23 research outputs found
Cepheid Calibration of the Peak Brightness of SNe Ia. X. SN 1991T in NGC 4527
Repeated imaging observations have been made of NGC 4527 with the Hubble
Space Telescope between April and June 1999, over an interval of 69 days.
Images were obtained on 12 epochs in the F555W band and on five epochs in the
F814W band. The galaxy hosted the type Ia supernova SN1991T, which showed
relatively unusual behavior by having both an abnormal spectrum near light
maximum, and a slower declining light curve than the proto-typical Branch
normal SNe Ia.
A total of 86 variables that are putative Cepheids have been found, with
periods ranging from 7.4 days to over 70 days. From photometry with the DoPHOT
program, the de-reddened distance modulus is determined to be (m-M)_0 = 30.67
+/- 0.12 (internal uncertainty) using a subset of the Cepheid data whose
reddening and error parameters are secure. A parallel analysis of the Cepheids
using photometry with ROMAFOT yields (m -M)_0 =30.82 +/- 0.11. The final
adopted modulus is (m -M)_0 =30.74 +/- 0.12 +/- 0.12 (d=14.1 +/- 0.8 +/- 0.8
Mpc).
The photometric data for SN1991T are used in combination with the Cepheid
distance to NGC 4527 to obtain the absolute magnitude for this supernova of
M_V^0(max) = -19.85 +/- 0.29. The relatively large uncertainty is a result of
the range in estimates of the reddening to the supernova. Thus SN1991T is seen
to be only moderately brighter (by ~ 0.3 mag) than the mean for
spectroscopically normal supernovae, although magnitude differences of up to
0.6 mag cannot be ruled out.Comment: 46 pages, LATEX using aaspp4.sty, including 9 embedded tables, 19
figures (gif and jpg files), a full-resolution version (ps files) is
available at http://www.astro.unibas.ch/forschung/ll/cepheid.shtml, accepted
for publication in the Astrophysical Journa
Diversity of Decline-Rate-Corrected Type Ia Supernova Rise Times: One Mode or Two?
B-band light-curve rise times for eight unusually well-observed nearby Type
Ia supernovae (SNe) are fitted by a newly developed template-building
algorithm, using light-curve functions that are smooth, flexible, and free of
potential bias from externally derived templates and other prior assumptions.
From the available literature, photometric BVRI data collected over many
months, including the earliest points, are reconciled, combined, and fitted to
a unique time of explosion for each SN. On average, after they are corrected
for light-curve decline rate, three SNe rise in 18.81 +- 0.36 days, while five
SNe rise in 16.64 +- 0.21 days. If all eight SNe are sampled from a single
parent population (a hypothesis not favored by statistical tests), the rms
intrinsic scatter of the decline-rate-corrected SN rise time is 0.96 +0.52
-0.25 days -- a first measurement of this dispersion. The corresponding global
mean rise time is 17.44 +- 0.39 days, where the uncertainty is dominated by
intrinsic variance. This value is ~2 days shorter than two published averages
that nominally are twice as precise, though also based on small samples. When
comparing high-z to low-z SN luminosities for determining cosmological
parameters, bias can be introduced by use of a light-curve template with an
unrealistic rise time. If the period over which light curves are sampled
depends on z in a manner typical of current search and measurement strategies,
a two-day discrepancy in template rise time can bias the luminosity comparison
by ~0.03 magnitudes.Comment: As accepted by The Astrophysical Journal; 15 pages, 6 figures, 2
tables. Explanatory material rearranged and enhanced; Fig. 4 reformatte
`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
Type Ia Supernovae: Influence of the Initial Composition on the Nucleosynthesis, Light Curves, Spectra and Consequences for the Determination of Omega_M & Lambda
The influence of the initial composition of the exploding white dwarf on the
nucleosynthesis, light curves and spectra of Type Ia supernovae has been
studied in order to evaluate the size of evolutionary effects on cosmological
time scales, how the effects can be recognized and how one may be able to
correct for them.
The calculations are based on a set of delayed detonation models which give a
good account of the optical and infrared light curves and of the spectral
evolution. The explosions and light curves are calculated using a one-
dimensional Lagrangian radiation-hydro code including a nuclear network. NLTE-
spectra are computed for various epochs using the structure resulting from the
light curve code.
The following questions are addressed : What do we learn about the progenitor
evolution and its metallicity? What are the systematic effects for the
determination of the cosmological parameters and and how
can we recognize this potential 'pitfalls' and correct for evolutionary
effects?Comment: 19 pages, TeX, Ap
The SN 1006 Remnant: Optical Proper Motions, Deep Imaging, Distance, and Brightness at Maximum
We report the first measurement of proper motions in the SN1006 remnant
(G327.6+14.6) based entirely on digital images. CCD images from three epochs
spanning a period of 11 years are used: 1987 from Las Campanas, and 1991 and
1998 from CTIO. Measuring the shift of delicate Balmer filaments along the
northwest rim of the remnant, we obtain proper motions of 280 +/- 8 mas/yr
along the entire length where the filaments are well defined, with little
systematic variation along the filaments. We also report very deep Halpha
imaging observations of the entire remnant that clearly show very faint
emission surrounding almost the entire shell, as well as some diffuse emission
regions in the (projected) interior. Combining the proper motion measurement
with a recent measurement of the shock velocity based on spectra of the same
filaments by Ghavamian et al. leads to a distance of 2.17 +/- 0.08 kpc to
SN1006. Several lines of argument suggest that SN1006 was a Type Ia event, so
the improved distance measurement can be combined with the peak luminosity for
SNeIa, as determined for events in galaxies with Cepheid-based distances, to
calculate the apparent brightness of the spectacular event that drew wide
attention in the eleventh century. The result, V_max = -7.5 =/- 0.4, lies
squarely in the middle of the wide range of estimates based on the historical
observations.Comment: 13 pages, 3 tables, 5 figures. Uses AASTeX5.02 and emulateapj
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
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
Optical Light Curves of the Type Ia Supernovae 1990N and 1991T
We present UBVRI light curves for the bright Type Ia supernovae SN 1990N in
NGC 4639 and SN 1991T in NGC 4527 based on photometry gathered in the course of
the Calan/Tololo supernova program. Both objects have well-sampled light curves
starting several days before maximum light and spanning well through the
exponential tail. These data supercede the preliminary photometry published by
Leibundgut et al (1991) and Phillips et al (1992). The host galaxies for these
supernovae have (or will have) accurate distances based on the Cepheid
period-luminosity relationship. The photometric data in this paper provide
template curves for the study of general population of Type Ia supernova and
accurate photometric indices needed for the Cepheid-supernova distance scale.Comment: AAS LaTeX, 30 pages, 10 figures, to appear in the Jan 1998
Astronomical Journal. Figs 1 and 2 (finding charts) not include
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
Hubble Space Telescope Spectroscopy of V471 Tauri: Oversized K Star, Paradoxical White Dwarf
We have used the GHRS onboard the HST to obtain Lyman-alpha spectra of the
hot white-dwarf (WD) component of the short-period eclipsing DA+dK2
pre-cataclysmic binary V471 Tauri, a member of the Hyades star cluster. Radial
velocities of the WD, combined with ground-based measurements of the dK
velocities, eclipse timings, and a determination of the dK star's rotational
velocity, yield dynamical masses for the components of M(WD)=0.84 and
M(dK)=0.93 Msun. Model-atmosphere fitting of the Ly-alpha profile provides the
effective temperature (34,500 K) and surface gravity (log g=8.3) of the WD. The
radius of the dK component is 18% larger than that of a normal Hyades dwarf of
the same mass. This expansion is attributed to the extensive coverage of the
surface by starspots, causing the star to expand in response. The WD radius,
determined from a radiometric analysis and from eclipse ingress timings, is
0.0107 Rsun. The position of the star in the M-R plane is in full accord with
theory for a degenerate CO WD. The high temperature and mass of the WD present
an evolutionary paradox: the WD is the most massive known in the Hyades, but
also the hottest and youngest. We suggest that the explanation is that the WD
is indeed very young, and is descended from a triple consisting of a blue
straggler and a more-distant dK companion. We estimate that the common-envelope
efficiency parameter, alpha_CE, was of order 0.3-1.0, in good agreement with
recent hydrodynamical simulations.Comment: Astrophysical Journal, in press. 34 text pages, 8 figure