Fast Estimation of Orbital Parameters in Milky Waylike Potentials
Abstract
Orbital parameters, such as eccentricity and maximum vertical excursion, of stars in the Milky Way are an important tool for understanding its dynamics and evolution, but calculation of such parameters usually relies on computationally expensive numerical orbit integration. We present and test a fast method for estimating these parameters using an application of the Stäckel fudge, used previously for the estimation of actionangle variables. We show that the method is highly accurate, to a level of <1% in eccentricity, over a large range of relevant orbits and in different Milky Waylike potentials, and demonstrate its validity by estimating the eccentricity distribution of the RAVETGAS data set and comparing it with that from orbit integration. Using this method, the orbital characteristics of the ∼7 million Gaia DR2 stars with radial velocity measurements are computed with Monte Carlo sampled errors in ∼116 hours of parallelized cpu time, at a speed that we estimate to be ∼3 to 4 orders of magnitude faster than using numerical orbit integration. We demonstrate using this catalog that Gaia DR2 samples a large range of orbits in the solar vicinity, down to those with r _{ap} ≲ 2.5 kpc, and out to r _{peri} ≳ 13 kpc. We also show that many of the features present in orbital parameter space have a low mean z _{max}, suggesting that they likely result from disk dynamical effects.
 Publication:

Publications of the Astronomical Society of the Pacific
 Pub Date:
 November 2018
 DOI:
 10.1088/15383873/aadcdd
 arXiv:
 arXiv:1802.02592
 Bibcode:
 2018PASP..130k4501M
 Keywords:

 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 11 Pages, 6 Figures, Accepted for publication in PASP, Full code and extra material available at https://github.com/jmackereth/orbitestimation , Supplementary data table is available (temporarily) at http://www.astro.ljmu.ac.uk/~astjmack/gaia_orbits/gaiarvs_orbitparams_units.csv