300 research outputs found
A Calibration of NICMOS Camera 2 for Low Count-Rates
NICMOS 2 observations are crucial for constraining distances to most of the
existing sample of z > 1 SNe Ia. Unlike the conventional calibration programs,
these observations involve long exposure times and low count rates. Reciprocity
failure is known to exist in HgCdTe devices and a correction for this effect
has already been implemented for high and medium count-rates. However
observations at faint count-rates rely on extrapolations. Here instead, we
provide a new zeropoint calibration directly applicable to faint sources. This
is obtained via inter-calibration of NIC2 F110W/F160W with WFC3 in the low
count-rate regime using z ~ 1 elliptical galaxies as tertiary calibrators.
These objects have relatively simple near-IR SEDs, uniform colors, and their
extended nature gives superior signal-to-noise at the same count rate than
would stars. The use of extended objects also allows greater tolerances on PSF
profiles. We find ST magnitude zeropoints (after the installation of the NICMOS
cooling system, NCS) of 25.296 +- 0.022 for F110W and 25.803 +- 0.023 for
F160W, both in agreement with the calibration extrapolated from count-rates
1,000 times larger (25.262 and 25.799). Before the installation of the NCS, we
find 24.843 +- 0.025 for F110W and 25.498 +- 0.021 for F160W, also in agreement
with the high-count-rate calibration (24.815 and 25.470). We also check the
standard bandpasses of WFC3 and NICMOS 2 using a range of stars and galaxies at
different colors and find mild tension for WFC3, limiting the accuracy of the
zeropoints. To avoid human bias, our cross-calibration was "blinded" in that
the fitted zeropoint differences were hidden until the analysis was finalized.Comment: Accepted for Publication in the Astronomical Journal. New version
contains added referenc
Rest-Frame R-band Lightcurve of a z~1.3 Supernova Obtained with Keck Laser Adaptive Optics
We present Keck diffraction limited H-band photometry of a z~1.3 Type Ia
supernova (SN) candidate, first identified in a Hubble Space Telescope (HST)
search for SNe in massive high redshift galaxy clusters. The adaptive optics
(AO) data were obtained with the Laser Guide Star facility during four
observing runs from September to November 2005. In the analysis of data from
the observing run nearest to maximum SN brightness, the SN was found to have a
magnitude H=23.9 +/- 0.14 (Vega). We present the H-band (approximately
rest-frame R) light curve and provide a detailed analysis of the AO photometric
uncertainties. By constraining the aperture correction with a nearby (4"
separation) star we achieve 0.14 magnitude photometric precision, despite the
spatially varying AO PSF.Comment: 11 pages, 8 figures, Accepted for Publication in AJ Updated the
citations, fixed typo
Preliminary Limits on the WIMP-Nucleon Cross Section from the Cryogenic Dark Matter Search (CDMS)
We are conducting an experiment to search for WIMPs, or weakly-interacting
massive particles, in the galactic halo using terrestrial detectors. This
generic class of hypothetical particles, whose properties are similar to those
predicted by extensions of the standard model of particle physics, could
comprise the cold component of non-baryonic dark matter. We describe our
experiment, which is based on cooled germanium and silicon detectors in a
shielded low-background cryostat. The detectors achieve a high degree of
background rejection through the simultaneous measurement of the energy in
phonons and ionization. Using exposures on the order of one kilogram-day from
initial runs of our experiment, we have achieved (preliminary) upper limits on
the WIMP-nucleon cross section that are comparable to much longer runs of other
experiments.Comment: 5 LaTex pages, 5 eps figs, epsf.sty, espcrc2dsa2.sty. Proceedings of
TAUP97, Gran Sasso, Italy, 7-11 Sep 1997, Nucl. Phys. Suppl., A. Bottino, A.
di Credico and P. Monacelli (eds.). See also http://cfpa.berkeley.ed
A New Determination of the High Redshift Type Ia Supernova Rates with the Hubble Space Telescope Advanced Camera for Surveys
We present a new measurement of the volumetric rate of Type Ia supernova up
to a redshift of 1.7, using the Hubble Space Telescope (HST) GOODS data
combined with an additional HST dataset covering the North GOODS field
collected in 2004. We employ a novel technique that does not require
spectroscopic data for identifying Type Ia supernovae (although spectroscopic
measurements of redshifts are used for over half the sample); instead we employ
a Bayesian approach using only photometric data to calculate the probability
that an object is a Type Ia supernova. This Bayesian technique can easily be
modified to incorporate improved priors on supernova properties, and it is
well-suited for future high-statistics supernovae searches in which
spectroscopic follow up of all candidates will be impractical. Here, the method
is validated on both ground- and space-based supernova data having some
spectroscopic follow up. We combine our volumetric rate measurements with low
redshift supernova data, and fit to a number of possible models for the
evolution of the Type Ia supernova rate as a function of redshift. The data do
not distinguish between a flat rate at redshift > 0.5 and a previously proposed
model, in which the Type Ia rate peaks at redshift >1 due to a significant
delay from star-formation to the supernova explosion. Except for the highest
redshifts, where the signal to noise ratio is generally too low to apply this
technique, this approach yields smaller or comparable uncertainties than
previous work.Comment: Accepted for publication in Ap
Subaru FOCAS Spectroscopic Observations of High-Redshift Supernovae
We present spectra of high-redshift supernovae (SNe) that were taken with the
Subaru low resolution optical spectrograph, FOCAS. These SNe were found in SN
surveys with Suprime-Cam on Subaru, the CFH12k camera on the
Canada-France-Hawaii Telescope (CFHT), and the Advanced Camera for Surveys
(ACS) on the Hubble Space Telescope (HST). These SN surveys specifically
targeted z>1 Type Ia supernovae (SNe Ia). From the spectra of 39 candidates, we
obtain redshifts for 32 candidates and spectroscopically identify 7 active
candidates as probable SNe Ia, including one at z=1.35, which is the most
distant SN Ia to be spectroscopically confirmed with a ground-based telescope.
An additional 4 candidates are identified as likely SNe Ia from the
spectrophotometric properties of their host galaxies. Seven candidates are not
SNe Ia, either being SNe of another type or active galactic nuclei. When SNe Ia
are observed within a week of maximum light, we find that we can
spectroscopically identify most of them up to z=1.1. Beyond this redshift, very
few candidates were spectroscopically identified as SNe Ia. The current
generation of super red-sensitive, fringe-free CCDs will push this redshift
limit higher.Comment: 19 pages, 26 figures. PASJ in press. see
http://www.supernova.lbl.gov/2009ClusterSurvey/ for additional information
pertaining to the HST Cluster SN Surve
The Hubble Space Telescope Cluster Supernova Survey: VI. The Volumetric Type Ia Supernova Rate
We present a measurement of the volumetric Type Ia supernova (SN Ia) rate out
to z ~ 1.6 from the Hubble Space Telescope Cluster Supernova Survey. In
observations spanning 189 orbits with the Advanced Camera for Surveys we
discovered 29 SNe, of which approximately 20 are SNe Ia. Twelve of these SNe Ia
are located in the foregrounds and backgrounds of the clusters targeted in the
survey. Using these new data, we derive the volumetric SN Ia rate in four broad
redshift bins, finding results consistent with previous measurements at z > 1
and strengthening the case for a SN Ia rate that is equal to or greater than
~0.6 x 10^-4/yr/Mpc^3 at z ~ 1 and flattening out at higher redshift. We
provide SN candidates and efficiency calculations in a form that makes it easy
to rebin and combine these results with other measurements for increased
statistics. Finally, we compare the assumptions about host-galaxy dust
extinction used in different high-redshift rate measurements, finding that
different assumptions may induce significant systematic differences between
measurements.Comment: 11 pages, 7 figures. Submitted to the Astrophysical Journal. Revised
version following referee comments. See the HST Cluster SN Survey website at
http://supernova.lbl.gov/2009ClusterSurvey for control time simulations in a
machine-readable table and a complete listing of transient candidates from
the surve
Spectra of High-Redshift Type Ia Supernovae and a Comparison with their Low-Redshift Counterparts
We present spectra for 14 high-redshift (0.17 < z < 0.83) supernovae, which
were discovered by the Supernova Cosmology Project as part of a campaign to
measure cosmological parameters. The spectra are used to determine the redshift
and classify the supernova type, essential information if the supernovae are to
be used for cosmological studies. Redshifts were derived either from the
spectrum of the host galaxy or from the spectrum of the supernova itself. We
present evidence that these supernovae are of Type Ia by matching to spectra of
nearby supernovae. We find that the dates of the spectra relative to maximum
light determined from this fitting process are consistent with the dates
determined from the photometric light curves, and moreover the spectral
time-sequence for SNe Type Ia at low and high redshift is indistinguishable. We
also show that the expansion velocities measured from blueshifted CaHK are
consistent with those measured for low-redshift Type Ia supernovae. From these
first-level quantitative comparisons we find no evidence for evolution in SNIa
properties between these low- and high-redshift samples. Thus even though our
samples may not be complete, we conclude that there is a population of SNe Ia
at high redshift whose spectral properties match those at low redshift.Comment: Accepted for publication in AJ. Also available at
http://supernova.lbl.gov
Spectroscopic Observations and Analysis of the Unusual Type Ia SN 1999ac
We present optical spectra of the peculiar Type Ia supernova (SN Ia) 1999ac.
The data extend from -15 to +42 days with respect to B-band maximum and reveal
an event that is unusual in several respects. Prior to B-band maximum, the
spectra resemble those of SN 1999aa, a slowly declining event, but possess
stronger SiII and CaII signatures (more characteristic of a spectroscopically
normal SN). Spectra after B-band maximum appear more normal. The expansion
velocities inferred from the Iron lines appear to be lower than average;
whereas, the expansion velocity inferred from Calcium H and K are higher than
average. The expansion velocities inferred from SiII are among the slowest ever
observed, though SN 1999ac is not particularly dim. The analysis of the
parameters v_10, R(SiII), dv(SiII)/dt, and d_m15 further underlines the unique
characteristics of SN 1999ac. We find convincing evidence of CII 6580 in the
day -15 spectrum with ejection velocity v > 16,000 km/s, but this signature
disappears by day -9. This rapid evolution at early times highlights the
importance of extremely early-time spectroscopy.Comment: 40 pages, 24 figures, accepted for publication in The Astronomical
Journa
The Hubble Space Telescope Cluster Supernova Survey: II. The Type Ia Supernova Rate in High-Redshift Galaxy Clusters
We report a measurement of the Type Ia supernova (SN Ia) rate in galaxy
clusters at 0.9 < z < 1.45 from the Hubble Space Telescope (HST) Cluster
Supernova Survey. This is the first cluster SN Ia rate measurement with
detected z > 0.9 SNe. Finding 8 +/- 1 cluster SNe Ia, we determine a SN Ia rate
of 0.50 +0.23-0.19 (stat) +0.10-0.09 (sys) SNuB (SNuB = 10^-12 SNe L_{sun,B}^-1
yr^-1). In units of stellar mass, this translates to 0.36 +0.16-0.13 (stat)
+0.07-0.06 (sys) SNuM (SNuM = 10^-12 SNe M_sun^-1 yr^-1). This represents a
factor of approximately 5 +/- 2 increase over measurements of the cluster rate
at z < 0.2. We parameterize the late-time SN Ia delay time distribution with a
power law (proportional to t^s). Under the assumption of a cluster formation
redshift of z_f = 3, our rate measurement in combination with lower-redshift
cluster SN Ia rates constrains s = -1.41 +0.47/-0.40, consistent with
measurements of the delay time distribution in the field. This measurement is
generally consistent with expectations for the "double degenerate" scenario and
inconsistent with some models for the "single degenerate" scenario predicting a
steeper delay time distribution at large delay times. We check for
environmental dependence and the influence of younger stellar populations by
calculating the rate specifically in cluster red-sequence galaxies and in
morphologically early-type galaxies, finding results similar to the full
cluster rate. Finally, the upper limit of one host-less cluster SN Ia detected
in the survey implies that the fraction of stars in the intra-cluster medium is
less than 0.47 (95% confidence), consistent with measurements at lower
redshifts.Comment: 29 pages, 14 figures. Accepted for publication in ApJ on 16 February
2011. See the HST Cluster Supernova Survey website at
http://supernova.lbl.gov/2009ClusterSurvey for a version with full-resolution
images and a complete listing of transient candidates from the survey. This
version fixes a typo in the metadata; the paper is unchanged from v
Measurement of the Boson Mass
A measurement of the mass of the boson is presented based on a sample of
5982 decays observed in collisions at
= 1.8~TeV with the D\O\ detector during the 1992--1993 run. From a
fit to the transverse mass spectrum, combined with measurements of the
boson mass, the boson mass is measured to be .Comment: 12 pages, LaTex, style Revtex, including 3 postscript figures
(submitted to PRL
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