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Resim Yükleyin
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Ýlgili Makaleler
A multiwavelength investigation of the temperature of the cold neutral medium
We present measurements of the HI spin temperatures (Ts) ofthe cold neutral medium (CNM) towards radio sources that are closelyaligned with stars for which published H2 ortho-paratemperatures (T01) are available from ultraviolet (UV)observations. Our sample consists of 18 radio sources close to 16 nearbystars. The transverse separation of the lines of sight of thecorresponding UV and radio observations varies from 0.1 to 12.0 pc atthe distance of the star. The UV measurements do not have velocityinformation, so we use the velocities of low ionization species (e.g.NaI/KI/CI) observed towards these same stars to make a plausibleidentification of the CNM corresponding to the H2 absorption.We then find that T01 and Ts match withinobservational uncertainties for lines of sight with H2 columndensity above 1015.8cm-2, but deviate from eachother below this threshold. This is consistent with the expectation thatin the CNM Ts tracks the kinetic temperature due tocollisions and that T01 is driven towards the kinetictemperature by proton exchange reactions.
| Large Silicon Abundance in Photodissociation Regions
We have made one-dimensional raster scan observations of the ρ Ophand σ Sco star-forming regions with two spectrometers (SWS andLWS) on board the ISO. In the ρ Oph region, [Si II] 35 μm, [O I]63 μm, 146 μm, [C II] 158 μm, and the H2 purerotational transition lines S(0) to S(3) are detected, and thephotodissociation region (PDR) properties are derived as the radiationfield scaled by the solar neighborhood value G0~30-500, thegas density n~250-2500 cm-3, and the surface temperatureT~100-400 K. The ratio of [Si II] 35 μm to [O I] 146 μm indicatesthat silicon of 10%-20% of the solar abundance must be in the gaseousform in the PDR, suggesting that efficient dust destruction is ongoingeven in the PDR and that a fraction of the silicon atoms may becontained in volatile forms in dust grains. The [O I] 63 μm and [CII] 158 μm emissions are too weak relative to [O I] 146 μm to beaccounted for by standard PDR models. We propose a simple model, inwhich overlapping PDR clouds along the line of sight absorb the [O I] 63μm and [C II] 158 μm emissions, and show that the proposed modelreproduces the observed line intensities fairly well. In the σ Scoregion, we have detected three fine-structure lines, [O I] 63 μm, [NII] 122 μm, and [C II] 158 μm, and derived that 30%-80% of the [CII] emission comes from the ionized gas. The upper limit of the [Si II]35 μm is compatible with the solar abundance relative to nitrogen,and no useful constraint on the gaseous Si is obtained for the σSco region.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.
| The Dust-scattered X-Ray Halo around Swift GRB 050724
This paper discusses the X-ray halo around the Swift γ-ray burstGRB 050724 (z=0.258), detected by the Swift X-Ray Telescope. The halo,which forms a ring around the fading X-ray source, expands to a radiusof 200" within 8 ks of the burst, exactly as expected for small-angleX-ray scattering by Galactic dust along the line of sight to acosmologically distant GRB. The expansion curve and radial profile ofthe halo constrain the scattering dust to be concentrated at a distanceof D=139+/-9 pc (from Earth) in a cloud/sheet of thicknessΔD<22 pc. The halo was observed only out to scattering anglesof 200", for which the scattering is dominated by the largest grains,with a maximum size estimated to be amax~0.4-0.5 μm. Thescattering-to-extinction ratio was estimated to beτscat/AV>~0.022 this is a lower limit tothe true value because contribution from smaller grains, which scatterto larger angles, was not directly observed. The line of sight to theGRB passes close to the Ophiuchus molecular cloud complex, whichprovides a plausible site for the scattering dust.
| A high-resolution spectroscopy survey of β Cephei pulsations in bright stars
We present a study of absorption line-profile variations in early-B typenear-main-sequence stars without emission lines. We have surveyed atotal of 171 bright stars using the Nordic Optical Telescope (NOTSA),William Herschel Telescope (ING) and Coudé Auxiliary Telescope(ESO). Our sample contains 75% of all O9.5-B2.5 III-V non-emission-linestars brighter than 5.5 mag. We obtained high signal-to-noise,high-resolution spectra of the SiIII λ4560 triplet - for 125stars of our sample we obtained more than one spectrum - and examinedthese for pulsational-like line-profile variations and/or structure. Weconclude that about half of our sample stars show evidence forline-profile variations (LPV). We find evidence for LPV in about 65% ofour sample stars brighter than V=5.5. For stars with rotationalbroadening V sin i 100 km s-1, we find evidence for LPVin about 75% of the cases. We argue that it is likely that these LPV areof pulsational origin, and that hence more than half of thesolar-neighbourhood O9.5-B2.5 III-V stars is pulsating in modes that canbe detected with high-resolution spectroscopy. We detected LPV in 64stars previously unknown to be pulsators, and label these stars as newβ Cep candidates. We conclude that there is no obvious differencein incidence of (pulsational) LPV for early-B type near-main-sequencestars in binaries or in OB associations, with respect to single fieldstars.
| Radial velocity measurements of B stars in the Scorpius-Centaurus association
We derive single-epoch radial velocities for a sample of 56 B-type starsmembers of the subgroups Upper Scorpius, Upper Centaurus Lupus and LowerCentaurus Crux of the nearby Sco-Cen OB association. The radial velocitymeasurements were obtained by means of high-resolution echelle spectravia analysis of individual lines. The internal accuracy obtained in themeasurements is estimated to be typically 2-3 km s-1, butdepends on the projected rotational velocity of the target. Radialvelocity measurements taken for 2-3 epochs for the targets HD 120307, HD142990 and HD 139365 are variable and confirm that they arespectroscopic binaries, as previously identified in the literature.Spectral lines from two stellar components are resolved in the observedspectra of target stars HD 133242, HD 133955 and HD 143018, identifyingthem as spectroscopic binaries.
| The Large Magellanic Cloud: diffuse interstellar bands, atomic lines and the local environmental conditions
The Large Magellanic Cloud (LMC) offers a unique laboratory to study thediffuse interstellar bands (DIBs) under conditions that are profoundlydifferent from those in the Galaxy. DIB carrier abundances depend onseveral environmental factors, in particular the local UV radiationfield. In this paper we present measurements of twelve DIBs in fivelines of sight to early-type stars in the LMC, including the 30Doradus region. From the high resolution spectra obtained withVLT/UVES we also derive environmental parameters that characterise thelocal interstellar medium (ISM) in the probed LMC clouds. These includethe column density components (including total column density) for theatomic resonance lines of Na I, Ca II, Ti II, K I. In addition, wederive the H I column density from 21 cm line profiles, thetotal-to-selective visual extinction RV and the gas-to-dustratio N(H I)/A_V. Furthermore, from atomic line ratios we derive theionisation balance and relative UV field strength in these environments.We discuss the properties of the LMC ISM in the context of DIB carrierformation. The behaviour of DIBs in the LMC is compared to that of DIBsin different local environmental conditions in the Milky Way. A keyresult is that in most cases the diffuse band strengths are weak (up tofactor 5) with respect to Galactic lines of sight of comparablereddening, EB-V. In the line of sight towards Sk -69223 the 5780 and 5797 Å DIBs are very similar instrength and profile to those observed towards HD144217, which is typical of an environment exposed to a strongUV field. From the velocity analysis we find that DIB carriers (towardsSk -69 243) are better correlated with the ionisedspecies like Ca II than with neutrals (like Na I and CO). The mostsignificant parameter that governs the behaviour of the DIB carrier isthe strength of the UV field.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| Dust extinction and absorption: the challenge of porous grains
In many models of dusty objects in space the grains are assumed to becomposite or fluffy. However, the computation of the optical propertiesof such particles is still a very difficult problem. We analyze how theincrease of grain porosity influences basic features of cosmic dust -interstellar extinction, dust temperature, infrared bands and millimeteropacity. It is found that an increase of porosity leads to an increaseof extinction cross sections at some wavelengths and a decrease atothers depending on the grain model. However, this behaviour issufficient to reproduce the extinction curve in the direction of thestar σ Sco using current solar abundances. In the case of the starζ Oph our model requires larger amounts of carbon and iron in thedust-phase than is available. Porous grains can reproduce the flatextinction across the 3 - 8 μm wavelength range measured for severallines of sight by ISO and Spitzer. Porous grains are generally coolerthan compact grains. At the same time, the temperature of very porousgrains becomes slightly larger in the case of the EMT-Mie calculationsin comparison with the results found from the layered-sphere model. Thelayered-sphere model predicts a broadening of infrared bands and a shiftof the peak position to larger wavelengths as porosity grows. In thecase of the EMT-Mie model variations of the feature profile are lesssignificant. It is also shown that the millimeter mass absorptioncoefficients grow as porosity increases with a faster growth occurringfor particles with Rayleigh/non-Rayleigh inclusions. As a result, forvery porous particles the coefficients given by two models can differ bya factor of about 3.
| 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.
| Correlation patterns between 11 diffuse interstellar bands and ultraviolet extinction
We relate the equivalent widths of 11 diffuse interstellar bands,measured in the spectra of 49 stars, to different colour excesses in theultraviolet. We find that most of the observed bands correlatepositively with the extinction in the neighbourhood of the2175-Åbump. Correlation with colour excesses in other parts of theextinction curve is more variable from one diffuse interstellar band toanother; we find that some diffuse bands (5797, 5850 and 6376 Å)correlate positively with the overall slope of the extinction curve,while others (5780 and 6284 Å) exhibit negative correlation. Wediscuss the implications of these results on the links between thediffuse interstellar band carriers and the properties of theinterstellar grains.
| Interstellar Ca II Line Intensities and the Distances of the OB stars
We show that the equivalent widths of the well-known interstellar Ca IIH and K lines can be used to determine the distances to OB stars in ourGalaxy. The equivalent widths, measured in the spectra of 147 early-typestars, are strongly related to the Hipparcos parallaxes of thoseobjects. The lines fitted to the parallax-equivalent width data aregiven by the formulae π=1/[2.78EW(K)+95] and π=1/[4.58EW(H)+102],where π is in arcseconds and EW is in milliangstroms. The form of theformulae, yielding a finite parallax even for zero absorption, showsthat space within ~100 pc of the Sun contains very little Ca II, whichis in agreement with the known dimensions of the Local Bubble. Using CaII lines for distance determination does not require the knowledge ofthe absolute magnitude of the object; it is thus well suited for targetsfor which the absolute calibration is either not precise (OBsupergiants) or not available at all (peculiar objects). We alsodemonstrate that neither the reddening E(B-V) nor the equivalent widthsof interstellar K I and CH lines are suitable candidates for distanceestimation, their relation with parallaxes being far less tight than forCa II.
| A Mid-Infrared Imaging Survey of Embedded Young Stellar Objects in the ρ Ophiuchi Cloud Core
Results of a comprehensive, new, ground-based mid-infrared imagingsurvey of the young stellar population of the ρ Ophiuchi cloud arepresented. Data were acquired at the Palomar 5 m and at the Keck 10 mtelescopes with the MIRLIN and LWS instruments, at 0.5" and 0.25"resolutions, respectively. Of 172 survey objects, 85 were detected.Among the 22 multiple systems observed, 15 were resolved and theirindividual component fluxes determined. A plot of the frequencydistribution of the detected objects with SED spectral slope shows thatYSOs spend ~4×105 yr in the flat-spectrum phase,clearing out their remnant infall envelopes. Mid-infrared variability isfound among a significant fraction of the surveyed objects and is foundto occur for all SED classes with optically thick disks. Large-amplitudenear-infrared variability, also found for all SED classes with opticallythick disks, seems to occur with somewhat higher frequency at theearlier evolutionary stages. Although a general trend of mid-infraredexcess and near-infrared veiling exists progressing through SED classes,with Class I objects generally exhibiting rK>=1,flat-spectrum objects with rK>=0.58, and Class III objectswith rK=0, Class II objects exhibit the widest range ofrK values, ranging from 0<=rK<=4.5. However,the highly variable value of veiling that a single source can exhibit inany of the SED classes in which active disk accretion can take place isstriking and is direct observational evidence for highly time-variableaccretion activity in disks. Finally, by comparing mid-infrared versusnear-infrared excesses in a subsample with well-determined effectivetemperatures and extinction values, disk-clearing mechanisms areexplored. The results are consistent with disk clearing proceeding fromthe inside out.
| FUSE Measurements of Far-Ultraviolet Extinction. I. Galactic Sight Lines
We present extinction curves that include data down to far-ultravioletwavelengths (FUV; 1050-1200 Å) for nine Galactic sight lines. TheFUV extinction was measured using data from the Far UltravioletSpectroscopic Explorer. The sight lines were chosen for their unusualextinction properties in the infrared through the ultraviolet; that theyprobe a wide range of dust environments is evidenced by the large spreadin their measured ratios of total to selective extinction,RV=2.43-3.81. We find that extrapolation of the Fitzpatrick& Massa relationship from the ultraviolet appears to be a goodpredictor of the FUV extinction behavior. We find that predictions ofthe FUV extinction based on the Cardelli, Clayton, & Mathis (CCM)dependence on RV give mixed results. For the seven extinctioncurves well represented by CCM in the infrared through ultraviolet(x<8 μm-1), the FUV extinction is well predicted inthree sight lines, overpredicted in two sight lines, and underpredictedin two sight lines. A maximum entropy method analysis using a simplethree-component grain model shows that seven of the nine sight lines inthe study require a larger fraction of grain materials to be in dustwhen FUV extinction is included in the models. Most of the added grainmaterial is in the form of small (radii <~ 200 Å) grains.Based on observations with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer, which is operated by the Johns HopkinsUniversity under NASA contract NAS5-32985.
| A Study of Far-Ultraviolet Extinction in the Upper Scorpius Cloud Using the SPINR Sounding Rocket Experiment
In this study, six new interstellar extinction curves in thefar-ultraviolet are presented using data from a sounding rocketexperiment. The sounding rocket data were combined with IUE data for sixlines of sight in the Upper Scorpius group to cover the wavelength rangeof 912-3030 Å. The extinction curves were produced using the paircomparison method with B stars of similar spectral types.Parameterizations from Fitzpatrick & Massa, Cardelli et al., andFitzpatrick were then fitted to the derived extinction curves. From thederived extinction curves, their corresponding fits, and the dust modelof Weingartner & Draine, it is concluded that the dust population inthe Upper Scorpius region exhibits a larger than average grainpopulation with a depletion of smaller grains.
| Optical Spectroscopy of the Surface Population of the ρ Ophiuchi Molecular Cloud: The First Wave of Star Formation
We present the results of optical spectroscopy of 139 stars obtainedwith the Hydra multiobject spectrograph. The objects extend over a 1.3deg2 area surrounding the main cloud of the ρ Ophcomplex. The objects were selected from narrowband images to haveHα in emission. Using the presence of strong Hα emission,lithium absorption, location in the Hertzsprung-Russell diagram, orpreviously reported X-ray emission, we were able to identify 88 objectsas young stars associated with the cloud. Strong Hα emission wasconfirmed in 39 objects with line widths consistent with their origin inmagnetospheric accretion columns. Two of the strongest emission-lineobjects are young, X-ray-emitting brown dwarf candidates with M8spectral types. Comparisons of the bolometric luminosities and effectivetemperatures with theoretical models suggest a median age for thispopulation of 2.1 Myr, which is significantly older than the agesderived for objects in the cloud core. It appears that these starsformed contemporaneously with low-mass stars in the Upper Scorpiussubgroup, likely triggered by massive stars in the Upper Centaurussubgroup.
| Unresolved Hα Enhancements at High Galactic Latitude in the WHAM Sky Survey Maps
We have identified 85 regions of enhanced Hα emission at|b|>10deg subtending approximately 1° or less on theWisconsin Hα Mapper (WHAM) sky survey. These high-latitude ``WHAMpoint sources'' have Hα fluxes of 10-11-10-9ergs cm-2 s-1, radial velocities within about 70km s-1 of the LSR, and line widths that range from less than20 to about 80 km s-1 (FWHM). Twenty-nine of theseenhancements are not identified with either cataloged nebulae or hotstars and appear to have kinematic properties that differ from thoseobserved for planetary nebulae. Another 14 enhancements are near hotevolved low-mass stars that had no previously reported detections ofassociated nebulosity. The remainder of the enhancements are catalogedplanetary nebulae and small, high-latitude H II regions surroundingmassive O and early B stars.
| A multiplicity survey of the ρ Ophiuchi molecular clouds
We present a volume-limited multiplicity survey with magnitude cutoff({m}K≤ 10.5 mag) of 158 young stellar objects locatedwithin or in the vicinity of the ρ Ophiuchi Dark Cloud. Withexception of eleven already well observed objects, all sources have beenobserved by us in the K-band with 3.5 m telescopes by using speckletechniques. The separation range covered by our survey is0.13''≤θ≤ 6.4'', where the lower limit is given by thediffraction limit of the telescopes and the upper limit by confusionwith background stars. The multiplicity survey is complete for fluxratios ≥ 0.1 (Δ{m}K≤ 2.5) at the diffractionlimit. After taking the background density into account the degree ofmultiplicity is 29.1%± 4.3% and thus only marginally higher thanthe value 23.5%± 4.8 % derived for the given separation range forthe main-sequence solar-like stars in the solar neighbourhood (Duquennoy& Mayor 1991). We discuss the implications of these findings.
| Metallicity of mono- and multiperiodic β Cephei stars
Analyzing IUE ultraviolet spectra of β Cep pulsating stars wenoticed that multiperiodic variables have a larger mean metal abundancein the photosphere, [ m/H] , than monoperiodic ones. We applystatistical tests to verify this dichotomy. We obtain that, with a largeprobability, the multiperiodic β Cep stars have greater values of [m/H] . This result is consistent with the linear non-adiabatic theory ofpulsation of early B-type stars.
| Metallicities of the β Cephei stars from low-resolution ultraviolet spectra
We derive basic stellar parameters (angular diameters, effectivetemperatures, metallicities) and interstellar reddening for all βCephei stars observed during the IUE satellite mission, including thosebelonging to three open clusters. The parameters are derived by means ofan algorithmic procedure of fitting theoretical flux distributions tothe low-resolution IUE spectra and ground-based spectrophotometricobservations. Since the metallicity has a special importance forpulsating B-type stars, we focus our attention in particular on thisparameter.Tables 1, 2, 4 and 5 are only available in electronic form athttp://www.edpsciences.org
| 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
| The β Cephei variable in the eclipsing binary HD 92024. I. Determination of the orbit
HD 92024 is a member of the open cluster NGC3293; it is the only eclipsing binary system with a β Cepheicomponent known in the southern hemisphere. This paper presents thefirst spectroscopic analysis of the single-lined binary and provides anorbital analysis based on recent high-resolution spectroscopy andphotometry. A procedure to derive orbital elements with minimalinfluence of the pulsational line-profile variations on the radialvelocities is applied, and we find the stellar masses to be 15.0+3.0-4.0Mȯ and 3.0±0.5 Mȯ respectively, and radii of8.4±0.8 Rȯ, 2.1±0.4 Rȯ. The temperatures are 25500±500 K and 12 500±1000 K. The surface gravity values oflog g= 3.77±0.08 and 4.27±0.18 indicate that the binaryconsists of an evolved early B-type primary and a late-B main sequencecompanion. The resulting distance 2.8±0.3 kpc and systemicvelocity -16 km s-1 confirm cluster membership. Theoretical stellarmodels indicate an age of 10-13 Myr, somewhat higher than theliterature value for the brightest members of NGC 3293.Based on observations made with ESO Telescopes at the La SillaObservatory, Chile, under programmes 66.D-0297, 67.D-0023, 68.D-028, andwith the Strömgren Automatic Telescope, La Silla.
| The Ultraviolet and Optical Spectra of Luminous B-Type Stars in the Small Magellanic Cloud
We present ultraviolet spectra from the Space Telescope ImagingSpectrograph (STIS) of 12 early B-type stars in the Small MagellanicCloud (SMC), composed of nine supergiants and three giants. Amorphological comparison with Galactic analogs is made using archivaldata from the International Ultraviolet Explorer (IUE). In general, theintensity of the P Cygni emission in the UV resonance lines is greaterand is seen to later spectral types in the Galactic spectra than intheir metal-deficient SMC counterparts. We attribute these effects asmost likely arising from weaker stellar winds in the SMC targets, aspredicted by radiatively driven wind theory. We also include unpublishedSTIS observations of two late O-type stars in the SMC. In combinationwith published O-type STIS data, we now have an extensive ultravioletspectral library of metal-deficient stars to use in the study ofunresolved starbursts and high-redshift star-forming galaxies. In thiscontext, we present empirical measurements for the B-type spectra of thenew ``1978 index'' suggested by Rix et al. as a probe of metallicity insuch systems.
| A near-infrared stellar spectral library: I. H-band spectra.
This paper presents the H band near-infrared (NIR) spectral library of135 solar type stars covering spectral types O5-M3 and luminosityclasses I-V as per MK classification. The observations were carried outwith 1.2 meter Gurushikhar Infrared Telescope (GIRT), at Mt. Abu, Indiausing a NICMOS3 HgCdTe 256 x 256 NIR array based spectrometer. Thespectra have a moderate resolution of 1000 (about 16 A) at the H bandand have been continuum shape corrected to their respective effectivetemperatures. This library and the remaining ones in J and K bands oncereleased will serve as an important database for stellar populationsynthesis and other applications in conjunction with the newly formedlarge optical coude feed stellar spectral library of Valdes et al.(2004). The complete H-Band library is available online at: http://vo.iucaa.ernet.in/~voi/NIR_Header.html
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| A Uniform Database of 2.2-16.5 μm Spectra from the ISOCAM CVF Spectrometer
We present all ISOCAM circular variable filter (CVF) spectra that covermore than one-third of the 2.2-16.5 μm spectral range of theinstrument. The 364 spectra have been classified according to theclassification system of Kraemer et al., as modified by Hodge et al. toaccount for the shorter wavelength range. Prior to classification, thespectra were processed and recalibrated to create a uniform database.Aperture photometry was performed at each wavelength centered on thebrightest position in each image field and the various spectral segmentsmerged into a single spectrum. The aperture was the same for all scalesizes of the images. Since this procedure differs fundamentally fromthat used in the initial ISOCAM calibration, a recalibration of thespectral response of the instrument was required for the aperturephotometry. The recalibrated spectra and the software used to createthem are available to the community on-line via the ISO Data Archive.Several new groups were added to the KSPW system to describe spectrawith no counterparts in either the SWS or PHT-S databases: CA, E/SA,UE/SA, and SSA. The zodiacal dust cloud provides the most commonbackground continuum to the spectral features, visible in almost 40% ofthe processed sources. The most characteristic and ubiquitous spectralfeatures observed in the CVF spectral atlas are those of theunidentified infrared bands (UIR), which are typically attributed toultraviolet-excited fluorescence of large molecules containing aromatichydrocarbons. The UIR features commonly occur superimposed on thezodiacal background (18%) but can also appear in conjunction with otherspectral features, such as fine-structure emission lines or silicateabsorption. In at least 13 of the galaxies observed, the pattern of UIRemission features has been noticeably shifted to longer wavelengths.Based on observations with the Infrared Space Observatory, a EuropeanSpace Agency (ESA) project with instruments funded by ESA Member States(especially the Principal Investigator countries: France, Germany, theNetherlands, and the United Kingdom) and with the participation of theInstitute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Near-Infrared Molecular Hydrogen Emission from the Central Regions of Galaxies: Regulated Physical Conditions in the Interstellar Medium
The central regions of many interacting and early-type spiral galaxiesare actively forming stars. This process affects the physical andchemical properties of the local interstellar medium, as well as theevolution of the galaxies. We observed near-infrared H2emission lines: v=1-0 S(1), 3-2 S(3), 1-0 S(0), and 2-1 S(1) from thecentral ~1 kpc regions of the archetypical starburst galaxies M82 andNGC 253 and the less dramatic but still vigorously star-forming galaxiesNGC 6946 and IC 342. Like the far-infrared continuum luminosity, thenear-infrared H2 emission luminosity can directly trace theamount of star formation activity because the H2 emissionlines arise from the interaction between hot and young stars and nearbyneutral clouds. The observed H2 line ratios show that boththermal excitation and nonthermal excitation are responsible for theemission lines but that the great majority of the near-infraredH2 line emission in these galaxies arises from energy statesexcited by ultraviolet fluorescence. The derived physical conditions,e.g., far-ultraviolet radiation field and gas density, from [C II] and[O I] lines and far-infrared continuum observations when used as inputsto photodissociation models also explain the luminosity of the observedH2 1-0 S(1) line. The ratio of the H2 1-0 S(1)line to far-IR continuum luminosity is remarkably constant over a broadrange of galaxy luminosities:LH2/LFIR~=10-5, in normallate-type galaxies (including the Galactic center), in nearby starburstgalaxies, and in luminous IR galaxies (LIRGs:LFIR>1011 Lsolar). Examining thisconstant ratio in the context of photodissociation region models, weconclude that it implies that the strength of the incident UV field ontypical molecular clouds follows the gas density at the cloud surface.
| Reanalysis of Copernicus Measurements of Interstellar Carbon Monoxide
We used archival data acquired with Copernicus to reexamine CO columndensities, as self-consistent oscillator strengths are now available.Our focus is on lines of sight containing modest amounts of molecularspecies. Our resulting column densities are small enough thatself-shielding from photodissociation does not occur in the cloudsprobed by the observations. While our sample shows that the columndensities of CO and H2 are related, no correspondence withthe CH column density is evident. The case for the CH+ columndensity is less clear. Recent chemical models for these sight linessuggest that CH is mainly a by-product of CH+ synthesis inlow-density gas. The models are most successful in reproducing theamounts of CO in the densest sight lines. Thus, much of the COabsorption must arise from denser clumps along the line of sight toaccount for the trend with H2.
| Thermal Emission as a Test for Hidden Nuclei in Nearby Radio Galaxies
The clear sign of a hidden quasar inside a radio galaxy is theappearance of quasar spectral features in its polarized (scattered)light. However, that observational test requires suitably placedscattering material to act as a mirror, allowing us to see the nuclearlight. A rather robust and more general test for a hidden quasar is tolook for the predicted high mid-IR luminosity from the nuclear obscuringmatter. The nuclear waste heat is detected and well isolated in thenearest narrow-line radio galaxy, Cen A. This confirms other indicationsthat Cen A does contain a modest quasar-like nucleus. However, we showhere that M87 does not: at high spatial resolution, the mid-IR nucleusis seen to be very weak and consistent with simple synchrotron emissionfrom the base of the radio jet. This fairly robustly establishes thatthere are ``real'' narrow-line radio galaxies, without the putativeaccretion power and with essentially all the luminosity in kinetic form.Next, we show the intriguing morphology of Cygnus A, where all of themid-IR emission is consistent with reprocessing by the hidden quasarknown to exist from spectropolarimetry and other evidence.
| Speckle Observations of Binary Stars with the WIYN Telescope. IV. Differential Photometry
Five hundred seventy-six magnitude difference measures are presented for260 binary stars. These measures are derived from CCD-based speckleobservations taken at the WIYN 3.5 m telescope at Kitt Peak NationalObservatory during the period 1997-2000. Separations of the systemsrange from over 1" down to near the diffraction limit of the telescope.A study of multiple measures of the same targets indicates that themeasures have a typical uncertainty of better than 0.13 mag per 2 minuteobservation, and that multiple observations can be averaged to arrive atsmaller uncertainties. Results presented here are also compared, insofaras it is possible, with measures in the Hipparcos Catalogue and toprevious studies using adaptive optics. No major systematic errors wereidentified.The WIYN Observatory is a joint facility of the University ofWisconsin-Madison, Indiana University, Yale University, and the NationalOptical Astronomy Observatory.
| Interpretation of the variability of the β Cephei star λ Scorpii. I. The multiple character
We derive accurate values of the orbital parameters of the close binaryβ Cephei star λ Scorpii. Moreover, we present the firstdetermination of the properties of the triple system to which λScorpii belongs. Our analysis is based on a time series of 815high-resolution spectra, covering a timespan of 14 years. We find aclose orbit of 5.9525 d days (e=0.26) and a wide orbit of approximately1082d days (e=0.23). The orbital parameters of the triplestar and a spectrum synthesis lead us to conclude that the system iscomposed of two early-type B stars and a low-mass pre-main-sequence starrather than containing an ultra-massive white dwarf as claimed before.Our proposed configuration is compatible with population synthesis. Theradial velocity variations of the primary allow us to confirm thepresence of at least one pulsation mode with frequency 4.679410 cd-1 which is subject to the light-time effect in the triplesystem. A detailed analysis of the complex line-profile variations isdescribed in a subsequent paper.Based on observations obtained with the Coudé EchelleSpectrograph on the ESO CAT telescope and with the CORALIE EchelleSpectrograph on the 1.2-m Euler Swiss telescope, both situated at LaSilla, ChileTable \ref{observations} is only available in electronic form athttp://www.edpsciences.org
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| Takýmyýldýz: | Akrep |
| Sað Açýklýk: | 16h21m11.30s |
| Yükselim: | -25°35'34.0" |
| Görünürdeki Parlaklýk: | 2.89 |
| Uzaklýk: | 225.225 parsek |
| özdevim Sað Açýklýk: | -9.9 |
| özdevim Yükselim: | -21.1 |
| B-T magnitude: | 3.024 |
| V-T magnitude: | 2.911 |
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