469 research outputs found
Proper Motions in Kapteyn Selected Area 103: A Preliminary Orbit for the Virgo Stellar Stream
We present absolute proper motions in Kapteyn Selected Area (SA) 103. This
field is located 7 degrees west of the center of the Virgo Stellar Stream (VSS,
Duffau et al. 2006), and has a well-defined main sequence representing the
stream. In SA 103 we identify one RR Lyrae star as a member of the VSS
according to its metallicity, radial velocity and distance. VSS candidate
turnoff stars and subgiant stars have proper motions consistent with that of
the RR Lyrae star. The 3D velocity data imply an orbit with a pericenter of 11
kpc and an apocenter of ~90 kpc. Thus, the VSS comprises tidal debris found
near the pericenter of a highly destructive orbit. Examining the six globular
clusters at distances larger than 50 kpc from the Galactic center, and the
proposed orbit of the VSS, we find one tentative association, NGC 2419. We
speculate that NGC 2419 is possibly the nucleus of a disrupted system of which
the VSS is a part.Comment: ApJL accepte
Young stars in the periphery of the Large Magellanic Cloud
Despite their close proximity, the complex interplay between the two
Magellanic Clouds, the Milky Way, and the resulting tidal features, is still
poorly understood. Recent studies have shown that the Large Magellanic Cloud
(LMC) has a very extended disk strikingly perturbed in its outskirts. We search
for recent star formation in the far outskirts of the LMC, out to ~30 degrees
from its center. We have collected intermediate-resolution spectra of
thirty-one young star candidates in the periphery of the LMC and measured their
radial velocity, stellar parameters, distance and age. Our measurements confirm
membership to the LMC of six targets, for which the radial velocity and
distance values match well those of the Cloud. These objects are all young
(10-50 Myr), main-sequence stars projected between 7 and 13 degrees from the
center of the parent galaxy. We compare the velocities of our stars with those
of a disk model, and find that our stars have low to moderate velocity
differences with the disk model predictions, indicating that they were formed
in situ. Our study demonstrates that recent star formation occurred in the far
periphery of the LMC, where thus far only old objects were known. The spatial
configuration of these newly-formed stars appears ring-like with a radius of 12
kpc, and a displacement of 2.6 kpc from the LMC's center. This structure, if
real, would be suggestive of a star-formation episode triggered by an
off-center collision between the Small Magellanic Cloud and the LMC's disk.Comment: Accepted for publication in MNRA
In-Situ Star Formation in the Outskirts of the Large Magellanic Cloud: Gaia DR2 Confirmation
We explore the Gaia DR2 proper motions of six young, main-sequence stars,
members of the Large Magellanic Cloud (LMC) reported by Moni Bidin et al.
(2017). These stars are located in the outskirts of the disk, between 7 and 13
degrees from the LMC's center where there is very low H I content. Gaia DR2
proper motions confirm that four stars formed locally, in situ, while two are
consistent with being expelled via dynamical interactions from inner, more
gas-rich regions of the LMC. This finding establishes that recent star
formation occurred in the periphery of the LMC, where thus far only old
populations are known.Comment: Accepted for publication in Astrophysical Journal Letter
Chemical Composition of Young Stars in the Leading Arm of the Magellanic System
Chemical abundances of eight O- and B-type stars are determined from
high-resolution spectra obtained with the MIKE instrument on the Magellan 6.5m
Clay telescope. The sample is selected from 42 candidates of membership in the
Leading Arm of the Magellanic System. Stellar parameters are measured by two
independent grids of model atmospheres and analysis procedures, confirming the
consistency of the stellar parameter results. Abundances of seven elements (He,
C, N, O, Mg, Si, and S) are determined for the stars, as are their radial
velocities and estimates of distances and ages.
Among the seven B-type stars analyzed, the five that have radial velocities
compatible with membership to the LA have an average [Mg/H] of ,
significantly lower than the average of the remaining two [Mg/H] =
that are kinematical members of the Galactic disk. Among the
five LA members, four have individual [Mg/H] abundance compatible with that in
the LMC. Within errors, we can not exclude the possibility that one of these
stars has a [Mg/H] consistent with the more metal-poor, SMC-like material. The
remaining fifth star has a [Mg/H] close to MW values. Distances to the LA
members indicate that they are at the edge of the Galactic disk, while ages are
of the order of Myr, lower than the dynamical age of the LA,
suggesting a single star-forming episode in the LA. V the LA
members decreases with decreasing Magellanic longitude, confirming the results
of previous LA gas studies.Comment: 61 pages, 18 figures, 5 tables. Accepted for publication in Ap
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