MEASURING TINY MASS ACCRETION RATES ONTO YOUNG BROWN DWARFS
MEASURING TINY MASS ACCRETION RATES ONTO YOUNG BROWN DWARFS
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测量年轻褐矮星的微小质量吸积率
DOI：
10.1088/0004-637x/696/2/1589
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
L. Hillenbrand
中科院分区：
文献类型：
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作者：
G. Herczeg;K. Cruz;L. Hillenbrand
我们目前的低分辨率凯克I/LRIS光谱跨度从3200到9000年的九个年轻的棕矮星和三个低质量的恒星在TW Hya协会和上斯科。棕矮星的光谱类型从M5.5到M8.75不等，其中两颗有早期L型矮星的近红外光谱类型。我们报告了低质量恒星TW Hya和Hen 3- 600 A以及棕矮星2 MASS J12073347 - 3932540、USCoCTIO 128、SSSPM J1102 - 3431、USCo J160606.29 - 233513.3、DENIS-P J160603.9 - 205644和Oph J162225 - 240515 B的过量巴耳末连续辐射的新吸积率。以及低质量星星Hen 3- 600 B和棕矮星UScoCTIO 112、Oph J162225− 240515 A和USco J160723.82−221102.0的吸积上限。对于我们样本中在短波长下最暗的六颗褐矮星，吸积光度或上限只有在图像在大波长间隔上进行分箱时才能测量。这种方法将我们对棕矮星吸积速率的敏感度扩展到10−13 M/年。由于从过量的巴耳末连续辐射测量吸积率的能力取决于过量的连续辐射和底层光球之间的对比度，对于具有早期光谱类型的天体，吸积率的上限要高得多。在我们的吸积率测量的绝对不确定性，包括吸积模型，褐矮星质量和距离的不确定性。2 MASS J12073347 - 3932540的吸积速率为2 × 10−12 M/年，与之前两次测量的结果相差不到15%，尽管Hα通量变化很大。
We present low-resolution Keck I/LRIS spectra spanning from 3200 to 9000 Å of nine young brown dwarfs and three low-mass stars in the TW Hya Association and in Upper Sco. The optical spectral types of the brown dwarfs range from M5.5 to M8.75, though two have near-IR spectral types of early L dwarfs. We report new accretion rates derived from excess Balmer continuum emission for the low-mass stars TW Hya and Hen 3-600A and the brown dwarfs 2MASS J12073347−3932540, UScoCTIO 128, SSSPM J1102−3431, USco J160606.29−233513.3, DENIS-P J160603.9−205644, and Oph J162225−240515B, and upper limits on accretion for the low-mass star Hen 3-600B and the brown dwarfs UScoCTIO 112, Oph J162225−240515A, and USco J160723.82−221102.0. For the six brown dwarfs in our sample that are faintest at short wavelengths, the accretion luminosity or upper limit is measurable only when the image is binned over large wavelength intervals. This method extends our sensitivity to accretion rate down to ∼10−13 M☉yr-1 for brown dwarfs. Since the ability to measure an accretion rate from excess Balmer continuum emission depends on the contrast between excess continuum emission and the underlying photosphere, for objects with earlier spectral types the upper limit on accretion rate is much higher. Absolute uncertainties in our accretion rate measurements of ∼3–5 include uncertainty in accretion models, brown dwarf masses, and distance. The accretion rate of 2 × 10−12 M☉ yr−1 onto 2MASS J12073347−3932540 is within 15% of two previous measurements, despite large changes in the Hα flux.