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Dust-enshrouded giants in clusters in the Magellanic Clouds
We present the results of an investigation of post-Main Sequence massloss from stars in clusters in the Magellanic Clouds, based around animaging survey in the L'-band (3.8 μm) performed with the VLT at ESO.The data are complemented with JHKs (ESO and 2MASS) andmid-IR photometry (TIMMI2 at ESO, ISOCAM on-board ISO, and data fromIRAS and MSX). The goal is to determine the influence of initialmetallicity and initial mass on the mass loss and evolution during thelatest stages of stellar evolution. Dust-enshrouded giants areidentified by their reddened near-IR colours and thermal-IR dust excessemission. Most of these objects are Asymptotic Giant Branch (AGB) carbonstars in intermediate-age clusters, with progenitor masses between 1.3and ~5 M_ȯ. Red supergiants with circumstellar dust envelopes arefound in young clusters, and have progenitor masses between 13 and 20M_ȯ. Post-AGB objects (e.g., Planetary Nebulae) and massive starswith detached envelopes and/or hot central stars are found in severalclusters. We model the spectral energy distributions of the cluster IRobjects, in order to estimate their bolometric luminosities andmass-loss rates. The IR objects are the most luminous cluster objects,and have luminosities as expected for their initial mass andmetallicity. They experience mass-loss rates in the range from a few10-6 up to 10-4 M_ȯ yr-1 (ormore), with most of the spread being due to evolutionary effects andonly a weak dependence on progenitor mass and/or initial metallicity.About half of the mass lost by 1.3-3 M_ȯ stars is shed during thesuperwind phase, which lasts of order 105 yr. Objects withdetached shells are found to have experienced the highest mass-lossrates, and are therefore interpreted as post-superwind objects. We alsopropose a simple method to measure the cluster mass from L'-band images.
| Mid-Infrared Observations of van Maanen 2: No Substellar Companion
The results of a comprehensive infrared imaging search for the putative0.06 Msolar astrometric companion to the 4.4 pc white dwarfvan Mannen 2 are reported. Adaptive optics images acquired at 3.8 μmreveal a diffraction-limited core of 0.09" and no direct evidence of asecondary. Models predict that at 5 Gyr, a 50MJ brown dwarfwould be only 1 mag fainter than van Maanen 2 at this wavelength, andthe astrometric analysis suggested a separation of 0.2". In the case ofa chance alignment along the line of sight, a 0.4 mag excess should bemeasured. An independent photometric observation at the same wavelengthreveals no excess. In addition, there exist published Infrared SpaceObservatory observations of van Maanen 2 at 6.8 and 15.0 μm that areconsistent with the photospheric flux of a 6750 K white dwarf. If recentbrown dwarf models are correct, there is no substellar companion withTeff>~500 K.
| Diffraction-limited bispectrum speckle interferometry of the nuclear region of the Seyfert galaxy NGC 1068 in the H and K' bands
We present near-infrared bispectrum speckle interferometry studies ofthe nuclear region of the Seyfert 2 galaxy NGC 1068.A diffraction-limited K'-band image with 74 mas resolution and the firstH-band image with 57 mas resolution were reconstructed from speckleinterferograms obtained with the SAO 6 m telescope. The resolvedstructure consists of a compact core and an extended northern andsouth-eastern component. The compact core is resolved at all positionangles and has a north-western, tail-shaped extension as well as afainter, south-eastern extension. The K'-band FWHM diameter of thiscompact core is approximately 18 × 39 mas or 1.3 × 2.8 pc(FWHM of a single-component Gaussian fit; fit range 30-80&%slash; ofthe telescope cut-off frequency; the diameter errors are ±4 mas),and the position angle (PA) of the north-western extension is -16± 4 °. If 40% of the flux from the compact K' core isemission from a point source and 60% from a Gaussian intensitydistribution, then a slightly larger FWHM of approximately 26 × 58mas is obtained for the compact K' component. In the H band, the FWHMdiameter of the compact core is approximately 18 × 45 mas(±4 mas), and the PA is -18 ± 4 °. The extendednorthern component (PA 0 °) has an elongated structure with alength of about 400 mas or 29 pc. The extended south-eastern componentis fainter than the northern component. The K'- and H-band fluxes fromthe resolved compact core were measured to be 350 ± 90 mJy (i.e.,K' 8.2m) and 70 ± 20 mJy (H 10.4m), respectively. The PA of -16 ± 4 ° of thecompact 18 × 39 mas core is very similar to that of the westernwall (PA -15 °) of the bright region of the ionization cone.This suggests that the H- and K'-band emission from the compact core isboth thermal emission and scattered light from dust near the westernwall of a low-density, conical cavity or from the innermost region of aparsec-scale dusty torus that is heated by the central source (the dustsublimation radius of NGC 1068 is approximately 0.1-1pc). The northern extended 400 mas structure lies near the western wallof the ionization cone and coincides with the inner radio jet (PA 11 °). The large distance from the core suggests that the K'-bandemission of the northern extended component is scattered light from thewestern cavity region and the radio jet region.Based on observations made with the 6 m BTA telescope, which is operatedby the Special Astrophysical Observatory (SAO), Russia.
| High-resolution near-infrared speckle interferometry and radiative transfer modeling of the OH/IR star OH 104.9+2.4
We present near-infrared speckle interferometry of the OH/IR starOH 104.9+2.4 in the K' band obtained with the 6 mtelescope of the Special Astrophysical Observatory (SAO). At awavelength of λ = 2.12 μm the diffraction-limited resolutionof 74 mas was attained. The reconstructed visibility reveals aspherically symmetric, circumstellar dust shell (CDS) surrounding thecentral star. The visibility function shows that the stellarcontribution to the total flux at λ = 2.12 μm is less than50%, indicating a rather large optical depth of the CDS. Theazimuthally averaged 1-dimensional Gaussian visibility fit yields adiameter of 47 ± 3 mas (FHWM), which corresponds to 112 ±13 AU for an adopted distance of D = 2.38 ± 0.24 kpc. Todetermine the structure and the properties of the CDS of OH104.9+2.4, radiative transfer calculations using the codeDUSTY were performed to simultaneously model its visibility and thespectral energy distribution (SED). We found that both the ISO spectrumand the visibility of OH 104.9+2.4 can be wellreproduced by a radiative transfer model with an effective temperatureTeff = 2500 ± 500 K of the central source, a dusttemperature Tin = 1000 ± 200 K at the inner shellboundary Rin ≃ 9.1 R* = 25.4 AU, an opticaldepth τ2.2 μm = 6.5 ± 0.3, and dust g rainradii ranging from amin = 0.005 ± 0.003 μm toamax = 0.2 ± 0.02 μm with a power law n(a) ∝a-3.5. It was found that even minor changes inamax have a major impact on both the slope and the curvatureof the visibility function, while the SED shows only minor changes. Ourdetailed analysis demonstrates the potential of dust shell modelingconstrained by both the SED and visibilities.Based on data collected at the 6 m BTA telescope of the SpecialAstrophysical Observatory in Russia.
| 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.
| 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 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.
| H II Emission from a Complete Spectroscopic Survey of Be Stars in h and χ Persei
We describe data for emission-line B stars observed in a spectroscopicsurvey of h and χ Persei. The survey is complete to V=12.5 andcovers an area of ~1100 arcmin2 roughly centered on the twoclusters. We detect 32 Be stars; some have low Hα emissionstrength. Seven of these are new identifications; seven others areconfirmations of Be stars previously identified using photometry. Fiveof the observed Be stars show significant Hα profile variationsfrom epoch to epoch. We show that spectral indices yield physicalcharacteristics of the H II emission region. This automatic method isrobust and easily applied to large spectroscopic samples. We inferHα:Hβ flux ratios of 2-5 and observe a linear relationshipbetween Hα emission and J-K color for these stars. We include aHertzsprung-Russell diagram for the B-type stars in the clusters.
| The deeply embedded starburst in SBS 0335-052
We present 4 mu m ISAAC imaging and spectroscopy of the extremelymetal-poor dwarf galaxy SBS 0335-052, aimed at a better understanding ofthe dust in this low-metallicity galaxy. The 4 mu m emission turns outto be very compact, confined to the brightest pair of Super StarClusters (SSCs). The Ks-L' color is extremely red, and theL' emission is consistent with the extrapolation of the ISOmid-infrared spectral energy distribution (SED). From hydrogenrecombination lines and a fit to the near-/mid-infrared SED, we confirma visual extinction of ga 15 mag. Our data suggest that the sites of theoptical and infrared emission are distinct: the optical spectral linescome from an almost dustless region with a high star formation rate anda few thousand OB stars. This region lies along the line-of-sight to avery dusty central star cluster in which there are more than three timesas many massive stars, completely hidden in the optical. From theextinction, we derive an upper limit for the dust mass of 105M_sun which could be produced by recent supernovae. Based on dataobtained at ESO VLT UT1 on Cerro Paranal, Chile.
| Near-IR imaging photometry of NGC 1333: a 3-μm imaging survey
We combine new near-infrared 3.42-μm imaging photometry with JHK datafrom Paper I to further probe the membership and physicalcharacteristics of the embedded pre-main-sequence (PMS) population inthe active star formation region NGC 1333-S. Our new data set coversapproximately 44 per cent of the 10x10 arcmin^2 area previouslysurveyed. In the current survey region we have detected 36 sources, 26being brighter than our 5sigma limiting magnitude of m_L=12.2. These 36objects represent 45 per cent of the 80 objects detected in the sameregion at K. From a near-IR J-K versus K-L colour-colour diagram weinfer the evolutionary state of the stars and compare the results withthose obtained from our JHK data. We additionally discuss the effect of3.08-μm ice absorption on photometry at 3.42mum for heavily embeddedobjects.
| The Deep Silicate Absorption Feature in IRAS 08572+3915 and Other Infrared Galaxies
New mid-infrared (10 and 20 mu m) spectrophotometry of the ultraluminousinfrared galaxy IRAS 08572+3915 is presented. The 10 mu m spectrumreveals a deep silicate absorption feature, while the 20 mu m spectrumshows no clear evidence for an 18 mu m silicate absorption feature. Aninterstellar extinction curve is fitted to IRAS 08572+3915 and two otherdeep silicate infrared galaxies, NGC 4418 and Arp 220. It is found thatpure extinction cannot explain the spectral energy distributions ofthese sources. On the other hand, both the strength of the silicateabsorption and the overall spectral energy distributions of the threegalaxies agree well with scaled-up models of galactic protostars. Fromthis agreement, we conclude that the infrared emission comes from anoptically thick dust shell surrounding a compact power source. The sizeof the power source is constrained to be smaller than a few parsecs. Weargue that a significant portion of the total luminosities of thesegalaxies arises from an active galactic nucleus deeply embedded in dust.
| Wind-Disk-Ambient Cloud Interactions in the Near Environment of T Tauri
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..744H&db_key=AST
| Multiwavelength Observations of Collisional Ring Galaxies.I.Broad-Band Images, Global Properties, and Radial Colors of the Sample Galaxies
This is one of a series of papers discussing the optical, infrared andradio continuum properties of a sample of collisional ring galaxies. Thepresent paper concentrates on the global broad-band optical (B, V and R)and near-IR (J, H and K) images of the galaxies and describe theirglobal properties. An analysis of the colors of the galaxies over avariety of wavelength baselines is described. In the B and V bands, thebluest colors are found in the outer bright ring. The B-V colors of thesample of galaxies are blue, the median value for the sample is B-V =0.60, and V-K= 2.33 mag. The IR morphology of the galaxies is, in mostcases, very similar to that of the B-band data, suggesting that theclumpy appearance of the star formation in the outer rings is real, andnot a result of patchy dust obscuration. Only in one ring (WN1, aSeyfert ring galaxy) was the IR morphology different from the optical,suggesting the presence of significant dust in the disk. In II Hz 4,faint spiral arms are seen within the ring. There is a suggestion thatthe larger rings have redder V-K colors, which may be due to anincreased incidence of nuclear bulges in larger ring galaxies. Radialprofiles of surface brightness and color are presented for fourgalaxies. In all cases, the colors becomes bluer as one proceedsradially outwards, but in two galaxies, the rings redden again outsidethe main ring, suggesting the existence of a red stellar population thatmay have pre-dated the collisions.
| Properties of Low-Mass Objects in NGC 2024
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...473..294C&db_key=AST
| The Cold, Massive Molecular Cloud G216-2.5. III. Infrared Properties
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...472..275L&db_key=AST
| Multiwavelength observations of ring galaxies. 2: Global star formation in ring galaxies
We present optical H-alpha emission-line images and K band near-infraredimages of a sample of collisionally formed ring galaxies. These are usedto determine the distribution of star formation and the distribution ofthe old stellar population, respectively, in the galaxies. Our resultsshow ring galaxies to have similar Hcx luminosities to starburstgalaxies, with star formation being contained almost exclusively in thering. In the larger ring galaxies we observe the ionized hydrogen to lieon the outer edge of the underlying, broader, K band ring. No conclusiveevidence is found in our sample for a true underlying stellar densitywave. Rather, the evidence suggests that either the density waves havepassed into the outer, mainly H I disk of the galaxies or that theprogenitor galaxies were mainly gas-rich low surface brightness objectsand that most of the optical/IR light we now observe has resulted fromrecent star formation in the expanding ring.
| A K' imaging survey of molecular outflow sources
A K'-band imaging survey with a approximately equals 8 min x 3 min fieldof view of all regions associated with CO molecular outflow from thelist of Fukui (1989) has been conducted. We present the individualimages and describe individual nebulous objects and star clusters. Thedata, including photometric calibration data, are being published asFITS files on a CD-ROM. The vast majority of all outflow sources areassociated with nebulosity detectable in K', so such nebulae can be usedas tracers for very young stars. We find a significant fraction(one-third) of molecular outflow sources to be associated with clustersof young stars. Most of the young embedded clusters show peaks in theirK' magnitude histograms that, if interpreted as an evolutionary effect,indicate average ages of the embedded star population of is less than 1x 106 yr.
| A near-infrared study of the Monoceros R2 star formation region
We present H (1.65 micron), K (2.23 micron), and Ldoubleprime(3.81 micron) broad-band images as well as Br(gamma) (n = 7approaches 4, 2.166 micron) and Br(alpha) (n = 5 approaches 4, 4.052micron) hydrogen recombination line images, and 3.29 micron and 3.4micron unidentified feature emission images of the Monoceros R2 starformation region at a plate scale of approximately 0.9 sec/pixel. TheBrackett line images ar combined with 5 GHz data to map theline-of-sight dust extinction to the compact H II region on a smallspatial scale. This extinction map is then used to deredden regions ofthe H and K imges interior to the H II region. IRS 1SW, theionizing source, is found to be consistent with a B0 star. Comparison ofdereddened H and K images with the Brackett images and recenthigh-resolution HCO(+) measurements leads to the development of a torusmodel for the dense molecular gas surrounding the H II region. The 3.29micron emission is found to be coincident with the ring of scatteredlight at 2.2 micron and just outside the Br(alpha) and Br(gamma)emission. The 3.4 micron image is of too low a signal-to-noise ratio todetermine if any variation in the 3.29 to 3.4 micron emission ratio withdistance from the ionizing source is seen; however, 3.4 micron emissionis detected in a ring coincident with the 3.29 micron emission.
| The lowest mass stars in the Hyades
In Bryja et al. (1992), we presented proper motions and photometry of 12very low mass star and brown dwarf candidates in the Hyades cluster,selected on the basis of colors and proper motions measured from threeepochs of plate material. We here present new observations of some ofthese candidates, including seven low resolution spectra, plus motionsand photometry of 17 fainter additional candidates. Most of thecandidates have JHK colors typical of M5-M8 dwarfs, while their opticalcolors are consistent with earlier M spectral types. The availablespectra consist of late M dwarfs with H alpha emission featuresindicative of Hyades membership, earlier M dwarf background stars, andtwo anomalous objects with early M dwarf features but unusually redcontinua. We find that the proper motion distribution of faint red fieldstars in the region is irregular, and it is not possible to determine ifthe anomalous objects are Hyades members or background field stars. Inthe most conservative view, only five of our 29 candidates are Hyades.These five stars have optical and infrared colors consistent with thebottom of the Hyades main sequence, with four of them also shown to havelate M dwarf spectra. It follows that these are the lowest mass starsknown in the Hyades (M is about 0.1 solar mass).
| Near-IR imaging photometry of NGC 1333. I. The embedded PMS stellar population
We present near-IR (NIR) J, H and K mosaic images of the active starforming region associated with the optical reflection nebula NGC 1333.These observations cover an area of 10'x10' and are centered on theenergetic outflow source SSV 13. From these data, we have obtained NIRphotometry of 134 objects down to a 5σ limiting K magnitude ofm_K_=16.2 and a conservative survey completeness limit of m_K_=16.0.With the addition of new optical R and I band CCD photometry, and both(sub)mm line and continuum maps, we analyse and discuss the region'smorphology and spatial source distribution with additional reference toexisting multi-wavelength data. Within the survey field, NGC 1333-S, wefind a significant population of young, PMS stars. Specifically, weconsider 55 sources or ~41% of the total stellar population are likelyin a PMS evolutionary state. These sources exhibiting clustering in thevicinity of SSV 13 although SSV 13 is not at the cluster centre. Theimplied stellar PMS population has a range of M_K_ of 0-9 magnitudes andJ-K colours of ~1-5. We interpret the data as evidence that i) theembedded population is dominated by relatively low-mass stars i.e.<0.3 Msun_ (~55%), and ii) there exists smallerpopulations of objects consistent with standard young star classesnamely, classical T Tauri stars (~25%), Herbig Ae/Be stars (<10%) andClass I sources (<10%). We demonstrate that an apparent turn-over inthe m_K_ luminosity function for all sources in the survey field can bemodelled by the combined effect of the survey detection limit andspatially variable extinction over the survey region. This suggests thata combination of a de-reddened sample of PMS star, and a detection limitseveral magnitudes below the expected faintest m_K_ for those sources isrequired before inferences can be drawn on the luminosity/mass function.We additionally present the discovery of several new compact nebulousfeatures in the region. Two such objects are possibly associated withSSV 13 and HH 7-11. Almost all of these features are associated withblue-shifted CO in the outflows from IRAS sources in the region. Weconsider in some detail the usage of NIR photometry and colours in aregion of significant extinction, e.g. within the boundaries ofmolecular clouds, to both determine the evolutionary state of anobserved sample of stars and subsequently to characterize them intomass, luminosity, activity and age classes. We discuss and apply severalmethods to separate a population of embedded young pre-main sequence(PMS) stars from the generally larger population of reddened backgroundgalactic sources.
| Molecular Hydrogen in the IRAS 03282+3035 Stellar Jet
Not Available
| Infrared imaging of MG 0414 + 0534 - The red gravitational lens systems as lensed radio galaxies
We present an IR image of the gravitational lens system MG 0414 + 0534,and IR photometry of PG 1115 + 080, H1413 + 117, and Q1429 - 008. The IRof MG 0414 + 0534 shows a morphology that is similar to the radio andoptical morphologies. The object is bright (K-prime = 13.7) andextremely red (I-K-prime = 5.7). MG 0414 + 0534 thus becomes the secondradio-selected lens system to have very red optical IR colors. Whenplotted on a color-magnitude diagram of objects from a radio survey, MG0414 + 0534 and the other very red system, MG 1131 + 0456, lie near thelocus of radio galaxies. We therefore suggest that these systems arelensed high-redshift radio galaxies. In general, lensed radio galaxiesshould be common among lens systems selected from radio surveys, since ahigh proportion of radio sources are radio galaxies.
| A filter for deep near-infrared imaging
The K passband (central wavelength 2.2 microns, FWHM 0.4 micron) is thelongest wavelength standard near-IR passband through which deepground-based imaging is possible. Thermal emission from telescope,instrument, and sky limits the depth to which such imaging can reach byproducing strongly temperature-dependent backgrounds in the range11-13.5 mag/sq arcsec. This paper describes how a passband, which isdenoted as K-prime, located slightly shortward of the standard Kpassband (central wavelength 2.1 microns), yet still within the sameatmospheric window, leads to a significantly lower thermal component ofthe background, reducing the background surface brightness by up to 0.9mag sq arcsec, and thereby allowing deeper imaging to be obtained in thesame integration time. The photometric differences between the K-primefilter and the standard K filter are discussed.
| Two protostar candidates in the bright-rimmed dark cloud LDN 1206
The discovery of several near IR objects associated with two IRAS pointsources in the LDN 1206 region is reported. IRAS 22272 + 6358A isprobably a 'protostar' which is seen only in scattered light at near-IRwavelengths because of heavy obscuration by an almost edge-oncircumstellar disk. In contrast, IRAS 22272 + 6358B is directly visibleat these wavelengths and is perhaps an object which lies betweenprotostars and T-Tauri stars in its evolution. Both direct andpolarimetric K-band images of the region are presented, as well asspectral energy distributions constructed from J, H, K, L, L-prime, andM data and published far-IR and mm data.
| 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.
| 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.
| An infrared reflection nebula surrounding SGS 1 in the NGC 1333 dark cloud
Strom et al. (1974) have conducted a search for infrared sourcesassociated with Herbig-Haro objects. They found an infrared source, SGS1, near HH 12, embedded in at least 20 visual mag of extinction in theNGC 1333 dark cloud. Various factors suggest the presence of an infraredreflection nebula. In the context of the present investigation, highspatial resolution observations in the infrared have provided the basisfor the development of a consistent model for SGS which consists of alow-luminosity, cool star with an accretion disk tilted to the line ofsight, and one observed reflection lobe caused by the illumination ofmaterial above one of the polar regions of the accretion disk. It ispointed out that this model is similar to that of the infraredreflection nebula GSS 30 in the Ophiuchus dark cloud.
| 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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