3,279 research outputs found
STROZ Lidar Results at the MOHAVE III Campaign, October, 2009, Table Mountain, CA
During October, 2009 the GSFC STROZ Lidar participated in a campaign at the JPL Table Mountain Facility (Wrightwood, CA, 2285 m Elevation) to measure vertical profiles of water vapor from near the ground to the lower stratosphere. On eleven nights, water vapor, aerosol, temperature and ozone profiles were measured by the STROZ lidar, two other similar lidars, frost-point hygrometer sondes, and ground-based microwave instruments made measurements. Results from these measurements and an evaluation of the performance of the STROZ lidar during the campaign will be presented in this paper. The STROZ lidar was able to measure water vapor up to 13-14 km ASL during the campaign. We will present results from all the STROZ data products and comparisons with other instruments made. Implications for instrumental changes will be discussed
The Stellar Content of Obscured Galactic Giant H II Regions IV.: NGC3576
We present deep, high angular resolution near-infrared images of the obscured
Galactic Giant H II region NGC3576. Our images reach objects to ~3M_sun. We
collected high signal-to-noise K-band spectra of eight of the brightest
objects, some of which are affected by excess emission and some which follow a
normal interstellar reddening law. None of them displayed photospheric features
typical of massive OB type stars. This indicates that they are still enshrouded
in their natal cocoons. The K-band brightest source (NGC3576 #48) shows CO 2.3
micron bandhead emission, and three others have the same CO feature in
absorption. Three sources display spatially unresolved H_2 emission, suggesting
dense shocked regions close to the stars. We conclude that the remarkable
object NGC3576 #48 is an early-B/late-O star surrounded by a thick
circumstellar disk. A number of other relatively bright cluster members also
display excess emission in the K-band, indicative of reprocessing disks around
massive stars (YSOs). Such emission appears common in other Galactic Giant H II
regions we have surveyed. The IMF slope of the cluster, Gamma = -1.51, is
consistent with Salpeter's distribution and similar to what has been observed
in the Magellanic Cloud clusters and in the periphery of our Galaxy.Comment: 14 pages, 11 figures, accepted for publication in A
A New Differential Absorption Lidar to Measure Sub-Hourly Fluctuation of Tropospheric Ozone Profiles in the Baltimore - Washington D.C. Region
Tropospheric ozone profiles have been retrieved from the new ground based National Aeronautics and Space Administration (NASA) Goddard Space Flight Center TROPospheric OZone DIfferential Absorption Lidar (GSFC TROPOZ DIAL) in Greenbelt, MD (38.99 N, 76.84 W, 57 meters ASL) from 400 m to 12 km AGL. Current atmospheric satellite instruments cannot peer through the optically thick stratospheric ozone layer to remotely sense boundary layer tropospheric ozone. In order to monitor this lower ozone more effectively, the Tropospheric Ozone Lidar Network (TOLNet) has been developed, which currently consists of five stations across the US. The GSFC TROPOZ DIAL is based on the Differential Absorption Lidar (DIAL) technique, which currently detects two wavelengths, 289 and 299 nm. Ozone is absorbed more strongly at 289 nm than at 299 nm. The DIAL technique exploits this difference between the returned backscatter signals to obtain the ozone number density as a function of altitude. The transmitted wavelengths are generated by focusing the output of a quadrupled Nd:YAG laser beam (266 nm) into a pair of Raman cells, filled with high pressure hydrogen and deuterium. Stimulated Raman Scattering (SRS) within the focus generates a significant fraction of the pump energy at the first Stokes shift. With the knowledge of the ozone absorption coefficient at these two wavelengths, the range resolved number density can be derived. An interesting atmospheric case study involving the Stratospheric-Tropospheric Exchange (STE) of ozone is shown to emphasize the regional importance of this instrument as well as assessing the validation and calibration of data. The retrieval yields an uncertainty of 16-19 percent from 0-1.5 km, 10-18 percent from 1.5-3 km, and 11-25 percent from 3 km to 12 km. There are currently surface ozone measurements hourly and ozonesonde launches occasionally, but this system will be the first to make routine tropospheric ozone profile measurements in the Baltimore-Washington DC area
GASP II. A MUSE view of extreme ram-pressure stripping along the line of sight: kinematics of the jellyfish galaxy JO201
This paper presents a spatially-resolved kinematic study of the jellyfish
galaxy JO201, one of the most spectacular cases of ram-pressure stripping (RPS)
in the GASP (GAs Stripping Phenomena in Galaxies with MUSE) survey. By studying
the environment of JO201, we find that it is moving through the dense
intra-cluster medium of Abell 85 at supersonic speeds along our line of sight,
and that it is likely accompanied by a small group of galaxies. Given the
density of the intra-cluster medium and the galaxy's mass, projected position
and velocity within the cluster, we estimate that JO201 must so far have lost
~50% of its gas during infall via RPS. The MUSE data indeed reveal a smooth
stellar disk, accompanied by large projected tails of ionised (Halpha) gas,
composed of kinematically cold (velocity dispersion <40km/s) star-forming knots
and very warm (>100km/s) diffuse emission which extend out to at least ~50 kpc
from the galaxy centre. The ionised Halpha-emitting gas in the disk rotates
with the stars out to ~6 kpc but in the disk outskirts becomes increasingly
redshifted with respect to the (undisturbed) stellar disk. The observed
disturbances are consistent with the presence of gas trailing behind the
stellar component, resulting from intense face-on RPS happening along the line
of sight. Our kinematic analysis is consistent with the estimated fraction of
lost gas, and reveals that stripping of the disk happens outside-in, causing
shock heating and gas compression in the stripped tails.Comment: ApJ, revised version after referee comments, 15 pages, 16 figures.
The interactive version of Figure 9 can be viewed at
web.oapd.inaf.it/gasp/publications.htm
Parker Instability in a Self-Gravitating Magnetized Gas Disk: I. Linear Stability Analysis
To be a formation mechanism of such large-scale structures as giant molecular
clouds (GMCs) and HI superclouds, the classical Parker instability driven by
external gravity has to overcome three major obstacles: The convective motion
accompanying the instability generates thin sheets than large condensations.
The degree of density enhancement achieved by the instability is too low to
make dense interstellar clouds. The time and the length scales of the
instability are significantly longer and larger than the estimated formation
time and the observed mean separation of the GMCs, respectively. This paper
examines whether a replacement of the driving agent from the external to the
self gravity might remove these obstacles by activating the gravitational
instability in the Galactic ISM disk. The self gravity can suppress the
convective motions, and a cooperative action of the Jeans and the Parker
instabilities can remove all the obstacles confronting the classical version of
the Parker instability. The mass and mean separation of the structures
resulting from the odd-parity undular mode solution are shown to agree better
with the HI superclouds than with the GMCs. We briefly discuss how inclusions
of the external gravity and cosmic rays would modify behaviors of the
odd-parity undular mode solution.Comment: 53 pages, 21 figure
Improving Underrepresented Minority Student Persistence in STEM.
Members of the Joint Working Group on Improving Underrepresented Minorities (URMs) Persistence in Science, Technology, Engineering, and Mathematics (STEM)-convened by the National Institute of General Medical Sciences and the Howard Hughes Medical Institute-review current data and propose deliberation about why the academic "pathways" leak more for URM than white or Asian STEM students. They suggest expanding to include a stronger focus on the institutional barriers that need to be removed and the types of interventions that "lift" students' interests, commitment, and ability to persist in STEM fields. Using Kurt Lewin's planned approach to change, the committee describes five recommendations to increase URM persistence in STEM at the undergraduate level. These recommendations capitalize on known successes, recognize the need for accountability, and are framed to facilitate greater progress in the future. The impact of these recommendations rests upon enacting the first recommendation: to track successes and failures at the institutional level and collect data that help explain the existing trends
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