IRAS observations of nearby main sequence stars and modeling of excess infrared emission |
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| Institution: | 1. Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, P.O. Box 64, Helsinki 00014, Finland;2. Helsinki Institute of Sustainability Science, University of Helsinki, P.O. Box 4, Helsinki 00014, Finland;3. Kjeller Vindteknikk, Tekniikantie 14, Espoo 02150, Finland;4. Aerosol Physics Laboratory, Physics Unit, Faculty of Engineering and Natural Sciences, Tampere University, P.O. Box 692, Tampere 33014, Finland;5. Atmospheric Composition Research, Finnish Meteorological Institute, P.O. Box 503, Helsinki 00101, Finland;6. Helsinki Region Environmental Services Authority, Ilmalantori 1, Helsinki 00240, Finland;7. Department of Automotive and Mechanical Engineering, Metropolia Applied University, P.O. Box 4071, Vantaa 01600, Finland;1. National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China;2. State Key Laboratory of Remote Sensing Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100101, China;3. College of Geography and Environmental Science, Northwest Normal University, Lanzhou 730070, China;1. Department Earth, Planetary and Space Sciences, University of California, Los Angeles, CA 90095, USA;2. Johns Hopkins University, Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USA;3. Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet Street, London, WC1E 7HX, UK |
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| Abstract: | IRAS observations of the 50 stellar systems within 5.2 pc reveal 6 systems with significant flux in excess of that expected from photospheric emission at wavelengths of 25 to 100 μm. No star in this sample has a significant excess at 12 μm. Ground-based measurements of the near-infrared flux were used to determine the brightness of the stellar photospheres for extrapolation to the far infrared.Examples of far-infrared excess in the 5-pc sample, in addition to the previously known case of ε Eri (Gliese 144), are: τ Ceti (Gliese 71), which has an excess at 60 μm but was not detected at 100 μm; Ross 128 (Gliese 447), with excess at 60 and 100 μm; 61 Cygni (Gliese 820) with excess at 60 and 100 μm; and α CMa (Gliese 244) and BD+43° 4305 (Gliese 873), with excess at 100 μm only. There is cold extended emission from “infrared cirrus” near the line of sight to the latter three stars that may contribute to the apparent excesses.Bright far-infrared excesses associated with the main sequence stars α Lyr, α PsA, β Pic, and ε Eri have been interpreted as emission from shells of orbiting particles, possibly connected to the process of planet formation. The excesses determined here are all much fainter than those four. Precise measurement of the source profile shapes and peak positions of the fainter excesses was not possible. For that reason and because of the possibility that background ISM emission is involved, they are considered candidates rather than definite discoveries of new circumstellar particle clouds. The excesses associated with Ross 128 and 61 Cygni are discussed in terms of the characteristic radii and effective radiating areas of clouds of particles that could produce the observed emission. |
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