The Discovery of a Second Field Methane Brown Dwarf from Sloan Digital Sky Survey Commissioning Data     

Tsvetanov ZI  Golimowski DA  Zheng W  Geballe TR  Leggett SK  Ford HC  Davidsen AF  Uomoto A  Fan X  Knapp GR  Strauss MA  Brinkmann J  Lamb DQ  Newberg HJ  Rechenmacher R  Schneider DP  York DG  Lupton RH  Pier JR  Annis J  Csabai I  Hindsley RB  Ivesic Z  Munn JA  Thakar AR  Waddell P 《The Astrophysical journal》2000,531(1):L61-L65

We report the discovery of a second field methane brown dwarf from the commissioning data of the Sloan Digital Sky Survey (SDSS). The object, SDSS J134646.45-003150.4 (hereafter SDSS 1346-00), was selected because of its very red color and stellar appearance. Its spectrum between 0.8 and 2.5 μm is dominated by strong absorption bands of H2O and CH4 and closely mimics those of Gliese 229B and SDSS 162414.37+002915.6 (hereafter SDSS 1624+00), two other known methane brown dwarfs. SDSS 1346-00 is approximately 1.5 mag fainter than Gliese 229B, suggesting that it lies about 11 pc from the Sun. The ratio of flux at 2.1 μm to that at 1.27 μm is larger for SDSS 1346-00 than for Gliese 229B and SDSS 1624+00, which suggests that SDSS 1346-00 has a slightly higher effective temperature than the others. Based on a search area of 130 deg2 and a detection limit of z*=19.8, we estimate a space density of 0.05 pc-3 for methane brown dwarfs with Teff approximately 1000 K in the 40 pc3 volume of our search. This estimate is based on small-sample statistics and should be treated with appropriate caution.  相似文献   

X-ray observations of filament eruption in the 1980 May 21 flare     

D. A. Batchelor  K. P. Hindsley 《Solar physics》1991,135(1):99-105

X-ray and H observations of an erupting filament, discussed herein, and other observations of the associated flare on 1980 May 21, suggest that an erupting filament played a major role in the X-ray flare. While Antonucci et al. (1985) analyzed the May 21 flare as one of the best cases of chromospheric evaporation, the possible contribution from X-ray emitting erupting plasma has been ignored. We show that pre-heated plasma existed and may have contributed part of the blue-shifted X-ray emission observed in the Caxix line, which was formerly attributed solely to chromospheric evaporation. Thus it remains an open question - in two-ribbon flares in particular - just how important chromospheric evaporation is in flare dynamics.  相似文献