infrared sources


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infrared sources

A variety of objects emitting strongly in the infrared (see infrared radiation). Many stars exhibit an infrared excess in that they radiate more strongly in the 1–20 μm waveband than would be expected from their spectral type. In most cases the excess arises from circumstellar shells containing cosmic dust grains that are heated by the visible and UV radiation from the central star. Protostars and their associated dust clouds are also strong infrared emitters. Many T Tauri stars emit infrared radiation, in some cases by thermal bremsstrahlung and/or emission from heated dust. At longer wavelengths (60–200 μm) cool molecular clouds containing dust are found to be infrared sources.

Infrared line emission occurs from a variety of different complex regions, particularly from H II regions and associated molecular-cloud interfaces. Lines from atomic hydrogen are seen in the near-infrared (Brackett and Paschen lines), and in the mid- and far-infrared the lines occur from neutral and ionized states of neon, oxygen, nitrogen, sulfur, and iron. Highly ionized species of, for example, oxygen (O III) and nitrogen (N III) can be identified by the forbidden lines in their infrared spectra. The molecule carbon monoxide has been detected in the far-infrared from some sources, the lines measured arising from the rotational spectrum of the molecule.

Infrared emission is also found in extragalactic sources (see IRAS) and is strongly correlated with galaxy type: elliptical and lenticular galaxies emit little or no infrared while most spiral galaxies are infrared emitters. Active galaxies, such as Seyfert type II, BL Lac objects, and quasars, exhibit infrared emission from their nuclei. It is unclear at the present time whether this is thermal emission by dust in the nuclei or is due to nonthermal synchrotron emission. Galaxies that are interacting or merging are also seen to be strong infrared continuum emitters. This may be due to the triggering of star formation in one or both galaxies.

References in periodicals archive ?
In just 10 months, IRAS detected 350,000 cosmic infrared sources, increasing the cosmic catalog of such sources by 70 percent.
The trick is to separate this faint signal from the intense infrared sources in the neighborhood of Earth.
This unique kiosk will be wireless enabled for fall shipment dates in order to make prints from Bluetooth(R) and infrared sources, and also provides additional workflow capabilities by increasing the number of images viewed on screen at a given time.
When its diffraction grating is placed in the light path, MIPS can record infrared sources at a multitude of wavelengths between 50 and 100 microns--thus providing both spatial and spectral information.
This is a huge step forward in realizing the dream of using infrared sources to analyze the chemical contents of any mixture," said Professor Richard Zare of Stanford University's chemistry department, a world-renowned authority in spectroscopic techniques.
But already it includes 163 million cataloged infrared sources.
Searching the catalog of infrared sources made by the Infrared Astronomy Satellite, they found that their 2-micron source corresponds to one of the brightest infrared sources in the Orion cloud, which has an infrared luminosity between 250 and 300 times that of the sun.
And since planetary nebulae follow the red-giant phase, then proto-planetary nebulae must also be infrared sources and a deeper probe than the AFGL survey might uncover them as well.
The Infrared Astronomy Satellite (IRAS), which in 1983 performed the first survey of infrared sources across the entire sky before finally running out of its vital cooling fluid, is taking on a new job.

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