4,797 research outputs found
Chemical composition and mixing in giant HII regions: NGC3603, 30Doradus, and N66
We investigate the chemical abundances of NGC3603 in the Milky Way, of
30Doradus in the Large Magellanic Cloud, and of N66 in the Small Magellanic
Cloud. Mid-infrared observations with the Infrared Spectrograph onboard the
Spitzer Space Telescope allow us to probe the properties of distinct physical
regions within each object: the central ionizing cluster, the surrounding
ionized gas, photodissociation regions, and buried stellar clusters. We detect
[SIII], [SIV], [ArIII], [NeII], [NeIII], [FeII], and [FeIII] lines and derive
the ionic abundances. Based on the ionic abundance ratio (NeIII/H)/(SIII/H), we
find that the gas observed in the MIR is characterized by a higher degree of
ionization than the gas observed in the optical spectra. We compute the
elemental abundances of Ne, S, Ar, and Fe. We find that the alpha-elements Ne,
S, and Ar scale with each other. Our determinations agree well with the
abundances derived from the optical. The Ne/S ratio is higher than the solar
value in the three giant HII regions and points toward a moderate depletion of
sulfur on dust grains. We find that the neon and sulfur abundances display a
remarkably small dispersion (0.11dex in 15 positions in 30Doradus), suggesting
a relatively homogeneous ISM, even though small-scale mixing cannot be ruled
out.Comment: Accepted for submission to ApJ. The present version replaces the
submitted one. Changes: new title, new figure, the text was modified in the
discussio
Spitzer/IRS Imaging and Spectroscopy of the luminous infrared galaxy NGC 6052 (Mrk 297)
We present photometric and spectroscopic data of the interacting starburst
galaxy NGC 6052 obtained with the Spitzer Space Telescope. The mid-infrared
(MIR) spectra of the three brightest spatially resolved regions in the galaxy
are remarkably similar and are consistent with dust emission from young nearly
coeval stellar populations. Analysis of the brightest infrared region of the
system, which contributes ~18.5 % of the total 16\micron flux, indicates that
unlike similar off-nuclear infrared-bright regions found in Arp 299 or NGC
4038/9, its MIR spectrum is inconsistent with an enshrouded hot dust (T > 300K)
component. Instead, the three brightest MIR regions all display dust continua
of temperatures less than ~ 200K. These low dust temperatures indicate the dust
is likely in the form of a patchy screen of relatively cold material situated
along the line of sight. We also find that emission from polycyclic aromatic
hydrocarbons (PAHs) and the forbidden atomic lines is very similar for each
region. We conclude that the ionization regions are self-similar and come from
young (about 6 Myr) stellar populations. A fourth region, for which we have no
MIR spectra, exhibits MIR emission similar to tidal tail features in other
interacting galaxies.Comment: 20 pages in preprint form, estimated 7 pages in ApJ Aeptember 10,
2007, v666n 2 issue, six encapsulated postscript figure
Characterizing the Rigidly Rotating Magnetosphere Stars HD 345439 and HD 23478
The SDSS III APOGEE survey recently identified two new Ori E type
candidates, HD 345439 and HD 23478, which are a rare subset of rapidly rotating
massive stars whose large (kGauss) magnetic fields confine circumstellar
material around these systems. Our analysis of multi-epoch photometric
observations of HD 345439 from the KELT, SuperWASP, and ASAS surveys reveals
the presence of a 0.7701 day period in each dataset, suggesting the
system is amongst the faster known Ori E analogs. We also see clear
evidence that the strength of H-alpha, H I Brackett series lines, and He I
lines also vary on a 0.7701 day period from our analysis of multi-epoch,
multi-wavelength spectroscopic monitoring of the system from the APO 3.5m
telescope. We trace the evolution of select emission line profiles in the
system, and observe coherent line profile variability in both optical and
infrared H I lines, as expected for rigidly rotating magnetosphere stars. We
also analyze the evolution of the H I Br-11 line strength and line profile in
multi-epoch observations of HD 23478 from the SDSS-III APOGEE instrument. The
observed periodic behavior is consistent with that recently reported by Sikora
and collaborators in optical spectra.Comment: Accepted in ApJ
NASA Light Emitting Diode Medical Applications from Deep Space to Deep Sea
This work is supported and managed through the NASA Marshall Space Flight Center-SBIR Program. LED-technology developed for NASA plant growth experiments in space shows promise for delivering light deep into tissues of the body to promote wound healing and human tissue growth. We present the results of LED-treatment of cells grown in culture and the effects of LEDs on patients’ chronic and acute wounds. LED-technology is also biologically optimal for photodynamic therapy of cancer and we discuss our successes using LEDs in conjunction with light-activated chemotherapeutic drugs
Gravitational waves from Sco X-1: A comparison of search methods and prospects for detection with advanced detectors
The low-mass X-ray binary Scorpius X-1 (Sco X-1) is potentially the most
luminous source of continuous gravitational-wave radiation for interferometers
such as LIGO and Virgo. For low-mass X-ray binaries this radiation would be
sustained by active accretion of matter from its binary companion. With the
Advanced Detector Era fast approaching, work is underway to develop an array of
robust tools for maximizing the science and detection potential of Sco X-1. We
describe the plans and progress of a project designed to compare the numerous
independent search algorithms currently available. We employ a mock-data
challenge in which the search pipelines are tested for their relative
proficiencies in parameter estimation, computational efficiency, robust- ness,
and most importantly, search sensitivity. The mock-data challenge data contains
an ensemble of 50 Scorpius X-1 (Sco X-1) type signals, simulated within a
frequency band of 50-1500 Hz. Simulated detector noise was generated assuming
the expected best strain sensitivity of Advanced LIGO and Advanced VIRGO ( Hz). A distribution of signal amplitudes was then
chosen so as to allow a useful comparison of search methodologies. A factor of
2 in strain separates the quietest detected signal, at
strain, from the torque-balance limit at a spin frequency of 300 Hz, although
this limit could range from (25 Hz) to (750 Hz) depending on the unknown frequency of Sco X-1. With future
improvements to the search algorithms and using advanced detector data, our
expectations for probing below the theoretical torque-balance strain limit are
optimistic.Comment: 33 pages, 11 figure
Global Properties of Neutral Hydrogen in Compact Groups
Compact groups of galaxies provide a unique environment to study the
evolution of galaxies amid frequent gravitational encounters. These nearby
groups have conditions similar to those in the earlier universe when galaxies
were assembled and give us the opportunity to witness hierarchical formation in
progress. To understand how the compact group environment affects galaxy
evolution, we examine the gas and dust in these groups. We present new
single-dish GBT neutral hydrogen (HI) observations of 30 compact groups and
define a new way to quantify the group HI content as the HI-to-stellar mass
ratio of the group as a whole. We compare the HI content with mid-IR indicators
of star formation and optical [g-r] color to search for correlations between
group gas content and star formation activity of individual group members.
Quiescent galaxies tend to live in HI-poor groups, and galaxies with active
star formation are more commonly found in HI-rich groups. Intriguingly, we also
find "rogue" galaxies whose star formation does not correlate with group HI
content. In particular, we identify three galaxies (NGC 2968 in RSCG 34, KUG
1131+202A in RSCG 42, and NGC 4613 in RSCG 64) whose mid-IR activity is
discrepant with the HI. We speculate that this mismatch between mid-IR activity
and HI content is a consequence of strong interactions in this environment that
can strip HI from galaxies and abruptly affect star-formation. Ultimately,
characterizing how and on what timescales the gas is processed in compact
groups will help us understand the interstellar medium in complex, dense
environments similar to the earlier Universe.Comment: Accepted to A
Adventures of the Coupled Yang-Mills Oscillators: I. Semiclassical Expansion
We study the quantum mechanical motion in the potentials with
, which arise in the spatially homogeneous limit of the Yang-Mills (YM)
equations. These systems show strong stochasticity in the classical limit
() and exhibit a quantum mechanical confinement feature. We
calculate the partition function going beyond the Thomas-Fermi (TF)
approximation by means of the semiclassical expansion using the Wigner-Kirkwood
(WK) method. We derive a novel compact form of the differential equation for
the WK function. After separating the motion in the channels of the
equipotential surface from the motion in the central region, we show that the
leading higher-order corrections to the TF term vanish up to eighth order in
, if we treat the quantum motion in the hyperbolic channels correctly by
adiabatic separation of the degrees of freedom. Finally, we obtain an
asymptotic expansion of the partition function in terms of the parameter
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