737 research outputs found
Fuzzy Supernova Templates II: Parameter Estimation
Wide field surveys will soon be discovering Type Ia supernovae (SNe) at rates
of several thousand per year. Spectroscopic follow-up can only scratch the
surface for such enormous samples, so these extensive data sets will only be
useful to the extent that they can be characterized by the survey photometry
alone. In a companion paper (Rodney and Tonry, 2009) we introduced the SOFT
method for analyzing SNe using direct comparison to template light curves, and
demonstrated its application for photometric SN classification. In this work we
extend the SOFT method to derive estimates of redshift and luminosity distance
for Type Ia SNe, using light curves from the SDSS and SNLS surveys as a
validation set. Redshifts determined by SOFT using light curves alone are
consistent with spectroscopic redshifts, showing a root-mean-square scatter in
the residuals of RMS_z=0.051. SOFT can also derive simultaneous redshift and
distance estimates, yielding results that are consistent with the currently
favored Lambda-CDM cosmological model. When SOFT is given spectroscopic
information for SN classification and redshift priors, the RMS scatter in
Hubble diagram residuals is 0.18 mags for the SDSS data and 0.28 mags for the
SNLS objects. Without access to any spectroscopic information, and even without
any redshift priors from host galaxy photometry, SOFT can still measure
reliable redshifts and distances, with an increase in the Hubble residuals to
0.37 mags for the combined SDSS and SNLS data set. Using Monte Carlo
simulations we predict that SOFT will be able to improve constraints on
time-variable dark energy models by a factor of 2-3 with each new generation of
large-scale SN surveys.Comment: 20 pages, 7 figures, accepted to ApJ; paper 1 is arXiv:0910.370
Investigations into the triggered lightning response of the F106B thunderstorm research aircraft
An investigation has been conducted into the lightning characteristics of the NASA F106B thunderstorm research aircraft. The investigation includes analysis of measured data from the aircraft in the time and frequency domains. Linear and nonlinear computer modelling has also been performed. In addition, new computer tools have been developed, including a new enhanced nonlinear air breakdown model, and a subgrid model useful for analyzing fine details of the aircraft's geometry. Comparison of measured and calculated electromagnetic responses of the aircraft to a triggered lightning environment are presented
Characterizing Charge Diffusion in CCDs with X-rays
We demonstrate the effectiveness of two techniques for using x-rays to
evaluate the amount of charge diffusion in charge coupled devices (CCDs). We
quantify the degree of charge diffusion with two parameters: sigma_d, the
standard deviation for a Gaussian diffusion model, and Q, a ratio of the point
spread function (PSF) peak to its wings. sigma_d and Q are determined by
fitting a model to a pixel energy histogram, and by summing the PSF of all
x-ray events, respectively. Using seven test devices, we investigate the
precision of these two techniques and demonstrate that they produce compatible
results. The histogram fitting method is sensitive to the structure of the
electric field within these devices, in addition to the inherent charge
diffusion properties. The Q ratio is a very simple parameter to measure and
provides an easily accessible method for quickly evaluating a CCD's diffusion
length.Comment: 12 pages, 8 figures, accepted for publication in PAS
A Cluster of Compact Radio Sources in W40
We present deep 3.6 cm radio continuum observations of the HII region W40
obtained using the Very Large Array in its A and B configurations. We detect a
total of 20 compact radio sources in a region of 4 x 4 arcmin, with 11 of them
concentrated in a band with 30 arcsec of extent. We also present JHK photometry
of the W40 cluster taken with the QUIRC instrument on the University of Hawaii
2.2 meter telescope. These data reveal that 15 of the 20 VLA sources have
infrared counterparts, and 10 show radio variability with periods less than 20
days. Based on these combined radio and IR data, we propose that 8 of the radio
sources are candidate ultracompact HII regions, 7 are likely to be young
stellar objects, and 2 may be shocked interstellar gas.Comment: Accepted for publication in the Astronomical Journal. 10 pages, 4
figures, plus online table in electronic versio
Improving Dark Energy Constraints with High Redshift Type Ia Supernovae from CANDELS and CLASH
Aims. We investigate the degree of improvement in dark energy constraints
that can be achieved by extending Type Ia Supernova (SN Ia) samples to
redshifts z > 1.5 with the Hubble Space Telescope (HST), particularly in the
ongoing CANDELS and CLASH multi-cycle treasury programs.
Methods. Using the popular CPL parametrization of the dark energy, w = w0
+wa(1-a), we generate mock SN Ia samples that can be projected out to higher
redshifts. The synthetic datasets thus generated are fitted to the CPL model,
and we evaluate the improvement that a high-z sample can add in terms of
ameliorating the statistical and systematic uncertainties on cosmological
parameters.
Results. In an optimistic but still very achievable scenario, we find that
extending the HST sample beyond CANDELS+CLASH to reach a total of 28 SN Ia at z
> 1.0 could improve the uncertainty in the wa parameter by up to 21%. The
corresponding improvement in the figure of merit (FoM) would be as high as 28%.
Finally, we consider the use of high-redshift SN Ia samples to detect
non-cosmological evolution in SN Ia luminosities with redshift, finding that
such tests could be undertaken by future spacebased infrared surveys using the
James Webb Space Telescope (JWST).Comment: 9 pages, 6 figures, accepted for publication on Astronomy &
Astrophysic
The Dwarf Starburst Host Galaxy of a Type Ia SN at z = 1.55 from CANDELS
We present VLT/X-shooter observations of a high redshift, type Ia supernova
host galaxy, discovered with HST/WFC3 as part of the CANDELS Supernova project.
The galaxy exhibits strong emission lines of Ly{\alpha}, [O II], H{\beta}, [O
III], and H{\alpha} at z = 1.54992(+0.00008-0.00004). From the emission-line
fluxes and SED fitting of broad-band photometry we rule out AGN activity and
characterize the host galaxy as a young, low mass, metal poor, starburst galaxy
with low intrinsic extinction and high Ly{\alpha} escape fraction. The host
galaxy stands out in terms of the star formation, stellar mass, and metallicity
compared to its lower redshift counterparts, mainly because of its high
specific star-formation rate. If valid for a larger sample of high-redshift SN
Ia host galaxies, such changes in the host galaxy properties with redshift are
of interest because of the potential impact on the use of SN Ia as standard
candles in cosmology.Comment: 25 pages, 8 figures. Accepted for publication in Ap
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