70 research outputs found
Integral field spectroscopy of supernova explosion sites: constraining mass and metallicity of the progenitors -- II. Type II-P and II-L supernovae
Thirteen explosion sites of type II-P and II-L supernovae in nearby galaxies
have been observed using integral field spectroscopy, enabling both spatial and
spectral study of the explosion sites. We used the properties of the parent
stellar population of the coeval supernova progenitor star to derive its
metallicity and initial mass (c.f. Paper I). The spectrum of the parent stellar
population yields the estimates of metallicity via strong-line method, and age
via comparison with simple stellar population (SSP) models. These metallicity
and age parameters are adopted for the progenitor star. Age, or lifetime of the
star, was used to derive initial (ZAMS) mass of the star by comparing with
stellar evolution models. With this technique, we were able to determine
metallicity and initial mass of the SN progenitors in our sample. Our result
indicates that some type-II supernova progenitors may have been stars with mass
comparable to SN Ib/c progenitors.Comment: Accepted to the Astronomical Journa
Going Forward with the Nancy Grace Roman Space Telescope Transient Survey: Validation of Precision Forward-Modeling Photometry for Undersampled Imaging
The Nancy Grace Roman Space Telescope (Roman) is an observatory for both
wide-field observations and coronagraphy that is scheduled for launch in the
mid 2020's. Part of the planned survey is a deep, cadenced field or fields that
enable cosmological measurements with type Ia supernovae (SNe Ia). With a pixel
scale of 0".11, the Wide Field Instrument will be undersampled, presenting a
difficulty for precisely subtracting the galaxy light underneath the SNe. We
use simulated data to validate the ability of a forward-model code (such codes
are frequently also called "scene-modeling" codes) to perform precision
supernova photometry for the Nancy Grace Roman Space Telescope SN survey. Our
simulation includes over 760,000 image cutouts around SNe Ia or host galaxies
(~ 10% of a full-scale survey). To have a realistic 2D distribution of
underlying galaxy light, we use the VELA simulated high-resolution images of
galaxies. We run each set of cutouts through our forward-modeling code which
automatically measures time-dependent SN fluxes. Given our assumed inputs of a
perfect model of the instrument PSFs and calibration, we find biases at the
millimagnitude level from this method in four red filters (Y106, J129, H158,
and F184), easily meeting the 0.5% Roman inter-filter calibration requirement
for a cutting-edge measurement of cosmological parameters using SNe Ia.
Simulated data in the bluer Z087 filter shows larger ~ 2--3 millimagnitude
biases, also meeting this requirement, but with more room for improvement. Our
forward-model code has been released on Zenodo.Comment: Accepted for Publication in PAS
The Rise Times of High and Low Redshift Type Ia Supernovae are Consistent
We present a self-consistent comparison of the rise times for low- and
high-redshift Type Ia supernovae. Following previous studies, the early light
curve is modeled using a t-squared law, which is then mated with a modified
Leibundgut template light curve. The best-fit t-squared law is determined for
ensemble samples of low- and high-redshift supernovae by fitting simultaneously
for all light curve parameters for all supernovae in each sample. Our method
fully accounts for the non-negligible covariance amongst the light curve
fitting parameters, which previous analyses have neglected. Contrary to Riess
et al. (1999), we find fair to good agreement between the rise times of the
low- and high-redshift Type Ia supernovae. The uncertainty in the rise time of
the high-redshift Type Ia supernovae is presently quite large (roughly +/- 1.2
days statistical), making any search for evidence of evolution based on a
comparison of rise times premature. Furthermore, systematic effects on rise
time determinations from the high-redshift observations, due to the form of the
late-time light curve and the manner in which the light curves of these
supernovae were sampled, can bias the high-redshift rise time determinations by
up to +3.6/-1.9 days under extreme situations. The peak brightnesses - used for
cosmology - do not suffer any significant bias, nor any significant increase in
uncertainty.Comment: 18 pages, 4 figures, Accepted for publication in the Astronomical
Journal. Also available at http://www.lbl.gov/~nugent/papers.html Typos were
corrected and a few sentences were added for improved clarit
Multi-Color Light Curves of Type Ia Supernovae on the Color-Magnitude Diagram: a Novel Step Toward More Precise Distance and Extinction Estimates
We show empirically that fits to the color-magnitude relation of Type Ia
supernovae after optical maximum can provide accurate relative extragalactic
distances. We report the discovery of an empirical color relation for Type Ia
light curves: During much of the first month past maximum, the magnitudes of
Type Ia supernovae defined at a given value of color index have a very small
magnitude dispersion; moreover, during this period the relation between
magnitude and color (or or color) is strikingly linear, to
the accuracy of existing well-measured data. These linear relations can provide
robust distance estimates, in particular, by using the magnitudes when the
supernova reaches a given color. After correction for light curve strech factor
or decline rate, the dispersion of the magnitudes taken at the intercept of the
linear color-magnitude relation are found to be around 0.08 for the
sub-sample of supernovae with \BVm , and around 0.11 for the
sub-sample with \BVm . This small dispersion is consistent with
being mostly due to observational errors. The method presented here and the
conventional light curve fitting methods can be combined to further improve
statistical dispersions of distance estimates. It can be combined with the
magnitude at maximum to deduce dust extinction. The slopes of the
color-magnitude relation may also be used to identify intrinsically different
SN Ia systems. The method provides a tool that is fundamental to using SN Ia to
estimate cosmological parameters such as the Hubble constant and the mass and
dark energy content of the universe.Comment: ApJ, in pres
Precise Mass Determination of SPT-CL J2106-5844, the Most Massive Cluster at z \u3e 1
We present a detailed high-resolution weak-lensing study of SPT-CL J2106-5844 at z = 1.132, claimed to be the most massive system discovered at z \u3e 1 in the South Pole Telescope Sunyaev–Zel\u27dovich survey. Based on the deep imaging data from the Advanced Camera for Surveys and Wide Field Camera 3 on board the Hubble Space Telescope, we find that the cluster mass distribution is asymmetric, composed of a main clump and a subclump ~640 kpc west thereof. The central clump is further resolved into two smaller northwestern and southeastern substructures separated by ~150 kpc. We show that this rather complex mass distribution is more consistent with the cluster galaxy distribution than a unimodal distribution as previously presented. The northwestern substructure coincides with the brightest cluster galaxy and the X-ray peak while the southeastern one agrees with the location of the peak in number density. These morphological features and the comparison with the X-ray emission suggest that the cluster might be a merging system. We estimate the virial mass of the cluster to be , where the second error bar is the systematic uncertainty. Our result confirms that the cluster SPT-CL J2106-5844 is indeed the most massive cluster at z \u3e 1 known to date. We demonstrate the robustness of this mass estimate by performing a number of tests with different assumptions on the centroids, mass–concentration relations, and sample variance
V1647 Orionis: Reinvigorated Accretion and the Re-Appearance of McNeil's Nebula
In late 2003, the young eruptive variable star V1647 Orionis optically
brightened by over 5 magnitudes, stayed bright for around 26 months, and then
decline to its pre-outburst level. In August 2008 the star was reported to have
unexpectedly brightened yet again and we herein present the first detailed
observations of this new outburst. Photometrically, the star is now as bright
as it ever was following the 2003 eruption. Spectroscopically, a pronounced P
Cygni profile is again seen in Halpha with an absorption trough extending to
-700 km/s. In the near-infrared, the spectrum now possesses very weak CO
overtone bandhead absorption in contrast to the strong bandhead emission seen
soon after the 2003 event. Water vapor absorption is also much stronger than
previously seen. We discuss the current outburst below and relate it to the
earlier event.Comment: 6 pages, 3 figure
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