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HD 41473


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Discovery of the Coolest Extreme Subdwarf
We report the discovery of LEHPM 2-59 as the coolest extreme M subdwarf(esdM) found to date. Optical and near-infrared spectroscopy demonstratethat this source is of later spectral type than the esdM7 APMPMJ0559-2903, with the presence of strong alkali lines (including Rb I),VO absorption at 7400 Å, and H2O absorption at 1.4μm. Current optical classification schemes yield a spectral type ofesdM8, making LEHPM 2-59 one of only two ultracool esdMs known. Thesubstantial space velocity of this object (Vgalactic~-180 kms-1) identifies it as a halo star. Spectral model fits to theoptical and near-infrared spectral data for this and four otherlate-type esdMs indicate that LEHPM 2-59 is the coolest esdM currentlyknown, with Teff=2800-3000 K and -1.5<~[M/H]<~-2.0.Comparison of Teff determinations for M dwarfs and esdMsbased on spectral model fits from this study and the literaturedemonstrate a divergence in Teff scales beyond spectral types~M5/esdM5, as large as 600-800 K by types M8/esdM8. While thisdivergence is likely an artifact of the underlying classificationscheme, it may lead to systematic errors in the derived properties ofintermediate metallicity subdwarfs. We comment on the future ofultracool subdwarf classification and suggest several ideas foraddressing shortcomings in current (largely extrapolated) schemes.

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观测天体数据

星座:天鴿座
右阿森松:06h04m07.22s
赤纬:-29°20'20.5"
视星:7.792
距离:332.226 天文距离
右阿森松适当运动:-6.8
赤纬适当运动:-0.8
B-T magnitude:7.761
V-T magnitude:7.79

目录:
适当名称   (Edit)
HD 1989HD 41473
TYCHO-2 2000TYC 6504-815-1
USNO-A2.0USNO-A2 0600-02917278
HIPHIP 28735

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