Daniel F. Lester

Testing models of low-mass star formation - High-resolution far-infrared observations of L1551 IRS 5

A 50 and 100 micron wavelength study of L151 IRS 5 has yielded data consistent with the Adams et al. (1987) theoretical model prediction. It has proven possible to constrain a range of possible density gradients through source-emission modeling on the basis of the spherically-symmetric radiative transfer program of Egan et al. (1988) and a comparison of the observed scans at 50 and 100 microns. Attention is given to the effects of varying the dust grain properties of the spherical energy distribution of the source; the amount of mid-IR emission is highly sensitive to dust opacity and, because of poorly understood dust properties, is not a sensitive test for the presence of disks. 55 refs.

Observation of the nu-squared band of PH3 in the atmosphere of Saturn

Observation of the

Near-infrared line and continuum emission from the blue dwarf galaxy II Zw 40

nu

The far-infrared structure of the luminous interacting galaxy Arp 299

sub 2

Detection of fluorescent molecular hydrogen emission in the planetary nebula Hubble 12

band of PH

Infrared emission from young stars in the nucleus of M82

sub 3

The science case and mission concept for the Single Aperture Far-Infrared (SAFIR) Observatory

in the Saturnian atmosphere represents the first positive identification of this compound in the planet. The observed spectrum is consistent with line formation in the planets troposphere where the dominant sources of opacity are molecular hydrogen and unsaturated phosphine vapor. (AIP)

G5.89-0.39: A compact H II region with a very dense circumstellar dust torus

A multicolor analysis of new near-infrared line and continuum measurements indicates that nebular recombination emission and photospheric radiation from young blue stars produce most of the near-infrared continuum emission in the central 6 arcsec of the dwarf galaxy II Zw 40. The derived nebular recombination level is in excellent agreement with independent observations of the radio free-free continuum. It is found that evolved stars, which dominate the near-infrared emission from normal galaxies, contribute no more than 25 percent of the total 2.2 micron flux in the central region of II Zw 40. It is concluded that the total mass of the evolved stellar population in the central 400 pc of the galaxy is less than about two hundred million solar. The total mass of recently formed stars is about two million solar, and the stellar mass ratio is exceptionally large. Thus, II Zw 40 is a quintessential starburst galaxy. 27 references.

Single aperture far-infrared observatory (SAFIR)

High-resolution far-infrared observations of the galaxy NGC 4945 have been obtained from the Kuiper Airborne Observatory. Using new observational techniques and nonlinear deconvolution routines, it is found that virtually all of the far-infrared luminosity originates from a nuclear source no larger than 12 arcsec x 9 arcsec (225 pc x 170 pc) in extent. This size constraint, coupled with the far-infrared dust temperature, indicates that the source is deeply embedded in dust: the lower limit for the 100 micron optical depth is 0.35, which is by far the largest yet measured in an external galaxy. Published optical spectra of NGC 4945 reveal a heavily obscured nonthermal source which exhibits broad line profiles typical of a Seyfert 2 active nucleus; it is concluded that the far-infrared emission is probably due to thermal radiation from dust grains surrounding the nonthermal nuclear source. A compact cluster of massive young stars may also contribute to the infrared luminosity, but the evidence for such star-forming activity is weak.