644 research outputs found
Intensive HST survey for z > 1 type Ia supernovae by targeting galaxy clusters
ManuscriptWe present a new survey strategy to discover and study high redshift Type Ia supernovae (SNe Ia) using the Hubble Space Telescope (HST). By targeting massive galaxy clusters at 0.9 0.95, nine of which were in galaxy clusters. This strategy provides a SN sample that can be used to decouple the effects of host galaxy extinction and intrinsic color in high redshift SNe, thereby reducing one of the largest systematic uncertainties in SN cosmology
Using visual analytics to develop situation awareness in astrophysics
We present a novel collaborative visual analytics application for cognitively overloaded users in the astrophysics domain. The system was developed for scientists who need to analyze heterogeneous, complex data under time pressure, and make predictions and time-critical decisions rapidly and correctly under a constant influx of changing data. The Sunfall Data Taking system utilizes several novel visualization and analysis techniques to enable a team of geographically distributed domain specialists to effectively and remotely maneuver a custom-built instrument under challenging operational conditions. Sunfall Data Taking has been in production use for 2 years by a major international astrophysics collaboration (the largest data volume supernova search currently in operation), and has substantially improved the operational efficiency of its users. We describe the system design process by an interdisciplinary team, the system architecture and the results of an informal usability evaluation of the production system by domain experts in the context of Endsley's three levels of situation awareness
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
On the Time Variation of Dust Extinction and Gas Absorption for Type Ia Supernovae Observed through a Nonuniform Interstellar Medium
For Type Ia supernovae (SNe Ia) observed through a nonuniform interstellar medium (ISM) in its host galaxy, we investigate whether the nonuniformity can cause observable time variations in dust extinction and in gas absorption due to the expansion of the SN photosphere with time. We show that, owing to the steep spectral index of the ISM density power spectrum, sizable density fluctuation amplitudes at the length scale of typical ISM structures () will translate to much smaller fluctuations on the scales of an SN photosphere. Therefore, the typical amplitude of time variation due to a nonuniform ISM, of absorption equivalent widths, and of extinction, would be small. As a result, we conclude that nonuniform ISM density should not impact cosmology measurements based on SNe Ia. We apply our predictions based on the ISM density power-law power spectrum to the observations of two highly reddened SNe Ia, SN 2012cu and SN 2014J
Measuring Type Ia Supernova Distances and Redshifts From Their Multi-band Light Curves
The distance and redshift of a type Ia supernova can be determined
simultaneously through its multi-band light curves. This fact may be used for
imaging surveys that discover and obtain photometry for large numbers of
supernovae; so many that it would be difficult to obtain a spectroscopic
redshift for each. Using available supernova-analysis tools we find that there
are several conditions in which a viable distance-redshift can be determined.
Uncertainties in the effective distance at z~0.3 are dominated by redshift
uncertainties coupled with the steepness of the Hubble law. By z~0.5 the Hubble
law flattens out and distance-modulus uncertainties dominate. Observations that
give S/N=50 at peak brightness and a four-day observer cadence in each of
griz-bands are necessary to match the intrinsic supernova magnitude dispersion
out to z=1.0. Lower S/N can be tolerated with the addition of redshift priors
(e.g. from a host-galaxy photometric redshift), observations in an additional
redder band, or by focusing on supernova redshifts that have particular
leverage for this measurement. More stringent S/N requirements are anticipated
as improved systematics control over intrinsic color, metallicity, and dust is
attempted to be drawn from light curves.Comment: 16 pages, 4 figures, Astroparticle Physics, accepte
Constraints on core-collapse supernova progenitors from explosion site integral field spectroscopy
Observationally, supernovae (SNe) are divided into subclasses pertaining to
their distinct characteristics. This diversity reflects the diversity in the
progenitor stars. It is not entirely clear how different evolutionary paths
leading massive stars to become a SN are governed by fundamental parameters
such as progenitor initial mass and metallicity. This paper places constraints
on progenitor initial mass and metallicity in distinct core-collapse SN
subclasses, through a study of the parent stellar populations at the explosion
sites. Integral field spectroscopy (IFS) of 83 nearby SN explosion sites with a
median distance of 18 Mpc has been collected and analysed, enabling detection
and spectral extraction of the parent stellar population of SN progenitors.
From the parent stellar population spectrum, the initial mass and metallicity
of the coeval progenitor are derived by means of comparison to simple stellar
population models and strong-line methods. Additionally, near-infrared IFS was
employed to characterise the star formation history at the explosion sites. No
significant metallicity differences are observed among distinct SN types. The
typical progenitor mass is found to be highest for SN Ic, followed by type Ib,
then types IIb and II. SN IIn is the least associated with young stellar
populations and thus massive progenitors. However, statistically significant
differences in progenitor initial mass are observed only when comparing SNe IIn
with other subclasses. Stripped-envelope SN progenitors with initial mass
estimate lower than 25~ are found; these are thought to be the result
of binary progenitors. Confirming previous studies, these results support the
notion that core-collapse SN progenitors cannot arise from single-star channel
only, and both single and binary channels are at play in the production of
core-collapse SNe. [ABRIDGED]Comment: 18 pages, 10 figures, accepted to A&
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
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