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首页> 外文期刊>The Astrophysical journal >THE GALACTIC INNER HALO: SEARCHING FOR WHITE DWARFS AND MEASURING THE FUNDAMENTAL GALACTIC CONSTANT, Θ_0/R_0
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THE GALACTIC INNER HALO: SEARCHING FOR WHITE DWARFS AND MEASURING THE FUNDAMENTAL GALACTIC CONSTANT, Θ_0/R_0

机译:银河内部晕轮:寻找白矮星并测量基本银河常数,Θ_0/ R_0

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We establish an extragalactic, zero-motion frame of reference within the deepest optical image of a globular star cluster, a Hubble Space Telescope (HST) 123 orbit exposure of M4 (GO 8679, Cycle 9). The line of sight beyond M4 (l, b = 351°, 16°) intersects the inner halo (spheroid) of our Galaxy at a tangent-point distance of 7.6 kpc (for R_0 = 8 kpc). The main sequence of this population can be clearly seen on the color-magnitude diagram (CMD) below the M4 main sequence. We isolate these spheroid stars from the cluster on the basis of their proper motions over the 6 yr baseline between these observations and others made at a previous epoch with HST (GO 5461, Cycle 4). Distant background galaxies are also found on the same sight line by using image-morphology techniques. This fixed-reference frame allows us to determine an independent measurement of the fundamental Galactic constant, Ω_0 =Θ _0/R_0 = 25.3 +- 2.6 km s~(-1) kpc~(-1), thus providing a velocity of the local standard of rest υ_(LSR) = Θ_0 = 202.7 +- 24.7 km s~(-1) for R_0 = 8.0 +- 0.5 kpc. Second, the galaxies allow a direct measurement of M4's absolute proper motion, μ_α α=-12.26 +- 0.54 mas yr~(-1), μ_δ δ= -18.95 +- 0.54 mas yr~(-1), in excellent agreement with recent studies. The clear separation of galaxies from stars in these deep data also allow us to search for inner halo white dwarfs. We model the conventional Galactic contributions of white dwarfs along our line of sight and predict 7.9 thin-disk, 6.3 thick-disk, and 2.2 spheroid objects to the limiting magnitude at which we can clearly delineate stars from galaxies (V ~29). An additional 2.5 objects are expected from a 20% white dwarf dark halo consisting of 0.5 solar mass objects, 70% of which are of the DA type. After considering the kinematics and morphology of the objects in our data set, we find the number of white dwarfs to be consistent with the predictions for each of the conventional populations. However, we do not find any evidence for dark halo white dwarfs.
机译:我们在球状星团的最深光学图像,M4的哈勃太空望远镜(HST)123轨道曝光(GO 8679,周期9)中建立了银河外零运动参考系。 M4(l,b = 351°,16°)以外的视线与银河系的内部光晕(球体)相交,相切点距离为7.6 kpc(对于R_0 = 8 kpc)。在M4主序列下方的色度图(CMD)上可以清楚地看到该总体的主序列。我们根据这些观测值与之前的HST时代(GO 5461,周期4)进行的其他观测之间在6年基线上的适当运动,将它们从星团中分离出来。通过使用图像形态学技术,在同一视线上还可以发现遥远的背景星系。这个固定参考框架使我们能够确定基本银河常数的独立测量值,Ω_0=Θ_0 / R_0 = 25.3 +-2.6 km s〜(-1)kpc〜(-1),从而提供了局部速度静止标准υ_(LSR)=Θ_0= 202.7 +-24.7 km s〜(-1),R_0 = 8.0 +-0.5 kpc。其次,星系可以直接测量M4的绝对固有运动,μ_αα= -12.26 +-0.54 mas yr〜(-1),μ_δδ= -18.95 +-0.54 mas yr〜(-1),与最近的研究。在这些深层数据中,银河系与恒星的清晰分离也使我们能够寻找内部的晕白矮星。我们沿我们的视线模拟了白矮星的常规银河系贡献,并预测了7.9个薄盘,6.3个厚盘和2.2个椭球体到有限的幅度,在此范围内我们可以清楚地描绘出星系中的恒星(V〜29)。 20%的白矮星暗光晕有望再带来2.5个物体,其中包括0.5个太阳质量物体,其中70%是DA型。在考虑了我们数据集中物体的运动学和形态之后,我们发现白矮星的数量与每个常规种群的预测相符。但是,我们没有发现暗晕白矮星的任何证据。

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