1,675 research outputs found
Characterizing Supernova Progenitors via the Metallicities of their Host Galaxies, from Poor Dwarfs to Rich Spirals
We investigate how the different types of supernovae are relatively affected
by the metallicity of their host galaxy. We match the SAI Supernova Catalog to
the SDSS-DR4 catalog of star-forming galaxies with measured metallicities.
These supernova host galaxies span a range of oxygen abundance from 12 +
log(O/H) = 7.9 to 9.3 (~ 0.1 to 2.7 solar) and a range in absolute magnitude
from MB = -15.2 to -22.2. To reduce the various observational biases, we select
a subsample of well-characterized supernovae in the redshift range from 0.01 to
0.04, which leaves us with 58 SN II, 19 Ib/c, and 38 Ia. We find strong
evidence that SN Ib/c are occurring in higher-metallicity host galaxies than SN
II, while we see no effect for SN Ia relative to SN II. We note some extreme
and interesting supernova-host pairs, including the metal-poor (~ 1/4 solar)
host of the recent SN Ia 2007bk, where the supernova was found well outside of
this dwarf galaxy. To extend the luminosity range of supernova hosts to even
fainter galaxies, we also match all the historical supernovae with z < 0.3 to
the SDSS-DR6 sky images, resulting in 1225 matches. This allows us to identify
some even more extreme cases, such as the recent SN Ic 2007bg, where the likely
host of this hypernova-like event has an absolute magnitude MB ~ -12, making it
one of the least-luminous supernova hosts ever observed. This low-luminosity
host is certain to be very metal poor (~ 1/20 solar), and therefore this
supernova is an excellent candidate for association with an off-axis GRB. The
two catalogs that we have constructed are available online and will be updated
regularly. Finally, we discuss various implications of our findings for
understanding supernova progenitors and their host galaxies.Comment: ApJ accepted, 26 pages, 5 figures, 1 table. Updated catalogs are
available at http://www.astronomy.ohio-state.edu/~prieto/snhosts
Binary Population and Spectral Synthesis Version 2.1: construction, observational verification and new results
The Binary Population and Spectral Synthesis (BPASS) suite of binary stellar
evolution models and synthetic stellar populations provides a framework for the
physically motivated analysis of both the integrated light from distant stellar
populations and the detailed properties of those nearby. We present a new
version 2.1 data release of these models, detailing the methodology by which
BPASS incorporates binary mass transfer and its effect on stellar evolution
pathways, as well as the construction of simple stellar populations. We
demonstrate key tests of the latest BPASS model suite demonstrating its ability
to reproduce the colours and derived properties of resolved stellar
populations, including well- constrained eclipsing binaries. We consider
observational constraints on the ratio of massive star types and the
distribution of stellar remnant masses. We describe the identification of
supernova progenitors in our models, and demonstrate a good agreement to the
properties of observed progenitors. We also test our models against photometric
and spectroscopic observations of unresolved stellar populations, both in the
local and distant Universe, finding that binary models provide a
self-consistent explanation for observed galaxy properties across a broad
redshift range. Finally, we carefully describe the limitations of our models,
and areas where we expect to see significant improvement in future versions.Comment: 69 pages, 45 figures. Accepted for publication in PASA. Accompanied
by a full, documented data release at http://bpass.auckland.ac.nz and
http://warwick.ac.uk/bpas
Raman Channel Temperature Measurement of SiC MESFET as a Function of Ambient Temperature and DC Power
Raman spectroscopy is used to measure the junction temperature of a Cree SiC MESFET as a function of the ambient temperature and DC power. The carrier temperature, which is approximately equal to the ambient temperature, is varied from 25 C to 450 C, and the transistor is biased with VDS=10V and IDS of 50 mA and 100 mA. It is shown that the junction temperature is approximately 52 and 100 C higher than the ambient temperature for the DC power of 500 and 1000 mW, respectively
A Comprehensive Comparative Test of Seven Widely-Used Spectral Synthesis Models Against Multi-Band Photometry of Young Massive Star Clusters
We test the predictions of spectral synthesis models based on seven different
massive-star prescriptions against Legacy ExtraGalactic UV Survey (LEGUS)
observations of eight young massive clusters in two local galaxies, NGC 1566
and NGC 5253, chosen because predictions of all seven models are available at
the published galactic metallicities. The high angular resolution, extensive
cluster inventory and full near-ultraviolet to near-infrared photometric
coverage make the LEGUS dataset excellent for this study. We account for both
stellar and nebular emission in the models and try two different prescriptions
for attenuation by dust. From Bayesian fits of model libraries to the
observations, we find remarkably low dispersion in the median E(B-V) (~0.03
mag), stellar masses (~10^4 M_\odot) and ages (~1 Myr) derived for individual
clusters using different models, although maximum discrepancies in these
quantities can reach 0.09 mag and factors of 2.8 and 2.5, respectively. This is
for ranges in median properties of 0.05-0.54 mag, 1.8-10x10^4 M_\odot and
1.6-40 Myr spanned by the clusters in our sample. In terms of best fit, the
observations are slightly better reproduced by models with interacting binaries
and least well reproduced by models with single rotating stars. Our study
provides a first quantitative estimate of the accuracies and uncertainties of
the most recent spectral synthesis models of young stellar populations,
demonstrates the good progress of models in fitting high-quality observations,
and highlights the needs for a larger cluster sample and more extensive tests
of the model parameter space.Comment: Accepted for publication in MNRAS (14 Jan. 2016). 30 pages, 16
figures, 9 table
Dryland ecohydrology and climate change: critical issues and technical advances
Drylands cover about 40% of the terrestrial land surface and account for approximately 40% of global net primary productivity. Water is fundamental to the biophysical processes that sustain ecosystem function and food production, particularly in drylands where a tight coupling exists between ecosystem productivity, surface energy balance, biogeochemical cycles, and water resource availability. Currently, drylands support at least 2 billion people and comprise both natural and managed ecosystems. In this synthesis, we identify some current critical issues in the understanding of dryland systems and discuss how arid and semiarid environments are responding to the changes in climate and land use. The issues range from societal aspects such as rapid population growth, the resulting food and water security, and development issues, to natural aspects such as ecohydrological consequences of bush encroachment and the causes of desertification. To improve current understanding and inform upon the needed research efforts to address these critical issues, we identify some recent technical advances in terms of monitoring dryland water dynamics, water budget and vegetation water use, with a focus on the use of stable isotopes and remote sensing. These technological advances provide new tools that assist in addressing critical issues in dryland ecohydrology under climate change
Resolved photometry of extragalactic young massive star clusters
We present colour-magnitude diagrams (CMDs) for a sample of seven young
massive clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC
7793. The clusters have ages in the range 5-50 million years and masses of 10^5
-10^6 Msun. Although crowding prevents us from obtaining photometry in the
central regions of the clusters, we are still able to measure up to 30-100
supergiant stars in each of the richest clusters, along with the brighter main
sequence stars. The resulting CMDs and luminosity functions are compared with
photometry of artificially generated clusters, designed to reproduce the
photometric errors and completeness as realistically as possible. In agreement
with previous studies, our CMDs show no clear gap between the H-burning main
sequence and the He-burning supergiant stars, contrary to predictions by common
stellar isochrones. In general, the isochrones also fail to match the observed
number ratios of red-to-blue supergiant stars, although the difficulty of
separating blue supergiants from the main sequence complicates this comparison.
In several cases we observe a large spread (1-2 mag) in the luminosities of the
supergiant stars that cannot be accounted for by observational errors. This
spread can be reproduced by including an age spread of 10-30 million years in
the models. However, age spreads cannot fully account for the observed
morphology of the CMDs and other processes, such as the evolution of
interacting binary stars, may also play a role.Comment: 15 pages, 12 figures, accepted for publication in A&
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