1,835 research outputs found
The Initial Mass Functions in the Super-Star-Clusters NGC 1569A and NGC 1705-1
I use recent photometric and stellar velocity dispersion measurements of the
super-star-clusters (SSCs) NGC 1569A and NGC 1705-1 to determine their
present-day luminosity/mass (L_V/M) ratios. I then use the inferred L_V/M
ratios, together with population synthesis models of evolving star-clusters, to
constrain the initial-mass-functions (IMFs) in these objects.
I find that (L_V/M)_solar=28.9 in 1569A, and (L_V/M)_solar=126 in 1705-1. It
follows that in 1569A the IMF is steep with alpha~2.5 for m**(-alpha)dm IMFs
which extend to 0.1 M_sun. This implies that most of the stellar mass in 1569A
is contained in low-mass (< 1 M_sun) stars. However, in 1705-1 the IMF is
either flat, with alpha<2$, or it is truncated at a lower mass-limit between 1
and 3 M_sun.
I compare the inferred IMFs with the mass functions (MFs) of Galactic
globular clusters. It appears that 1569A has a sufficient reservoir of low-mass
stars for it to plausibly evolve into an object similar to Galactic globular
clusters. However, the apparent deficiency of low-mass stars in 1705-1 may make
it difficult for this SSC to become a globular cluster. If low-mass stars do
dominate the cluster mass in 1705-1, the large L_V/M ratio in this SSC may be
evidence that the most massive stars have formed close to the cluster cores.Comment: ApJ, in press. 19 Pages, Latex; [email protected]
Observations of the rotational transitions of OH from the Orion molecular cloud
A summary of observed rotationally excited, far infrared OH line emissions from Orion-KL made using the Kuiper Airborne Observatory is given, together with a list of the resulting publications, talks, and lectures based on this data. In addition, a paper is appended, particularly addressing the (16)OH and (18)OH emission from Orion-KL. The first detections of the (16)OH (2)pi(1/2) to (2)pi(3/2) J = 3/2(-) to 3/2(+) rotational cross-ladder transition (53.351 micrometer) and the (18)OH (2)pi(3/2) J = 5/2(+) to 3/2(-) rotational ground-state transition (120.1719 micrometer). It is found that both of these lines exhibit a P-Cygni profile
Herschel observations of EXtra-Ordinary Sources (HEXOS): Observations of H_2O and its isotopologues towards Orion KL
We report the detection of more than 48 velocity-resolved ground rotational state transitions of H^(16)_2O, H^(18)
_2O, and ^(17)_2O – most for the first time
– in both emission and absorption toward Orion KL using Herschel/HIFI. We show that a simple fit, constrained to match the known emission
and absorption components along the line of sight, is in excellent agreement with the spectral profiles of all the water lines. Using the measured H^(18)_2O line fluxes, which are less affected by line opacity than their H^(16)_2O counterparts, and an escape probability method, the column densities
of H^(18)_2O associated with each emission component are derived. We infer total water abundances of 7.4 × 10^(−5), 1.0 × 10^(−5), and 1.6 × 10^(−5) for the
plateau, hot core, and extended warm gas, respectively. In the case of the plateau, this value is consistent with previous measures of the Orion-KL water abundance as well as those of other molecular outflows. In the case of the hot core and extended warm gas, these values are somewhat higher than water abundances derived for other quiescent clouds, suggesting that these regions are likely experiencing enhanced water-ice sublimation from (and reduced freeze-out onto) grain surfaces due to the warmer dust in these sources
A dozen colliding wind X-ray binaries in the star cluster R136 in the 30Doradus region
We analyzed archival Chandra X-ray observations of the central portion of the
30 Doradus region in the Large Magellanic Cloud. The image contains 20 X-ray
point sources with luminosities between and erg s (0.2 -- 3.5 keV). A dozen sources have bright WN
Wolf-Rayet or spectral type O stars as optical counterparts. Nine of these are
within pc of R136, the central star cluster of NGC2070. We derive an
empirical relation between the X-ray luminosity and the parameters for the
stellar wind of the optical counterpart. The relation gives good agreement for
known colliding wind binaries in the Milky Way Galaxy and for the identified
X-ray sources in NGC2070. We conclude that probably all identified X-ray
sources in NGC2070 are colliding wind binaries and that they are not associated
with compact objects. This conclusion contradicts Wang (1995) who argued, using
ROSAT data, that two earlier discovered X-ray sources are accreting black-hole
binaries. Five of the eighteen brightest stars in R136 are not visible in our
X-ray observations. These stars are either single, have low mass companions or
very wide orbits. The resulting binary fraction among early type stars is then
unusually high (at least 70%).Comment: 23 pages, To appear in August in Ap
Calculation of an optimized telescope apodizer for Terrestrial Planet Finder coronagraphic telescope
One of two approaches to implementing NASA's Terrestrial Planet Finder is to
build a space telescope that utilizes the techniques of coronagraphy and
apodization to suppress diffraction and image exo-planets. We present a method
for calculation of a telescope's apodizer which suppresses the side lobes of
the image of a star so as to optimally detect an Earth-like planet. Given the
shape of a telescope's aperture and given a search region for a detector, we
solve an integral equation to determine an amplitude modulation (an apodizer)
which suppresses the star's energy in the focal plane search region. The method
is quite general and yields as special cases the product apodizer reported by
Nisenson and Papaliolios (2001) and the Prolate spheroidal apodizer of Kasdin
et al (2002), and Aime et al (2002). We show computer simulations of the
apodizers and the corresponding point spread functions for various
aperture-detector configurations.Comment: 16 Pages, 9 figures, Accepted for publication in June issue of PAS
Weak Lensing Effects on the Galaxy Three-Point Correlation Function
We study the corrections to the galaxy three-point correlation function
(3PCF) induced by weak lensing magnification due to the matter distribution
along the line of sight. We consistently derive all the correction terms
arising up to second order in perturbation theory and provide analytic
expressions as well as order of magnitude estimates for their relative
importance. The magnification contributions depend on the geometry of the
projected triangle on the sky plane, and scale with different powers of the
number count slope and redshift of the galaxy sample considered. We evaluate
all terms numerically and show that, depending on the triangle configuration as
well as the galaxy sample considered, weak lensing can in general significantly
contribute to and alter the three-point correlation function observed through
galaxy and quasar catalogs.Comment: 24 pages, 11 figures; version accepted for publication in Phys. Rev.
D; v2: typos corrected, figure caption clarifie
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