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Resim Yükleyin
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Ýlgili Makaleler
An Extended FUSE Survey of Diffuse O VI Emission in the Interstellar Medium
We present a survey of diffuse O VI emission in the interstellar medium(ISM) obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).Spanning 5.5 yr of FUSE observations, from launch through 2004 December,our data set consists of 2925 exposures along 183 sight lines, includingall of those with previously published O VI detections. The data wereprocessed using an implementation of CalFUSE version 3.1 modified tooptimize the signal-to-noise ratio and velocity scale of spectra from anaperture-filling source. Of our 183 sight lines, 73 show O VIλ1032 emission, 29 at >3 σ significance. Six of the 3σ features have velocities |vLSR|>120 kms-1, while the others have |vLSR|<=50 kms-1. Measured intensities range from 1800 to 9100 LU (lineunit; 1 photon cm-2 s-1 sr-1), with amedian of 3300 LU. Combining our results with published O VI absorptiondata, we find that an O VI-bearing interface in the local ISM yields anelectron density ne=0.2-0.3 cm-3 and a path lengthof 0.1 pc, while O VI-emitting regions associated with high-velocityclouds in the Galactic halo have densities an order of magnitude lowerand path lengths 2 orders of magnitude longer. Although the O VIintensities along these sight lines are similar, the emission isproduced by gas with very different properties.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer. FUSE is operated for NASA by Johns HopkinsUniversity under NASA contract NAS5-32985.
| The first 8-13 μm spectra of globular cluster red giants: circumstellar silicate dust grains in 47 Tucanae (NGC 104)
We present 8-13 μm spectra of eight red giants in the globularcluster 47 Tucanae (NGC 104), obtained at the European SouthernObservatory 3.6 m telescope. These are the first mid-infrared spectra ofmetal-poor, low-mass stars. The spectrum of at least one of these,namely the extremely red, large-amplitude variable V1, shows directevidence of circumstellar grains made of amorphous silicate.
| New insights on the complex planetary nebula Hen 2-113
We report on infrared observations of the planetary nebula Hen 2-113obtained with VLT/NACO, VLTI/MIDI, VLT/ISAAC and TIMMI at the ESO 3.6 m.Hen 2-113 exhibits a clear ring-like structure superimposed to a morediffuse environment visible in the L' (3.8 μm), M' (4.78 μm) and8.7 μm bands. No clear core at 8.7 μm and no fringes through the Nband could be detected for this object with MIDI. A qualitativeinterpretation of the object structure is proposed using a diabolo-likegeometrical model. The PAH content of the nebula was also studied withISAAC and TIMMI observations. This indicates that the PAHs are mostlyconcentrated towards the lobes of the diabolo and the bipolar lobes ofthe nebula. In L' band, a void 0.3 arcsec in diameter was discoveredwith NACO around the central source. The L' and M' fluxes from thecentral source were derived from NACO data indicating an importantinfrared excess with respect to the expected stellar emission based onstellar models and short wavelength data. The observed flux from thissource in the L' and M' is about 300 and 800 times respectively thanthose expected from a model including only the central star. Moreover,the central object appears resolved in L' band with measured FWHM of 155mas. This infrared excess can be explained by emission from a cocoon ofhot dust (T1000 K) with a total mass~10-9~Mȯ.
| Atlas and Catalog of Dark Clouds Based on Digitized Sky Survey I
We present a quantitative atlas and catalog of dark clouds derived byusing the optical database ``Digitized Sky Survey I''. Applying atraditional star-count technique to 1043 plates contained in thedatabase, we produced an AV map covering the entire region inthe galactic latitude range |b| ≤ 40°. The map was drawn at twodifferent angular resolutions of 6' and 18', and is shown in detail in aseries of figures in this paper. Based on the AV map, weidentified 2448 dark clouds and 2841 clumps located inside them. Somephysical parameters, such as the position, extent, and opticalextinction, were measured for each of the clouds and clumps. We alsosearched for counterparts among already known dark clouds in theliterature. The catalog of dark clouds presented in this paper lists thecloud parameters as well as the counterparts.
| Variability of Stars in the Pulkovo Spectrophotometric Catalog
We present the results of a statistical study of brightness variabilityfor 693 stars of the Pulkovo spectrophotometric database in fivespectral bands in the range λλ 320 1080 nm. Significantbrightness variations were detected in at least one spectral bandagainst the background of the random noise for one-third of the starsnot earlier believed to be variable. A comparison of the distributionsof these variations in amplitude and spectral band for the normal andvariable stars shows that variability is inherent to most stars to someextent and is often wavelength dependent.
| Can Life Develop in the Expanded Habitable Zones around Red Giant Stars?
We present some new ideas about the possibility of life developingaround subgiant and red giant stars. Our study concerns the temporalevolution of the habitable zone. The distance between the star and thehabitable zone, as well as its width, increases with time as aconsequence of stellar evolution. The habitable zone moves outward afterthe star leaves the main sequence, sweeping a wider range of distancesfrom the star until the star reaches the tip of the asymptotic giantbranch. Currently there is no clear evidence as to when life actuallyformed on the Earth, but recent isotopic data suggest life existed atleast as early as 7×108 yr after the Earth was formed.Thus, if life could form and evolve over time intervals from5×108 to 109 yr, then there could behabitable planets with life around red giant stars. For a 1Msolar star at the first stages of its post-main-sequenceevolution, the temporal transit of the habitable zone is estimated to beseveral times 109 yr at 2 AU and around 108 yr at9 AU. Under these circumstances life could develop at distances in therange 2-9 AU in the environment of subgiant or giant stars, and in thefar distant future in the environment of our own solar system. After astar completes its first ascent along the red giant branch and the Heflash takes place, there is an additional stable period of quiescent Hecore burning during which there is another opportunity for life todevelop. For a 1 Msolar star there is an additional109 yr with a stable habitable zone in the region from 7 to22 AU. Space astronomy missions, such as proposed for the TerrestrialPlanet Finder (TPF) and Darwin, that focus on searches for signatures oflife on extrasolar planets, should also consider the environments ofsubgiants and red giant stars as potentially interesting sites forunderstanding the development of life. We performed a preliminaryevaluation of the difficulty of interferometric observations of planetsaround red giant stars compared to a main-sequence star environment. Weshow that pathfinder missions for TPF and Darwin, such as Eclipse andFKSI, have sufficient angular resolution and sensitivity to search forhabitable planets around some of the closest evolved stars of thesubgiant and red giant class.
| The Extended Mid-Infrared Structure of the Circinus Galaxy
We present subarcsecond resolution mid-IR images of the Circinus galaxyat 8.74 and 18.33 μm. We resolve extended emission at bothwavelengths, extending ~2" from each side of the nucleus in anapproximate east-west direction. These extensions are spatiallycoincident with previously detected compact (~30 pc) V-shaped [O III]emission extending northwest of the nucleus as well as countercone [SiVI] emission, emission at these wavelengths interpreted as delineatingthe interface between inflowing material and the ionization cone. Wedetect no extended mid-IR emission associated with the structureresponsible for collimating the ionizing photons (i.e., obscuring torusor disk of material), limiting the flux density of the obscuringstructure to <=0.27 mJy or a diameter of <=0.20" (<=4 pc).
| Bipolar Symbiotic Planetary Nebulae in the Thermal Infrared: M2-9, Mz 3, and He 2-104
We present thermal-infrared images of three extreme bipolar objects,M2-9, Mz 3, and He 2-104. They are bipolar planetary nebulae with brightcentral stars and are thought to be powered by symbiotic binary systems.The mid-infrared images spatially resolve the spectral energydistributions of the central engines from the surrounding nebulae. Awarm dust component of several hundred degrees can account for the coreemission, while a cooler component of ~100 K produces the more extendedemission from the bipolar lobes. In every case, the dust mass for theunresolved core region is orders of magnitude less than that in theextended lobes, raising doubts that the hypothetical disks in the corecould have been responsible for pinching the waists of the nebulae. Wefind total masses of roughly 0.5-1 Msolar in the nebulae ofM2-9 and Mz 3, requiring that this material was donated byintermediate-mass progenitor stars. The mass of He 2-104's nebula ismuch lower, and any extended emission is too faint to detect in ourimages. Extended dust emission is detected around both M2-9 and Mz 3, inboth cases resembling the distribution of ionized gas. Our images of Mz3 have the highest signal-to-noise ratio in the extended polar lobes,and we show that the fairly uniform color temperature derived from ourimages can explain the 110 K dust component that dominates thefar-infrared spectral energy distribution. In the case of Mz 3, most ofthe mass traced by dust is concentrated at high latitudes, and we notepossible evidence for grain destruction in shocks indicated by ananticorrelation between [Fe II] and dust emission. Except for theseregions with enhanced [Fe II] emission, the dust continuum closelyresembles the distribution of ionized gas.
| Infrared Irradiance Calibration
Infrared astronomical measurements are calibrated against referencesources, usually primary standard stars that are, in turn, calibratedeither by direct or indirect means. A direct calibration compares thestar with a certified source, typically a blackbody. Indirect methodsextrapolate a direct measurement of the flux at one wavelength to theflux at another. Historically, α Lyr (Vega) has been used as theprimary standard as it is bright, easily accessible from the northernhemisphere, and is well calibrated in the visual. Until recently, thedirect absolute infrared calibrations of α Lyr and those derivedfrom the absolute solar flux scaled to the observed spectral energydistributions of solar type stars increasingly diverged with wavelengthfrom those obtained using a model atmosphere to extrapolate the absolutevisual flux of Vega into the infrared. The exception is the directcalibration by the 1996/97 Midcourse Space Experiment of the absolutefluxes for a number of the commonly used infrared standard stars,including Vega.
| Multiwavelength diameters of nearby Miras and semiregular variables
We have used optical interferometry to obtain multiwavelength visibilitycurves for eight red giants over the wavelength range 650-1000 nm. Theobservations consist of wavelength-dispersed fringes recorded withMAPPIT (Masked Aperture-Plane Interference Telescope) at the 3.9-mAnglo-Australian Telescope. We present results for four Miras (R Car, oCet, R Hya and R Leo) and four semiregular variables (R Dor, W Hya,L2 Pup and γ Cru). All stars except γ Cru showstrong variations of angular size with wavelength. A uniform-disc modelwas found to be a poor fit in most cases, with Gaussian (or other moretapered) profiles preferred. This, together with the fact that moststars showed a systematic increase in apparent size towards the blue anda larger-than-expected linear size, even in the red, all point towardssignificant scattering by dust in the inner circumstellar environment.Some stars showed evidence for asymmetric brightness profiles, whileL2 Pup required a two-component model, indicating anasymmetrical circumstellar dust shell.
| 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.
| Spectral Irradiance Calibration in the Infrared. XV. Absolute Calibration of Standard Stars by Experiments on the Midcourse Space Experiment
Calibration experiments were conducted with the SPIRIT III infraredinstrument on the Midcourse Space Experiment (MSX) against a number ofinfrared standard stars and five emissive reference spheres that wereejected at various times during the mission. The physical properties ofthe 2 cm diameter spheres, such as size and emissivity, were preciselymeasured in the laboratory. The energy balance equation between thetotal flux absorbed and that emitted by the sphere is solved to obtainthe time-dependent temperature of the sphere under the assumption thatthe sphere radiates as a blackbody with the measuredwavelength-dependent emissivity. The estimated uncertainties in themodeling of the sphere are about 1 K in the thermal component and 3% forthe geometric contribution. MSX also measured over 150 mean fluxes foreight standard infrared calibration stars during the 10 month mission.The measurements were scaled to the absolute fluxes that Cohen et al.adopt for α CMa (Sirius). The measured spectral energydistributions of the calibration stars relative to Sirius are within theuncertainties that Cohen et al. assign to the absolute fluxes from thesestars, with a few exceptions. However, the MSX measurement uncertaintiesare generally much smaller, and the mission-averaged fluxes revealstatistically significant deviations from the Cohen et al. values. Ofthe calibration stars, only β Peg was found to be variable. MSXalso measured excess fluxes for α Lyr (Vega) in the 12.1, 14.7,and 21.3 μm spectral bands; the excesses in the latter two bands areconsistent with the published thermal model for the dust ring aroundthis star. The absolute calibration of the fluxes of the stellarstandards based on the average of the measurements of the spheres overall MSX bands and the five experiments agrees with those predicted towithin the 1.4% MSX measurement uncertainties. The zero-magnitudeabsolute fluxes proposed by Cohen et al. are validated if the flux fromSirius is increased by 1%.
| Spatially Resolved Circumnuclear Dust in Centaurus A
In this Letter, we present results from our exploratory mid-IR study ofCentaurus A circumnuclear environment using high angular resolutionimaging at the Magellan 6.5 m telescope with the MIRAC/BLINC camera. Wedetected emission from a compact region surrounding the nuclear sourceand obtained photometry at 8.8 μm and in the N band. Our analysissuggests that the nuclear region is resolved with a size of ~3 pc. Themid-IR emission from this region is likely associated with cool dustwith an estimated temperature of ~160 K, surrounding the central``hidden'' active galactic nucleus (AGN). We discuss the characteristicsof this emission in relation to other mid-IR observations and theimplications on models of dust formation in AGNs.
| 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.
| ISO-SWS calibration and the accurate modelling of cool-star atmospheres. II. General results
The fine calibration of the ISO-SWS detectors (Infrared SpaceObservatory - Short Wavelength Spectrometer) has proven to be a delicateproblem. We therefore present a detailed spectroscopic study in the2.38-12 mu m wavelength range of a sample of 16 A0-M2 stars used for thecalibration of ISO-SWS. By investigating the discrepancies between theISO-SWS data of these sources, the theoretical predictions of theirspectra, the high-resolution FTS-KP (Kitt Peak) spectrum of alpha Booand the solar FTS-ATMOS (Atmospheric Trace Molecule Spectroscopy)spectrum, both calibration problems and problems in computing thetheoretical models and the synthetic spectra are revealed. Theunderlying reasons for these problems are sought for and the impact onthe further calibration of ISO-SWS and on the theoretical modelling isdiscussed extensively.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Appendix is only available in electronic form athttp://www.edpsciences.org
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| The latitude and epoch for the formation of the southern Greek constellations
Not Available
| The Structure of the Local Interstellar Medium. I. High-Resolution Observations of Fe II, Mg II, and Ca II toward Stars within 100 Parsecs
High-resolution absorption measurements(λ/Δλ>~100,000) of the resonance lines of Fe II,Mg II, and Ca II are presented for all available observed targets within100 pc. The Fe II and Mg II spectra were obtained with the Goddard HighResolution Spectrograph (GHRS) and the Space Telescope ImagingSpectrograph (STIS) instruments aboard the Hubble Space Telescope (HST).Of the 63 observations of targets within 100 pc, we present newmeasurements for 24 lines of sight. We also compiled all publishedabsorption measurements based on Ca II spectra obtained by variousground-based instruments. For each observation we provide measurementsof the central velocity, Doppler parameter, and column density for eachabsorption component. These three ions provide the best opportunity tomeasure the component velocity structure. Because these are the heaviestions observed in absorption through the warm local interstellar medium(LISM), the narrow line widths minimize significant blending ofcomponents and allow for accurate measurements of the central velocity.We present a statistical analysis of the LISM absorption measurements,which provides an overview of some physical characteristics of warmclouds in the LISM, such as, temperature, turbulent velocity, ionizationdegree, and depletion. The complete collection and reduction of all LISMabsorption measurements provides an important database for studying thestructure of nearby warm clouds. Subsequent papers will present modelsfor the morphology and physical properties of individual structures(clouds) in the LISM.
| A Disrupted Circumstellar Torus inside η Carinae's Homunculus Nebula
We present thermal infrared images of the bipolar nebula surroundingη Carinae at six wavelengths from 4.8 to 24.5 μm. These wereobtained with the MIRAC3 camera system at the Magellan Observatory. Ourimages reveal new intricate structure in the bright core of the nebula,allowing us to reevaluate interpretations of morphology seen in imageswith lower resolution. Complex structures in the core might not arisefrom a pair of overlapping rings or a cool (110 K) and very massive dusttorus, as has been suggested recently. Instead, it seems more likelythat the arcs and compact knots comprise a warm (200-350 K) disruptedtorus at the intersection of the larger polar lobes. Some of the arcsappear to break out of the inner core region and may be associated withequatorial features seen in optical images. The torus could have beendisrupted by a posteruption stellar wind or by ejecta from the GreatEruption itself if the torus existed before that event. Kinematic dataare required to rule out either possibility. Based on observations madeat the Baade telescope of the Magellan Observatory, a joint facility ofthe Carnegie Observatories, Harvard University, Massachusetts Instituteof Technology, University of Arizona, and University of Michigan.
| The Henize sample of S stars. IV. New symbiotic stars
The properties of the few symbiotic stars detected among the 66 binary Sstars from the Henize sample are discussed. Two stars (Hen 18 and Hen121) exhibit both a strong blue-violet continuum and strongHalpha emission (FWHM of 70 km s-1), whereas Hen134 and 137 exhibit weak Halpha emission. TheHalpha profiles are typical of non-dusty symbiotic starsbelonging to class S-3 as defined by Van Winckel et al. (1993, A&AS102, 401). In that class as in the Henize symbiotic S stars, He I, [NII] or [S II] emission lines are absent, suggesting that the nebulardensity is high but the excitation rather low. The radial velocity ofthe centre of the Halpha emission is identical to that of thecompanion star (at least for Hen 121 where this can be checked from theavailable orbital elements), thus suggesting that the Halphaemission originates in gas moving with the companion star. For Hen 121,this is further confirmed by the disappearance of the ultraviolet Balmercontinuum when the companion is eclipsed by the S star. Hen 121 is thusthe second eclipsing binary star discovered among extrinsic S stars (thefirst one is HD 35155). A comparison of the available data on orbitalperiods and Halpha emission leads to the conclusion thatHalpha emission in s stars seems to be restricted to binarysystems with periods in the range 600-1000 d, in agreement with thesituation prevailing for red symbiotic stars (excluding symbioticnovae). Symbiotic S stars are found among the most evolved extrinsic Sstars. Based on observations carried out at the European SouthernObservatory (ESO, La Silla, Chile; program 60.E-0805) and at the Swiss70 cm telescope (La Silla, Chile).
| Infrared spectral classification of normal stars.
Moderate resolution (~400) 2.38-45.2 mu m infrared spectra of starswithout dust features were obtained with the Short WavelengthSpectrometer (SWS) on board the Infrared Space Observatory (ISO). Theobservations are part of a larger program with the objective to extendand refine the current infrared classification schemes. In particular,our data provide the basis for a more detailed classification of the1.N-1.NO sources (ordinary and oxygen rich naked stars) as defined byKraemer et al. (\cite{kraemer}) in a comprehensive classification of theISO-SWS spectra. For our analysis, the continuum was determined byfitting Engelke's function (Engelke \cite{engelke}) to the SWS data. Thestellar angular diameters derived from these estimates of the continuumare in good agreement with values obtained by other methods. Analysis ofthe equivalent widths of the CO fundamental and first overtone molecularbands, the SiO fundamental and first overtone, as well as theH2O bending mode band as a function of MK class, reveals thatthere is sufficient information in the SWS spectra to distinguishbetween hot (B, A, F) and cool stars. Furthermore, it is possible todetermine the spectral type for the G, K and M giants, and subtyperanges in a sequence of K and M giants. The equivalent widths of the COand SiO bands are found to be well correlated in K and M stars, suchthat the equivalent widths of the CO fundamental, the SiO first overtoneand the SiO fundamental can be reasonably well extrapolated from thedepth of the CO first overtone. We have identified two stars,HR 365 and V Nor, whosemid-infrared spectrum does not correspond to their respective opticalclassification. HR 365 may have a late M companion,which dominates the observed infrared spectrum while VNor is a late type giant that was included because itsspectrum was classified as featureless under the IRAS LRS scheme.According to Kraemer et al. (\cite{kraemer}), V Norhas a thin dust shell, which distorts the analysis of its mid-infraredabsorption bands. Based on observations with ISO, an ESA project withinstruments funded by ESA Member States (especially the PI countries:France, Germany, The Netherlands and the UK) and with the participationof ISAS and NASA.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 1 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?/A+A/390/1033
| Infrared polarimetry of the southern massive star-forming region G333.6-0.2
We present 8-13μm spectropolarimetry, and 12- and 2-μm imagingpolarimetry of the southern massive star-forming region G333.6-0.2.Spectro-polarimetry measurements show that the polarization observedtowards the nebula contains a mixture of both absorptive and emissivepolarizations. Model fitting to the spectra indicates that thetemperature of the mid-infrared emitting dust grains is generally ~200Kand the optical depth of the absorbing dust at 9.7μm is ~1.5. Fitsare also made to the polarimetry spectra, which show a reasonablyconstant peak absorptive polarization (~3.4 per cent at 43°) acrossthe face of the Hii region. This absorptive polarization position angleis consistent with that found by the 2-μm imaging polarimetry(38°+/-6°) and is most likely due to the Galactic magnetic fieldlocal to G333.6-0.2. When the absorptive polarization is subtracted fromthe 12-μm polarization image, the emissive polarization pattern thatis intrinsic to the star-forming region is revealed. A probable magneticfield configuration implied by the intrinsic polarization suggests starformation initially influenced by the Galactic magnetic field which iseventually perturbed by the star formation process.
| Mid-infrared observations of methanol maser sites and ultracompact H ii regions: signposts of high-mass star formation
N-band (10.5μm) and/or Q-band (20.0μm) images taken with MANIAC onthe ESO/MPI 2.2-m telescope are presented for 31 methanol maser sitesand 19 ultracompact (UC) Hii regions. Most of the maser sites and UC Hiiregions are coincident with mid-infrared (MIR) sources to within thepositional uncertainties of ~3arcsec, consistent with the maser emissionbeing powered by the MIR source. The IRAS source positions, however, donot always coincide with the MIR sources. Based on an average infraredspectral energy distribution, we deduce that the MIR objects areluminous enough that they should also produce a strong ionizingradiation. Some sources are consistent with stars of later spectraltype, but not all can be. A number of maser sites show no detectableradio continuum emission associated with MIR emission, despite apowering source luminous enough potentially to produce an UC Hii region.Since no signs of an UC Hii region are detected here, these maser sitesmight be produced during a very early stage of stellar evolution. Wepresent objects that show evidence of outflow activity stemming from amaser site, exhibiting CO and/or CS line profiles indicative of outflowscoincident with the MIR source. These cases are promising examples ofmaser sites signposting the earliest stages of high-mass star formation.
| N-Band Imaging of Seyfert Nuclei and the Mid-Infrared-X-Ray Correlation
We present new mid-infrared (N-band) images of a sample of eight nearbySeyfert galaxies. In all of our targets, we detect a central unresolvedsource, which in some cases has been identified for the first time. Inparticular, we have detected the mid-infrared emission from the activenucleus of NGC 4945, which previously remained undetected at anywavelength but hard X-rays. We also detect circumnuclear extendedemission in the Circinus galaxy along its major axis and find marginalevidence for extended circumnuclear emission in NGC 3281. The highspatial resolution (1.7") of our data allows us to separate the flux ofthe nuclear point sources from the extended circumnuclear starburst (ifpresent). We complement our sample with literature data for a number ofnonactive starburst galaxies and relate the nuclear N-band flux topublished hard (2-10 keV) X-ray fluxes. We find tight and well-separatedcorrelations between the nuclear N-band flux and X-ray flux for bothSeyfert and starburst nuclei that span over 3 orders of magnitude inluminosity. We demonstrate that these correlations can be used as apowerful classification tool for galactic nuclei. For example, we findstrong evidence against NGC 1808 currently harboring an active Seyfertnucleus based on its position in the mid-infrared-X-ray diagram. On theother hand, we confirm that NGC 4945 is in fact a Seyfert 2 galaxy.
| Identification of Fe II Emission Lines in FUSE Stellar Spectra
We identify two complexes of Fe II emission lines in far-ultravioletspectra of the stars α TrA and HD 104237. Using spectra from boththe Far Ultraviolet Spectroscopic Explorer (FUSE) and the SpaceTelescope Imaging Spectrograph (STIS) on board the Hubble SpaceTelescope (HST), we show that these emission lines, which represent themajority of previously unidentifed emission features in cool starspectra between 912 and 1180 Å, are fluorescent decays in Fe IIfollowing excitation by H Lyα. Specifically, followingphotoexcitation from the third term (4s a 4D) of Fe II,subsequent decays are observed to the two lowest terms (4s a6D and 3d7 a 4F) which are observednear 1100 and 1135 Å, respectively. Decays to higher terms, andhence longer wavelengths, also are clearly seen in the STIS spectra.Differences in the fluorescent Fe II spectra of α TrA and HD104237 are tentatively identified as resulting from differences in theintrinsic width of the density-weighted H Lyα radiation fields.The additional Fe II lines observed in α TrA result from abroadened H Lyα profile. Two features near 1060 Å appear tobe fluorescent lines of Cr II, also excited by H Lyα.
| The Disk and Environment of the Herbig Be Star HD 100546
Coronagraphic imaging of the nearest Herbig Be star with the SpaceTelescope Imaging Spectrograph (STIS) on board the Hubble SpaceTelescope, Ks (2.15 μm) imaging with ADONIS at the 3.6 m telescope atLa Silla, and mid-infrared imaging with OSCIR using the 4 m BlancoTelescope at Cerro Tololo Inter-American Observatory confirm thedetection of the disk reported by Pantin et al. and map the disk out to5" (~515 AU) in the optical and at Ks. While the source is unresolved at10 and 18 μm, it can be traced to 1.5" at 11.7 μm. We confirm thechange in the radial dependence of the disk surface brightness near 2.7"seen at 1.6 μm by Augereau et al. at Ks. No such break in the powerlaw is seen in the optical. The STIS data reveal spiral dark lanestructure, making HD 100546 the third near-zero-age main-sequence HerbigAe/Be star with structure more than 100 AU from the star. We alsooptically detect a low surface brightness envelope extending 10" (1000AU) from the star, in addition to nebulosity, which is probablyassociated with DC 292.6-7.9. The survival of the envelope throughessentially the entire pre-main-sequence lifetime of the star, coupledwith the absence of physical companions within 1500 AU of the star,suggests that envelope lifetimes owe more to the star-formingenvironment than to mass-loss activity from the Herbig Ae/Be star. Basedon observations made with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555. This study is part of the STIS IDT protoplanetarydisk Key Project. This work is also based on observations collected atthe European Southern Observatory, La Silla, Chile, Proposal ID63.I-0196. This work is also based on observations made at the CerroTololo Inter-American Observatory. CTIO is operated by AURA, Inc., undercooperative agreement with the National Science Foundation.
| Polarimetry of 167 Cool Variable Stars: Data
Multicolor photoelectric polarimetry is presented for 167 stars, most ofwhich are variable stars. The observations constitute a data set thatfor some stars covers a time span of 35 yr. Complex variations are foundover time and wavelength and in both the amount of polarization and itsposition angle, providing constraints for understanding the polarizingenvironments in and around these cool stars.
| Spectral Irradiance Calibration in the Infrared. XII. Radiometric Measurements from the Midcourse Space Experiment
We describe the series of absolute stellar irradiance calibrationexperiments conducted by the Midcourse Space Experiment (MSX). Theseexperiments validate the published absolute irradiances of our primaryand secondary standards, namely, α CMa and a set of bright K-Mgiant stars, and confirm their radiometric ``closure'' (relativeirradiances). We also validate the absolute spectra of 29 of the faintercalibrators that have been previously published using MSX data. Thiswork underpins the absolute calibrators provided for DIRBE, IRTS, ISO,our all-sky network of 422 fainter calibration stars (Paper X), and theMSX Point Source Catalog, and it is now being extended to accommodatecalibrators for SIRTF.
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| Takýmyýldýz: | Guney Haci |
| Sað Açýklýk: | 12h31m16.70s |
| Yükselim: | -57°04'52.0" |
| Görünürdeki Parlaklýk: | 6.42 |
| özdevim Sað Açýklýk: | 5.1 |
| özdevim Yükselim: | -13.5 |
| B-T magnitude: | 6.588 |
| V-T magnitude: | 6.45 |
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