THE BROWN DWARF KINEMATICS PROJECT (BDKP). III. PARALLAXES FOR 70 ULTRACOOL DWARFS
THE BROWN DWARF KINEMATICS PROJECT (BDKP). III. PARALLAXES FOR 70 ULTRACOOL DWARFS
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棕矮星运动学项目（BDKP）。
DOI：
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发表时间：
2012
期刊：
影响因子：
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通讯作者：
G. Anglada
中科院分区：
文献类型：
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作者：
J. Faherty;A. Burgasser;F. Walter;N. S. van der Bliek;M. Shara;K. Cruz;A. West;F. Vrba;G. Anglada
我们报道了70颗超冷矮星的视差测量，其中包括11颗M晚期矮星、32颗L矮星和27颗T矮星。在这个样本中，14颗M和L矮星表现出低表面重力特征，6颗是紧密双星系统，2颗是贫金属亚矮星。我们将我们的新测量结果与之前发布的114个UCD视差和光学中红外光度法相结合，以检查光谱类型/绝对星等和颜色-颜色图的趋势。我们报道了谱型与MJHK之间的新的多项式关系。将已解析的L/T跃迁双星包括在关系中，我们发现没有理由在L/T边界上区分“亮”(未解析的双星)和“弱”(单源)样品。分离早期的T矮星，我们发现T0-T4源的亮化在存在[1.2-1.4]MAG差的MJ中非常明显。在MH发生了类似的但被抑制的亮化，而在MK可以看到[−0.2to−0.3]MAG的平台化或变暗。通过与重力、金属度和云层厚度变化的演化模式的比较，验证了对于T矮星，减小云层厚度重现了棕矮星的近红外色等图。然而，我们发现，为了解释L-矮星/T-矮星跃迁的发亮和色星等图，需要沿着T0-T4窄谱亚型的1200±100K的接近恒定的温度。与模型相比，L矮星和T矮星都有相当多的红色或潜在的“超云层”，其中许多已知是年轻的，这表明增强的光球尘埃和年轻之间存在关联。对于低表面重力或年轻伴星L矮星，我们发现与同等光谱类型的天体相比，MJH和/或MK中的10个矮星中有8个至少是[0.21.0]MAG弱光。我们推测这是尘埃不透明度增加的结果，并得出结论，低表面重力的L矮星需要一个全新的谱型/绝对星等多项式来进行分析。
We report parallax measurements for 70 ultracool dwarfs (UCDs) including 11 late-M, 32 L, and 27 T dwarfs. In this sample, 14 M and L dwarfs exhibit low surface gravity features, 6 are close binary systems, and 2 are metal-poor subdwarfs. We combined our new measurements with 114 previously published UCD parallaxes and optical–mid-IR photometry to examine trends in spectral-type/absolute magnitude, and color–color diagrams. We report new polynomial relations between spectral type and MJHK. Including resolved L/T transition binaries in the relations, we find no reason to differentiate between a “bright” (unresolved binary) and a “faint” (single source) sample across the L/T boundary. Isolating early T dwarfs, we find that the brightening of T0–T4 sources is prominent in MJ where there is a [1.2–1.4] mag difference. A similar yet dampened brightening of [0.3–0.5] mag happens at MH and a plateau or dimming of [−0.2 to −0.3] mag is seen in MK. Comparison with evolutionary models that vary gravity, metallicity, and cloud thickness verifies that for L into T dwarfs, decreasing cloud thickness reproduces brown dwarf near-IR color–magnitude diagrams. However we find that a near constant temperature of 1200 ±100 K along a narrow spectral subtype of T0–T4 is required to account for the brightening and color–magnitude diagram of the L-dwarf/T-dwarf transition. There is a significant population of both L and T dwarfs which are red or potentially “ultra-cloudy” compared to the models, many of which are known to be young indicating a correlation between enhanced photospheric dust and youth. For the low surface gravity or young companion L dwarfs we find that 8 out of 10 are at least [0.2–1.0] mag underluminous in MJH and/or MK compared to equivalent spectral type objects. We speculate that this is a consequence of increased dust opacity and conclude that low surface gravity L dwarfs require a completely new spectral-type/absolute magnitude polynomial for analysis.
L Subdwarf SDSS 的光学和近红外光谱 J125637 13â022452 4
DOI：
10.1088/0004-637x/697/1/148
发表时间：
2009
期刊：
The Astrophysical Journal
影响因子：
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作者：
Burgasser;Adam J;Soeren;Helling;Christiane;Sanderson;Robyn E;Bochanski;John J;Hauschildt;Peter H.
通讯作者：
Peter H.