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Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. I. The Stellar Calibrator Sample and the 24 μm Calibration
We present the stellar calibrator sample and the conversion frominstrumental to physical units for the 24 μm channel of the MultibandImaging Photometer for Spitzer (MIPS). The primary calibrators are Astars, and the calibration factor based on those stars is4.54×10-2 MJy sr-1 (DNs-1)-1, with a nominal uncertainty of 2%. Wediscuss the data reduction procedures required to attain this accuracy;without these procedures, the calibration factor obtained using theautomated pipeline at the Spitzer Science Center is 1.6%+/-0.6% lower.We extend this work to predict 24 μm flux densities for a sample of238 stars that covers a larger range of flux densities and spectraltypes. We present a total of 348 measurements of 141 stars at 24 μm.This sample covers a factor of ~460 in 24 μm flux density, from 8.6mJy up to 4.0 Jy. We show that the calibration is linear over that rangewith respect to target flux and background level. The calibration isbased on observations made using 3 s exposures; a preliminary analysisshows that the calibration factor may be 1% and 2% lower for 10 and 30 sexposures, respectively. We also demonstrate that the calibration isvery stable: over the course of the mission, repeated measurements ofour routine calibrator, HD 159330, show a rms scatter of only 0.4%.Finally, we show that the point-spread function (PSF) is well measuredand allows us to calibrate extended sources accurately; InfraredAstronomy Satellite (IRAS) and MIPS measurements of a sample of nearbygalaxies are identical within the uncertainties.
| Calibration of the Infrared Telescope Facility National Science Foundation Camera Jupiter Galileo Data Set
The NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, setaside some time on about 500 nights from 1995 to 2002, when the NSFCAMfacility infrared camera was mounted and Jupiter was visible, for astandardized set of observations of Jupiter in support of the Galileomission. The program included observations of Jupiter, nearby referencestars, and dome flats in five filters: narrowband filters centered at1.58, 2.28, and 3.53 μm, and broader L' and M' bands that probe theatmosphere from the stratosphere to below the main cloud layer. Thereference stars were not cross-calibrated against standards. Weperformed follow-up observations to calibrate these stars and Jupiter in2003 and 2004. We present a summary of the calibration of the Galileosupport monitoring program data set. We present calibrated magnitudes ofthe six most frequently observed stars, calibrated reflectivities, andbrightness temperatures of Jupiter from 1995 to 2004, and a simplemethod of normalizing the Jovian brightness to the 2004 results. Ourstudy indicates that the NSFCAM's zero-point magnitudes were not stablefrom 1995 to early 1997, and that the best Jovian calibration possiblewith this data set is limited to about +/-10%. The raw images andcalibration data have been deposited in the Planetary Data System.
| L' and M' standard stars for the Mauna Kea Observatories Near-Infrared system
We present L' and M' photometry, obtained at the United Kingdom InfraredTelescope (UKIRT) using the Mauna Kea Observatories Near-Infrared(MKO-NIR) filter set, for 46 and 31 standard stars, respectively. The L'standards include 25 from the in-house `UKIRT Bright Standards' withmagnitudes deriving from Elias et al. and observations at the InfraredTelescope Facility in the early 1980s, and 21 fainter stars. The M'magnitudes derive from the results of Sinton and Tittemore. We estimatethe average external error to be 0.015 mag for the bright L' standardsand 0.025 mag for the fainter L' standards, and 0.026 mag for the M'standards. The new results provide a network of homogeneously observedstandards, and establish reference stars for the MKO system, in thesebands. They also extend the available standards to magnitudes whichshould be faint enough to be accessible for observations with moderndetectors on large and very large telescopes.
| The enigmatic outburst of V445 Puppis - A possible helium nova?
JHK spectroscopic and photometric observations are reported for theenigmatic, nova-like, variable V445 Puppis which erupted at the end of2000. The near-IR spectra are hydrogen-deficient and unusually rich inCI lines. The important CI lines are found to be positioned at 1.133,1.166, 1.175, 1.189, 1.26 and 1.689 mu m. Model calculations for the CIlines are done to make the identification of the lines secure.Photometric data, taken on January 2.90 UT, 2001 shortly after theoutburst, show the formation of an optically thin dust shell around V445Puppis. The temperature and upper limit for the mass of the dust shellare estimated to be 1800 K and Mdust ~ 10-9Msun respectively. A subsequent episode of massive dustformation - indicated by the observed, deep visual dimming - is alsoseen in JHK images of early November 2001. V445 Puppis has shown twounusual properties for a nova: (i) the hydrogen-deficiency and He/Cenrichment of the object as seen from optical and IR data and (ii)synchrotron radio emission which was detected nearly a year after itsoutburst by other workers. The strange nature of the object is discussedand it is shown that it is difficult to place it in the known categoriesof eruptive variables viz. novae (classical, recurrent or symbiotic);born-again AGB stars; the new class of eruptive variables like V838 Mon;and RCB/HdC stars. Tentative evidence for an accretion disk and binarityof the V445 Puppis system is presented. It is debated whether V445Puppis is a rare helium nova or a unique object.
| Deep Keck Adaptive Optics Searches for Extrasolar Planets in the Dust of ? Eridani and Vega
A significant population of nearby stars have strong far-infraredexcesses, now known to be due to circumstellar dust in regions analogousto the Kuiper Belt of our solar system, although orders of magnitudemore dense. Recent submillimeter and millimeter imaging of these systemsresolves the circumstellar dust and reveals complex structures, often inthe form of rings with azimuthal nonaxisymmetric variations. Thisstructure might well be due to the presence of embedded brown dwarfs orplanets. We have carried out deep adaptive optics imaging of two nearbystars with such asymmetric dust: ? Eri and Vega. Ten and sevencandidate companions were seen in and near the dust rings of ? Eriand Vega, respectively, but second-epoch proper motion measurementsindicate that all are background objects. Around these two stars we canthus exclude planetary companions at spatial scales comparable to theradius of the dust structures to a level of MK=24,corresponding to 5 Jupiter masses, for ? Eri, andMK=19-21, corresponding to 6-8 Jupiter masses, for Vega.
| JHK Standard Stars on the CIT Photometric System
We present a set of 58 stars with JHK standard values on the CIT systemand with a suitable magnitude range for use with array detectors onsmall- to moderate-size telescopes. Each final value is based on six to47 measures (with a mean of 17) obtained on separate nights with the USNaval Observatory (USNO) NICMOS3 (HgCdTe) camera. The objects include 20primary CIT standards from Elias et al. and 38 secondary sourcesselected from the SAAO and UKIRT standards lists, cover a K-magnituderange between 6.0 and 10.8, and lie north of declination -20°. Thestars were reduced to the CIT system as defined by Elias et al.,producing a USNO system that is identical to the near-infrared CITsystem. This work densifies the original CIT system by nearly a factorof 3 and extends its range by about 3 mag. The SAAO and UKIRT standardsare also compared with the CIT system.
| Near infrared coronagraph images of IRC +10216. Faint structures at 1-5arcsec from the central star
We present J, H and K band coronagraph images of the circumstellarenvelope around IRC +10216 (CWLeo) obtained with a near infrared camera, CIAO and the 8.2 mSubaru telescope. A circular occulting mask of 2arcsec in diameter wasused to block out the light from the bright central object. The imagesshow 2 collimated radial structures to the NNW and WNW, 2 fan-likestructures to the S and NE, respectively, and 3 arc-like structures at aradius of 4 to 5 arcsec from the stellar center. We compare thisintermediate size-scale structure to that seen on larger and smallerscales and find evidence for a deviation from spherically symmetricoutflow beginning ~ 150 years ago. Previous near infrared speckleimaging has revealed a complex clumpy structure on a scale of less than200 mas, and it is likely that at least some of the radial features seenin our images could be due to shadowing by dust clumps close to thestar.
| Do galaxy mergers form elliptical galaxies? A comparison of kinematic and photometric properties
We present near-infrared K-band imaging and spectroscopy of a sample ofgalaxy mergers, which we use to derive light profile indices, absolutemagnitudes and central velocity dispersions. We find that the lightdistributions of mergers more nearly resemble those of ellipticals thanthose of bulges, but that the mergers lie well away from the FundamentalPlane defined by the ellipticals. We interpret this as being due toenhancement of the K-band surface brightness of the mergers by asignificant population of supergiant stars, and independent evidence forsuch a population is inferred from measurements of the depth of the2.3-μm CO absorption feature.
| The obscured BLR in the radio galaxy 3C 234
We present spectropolarimetric observations of the radio galaxy 3C 234at optical and, for the first time, near-IR wavelengths. In agreementwith previous observations we detect broad H-alpha in total andpolarized flux, consistent with the scenario in which the central activenucleus is hidden from view and observed via scattered radiation. Wemodel the flux and polarization properties at optical and near-IRwavelengths, which result in a point-source, cone-based scatteringgeometry in the optical and an extended source scattering in thenear-IR, with a dichroic view to the emission regions, which becomesimportant only at the longer wavelengths. From this model we calculatean intrinsic H-alpha luminosity of 4.9 x 10 exp 44 erg/s, and anextinction to the near-IR emission region of 60 mag for A(V). Thescattered radiation also undergoes extinction, this time by 1 mag forA(V), assuming a source function of a typical stellar-subtracted Seyfert1 galaxy. We also require that the scatterers are in bulk radial outflowat approximately 600 km/s to explain an observed increase in theintrinsic polarization of the scattered broad H-alpha line in the redwing, and blueshifted narrowline components in polarized flux.
| Infrared and optical spectroscopy of Type IA supernovae in the nebular phase
We present near-infrared (NIR) spectra for Type Ia supernovae at epochsof 13 to 338d after maximum blue light. Some contemporary opticalspectra are also shown. All the NIR spectra exhibit considerablestructure throughout the J, H and K bands. In particular, they exhibit aflux `deficit' in the J band which persists as late as 175d. This isresponsible for the well-known red J-H colour. To identify the emissionfeatures and test the ^56Ni hypothesis for the explosion and subsequentlight curve, we compare the NIR and optical nebular-phase data with asimple non-LTE nebular spectral model. We find that many of the spectralfeatures are due to iron-group elements, and that the J-band deficit isdue to a lack of emission lines from species that dominate the rest ofthe IR/optical spectrum. Nevertheless, some emission is unaccounted for,possibly due to inaccuracies in the cobalt atomic data. For somesupernovae, blueshifts of 1000-3000 km s^-1 are seen in infrared andoptical features at 3 months. We suggest that this is due to clumping inthe ejecta. The evolution of the cobalt/iron mass ratio indicates that^56Co-decay dominates the abundances of these elements. The absolutemasses of iron-group elements which we derive support the basicthermonuclear explosion scenario for Type Ia supernovae. A core-collapseorigin is less consistent with our data.
| Optical and near-infrared spectropolarimetry of the infrared-luminous galaxy IRAS 23060+0505
We present optical and near-IR spectropolarimetry of the type 2infrared-luminous galaxy IRAS 23060+0505, which clearly shows both broadHα and Paalpha in polarized flux. The full widths at half maximum(FWHM) of these lines are consistent with that of Paalpha in total fluxas measured by Hines. From the ratio of the polarized and total broadHα fluxes, we calculate the intrinsic polarization to be ~25 percent, assuming that the scattering geometry is the same for both thecontinuum and broad-line radiation. We model the flux density andpolarization characteristics as a combination of scattered continuum anda dichroic view of the near-IR-emitting regions through the postulatedtorus, which obscures the type 1 nucleus from the line of sight. Theextinction along the path of the scattered radiation is A_V~2.9 mag,whilst that of the direct view to the near-IR emission region is 20 mag,and to the BLR is ~30 mag, substantially higher than previous estimates.The presence of high extinction along the scattering path may havestrong implications for the observability of scattered optical broadlines in other objects. The calculated broad Hα luminosity is(2.3+/-0.3)x10^44 erg s^-1, consistent with that of QSOs.
| UvbyHbeta_ photometry of main sequence A type stars.
We present Stroemgren uvby and Hbeta_ photometry for a set of575 northern main sequence A type stars, most of them belonging to theHipparcos Input Catalogue, with V from 5mag to 10mag and with knownradial velocities. These observations enlarge the catalogue we began tocompile some years ago to more than 1500 stars. Our catalogue includeskinematic and astrophysical data for each star. Our future goal is toperform an accurate analysis of the kinematical behaviour of these starsin the solar neighbourhood.
| Observation of a Lunar Occultation of T Tauri
We observed the 1994 December 16 (UT) lunar occultation of the binarysystem T Tau in the infrared K and L' bands. T Tau N, the visible lightstar, and T Tau S, the IR luminous companion, appeared unresolved alongthe direction of the occultation. At L', both objects are smaller than 3AU. At K, T Tau N and S are smaller than 1 AU. The naturalinterpretation is that both components are stellar and that theextinction along our line of sight to T Tau S is greater than that to TTau N. At the time of the occultation, the K-band flux of T Tau S haddecreased to nearly the value it had before the flare that began in thelate 1980s while the L'-band flux was still elevated; this flux decreasewith time supports the suggestion published by Ghez et al. in 1991 thatT Tau S experienced a FU Orionis--like outburst.
| Near-IR spectropolarimetry and modelling of NGC 1068
We present new spectropolarimetric data for NGC 1068, including, for thefirst time, coverage in the near-IR. Using these, and other previouslypublished data, we develop a scattering model for NGC 1068, using NGC5548 for the underlying Seyfert 1 continuum spectrum and M31 for thestellar contribution. Although electron scattering is the dominantprocess, if NGC 5548 is typical of Seyfert 1s in the near-IR thenelectron scattering alone cannot be soley responsible for the observedpolarization of NGC 1068 at these wavelengths, and a contribution fromdichroic absorption of the radiation from the IR-emitting regions of theactive nucleus, through the postulated torus, is required. Theextinction in this region is A_V>=45 mag, although we note that theextinction to broad-line region and nucleus is much higher.
| Near Infrared Imaging of Dwarf Ellipticals Irregulars and Blue Compact Galaxies in the Virgo Cluster
New near-IR images are presented for 13 dwarf galaxies in the Virgocluster. Together with previous data these provide a data base of JHKimaging for 26 dwarf ellipticals (dEs), dwarf irregulars (dIs) and bluecompact dwarfs (BCDs). These images show the dIs to be highly asymmetricand unrelaxed, implying that they are dynamically young and unevolved.This is consistent with their blue near-IR and optical-IR colours whichare most easily explained by young stellar populations. The dEs aresymmetrical and apparently relaxed, with very uniform colours indicatingthat they are dominated by old stars. They generally have exponentiallight profiles, but the brighter galaxies tend to exhibit more cuspedlight distributions, similar to the de Vaucouleurs profiles of brightellipticals. The BCDs have moderately asymmetric light profiles, andparadoxically red colours, possibly indicating an intermediate-agestellar population. They are probably dEs which have undergone bursts ofstar formation in the last few X 10^9^ years, whilst the dIs are afundamentally distinct population. Colour gradients are present in manyof the galaxies, invariably in the sense that the nuclei are redder thanthe surrounding galaxy light.
| K'-band observations of the evil eye galaxy: Are the optical and near-infrared dust albedos identical?
New measurements of the reduction of the V-band surface brightnessacross the prominent dust feature in the galaxy NGC 4826 are comparedwith corresponding increases in the V-K' color within the context ofradiative transfer models invoking both absorption and scattering. TheK'-band surface brightness is found to be higher than expected fromstandard dust models. We interpret the difference as resulting from ahigh effective dust albedo at K', with a likely value in excess of 0.8,provided the near-IR extinction curve in NGC 4826 is identical to theGalactic one. The high effective albedo may result from scattering bydust with a maximum grain size at least twice as large as assumed bystandard models, a conclusion already indirectly hinted at by recentstudies of dust star-forming regions and reflection nebulae. At leastpart of the high effective albedo at K' may result from near-IRnonequilibrium continuum emission attributable to very small grains.
| The L1448 Molecular Jet
We have obtained near-infrared images of the L1448 molecular outflowin the J, H, and K bands and through a 1% passband filter centered onthe 2.122 microns V = 1-0 S(1) line of molecular hydrogen. We reportthe discovery of a highly collimated, clumpy, and bipolar molecularhydrogen jet associated with the L1448 molecular outflow. We estimatethat the total H2 luminosity of the L1448 outflow is about0.2 Lsun. Most of the line emission in the northern outflowlobe arises from a narrow, curving filament consisting of a chain ofknots. Some H2 knots and the bow-shaped emission regionsprotruding several arcseconds to the west of the filament may beshocks associated with CO- and SiO-emitting "bullets" seen inmillimeter-wave observations. We interpret the H2 emissionin the context of a jet-driven model for molecular outflows. BrightH2 emission near the molecular "bullets" may be produced byshocks propagating into the moving medium, while the extended andcurving filament may be driven by expanding bow shocks in the wakes ofthe "bullets." A conical 2.2 microns continuum nebula extends from thedriving source of the L1448 outflow toward the blueshifted outflowlobe. Several knots of H2 emission to the northeast of themain L1448 H2 filament may be associated with a separateoutflow emerging from L1448 IRS 3, which we estimate has a totalH2 luminosity of about 0.01 Lsun.
| Variation in the near-infrared surface brightness distribution of the bipolar nebula OH 231.8 + 4.2
Near-infrared images of the bipolar nebula OH 231.8 + 4.2 obtained overa 3 yr period suggest that its surface brightness distribution varieswith time. We present a model in which the variations are explained bythe differences in travel times for photons scattered off dust grains atvarious positions along the polar axis of the nebula. This formulationallows us to determine the brightness fluctuations and heliocentricdistance (d) of the embedded source and the inclination of the nebula(i). To explain the observed variations, the central star must possess a2.2-micron amplitude of about 2 mag - larger than determined previouslyfrom aperture photometry and consistent with the classification of thecentral star as a Mira variable, rather than as a supergiant. Weestimated d of about 1300 pc, and i of greater than about 35 deg withthe south lobe further away. Comparison with published 2.2-micronphotometry suggests that the nebula is brighter at maximum and shows alarger variation in integrated surface brightness than measured about 10yr ago. These results demonstrate the potential utility of long-termmonitoring, via near-IR imaging, of reflection nebulae around variablestars.
| Infrared mapping of M82 - A starburst in an edge-on barred galaxy
New 1-30-micron images of the starburst galaxy M82 are presented. Theappearance of M82 at 2 microns indicates that a bar about 1 kpc long islocated at its center. This bar may dramatically influence the gasdynamics and may have caused the formation of the central gas and dusttoroid associated with the luminous episode of star formation. Themid-IR maps define the structure of the toroid out to 30 microns andshow that the extent of the emitting region is at least 1.3 kpc. Theabsorption optical depth determined from 1-2 micron colors correspondsto A(v) less than about 8 and is distributed in a ridge spanning thestarburst region and closely resembling the distribution of H I opticaldepth. Finally, the contribution that very small grains may make to the10-micron emission is considered, and it is concluded, by comparison toGalactic H II regions, that their mid-IR emission is significant.
| The source of flux for a red nebulous object in NGC 2264
Inspection of red prints of the NGC 2264 region show three red nebulaeabout 17 arcmin south of S Mon. The red nebulae are spatially coincidentwith a molecular cloud and far-infrared emission. The red nebulae weresearched for their source of flux, and two point sources separated by2.8 arcsec at a position angle of 265 deg were found. These sources arelocated in the molecular cloud and at the far-infrared emission peak.The eastern source has an effective temperature less than 2800 K, andthe western source has an effective temperature less than 10,000 K. Thetotal luminosity of the combined stars is about 550 solar luminosities.
| Color evolution in high-redshift galaxies
The Simultaneous Photometer for Infrared and Visual Light has been usedto observe 40 radio- and 39 optically-selected giant elliptical galaxiesof known redshift in the 0.019-1.6 range. There is no indication in theresults obtained of differences between the colors of radio and nonradiogalaxies, with the exception of H-K in the z=0.2-0.4 range; the H-Kcolor is best fitted by a passively evolving model with little residualstar formation. Some galaxies exhibit strong blueward deviations. Thisbehavior is most easily explained by star formation episodes involvingsmall fractions of the total number of stars.
| Infrared and optical observations of low-activity comets, P/Arend-Rigaux (1984k) and P/Neujmin 1 (1984c)
Optical observations obtained with the 1.2-m UK Schmidt telescope, andIR observations obtained with the 2.8-m United Kingdom InfraredTelescope on Mauna Kea, Hawaii in 1984, of Comets P/Arend-Rigaux 1984kand P/Neujmin 1 1984c are presented. Data indicate that Arend-Rigaux isan active comet with an appreciable dust coma and anisotropic dustemission. An effective radius of about 4.5 and an albedo of 0.06 + or0.03 are found at 1.25 microns. Comet Neujmin 1 showed only minoractivity and is suggested to be a transitional object. Some data onComet Shoemaker 1984s are also presented, and all three cometsinvestigated have colors similar to C-type or RD-type asteroidssuggesting dark carbonaceous material.
| Infrared standard stars
The results of an observational program aimed at setting up a network offaint near-infrared standards of sufficient accuracy are reported. Thenetwork covers both northern and southern hemispheres and includesstandards red enough to provide at least a limited check on colortransformations. The standards are set up at J (1.2 micron), H (1.6micron), K (2.2 microns), and L (3.5 microns), and their H2O and COmolecular absorption indices are determined. The problem of colortransformations between observatories is discussed briefly. Allmagnitudes presented are transformed to the natural system defined bythe CIT observations.
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Dades d'Observació i Astrometria
| Constel·lació: | Hydra |
| Ascensió Recta: | 09h01m38.01s |
| Declinació: | -01°28'34.8" |
| Magnitud Aparent: | 7.356 |
| Distancia: | 147.275 parsecs |
| Moviment propi RA: | -16.3 |
| Moviment propi Dec: | -12 |
| B-T magnitude: | 7.531 |
| V-T magnitude: | 7.371 |
Catàlegs i designacions:
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