Bibcode
López-Corredoira, M.; González-Fernández, C.
Referencia bibliográfica
The Astronomical Journal, Volume 151, Issue 6, article id. 165, 6 pp. (2016).
Fecha de publicación:
6
2016
Número de citas
14
Número de citas referidas
13
Descripción
Average stellar orbits of the Galactic disk may have some small
intrinsic ellipticity which breaks the exact axisymmetry and there may
also be some migration of stars inwards or outwards. Both phenomena can
be detected through kinematic analyses. We use the red clump stars
selected spectroscopically from the APO Galactic Evolution Experiment,
with known distances and radial velocities, to measure the radial
component of the Galactocentric velocities within 5 kpc < R < 16
kpc, | b| \lt 5^\circ , and within 20° from the Sun–Galactic
center line. The average Galactocentric radial velocity is VR
= (1.48 ± 0.35)[R(kpc) ‑ (8.8 ± 2.7)] km
s‑1 outwards in the explored range, with a higher
contribution from stars below the Galactic plane. Two possible
explanations can be given for this result: (i) the mean orbit of the
disk stars is intrinsically elliptical with a Galactocentric radial
gradient of eccentricity around 0.01 kpc‑1 or (ii)
there is a net secular expansion of the disk, in which stars within R
≈ 9–11 kpc are migrating to the region R ≳ 11 kpc at the
rate of ∼2 M⊙ yr‑1, and stars with R
≲ 9 kpc are falling toward the center of the Galaxy. This migration
ratio would be unattainable for a long time and should decelerate,
otherwise the Galaxy would fade away in around 1 Gyr. At present, both
hypotheses are speculative and one would need data on the Galactocentric
radial velocities for other azimuths different to the center or
anticenter in order to confirm one of the scenarios.