M. F. Campbell

Mid-Infrared Emission at Photodissociation Regions in the Orion Nebula

The mid-infrared emission from a photodissociation region (PDR) viewed edge-on in the Orion Nebula is examined through 8.7-20.6 ?m images and 8-13 ?m spectra. The polycyclic aromatic hydrocarbon (PAH) emission is located between the edges of H II regions and layers of [C I] emission, agreeing with PDR theory. Using a simple model, the spatial variations in the emission from PAHs detected at 8.6, 11.2, and 12.7 ?m are demonstrated to be directly proportional to the material column density and the intensity of the UV field. For a homogeneous, neutral cloud illuminated by a bright OB star, PDR theory predicts that the ultraviolet (UV) radiation is attenuated exponentially (e). The predicted UV attenuation is confirmed by observations of broad PAH emission features found at 8.6, 11.2, and 12.7 ?m. The PAH emission is found in cool regions having greater optical depths relative to regions where mid-infrared emission from ionized gas is observed. Through modeling we determine a gas density of 9.7 ? 104 cm-3. On large and small size scales, the relative strengths of the 8.6, 11.2, and 12.7 ?m PAH features at the bar of the Orion Nebula indicate that there is not a simple transition from ionized to neutral PAHs across the PDR.

Far-infrared observations of the Carina I and II H II regions

Far-infrared (35-175 microns) mapping and photometry are presented of the Carina I and II H II regions in the Carina Nebula (NGC 3372). The far-infrared source associated with Carina I has a half-power width of 2.7 arcmin and has no compact high-surface-brightness condensations, unlike many northern H II regions such as W51 or W49. The peak emission region is offset from the radio continuum peak in the direction of a dust lane to the west. It is proposed that the H II regions and far-IR source are both powered by the O-star cluster Tr 14 about 4 arcmin to the east. The H II region then represents an ionization front at the boundary of the dense cloud west of Tr 14, and the far-infrared emission is due to thermal radiation from the heated dust in the dark cloud. A similar model may also be applicable to the Carina II region.

Star formation in the NGC 7129 region - A CO molecular-line and far-infrared continuum study

Results are presented for a joint radio/IR study of the region around NGC 7129, a reflection nebula seen against a large dark cloud. The results reported include high-angular-resolution (C-12)O and (C-13)O line measurements, high-angular-resolution observations in the range from 35 to 200 microns, and observations at 10 to 20 microns of selected objects in the nebula. Important constraints are placed on the total stellar luminosities, dust densities and temperatures, and heating and cooling processes occurring in the nebula. Specifically, it is found that: (1) the (C-13)O and dust column densities increase significantly from west to east across the nebula; (2) the (C-13)O column density in the vicinity of the two brightest visible stars decreases relative to the column density north and south of those stars; (3) kinetic temperature increases along the whole boundary of the nebulosity; and (4) the strongest far-IR source in NGC 7129 is coincident with the pre-main-sequence star LkH-alpha 234.

Infrared observations of NGC 2071/IRS/ and AFGL 490 - Two low-luminosity young stars

Infrared observations are presented of two compact sources associated with molecular clouds. Photometry from 2 to 200 microns of the source associated with an OH maser in NGC 2071, OH 205.1-14.1, shows a steep increase in flux from 2 to 50 microns. Scans at several wavelengths fail to resolve the source. Photometry at 50-200 microns of the other object, GL 490, when combined with earlier 2-20-micron spectrophotometry, shows an infrared energy distribution that is much broader than that of the NGC 2071 source. Both sources are interpreted as young, possibly pre-main-sequence objects with differences in energy distributions due principally to differences in the distribution of circumstellar matter.

High spatial resolution far-infrared scans of W3(OH)

The strong far-infrared continuum source associated with the OH maser-ultracompact H II region W3(OH) was observed from the Kuiper Airborne Observatory in order to determine its size at 50 and 100 microns. Maximum entropy deconvolutions of the slit scans made in orthogonal directions across the source show it to be approximately circular with FWHM sizes of 8 arcsec and 13 arcsec at 50 and 100 microns, respectively. For these sizes, W3(OH) is optically thick in the far-infrared. A spherically symmetric, dusty molecular cloud model is developed to fit the data. 35 refs.

MID-INFRARED OBSERVATIONS OF M17

ABSTRACTMosaicsoftheM17southwestphotodissociationregion(PDR)atthemid-infraredwavelengths9.8,10.53,11.7, and 20.6 lm are presented. Mapsof hydrocarbon and ionized gas emission were derived by subtractingthe continuum at 9.8 lm from the 10.5 and 11.7 lm maps, respectively. Comparisons of the emission fromhydrocarbons and ionized gas to the 9.8 lm/20.6 lm color temperature and 9.8 lm opacity maps show thatregions of hotter 9.8 lm/20.6 lm color temperatures have increased emission from ionized gas, while thehydrocarbons are found in cooler regions with high 9.8 lm opacities. Emission at 20.6 lm is spatially corre-lated with 11.3 lm hydrocarbon emission. Two bright point sources found in the southwest PDR are high-mass young stellar objects caught at distinctly different early evolutionary phases. M17-UC1 appears to beolder than IRS 5 because it has less maser emission and has an observable H ii region in radio continuum.Both sources are modeled with a radiative transfer code, which takes advantage of both the spatial and spec-tral information available. Models that best match the profiles and spectral energy distribution of the ultra-compact H iiregion, M17-UC1, havecentral stars with aluminosity andtemperatureequal tothat ofazero-agemain-sequence(ZAMS)B0star,anouterradiuslessthan0.032pc,aninnerradiusaboutthesamesizeasthe radio observed H ii region, and a total shell mass of 0.6–3.4 M . The best-fit models underestimate thetotal observed flux found at near-infrared wavelengths, which suggests that a small, hot disk may be presentin M17-UC1. A second source, identified with the near-infrared source IRS 5, has comparable mid-infraredemission to M17-UC1. The best-fitting model to IRS 5 has a central star with a luminosity and temperatureequal to that of a ZAMS B0 star, an outer radius on the order of 1 pc, a small inner radius (0.001 pc), and atotalshellmassof70M .Keywords:Hiiregions — infraredradiation — ISM:individual(M17) — stars:formation

Strong far-infrared emission from a compact source in sharpless 140

High-spatial-resolution observations of S140 are presented at wavelengths from 35 to 175 microns. A single strong far-infrared source has been found coincident with a compact near-infrared and H2O maser source and the center of a molecular cloud. The far-infrared spectrum suggests either significant absorption in the 20-micron region or a two-temperature dust structure. The infrared luminosity of approximately 20,000 suns is comparable to that of a late O or early B star, although no radio continuum flux has been seen from this object. The source is quite likely a dust-embedded protostar.

Mid-Infrared Photometry and Spectra of Three High-Mass Protostellar Candidates at IRAS 18151–1208 and IRAS 20343+4129

We present arcsecond-scale mid-IRphotometry (in the 10.5 � mN bandand at24.8 � m), and low-resolutionspectra intheNband(R ’100)of acandidatehigh-massprotostellarobject(HMPO)inIRAS18151� 1208andof twoHMPO candidatesinIRAS20343+4129,IRS1andIRS3.Inaddition,wepresenthigh-resolutionmid-IRspectra(R ’ 80;000) of the two HMPO candidates in IRAS 20343+4129. These data are fitted with simple models to estimate the masses of gas and dust associated with the mid-IR-emitting clumps, the column densities of overlying absorbing dustandgas,theluminositiesof theHMPOcandidates,andthelikelyspectraltypeof theHMPOcandidateforwhich [Ne ii] 12.8 � m emission was detected (IRAS 20343+4129 IRS 3). We suggest that IRAS 18151� 1208 is a preultracompact H ii region HMPO, IRAS 20343+4129 IRS 1 is an embedded young stellar object with the luminosity of a B3 star, and IRAS 20343+4129 IRS 3i s aB 2 ZAMS star that has formed an ultracompact Hii region and disrupted its natal envelope. Subject headingg circumstellar matter — H ii regions — infrared: ISM — ISM: jets and outflows — stars: formation — stars: preYmain-sequence

High-resolution far-infrared observations of the galactic center

A map at 53 microns with 17-arcsec resolution and three-color observations at 53, 100, and 175 microns with 30-arcsec beams of Sgr A are presented. Sagittarius A is resolved into two main sources, one associated with the cluster of strong 10-micron sources and another about 45 arcsec to the southwest coincident with a weak 10-micron source. The dust temperature peaks near the strong 10-micron sources, but the 100-micron and 175-micron fluxes and the far-infrared optical depth are greatest near the southwest source. The amount of dust required to explain the far-infrared emission is comparable to that observed in absorption in the near-infrared.

An extended far-infrared emission complex at IC 1318b and IC 1318c

A map of extended 90 micron emission with 15 arcmin resolution is presented for sources centered on IC 1318b and c. A strong correlation is found between far-infrared emission and radio continuum emission, although a comparison of far-infrared and CO molecular line maps shows no similarity. Extended far-infrared sources have inferred gas densities, which implies that far-infrared emitting dust is mixed with the ionized gas. Far-infrared emission from dust is also observed in the nonthermal radio source DR 4 which is part of a supernova remnant, and the data are compatible with a core-halo model for the compact source DR 7.