Astron.J.128:387-404,2004 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.
Astrophys.J.577:120-132,2002 We present a measurement of the rate of distant Type Ia supernovae derived
using 4 large subsets of data from the Supernova Cosmology Project. Within this
fiducial ...sample, which surveyed about 12 square degrees, thirty-eight
supernovae were detected at redshifts 0.25--0.85. In a spatially-flat
cosmological model consistent with the results obtained by the Supernova
Cosmology Project, we derive a rest-frame Type Ia supernova rate at a mean
redshift $z\simeq0.55$ of $1.53 {^{+0.28}_{-0.25}} {^{+0.32}_{-0.31}} 10^{-4}
h^3 {\rm Mpc}^{-3} {\rm yr}^{-1}$ or $0.58 {^{+0.10}_{-0.09}}
{^{+0.10}_{-0.09}} h^2 {\rm SNu}$ (1 SNu = 1 supernova per century per
$10^{10}$\Lbsun), where the first uncertainty is statistical and the second
includes systematic effects. The dependence of the rate on the assumed
cosmological parameters is studied and the redshift dependence of the rate per
unit comoving volume is contrasted with local estimates in the context of
possible cosmic star formation histories and progenitor models.
Mon.Not.Roy.Astron.Soc. 340 (2003) 1057 (Abridged) We present new results on the Hubble diagram of distant type Ia
supernovae (SNe Ia) segregated according to the type of host galaxy. This makes
it ...possible to check earlier evidence for a cosmological constant by explicitly
comparing SNe residing in galaxies likely to contain negligible dust with the
larger sample. The cosmological parameters derived from these SNe Ia hosted by
presumed dust-free early-type galaxies supports earlier claims for a
cosmological constant, which we demonstrate at 5 sigma significance, and the
internal extinction implied is small even for late-type systems (A_B<0.2).
Thus, our data demonstrate that host galaxy extinction is unlikely to
systematically dim distant SNe Ia in a manner that would produce a spurious
cosmological constant. We classify the host galaxies of 39 distant SNe
discovered by the Supernova Cosmology Project (SCP) using the combination of
HST STIS imaging, Keck ESI spectroscopy and ground-based broad-band photometry.
We compare with a low-redshift sample of 25 SNe Ia. The scatter observed in the
SNe Ia Hubble diagrams correlates closely with host galaxy morphology. We find
the scatter in the SNe Ia Hubble diagram is smallest for SNe occurring in
early-type hosts and largest for those occurring in late-type galaxies.
Moreover, SNe residing in early-type hosts appear only ~0.14+/-0.09 mag
brighter in their light-curve-width-corrected luminosity than those in
late-type hosts, implying only a modest amount of dust extinction even in the
late-type systems.
Besides the usual conductance plateaus at multiples of 2e2/h, quantum point contacts typically show an extra plateau at ~ 0.7(2e2/h), believed to arise from electron-electron interactions that ...prohibit the two spin channels from being simultaneously occupied. We present evidence that the disappearance of the 0.7 structure at very low temperature signals the formation of a Kondo-like correlated spin state. Evidence includes a zero-bias conductance peak that splits in a parallel field, scaling of conductance to a modified Kondo form, and consistency between peak width and the Kondo temperature.
PDF
