45 research outputs found
New analysis in the field of open cluster Collinder 223
The present study of the open cluster Collinder 223 (Cr 223) has been mainly
depended on the photoelectric data of Claria & Lapasset (1991; hereafter CL91).
This data of CL91 has been used with the cluster's image of AAO-DSS in order to
re-investigate and improve the main parameters of Cr 223. Stellar count has
been achieved to determine the stellar density, the cluster's center and the
cluster's diameter. In addition, the luminosity function, mass function, and
the total mass of the cluster have been estimated.Comment: 12 pages, 8 figure
Ground state cooling, quantum state engineering and study of decoherence of ions in Paul traps
We investigate single ions of in Paul traps for quantum
information processing. Superpositions of the S electronic ground state
and the metastable D state are used to implement a qubit. Laser light
on the S D transition is used for the
manipulation of the ion's quantum state. We apply sideband cooling to the ion
and reach the ground state of vibration with up to 99.9% probability. Starting
from this Fock state , we demonstrate coherent quantum state
manipulation. A large number of Rabi oscillations and a ms-coherence time is
observed. Motional heating is measured to be as low as one vibrational quantum
in 190 ms. We also report on ground state cooling of two ions.Comment: 12 pages, 6 figures. submitted to Journal of Modern Optics, Special
Issue on Quantum Optics: Kuehtai 200
A multi-wavelength study of a double intermediate-mass protostar - from large-scale structure to collimated jets
(abridged) We study a previously discovered protostellar source that is
deeply embedded and drives an energetic molecular outflow. The source, UYSO1,
is located close to IRAS 07029-1215 at a distance of ~1 kpc. The
multi-wavelength observations resulted in the detection of a double
intermediate-mass protostar at the location of UYSO1. In addition to the
associated molecular outflow, with a projected size of 0.25 pc, two
intersecting near-infrared jets with projected sizes of 0.4 pc and 0.2 pc were
found. However, no infrared counterparts to the driving sources could be
detected in sensitive near- to far-infrared observations. In interferometric
millimeter observations, UYSO1 was resolved into two continuum sources with
high column densities and gas masses of 3.5 Mo and 1.2 Mo, with a linear
separation of 4200 AU. We report the discovery of a H2O maser toward one of the
two sources. The total luminosity is roughly estimated to be ~50 Lo, shared by
the two components, one of which is driving the molecular outflow that has a
dynamical timescale of less than a few thousand years. The jets of the two
individual components are not aligned. Submillimeter observations show that the
region lacks typical hot-core chemistry. We thus find two protostellar objects,
whose associated circumstellar and parent core masses are high enough to
suggest that they may evolve into intermediate-mass stars. This is corroborated
by their association with a very massive and energetic CO outflow, suggesting
high protostellar accretion rates. The short dynamical timescale of the
outflow, the pristine chemical composition of the cloud core and absence of hot
core tracers, the absence of detectable radio continuum emission, and the very
low protostellar luminosity argue for an extremely early evolutionary stage.Comment: 10 pages, 10 figures, accepted for publication in A&A; minor changes:
typos corrected, revised argument in Section
Maximum stellar mass versus cluster membership number revisited
We have made a new compilation of observations of maximum stellar mass versus
cluster membership number from the literature, which we analyse for consistency
with the predictions of a simple random drawing hypothesis for stellar mass
selection in clusters. Previously, Weidner and Kroupa have suggested that the
maximum stellar mass is lower, in low mass clusters, than would be expected on
the basis of random drawing, and have pointed out that this could have
important implications for steepening the integrated initial mass function of
the Galaxy (the IGIMF) at high masses. Our compilation demonstrates how the
observed distribution in the plane of maximum stellar mass versus membership
number is affected by the method of target selection; in particular, rather low
n clusters with large maximum stellar masses are abundant in observational
datasets that specifically seek clusters in the environs of high mass stars.
Although we do not consider our compilation to be either complete or unbiased,
we discuss the method by which such data should be statistically analysed. Our
very provisional conclusion is that the data is not indicating any striking
deviation from the expectations of random drawing.Comment: 7 pages, 3 Figures; accepted by MNRAS; Reference added
Structure of the Large Magellanic Cloud from 2MASS
We derive structural parameters and evidence for extended tidal debris from
star count and preliminary standard candle analyses of the Large Magellanic
Cloud based on Two Micron All Sky Survey (2MASS) data. The full-sky coverage
and low extinction in K_s presents an ideal sample for structural analysis of
the LMC.
The star count surface densities and deprojected inclination for both young
and older populations are consistent with previous work. We use the full areal
coverage and large LMC diameter to Galactrocentric distance ratio to infer the
same value for the disk inclination based on perspective.
A standard candle analysis based on a sample of carbon long-period variables
(LPV) in a narrow color range, 1.6<J-K_s<1.7 allows us to probe the
three-dimensional structure of the LMC along the line of sight. The intrinsic
brightness distribution of carbon LPVs in selected fields implies that
\sigma_M\simlt 0.2^m for this color cut. The sample provides a {\it direct}
determination of the LMC disk inclination: .
Distinct features in the photometric distribution suggest several distinct
populations. We interpret this as the presence of an extended stellar component
of the LMC, which may be as thick as 14 kpc, and intervening tidal debris at
roughly 15 kpc from the LMC.Comment: 24 pages, 9 figures. Submitted to Ap
Quantum state engineering on an optical transition and decoherence in a Paul trap
A single Ca+ ion in a Paul trap has been cooled to the ground state of
vibration with up to 99.9% probability. Starting from this Fock state |n=0> we
have demonstrated coherent quantum state manipulation on an optical transition.
Up to 30 Rabi oscillations within 1.4 ms have been observed. We find a similar
number of Rabi oscillations after preparation of the ion in the |n=1> Fock
state. The coherence of optical state manipulation is only limited by laser and
ambient magnetic field fluctuations. Motional heating has been measured to be
as low as one vibrational quantum in 190 ms.Comment: 4 pages, 5 figure
The Parker Instability in 3-D: Corrugations and Superclouds Along the Carina-Sagittarius Arm
Here we present three-dimensional MHD models for the Parker instability in a
thick magnetized disk, including the presence of a spiral arm. The -field is
assumed parallel to the arm, and the model results are applied to the optical
segment of the Carina-Sagittarius arm. The characteristic features of the
undular and interchange modes are clearly apparent in the simulations. The
undular mode creates large gas concentrations distributed along the arm. This
results in a clear arm/inter-arm difference: the instability triggers the
formation of large interstellar clouds inside the arms, but generates only
small structures with slight density enhancements in the inter-arm regions. The
resulting clouds are distributed in an antisymmetric way with respect to the
midplane, creating an azimuthal corrugation along the arm. For conditions
similar to those of the optical segment of the Carina-Sagittarius arm, it has a
wavelength of about 2.4 kpc. This structuring can explain the origin of both HI
superclouds and the azimuthal corrugations in spiral arms. The wavelength
matches the corrugation length derived with the young stellar groups located in
the optical segment of the Carina-Sagittarius arm. Keywords: Galaxy: kinematics
and dynamics -- Galaxy: structure -- Instabilities -- ISM: clouds -- ISM:
magnetic fields -- ISM: structure -- MHDComment: 29 pages, 12 figures, Latex, Accepted by the Astrophysical Journa
Solar-Type Post-T Tauri Stars in the Nearest OB Subgroups
I discuss results from the recent spectroscopic survey for solar-type pre-MS
stars in the Lower Centaurus-Crux (LCC) and Upper Centaurus-Lupus (UCL) OB
subgroups by Mamajek, Meyer, & Liebert (2002, AJ, 124, 1670). LCC and UCL are
subgroups of the Sco-Cen OB association, and the two nearest OB subgroups to
the Sun. In the entire survey of 110 pre-main sequence stars, there exists only
one Classical T Tauri star (PDS 66), implying that only ~1% of ~1 Msun stars
are still accreting at age 137 (1) Myr. Accounting for
observational errors, the HRD placement of the pre-MS stars is consistent with
the bulk of star-formation taking place within 5-10 Myr. In this contribution,
I estimate conservative upper limits to the intrinsic velocity dispersions of
the post-T Tauri stars in the LCC and UCL subgroups (<1.6 km/s and <2.2 km/s,
respectively; 95% CL) using Monte-Carlo simulations of Tycho-2 proper motions
for candidate subgroup members. I also demonstrate that a new OB subgroup
recently proposed to exist in Chamaeleon probably does not.Comment: 8 pages, 2 figures, to appear in proceedings for "Open Issues in
Local Star Formation and Early Stellar Evolution", eds. J. Gregorio-Hetem &
J. Lepine. Minor edits (5/30/03
Optical fibers with interferometric path length stability by controlled heating for transmission of optical signals and as components in frequency standards
We present a simple method to stabilize the optical path length of an optical
fiber to an accuracy of about 1/100 of the laser wavelength. We study the
dynamic response of the path length to modulation of an electrically conductive
heater layer of the fiber. The path length is measured against the laser
wavelength by use of the Pound-Drever-Hall method; negative feedback is applied
via the heater. We apply the method in the context of a cryogenic resonator
frequency standard.Comment: Expanded introduction and outlook. 9 pages, 5 figure