548 research outputs found
Evidence of a large scale positive rotation-metallicity correlation in the Galactic thick disk
This study is based on high quality astrometric and spectroscopic data from
the most recent releases by Gaia and APOGEE. We select thin and thick
disk red giants, in the Galactocentric (cylindrical) distance range ~kpc and within ~kpc, for which full chemo-kinematical information
is available. Radial chemical gradients, , and rotational velocity-metallicity correlations, , are re-derived firmly uncovering that the thick disk
velocity-metallicity correlation maintains its positiveness over the ~kpc
range explored. This observational result is important as it sets experimental
constraints on recent theoretical studies on the formation and evolution of the
Milky Way disk and on cosmological models of Galaxy formation.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
New Signatures of the Milky Way Formation in the Local Halo and Inner Halo Streamers in the Era of Gaia
We explore the vicinity of the Milky Way through the use of
spectro-photometric data from the Sloan Digital Sky Survey and high-quality
proper motions derived from multi-epoch positions extracted from the Guide Star
Catalogue II database. In order to identify and characterise streams as relics
of the Milky Way formation, we start with classifying, select, and study
subdwarfs with up to kpc away from the Sun as tracers
of the local halo system. Then, through phase-space analysis, we find
statistical evidence of five discrete kinematic overdensities among of the
fastest-moving stars, and compare them to high-resolution N-body simulations of
the interaction between a Milky-Way like galaxy and orbiting dwarf galaxies
with four representative cases of merging histories. The observed overdensities
can be interpreted as fossil substructures consisting of streamers torn from
their progenitors, such progenitors appear to be satellites on prograde and
retrograde orbits on different inclinations. In particular, of the five
detected overdensities, two appear to be associated, yelding twenty-one
additional main-sequence members, with the stream of Helmi et al. (1999) that
our analysis confirms on a high inclination prograde orbit. The three newly
identified kinematic groups could be associated with the retrograde streams
detected by Dinescu (2002) and Kepley et al. (2007), whatever their origin, the
progenitor(s) would be on retrograde orbit(s) and inclination(s) within the
range . Finally, we use our simulations to
investigate the impact of observational errors and compare the current picture
to the promising prospect of highly improved data expected from the Gaia
mission.Comment: 16 pages, 10 figures, 6 Tables. Accepted for publication in The
Astronomical Journa
The radial metallicity gradients in the Milky Way thick disk as fossil signatures of a primordial chemical distribution
In this letter we examine the evolution of the radial metallicity gradient
induced by secular processes, in the disk of an -body Milky Way-like galaxy.
We assign a [Fe/H] value to each particle of the simulation according to an
initial, cosmologically motivated, radial chemical distribution and let the
disk dynamically evolve for 6 Gyr. This direct approach allows us to take into
account only the effects of dynamical evolution and to gauge how and to what
extent they affect the initial chemical conditions. The initial [Fe/H]
distribution increases with R in the inner disk up to R ~ 10 kpc and decreases
for larger R. We find that the initial chemical profile does not undergo major
transformations after 6 Gyr of dynamical evolution. The final radial chemical
gradients predicted by the model in the solar neighborhood are positive and of
the same order of those recently observed in the Milky Way thick disk.
We conclude that: 1) the spatial chemical imprint at the time of disk
formation is not washed out by secular dynamical processes, and 2) the observed
radial gradient may be the dynamical relic of a thick disk originated from a
stellar population showing a positive chemical radial gradient in the inner
regions.Comment: 10 pages, 5 figures, Accepted for publication on Astrophysical
Journal Letter
Detection and measurement of planetary systems with GAIA
We use detailed numerical simulations and the Andromedae,
planetary system as a template to evaluate the capability of the ESA
Cornerstone Mission GAIA in detecting and measuring multiple planets around
solar-type stars in the neighborhood of the Solar System. For the outer two
planets of the Andromedae, system, GAIA high-precision global
astrometric measurements would provide estimates of the full set of orbital
elements and masses accurate to better than 1--10%, and would be capable of
addressing the coplanarity issue by determining the true geometry of the system
with uncertainties of order of a few degrees. Finally, we discuss the
generalization to a variety of configurations of potential planetary systems in
the solar neighborhood for which GAIA could provide accurate measurements of
unique value for the science of extra-solar planets.Comment: 4 pages, 2 pictures, accepted for publication in A&A Letter
- …