Subaru/VLT/MMT对绕HR 8799轨道运行的行星的1- 5微米联合研究：大气性质、质量和形成的意义
A Combined Subaru/VLT/MMT 1--5 Micron Study of Planets Orbiting HR 8799: Implications for Atmospheric Properties, Masses, and Formation
摘要：
我们提供了HR 8799的新的1- 1.25微米（z和J波段）Subaru/IRCS和2微米（K波段）VLT/NaCo数据，以及Hinz等人（2010）首次提供的3- 5微米MMT/Clio数据的重新还原。我们的VLT/NaCo数据产生了第四颗行星的探测，预计距离约为15 AU -“HR 8799 e”。我们还报告了新的，虽然在1.03微米和3.3微米的HR 8799 b的微弱检测。与野外褐矮星的经验比较表明，至少HR 8799 b和HR 8799 c，可能还有HR 8799 d，具有近中红外颜色/星等，与L/T矮星序列显着不同。适用于棕矮星的标准云顶大气模型只提供（勉强）有统计意义的拟合HR 8799 b和c的非物理小半径。具有棕矮星中不存在的较厚云层的模型更准确地再现了行星的SED，并且不需要重新调整行星的半径。我们的初步模型表明HR 8799 b的log（g）= 4- 4.5，Teff = 900 K，而HR 8799 c、d和（通过推断）e的log（g）= 4- 4.5，Teff = 1000- 1200 K。结合行星演化模型和新的动力学稳定性极限的结果，HR 8799 b、c、d和e的质量分别为6- 7 Mj、7- 10 Mj、7- 10 Mj和7- 10 Mj。“补丁”云处方可以提供更好的拟合数据，并可能降低估计的表面重力和质量。最后，与最近的一些说法相反，通过核心吸积形成HR 8799行星仍然是合理的，尽管这样的系统可能很罕见。
英文摘要：
We present new 1--1.25 micron (z and J band) Subaru/IRCS and 2 micron (K band) VLT/NaCo data for HR 8799 and a rereduction of the 3--5 micron MMT/Clio data first presented by Hinz et al. (2010). Our VLT/NaCo data yields a detection of a fourth planet at a projected separation of ~ 15 AU -- "HR 8799e". We also report new, albeit weak detections of HR 8799b at 1.03 microns and 3.3 microns. Empirical comparisons to field brown dwarfs show that at least HR 8799b and HR8799c, and possibly HR 8799d, have near-to-mid IR colors/magnitudes significantly discrepant from the L/T dwarf sequence. Standard cloud deck atmosphere models appropriate for brown dwarfs provide only (marginally) statistically meaningful fits to HR 8799b and c for unphysically small radii. Models with thicker cloud layers not present in brown dwarfs reproduce the planets' SEDs far more accurately and without the need for rescaling the planets' radii. Our preliminary modeling suggests that HR 8799b has log(g) = 4--4.5, Teff = 900K, while HR 8799c, d, and (by inference) e have log(g) = 4--4.5, Teff = 1000--1200K. Combining results from planet evolution models and new dynamical stability limits implies that the masses of HR 8799b, c, d, and e are 6--7 Mj, 7--10 Mj, 7--10 Mj and 7--10 Mj. 'Patchy" cloud prescriptions may provide even better fits to the data and may lower the estimated surface gravities and masses. Finally, contrary to some recent claims, forming the HR 8799 planets by core accretion is still plausible, although such systems are likely rare.
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