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Absolute Physical Calibration in the Infrared
We determine an absolute calibration for the Multiband ImagingPhotometer for Spitzer 24 μm band and recommend adjustments to thepublished calibrations for Two Micron All Sky Survey (2MASS), InfraredArray Camera (IRAC), and IRAS photometry to put them on the same scale.We show that consistent results are obtained by basing the calibrationon either an average A0V star spectral energy distribution (SED), or byusing the absolutely calibrated SED of the Sun in comparison withsolar-type stellar photometry (the solar analog method). After therejection of a small number of stars with anomalous SEDs (or badmeasurements), upper limits of ~1.5% root mean square (rms) are placedon the intrinsic infrared (IR) SED variations in both A-dwarf andsolar-type stars. These types of stars are therefore suitable asgeneral-purpose standard stars in the IR. We provide absolutelycalibrated SEDs for a standard zero magnitude A star and for the Sun toallow extending this work to any other IR photometric system. They allowthe recommended calibration to be applied from 1 to 25 μm with anaccuracy of ~2%, and with even higher accuracy at specific wavelengthssuch as 2.2, 10.6, and 24 μm, near which there are directmeasurements. However, we confirm earlier indications that Vega does notbehave as a typical A0V star between the visible and the IR, making itproblematic as the defining star for photometric systems. Theintegration of measurements of the Sun with those of solar-type starsalso provides an accurate estimate of the solar SED from 1 through 30μm, which we show agrees with theoretical models.
| 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.
| Debris Disk Evolution around A Stars
We report 24 and/or 70 μm measurements of ~160 A-type main-sequencestars using the Multiband Imaging Photometer for Spitzer (MIPS). Theirages range from 5 to 850 Myr, based on estimates from the literature(cluster or moving group associations) or from the H-R diagram andisochrones. The thermal infrared excess is identified by comparing thedeviation (~3% and ~15% at the 1 σ level at 24 and 70 μm,respectively) between the measurements and the synthetic Kuruczphotospheric predictions. Stars showing excess infrared emission due tostrong emission lines or extended nebulosity seen at 24 μm areexcluded from our sample; therefore, the remaining infrared excesses arelikely to arise from circumstellar debris disks. At the 3 σconfidence level, the excess rate at 24 and 70 μm is 32% and >=33%(with an uncertainty of 5%), considerably higher than what has beenfound for old solar analogs and M dwarfs. Our measurements placeconstraints on the fractional dust luminosities and temperatures in thedisks. We find that older stars tend to have lower fractional dustluminosity than younger ones. While the fractional luminosity from theexcess infrared emission follows a general 1/t relationship, the valuesat a given stellar age vary by at least 2 orders of magnitude. We alsofind that (1) older stars possess a narrow range of temperaturedistribution peaking at colder temperatures, and (2) the disk emissionat 70 μm persists longer than that at 24 μm. Both results suggestthat the debris disk clearing process is more effective in the innerregions.
| The European Large-Area ISO Survey (ELAIS): the final band-merged catalogue
We present the final band-merged European Large-Area ISO Survey (ELAIS)Catalogue at 6.7, 15, 90 and 175 μm, and the associated data at U,g', r', i', Z, J, H, K and 20 cm. The origin of the survey, infrared andradio observations, data-reduction and optical identifications arebriefly reviewed, and a summary of the area covered and the completenesslimit for each infrared band is given. A detailed discussion of theband-merging and optical association strategy is given. The totalCatalogue consists of 3762 sources. 23 per cent of the 15-μm sourcesand 75 per cent of the 6.7-μm sources are stars. For extragalacticsources observed in three or more infrared bands, colour-colour diagramsare presented and discussed in terms of the contributing infraredpopulations. Spectral energy distributions (SEDs) are shown for selectedsources and compared with cirrus, M82 and Arp220 starburst, and activegalactic nuclei (AGN) dust torus models.Spectroscopic redshifts are tabulated, where available. For the N1 andN2 areas, the Isaac Newton Telescope ugriz Wide Field Survey permitsphotometric redshifts to be estimated for galaxies and quasars. Theseagree well with the spectroscopic redshifts, within the uncertainty ofthe photometric method [~10 per cent in (1 +z) for galaxies]. Theredshift distribution is given for selected ELAIS bands andcolour-redshift diagrams are discussed.There is a high proportion of ultraluminous infrared galaxies(log10 of 1-1000 μm luminosity Lir > 12.22)in the ELAIS Catalogue (14 per cent of 15-μm galaxies with known z),many with Arp220-like SEDs. 10 per cent of the 15-μm sources aregenuine optically blank fields to r'= 24: these must have very highinfrared-to-optical ratios and probably have z > 0.6, so arehigh-luminosity dusty starbursts or Type 2 AGN. Nine hyperluminousinfrared galaxies (Lir > 13.22) and nine extremely redobjects (EROs) (r-K > 6) are found in the survey. The latter areinterpreted as ultraluminous dusty infrared galaxies at z~ 1. The largenumbers of ultraluminous galaxies imply very strong evolution in thestar formation rate between z= 0 and 1. There is also a surprisinglylarge population of luminous (Lir > 11.5), cool(cirrus-type SEDs) galaxies, with Lir-Lopt > 0,implying AV > 1.
| The Nature of the Mid-Infrared Population from Optical Identifications of the ELAIS-S1 Sample
We present a multiwavelength catalog (15 μm, R-band, K-band, and 1.4GHz flux) plus spectroscopic identifications for 406 15 μm sourcesdetected in the European Large Area ISO Survey (ELAIS) region S1, overthe flux density range 0.5
| Fe II/Mg II Emission-Line Ratio in High-Redshift Quasars
We present results of the analysis of near-infrared spectroscopicobservations of six high-redshift quasars (z>~4), emphasizing themeasurement of the ultraviolet Fe II/Mg II emission-line strength toestimate the beginning of intense star formation in the early universe.To investigate the evolution of the Fe II/Mg II ratio over a wider rangein cosmic time, we measured this ratio for composite quasar spectra thatcover a redshift range 0<~z<~5 with nearly constant luminosity, aswell as for those that span ~6 orders of magnitude in luminosity. Adetailed comparison of the high-redshift quasar spectra with those oflow-redshift quasars with comparable luminosity shows essentially thesame Fe II/Mg II emission ratios and very similar continuum and linespectral properties, i.e., a lack of evolution of the relativeiron-to-magnesium abundance of the gas in bright quasars since z~=5.Current nucleosynthesis and stellar evolution models predict thatα-elements such as magnesium are produced in massive stars endingin Type II supernovae, while iron is formed predominantly in Type Iasupernovae with intermediate-mass progenitors. This results in an ironenrichment delay of ~0.2-0.6 Gyr. We conclude that intense starformation activity in the host galaxies of z>~4 quasars must havestarted already at an epoch corresponding to zf~=6-9, whenthe age of the universe was ~0.5 Gyr (H0=72 km s-1Mpc-1, ΩM=0.3,ΩΛ=0.7). This epoch corresponds well to thereionization era of the universe.Based on observations collected at the Cerro Tololo Inter-AmericanObservatory, Chile, at the European Southern Observatory, Paranal,Chile, and the W. M. Keck Observatory, Hawaii.
| A new method for ISOCAM data reduction - I. Application to the European Large Area ISO Survey Southern Field: method and results
We develop a new data reduction technique for ISOCAM LW data and applyit to the European Large Area ISO Survey (ELAIS) LW3 (15-μm)observations in the southern hemisphere (S1). This method, known as LARItechnique and based on the assumption of the existence of two differenttime-scales in ISOCAM transients (accounting for either fast or slowdetector response), is particularly designed for the detection of faintsources. In the ELAIS S1 field we obtain a catalogue of 462 15-μmsources with signal-to-noise ratios >=5 and flux densities in therange 0.45-150mJy (filling the whole flux range between the Deep ISOCAMSurveys and the IRAS Faint Source Survey). The completeness at differentflux levels and the photometric accuracy of this catalogue are testedwith simulations. Here we present a detailed description of the methodand discuss the results obtained by its application to the S1 LW3 data.
| High-resolution imaging of ultracompact HII regions. III. G11.11-0.40 and G341.21-0.21
We present the first near-infrared images of the two massive southernstar-forming regions G11.11-0.40 and G341.21-0.21, obtained withadaptive optics at sub-arcsecond resolution. Together with conventionalnarrow-band near-infrared images and polarization maps, mid-infrareddata, millimetre and radio data, we were able to determine themorphological structure and to constrain the stellar content of theregions. In both cases the molecular cloud cores have masses of about500 Msun} and contain clusters of OB stars. This supports theview that massive stars do not form in isolation. In the case ofG11.11-0.40 we could identify the central O star responsible for theionization of the ultracompact Hii region. Our results for G341.21-0.21indicate that this source is a precursor of an ultracompact Hii region.Based on observations collected at the European Southern Observatory, LaSilla, Chile. Based on observations collected at the DSAZ Calar Alto,Spain.
| Determination of the temperatures of selected ISO flux calibration stars using the Infrared Flux Method
Effective temperatures for 420 stars with spectral types between A0 andK3, and luminosity classes between II and V, selected for a fluxcalibration of the Infrared Space Observatory, ISO, have been determinedusing the Infrared Flux Method (IRFM). The determinations are based onnarrow and wide band photometric data obtained for this purpose, andtake into account previously published narrow-band measures oftemperature. Regression coefficients are given for relations between thedetermined temperatures and the photometric parameters (B2-V1), (b-y)and (B-V), corrected for interstellar extinction through use ofHipparcos parallaxes. A correction for the effect of metallicity on thedetermination of integrated flux is proposed. The importance of aknowledge of metallicity in the representation of derived temperaturesfor Class V, IV and III stars by empirical functions is discussed andformulae given. An estimate is given for the probable error of eachtemperature determination. Based on data from the ESA HipparcosAstrometry Satellite.
| JHKLM standard stars in the ESO system
A list of 199 standard stars suitable for the ESO standard photometricsystem at JHKLM is given. Faint stars (although brighter than K = 7.7)to be used on larger telescopes are included. This list is based on ananalysis of all infrared photometric observations carried out at LaSilla from 1979 until 1989 inclusive. The accuracy of the data (about0.02 mag. at J, H, K, L, and M) is similar to the one achieved at SAAOand CTIO. Comparisons with these systems, as well as with the AAO andMSSO systems, are made: it is shown that the ESO system is very close tothe other ones, with the exception of CTIOs.
| Southern JHKL standards
The basis for the current SAAO standard photometric system at JHKL isgiven. This depends on an extensive investigation involving 230 starsdistributed around the sky. The accuracy is estimated at + or - 0.02 magfor J, H and K and + or - 0.05 mag for L.
| 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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