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Wireless transmission of power from point to point has been developed in two predominate electromagnetic frequency ranges: near-infrared and microwave. In this paper, the prospect of wireless power beaming in the terahertz frequency range is explored with emphasis on the role of adverse weather. Link distance, power transmission, and safety performance of near-infrared, microwave, and terahertz power beaming are compared under clear and adverse weather conditions. While infrared power beaming provides the longest link distances of the three under clear weather conditions, terahertz power beaming can provide better performance under adverse weather conditions.

Using a cross-polarization transmission geometry, stress maps for the normalized birefringence and intrinsic stress direction of polymeric materials may be obtained using terahertz nondestructive evaluation. The analysis method utilizes a deconvolution method to determine the arrival times and amplitude of the cross-polarized terahertz pulses through a birefringent material. Using amber (a naturally occurring polymer) as a material of interest, stress maps show that inclusion-free Lebanese amber samples behave as classic uniaxial birefringent (photoelastic) materials whose principal stress directions, as inferred in the terahertz spectral range, agree well with visible photoelasticity measurements. Since amber samples, depending upon their source, may be either transparent or opaque to visible light, comparing birefringence measurements in the visible and terahertz spectral ranges cross-validates the stress measurements, thereby establishing a strong and unique stress analysis methodology for visibly opaque samples. While the material of interest for this paper is amber, the method is generally applicable for any terahertz-transparent polymer. The cross-polarization experimental configuration enables stress levels within the amber matrix to be visualized while also outlining highly localized regions of stress surrounding inclusions. Birefringence stress maps clearly show localized increases in stress magnitude and directional changes surrounding inclusions.

Fossilized plant resins, or ambers, offer a unique paleontological window into the history of life. A natural polymer, amber can preserve aspects of ancient environments, including whole organisms, for tens or even hundreds of millions of years. While most amber research involves imaging with visual light, other spectra are increasingly used to characterize both organismal inclusions as well as amber matrix. Terahertz (THz) radiation, which occupies the electromagnetic band between microwave and infrared light wavelengths, is non-ionizing and frequently used in polymer spectroscopy. Here, we evaluate the utility of amber terahertz spectroscopy in a comparative setting for the first time by analyzing the terahertz optical properties of samples from 10 fossil deposits ranging in age from the Miocene to the Early Cretaceous. We recover no clear relationships between amber age or botanical source and terahertz permittivity; however, we do find apparent deposit-specific permittivity among transparent amber samples. By comparing the suitability of multiple permittivity models across sample data we find that models with a distribution of dielectric relaxation times best describe the spectral permittivity of amber. We also demonstrate a process for imaging amber inclusions using terahertz transmission and find that terahertz spectroscopy can be used to identify some synthetic amber forgeries.

While Terahertz imaging has shown promise, there have been relatively few implementations of Terahertz non-destructive evaluation in industry. Current industrial implementations of THz imaging are described as well as several highly promising applications.

High-resolution Airborne Wide-band Camera (HAWC[Formula: see text]) is the facility far-infrared imager and polarimeter for SOFIA, NASA’s Stratospheric Observatory for Infrared Astronomy. It is designed to cover the portion of the infrared spectrum that is completely inaccessible to ground-based observatories and which is essential for studies of astronomical sources with temperatures between tens and hundreds of degrees Kelvin. Its ability to make polarimetric measurements of aligned dust grains provides a unique new capability for studying interstellar magnetic fields. HAWC[Formula: see text] began commissioning flights in April 2016 and was accepted as a facility instrument in early 2018. In this paper, we describe the instrument, its operational procedures, and its performance on the observatory.

Measurements of Iapetus as seen at 20 and 2.2 μm in the shadow of Saturn's ring are given, providing the thermal response to a rapidly varying heat input. The 20 μm thermal emission follows the 2.2 μm flux input closely. The observations, plus a simple diffusion calculation, imply that the surface of Iapetus is made of material having a very small thermal inertia, probably / ≾ 10Jm^(-2)s^(-½)K^(-1).

Chandra X-ray Observatory (CXO) images have revealed that the X-ray emitting regions of the molecule-rich young planetary nebulae (PNs) BD+30 3639 (BD+30) and NGC 7027 are much more asymmetric than their optical nebulosities. To evaluate the potential origins of these X-ray asymmetries, we analyze X-ray images of BD+30, NGC 7027, and another planetary nebula resolved by CXO, NGC 6543, within specific energy bands. Image resolution has been optimized by sub-pixel repositioning of individual X-ray events. The resulting subarcsecond-resolution images reveal that the soft (E < 0.7 keV) X-ray emission from BD+30 is more uniform than the harder emission, which is largely confined to the eastern rim of the optical nebula. In contrast, soft X-rays from NGC 7027 are highly localized and this PN is more axially symmetric in harder emission. The broad-band X-ray morphologies of BD+30 and NGC 7027 are highly anticorrelated with their distributions of visual extinction, as determined from high-resolution, space- and ground-based optical and infrared imaging. Hence, it is likely that the observed X-ray asymmetries of these nebulae are due in large part to the effects of nonuniform intranebular extinction. However, the energy-dependent X-ray structures in both nebulae and in NGC 6543 -- which is by far the least dusty and molecule-rich of the three PNs, and displays very uniform intranebular extinction -- suggests that other mechanisms, such as the action of collimated outflows and heat conduction, are also important in determining the detailed X-ray morphologies of young planetary nebulae., 33 pages, 12 figures; to appear in the Astrophysical Journal

We present high spectral resolution maps of near-infrared molecular hydrogen emission from the bipolar pre-planetary nebulae RAFGL 2688 and RAFGL 618, obtained with the NOAO Phoenix spectrometer. The measured velocity gradients along the polar axes of both nebulae indicate that the highest velocity gas lies closest to the central stars. These results support the suggestion that the polar H_2 emission regions of both nebulae contain shocked gas formed as fast (~50-150 km/s), collimated, post-asymptotic giant branch (AGB) winds collide with slower-moving (~10-20 km/s) material previously ejected while the central stars were still on the AGB. The kinematics of H_2 emission perpendicular to the polar axis of RAFGL 2688 are consistent with a model combining expansion along the equator at 5-10 km/s with rotation about the polar axis at 5-10 km/s. The rapid onset of the common envelope phase of a close binary system may explain both the bipolar structure of RAFGL 2688 and the presence and complex kinematics of its shocked H_2 emission., 21 pages, 8 figures; to be published in the Astrophysical Journal (Jan. 1, 2001 issue)

We have used the SPIREX telescope to conduct a wide-—eld thermal infrared imaging study of the star formation complex NGC 6334 in the southern Galactic plane. We imaged a 30@ region along the main star-forming ridge of NGC 6334 with pixel scale through broadband —lters for L (3.5 km) and 0A.6 M (4.8 km) and through narrowband —lters for the v \ 1¨0 Q-branch (2.42 km), polycyclic aromatic H 2 hydrocarbon (PAH) (3.3 km), and Bra (4.05 km) lines. The images reveal the spectacular, complex struc- ture of the photodissociation regions (PDRs) that pervade the region, with enhanced line emission around each of the seven sites of massive star formation along the ridge. Bubbles and loops of PAH emission, typically 1¨1.5 pc across, have been carved out of the parent molecular cloud by the intense UV radiation from the massive stars and surround H II regions (seen in Bra) typically 0.2¨0.3 pc across. The PAH emission regions coincide with both (C II) 158 km line emission, indicating that the PAHs are excited in PDR gas, and extensive emission, which therefore must be —uorescent. However, the tex- H 2 tures of the emission regions in PAH and are diUerent. This is attributable to variations in the physi- H 2 cal environment in which the gas is excited. Several compact reddened objects are observed; these are likely to be massive protostars. Subject headings: infrared: generalinfrared: ISM: lines and bandsISM: molecules ¨ ISM: structurestars: formationtelescopes

Velocity-resolved 2.12 μm H2 maps of the Egg Nebula (AFGL 2688), obtained with the NOAO Phoenix spectrometer, elaborate on previous observations of large velocity gradients in molecular emission both along and perpendicular to the polar axis of the system. The measured gradients along the polar axis support the notion that the polar H2 emission regions are formed in shocks as fast, collimated winds collide with material ejected while the central star was still on the AGB. The kinematics of H2 emission along the equatorial plane, meanwhile, are consistent with a model combining spherical expansion with rotation about the polar axis, although a model invoking multiple outflow axes cannot be ruled out.We also obtained the first direct near-infrared images of QX Pup, a Mira variable embedded within the evolved bipolar nebula OH 231.8+4.2. The inferred absolute K magnitude of the central Mira appears “normal” given its ∼ 700 day period, which is remarkable in light of its position at the heart of such an unusual object.

This paper presents results obtained from high-resolution spectroscopy of the 2.1218 μm emission line of molecular hydrogen toward five bipolar pre-planetary nebulae. Our detections of IRAS 17441-2411 and AFGL 6815S bring to four, including AFGL 618 and AFGL 2688, the number of bipolar preplanetaries that have been detected as sources of H2 emission at 2.1218 μm. The spatially resolved H2 line profile of AFGL 6815S suggests that the bulk of the detected emission arises in an expanding molecular torus surrounding the central star. All of the H2-emitting pre-planetary nebulae are found at low galactic latitudes, consistent with previous results for planetary nebulae, and have central stars with intermediate or early spectral types. We were unable to detect H2 emission from the bipolar, post-main-sequence sources OH 231.8+4.2, IRAS 07131-0147, and IRAS 09371+1212, all of which have M-type central stars. These results suggest that the event that triggers the production of emission from shocked H2 occurs at an intermediate evolutionary epoch in the postasymptotic giant branch evolution of transition objects, after the generation of bipolar structure and before the nebular envelopes are ionized. From constraints imposed by the galactic distribution of H2-emitting planetaries, we estimate distances to the four pre-planetary nebulae that display H2 emission.

We combine our previous optical spectroscopic and photometric analysis of ~1600 stars located in the Orion Nebula Cluster (ONC) with our own and published near-infrared photometric surveys of the region in order to investigate the evidence for and properties of circumstellar disks. We use the near-infrared continuum excess as our primary disk diagnostic, although we also study sources with Ca II triplet emission and those designated as "proplyds." The measured near-infrared excess is influenced by (1) the presence or absence of a circumstellar disk, (2) the relative importance of disk accretion and inner disk holes, (3) the relative contrast between photospheric and disk emission, and (4) system inclination. After attempting to understand the effects of these influences, we estimate the frequency of circumstellar disks and discuss the evidence for trends in the disk frequency with stellar mass (over the mass range

A candidate radio-loud broad absorption line (RLBALQ) has been recently reported by Becker et al. We present JHK observations of this object and three other radio-detected BALQs taken with the new Michigan-Dartmouth-MIT/Ohio State/Aladdin Infrared Camera (MOSAIC) on the KPNO 4 m telescope. The candidate RLBALQ 1556+3517 has B - K = 6.63, redder than all but one or two known z > 1 quasars. This strongly suggests that the observed continuum of this quasar is reddened by dust. Even when this extreme reddening is taken into account, 1556+3517 is still probably radio loud, although near-infrared spectroscopy to measure its Balmer decrement will be needed to verify this. In addition, since it is a flat-spectrum object, VLBI observations to determine the extent (if any) to which beaming affects our estimate of its radio luminosity will be needed before 1556+3517 can be unequivocally declared a radio-loud BALQ. We also use our data and data from the literature to show that optically selected BALQs as a class have B - K colors consistent with the observed distribution for optically selected quasars as a whole. Thus, there is currently no evidence that the tendency of optically selected BALQs to be preferentially radio intermediate (see the work of Francis, Hooper, and Impey) is due to extinction artificially lowering estimated BALQ optical luminosities. However, as most quasar surveys, both radio and optical, would be insensitive to a population of reddened radio-quiet BALQs, the existence of a large population of reddened BALQs similar to 1556+3517 cannot yet be ruled out.

We used the new high spatial resolution observing mode of the Kitt Peak near-IR Cryogenic Optical Bench on the 4 m telescope to detect and determine the locations of the powering sources of three protostellar outflows. Diffraction limited images at 3.8 μm of the cores of AFGL 437, L1287, and NGC 7129 demonstrate that, in each case, a young stellar object—WK 34, IRAS 00338+6312, and NGC 7129 PS 1, respectively—lies at the position predicted for the outflow source on the basis of near-IR polarimetric imaging at 2.2 μm. WK 34 and NGC 7129 PS 1 display nebulosity at 3.8 μm, confirming that each illuminates an outflow cavity. These data support the hypotheses that protostellar outflows are almost always associated with very young, heavily extincted sources, that associations of outflows with pre-main sequence stars are likely to be incorrect, and that infrared polarimetric imaging is a dependable tool for probing reflection nebulae to locate embedded young stellar objects.

From a magnitude-limited infrared survey of the 30 Doradus complex four candidate protostars have been identified. These are associated with dense knots in the nebular arcs, and have luminosities of 1-5 × 10 4 L ⊙ and masses of 15-20 M ⊙ . The results indicate that both the knots and the associated star formation are likely to be caused by the compression of interacting arcs of mass-loss winds from hot massive stars in the central cluster, and other nearby clusters. This mode of star formation differs from the classical star formation scenario within dense molecular clouds, and appears to be highly efficient

Detection d'une enveloppe etendue de poussiere autour de l'etoile de type avance IRC+10216 revelee par des observations photometriques et polarimetriques. L'extension de l'enveloppe IR, de symetrie quasi circulaire, est superieure a 1' et est comparable en dimension a l'enveloppe de gaz. La distribution radiale des grains de poussieres obeit a une loi de carre inverse qui suggere une perte de masse constante

Observations of planetary and protoplanetary nebulae in the spectral line of molecular hydrogen at 2.1218 μm are providing new insights into the processes of formation and evolution of post-AGB stars. In this paper, we present three significant results from the study of H2 toward planetary and protoplanetary nebulae. First, the presence of H2 emission is sufficient to determine that the source is bipolar; second, the formation of bipolar structure in protoplanetary nebulae precedes the event(s) that produces H2 emission; and third, along the polar axes of PPNe, the velocity of molecular gas H2 emission decreases with distance from the central star.

The MDM/Ohio State/ALADDIN IR Camera (MOSAIC) is a general purpose near IR imaging camera and medium-resolution long- slit spectrometer in use on the MDM 1.3-m and 2.4-m telescopes and the Kitt Peak 2.1-m and 4-m telescopes. In cooperation with NOAO and USNO, MOSAIC is one of the first general-purpose near-IR instruments available to the astronomical community that uses a first-generation 1024 X 512 ALADDIN InSb array, with the capability to use a full 1024 X 1024 array once one becomes available. MOSAIC provides tow imaging plate scales, and a variety of long- slit grism spectroscopic modes. This paper describes the general instrument design and capabilities, and presents representative scientific results.

Seven Aladdin sensor chip assemblies (SCAs) have been produced and nine more are in production. In this paper we cover the design, description, and measured performance of the Aladdin SCA. At over 7.5 square cm Aladdin is the largest single chip infrared array in use today. It is a hybrid assembly made up from an InSb detector coupled, via indium bumps, to a silicon readout. An array of this size is only possible because the InSb detector material is thinned to less than 10 microns which allows it to accommodate the InSb/silicon thermal mismatch. The Aladdin development program is a success and the resulting devices met most of the original design goals. Experience with Aladdin I led to improvements in the readout multiplexer design and, with these changes, we expect to meet the remaining goals. The new readouts have completed processing but testing has just started. The ALADDIN program is a joint collaboration between the National Optical Astronomy Observatories (NOAO) and the U.S. Naval Observatory (USNO) with Santa Barbara Research Center (SBRC).

The ALADDIN 1024 X 1024 InSb array is now a fact rather than a concept, and the time has come to show test results. In this paper we present lab test data but we have also taken it to the telescope. The development program was a success and the array has met the design goals of the program. The few remaining problems involve hybridization and are expected to be solved soon. The ALADDIN program is a joint collaboration between the National Optical Astronomy Observatories (NOAO) and the U. S. Naval Observatory (USNO) with Santa Barbara Research Center (SBRC).

The present state of the art for scientific InSb focal planes is the Santa Barbara Research Center (SBRC) 256 X 256 device. In this paper we will present the status of the 1024 X 1024 focal plane development effort, technical details on the design, and both warm and cryogenic test data on the readout multiplexer. As the largest InSb infrared hybrid focal plane in development, this information should be of great interest to many groups. The current status and test data are presented here so that those planning future space instrumentation projects can be brought up to date on this advanced technology.

The Cryogenic Optical Bench (COB) is a 1-4 (mu) IR array camera with multiple cold spectral and spatial filtering capabilities which can be combined in a variety of configurations. The array is driven by a transputer based high speed data system using fiber optic links and dedicated processors. We describe the instrument functions and the mechanical, optical, electronic, and cryogenic implementation. COB is a facility instrument at Kitt Peak National Observatory, available for use by scientists worldwide on the basis of scientific merit.

The present state of the art in scientific InSb focal plane arrays is defined by the Santa Barbara Research Center (SBRC) 256x256 device. In this paper we will discuss the status of the USNO-NOAO 1024x1024 focal plane development effort at SBRC. The project is in its ealy phases, and so this report consists of the device description, design goals, testing plans, and schedule. Drivers for even larger IR arrays include plans for large (8 meter class) telescopes, high resolution spectroscopy, astrometry of large fields, and wide field imaging amongst others. Focal planes of 640x480 have already been demonstrated, and so the step up to 124x1024 seems reasonable at this time.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Extended legions of polarized near-infrared light can be produced either by scattering by particles or by transmission through a medium of aligned paramagnetic grains. In principle, if the latter process dominates, polarization studies of extended sources can be used to probe magnetic field structure. Here, we present preliminary results from a polarimetric line study of the bipolar HII region S106.

Recent progress in infrared astronomy has been very rapid because of the introduction of two dimensional detector arrays. Practical experience in using these arrays has changed the techniques and outcomes of infrared astronomical research profoundly. In this paper those changes are illustrated by an assortment of images and spectra.

The Simultaneous Quad-Color Infrared Imaging Device (SQIID) is the first of a new generation of infrared instruments to be put into service at the Kitt Peak National Observatory (KPNO). The camera has been configured to be modular in design and to accept new innovations in detector format as they become available. Currently the camera is equipped with four 256 x 256 platinum silicide arrays with 30 micron pixels for each of the four bands J (1.1-1.4 microns), H (1.5-1.8 microns), K (2.0-2.4 microns), and L' (3.52-4.12 microns). The optics of the instrument have been designed to accept detector arrays as large as 512 x 512, or an equivalent field size of 12.4 mm x 12.4 mm. The instrument is cooled with a pair of closed cycle cryogenic coolers, which are mechanically aligned and electrically phased to eliminate vibration. In addition, a transputer based electronics system has been incorporated to facilitate fast frame rates, co-add frames, and ease the data handling burden.

The low background performance of most infrared systems has been limited by the read noise of the focal plane array (FPA). In many cases the cause has been attributed to the use of MOSFETS or to the detector itself. In this paper we describe a multiple correlated sampling technique and demonstrate noise improvements by a factor of 9 over conventional readout techniques in use today. The FPA under discussion is a `Source Follower per Detector' or SFD type readout structure; specifically, the Santa Barbara Research Center 58 X 62 InSb FPA and the Hughes Technology Center (HTC) 256 X 256 PtSi FPA. The quoted read noise for the SBRC FPA (typically 400 electrons rms) has been reduced to 45 electrons rms using this technique.

The development of a PtSi array for use in ground-based astronomy has been the goal of a joint effort between the National Optical Astronomy Observatories (NOAO) and the Hughes Microelectronics Center. This has been accomplished by the introduction of the SWIR PtSi hybrid array for astronomy. The resulting array has an optical cavity tuned to enhance the internal quantum efficiency at 1.7 microns, low noise, and low dark current. The use of PtSi Schottky detector material yields high uniformity and exceptional stability of performance compared to other SWIR materials. Hybrid technology allows the array to achieve the 100% fill factor needed for astronomical applications and the NMOS SFD readout yields very low noise performance. In this paper we describe these characteristics in more detail and present test data to demonstrate the array performance.

Near infrared imaging can be a powerful tool in tracing the densest molecular structures in galaxies. The observable molecular emission originates in large molecular cloud complexes which are also subject to significant extinctions caused by the associated dust. It can be difficult to distinguish between regions of moderate and large molecular density with optical observations as both will appear optically thick. Since extinction in the near infrared is only about a tenth of the corresponding visual extinction, multi-band near infrared imaging will trace the regions of the highest optical depths much more effectively. With the advent of large format infrared imaging arrays it is now possible to use infrared extinction maps as a probe of the large scale distribution of molecular emission in extragalactic sources.

We present an unbiased survey at 1.25-2.2 micrometers of a 0.025 sq. deg. region surrounding the core of Orion Molecular Cloud 2 (OMC-2). Analysis of the source counts and colors indicates that the majority of the sources brighter than K = +13 are not field stars. They must be members of a young association or associations within the survey area. The K band luminosity function (corrected for field star contamination using model calculations) exhibits a drop in counts at magnitudes fainter than K = +13 (approximately 0.15 solar luminosity). This is most easily explained by assuming that the association(s) are young. The lowest mass stars simply have not yet reached the main sequence. The distribution of colors across the region shows moderate correlation with molecular gas, but both reddened and unreddened stars are present along most lines of sight. Considerable reflection nebulosity is present in the region of the core cluster of OMC2 itself. Of particular interest are the thin streamers emanating from the star J9, which may be the remnant of a bipolar nebula produced by the star in the recent past.

From study of a sample of 34 T Tauri stars with photometrically derived rotation periods and spectral types later than KS, we find that the observed periods appear to be related to the presence or absence of an accretion disk. Those stars which we infer to be surrounded by accretion disks have rotation periods P(rot) over 4 days with a most probable P(rot) of about 8.5 days, while those stars which lack accretion disk signatures cover a wide range of P(rot) from 1.5 to 16 days, including a significant number of objects with P(rot) less than 4 days. This suggests the possibility that the 'initial' angular momentum of a star is not established until it dissipates its circumstellar accretion disk. During the disk accretion phase, the stellar angular velocity appears to be regulated at a low value, countering the tendency of the star to spin up both from contraction toward the main sequence and from the accretion of inner disk material of high specific angular momentum. When the accretion disk is dissipated, this regulation mechanism will cease to function. At this point, the star is no longer maintained at a low angular velocity, but is 'free' to conserve its angular momentum, and thus to increase its angular velocity in response to contraction and changes in moment of inertia. This hypothesis, combined with a spread in disk dispersal time scales, provides a context for explaining the observed distribution of stellar rotational velocities for stars on the ZAMS in young clusters.

We present near-infrared images in the J, H, and K bands of the starburst galaxy Maffei 2 taken with the NOAO Simultaneous Quad Infrared Imaging Device at Kitt Peak. These images reveal a morphology that is optically hidden by the ∼5 mag of visual extinction at its low galactic latitude (b=−0.3°). In the near-infrared, Maffei 2 can clearly be identified as a barred spiral of revised Hubble morphological type SBb(s) pec. The infrared extinction seen in the nucleus closely matches the known molecular morphology, indicating that such extinction can be a good tracer of molecular cloud complexes along density waves in galaxies

Near-infrared images of the bipolar nebula OH 231.8+4.2 obtained over a 3 yr period suggest that its surface brightness distribution varies with time. A model in which the variations are explained by the differences in travel times for photons scattered off dust grains at various positions along the polar axis of the nebula is presented. This formulation allows us to determine the brightness fluctuations and heliocentric distance of the embedded source and the inclination of the nebula

A circumstellar nebula that lies symmetrically around the pre-main-sequence star T Tauri was imaged, using a 6″ diameter coronagraphic spot placed in front of an infrared array camera. The nebula is detected in polarized light our to ∼10″ (1400 AU) at both 1.25 μm and 2.2 μm, twice as far from T Tauri as the structure previously seen in the J=1→0 rotational transition of carbon monoxide. The intensity of scattered light, measured as a function of distance fom T Tauri, reveals an approximate r -2.5 dependence

The inefficiency of the stellar formation process leads rather generally to high residual dust densities, and so to the existence of infrared reflection nebulosity (IRN), in regions of star formation. Polarization images of several star-forming regions with mass outflows (GSS 30, S255, GL 5180, GL 2591, GGD 27, and NGC 7538) presented here: (1) establish the universality of bipolarity and of shell or cavity structure in the IRN consistent with that of CO outflow; (2) identify the source of the mass outflow in each case; (3) show that the opening angle near this central source is large; and (4) demonstrate several instances of multiple shells, probably arising from episodic mass loss. Astrometry of 2.2-micron sources with arcsecond accuracy identifies the illuminating source of each IRN uniquely with a compact H II region or a bright IR source. The polarization images provide strong evidence for large-scale dust toroids around each of these sources. The density and mass of these disks are estimated from the extinction through the disk.

It is shown here that the published emission line ratios for vibrationally excited molecular hydrogen in the near-IR for the highly luminous galaxy merger system NGC 6240 imply UV excitation followed by IR fluorescence. The line ratios for the central 2 kpc or so of the system are well-reproduced as a mixture of fluorescent and thermal components. Of the total H2 luminosity of 3 {times} 10 to the 9th solar, 70 percent is due to fluorescence. This emission is excited by UV photons probably radiated by many early B stars. The abundance of such stars and the deficit of O stars indicate a sharp upper mass cutoff at about 20 solar masses in the present-day mass spectrum in the central region. A starburst model is presented in which the observations can be reproduced if the central region experienced a cataclysmic starburst which stopped suddenly a few ten billion yr ago and if the initial mass function there had a lower mass cutoff at about 5 solar. 31 refs.

A 256 x 256 near-IR camera at NOAO to image a large portion of the M17 star formation complex. A mosaic image of total size 9 x 9 arcmin is constructed in each of three infrared colors-J, H, and K. The observations determine the size and extent of the obscured cluster of stars which excites the powerful H II region and heats the luminous dust in the adjacent molecular cloud. More than 100 OB stars are found in a clustering several parsecs in diameter within an obscured portion of the H II region. The K luminosity function of this cluster differs significantly from that of the field stars, and has the form expected from the Salpeter initial mass function. The present level of star formation activity in the adjacent molecular clouds M17 SW is found to be considerably lower than that which produced the OB cluster in the H II region. Most of the cluster members are found to have infrared colors which are not consistent with those of purely reddened stellar photospheres. These stars that display IR excesses may be surrounded by circumstellar disks. 26 refs.

Results of a deep near-infrared imaging survey of low-luminosity cold IRAS sources in the Taurus dark cloud are discussed. The images involved identify the compact sources energizing the IRAS sources, identify infrared nebulosity around numbers of the invisible sources, and reveal the large-scale (about 1000 to 10,000 AU) morphology of this nebulosity. Some of the invisible sources show a clear bipolar or monopolar morphology suggesting a close relation of the nebulosity with a bipolar mass outflow. It is concluded that the nebulosity is likely due to scattering of radiation from the central source by the dust associated with the mass outflow extending to the poles of a circumstellar dust disk.

New, high-angular resolution observations of 12 CO, 13 CO, C 18 O J = 1-0 and H 33 α hydrogen recombination line emission from the energetic DR 21 outflow are presented and discussed. The high-velocity CO emission is clearly bipolar with the blueshifted outflow lobe lying to the west and the redshifted lobe to the east of the DR 21 cloud core. These observations suggest that the DR 21 outflow is probably the most massive and energetics young-stellar outflow yet discovered in the Galaxy. In addition to the main outflow, the CO maps reveal a second high-velocity bipolar flow which also originates from within the DR 21 cloud core but extends along a N-S axis, perpendicular to the E-W axis of the main outflow

A 2.2 micron survey of a significant portion of the L1630 molecular cloud was carried out using the NOAO infrared array camera on the Kitt Peak 1.3 m telescope. This survey is estimated to be complete to 13th magnitude at K, which corresponds to a main-sequence star of about 0.6 solar mass. Therefore this survey has provided a sensitive census of the young stellar objects within this molecular cloud. As a result, 912 sources having m(K) less than 13.0 have been detected. It is estimated that 50 percent of these sources are associated with the molecular cloud. These sources are not distributed uniformly throughout the surveyed region but rather appear grouped or clustered. In fact, four embedded infrared clusters were identified. These clusters contain at least 58 percent but possibly as much as 96 percent of the total number of sources associated with this molecular cloud suggesting that the dominant mode of star formation in this region is in clusters.

Large-scale mapping and high-spectral resolution profile measurements of the vibrational H 2 v = 1-0 S(1) line are used to investigate the morphology and kinematic structure of the hot, shocked gas associated with the ultraluminous DR 21 young-stellar outflow. It is found that the H 2 line profiles at certain locations within the outflow possess high-velocity wings which extend to beyond 100 km s -1 from the DR 21 rest velocity. It is argued that the jets, which shock the surrounding molecular cloud medium and produce the bright H 2 line emission, are composed primarily of hot atomic gas which is confined by the thermal pressure of the ambient cloud medium.

Sellgren (1983) has shown that the young stellar cluster within the molecular cloud associated with the reflection nebula NGC 2023 has a luminosity function consistent with the Salpeter IMF for stars brighter than K = 12 mag. Extrapolation predicts that approximately 50 additional stars brighter than K = 15 mag, arguably of spectral types G through K, should be present. However, images of the cluster using a sensitive two-dimensional IR array reveal no additional cluster members, which suggests that either no low-mass stars have formed or that they are still heavily shrouded in molecular 'cocoons' left over from the star formation process. A straightforward experimental resolution of the alternatives is proposed. 22 refs.

High-resolution emission-line images of the central arcminute of S106 in Br-gamma and H2 v = 1-0 S(1) are presented. The high density, together with the low excitation temperature reported earlier for S106, suggests that the origin of the thermal component in the H2 emission measured by Tanaka et al. (1989) is either high-density fluorescence, that is, collisional de-excitation of the UV pumped H2 in photodissociation regions formed on the dense molecular clumps beyond the ionization fronts, or it is radiation from slow shocks driven by the wind from the central source, propagating into the dense clumps. In either case, a novel physical environment is required to understand the observations. 41 refs.

Un allgorithme de reduction du bruit de lecture des donnees d'observation IR est presente. Une application aux observations spectroscopiques de l'emission d'hydrogene moleculaire excite vibrationnellement de la nebuleuse proto-planetaire CRL 2688 est realisee

Detailed observations of CO, CS, IR continuum, and H2 emission from a large, highly collimated, bipolar outflow in the Monoceros OB1 molecular cloud are presented. The CO observations suggest that molecular gas in the outflow is contained in a shell with higher velocity material situated interior to lower velocity material. The velocities of outflow emission are found to increase with increasing distance from the center of the outflow. Additional detections include shock-excited molecular hydrogen emission from the blueshifted lobe of the outflow and six 2-micron sources in the direction of the outflow. Near-IR and IRAS observations suggest that the driving source for the outflow must have a bolometric luminosity below about 4.5 solar luminosities. It is concluded that the flow is probably not driven by stellar radiation from a central source.