Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aj....110.2288l&link_type=abstract
Astronomical Journal v.110, p.2288
Astronomy and Astrophysics
Astronomy
56
Galaxy: Structure, Stars: Abundances, Stars: Kinematics, Galaxy: Formation
Scientific paper
We investigate the kinematics and spatial distribution of a sample of 302 nearby RR Lyrae variable stars with the goal of learning more about the formation history and present-day structure of the galaxy. We find that the kinematics change abruptly at [Fe/H]≍-1.0. Above this value, the stars exhibit kinematic properties like those of other tracers of the galaxy's thick disk, while below [Fe/H] = -1.3, halo kinematics are observed. The stars with -1.3≤[Fe/H]≤-1.0 are a mixture of these populations, though the fraction of thick disk RR Lyrae stars with [Fe/H]≤-1.0 is significantly smaller than found among red giant stars by other authors; we discuss several possibilities for this discrepancy. The RR Lyraes with [Fe/H]>-0.5 exhibit somewhat cooler kinematics and a flatter spatial distribution than those of the thick disk, and may include some members of the old thin disk population. We find the kinematics of the halo RR Lyraes to be uncorrelated with abundance over the range -2.2≤[Fe/H]≤-1.0, and interpret this as evidence that the motions and chemical enrichment of gas in the early galaxy was characterized by a high degree of randomization, consistent with fragment accretion pictures of galaxy formation. We argue that the small number of thick disk stars with [Fe/R]≤-1.0 cannot be called upon to balance the net kinematics of a retrograde-rotating halo to produce the slow prograde rotations seen in this and other local samples; however, a hotter, slowly rotating, somewhat flattened second halo component may be consistent with kinematics both of local samples and of samples far from the galactic plane. We find the local density of halo RR Lyraes to be 11-15 , with a firm lower limit of 8±3kpc-3. This is larger than that predicted from counts of faint RR Lyraes far from the plane; either the flattening of the local halo is larger than c/a≍0.7, or a two-component halo exists in which one component is quite flattened. We derive an exponential scale height of 0.7+0.5-0.3 kpc and a midplane density of 10±4 kpc-3 for the disk RR Lyraes with [Fe/H]>-1.0.
No associations
LandOfFree
The Metallicities and Kinematics of RR Lyrae Variables.II. Galactic Structure and Formation from Local Stars does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Metallicities and Kinematics of RR Lyrae Variables.II. Galactic Structure and Formation from Local Stars, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Metallicities and Kinematics of RR Lyrae Variables.II. Galactic Structure and Formation from Local Stars will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1178786