-like sources both show UIR-bandemission, attributed to hydrocarbon materials. Detailed comparisons ofthe optical and IRAS positions suggest that in some cases the IRASsource is not physically associated with the visible star. Alternativeassociations are suggested for several of these sources. Fractionalexcess luminosities are derived from the observed spectral energydistributions. The values found are comparable to those measuredpreviously for other Vega-like sources.
| Dust features in the 10-mu m infrared spectra of oxygen-rich evolved stars
We have analyzed the 8-13.5 mu m UKIRT CGS3 spectra of 142 M-type starsincluding 80 oxygen-rich AGB stars and 62 red supergiants, with a viewto understanding the differences and similarities between the dustfeatures of these stars. We have classified the spectra into groupsaccording to the observed appearance of the infrared features. In eachcase the normalized continuum-subtracted spectrum has been compared tothose of the other stars to find similarities and form groups. The dustfeatures of the AGB stars are classified into six groups: broad AGB,where the feature extends from 8 mu m to about 12.5 mu m with littlestructure; broad+sil AGB, which consists of a broad feature with anemerging 9.7 mu m silicate bump; and four silicate AGB groups in which a``classic'' 9.7 mu m silicate feature gets progressively narrower.Likewise, the supergiant spectra have also been classified into groups,however these do not all coincide with the AGB star groups. In thesupergiant case we again have six groups: featureless, where there islittle or no emission above the continuum; broad Super, where thefeature extends from about 9 mu m to about 13 mu m; and four silicateSuper groups, which again show a progression towards the narrowest``classic'' 9.7 mu m silicate feature. We compare the mean spectrum foreach group, which yields two main results. Firstly, while the``classic'' silicate feature is essentially identical for both AGB starsand red supergiants, the broad features observed for these two stellartypes are quite different. We suggest that the dust in these twoenvironments follows different evolutionary paths, with the dust aroundMira stars, whose broad feature spectra can be fit by a combination ofalumina (Al2O3) and magnesium silicate,progressing from this composition to dust dominated by magnesiumsilicate only, while the dust around supergiants, whose broad featurecan be fit by a combination of Ca-Al-rich silicate andAl2O3, progresses from this initial composition toone eventually also dominated by magnesium silicate. The reason for thedifference in the respective broad features is not clear as yet, butcould be influenced by lower C/O ratios and chromospheric UV radiationfields in supergiant outflow environments. The second result concernsthe 12.5 - 13.0 mu m feature discovered in IRAS LRS spectra and widelyattributed to Al2O3. This feature is seenpredominantly in the spectra of semiregular variables, sometime in Mirasand only once (so far) in supergiant spectra. We argue that it isunlikely that this feature is due to Al2O3 or, ashas more recently been suggested, spinel(MgAl2O4), but could be associated with silicondioxide or highly polymerized silicates (not pyroxenes or olivines).
| Infrared spectra of evolved stars with unusual dust shells
New mid-infrared spectra are presented of a number of oxygen-richevolved stars which have IRAS LRS (Low Resolution Spectrometer) spectrathat were classified as showing SiC emission. Two of the sources,IRC-20445 and IRC-20461, show the unidentified infrared (UIR) bandssuperposed on silicate emission features. Both objects have beenclassified as M supergiants. Several other sources show three-componentspectra, with peaks at 10, 11 and 13μm. The 13-μm source FI Lyrshows a narrow emission feature at 19μm. Emission by oxide grains maybe responsible for the 11-, 13- and 19-μm features. One object,IRC-20455, shows a self-absorbed silicate feature. There is no clearevidence for SiC emission in any of the spectra: the LRS spectra wereerroneously classified as showing SiC emission because of the relativelystrong 11-μm emission.
| Near- and mid-infrared imaging polarimetry of NGC 1068
We present the results of a series of observations of the near- andmid-infrared polarization properties of the type 2 Seyfert galaxy NGC1068. Our data agree well with previously published results in showingthe need for a separate polarization mechanism in the near-infraredapart from scattering. We find that the predictions of a simple model inwhich this component arises through absorptive dichroism caused byaligned grains within the extended warm (~ 400 K) dust fit the datareasonably if the obscured background source is itself the result ofdust emission (at temperature >1000 K). By considering the change ofpolarization with wavelength we show that the extinction to this hotdust region is in the range A_V=20-40. Consideration of the observeddata then leads us to the conclusion that, if viewed face-on, NGC 1068would have a strong near-infrared excess similar to type 1 Seyfertgalaxies. Comparison with other independent measures of the extinctionto the active nucleus itself leads us to the conclusion that the hotdust must provide screening equivalent to at least A_V=40, and possiblymuch higher. We speculate that this component alone may be the`classical' torus discussed in terms of the unified model, and the moreextensive mid-infrared emission may arise from circumnuclear molecularcloud material, and dust in the ionization cones.
| A Mid-infrared Imaging Survey of Proto-Planetary Nebula Candidates
We present the data from a mid-infrared (MIR) imaging survey of 66proto-planetary nebula candidates using two MIR cameras (MIRAC2 andBerkcam) at the NASA Infrared Telescope Facility and the United KingdomInfrared Telescope. The goal of this survey is to determine the size,flux, and morphology of the MIR emission regions, which sample the innerregions of the circumstellar dust shells of proto-planetary nebulae. Weimaged these proto-planetary nebulae with narrowbandfilters(Deltalambda/lambda~10%) at wavelengths of notable dust features.With our typical angular resolution of 1", we resolve 17 sources, find48 objects unresolved, and do not detect one source. For several sourceswe checked optical and infrared associations and positions of thesources. In table format, we list the size and flux measurements for allof the detected objects and show figures of all of the resolved sources.The proto-planetary nebula candidate sample includes, in addition to thepredominant proto-planetary nebulae, extreme asymptotic giant branchstars, young planetary nebulae, a supergiant, and a luminous bluevariable. We find that dust shells that are cooler (T~150 K) andbrighter in the infrared are more easily resolved. Eleven of theseventeen resolved sources are extended and fall into one of two typesof MIR morphological classes: core/elliptical or toroidal.Core/elliptical structures show unresolved cores with lower surfacebrightness elliptical nebulae. Toroidal structures show limb-brightenedpeaks suggesting equatorial density enhancements. We argue thatcore/ellipticals have denser dust shells than toroidals.
| High-resolution imaging of ultracompact H II regions regions. II. G5.89-0.39 revisited
We present the results of an extensive imaging campaign on theultracompact Hii region G5.89-0.39 at near- and mid-infraredwavelengths. High-resolution data were taken in the H, K', and L bandsusing ESO's adaptive optics system ADONIS. They are complemented byconventional narrow-band images in Br gamma and H_2(1-0)}S1 as well asby mid-infrared broad- and narrow-band images. We also mapped the 1.3 mmcontinuum emission from the source using the SEST. We use our data toconsistently explain the morphological appearance of G5.89-0.39 at allobserved wavelengths as well as its spectral energy distribution. Thecomplete model of the source consists of a spherical shell of dust withan inner, dust-free cavity of 7.6x 10(16) cm radius surrounding a starof spectral type O6 ZAMS. Two outflows escape this shell in oppositedirections. Half of the whole configuration is evidently obscured by avery massive cloud of cold dust. Comparisons with earlier models andother ultracompact Hii regions are drawn to put G5.89-0.39 in thecontext of massive star formation. Based on observations collected atthe European Southern Observatory, La Silla, Chile
| Stellar radii of M giants
We determine the stellar radii of the M giant stars in the Hipparcoscatalogue that have a parallax measured to better than 20% accuracy.This is done with the help of a relation between a visual surfacebrightness parameter and the Cousins (V - I) colour index, which wecalibrate with M giants with published angular diameters.The radii of(non-Mira) M giants increase from a median value of 50 R_Sun at spectraltype M0 III to 170 R_Sun at M7/8 III. Typical intermediate giant radiiare 65 R_Sun for M1/M2, 90 R_Sun for M3, 100 R_Sun for M4, 120 R_Sun forM5 and 150 R_Sun for M6. There is a large intrinsic spread for a givenspectral type. This variance in stellar radius increases with latertypes but in relative terms, it remains constant.We determineluminosities and, from evolutionary tracks, stellar masses for oursample stars. The M giants in the solar neighbourhood have masses in therange 0.8-4 M_Sun. For a given spectral type, there is a close relationbetween stellar radius and stellar mass. We also find a linear relationbetween the mass and radius of non-variable M giants. With increasingamplitude of variability we have larger stellar radii for a given mass.
| Silicate and hydrocarbon emission from Galactic M supergiants
Following our discovery of unidentified infrared (UIR) band emission ina number of M supergiants in h and chi Per, we have obtained 10-μmspectra of a sample of 60 galactic M supergiants. Only three newsources, V1749 Cyg, UW Aql and IRC+40 427, appear to show the UIR bands;the others show the expected silicate emission or a featurelesscontinuum. The occurrence of UIR-band emission in M supergiants istherefore much higher in the h and chi Per cluster than in the Galaxy asa whole. Possible explanations for the origin and distribution of UIRbands in oxygen-rich supergiants are discussed. We use our spectra toderive mass-loss rates ranging from 10^-8 to 10^-4 M_solar yr^-1 for thenew sample, based on the power emitted in the silicate feature. Therelationship between mass-loss rate and luminosity for M supergiants isdiscussed, and correlations are explored between their mid-infraredemission properties.
| The Infrared Spectral Classification of Oxygen-rich Dust Shells
This paper presents infrared spectral classifications for a flux-limitedsample of 635 optically identified oxygen-rich variables includingsupergiants and sources on the asymptotic giant branch (AGB). Severalclasses of spectra from oxygen-rich dust exist, and these can bearranged in a smoothly varying sequence of spectral shapes known as thesilicate dust sequence. Classification based on this sequence revealsseveral dependencies of the dust emission on the properties of thecentral star. Nearly all S stars show broad emission features fromalumina dust, while most of the supergiants exhibit classic featuresfrom amorphous silicate dust. Mira variables with symmetric light curvesgenerally show broad alumina emission, while those with more asymmetriclight curves show classic silicate emission. These differences may arisefrom differences in the photospheric C/O ratio.
| Infrared Ionic Line Emission in W33
We have mapped the central parsec of the H ii region W33 in the infraredfine-structure lines of [Ne ii] (12.8 μm) and [Ar iii] (8.99 μm),and have measured spectra of [Ar ii] (6.99 μm) at selected locations.This is the first observation of the 6.99 μm line from the ground.The spatial distribution of the infrared lines resembles that of theradio continuum, except for one region where the extinction isapparently very high (even at 12.8 μm). The abundances of neon andargon in W33 are a factor of 4 lower than solar. We have analyzed theratios of the mapped lines to derive the types of the exciting stars,their ages, and other features of the source. The cluster contains threedistinct subsources, one of which appears to be a cometary and another ashell-like ultracompact H ii region, although they are larger and lessdense than most objects of this class. The stars are of types O6 to O7and less than a few million years old. We suggest that star formation inthis object has been proceeding simultaneously in at least threecenters, and that the H ii regions have not yet expanded to form onesource.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| 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.
| Sub-arcsec resolution infrared images of the star forming region G 35.20-1.74.
We present J(1.25μm), H(1.65μm), K(2.2μm), H_2_(2.125μm) and11.2μm infrared images at sub-arcsec resolution of an area centeredaround the star forming region G 35.20-1.74. In J, H and K a cluster ofearly type stellar sources with infrared excess clearly stands out withrespect to the background distribution and is associated with a diffuseK emission around an UC HII region (which is the brightest source at K).No H_2_ emission is detected in narrow-band images at 2.125μm. At11.2μm six components are detected. The brightest one (MIR3) isextended and coincides with the UC HII region. The source with steepestIR spectrum and the largest infrared excess (MIR1) is associated with anH_2_O maser and a near IR source detected only at K. It is separatedfrom the IR cluster and at a distance of 20'' from the UC HII region.The IR emission comes from a local young stellar object (YSO) associatedwith the maser. The lack of radio continuum emission from MIR1 confirmsthat H_2_O masers can trace the youngest evolutionary stages of massiveYSOs, much before the appearance of a radio UC HII region and shows thatstar formation is not limited to the IR cluster (where most probably ithas already come to an end) but is still taking place in other parts ofthe molecular cloud. Of the other 11.2μm sources, three (MIR2, MIR4and MIR5) present IR excesses and are similar to MIR1, while MIR6appears to be a reddened early-type star. The morphology of the entirestar forming complex, taking into account also molecular and sub-mmobservations, is indicative of different and independent episodes ofstar formation taking place in the same molecular cloud.
| 10-μm imaging of the bipolar protoplanetary nebula Mz-3
A 10-μm image is presented of the bipolar protoplanetary nebula Mz-3made at the 3.9-m Anglo-Australian Telescope using the NIMPOLmid-infrared imaging polarimeter. The image shows extended emission fromwarm (110-130K) dust both to the north and to the south of the centralstar, which correlates well with the visible bipolar lobes. The observedsurface brightness of this emission is consistent with radiative heatingof the dust by both direct stellar illumination and trapped Lyman alphaphotons. Emission in excess of the point-source profile indicates thatthere is also an extended shell of dust surrounding the central star.
| Optical, infrared and millimetre-wave properties of Vega-like systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996MNRAS.279..915S&db_key=AST
| 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%.
| 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
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| Takýmyýldýz: | Yay |
| Sað Açýklýk: | 18h17m37.60s |
| Yükselim: | -36°45'42.0" |
| Görünürdeki Parlaklýk: | 3.11 |
| Uzaklýk: | 45.725 parsek |
| özdevim Sað Açýklýk: | -131.2 |
| özdevim Yükselim: | -167.9 |
| B-T magnitude: | 5.153 |
| V-T magnitude: | 3.298 |
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