42 research outputs found
Multi-Color Light Curves of Type Ia Supernovae on the Color-Magnitude Diagram: a Novel Step Toward More Precise Distance and Extinction Estimates
We show empirically that fits to the color-magnitude relation of Type Ia
supernovae after optical maximum can provide accurate relative extragalactic
distances. We report the discovery of an empirical color relation for Type Ia
light curves: During much of the first month past maximum, the magnitudes of
Type Ia supernovae defined at a given value of color index have a very small
magnitude dispersion; moreover, during this period the relation between
magnitude and color (or or color) is strikingly linear, to
the accuracy of existing well-measured data. These linear relations can provide
robust distance estimates, in particular, by using the magnitudes when the
supernova reaches a given color. After correction for light curve strech factor
or decline rate, the dispersion of the magnitudes taken at the intercept of the
linear color-magnitude relation are found to be around 0.08 for the
sub-sample of supernovae with \BVm , and around 0.11 for the
sub-sample with \BVm . This small dispersion is consistent with
being mostly due to observational errors. The method presented here and the
conventional light curve fitting methods can be combined to further improve
statistical dispersions of distance estimates. It can be combined with the
magnitude at maximum to deduce dust extinction. The slopes of the
color-magnitude relation may also be used to identify intrinsically different
SN Ia systems. The method provides a tool that is fundamental to using SN Ia to
estimate cosmological parameters such as the Hubble constant and the mass and
dark energy content of the universe.Comment: ApJ, in pres
Can Deflagration-Detonation-Transitions occur in Type Ia Supernovae?
The mechanism for deflagration-detonation-transition (DDT) by turbulent
preconditioning, suggested to explain the possible occurrence of delayed
detonations in Type Ia supernova explosions, is argued to be conceptually
inconsistent. It relies crucially on diffusive heat losses of the burned
material on macroscopic scales. Regardless of the amplitude of turbulent
velocity fluctuations, the typical gradient scale for temperature fluctuations
is shown to be the laminar flame width or smaller, rather than the factor of
thousand more required for a DDT. Furthermore, thermonuclear flames cannot be
fully quenched in regions much larger than the laminar flame width as a
consequence of their simple ``chemistry''. Possible alternative explosion
scenarios are briefly discussed.Comment: 8 pages, uses aastex; added references. Accepted by ApJ Letter
`Pure' Supernovae and Accelerated Expansion of the Universe
A special class of type Ia supernovae that is not subject to ordinary and
additional intragalactic gray absorption and chemical evolution has been
identified. Analysis of the Hubble diagrams constructed for these supernovae
confirms the accelerated expansion of the Universe irrespective of the chemical
evolution and possible gray absorption in galaxies.Comment: 2 figures, 1 tabl
Thermonuclear Burning Regimes and the Use of SNe Ia in Cosmology
The calculations of the light curves of thermonuclear supernovae are carried
out by a method of multi-group radiation hydrodynamics. The effects of spectral
lines and expansion opacity are taken into account. The predictions for UBVI
fluxes are given. The values of rise time for B and V bands found in our
calculations are in good agreement with the observed values. We explain why our
results for the rise time have more solid physical justification than those
obtained by other authors. It is shown that small variations in the chemical
composition of the ejecta, produced in the explosions with different regimes of
nuclear burning, can influence drastically the light curve decline in the B
band and, to a lesser extent, in the V band. We argue that recent results on
positive cosmological constant Lambda, found from the high redshift supernova
observations, could be wrong in the case of possible variations of the
preferred mode of nuclear burning in the earlier Universe.Comment: 20 pages, 5 figures, presented at the conference "Astronomy at the
Eve of the New Century", Puschino, May 17-22, 1999. A few references and a
table added, typos correcte
The Rise Time of Type Ia Supernovae from the Supernova Legacy Survey
We compare the rise times of nearby and distant Type Ia supernovae (SNe Ia)
as a test for evolution using 73 high-redshift spectroscopically-confirmed SNe
Ia from the first two years of the five year Supernova Legacy Survey (SNLS) and
published observations of nearby SN. Because of the ``rolling'' search nature
of the SNLS, our measurement is approximately 6 times more precise than
previous studies, allowing for a more sensitive test of evolution between
nearby and distant supernovae. Adopting a simple early-time model (as in
previous studies), we find that the rest-frame rise times for a fiducial SN
Ia at high and low redshift are consistent, with values
and
days, respectively; the statistical significance of this difference is only 1.4
\sg . The errors represent the uncertainty in the mean rather than any
variation between individual SN. We also compare subsets of our high-redshift
data set based on decline rate, host galaxy star formation rate, and redshift,
finding no substantive evidence for any subsample dependence.Comment: Accepted for publication in AJ; minor changes (spelling and
grammatical) to conform with published versio
A Parameter Study of Type II Supernova Light Curves Using 6 M_odot He Cores
Results of numerical calculations of Type II supernova light curves are
presented. The model progenitor stars have 6 cores and various
envelopes, originating from a numerically evolved 20 star. Five
parameters that affect the light curves are examined: the ejected mass, the
progenitor radius, the explosion energy, the Ni mass, and the extent of
Ni mixing. The following affects have been found: 1) the larger the
progenitor radius the brighter the early--time light curve, with little affect
on the late--time light curve, 2) the larger the envelope mass the fainter the
early light curve and the flatter the slope of the late light curve, 3) the
larger the explosion energy the brighter the early light curve and the steeper
the slope of the late light curve, 4) the larger the Ni mass the
brighter the overall light curve after 20 to 50 days, with no affect on the
early light curve, 5) the more extensive the Ni mixing the brighter the
early light curve and the steeper the late light curve. The primary parameters
affecting the light curve shape are the progenitor radius and the ejected mass.
The secondary parameters are the explosion energy, Ni mass and Ni
mixing. I find that while in principle the general shape and absolute magnitude
of a light curve indicate a unique set of parameters, in practice it is
difficult to avoid some ambiguity in the parameters. I find that the
nickel--powered diffusion wave and the recombination of helium produce a
prominent secondary peak in all our calculations. The feature is less prominent
when compositional mixing, both Ni mixing and mixing between the
hydrogen and helium layers, occurs. The model photospheric temperatures and
velocities are presented, for comparison to observation.Comment: 39 pages, 15 figures. Astrophysical Journal (Accepted, Dec. 20, 2004
Testing SNe Ia distance measurement methods with SN 2011fe
The nearby, bright, almost completely unreddened Type Ia supernova 2011fe in
M101 provides a unique opportunity to test both the precision and the accuracy
of the extragalactic distances derived from SNe Ia light curve fitters. We
apply the current, public versions of the independent light curve fitting codes
MLCS2k2 and SALT2 to compute the distance modulus of SN 2011fe from
high-precision, multi-color (BVRI) light curves. The results from the two
fitting codes confirm that 2011fe is a "normal" (not peculiar) and only
slightly reddened SN Ia. New unreddened distance moduli are derived as 29.21
+/- 0.07 mag (D ~ 6.95 +/- 0.23$ Mpc, MLCS2k2), and 29.05 +/- 0.07 mag (6.46
+/- 0.21 Mpc, SALT2). Despite the very good fitting quality achieved with both
light curve fitters, the resulting distance moduli are inconsistent by 2 sigma.
Both are marginally consistent (at ~1 sigma) with the HST Key Project distance
modulus for M101. The SALT2 distance is in good agreement with the recently
revised Cepheid- and TRGB-distance to M101. Averaging all SN- and Cepheid-based
estimates, the absolute distance to M101 is ~6.6 +/- 0.5 Mpc.Comment: 8 pages, 7 figures, accepted for publication in A&
The estimation of black-hole masses in distant radio galaxies
We have estimated the masses of the central supermassive black holes of 2442
radio galaxies froma catalog compiled using data from the NED, SDSS, and CATS
databases. Mass estimates based on optical photometry and radio data are
compared. Relationships between the mass of the central black hole
and the redshift are constructed for both wavelength ranges. The
distribution of the galaxies in these diagrams and systematic effects
influencing estimation of the black-hole parameters are discussed.
Upperenvelope cubic regression fits are obtained using the maximum estimates of
the black-hole masses. The optical and radio upper envelopes show similar
behavior, and have very similar peaks in position, , and
amplitude, = 9.4. This is consistent with a model in which the
growth of the supermassive black holes is self-regulating, with this redshift
corresponding to the epoch when the accretion-flow phase begins to end and the
nuclear activity falls off.Comment: 8 pages, 6 figure
Direct Determination of Hubble Parameter Using Type IIn Supernovae
We introduce a novel approach, a Dense Shell Method (DSM), for measuring
distances for cosmology. It is based on original Baade idea to relate absolute
difference of photospheric radii with photospheric velocity. We demonstrate
that this idea works: the new method does not rely on the Cosmic Distance
Ladder and gives satisfactory results for the most luminous Type IIn
Supernovae. This allows one to make them good primary distance indicators for
cosmology. Fixing correction factors for illustration, we obtain with this
method the median distance of 68^{+19}_{-15} (68%CL) Mpc to SN 2006gy and
median Hubble parameter 79^{+23}_{-17} (68%CL) km/s/Mpc.Comment: 6 pages, 1 figure, typos correcte
The Hubble Constant
I review the current state of determinations of the Hubble constant, which
gives the length scale of the Universe by relating the expansion velocity of
objects to their distance. There are two broad categories of measurements. The
first uses individual astrophysical objects which have some property that
allows their intrinsic luminosity or size to be determined, or allows the
determination of their distance by geometric means. The second category
comprises the use of all-sky cosmic microwave background, or correlations
between large samples of galaxies, to determine information about the geometry
of the Universe and hence the Hubble constant, typically in a combination with
other cosmological parameters. Many, but not all, object-based measurements
give values of around 72-74km/s/Mpc , with typical errors of 2-3km/s/Mpc.
This is in mild discrepancy with CMB-based measurements, in particular those
from the Planck satellite, which give values of 67-68km/s/Mpc and typical
errors of 1-2km/s/Mpc. The size of the remaining systematics indicate that
accuracy rather than precision is the remaining problem in a good determination
of the Hubble constant. Whether a discrepancy exists, and whether new physics
is needed to resolve it, depends on details of the systematics of the
object-based methods, and also on the assumptions about other cosmological
parameters and which datasets are combined in the case of the all-sky methods.Comment: Extensively revised and updated since the 2007 version: accepted by
Living Reviews in Relativity as a major (2014) update of LRR 10, 4, 200