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HD 203725


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관련 글

The Spectra of T Dwarfs. I. Near-Infrared Data and Spectral Classification
We present near-infrared spectra for a sample of T dwarfs, including 11new discoveries made using the 2 Micron All Sky Survey. These objectsare distinguished from warmer (L-type) brown dwarfs by the presence ofmethane absorption bands in the 1-2.5 μm spectral region. A firstattempt at a near-infrared classification scheme for T dwarfs is made,based on the strengths of CH4 and H2O bands andthe shapes of the 1.25, 1.6, and 2.1 μm flux peaks. Subtypes T1 V-T8V are defined, and spectral indices useful for classification arepresented. The subclasses appear to follow a decreasing Teffscale, based on the evolution of CH4 and H2O bandsand the properties of L and T dwarfs with known distances. However, wespeculate that this scale is not linear with spectral type for cooldwarfs, due to the settling of dust layers below the photosphere andsubsequent rapid evolution of spectral morphology aroundTeff~1300-1500 K. Similarities in near-infrared colors andcontinuity of spectral features suggest that the gap between the latestL dwarfs and earliest T dwarfs has been nearly bridged. This argument isstrengthened by the possible role of CH4 as a minor absorber,shaping the K-band spectra of the latest L dwarfs. Finally, we discussone peculiar T dwarf, 2MASS 0937+2931, which has very blue near-infraredcolors (J-Ks=-0.89+/-0.24) due to suppression of the 2.1μm peak. The feature is likely caused by enhanced collision-inducedH2 absorption in a high-pressure or low-metallicityphotosphere.

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관측 및 측정 데이터

별자리:인디언자리
적경:21h25m23.47s
적위:-45°09'42.9"
가시등급:6.824
거리:152.207 파섹
적경상의 고유운동:17.8
적위상의 고유운동:-15
B-T magnitude:6.965
V-T magnitude:6.836

천체목록:
일반명   (Edit)
HD 1989HD 203725
TYCHO-2 2000TYC 8423-922-1
USNO-A2.0USNO-A2 0375-39430384
HIPHIP 105779

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