Hh Aumann

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.

DISCOVERY OF A SHELL AROUND ALPHA-LYRAE

IRAS observations of Alpha Lyrae reveal a large infrared excess beyond 12 microns. The excess over an extrapolation of a 10,000 K blackbody is a factor of 1.3 at 25 microns, 7 at 60 microns, and 16 at 100 microns. The source of 60 microns emission has a diameter of about 20 arcsec. This is the first detection of a large infrared excess from a main-sequence star without significant mass loss. The most likely origin of the excess is thermal radiation from solid particles more than a millimeter in radius, located approximately 85 AU from Alpha Lyr and heated by the star to an equilibrium temperature of 85 K. These results provide the first direct evidence outside of the solar system for the growth of large particles from the residual of the prenatal cloud of gas and dust.

Infrared cirrus - New components of the extended infrared emission

Extended sources of far-infrared emission superposed on the zodiacal and galactic backgrounds are found at high galactic latitudes and near the ecliptic plane. Clouds of interstellar dust at color temperatures as high as 35 K account for much of this complex structure, but the relationship to H I column density is not simple. Other features of the extended emission show the existence of warm structures within the solar system. Three bands of dust clouds at temperatures of 150-200 K appear within 10 deg on both sides of the ecliptic plane. Their ecliptic latitudes and derived distances suggest that they are associated with the main asteroid belt. A third component of the 100-micron cirrus, poorly correlated with H I, may represent cold material in the outer solar system or a new component of the interstellar medium.

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.

IRAS OBSERVATIONS OF THE DIFFUSE INFRARED BACKGROUND

IRAS data reveal bright emission from interplanetary dust which dominates the celestial background at 12, 25, and 60 microns except near the galactic plane. At 100 microns, interplanetary dust emission is prominent only near the ecliptic plane; diffuse galactic emission is found over the rest of the sky. At the galactic poles, the observed brightness implies that A(v) is likely to be of order 0.1 mag. The angular variation of the zodiacal emission in the ecliptic plane and in the plane at elongation 90 deg, and an annual modulation of the ecliptic pole brightness, are generally consistent with previously determined interplanetary dust distributions.

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.

The formation of solar type stars - IRAS observations of the dark cloud Barnard 5

Observations of the dark cloud Barnard 5 show two compact sources of radiation within the dense core. IRS 1 is associated with 30-800 K dust, has a total luminosity of about 10 L, and is presumably a newly formed star of rougly solar mass. IRS 2 has a much cooler color temperature, approximately 25 K, and emits only 1.3 L. Its status is unclear, but IRS 2 may be at a very early stage of gravitational within the cloud heated by the interstellar radiation field. Also within the confines of the cloud are two point sources, which, if associated with the cloud, each emit about 0.5 L in the IRAS bands. These may be T Tauri stars, separated from the cloud but still enshrouded in dust shells.

IRAS images of the galactic center

Some preliminary IRAS results in the form of images at 12, 25, 60, and 100 microns of an 8 deg x 15 deg area around the galactic center are presented. These absolute intensity maps have unprecedented sensitivity combined with high angular resolution, wide field coverage, and large wavelength range. They give a broad view of the central galaxy revealing previously unseen details, especially in regions far from the central few arcmin. Well-defined infrared features in the nucleus correspond to the nuclear radio sources Sgr A, B2, C, and D. Extremely faint structures are detected, such as the cold molecular cloud associated with Sgr B2 which has never before been detected at wavelenths shorter than 40 microns.

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.