Ian Gatley

A 2. 2 micron survey in the L1630 molecular cloud

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. 46 refs.

A spectroscopic study of the Dr 21 outflow source. III - The CO line emission

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

An infrared quintuplet near the Galactic center

A compact cluster of five luminous infrared sources has been found in the vicinity of the Galactic center radio arc. All of the sources have large polarizations in the near-infrared and deep silicate absorptions at 10 microns. Strong absorption lines of CO are seen at 4.6 microns toward each source. The observed polarization and spectral features are likely to be interstellar in origin. The temperatures of the sources, based on infrared photometry and corrected for extinction, are in the range 600-900 K. None of the sources show either infrared recombination line emission from atomic hydrogen, lines of molecular hydrogen, or overtone band of CO at 2.3 microns. Because the objects are tightly clustered, all are likely to be very young objects; however, accurate classifications cannot be made at the present time. 31 refs.

Submillimeter observations of evolved stars

Broad-band submillimeter observations of the thermal emission from evolved stars have been obtained with the United Kingdom Infrared Telescope on Mauna Kea, Hawaii. These observations, at an effective wavelength of 400 ..mu..m, provide the most direct method for estimating the mass loss rate in dust from these stars and also help to define the long-wavelength thermal spectrum of the dust envelopes. The mass loss rates in dust that we derive range from 10/sup -9/ to 10/sup -6/ M/sub sun/ yr/sup -1/ and are compared with mass loss rates derived from molecular line observations to estimate gas-to-dust ratios in outflowing envelopes. These values are found to be generally compatible with the interstellar gas-to-dust ratio of approx.100 if submillimeter emissivities appropriate to amorphous grain structures are assumed. Our analysis of the spectrum of IRC+10216 confirms previous suggestions that the grain emissivity varies as lambda/sup -1.2/ rather than as lambda/sup -2/ for 10

Molecular hydrogen maps of extended planetary nebulae - the Dumbbell, the Ring, and NGC 2346

The 3.8-m United Kingdom Infrared Telecsope at Mauna Kea was used to obtain complete H2 maps of three extended planetary nebulae (PNs) that are representative of two of the most common PN morphologies, bow tie and bipolar ring: the Dumbbell (NGC 6853), the Ring (NGC 6720), and the NG 2346, are discussed. The results of map analysis indicates that the S(1) emission from H2 closely follows the optical morphology of the three nebulae. The H2 emission is more extended than the main emitting mass of ionized gas and, in NGCC 2346, there is evidence for a dense torus of hot H2 surrounding the central star. The H2 emissionl appears to be shock-excited. Examinations of existing H2 measurements indicate that strong H2 emission is preferentially present in PNs that lie at small galactic latitude, implying that massive main-sequence stars produce ionization-bounded PNs, whereas low-mass stars produce density-bounded PNs. Thus, maps of H2 emission may not only be used to determine whether a given PN is ionization-bounded or density-bounded, but also to estimate the mass of the progenitor star. 83 references.

Infrared polarization images of star-forming regions. I - The ubiquity of bipolar structure

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.

Fluorescent molecular hydrogen emission from the reflection nebula NGC 2023

Observations of NGC 2023, obtained at 1.4-2.5 microns using the circular variable filter and a Fabry-Perot interferometer on the 3.8-m UKIRT during August 1984 and December 1985, are reported. Maps in the v = (1-0) S1 line of H2, in the J = (1-0) line of (C-12)O, and at 1.65 and 2.2 microns are presented and characterized in detail. UV-pumped H2 fluorescence is found to come from a circumstellar thin shell of radius 0.3 pc, which appears broken, clumpy, and nonspherical due to internal density variations and which lies just outside the nebula of 1-nm-radius grains proposed by Sellgren (1984) on the basis of continuum observations. 30 references.

Two micron morphology of candidate protostars

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. 28 refs.

Level population and para/ortho ratio of fluorescent H2 in NGC 2023

Observations of NGC 2023 and of peak 1 of Ori KL, obtained at 2.03-2.39 microns using the circular variable filter and a Fabry-Perot interferometer (spectral resolution 100 km/s) on the 3.8-m UKIRT on December 28-29, 1985, are reported. The data are presented in tables and graphs and characterized. Ten lines of vibrationally excited H2, indicating vibrational temperature Tv = 3600 K and rotational temperature Tr = 900-1500 K, are observed, and the para/ortho ratio is estimated as 1/(1.4-2.0). The corresponding values for Ori KL are found to be Tr = Tv = 1600-3300 K and para/ortho = 1/3. 20 references.

The evolution of the infrared emission from the type II supernova 1980k in NGC 6946: the dust formation model

The paper presents 1-4 micron photometry of supernova 1980 k in NGC 6946 obtained over a period of 1 year following the outburst. During the period between 1980 November 1 and December 19, the infrared emission probably originated from the extended atmosphere of the expanding star. The JHKL colors and a 1.3-2.6-micron spectrum observed during this period correspond to those of a blackbody with an average temperature of about 5000 K. Observations around 1981 May 31 showed that the supernova developed an infrared excess after 1980 December. This infrared excess persisted through 1981 October and is consistent with the appearance of thermal emission from about 700 to 900 K dust in addition to a hotter photosphere. The similarity of this behavior to that of the infrared evolution of some novae suggests that dust formation may be occurring in the supernova ejecta. The hypothesis, that the emission arises from preexisting grains in a circumstellar shell which are heated by the supernova outburst, is also consistent with the data.