Martin C. Smith, S. Hannah Whiteoak, N. W. Evans
We use the Stripe 82 proper motion catalogue of Bramich et al. (2008) to
study the kinematics of Galactic disk stars in the solar neighborhood. We
select samples of dwarf stars with reliable spectra and proper motions. They
have cylindrical polar radius between 7 < R < 9 kpc, heights from the Galactic
plane satisfying z < 2 kpc and span a range of metallicities -1.5 < [Fe/H] < 0.
We develop a method for calculating and correcting for the halo contamination
in our sample using the distribution of rotational velocities. Two Gaussians
representing disk and halo populations are used to fit the radial (v_R) and
vertical (v_z) velocity distributions via maximum likelihood methods. For the
azimuthal velocities (v_phi) the same technique is used, except that a skewed
non-Gaussian functional form now represents the disk velocity distribution.
This enables us to compute the dispersions {\sigma}R,{\sigma}z,{\sigma}{\phi}
and cross-terms (the tilt sig_Rz and the vertex deviation sig_Rphi) of the
velocity ellipsoid as a function of height and metallicity. We also investigate
the rotation lag of the disk, finding that the more metal-poor stars rotate
significantly slower than the metal-rich stars. These samples provide important
constraints on heating mechanisms in the Galactic disk and can be used for a
variety of applications. We present one such application, employing the Jeans
equations to provide a simple model of the potential close to the disk. Our
model is in excellent agreement with others in the literature and provides an
indication the disk, rather than the halo, dominates the circular speed at the
solar neighborhood. We obtain a surface mass density within 1.1 kpc of around
66 M/pc^2 and estimate a local halo density of 0.015 M/pc^3 = 0.57 GeV/cm^3.
View original:
http://arxiv.org/abs/1111.6920
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