论文标题
Ultacool矮小的M7至L2.5的局部垂直密度分布及其光度函数
The local vertical density distribution of ultracool dwarfs M7 to L2.5 and their luminosity function
论文作者
论文摘要
我们研究了银河磁盘中恒星的局部垂直密度曲线的形式，靠近银河面。我们使用34000 Ultracool矮人M7至L2.5的均匀样品，所有样品都位于飞机350 PC之内。我们符合SECH $^α$的形式的配置文件，其中$α= 2 $是理论上首选的等温轮廓，$α= 0 $是指数函数。 $α$的较大值对应于剖面向平面的更大变平。我们采用了一种可能性分析，该分析以一种直接的方式来解释样品中未解决的二进制文件，以及在每个光谱子类型内的绝对幅度$ m_j $中的扩散（恶敏偏差）。我们测量$α= 0.29^{+0.12} _ { - 0.13} $。 $α= 1 $（SECH）和平整概况被排除在该样本的信心中，而$α= 0 $（指数）包含在95％可靠的间隔中。任何相对于指数的扁平化都是适中的，并且仅限于平面的50 pc之内。 $α$的测量值与Xiang等人最近分析的结果一致。我们对$α$的价值也类似于De Grijs等人对附近螺旋星系确定的价值，该星系的光度法是根据观察到的边缘的光度法测量的。测得的曲线允许准确地确定超速矮的M7至L2.5的局部空间密度，我们使用它来对主序列底部的光度函数进行新的确定。我们对光度函数的结果比Bardalez Gagliuffi等人最近的测量值低2到三，该测量在局部25 PC半径泡中使用了恒星，但与Cruz等人的较旧研究非常一致。
We investigate the form of the local vertical density profile of the stars in the Galactic disk, close to the Galactic plane. We use a homogeneous sample of 34000 ultracool dwarfs M7 to L2.5 that all lie within 350 pc of the plane. We fit a profile of the form sech$^α$, where $α=2$ is the theoretically preferred isothermal profile and $α=0$ is the exponential function. Larger values of $α$ correspond to greater flattening of the profile towards the plane. We employ a likelihood analysis that accounts in a direct way for unresolved binaries in the sample, as well as for the spread in absolute magnitude $M_J$ within each spectral sub-type (Malmquist bias). We measure $α=0.29^{+0.12}_{-0.13}$. The $α=1$ (sech) and flatter profiles are ruled out at high confidence for this sample, while $α=0$ (exponential) is included in the 95% credible interval. Any flattening relative to exponential is modest, and is confined to within 50 pc of the plane. The measured value of $α$ is consistent with the results of the recent analysis by Xiang et al. Our value for $α$ is also similar to that determined for nearby spiral galaxies by de Grijs et al., measured from photometry of galaxies viewed edge on. The measured profile allows an accurate determination of the local space density of ultracool dwarfs M7 to L2.5, and we use this to make a new determination of the luminosity function at the bottom of the main sequence. Our results for the luminosity function are a factor two to three lower than the recent measurement by Bardalez Gagliuffi et al., that uses stars in the local 25 pc radius bubble, but agree well with the older study by Cruz et al.
