一颗L型次矮星的视差和亮度测量
Parallax and Luminosity Measurements of an L Subdwarf
摘要：
我们提出了第一个视差和光度测量的L亚矮星，sdL 7 2 MASS J 05325346 +8246465。USNO红外天体测量计划进行了三年多的观测，得出天体测量距离为26.7+/-1.2秒差距，自行为2.6241+/-0.0018”/年。结合宽带光谱和光度测量，我们确定了log（Lbol/Lsun）= -4.24+/-0.06和Teff = 1730+/-90 K（后者假设年龄为5-10 Gyr），与中型L场矮星相当。2 MASS J 05325346 +8246465的光度与理论演化模型的比较显示，它的质量刚好低于持续的氢燃烧极限，因此是一颗棕矮星。它的运动学表明，一个~ 1.1亿年，逆行的银河系轨道，这是偏心的（3 <~ R <~ 8.5 kpc）和延伸远离平面（Δ Z = +/-2 kpc），符合成员的内晕人口。2 MASS J 05325346 +8246465的相对明亮的J带幅度意味着在1.2微米区域内显着降低的不透明度，与先前提出的抑制冷凝物形成一致。它的太阳下金属丰度仍然是限制其质量的主要限制;这两个参数的测定将为低质量恒星和棕矮星的内部和演化模型提供强有力的测试。
英文摘要：
We present the first parallax and luminosity measurements for an L subdwarf, the sdL7 2MASS J05325346+8246465. Observations conducted over three years by the USNO infrared astrometry program yield an astrometric distance of 26.7+/-1.2 pc and a proper motion of 2.6241+/-0.0018"/yr. Combined with broadband spectral and photometric measurements, we determine a luminosity of log(Lbol/Lsun) = -4.24+/-0.06 and Teff = 1730+/-90 K (the latter assuming an age of 5-10 Gyr), comparable to mid-type L field dwarfs. Comparison of the luminosity of 2MASS J05325346+8246465 to theoretical evolutionary models indicates that its mass is just below the sustained hydrogen burning limit, and is therefore a brown dwarf. Its kinematics indicate a ~110 Myr, retrograde Galactic orbit which is both eccentric (3 <~ R <~ 8.5 kpc) and extends well away from the plane (Delta_Z = +/-2 kpc), consistent with membership in the inner halo population. The relatively bright J-band magnitude of 2MASS J05325346+8246465 implies significantly reduced opacity in the 1.2 micron region, consistent with inhibited condensate formation as previously proposed. Its as yet unknown subsolar metallicity remains the primary limitation in constraining its mass; determination of both parameters would provide a powerful test of interior and evolutionary models for low-mass stars and brown dwarfs.
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