2,100 research outputs found
The Arecibo HII Region Discovery Survey
We report the detection of radio recombination line emission (RRL) using the
Arecibo Observatory at X-band (9GHz, 3cm) from 37 previously unknown HII
regions in the Galactic zone 66 deg. > l > 31 deg. and |b| < 1 deg. This
Arecibo HII Region Discovery Survey (Arecibo HRDS) is a continuation of the
Green Bank Telescope (GBT) HRDS. The targets for the Arecibo HRDS have
spatially coincident 24 micron and 20 cm emission of a similar angular
morphology and extent. To take advantage of Arecibo's sensitivity and small
beam size, sources in this sample are fainter, smaller in angle, or in more
crowded fields compared to those of the GBT HRDS. These Arecibo nebulae are
some of the faintest HII regions ever detected in RRL emission. Our detection
rate is 58%, which is low compared to the 95% detection rate for GBT HRDS
targets. We derive kinematic distances to 23 of the Arecibo HRDS detections.
Four nebulae have negative LSR velocities and are thus unambiguously in the
outer Galaxy. The remaining sources are at the tangent point distance or
farther. We identify a large, diffuse HII region complex that has an associated
HI and 13CO shell. The ~90 pc diameter of the G52L nebula in this complex may
be the largest Galactic HII region known, and yet it has escaped previous
detection.Comment: Accepted to ApJ Data can be found here: http://go.nrao.edu/hrd
Defending Activists at Risk: Protecting Human Rights Defenders from Threats and Violence
This paper seeks to identify protection and security strategies that can be utilized to support human rights defenders. With the intention of making this paper useful to both human rights practitioners and grantmakers, we discuss important legislation, highlight case studies and conclude with a series of best practices drawn from our experience and the recommendations of experts in the field. We hope this work stimulates needed dialogue, enhancing the safety of human rights defenders and making them more effective in their tireless efforts on behalf of others
The Green Bank Telescope H II Region Discovery Survey: IV. Helium and Carbon Recombination Lines
The Green Bank Telescope H II Region Discovery Survey (GBT HRDS) found
hundreds of previously unknown Galactic regions of massive star formation by
detecting hydrogen radio recombination line (RRL) emission from candidate H II
region targets. Since the HRDS nebulae lie at large distances from the Sun,
they are located in previously unprobed zones of the Galactic disk. Here we
derive the properties of helium and carbon RRL emission from HRDS nebulae. Our
target sample is the subset of the HRDS that has visible helium or carbon RRLs.
This criterion gives a total of 84 velocity components (14% of the HRDS) with
helium emission and 52 (9%) with carbon emission. For our highest quality
sources, the average ionic He-4+/H+ abundance ratio by number, , is 0.068
+/- 0.023 (1-sigma). This is the same ratio as that measured for the sample of
previously known Galactic H II regions. Nebulae without detected helium
emission give robust y+ upper limits. There are 5 RRL emission components with
y+ less than 0.04 and another 12 with upper limits below this value. These H II
regions must have either a very low He-4 abundance or contain a significant
amount of neutral helium. The HRDS has 20 nebulae with carbon RRL emission but
no helium emission at its sensitivity level. There is no correlation between
the carbon RRL parameters and the 8 microns mid-infrared morphology of these
nebulae.Comment: Accepted to ApJ. The survey website can be found here:
http://go.nrao.edu/hrd
A Green Bank Telescope Survey of Large Galactic HII Regions
As part of our ongoing HII Region Discovery Survey (HRDS), we report the
Green Bank Telescope detection of 148 new angularly-large Galactic HII regions
in radio recombination line (RRL) emission. Our targets are located at a
declination greater than -45deg., which corresponds to 266deg. > l > -20deg. at
b = 0deg. All sources were selected from the WISE Catalog of Galactic HII
Regions, and have infrared angular diameters >260''. The Galactic distribution
of these "large" HII regions is similar to that of the previously-known sample
of Galactic HII regions. The large HII region RRL line width and peak line
intensity distributions are skewed toward lower values compared with that of
previous HRDS surveys. We discover 7 sources with extremely narrow RRLs <10
km/s. If half the line width is due to turbulence, these 7 sources have thermal
plasma temperatures <1100 K. These temperatures are lower than any measured for
Galactic HII regions, and the narrow line components may arise instead from
partially ionized zones in the HII region photo-dissociation regions. We
discover G039.515+00.511, one of the most luminous HII regions in the Galaxy.
We also detect the RRL emission from three HII regions with diameters >100 pc,
making them some of the physically largest known HII regions in the Galaxy.
This survey completes the HRDS HII region census in the Northern sky, where we
have discovered 887 HII regions and more than doubled the previously-known
census of Galactic HII regions.Comment: Accepted in ApJ
What Next? The Quest to Protect Journalists and Human Rights Defenders in a Digital World
Around the world, governments and non-state actors are using sophisticated techniques to monitor, threaten, and harass human rights defenders (HRDs) and journalists. The growing use of digital technology has empowered activists to rally citizens around common causes and hold governments accountable, but it has also opened new doors for surveillance and harassment of activists and citizens' activities online. On November 14 -- 15, 2013, Freedom House, funded by the United States Agency for International Development (USAID), held a global conference in Mexico City entitled "What Next? The Quest to Protect Journalists and Human Rights Defenders in a Digital World," which brought together over 60 policymakers, donors, and activists to explore the full range of emerging threats and best strategies to overcome them; take an honest look at what is and is not working; and chart a path forward for more proactive and realistic solutions to build the resilience, sustainability, and relevance of HRDs and their movements. The conference sought to answer "what's next?" by identifying opportunities that can be exploited to build up frontline defenders and their ability to uphold human rights principles fearlessly and strategically at home and abroad
A Complete Atlas of HI Absorption toward HII Regions in the Southern Galactic Plane Survey (SGPS1)
We present a complete catalog of H I emission and absorption spectrum pairs,
toward H II regions, detectable within the boundaries of the Southern Galactic
Plane Survey (SGPS I), a total of 252 regions. The catalog is presented in
graphical, numerical and summary formats. We demonstrate an application of this
new dataset through an investigation of the locus of the Near 3kpc Arm.Comment: Accepted for publication by ApJS Feb 6, 2014. Data files and Figure
Set (252 images) to appear in the on-line version of the journa
Optimal Integrated Abundances for Chemical Tagging of Extragalactic Globular Clusters
High resolution integrated light (IL) spectroscopy provides detailed
abundances of distant globular clusters whose stars cannot be resolved.
Abundance comparisons with other systems (e.g. for chemical tagging) require
understanding the systematic offsets that can occur between clusters, such as
those due to uncertainties in the underlying stellar population. This paper
analyses high resolution IL spectra of the Galactic globular clusters 47 Tuc,
M3, M13, NGC 7006, and M15 to (1) quantify potential systematic uncertainties
in Fe, Ca, Ti, Ni, Ba, and Eu and (2) identify the most stable abundance ratios
that will be useful in future analyses of unresolved targets. When stellar
populations are well-modelled, uncertainties are ~0.1-0.2 dex based on
sensitivities to the atmospheric parameters alone; in the worst case scenarios,
uncertainties can rise to 0.2-0.4 dex. The [Ca I/Fe I] ratio is identified as
the optimal integrated [alpha/Fe] indicator (with offsets <0.1 dex), while [Ni
I/Fe I] is also extremely stable to within <0.1 dex. The [Ba II/Eu II] ratios
are also stable when the underlying populations are well modelled and may also
be useful for chemical tagging.Comment: 28 pages, 4 figures, accepted for publication in the Monthly Notices
of the Royal Astronomical Societ
The hindered rotor density-of-states interpolation function
We construct an approximation to the partition function for hindered rotors based entirely on their asymptotic behavior and no fitting parameters. The approximant is shown to be quite accurate in all temperature ranges. Explicit auxiliary functions are derived for the Helmholtz free energy, internal energy, heat capacity, and entropy. We apply this function to estimating the heat capacity and unimolecular dissociation rate for ethane
Masses and Distance of the Young Binary NTTS 045251+3016
As part of our continuing campaign to measure the masses of pre-main sequence
stars dynamically and thus to assess the reliability of the discrepant
theoretical calculations of contraction to the main sequence, we present new
results for NTTS 045251+3016, a visual and double-lined spectroscopic binary in
the Taurus Star Forming Region. We obtained new high angular resolution
astrometry and high spectral resolution spectroscopy at Keck Observatory. The
new data lead to a significant revision of previously published orbital
parameters. In particular, we find that the masses of the primary and secondary
are 0.86+/-0.11 and 0.55+/-0.05 M_sun, respectively, smaller than previously
reported, and that the system lies 158.7+/-3.9 pc from the sun, further than
previously reported.Comment: 36pp; accepted for publication in the Ap
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