forgot password?
register here
Research articles
  search articles
  reviews guidelines
  articles index
My Pages
my alerts
  my messages
  my reviews
  my favorites
Members: 2922
Articles: 1'998'104
Articles rated: 2574

27 September 2020
  » » arxiv » 252787

 Article forum

Modeling complete distributions with incomplete observations: The velocity ellipsoid from Hipparcos data
David W. Hogg ; Michael R. Blanton ; Sam T. Roweis ; Kathryn V. Johnston ;
Date 3 May 2005
Journal Astrophys.J. 629 (2005) 268-275
Subject astro-ph
AffiliationNYU), Michael R. Blanton (NYU), Sam T. Roweis (Toronto), Kathryn V. Johnston (Wesleyan
Abstract[abridged] A "missing data" algorithm is developed to model (ie, reconstruct) the three-dimensional velocity distribution function of a sample of stars using data (velocity measurements) every one of which has one dimension unmeasured (the radial direction). It also accounts for covariant measurement uncertainties on the tangential velocity components. The algorithm is applied to tangential velocities measured in a kinematically unbiased sample of 11,865 stars taken from the Hipparcos catalog. The local stellar velocity distribution function of each of a set of 20 color-selected subsamples is modeled as a mixture of two three-dimensional Gaussian ellipsoids of arbitrary relative responsibility. In the fitting, one Gaussian (the "halo") is fixed at the known mean velocity and velocity variance tensor of the Galaxy halo, and the other (the "disk") is allowed to take arbitrary mean and arbitrary variance tensor. The mean and variance tensor (commonly the "velocity ellipsoid") of the disk velocity distribution are both found to be strong functions of stellar color, with long-lived populations showing larger velocity dispersion, slower mean rotation velocity, and smaller vertex deviation than short-lived populations. The local standard of rest (LSR) is inferred in the usual way and the Sun’s motion relative to the LSR is found to be (U,V,W)_{odot}=(10.1,4.0,6.7)+/-(0.5,0.8,0.2) km/s. Artificial data sets are made and analyzed, with the same error properties as the Hipparcos data, to demonstrate that the analysis is unbiased. The results are shown to be insensitive to the assumption that the velocity distributions are Gaussian.
Source arXiv, astro-ph/0505057
Services Forum | Review | PDF | Favorites   

No message found in this article forum.  You have a question or message about this article? Ask the community and write a message in the forum.
If you want to rate this article, please use the review section..

Subject of your forum message:
Write your forum message below (min 50, max 2000 characters)

2000 characters left.
Please, read carefully your message since you cannot modify it after submitting.

  To add a message in the forum, you need to login or register first. (free): registration page
» my Online CV
» Free

News, job offers and information for researchers and scientists:
home  |  contact  |  terms of use  |  sitemap
Copyright © 2005-2020 - Scimetrica