108 research outputs found
SN1991bg-like supernovae are associated with old stellar populations
SN1991bg-like supernovae are a distinct subclass of thermonuclear supernovae
(SNe Ia). Their spectral and photometric peculiarities indicate their
progenitors and explosion mechanism differ from `normal' SNe Ia. One method of
determining information about supernova progenitors we cannot directly observe
is to observe the stellar population adjacent to the apparent supernova
explosion site to infer the distribution of stellar population ages and
metallicities. We obtain integral field observations and analyse the spectra
extracted from regions of projected radius about the
apparent SN explosion site for 11 91bg-like SNe in both early- and late-type
galaxies. We utilize full-spectrum spectral fitting to determine the ages and
metallicities of the stellar population within the aperture. We find that the
majority of the stellar populations that hosted 91bg-like supernovae have
little recent star formation. The ages of the stellar populations suggest that
that 91bg-like SN progenitors explode after delay times of ,
much longer than the typical delay time of normal SNe Ia, which peaks at .Comment: 12 pages, 3 figures, 3 tables, submitted to Publications of the
Astronomical Society of Australi
The SkyMapper Transient Survey
The SkyMapper 1.3 m telescope at Siding Spring Observatory has now begun
regular operations. Alongside the Southern Sky Survey, a comprehensive digital
survey of the entire southern sky, SkyMapper will carry out a search for
supernovae and other transients. The search strategy, covering a total
footprint area of ~2000 deg2 with a cadence of days, is optimised for
discovery and follow-up of low-redshift type Ia supernovae to constrain cosmic
expansion and peculiar velocities. We describe the search operations and
infrastructure, including a parallelised software pipeline to discover variable
objects in difference imaging; simulations of the performance of the survey
over its lifetime; public access to discovered transients; and some first
results from the Science Verification data.Comment: 13 pages, 11 figures; submitted to PAS
Constraints on the Progenitor System of the Type Ia Supernova 2014J from Pre-Explosion Hubble Space Telescope Imaging
We constrain the properties of the progenitor system of the highly reddened
Type Ia supernova (SN) 2014J in Messier 82 (M82; d ~ 3.5 Mpc). We determine the
SN location using Keck-II K-band adaptive optics images, and we find no
evidence for flux from a progenitor system in pre-explosion near-ultraviolet
through near-infrared Hubble Space Telescope (HST) images. Our upper limits
exclude systems having a bright red giant companion, including symbiotic novae
with luminosities comparable to that of RS Ophiuchi. While the flux constraints
are also inconsistent with predictions for comparatively cool He-donor systems
(T < ~35,000 K), we cannot preclude a system similar to V445 Puppis. The
progenitor constraints are robust across a wide range of R_V and A_V values,
but significantly greater values than those inferred from the SN light curve
and spectrum would yield proportionally brighter luminosity limits. The
comparatively faint flux expected from a binary progenitor system consisting of
white dwarf stars would not have been detected in the pre-explosion HST
imaging. Infrared HST exposures yield more stringent constraints on the
luminosities of very cool (T < 3000 K) companion stars than was possible in the
case of SN Ia 2011fe.Comment: Accepted by ApJ 14 May 2014 with only minor revision
Diffuse Galactic antimatter from faint thermonuclear supernovae in old stellar populations
Our Galaxy hosts the annihilation of a few low-energy
positrons every second. Radioactive isotopes capable of supplying such
positrons are synthesised in stars, stellar remnants, and supernovae. For
decades, however, there has been no positive identification of a main stellar
positron source leading to suggestions that many positrons originate from
exotic sources like the Galaxy's central super-massive black hole or dark
matter annihilation. %, but such sources would not explain the
recently-detected positron signal from the extended Galactic disk. Here we show
that a single type of transient source, deriving from stellar populations of
age 3-6 Gyr and yielding ~0.03 of the positron emitter Ti, can
simultaneously explain the strength and morphology of the Galactic positron
annihilation signal and the solar system abundance of the Ti decay
product Ca. This transient is likely the merger of two low-mass white
dwarfs, observed in external galaxies as the sub-luminous, thermonuclear
supernova known as SN1991bg-like.Comment: 28 pages main text with 4 figures in preprint style; 26 pages of
Supplementary Informatio
Optical Identification of Cepheids in 19 Host Galaxies of Type Ia Supernovae and NGC 4258 with the Hubble Space Telescope
We present results of an optical search for Cepheid variable stars using the
Hubble Space Telescope (HST) in 19 hosts of Type Ia supernovae (SNe Ia) and the
maser-host galaxy NGC 4258, conducted as part of the SH0ES project (Supernovae
and H0 for the Equation of State of dark energy). The targets include 9 newly
imaged SN Ia hosts using a novel strategy based on a long-pass filter that
minimizes the number of HST orbits required to detect and accurately determine
Cepheid properties. We carried out a homogeneous reduction and analysis of all
observations, including new universal variability searches in all SN Ia hosts,
that yielded a total of 2200 variables with well-defined selection criteria --
the largest such sample identified outside the Local Group. These objects are
used in a companion paper to determine the local value of H0 with a total
uncertainty of 2.4%.Comment: ApJ, in press. v2 adds missing co-author to arXiv metadata and text
in acknowledgment
The Very Young Type Ia Supernova 2012cg: Discovery and Early-Time Follow-Up Observations
On 2012 May 17.2 UT, only 1.5 +/- 0.2 d after explosion, we discovered SN
2012cg, a Type Ia supernova (SN Ia) in NGC 4424 (d ~ 15 Mpc). As a result of
the newly modified strategy employed by the Lick Observatory SN Search, a
sequence of filtered images was obtained starting 161 s after discovery.
Utilizing recent models describing the interaction of SN ejecta with a
companion star, we rule out a ~1 M_Sun companion for half of all viewing angles
and a red-giant companion for nearly all orientations. SN 2012cg reached a
B-band maximum of 12.09 +/- 0.02 mag on 2012 June 2.0 and took ~17.3 d from
explosion to reach this, typical for SNe Ia. Our pre-maximum brightness
photometry shows a narrower-than-average B-band light curve for SN 2012cg,
though slightly overluminous at maximum brightness and with normal color
evolution (including some of the earliest SN Ia filtered photometry ever
obtained). Spectral fits to SN 2012cg reveal ions typically found in SNe Ia at
early times, with expansion velocities >14,000 km/s at 2.5 d past explosion.
Absorption from C II is detected early, as well as high-velocity components of
both Si II 6355 Ang. and Ca II. Our last spectrum (13.5 d past explosion)
resembles that of the somewhat peculiar SN Ia 1999aa. This suggests that SN
2012cg will have a slower-than-average declining light curve, which may be
surprising given the faster-than-average rising light curve.Comment: re-submitted to ApJL, 4 figures, 1 tabl
Earth Observations and Integrative Models in Support of Food and Water Security
Global food production depends upon many factors that Earth observing satellites routinely measure about water, energy, weather, and ecosystems. Increasingly sophisticated, publicly-available satellite data products can improve efficiencies in resource management and provide earlier indication of environmental disruption. Satellite remote sensing provides a consistent, long-term record that can be used effectively to detect large-scale features over time, such as a developing drought. Accuracy and capabilities have increased along with the range of Earth observations and derived products that can support food security decisions with actionable information. This paper highlights major capabilities facilitated by satellite observations and physical models that have been developed and validated using remotely-sensed observations. Although we primarily focus on variables relevant to agriculture, we also include a brief description of the growing use of Earth observations in support of aquaculture and fisheries
K2: Background Survey - The search for undiscovered transients in Kepler/K2 data
The K2 mission of the Kepler Space Telescope offers a unique possibility to examine sources of both Galactic and extragalactic origin with high-cadence photometry. Alongside the multitude of supernovae and quasars detected within targeted galaxies, it is likely that Kepler has serendipitously observed many transients throughout K2. Such events will likely have occurred in background pixels, coincidentally surrounding science targets. Analysing the background pixels presents the possibility to conduct a high-cadence survey with areas of a few square degrees per campaign. We demonstrate the capacity to independently recover key K2 transients such as KSN 2015K and SN 2018oh. With this survey, we expect to detect numerous transients and determine the first comprehensive rates for transients with lifetimes of <1 d.This research was supported by an Australian Government
Research Training Program (RTP) Scholarship and utilizes data
collected by the K2 missio
- …