DEAD, UNDEAD, AND ZOMBIE ZONES IN PROTOSTELLAR DISKS AS A FUNCTION OF STELLAR MASS
DEAD, UNDEAD, AND ZOMBIE ZONES IN PROTOSTELLAR DISKS AS A FUNCTION OF STELLAR MASS
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原恒星盘中的死亡区、不死区和僵尸区与恒星质量的关系
DOI：
10.1088/0004-637x/764/1/65
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发表时间：
2012
期刊：
影响因子：
--
通讯作者：
N. Turner
中科院分区：
文献类型：
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作者：
S. Mohanty;B. Ercolano;N. Turner
我们研究了太阳型恒星和极低质量恒星周围X射线电离粘性吸积盘中磁旋转不稳定性（MRI）的可行性。特别是，我们确定的磁盘区域，MRI可以关闭欧姆电阻率（所谓的死亡和不死区）或双极扩散（一个区域，我们称之为僵尸区）。我们考虑两个恒星质量：M* = 0.7 M和0.1 M。在每种情况下，我们假设：盘表面密度轮廓是缩放的最小质量太阳星云的表面密度轮廓，如当前数据所示，Mdisk/M* = 0.01;盘电离主要由恒星X射线驱动，并辅之以宇宙射线和放射性核素;恒星X射线光度与热光度成比例，如观察到的那样，为LX/L* ≈ 10 - 3.5。电离率用莫卡辛蒙特卡罗X射线输运程序计算，电离平衡用简化的化学网络确定，包括各种耗尽水平下混合良好的0.1 μm晶粒。我们发现：（1）双极扩散是控制太阳型和极低质量经典金牛T星周围盘MRI活动的主要因素。假设MRI在每个半径处产生最大可能场强，我们进一步发现：（2）MRI活性层仅占总盘质量的10.5%-10%;（3）吸积率（）的大小和符号都沿径向变化（向内或向外），意味着随时间变化的吸积以及盘间隙和密度过高的产生，对行星的形成和迁移产生影响;（4）在太阳型和极低质量恒星中获得经验吸积率需要消耗混合良好的小颗粒（通过颗粒生长和/或沉降）相对于标准粉尘-气体质量比10−2增加10-1000倍;以及（5）来自场的极化发射的当前未检测到，在外盘区域中的排列的颗粒与在那些半径处的活动MRI一致。
We investigate the viability of the magnetorotational instability (MRI) in X-ray ionized viscous accretion disks around both solar-type stars and very low mass stars. In particular, we determine the disk regions where the MRI can be shut off either by Ohmic resistivity (the so-called dead and undead zones) or by ambipolar diffusion (a region we term the zombie zone). We consider two stellar masses: M* = 0.7 M☉ and 0.1 M☉. In each case, we assume that: the disk surface density profile is that of a scaled Minimum Mass Solar Nebula, with Mdisk/M* = 0.01 as suggested by current data; disk ionization is driven primarily by stellar X-rays, complemented by cosmic rays and radionuclides; and the stellar X-ray luminosity scales with bolometric luminosity as LX/L* ≈ 10−3.5, as observed. Ionization rates are calculated with the moccasin Monte Carlo X-ray transport code, and ionization balance determined using a simplified chemical network, including well-mixed 0.1 μm grains at various levels of depletion. We find that (1) ambipolar diffusion is the primary factor controlling MRI activity in disks around both solar-type and very low mass classical T Tauri stars. Assuming that the MRI yields the maximum possible field strength at each radius, we further find that: (2) the MRI-active layer constitutes only ∼5%–10% of the total disk mass; (3) the accretion rate () varies radially in both magnitude and sign (inward or outward), implying time-variable accretion as well as the creation of disk gaps and overdensities, with consequences for planet formation and migration; (4) achieving the empirical accretion rates in solar-type and very low mass stars requires a depletion of well-mixed small grains (via grain growth and/or settling) by a factor of 10–1000 relative to the standard dust-to-gas mass ratio of 10−2; and (5) the current non-detection of polarized emission from field-aligned grains in the outer disk regions is consistent with active MRI at those radii.
X 射线照射的原行星盘大气。
DOI：
10.1088/0004-637x/699/2/1639
发表时间：
2009
期刊：
The Astrophysical Journal
影响因子：
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作者：
Ercolano B
通讯作者：
Ercolano B