63 research outputs found
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
Restframe I-band Hubble diagram for type Ia supernovae up to redshift z ~0.5
We present a novel technique for fitting restframe I-band light curves on a
data set of 42 Type Ia supernovae (SNe Ia). Using the result of the fit, we
construct a Hubble diagram with 26 SNe from the subset at 0.01< z<0.1. Adding
two SNe at z~0.5 yields results consistent with a flat
Lambda-dominated``concordance universe''
()=(0.25,0.75). For one of these, SN 2000fr, new near
infrared data are presented. The high redshift supernova NIR data are also used
to test for systematic effects in the use of SNe Ia as distance estimators. A
flat, Lambda=0, universe where the faintness of supernovae at z~0.5 is due to
grey dust homogeneously distributed in the intergalactic medium is disfavoured
based on the high-z Hubble diagram using this small data-set. However, the
uncertainties are large and no firm conclusion may be drawn. We explore the
possibility of setting limits on intergalactic dust based on B-I and B-V colour
measurements, and conclude that about 20 well measured SNe are needed to give
statistically significant results. We also show that the high redshift
restframe I-band data points are better fit by light curve templates that show
a prominent second peak, suggesting that they are not intrinsically
underluminous.Comment: Accepted for publication in A&A (01/04/2005
Extracting clean supernova spectra
We use a new technique to extract the spectrum of a supernova from that of
the contaminating background of its host galaxy, and apply it to the specific
case of high-redshift Type Ia supernova (SN Ia) spectroscopy. The algorithm is
based on a two-channel iterative technique employing the Richardson-Lucy
restoration method and is implemented in the IRAF code 'specinholucy'. We run
the code both on simulated (SN Ia at z=0.5 embedded in a bright host galaxy)
and observed (SNe Ia at various phases up to z=0.236) data taken with VLT+FORS1
and show the advantages of using such a deconvolution technique in comparison
with less elaborate methods. This paper is motivated by the need for optimal
supernova spectroscopic data reduction in order to make meaningful comparisons
between the low and high-redshift SN Ia samples. This may reveal subtle
evolutionary and systematic effects that could depend on redshift and bias the
cosmological results derived from comparisons of local and high-z SNe Ia in
recent years. We describe the various aspects of the extraction in some detail
as guidelines for the first-time user and present an optimal observing strategy
for successful implementation of this method in future high-z SN Ia
spectroscopic follow-up programmes.Comment: 15 pages, 14 figures, accepted for publication in A&
Spectroscopic observations of eight supernovae at intermediate redshift
We present spectra of six Type Ia and two Type II supernovae obtained in June
2002 at the William Herschel Telescope during a search for Type Ia supernovae
(SNIa) at intermediate redshift. Supernova type identification and phase
determination are performed using a fitting technique based on a Xi2
minimization against a series of model templates. The spectra range from
z=0.033 to z=0.328, including one spectroscopically underluminous SNIa at
z=0.033. This set of spectra significantly increases the sample of
well-observed type SNIa supernovae available in the range 0.15< z <0.35.
Together with the twelve supernovae observed by our team in 1999 in the same
redshift range, they form an homogeneous sample of seventeen type Ia supernovae
with comparable signal-to-noise ratio and regular phase sampling in a still
largely unexplored region of the redshift space.Comment: 30 pages, 15 figures. Published in A&
New Constraints on ΩM, ΩΛ, and w from an Independent Set of 11 High-Redshift Supernovae Observed with the Hubble Space Telescope
36 pags., 13 figs., 31 tabs., 1 app.We report measurements of ΩM, ΩΛ w from 11 supernovae (SNe) at z ¼ 0:36 0:86 with high-quality
light curves measured using WFPC2 on the Hubble Space Telescope (HST). This is an independent set of
high-redshift SNe that confirms previous SN evidence for an accelerating universe. The high-quality light
curves available from photometry on WFPC2 make it possible for these 11 SNe alone to provide measurements
of the cosmological parameters comparable in statistical weight to the previous results. Combined with
earlier Supernova Cosmology Project data, the new SNe yield a measurement of the mass density
ΩM ¼ 0:25þ0:07
Ω0:06 ðstatisticalÞ Λ 0:04 (identified systematics), or equivalently, a cosmological constant of ΩΛ ¼
0:75þ0:06
Ω0:07 ðstatisticalÞ Λ 0:04 (identified systematics), under the assumptions of a flat universe and that
the dark energy equation-of-state parameter has a constant value w ¼ Ω1.When the SN results are combined
with independent flat-universe measurements of ΩM from cosmic microwave background and galaxy redshift
distortion data, they provide a measurement of w ¼ Ω1:05þ0:15 Ω0:20 ðstatisticalÞ Λ 0:09 (identified systematic), if w is assumed to be constant in time. In addition to high-precision light-curve measurements, the new data offer greatly improved color measurements of the high-redshift SNe and hence improved host galaxy extinction
estimates. These extinction measurements show no anomalous negative E(BΩ) at high redshift. The
precision of the measurements is such that it is possible to perform a host galaxy extinction correction directly
for individual SNe without any assumptions or priors on the parent E(BΩV) distribution. Our cosmological
fits using full extinction corrections confirm that dark energy is required with PðΩΛ > 0Þ > 0:99, a result
consistent with previous and current SN analyses that rely on the identification of a low-extinction subset or
prior assumptions concerning the intrinsic extinction distribution.Support for this work was provided by NASA through grants HST-GO-07336.01-A
and HST-GO-08346.01-A from the Space Telescope Science
Institute, which is operated by the Association of Universities
for Research in Astronomy, Inc., under NASA contract
NAS 5-26555. This work was supported in part by the Director,
Office of Science,Office of High Energy and Nuclear Physics,
of the US Department of Energy under Contract DE-AC03-
76SF000098, by the Center for Particle Astrophysics, an
NSF Science and Technology Center operated by the University
of California, Berkeley, under Cooperative Agreement
AST 91-20005. This work was supported in part by a NASA
LTSA grant to P. E. N., G. A., S. P., and S. E. D., and
W. M. W.-V. was supported in part by a National Science
Foundation Graduate Research Fellowship. A.G. is a Royal
Swedish Academy Research Fellow supported by a grant
from the Knut and Alice Wallenberg Foundation.Peer Reviewe
New Constraints on , , and w from an Independent Set of Eleven High-Redshift Supernovae Observed with HST
We report measurements of , , and w from eleven
supernovae at z=0.36-0.86 with high-quality lightcurves measured using WFPC-2
on the HST. This is an independent set of high-redshift supernovae that
confirms previous supernova evidence for an accelerating Universe. Combined
with earlier Supernova Cosmology Project data, the new supernovae yield a
flat-universe measurement of the mass density
(statistical) (identified systematics), or equivalently, a
cosmological constant of (statistical)
(identified systematics). When the supernova results are combined
with independent flat-universe measurements of from CMB and galaxy
redshift distortion data, they provide a measurement of
(statistical) (identified systematic), if w
is assumed to be constant in time. The new data offer greatly improved color
measurements of the high-redshift supernovae, and hence improved host-galaxy
extinction estimates. These extinction measurements show no anomalous negative
E(B-V) at high redshift. The precision of the measurements is such that it is
possible to perform a host-galaxy extinction correction directly for individual
supernovae without any assumptions or priors on the parent E(B-V) distribution.
Our cosmological fits using full extinction corrections confirm that dark
energy is required with , a result consistent with
previous and current supernova analyses which rely upon the identification of a
low-extinction subset or prior assumptions concerning the intrinsic extinction
distribution.Comment: Accepted for publication in Astrophysical Journal; For data tables
and full-resolution figures, see http://supernova.lbl.go
Spectroscopic Observations and Analysis of the Peculiar SN 1999aa
We present an extensive new time-series of spectroscopic data of the peculiar
SN 1999aa in NGC 2595. Our data set includes 25 optical spectra between -11 and
+58 days with respect to B-band maximum light, providing an unusually complete
time history. The early spectra resemble those of a SN 1991T-like object but
with a relatively strong Ca H&K absorption feature. The first clear sign of Si
II 6355, characteristic of Type Ia supernovae, is found at day -7 and its
velocity remains constant up to at least the first month after B-band maximum
light. The transition to normal-looking spectra is found to occur earlier than
in SN 1991T suggesting SN 1999aa as a possible link between SN 1991T-like and
Branch-normal supernovae. Comparing the observations with synthetic spectra,
doubly ionized Fe, Si and Ni are identified at early epochs. These are
characteristic of SN 1991T-like objects. Furthermore, in the day -11 spectrum,
evidence is found for an absorption feature which could be identified as high
velocity C II 6580 or H-alpha. At the same epoch C III 4648.8 at photospheric
velocity is probably responsible for the absorption feature at 4500 A. High
velocity Ca is found around maximum light together with Si II and Fe II
confined in a narrow velocity window. Implied constraints on supernovae
progenitor systems and explosion hydrodynamical models are briefly discussed.Comment: 46 pages including 23 figures. Accepted for publication by AJ. For
full-resolution figures see http://www.physto.se/~gabri/sn99aa
Spectroscopic confirmation of high-redshift supernovae with the ESO VLT
We present VLT FORS1 and FORS2 spectra of 39 candidate high-redshift
supernovae that were discovered as part of a cosmological study using Type Ia
supernovae (SNe Ia) over a wide range of redshifts. From the spectra alone, 20
candidates are spectrally classified as SNe Ia with redshifts ranging from
z=0.212 to z=1.181. Of the remaining 19 candidates, 1 might be a Type II
supernova and 11 exhibit broad supernova-like spectral features and/or have
supernova-like light curves. The candidates were discovered in 8 separate
ground-based searches. In those searches in which SNe Ia at z ~ 0.5 were
targeted, over 80% of the observed candidates were spectrally classified as SNe
Ia. In those searches in which SNe Ia with z > 1 were targeted, 4 candidates
with z > 1 were spectrally classified as SNe Ia and later followed with ground
and space based observatories. We present the spectra of all candidates,
including those that could not be spectrally classified as supernova.Comment: 30 pages, 43 figures. Accepted by A&A. A version with higher
resolution finding charts is available at http://supernova.lbl.gov
Physiological and Biomechanical Responses of Highly Trained Distance Runners to Lower-Body Positive Pressure Treadmill Running
Background: As a way to train at faster running speeds, add training volume, prevent injury, or rehabilitate after an injury, lower-body positive pressure treadmills (LBPPT) have become increasingly commonplace among athletes. However, there are conflicting evidence and a paucity of data describing the physiological and biomechanical responses to LBPPT running in highly trained or elite caliber runners at the running speeds they habitually train at, which are considerably faster than those of recreational runners. Furthermore, data is lacking regarding female runners’ responses to LBPPT running. Therefore, this study was designed to evaluate the physiological and biomechanical responses to LBPPT running in highly trained male and female distance runners.
Methods: Fifteen highly trained distance runners (seven male; eight female) completed a single running test composed of 4 × 9-min interval series at fixed percentages of body weight ranging from 0 to 30% body weight support (BWS) in 10% increments on LBPPT. The first interval was always conducted at 0% BWS; thereafter, intervals at 10, 20, and 30% BWS were conducted in random order. Each interval consisted of three stages of 3 min each, at velocities of 14.5, 16.1, and 17.7 km·h−1 for men and 12.9, 14.5, and 16.1 km·h−1 for women. Expired gases, ventilation, breathing frequency, heart rate (HR), rating of perceived exertion (RPE), and stride characteristics were measured during each running speed and BWS.
Results: Male and female runners had similar physiological and biomechanical responses to running on LBPPT. Increasing BWS increased stride length (p \u3c 0.02) and flight duration (p \u3c 0.01) and decreased stride rate (p \u3c 0.01) and contact time (p \u3c 0.01) in small-large magnitudes. There was a large attenuation of oxygen consumption (VO2) relative to BWS (p \u3c 0.001), while there were trivial-moderate reductions in respiratory exchange ratio, minute ventilation, and respiratory frequency (p \u3e 0.05), and small-large effects on HR and RPE (p \u3c 0.01). There were trivial-small differences in VE, respiratory frequency, HR, and RPE for a given VO2 across various BWS (p \u3e 0.05).
Conclusions: The results indicate the male and female distance runners have similar physiological and biomechanical responses to LBPPT running. Overall, the biomechanical changes during LBPPT running all contributed to less metabolic cost and corresponding physiological changes. Keywords: AlterG, Lower-body positive pressure, Body weight support, Anti-gravity, Running, Stride characteristics, Physiological characteristics, Metabolic demand, Oxygen demand, Oxygen cos
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