P.E. Clegg

THE INFRARED ASTRONOMICAL SATELLITE (IRAS) MISSION

The Infrared Astronomical Satellite (IRAS) consists of a spacecraft and a liquid helium cryostat that contains a cooled IR telescope. The telescopes focal plane assembly is cooled to less than 3 K, and contains 62 IR detectors in the survey array which are arranged so that every source crossing the field of view can be seen by at least two detectors in each of four wavelength bands. The satellite was launched into a 900 km-altitude near-polar orbit, and its cryogenic helium supply was exhausted on November 22, 1983. By missions end, 72 percent of the sky had been observed with three or more hours-confirming scans, and 95 percent with two or more hours-confirming scans. About 2000 stars detected at 12 and 25 microns early in the mission, and identified in the SAO (1966) catalog, have a positional uncertainty ellipse whose axes are 45 x 9 arcsec for an hours-confirmed source.

Infrared galaxies in the IRAS minisurvey

A total of 86 galaxies have been detected at 60 μm in the high galactic latitude portion of the IRAS minisurvey. The surface density of detected galaxies with flux densities greater than 0.5 Jy is 0.25 deg^(-2). Virtually all the galaxies detected are spiral galaxies and have an infrared to blue luminosity ratio ranging from 50 to 0.5. For the infrared-selected sample, no obvious correlation exists between infrared excess and color temperature. The infrared flux from 10 to 100 μm contributes approximately 5% of the blue luminosity for galaxies in the magnitude range 14 < m_(pg) < 18 mag. The fraction of interacting galaxies is between one-eighth and one-fourth of the sample.

Quasars measured by the Infrared Astronomical Satellite

On presente les resultats dobservations 12-100 μm de 179 quasars obtenues par IRAS. La luminosite IR sechelonne jusqua 10 13,9 L ○. . Aucune propriete IR des quasars nest fortement correlee a leurs proprietes radio

INFRARED-EMISSION FROM M31

Maps of M31 have been obtained at wavelengths of 12, 25, 60, and 100 microns. Emission is detected from the center and from a ring of 50 arcmin radius. The ring is that also seen in H I, in H II, and in radio continuum radiation. The spectrum of the central emission suggests a hotter dust temperature than in the ring. M31 is a weak infrared source, the radiation measured longward of 12 microns being only 3 percent of its total luminosity. The two closest companion galaxies, M32 and NGC 205, have also been detected.

Unidentified point sources in the IRAS minisurvey

Nine bright pointlike 60 p.m sources have been selected from the sample of 8709 sources in the IRAS minisurvey. These sources have no counterparts in a variety of catalogs of nonstellar objects. Four objects have no visible counterparts, while five have faint stellar objects visible in the error ellipse. These sources do not resemble objects previously known to be bright infrared sources.

A 25 micron component in 3C 390.3

Infrared Astronomical Satellite (IRAS) observations show that there is a maximum in the continuum energy distribution of the broad-line radio galaxy 3C 390.3 near 25µm and that this active galaxy emits most of its energy in the infrared. If the 25µm component is thermal, its temperature is approximately 180 K, and its size must exceed tens of parsecs.

THE IRAS MINISURVEY

Before the main IRAS all-sky survey was started, a preliminary survey of 900 deg^2 was carried out. Some results from this minisurvey are given here. The completeness of the minisurvey at galactic latitudes lbl = 20°-40° drops sharply at flux densities below 0.4, 0.4, 0.5, and 2.5 Jy at 12, 25, 60, and 100 μm. The corresponding surface densities of point sources brighter than these flux levels are 1.1, 0.4, 0.65, and 1.25 deg^(-2) respectively. Outside the galactic plane, the majority of the sources at 12 and 25 μm are stars, while galaxies make up a significant proportion of 60 μm sources. The 100 μm band is dominated by emission from interstellar dust over much of the minisurvey area.

IRAS observations of radio-quiet and radio-loud quasars

Observations from 12 to 100 microns are presented of two radio-quiet and three radio-loud quasars. Over this wavelength range, all five have grossly similar continuum energy distributions. The continua of the radio-loud quasars are consistent with synchrotron radiation. There is an indication, however, of excess 100 micron emission in the two radio-quiet quasars.

A REVIEW OF THE 1ST OBSERVATIONS OF STARS USING THE INFRARED ASTRONOMICAL SATELLITE (IRAS)

The primary aim of the IRAS mission is a survey of the entire sky at infrared wavelengths of 12, 25, 60 and 100 μm. Some of the preliminary results of the IRAS mission relating to stars include: 1) a characterization of the properties of the infrared sky based on a careful survey of a 900 sq. dog. of sky; 2) the presence of young stars of roughly solar mass within the dense cores of dark clouds; 3) the existence of a cloud of large dust particles around the AO V star, Vega, implying, perhaps, the existence of a pre-planetary system around that star; and 4) the discovery of the infrared counterparts to a large number of stellar OH masers.