1,721,678 research outputs found
First cosmology results using type IA Supernovae from the Dark Energy Survey: Effects of chromatic corrections to supernova photometry on measurements of cosmological parameters
No full textABSTRACTCalibration uncertainties have been the leading systematic uncertainty in recent analyses using type Ia Supernovae (SNe Ia) to measure cosmological parameters. To improve the calibration, we present the application of Spectral Energy Distribution (SED)-dependent “chromatic corrections" to the supernova light-curve photometry from the Dark Energy Survey (DES). These corrections depend on the combined atmospheric and instrumental transmission function for each exposure, and they affect photometry at the 0.01 mag (1%) level, comparable to systematic uncertainties in calibration and photometry. Fitting our combined DES and low-z SN Ia sample with Baryon Acoustic Oscillation (BAO) and Cosmic Microwave Background (CMB) priors for the cosmological parameters m (the fraction of the critical density of the universe comprised of matter) and w (the dark energy equation of state parameter), we compare those parameters before and after applying the corrections. We find the change in w and m due to not including chromatic corrections are 􀀀0:002 and 0:000, respectively, for the DES-SN3YR sample with BAO and CMB priors, consistent with a larger DES-SN3YR-like simulation, which has a w-change of 0:0005 with an uncertainty of 0:008 and an m change of 0:000 with an uncertainty of 0:002 . However, when considering samples on individual CCDs we find large redshift-dependent biases ( 0:02 in distance modulus) for supernova distances.Key words: cosmology: dark energy, cosmology: observations, supernovae, techniques: photometri
Real-Time Recovery Efficiencies and Performance of the Palomar Transient Factory's Transient Discovery Pipeline: Fakes Catalog
No full textThis CSV file is a complete catalog of all the source stars and fake events in the observational data used in the analysis of PTF's real-time efficiency. From this the final efficiency grids can be reconstructed.
The accompanying README file describes the columns.
This catalogue supports the publication Frohmaier et al, (2017) "Real-Time Recovery Efficiencies and Performance of the Palomar Transient Factory's Transient Discovery Pipeline”, Astrophysical Journal.
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Observational properties of thermonuclear supernovae
No full textThe explosive death of a star as a supernova is one of the most dramatic events in the Universe. Supernovae have an outsized impact on many areas of astrophysics: they are major contributors to the chemical enrichment of the cosmos and significantly influence the formation of subsequent generations of stars and the evolution of galaxies. Here we review the observational properties of thermonuclear supernovae—exploding white dwarf stars resulting from the stellar evolution of low-mass stars in close binary systems. The best known objects in this class are type-Ia supernovae (SNe Ia), astrophysically important in their application as standardizable candles to measure cosmological distances and the primary source of iron group elements in the Universe. Surprisingly, given their prominent role, SN Ia progenitor systems and explosion mechanisms are not fully understood; the observations we describe here provide constraints on models, not always in consistent ways. Recent advances in supernova discovery and follow-up have shown that the class of thermonuclear supernovae includes more than just SNe Ia, and we characterize that diversity in this review.</p
First cosmology results using Type Ia Supernovae from the Dark Energy Survey: Photometric pipeline and light-curve data release
No full textWe present griz light curves of 251 SNe Ia from the first 3 years of the Dark Energy Survey Supernova Program's (DES-SN) spectroscopically classified sample. The photometric pipeline described in this paper produces the calibrated fluxes and associated uncertainties used in the cosmological parameter analysis by employing a scene modeling approach that simultaneously models a variable transient flux and temporally constant host galaxy. We inject artificial point sources onto DECam images to test the accuracy of our photometric method. Upon comparison of input and measured artificial supernova fluxes, we find that flux biases peak at 3 mmag. We require corrections to our photometric uncertainties as a function of host galaxy surface brightness at the transient location, similar to that seen by the DES Difference Imaging Pipeline used to discover transients. The public release of the light curves can be found at https://des.ncsa.illinois.edu/releases/sn
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The Unrepentant Liberal piece with an autobiographical sketch of the author, M
No full textThe Unrepentant Liberal piece with an autobiographical sketch of the author, Mark Sullivan. Sullivan, a native of Virginia, first came to the state to work with the Natural Resources Council of Maine on solid waste issues, and knew Gov. Angus King when he was working for Conservationists for Carter in 1976
The volumetric rate of calcium-rich transients in the local universe
No full textWe present a measurement of the volumetric rate of ‘calcium-rich’ optical transients in the local universe, using a sample of three events from the Palomar Transient Factory (PTF). This measurement builds on a detailed study of the PTF transient detection efficiencies, and uses a Monte Carlo simulation of the PTF survey. We measure the volumetric rate of calcium-rich transients to be higher than previous estimates: 1.21+1.13−0.39×10−5 events yr−1 Mpc−3. This is equivalent to 33-94% of the local volumetric type Ia supernova rate. This calcium-rich transient rate is sufficient to reproduce the observed calcium abundances in galaxy clusters, assuming an asymptotic calcium yield per calcium-rich event of ~0.05M⊙. We also study the PTF detection efficiency of these transients as a function of position within their candidate host galaxies. We confirm as a real physical effect previous results that suggest calcium-rich transients prefer large physical offsets from their host galaxies
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