1,526 research outputs found
The DDO IVC Distance Project: Survey Description and the Distance to G139.6+47.6
We present a detailed analysis of the distance determination for one
intermediate Velocity Cloud (IVC G139.6+47.6) from the ongoing DDO IVC Distance
Project. Stars along the line of sight to G139.6+47.6 are examined for the
presence of sodium absorption attributable to the cloud, and the distance
bracket is established by astrometric and spectroscopic parallax measurements
of demonstrated foreground and background stars. We detail our strategy
regarding target selection, observational setup, and analysis of the data,
including a discussion of wavelength calibration and sky subtraction
uncertainties. We find a distance estimate of 129 (+/- 10) pc for the lower
limit and 257 (+211-33) pc for the upper limit. Given the high number of stars
showing absorption due to this IVC, we also discuss the small-scale covering
factor of the cloud and the likely significance of non-detections for
subsequent observations of this and other similar IVC's. Distance measurements
of the remaining targets in the DDO IVC project will be detailed in a companion
paper.Comment: 10 pages, 6 figures, LaTe
Lower Limits on Aperture Size for an ExoEarth-Detecting Coronagraphic Mission
The yield of Earth-like planets will likely be a primary science metric for
future space-based missions that will drive telescope aperture size. Maximizing
the exoEarth candidate yield is therefore critical to minimizing the required
aperture. Here we describe a method for exoEarth candidate yield maximization
that simultaneously optimizes, for the first time, the targets chosen for
observation, the number of visits to each target, the delay time between
visits, and the exposure time of every observation. This code calculates both
the detection time and multi-wavelength spectral characterization time required
for planets. We also refine the astrophysical assumptions used as inputs to
these calculations, relying on published estimates of planetary occurrence
rates as well as theoretical and observational constraints on terrestrial
planet sizes and classical habitable zones. Given these astrophysical
assumptions, optimistic telescope and instrument assumptions, and our new
completeness code that produces the highest yields to date, we suggest lower
limits on the aperture size required to detect and characterize a
statistically-motivated sample of exoEarths.Comment: Accepted for publication in ApJ; 38 pages, 16 Figures, 3 Table
Ultrasound-guided Breast Biopsy in the Resource-limited Setting: An Initial Experience in Rural Uganda
Purpose: To describe the methodology and initial experience behind creation of an ultrasoundguided percutaneous breast core biopsy program in rural Uganda.
Methods and Materials: Imaging the World Africa (ITWA) is the registered non-governmental organization division of Imaging the World (ITW), a not-for-profit organization whose primary aim is the integration of affordable high-quality ultrasound into rural health centers. In 2013, ITWA began the pilot phase of an IRB-approved breast care protocol at a rural health center in Uganda. As part of the protocol’s diagnostic arm, an ultrasound-guided percutaneous breast core biopsy training curriculum was implemented in tandem with creation of regionally supplied biopsy kits.
Results: A surgeon at a rural regional referral hospital was successfully trained and certified to perform ultrasound-guided percutaneous breast core biopsies. Affordable and safe biopsy kits were created using locally available medical supplies with the cost of each kit totaling $10.62 USD.
Conclusion: Successful implementation of an ultrasound-guided percutaneous breast core biopsy program in the resource-limited setting is possible and can be made sustainable through incorporation of local health care personnel and regionally supplied biopsy materials. Our hope is that ITWA’s initial experience in rural Uganda can serve as a model for similar programs in the future
A New, Bright, Short-Period, Emission Line Binary in Ophiuchus
The 11th magnitude star LS IV-08°3 has been classified previously as an OB star in the Luminous Stars survey, or alternatively as a hot subdwarf. It is actually a binary star. We present spectroscopy, spectroscopic orbital elements, and time-series photometry from observations made at the Kitt Peak National Observatory 2.1 m, Steward Observatory 2.3 m, MDM Observatory 1.3 m and 2.4 m, Hobby-Eberly 9.2 m, and Michigan State University 0.6 m telescopes. The star exhibits emission of varying strength in the cores of H and He I absorption lines. Emission is also present at 4686 Å (He II) and near 4640/4650 Å (N III/C III). Time-series spectroscopy collected from 2005 July to 2007 June shows coherent, periodic radial velocity variations of the Hα line, which we interpret as orbital motion with a period of 0.1952894(10) days. High-resolution spectra show that there are two emission components, one broad and one narrow, moving in antiphase, as might arise from an accretion disk and the irradiated face of the mass donor star. Less coherent, low-amplitude photometric variability is also present on a timescale similar to the orbital period. Diffuse interstellar bands indicate considerable reddening, which however is consistent with a distance of ~100-200 pc. The star is the likely counterpart of a weak ROSAT X-ray source, whose properties are consistent with accretion in a cataclysmic variable (CV) binary system. We classify LS IV-08°3 as a new member of the UX UMa subclass of CV stars
ATLAST detector needs for direct spectroscopic biosignature characterization in the visible and near-IR
Are we alone? Answering this ageless question will be a major focus for
astrophysics in coming decades. Our tools will include unprecedentedly large
UV-Optical-IR space telescopes working with advanced coronagraphs and
starshades. Yet, these facilities will not live up to their full potential
without better detectors than we have today. To inform detector development,
this paper provides an overview of visible and near-IR (VISIR;
) detector needs for the Advanced Technology
Large Aperture Space Telescope (ATLAST), specifically for spectroscopic
characterization of atmospheric biosignature gasses. We also provide a brief
status update on some promising detector technologies for meeting these needs
in the context of a passively cooled ATLAST.Comment: 8 pages, Presented 9 August 2015 at SPIE Optics + Photonics, San
Diego, C
The AST/RO Survey of the Galactic Center Region. I. The Inner 3 Degrees
We present fully-sampled maps of 461 GHz CO (4-3), 807 GHz CO (7-6), and 492
GHz [CI] (3P1-3P0) emission from the inner 3 degrees of the Galactic Center
region taken with the Antarctic Submillimeter Telescope and Remote Observatory
(AST/RO) in 2001--2002. The data cover -1.3 < l < 2, -0.3 < b < 0.2 with 0.5
arcmin spacing, resulting in spectra in 3 transitions at over 24,000 positions
on the sky. The CO (4-3) emission is found to be essentially coextensive with
lower-J transitions of CO. The CO (7-6) emission is spatially confined to a far
smaller region than the lower-J CO lines. The [CI] (3P1-3P0) emission has a
spatial extent similar to the low-J CO emission, but is more diffuse. Bright CO
(7-6) emission is detected in the well-known Galactic Center clouds Sgr A and
Sgr B. We also detect CO (4-3) and CO (7-6) absorption from spiral arms in the
galactic disk at velocities near 0 km s^-1 along the line of sight to the
Galactic Center. Analyzing our CO (7-6) and CO (4-3) data in conjunction with J
= 1 - 0 12CO and 13CO data previously observed with the Bell Laboratories 7-m
antenna, we apply a Large Velocity Gradient (LVG) model to estimate the kinetic
temperature and density of molecular gas in the inner 200 pc of the Galactic
Center region. We show maps of the derived distribution of gas density and
kinetic temperature as a function of position and velocity for the entire
region. Kinetic temperature was found to decrease from relatively high values
(>70K) at cloud edges to low values (<50K) in the interiors. Typical gas
pressures in the Galactic Center gas are n(H_2) T_kin approx 10^5.2 K cm^-3. We
also present an (l,b) map of molecular hydrogen column density derived from our
LVG results.Comment: 41 pages, 29 figures reduced to low resolution for astro-ph, for high
resolution figures please go to http://cfa-www.harvard.edu/ASTRO/galcen_1.pdf
this version incorporates changes due to accepted erratum (to appear in ApJS
153
A Search for Exozodiacal Clouds with Kepler
Planets embedded within dust disks may drive the formation of large scale
clumpy dust structures by trapping dust into resonant orbits. Detection and
subsequent modeling of the dust structures would help constrain the mass and
orbit of the planet and the disk architecture, give clues to the history of the
planetary system, and provide a statistical estimate of disk asymmetry for
future exoEarth-imaging missions. Here we present the first search for these
resonant structures in the inner regions of planetary systems by analyzing the
light curves of hot Jupiter planetary candidates identified by the Kepler
mission. We detect only one candidate disk structure associated with KOI 838.01
at the 3-sigma confidence level, but subsequent radial velocity measurements
reveal that KOI 838.01 is a grazing eclipsing binary and the candidate disk
structure is a false positive. Using our null result, we place an upper limit
on the frequency of dense exozodi structures created by hot Jupiters. We find
that at the 90% confidence level, less than 21% of Kepler hot Jupiters create
resonant dust clumps that lead and trail the planet by ~90 degrees with optical
depths >~5*10^-6, which corresponds to the resonant structure expected for a
lone hot Jupiter perturbing a dynamically cold dust disk 50 times as dense as
the zodiacal cloud.Comment: 22 pages, 6 figures, Accepted for publication in Ap
Finding the Needles in the Haystacks: High-Fidelity Models of the Modern and Archean Solar System for Simulating Exoplanet Observations
We present two state-of-the-art models of the solar system, one corresponding
to the present day and one to the Archean Eon 3.5 billion years ago. Each model
contains spatial and spectral information for the star, the planets, and the
interplanetary dust, extending to 50 AU from the sun and covering the
wavelength range 0.3 to 2.5 micron. In addition, we created a spectral image
cube representative of the astronomical backgrounds that will be seen behind
deep observations of extrasolar planetary systems, including galaxies and Milky
Way stars. These models are intended as inputs to high-fidelity simulations of
direct observations of exoplanetary systems using telescopes equipped with
high-contrast capability. They will help improve the realism of observation and
instrument parameters that are required inputs to statistical observatory yield
calculations, as well as guide development of post-processing algorithms for
telescopes capable of directly imaging Earth-like planets.Comment: Accepted for publication in PAS
A New, Bright, Short-Period, Emission Line Binary in Ophiuchus
The 11th magnitude star LS IV -08 3 has been classified previously as an OB
star in the Luminous Stars survey, or alternatively as a hot subdwarf. It is
actually a binary star. We present spectroscopy, spectroscopic orbital
elements, and time series photometry, from observations made at the Kitt Peak
National Observatory 2.1m, Steward Observatory 2.3m, MDM Observatory 1.3m and
2.4m, Hobby-Eberly 9.2m, and Michigan State University 0.6m telescopes. The
star exhibits emission of varying strength in the cores of H and He I
absorption lines. Emission is also present at 4686 Angstroms (He II) and near
4640/4650 Angstroms (N III/C III). Time-series spectroscopy collected from 2005
July to 2007 June shows coherent, periodic radial velocity variations of the
H-alpha line, which we interpret as orbital motion with a period of
0.1952894(10) days. High-resolution spectra show that there are two emission
components, one broad and one narrow, moving in antiphase, as might arise from
an accretion disk and the irradiated face of the mass donor star. Less
coherent, low-amplitude photometric variability is also present on a timescale
similar to the orbital period. Diffuse interstellar bands indicate considerable
reddening, which however is consistent with a distance of ~100-200 pc. The star
is the likely counterpart of a weak ROSAT X-ray source, whose properties are
consistent with accretion in a cataclysmic variable (CV) binary system. We
classify LS IV -08 3 as a new member of the UX UMa subclass of CV stars.Comment: To be published in AJ, 16 pages, 6 figures. Uses AAS Late
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