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Spitzer Observations of 3C Quasars and Radio Galaxies: Mid-Infrared Properties of Powerful Radio Sources
We have measured mid-infrared radiation from an orientation-unbiasedsample of 3CRR galaxies and quasars at redshifts 0.4<=z<=1.2 withthe IRS and MIPS instruments on Spitzer. Powerful emission(L24μm>1022.4 W Hz-1sr-1) was detected from all but one of the sources. We fitthe Spitzer data and other measurements from the literature withsynchrotron and dust components. The IRS data provide powerfulconstraints on the fits. At 15 μm, quasars are typically 4 timesbrighter than radio galaxies with the same isotropic radio power. Basedon our fits, half of this difference can be attributed to the presenceof nonthermal emission in the quasars but not the radio galaxies. Theother half is consistent with dust absorption in the radio galaxies butnot the quasars. Fitted optical depths are anticorrelated with coredominance, from which we infer an equatorial distribution of dust aroundthe central engine. The median optical depth at 9.7 μm for objectswith core dominance factor R>10-2 is ~0.4 for objects withR<=10-2, it is ~1.1. We have thus addressed along-standing question in the unification of FR II quasars and galaxies:quasars are more luminous in the mid-infrared than galaxies because of acombination of Doppler-boosted synchrotron emission in quasars andextinction in galaxies, both orientation-dependent effects.
| The Distribution of Silicate Strength in Spitzer Spectra of AGNs and ULIRGs
A sample of 196 AGNs and ULIRGs observed by the Infrared Spectrograph(IRS) on Spitzer is analyzed to study the distribution of the strengthof the 9.7 μm silicate feature. Average spectra are derived forquasars, Seyfert 1 and Seyfert 2 AGNs, and ULIRGs. We find that quasarsare characterized by silicate features in emission and Seyfert 1sequally by emission or weak absorption. Seyfert 2s are dominated by weaksilicate absorption, and ULIRGs are characterized by strong silicateabsorption (mean apparent optical depth about 1.5). Luminositydistributions show that luminosities at rest frame 5.5 μm are similarfor the most luminous quasars and ULIRGs and are almost 105times more luminous than the least luminous AGN in the sample. Thedistributions of spectral characteristics and luminosities are comparedto those of optically faint infrared sources at z~2 being discovered bythe IRS, which are also characterized by strong silicate absorption. Itis found that local ULIRGs are a similar population, although they havelower luminosities and somewhat stronger absorption compared to thehigh-redshift sources.
| Mid-Infrared Galaxy Classification Based on Silicate Obscuration and PAH Equivalent Width
We present a new diagnostic diagram for mid-infrared spectra of infraredgalaxies based on the equivalent width of the 6.2 μm PAH emissionfeature and the strength of the 9.7 μm silicate feature. Based on thepositions in this diagram, we classify galaxies into nine classesranging from continuum-dominated AGN hot dust spectra and PAH-dominatedstarburst spectra to absorption-dominated spectra of deeply obscuredgalactic nuclei. We find that galaxies are systematically distributedalong two distinct branches: one of AGN and starburst-dominated spectraand one of deeply obscured nuclei and starburst-dominated spectra. Theseparation into two branches likely reflects a fundamental difference inthe dust geometry in the two sets of sources: clumpy versus nonclumpyobscuration. Spectra of ULIRGs are found along the full length of bothbranches, reflecting the diverse nature of the ULIRG family.
| Formation and Evolution of Planetary Systems: Upper Limits to the Gas Mass in Disks around Sun-like Stars
We have carried out a sensitive search for gas emission lines at IR andmillimeter wavelengths for a sample of 15 young Sun-like stars selectedfrom our dust disk survey with Spitzer. We have used mid-IR lines totrace the warm (300-100 K) gas in the inner disk and millimetertransitions of 12CO to probe the cold (~20 K) outer disk. Wereport no gas line detections from our sample. Line flux upper limitsare first converted to warm and cold gas mass limits using simpleapproximations allowing a direct comparison with values from theliterature. We also present results from more sophisticated modelsfollowing Gorti & Hollenbach that confirm and extend our simpleanalysis. These models show that the [S I] 25.23 μm line can setconstraining limits on the gas surface density at the disk inner radiusand traces disk regions up to a few AU. We find that none of the 15systems have more than 0.04MJ of gas within a few AU from thedisk inner radius for disk radii from 1 to ~40 AU. These gas mass upperlimits even in the eight systems younger than ~30 Myr suggest that mostof the gas is dispersed early. The gas mass upper limits in the 10-40 AUregion, which is mainly traced by our CO data, are <2M⊕. If these systems are analogs of the solar system,they either have already formed Uranus- and Neptune-like planets or willnot form them beyond 100 Myr. Finally, the gas surface density upperlimits at 1 AU are smaller than 0.01% of the minimum mass solar nebulafor most of the sources. If terrestrial planets form frequently andtheir orbits are circularized by gas, then circularization occurs early.
| A Spitzer Space Telescope Infrared Spectrograph Survey of Warm Molecular Hydrogen in Ultraluminous Infrared Galaxies
We have conducted a survey of ultraluminous infrared galaxies (ULIRGs)with the Infrared Spectrograph on the Spitzer Space Telescope, obtainingspectra from 5.0 to 38.5 μm for 77 sources with 0.022 Jy.The average warm molecular gas mass is ~2×108Msolar. High extinction, inferred from the 9.7 μm silicateabsorption depth, is not observed along the line of sight to themolecular gas. The derived H2 mass does not depend onF25μm/F60μm, which has been used to infereither starburst or AGN dominance. Similarly, the molecular mass doesnot scale with the 25 or 60 μm luminosities. In general, theH2 emission is consistent with an origin in photodissociationregions associated with star formation. We detect the S(0) 28.22 μmemission line in a few ULIRGs. Including this line in the model fitstends to lower the temperature by ~50-100 K, resulting in a significantincrease in the gas mass. The presence of a cooler component cannot beruled out in the remainder of our sample, for which we do not detect theS(0) line. The measured S(7) 5.51 μm line fluxes in six ULIRGsimplies ~3×106 Msolar of hot (~1400 K)H2. The warm gas mass is typically less than 1% of the coldgas mass derived from 12CO observations.Based on observations obtained with the Spitzer Space Telescope, whichis operated by the Jet Propulsion Laboratory, California Institute ofTechnology, for the National Aeronautics and Space Administration.
| A Spitzer mid-infrared spectral survey of mass-losing carbon stars in the Large Magellanic Cloud
We present a Spitzer Space Telescope spectroscopic survey of mass-losingcarbon stars (and one oxygen-rich star) in the Large Magellanic Cloud(LMC). The stars represent the superwind phase on the asymptotic giantbranch (AGB), which forms a major source of dust for the interstellarmedium (ISM) in galaxies. Bolometric magnitudes indicate progenitormasses of 1.5-2.5Msolar. The spectra cover the wavelengthrange 5-38μm. They show varying combinations of dust continuum, dustemission features (SiC, MgS) and molecular absorption bands(C2H2, HCN). A 10-μm absorption feature isattributed to C3. A weak band at 5.8μm is suggestive ofcarbonyl. The circumstellar 7.5-μm C2H2 band isfound to be stronger at lower metallicity, explained by higher C/Oratios at low metallicity. The J - K versus K - A colours, used toselect the sample, are shown to be relatively insensitive in separatingcarbon versus oxygen-rich AGB stars. The predominance of carbon starstherefore indicates that in the range 1.5-2.5Msolar, LMC AGBstars become carbon-rich before onset of the superwind. A set of fournarrow bands, dubbed the Manchester system, is used to define theinfrared continuum for dusty carbon stars. We investigate the strengthand central wavelength of the SiC and MgS dust bands as a function ofcolour and metallicity. The line-to-continuum ratio of these bands showssome indication of being lower at low metallicity. The MgS band is onlyseen at dust temperatures below 600K. Metal-poor carbon stars can formamorphous carbon dust from self-produced carbon. The formationefficiency of oxygen-rich dust depends more strongly on metallicity. Inlower-metallicity environments, the dust input into the ISM by AGB starsmay be strongly biased towards carbonaceous dust.
| Mid-Infrared Spectroscopy of Carbon Stars in the Small Magellanic Cloud
We have observed a sample of 36 objects in the Small Magellanic Cloud(SMC) with the Infrared Spectrometer on the Spitzer Space Telescope.Nineteen of these sources are carbon stars. An examination of the near-and mid-infrared photometry shows that the carbon-rich and oxygen-richdust sources follow two easily separated sequences. A comparison of thespectra of the 19 carbon stars in the SMC to spectra from the InfraredSpace Observatory (ISO) of carbon stars in the Galaxy revealssignificant differences. The absorption bands at 7.5 and 13.7 μm dueto C2H2 are stronger in the SMC sample, and theSiC dust emission feature at 11.3 μm is weaker. Our measurements ofthe MgS dust emission feature at 26-30 μm are less conclusive, butthis feature appears to be weaker in the SMC sample as well. All ofthese results are consistent with the lower metallicity in the SMC. Thelower abundance of SiC grains in the SMC may result in less efficientcarbon-rich dust production, which could explain the excessC2H2 gas seen in the spectra. The sources in theSMC with the strongest SiC dust emission tend to have redder infraredcolors than the other sources in the sample, which implies moreamorphous carbon, and they also tend to show stronger MgS dust emission.The weakest SiC emission features tend to be shifted to the blue; thesespectra may arise from low-density shells with large SiC grains.
| The Detection of Crystalline Silicates in Ultraluminous Infrared Galaxies
Silicates are an important component of interstellar dust, and thestructure of these grains (amorphous or crystalline) is sensitive to thelocal physical conditions. We have studied the infrared spectra of asample of ultraluminous infrared galaxies (ULIRGs). Here we report thediscovery of weak, narrow absorption features at 11, 16, 19, 23, and 28μm, characteristic of crystalline silicates, superimposed on thebroad absorption bands at 10 and 18 μm due to amorphous silicates ina subset of this sample. These features betray the presence offorsterite (Mg2SiO4), the magnesium-rich endmember of the olivines. Previously, crystalline silicates have only beenobserved in circumstellar environments. The derived fraction offorsterite to amorphous silicates is typically 0.1 in these ULIRGs. Thisis much larger than the upper limit for this ratio in the interstellarmedium of the Milky Way, 0.01. These results suggest that the timescalefor injection of crystalline silicates into the ISM is short in amerger-driven starburst environment (e.g., as compared to the total timeto dissipate the gas), pointing toward massive stars as a prominentsource of crystalline silicates. Furthermore, amorphization due tocosmic rays, which is thought to be of prime importance for the localISM, lags in vigorous starburst environments.
| The Unusual Silicate Dust around HV 2310, an Evolved Star in the Large Magellanic Cloud
The spectrum of HV 2310, an evolved star in the Large Magellanic Cloud,taken with the Infrared Spectrograph (IRS) on the Spitzer SpaceTelescope, reveals the presence of an optically thin shell of silicatedust with unusual spectral structure in the 10 μm feature: anemission peak at 9.7 μm, a saddle at 10.4 μm, and an extendedshoulder to 11.2 μm. This structure is similar to spectra fromcrystalline silicate grains, and of the available optical constants,forsterite provides the best fit. The spectrum also shows structure at14 μm that may arise from an unidentified dust feature.
| R CrB Candidates in the Small Magellanic Cloud: Observations of Cold, Featureless Dust with the Spitzer Infrared Spectrograph
We observed 36 evolved stars in the Small Magellanic Cloud (SMC) usingthe low-resolution mode of the Infrared Spectrograph (IRS) on theSpitzer Space Telescope. Two of these stars, MSX SMC 014 and 155, havenearly featureless spectral energy distributions over the IRS wavelengthrange (5.2-35 μm) and Fν peaking at ~8-9 μm. Thedata can be fit by sets of amorphous carbon shells or by single 600-700K blackbodies. The most similar spectra found in extant spectraldatabases are of R CrB, although the spectral structure seen in R CrBand similar stars is much weaker or absent in the SMC sources. Both SMCstars show variability in the near-infrared. Ground-based visual spectraconfirm that MSX SMC 155 is carbon-rich, as expected for R CrB (RCB)stars, and coincides with an object previously identified as an RCBcandidate. The temperature of the underlying star is lower for MSX SMC155 than for typical RCB stars. The strength of the C2 Swanbands and the low temperature suggest that it may be a rare DY Per-typestar, only the fifth such identified. MSX SMC 014 represents a new RCBcandidate in the SMC, bringing the number of RCB candidates in the SMCto six. It is the first RCB candidate discovered with Spitzer and thefirst identified by its infrared spectral characteristics rather thanits visual variability.
| The Detection of Silicate Emission from Quasars at 10 and 18 Microns
We report the spectroscopic detection of silicate emission at 10 and 18μm in five PG quasars, the first detection of these two features ingalaxies outside the Local Group. This finding is consistent with theunification model for active galactic nuclei (AGNs), which predicts thatan AGN torus seen pole-on should show a silicate emission feature in themid-infrared. The strengths of the detected silicate emission featuresrange from 0.12 to 1.25 times the continuum at 10 μm and from 0.20 to0.79 times the continuum at 18 μm. The silicate grain temperaturesinferred from the ratio of 18 μm to 10 μm silicate features underthe assumption of optically thin emission range from 140 to 220 K.
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| The Serendipitous Discovery of a Debris Disk around the A Dwarf HD 46190
The Infrared Spectrograph on the Spitzer Space Telescope has observedseveral A dwarfs as potential standards and cross-calibrators, and oneof these stars, HD 46190, shows the spectroscopic signature of a debrisdisk. The disk produces a spectral excess that can be fitted with a coolblackbody of ~81 K. If the emitting particles are spherical blackbodies,they would lie at a distance of ~82 AU from the central star. Thespectrum from the disk can also be fitted with a spectrum risingproportionally with wavelength, and this spectral behavior is consistentwith material falling into the inner disk as a result ofPoynting-Robertson drag.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Radial Velocities, Spectral Types, and Luminosity Classes of 820 Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1950ApJ...112...48M&db_key=AST
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