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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.
| Near-Infrared Photometric Survey of Proto-planetary Nebula Candidates
We present JHK' photometric measurements of 78 objects mostly consistingof proto-planetary nebula candidates. Photometric magnitudes aredetermined by means of imaging and aperture photometry. Unlike theobservations with a photometer with a fixed-sized beam, the method ofimaging photometry permits accurate derivation of photometric values,because the target sources can be correctly identified and confusionwith neighboring sources can be easily avoided. Of the 78 sourcesobserved, we report nearly 10 cases in which the source seems to havebeen misidentified or confused by nearby bright sources. We also presentnearly two dozen cases in which the source seems to have indicated avariability that prompts a follow-up monitoring. There are also a fewsources that show previously unreported extendedness. In addition, wepresent H-band finding charts of the target sources.
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| Stellar Companions and the Age of HD 141569 and Its Circumstellar Disk
We investigate the stellar environment of the β Pictoris-like starHD 141569 with optical spectroscopy and near-infrared imaging. The B9.5Ve primary and two other stars (types M2 and M4) both located inprojection less than 9" away have the same radial velocity and propermotion and therefore almost certainly form a triple star system. Fromtheir X-ray flux, lithium absorption, and location on pre-main-sequenceevolutionary tracks, the companions appear to be 5 Myr old. HD 141569Ais now one of the few main-sequence stars with a circumstellar disk thathas a well-determined age. The circumstellar disk is composed ofsecondary debris material, thus placing an upper limit on the timeneeded for disk processing. These three stars may be part of anassociation of young stars.
| The diversity of SCUBA-selected galaxies
We present extensive observations of a sample of distant, submillimetre(submm) galaxies detected in the field of the massive cluster lensAbell1835, using the Submm Common-User Bolometer Array (SCUBA). Taken inconjunction with earlier observations of other submm-selected sources,we now have detailed, multiwavelength observations of seven examples ofthe submm population, having exploited the combination of achromaticamplification by cluster lenses and lavish archival data sets. Thesesources, all clearly at z>~1, illustrate the wide range in the radioand optical properties of distant submm-selected galaxies. We includedetailed observations of the first candidate `pure' starburst submmgalaxy at high redshift, a z=2.56 interacting galaxy which shows noobvious sign of hosting an AGN. The remaining sources have varyingdegrees of inferred AGN activity (three out of seven of the mostluminous show some evidence of the presence of an AGN), although evenwhen an AGN is obviously present it is still not apparent whetherreprocessed radiation from this source dominates the submm emission. Incontrast with the variation in the spectral properties, we seerelatively homogeneous morphologies for the population, with a largefraction of merging or interacting systems. Our study shows thatvirtually identical spectral energy distributions are seen for galaxiesthat exhibit strikingly different optical/UV spectral-linecharacteristics. We conclude that standard optical/UV spectralclassifications are misleading when applied to distant, highly obscuredgalaxies, and that we must seek other means of determining the variouscontributions to the overall energy budget of submm galaxies and henceto the far-infrared extragalactic background.
| Barnard's Merope Nebula (IC 349): an Interstellar Interloper
Barnard's Merope Nebula (IC 349) is the optically brightest portion ofthe diffuse nebulosity that envelops the Pleaides but is notmorphologically similar to those nebulae. Knowledge of its true spacemotion can help clarify whether the object has a kinematic associationand possibly a common origin with the Pleiades. Here we report a meanradial velocity result obtained in 1996 from spectra where v_hel=-44.4km s^-1 and sigma_v=5.42 km s^-1 (N=5). The radial velocity result ispresented along with recent values for the object's proper motion,yielding its space motion vector. Galactic space velocity components (U,V, W)=(50.6+/-5.3, -10.3+/-6.7, 11.3+/-6.4) km s^-1, referred to theLSR, were calculated for the object. In addition, the region wasobserved in the near-infrared to determine if a protostellar object ispresent within the dusty envelope of the nebula; to an equivalentluminosity upper limit of L=0.23+/-0.05 L_solar, none was observed.These results suggest that IC 349 is kinematically unrelated to thePleiades and that it does not harbor a protostellar object in its dustyinterior.
| Towards a fundamental calibration of stellar parameters of A, F, G, K dwarfs and giants
I report on the implementation of the empirical surface brightnesstechnique using the near-infrared Johnson broadband { (V-K)} colour assuitable sampling observable aimed at providing accurate effectivetemperatures of 537 dwarfs and giants of A-F-G-K spectral-type selectedfor a flux calibration of the Infrared Space Observatory (ISO). Thesurface brightness-colour correlation is carefully calibrated using aset of high-precision angular diameters measured by moderninterferometry techniques. The stellar sizes predicted by thiscorrelation are then combined with the bolometric flux measurementsavailable for a subset of 327 ISO standard stars in order to determineone-dimensional { (T, V-K)} temperature scales of dwarfs and giants. Theresulting very tight relationships show an intrinsic scatter induced byobservational photometry and bolometric flux measurements well below thetarget accuracy of +/- 1 % required for temperature determinations ofthe ISO standards. Major improvements related to the actual directcalibration are the high-precision broadband { K} magnitudes obtainedfor this purpose and the use of Hipparcos parallaxes for dereddeningphotometric data. The temperature scale of F-G-K dwarfs shows thesmallest random errors closely consistent with those affecting theobservational photometry alone, indicating a negligible contributionfrom the component due to the bolometric flux measurements despite thewide range in metallicity for these stars. A more detailed analysisusing a subset of selected dwarfs with large metallicity gradientsstrongly supports the actual bolometric fluxes as being practicallyunaffected by the metallicity of field stars, in contrast with recentresults claiming somewhat significant effects. The temperature scale ofF-G-K giants is affected by random errors much larger than those ofdwarfs, indicating that most of the relevant component of the scattercomes from the bolometric flux measurements. Since the giants have smallmetallicities, only gravity effects become likely responsible for theincreased level of scatter. The empirical stellar temperatures withsmall model-dependent corrections are compared with the semiempiricaldata by the Infrared Flux Method (IRFM) using the large sample of 327comparison stars. One major achievement is that all empirical andsemiempirical temperature estimates of F-G-K giants and dwarfs are foundto be closely consistent between each other to within +/- 1 %. However,there is also evidence for somewhat significant differential effects.These include an average systematic shift of (2.33 +/- 0.13) % affectingthe A-type stars, the semiempirical estimates being too low by thisamount, and an additional component of scatter as significant as +/- 1 %affecting all the comparison stars. The systematic effect confirms theresults from other investigations and indicates that previousdiscrepancies in applying the IRFM to A-type stars are not yet removedby using new LTE line-blanketed model atmospheres along with the updatedabsolute flux calibration, whereas the additional random component isfound to disappear in a broadband version of the IRFM using an infraredreference flux derived from wide rather than narrow band photometricdata. Table 1 and 2 are only available in the electronic form of thispaper
| Young red supergiants and the near-infrared light appearance of disk galaxies
We have searched for spatial variations in the 2.3 m photometric COindex within the disks of three nearby galaxies. This index measures thestrength of the absorption bands of molecular CO in stellar atmospheresand is strong in cool, low surface gravity stars, reaching the largestvalues for red supergiants. We observe significant spatial CO indexvariations in two galaxies, indicating that the dominant stellarpopulation in the NIR is not everywhere the same. Central CO index peaksare present in two galaxies; these could be due to either metallicitygradients or to recent star formation activity. In addition, significantazimuthal CO index variations are observed in one. Because strongazimuthal metallicity gradients are physically implausible in diskgalaxies, these features are most naturally explained by the presence ofa young stellar population. The fraction of 2 m light due to youngstellar populations in star-forming regions can be calculated from ourdata. Overall, young stellar populations can contribute 3 percent of theNIR flux of a (normal) galaxy, which is consistent with other globalproperties. Locally, this fraction may rise to 33 percent. Thus, youngstars do not dominate the total NIR flux, but can be locally dominant instar-forming regions, and can bias estimates of spiral arm amplitude orother nonaxisymmetric structures in galaxies' mass distributions.
| The near-infrared extinction law and limits on the pre-main-sequence population of the Rho Ophiuchi dark cloud
We describe new techniques to measure the NIR extinction law and toplace limits on the premain-sequence stellar population of a dark cloud.We analyze JHK imaging data for the central 1 sq deg of the Rho Ophiuchicloud core and show that nearly all stars projected onto regions of lowCS intensity, ICS 10 K km/s, are background stars. Most sources atlarger CS intensities lie within cloud material. We use the backgroundstars to derive the slope of the NIR extinction law, E(J-H)/E(H-K) =1.57 +/- 0.03. This result is consistent with previous extinction lawsbut has a factor of two to three smaller uncertainty. The new Rho Ophextinction law yields strong constraints on the number of previouslyundiscovered premain-sequence stars in the cloud, 46 +/- 11, and thenumber of previously undiscovered young stars with near-IR excesses, 15+/- 4. Neither limit exceeds the number of known premain-sequence starsin the cloud about 100. Thus, current samples of premain-sequence starsare reasonably complete for K = 14 or less.
| A Near-Infrared Study of the K3-50 Region of High-Mass Star Formation
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...460..744H
| 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.
| The faintest stars - Infrared photometry, spectra, and bolometric magnitude
Infrared JHKLL-prime photometry, and low resolution IF spectra arepresented for the faintest stars. The stellar H2O bands which dominatethe atmospheres of these stars were studied. L band fluxes of thesestars are considerably depressed relative to L prime fluxes by thepresence of stellar H2O absorption. Strong H2O absorption is observed inthese infrared spectra. The amount of flux which is 'overcounted' whenH2O absorption bands are ignored is examined. Bolometric fluxes arecalculated using broadband photometry alone, requiring a correction ofonly approximately 5 percent to 10 percent. Photometric and spectraldata is used to evaluate bolometric corrections and magnitudes of asample of late type M dwarfs.
| 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.
| JHK infrared standard stars and absolute calibration of the San Pedro Martir Observatory (OAN) photometric system
A set of reliable standard stars for the JHK photometric system of theSan Pedro Martir National Observatory (OAN) is presented. Meanextinction coefficients for the near-IR of this site are first reportedhere; effective wavelengths and flux calibration from observations ofVega are derived for the various bandpasses. Comparison with otherwidely used photometric systems is presented and, finally,transformation equations to CIT, AAO, ESO, and Johnson's systems arederived.
| The accuracy of infrared photometry with arrays
The photometric accuracy and repeatability of an InSb array in theinfrared camera IRCAM is investigated. Measurements of standard starsare described; these were made using the United Kingdom Infrared 3.8-mTelescope (UKIRT) over five nights in May 1988, as part of anobservational program on globular clusters. Observations were made atwavelengths of 1.25 (J) and 2.2 microns (K). The results show clearlythat the camera-array combination is capable of a photometric accuracyof better than 1 percent when the standard-star images obtained withshort on-chip exposure (0.5 sec) are flat fielded with long on-chipexposure (7-50 sec) sky flats. Linearity corrections determined in thelaboratory were applied to the data and there was no evidence ofresidual nonlinearity of greater than 2 percent over the magnitude range6.5-13.0 m. The range of mean nightly zero points at K during the fivenights was 0.03 m, showing that both the site and the camera system werevery stable over this period. At J the zero points were less welldetermined and had twice this range during three nights.
| Infrared spectroscopy of the ultraluminous IRAS galaxy 14348-1447 - A distant detection of H2 line emission
The 1-0 S(1) line of molecular hydrogen has been detected in the mostdistant "ultraluminous" interacting IRAS galaxy 14348-1447. TheH2 is believed to be excited by shock waves, in analogy toother interacting and merging galaxies that have been studied in moredetail. A bright Paα line was also detected, possibly indicatingthat a burst of star formation resulting from the interaction is welladvanced.
| The cool components of symbiotic stars. II - Infrared photometry
This paper reports IR photometry for a sample of symbiotic binaries andK-M comparison stars. Measured CO absorption-band strengths of the coolcomponents in symbiotic stars generally are comparable to those ofsingle red giant and bright giant stars, but it is difficult todetermine the luminosity classes of these objects from their photometricCO indices. The 12-micron excesses observed in symbiotics require theircool components to lose mass more rapidly than do single red giantstars. Thus, mass-loss rates derived for red giants in close binarysystems may not be accurate estimates for mass loss in single redgiants.
| The surface composition of Charon - Tentative identification of water ice
The Mar. 3, 1987, Charon occultation by Pluto was observed in theinfrared at 1.5, 1.7, 2.0, and 2.35 micrometers. Subtraction of fluxesmeasured between second and third contacts from measurements made beforeand after the event has yielded individual spectral signatures for eachbody at these wavelengths. Charon's surface appears depleted in methanerelative to Pluto. Constancy of flux at 2.0 micrometers throughout theevent shows that Charon is effectively black at this wavelength, whichis centered on a very strong water absorption band. Thus, themeasurements suggest the existence of water ice on Pluto's moon.
| 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.
| A Finding List of Early-Type Stars in Regions of Intermediate Galactic Latitude
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...157..327U&db_key=AST
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Datos observacionales y astrométricos
| Constelación: | Virgo |
| Ascensión Recta: | 14h43m46.44s |
| Declinación: | -02°30'20.0" |
| Magnitud Aparente: | 7.227 |
| Distancia: | 128.535 parsecs |
| Movimiento Propio en Ascensión Recta: | -31.8 |
| Movimiento Propio en Declinación: | -24.7 |
| B-T magnitude: | 7.434 |
| V-T magnitude: | 7.245 |
Catálogos y designaciones:
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INHABITED SKY
