Rene J. Laureijs

Visual and Infrared Fluorescence from L1780

The paper presents IRAS survey observations of a high latitude galactic cloud with moderate extinction, L1780 (AB = 3m). The data are consistent with the hypothesis that the red excess observed in the visual spectrum of the cloud is due to fluorescence from the same species which gives rise to the 12 μm emission observed by IRAS.

Dust and molecular properties of the low-opacity cloud Lynds 1563

Optical, molecular, and far-infrared data are analyzed for L1563, estimated peak Ab 2.5 mag. The cloud is detected by IRAS at 12, 25, 60, and 100 microns, and with CO, (C-13)O, and H2CO molecules. A column density comparison yields an estimate of the temperature of the classical dust grains of 15.6 + or - 1 K, while the color temperature derived from the ratio I(60)/I(100) is 26 K. Both dust and color temperatures decrease toward the cloud center. 19 refs.

Fragmentation in Molecular Clouds

Fragments are detected in the outer parts of the B209 molecular cloud in a region of density 1000 cm−3 using 12CO, 13CO, H2CO, IRAS 60 and 100 µm images, discernable as velocity components, and have characteristics: ∼ 0.4 Pc; ∼2 M⨀;#x003C;MVRfragment>∼ 1.6 M⨀ km/s pc; Tgas ∼11 K; Tdusat ∼ 16 K??.The system of fragments has ∼ 0.5 pc and ∼ 1.6 M⨀ km/s pc.These are illustrated in Figure 1, which contains an IRAS 100 µm map made with Geisha and attendant U. Koln Gornergrat CO spectra for each respective fragment. The differing characteristic velocities of each fragment are readily apparent.

Infrared Properties of Interstellar Grains Derived from IRAS Observations

We have analyzed a sample of more than 10 isolated interstellar clouds, which have been observed by IRAS in all four bands (12, 25, 60 and 100 µm). The clouds range from very diffuse with no measurable extinction to dense objects with more than 4 m of blue extinction. The analysis of the distribution of energy emitted by each cloud over the four IRAS bands provides several results from which information on the general properties of grains in the infrared can be derived (Figure 1):

IRAS Observations of a ‘Typical’ Dark Cloud

We discuss the implications of the IRAS observations of a regular isolated diffuse cloud. The dependence of infrared radiation on the optical depth is different at short wavelengths (12 and 25 μm) and in the far-IR (60 and 100 μrn). Radiation at both 12 and 25 μrn appears to be due to nonequilibrium emission from the same population of small particles. The far-IR radiation can be explained by steady-state thermal emission from interstellar grains.