350 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
Kinematics of Stars in Kapteyn Selected Area 71: Sampling the Monoceros and Sagittarius Tidal Streams
We present a 3D kinematical analysis of stars located in Kapteyn Selected
Area 71 (l = 167.1, b = -34.7), where previously a stellar excess was found
(Dinescu et al. 2002, Newberg et al. 2002). Previous findings indicated that
the stellar excess has a cold kinematical signature as inferred from proper
motions, and was initially associated with debris from the Sagittarius dwarf
galaxy (Sgr) -- namely the southern trailing tail. We have obtained radial
velocities using the Hydra multiobject spectrograph on the WIYN 3.5 m
telescope. Results for 183 proper-motion selected stars indicate that the
dominant population in this stellar excess is not debris from Sgr, but rather a
population that kinematically belongs to the ring-like stream that is now known
as the Monoceros stream. The orbit determined for this population agrees very
well with the predictions for the Monoceros stream from Penarrubia et al.
(2005). The radial-velocity dispersion of this population is between 20 and 30
km/s, lower than that of the Galactic field. Also, the shape of the
radial-velocity distribution shows a sharp cut-off on one side, which is more
in line with model predictions of the disruption of a satellite rather than
with the distribution of the Galactic field. Despite the fact that we now
believe most of the stars in the stellar excess to be part of Monoceros, about
ten stars in this stellar excess have highly negative radial velocities, which
is a clear indication of their membership to the Sgr trailing tidal tail.Comment: Accepted for publication in the Astronomical Journal - 26 pages, 8
figures, (Figures 7 and 8 in lower resolution
Kinematics in Kapteyn's Selected Area 76: Orbital Motions Within the Highly Substructured Anticenter Stream
We have measured the mean three-dimensional kinematics of stars in Kapteyn's
Selected Area (SA) 76 (l=209.3, b=26.4 degrees) that were selected to be
Anticenter Stream (ACS) members on the basis of their radial velocities, proper
motions, and location in the color-magnitude diagram. From a total of 31 stars
ascertained to be ACS members primarily from its main sequence turnoff, a mean
ACS radial velocity (derived from spectra obtained with the Hydra multi-object
spectrograph on the WIYN 3.5m telescope) of V_helio = 97.0 +/- 2.8 km/s was
determined, with an intrinsic velocity dispersion sigma_0 = 12.8 \pm 2.1 km/s.
The mean absolute proper motions of these 31 ACS members are mu_alpha cos
(delta) = -1.20 +/- 0.34 mas/yr and mu_delta = -0.78 \pm 0.36 mas/yr. At a
distance to the ACS of 10 \pm 3 kpc, these measured kinematical quantities
produce an orbit that deviates by ~30 degrees from the well-defined swath of
stellar overdensity constituting the Anticenter Stream in the western portion
of the Sloan Digital Sky Survey footprint. We explore possible explanations for
this, and suggest that our data in SA 76 are measuring the motion of a
kinematically cold sub-stream among the ACS debris that was likely a fragment
of the same infalling structure that created the larger ACS system. The ACS is
clearly separated spatially from the majority of claimed Monoceros ring
detections in this region of the sky; however, with the data in hand, we are
unable to either confirm or rule out an association between the ACS and the
poorly-understood Monoceros structure.Comment: Accepted to ApJ. 48 pages, 20 figures, preprint forma
Characterization of a planar 8 mm wide radiofrequency atmospheric pressure plasma source by spectroscopy techniques
Atmospheric pressure planar radiofrequency (RF) 13.56 MHz discharge in Ar gas generated in a long gap is investigated. The discharge operation with and without a dielectric barrier on the electrodes is studied as a function of the applied power and gas flow. The source afterglow is characterized and is analyzed for possible large-scale biomedical applications where low gas temperature is required. The discharge is studied by relative and absolute emission spectroscopies. A gas temperature as low as 330 +/- 50 K is determined from the rotational-vibrational band of OH emission. The absolute value of the discharge continuum irradiation is used to determine the electron density and the electron temperature. The electron-atom and electron-ion contributions to the bremsstrahlung radiation are calculated and are compared with measured spectra. The electron density of 1.9 +/- 1 x 10(20) m(-3) and electron temperature of 1.75 +/- 0.25 eV are measured in the discharge without a dielectric barrier. It is found that presence of the dielectric has a negligible effect on electron temperature, whereas the electron number density is almost six times lower in the discharge with the dielectric barrier
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
Absolute Proper Motions to B~22.5: V. Detection of Sagittarius Dwarf Spheroidal Debris in the Direction of the Galactic Anticenter
We have detected a population of predominantly blue (B-V <= 1.1) stars in the
direction l = 167 deg., b = -35 deg. (Kapteyn Selected Area 71) that cannot be
accounted for by standard starcount models. Down to V ~ 20, the colors and
magnitudes of these stars are similar to those of the southern overdensity
detected by the Sloan Digital Sky Survey, and identified as stripped material
from the Sagittarius dwarf spheroidal galaxy. We present absolute proper
motions for the stars in SA 71, and we find that the excess blue stars
represent a distinct, kinematically cooler component than the Galactic field,
and in reasonable agreement with predictions of Sgr disruption models. The
density of the excess SA 71 stars at V ~ 18.8 and B-V <=1.1 is within a factor
of two of the density of the SDSS-south Sgr stripped material, and of that
predicted by the Helmi and White disruption model. Three additional anticenter
fields (SA 29, 45 and 118) show very good agreement with standard starcount
models.Comment: 13 pages, 3 figures, submitted to ApJL, accepted for Ap
A Deep Proper-Motion Survey in Kapteyn Selected Areas: I. Survey Description and First Results for Stars in the Tidal Tail of Sagittarius and in the Monoceros Ring
We describe a high-precision, deep (to V ~ 19-21) absolute proper-motion
survey that samples ~50 lines of sight in the Kapteyn Selected Areas along
declination zones -15, 0 and 15 degrees. In many fields the astrometric
baseline reaches nearly a century. We demonstrate that these data provide
typical per star precisions between ~ 1 and 3 mas/yr to the above magnitude
limits, with the absolute reference frame established by numerous extragalactic
sources in each survey field. Combined with existing and ongoing photometric
and radial velocity surveys in these fields, these astrometric data will
enable, among other things, accurate, detailed dynamical modeling of satellite
interactions with our Galaxy. In this contribution we describe the astrometric
part of our survey and show preliminary results along the trailing tail of the
Sagittarius dwarf galaxy, and in the Monoceros ring region.Comment: Accepter for publication in the Astronomical Journa
- …