108 research outputs found
PTF 11kx: A Type Ia Supernova with a Symbiotic Nova Progenitor
There is a consensus that type Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumstellar material are detected, and the SN ejecta are seen to interact with circumstellar material starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi
Data compression of measurements of peculiar velocities of Supernovae Ia
We study the compression of information present in the correlated
perturbations to the luminosity distance in the low-redshift ()
supernovae Ia due to peculiar velocities of these supernovae. We demonstrate
that the na\"{i}ve compression into angular velocity power spectrum does not
work efficiently, due to thickness of the spherical shell over which the
supernovae are measured. Instead, we show that measurements can be compressed
into measurements of , where is the logarithmic rate of growth of
linear perturbations and is their power spectrum. We develop an optimal
quadratic estimator and show that it recovers all information for
models for surveys of or more supernovae. We explicitly
demonstrate robustness with respect to the assumed fiducial model and the
number of power spectrum bins. Using mock catalogues of SNe Ia we estimate that
future low redshift surveys will be able to probe to 6% accuracy
with SNe Ia.Comment: Accepted to PRD; Added referenc
Type II-P Supernovae from the SDSS-II Supernova Survey and the Standardized Candle Method
We apply the Standardized Candle Method (SCM) for Type II Plateau supernovae
(SNe II-P), which relates the velocity of the ejecta of a SN to its luminosity
during the plateau, to 15 SNe II-P discovered over the three season run of the
Sloan Digital Sky Survey - II Supernova Survey. The redshifts of these SNe -
0.027 < z < 0.144 - cover a range hitherto sparsely sampled in the literature;
in particular, our SNe II-P sample contains nearly as many SNe in the Hubble
flow (z > 0.01) as all of the current literature on the SCM combined. We find
that the SDSS SNe have a very small intrinsic I-band dispersion (0.22 mag),
which can be attributed to selection effects. When the SCM is applied to the
combined SDSS-plus-literature set of SNe II-P, the dispersion increases to 0.29
mag, larger than the scatter for either set of SNe separately. We show that the
standardization cannot be further improved by eliminating SNe with positive
plateau decline rates, as proposed in Poznanski et al. (2009). We thoroughly
examine all potential systematic effects and conclude that for the SCM to be
useful for cosmology, the methods currently used to determine the Fe II
velocity at day 50 must be improved, and spectral templates able to encompass
the intrinsic variations of Type II-P SNe will be needed.Comment: Accepted for publication by ApJ; data used in this paper can be
downloaded from http://sdssdp47.fnal.gov/sdsssn/photometry/SNIIp.tgz;
citation errors correcte
PTF11kx: A Type-Ia Supernova with a Symbiotic Nova Progenitor
There is a consensus that Type-Ia supernovae (SNe Ia) arise from the
thermonuclear explosion of white dwarf stars that accrete matter from a binary
companion. However, direct observation of SN Ia progenitors is lacking, and the
precise nature of the binary companion remains uncertain. A temporal series of
high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex
circumstellar environment that provides an unprecedentedly detailed view of the
progenitor system. Multiple shells of circumsteller are detected and the SN
ejecta are seen to interact with circumstellar material (CSM) starting 59 days
after the explosion. These features are best described by a symbiotic nova
progenitor, similar to RS Ophiuchi.Comment: 27 pages, 5 figures. In pres
Hubble Space Telescope studies of low-redshift Type Ia supernovae: Evolution with redshift and ultraviolet spectral trends
We present an analysis of the maximum light, near ultraviolet (NUV; 2900-5500
A) spectra of 32 low redshift (0.001<z<0.08) Type Ia supernovae (SNe Ia),
obtained with the Hubble Space Telescope (HST). We combine this spectroscopic
sample with high-quality gri light curves obtained with robotic telescopes to
measure photometric parameters, such as stretch, optical colour, and
brightness. By comparing our data to a comparable sample of SNe Ia at
intermediate-z (0.4<z<0.9), we detect modest spectral evolution (3-sigma), in
the sense that our mean low-z NUV spectrum has a depressed flux compared to its
intermediate-z counterpart. We also see a strongly increased dispersion about
the mean with decreasing wavelength, confirming the results of earlier surveys.
These trends are consistent with changes in metallicity as predicted by
contemporary SN Ia spectral models. We also examine the properties of various
NUV spectral diagnostics in the individual spectra. We find a general
correlation between stretch and the velocity (or position) of many NUV spectral
features. In particular, we observe that higher stretch SNe have larger Ca II
H&K velocities, that also correlate with host galaxy stellar mass. This latter
trend is probably driven by the well-established correlation between stretch
and stellar mass. We find no trends between UV spectral features and optical
colour. Mean spectra constructed according to whether the SN has a positive or
negative Hubble residual show very little difference at NUV wavelengths,
indicating that the NUV evolution and variation we identify do not directly
correlate with Hubble residuals. Our work confirms and strengthens earlier
conclusions regarding the complex behaviour of SNe Ia in the NUV spectral
region, but suggests the correlations we find are more useful in constraining
progenitor models than improving the use of SNe Ia as cosmological probes.Comment: 22 pages, 14 figures, accepted in MNRAS with minor changes - Spectra
are available on WISeREP, http://www.weizmann.ac.il/astrophysics/wiserep
Supernova Simulations and Strategies For the Dark Energy Survey
We present an analysis of supernova light curves simulated for the upcoming
Dark Energy Survey (DES) supernova search. The simulations employ a code suite
that generates and fits realistic light curves in order to obtain distance
modulus/redshift pairs that are passed to a cosmology fitter. We investigated
several different survey strategies including field selection, supernova
selection biases, and photometric redshift measurements. Using the results of
this study, we chose a 30 square degree search area in the griz filter set. We
forecast 1) that this survey will provide a homogeneous sample of up to 4000
Type Ia supernovae in the redshift range 0.05<z<1.2, and 2) that the increased
red efficiency of the DES camera will significantly improve high-redshift color
measurements. The redshift of each supernova with an identified host galaxy
will be obtained from spectroscopic observations of the host. A supernova
spectrum will be obtained for a subset of the sample, which will be utilized
for control studies. In addition, we have investigated the use of combined
photometric redshifts taking into account data from both the host and
supernova. We have investigated and estimated the likely contamination from
core-collapse supernovae based on photometric identification, and have found
that a Type Ia supernova sample purity of up to 98% is obtainable given
specific assumptions. Furthermore, we present systematic uncertainties due to
sample purity, photometric calibration, dust extinction priors, filter-centroid
shifts, and inter-calibration. We conclude by estimating the uncertainty on the
cosmological parameters that will be measured from the DES supernova data.Comment: 46 pages, 30 figures, resubmitted to ApJ as Revision 2 (final author
revision), which has subtle editorial differences compared to the published
paper (ApJ, 753, 152). Note that this posting includes PDF only due to a bug
in either the latex macros or the arXiv submission system. The source files
are available in the DES document database:
http://des-docdb.fnal.gov/cgi-bin/ShowDocument?docid=624
Substructure revealed by RR Lyraes in SDSS Stripe 82
We present an analysis of the substructure revealed by 407 RR Lyraes in Sloan
Digital Sky Survey (SDSS) Stripe 82. Period estimates are determined to high
accuracy using a string-length method. A subset of 178 RR Lyraes with
spectrally derived metallicities are employed to derive
metallicity-period-amplitude relations, which are then used to find
metallicities and distances for the entire sample. The RR Lyraes lie between 5
and 115 kpc from the Galactic center. They are divided into subsets of 316 RRab
types and 91 RRc types based on their period, colour and metallicity. The
density distribution is not smooth, but dominated by clumps and substructure.
Samples of 55 and 237 RR Lyraes associated with the Sagittarius Stream and the
Hercules-Aquila Cloud respectively are identified. Hence, ~ 70 % of the RR
Lyraes in Stripe 82 belong to known substructure. There is a sharp break in the
density distribution at Galactocentric radii of 40 kpc, reflecting the fact
that the dominant substructure in Stripe 82 - the Hercules-Aquila Cloud and the
Sagittarius Stream - lies within 40 kpc. In fact, almost 60 % of all the RR
Lyraes in Stripe 82 are associated with the Hercules-Aquila Cloud alone, which
emphasises its pre-eminence. Additionally, evidence of a new and distant
substructure - the Pisces Overdensity - is found, consisting of 28 faint RR
Lyraes centered on Galactic coordinates (80 deg, -55 deg) and with distances of
~ 80 kpc. The total stellar mass in the Pisces Overdensity is ~10000 solar
masses and its metallicity is [Fe/H] ~ -1.5.Comment: 15 pages, submitted to MNRA
The Sloan Digital Sky Survey-II Supernova Survey: Search Algorithm and Follow-up Observations
The Sloan Digital Sky Survey-II Supernova Survey has identified a large
number of new transient sources in a 300 sq. deg. region along the celestial
equator during its first two seasons of a three-season campaign. Multi-band
(ugriz) light curves were measured for most of the sources, which include solar
system objects, Galactic variable stars, active galactic nuclei, supernovae
(SNe), and other astronomical transients. The imaging survey is augmented by an
extensive spectroscopic follow-up program to identify SNe, measure their
redshifts, and study the physical conditions of the explosions and their
environment through spectroscopic diagnostics. During the survey, light curves
are rapidly evaluated to provide an initial photometric type of the SNe, and a
selected sample of sources are targeted for spectroscopic observations. In the
first two seasons, 476 sources were selected for spectroscopic observations, of
which 403 were identified as SNe. For the Type Ia SNe, the main driver for the
Survey, our photometric typing and targeting efficiency is 90%. Only 6% of the
photometric SN Ia candidates were spectroscopically classified as non-SN Ia
instead, and the remaining 4% resulted in low signal-to-noise, unclassified
spectra. This paper describes the search algorithm and the software, and the
real-time processing of the SDSS imaging data. We also present the details of
the supernova candidate selection procedures and strategies for follow-up
spectroscopic and imaging observations of the discovered sources.Comment: Accepted for publication in The Astronomical Journal (66 pages, 13
figures); typos correcte
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