631 research outputs found
Near Infrared Spectra of Type Ia Supernovae
We report near infrared (NIR) spectroscopic observations of twelve
``Branch-normal'' Type Ia supernovae (SNe Ia) which cover the wavelength region
from 0.8-2.5 microns. Our sample more than doubles the number of SNe Ia with
published NIR spectra within three weeks of maximum light. The epochs of
observation range from thirteen days before maximum light to eighteen days
after maximum light. A detailed model for a Type Ia supernovae is used to
identify spectral features. The Doppler shifts of lines are measured to obtain
the velocity and, thus, the radial distribution of elements.
The NIR is an extremely useful tool to probe the chemical structure in the
layers of SNe Ia ejecta. This wavelength region is optimal for examining
certain products of the SNe Ia explosion that may be blended or obscured in
other spectral regions. We identify spectral features from MgII, CaII, SiII,
FeII, CoII, NiII and possibly MnII. We find no indications for hydrogen, helium
or carbon in the spectra. The spectral features reveal important clues about
the physical characteristics of SNe Ia. We use the features to derive upper
limits for the amount of unburned matter, to identify the transition regions
from explosive carbon to oxygen burning and from partial to complete silicon
burning, and to estimate the level of mixing during and after the explosion.Comment: 44 pages, 7 figures, 3 tables, accepted by Ap
Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydro Models
We have performed detailed NLTE spectral synthesis modeling of 2 types of 1-D
hydro models: the very highly parameterized deflagration model W7, and two
delayed detonation models. We find that overall both models do about equally
well at fitting well observed SNe Ia near to maximum light. However, the Si II
6150 feature of W7 is systematically too fast, whereas for the delayed
detonation models it is also somewhat too fast, but significantly better than
that of W7. We find that a parameterized mixed model does the best job of
reproducing the Si II 6150 line near maximum light and we study the differences
in the models that lead to better fits to normal SNe Ia. We discuss what is
required of a hydro model to fit the spectra of observed SNe Ia near maximum
light.Comment: 29 pages, 14 figures, ApJ, in pres
The absolute infrared magnitudes of type Ia supernovae
The absolute luminosities and homogeneity of early-time infrared (IR) light
curves of type Ia supernovae are examined. Eight supernovae are considered.
These are selected to have accurately known epochs of maximum blue light as
well as having reliable distance estimates and/or good light curve coverage.
Two approaches to extinction correction are considered. Owing to the low
extinction in the IR, the differences in the corrections via the two methods
are small. Absolute magnitude light curves in the J, H and K-bands are derived.
Six of the events, including five established ``Branch-normal'' supernovae show
similar coeval magnitudes. Two of these, SNe 1989B and 1998bu, were observed
near maximum infrared light. This occurs about 5 days {\it before} maximum blue
light. Absolute peak magnitudes of about -19.0, -18.7 and -18.8 in J, H & K
respectively were obtained. The two spectroscopically peculiar supernovae in
the sample, SNe 1986G and 1991T, also show atypical IR behaviour. The light
curves of the six similar supernovae can be represented fairly consistently
with a single light curve in each of the three bands. In all three IR bands the
dispersion in absolute magnitude is about 0.15 mag, and this can be accounted
for within the uncertainties of the individual light curves. No significant
variation of absolute IR magnitude with B-band light curve decline rate, Delta
m_{15}(B), is seen over the range 0.87<Delta m_{15}(B)<1.31. However, the data
are insufficient to allow us to decide whether or not the decline rate relation
is weaker in the IR than in the optical region. IR light curves of type Ia
supernovae should eventually provide cosmological distance estimates which are
of equal or even superior quality to those obtained in optical studies.Comment: 19 pages, 9 figures, MNRAS in press (includes Referee's changes
What lies beneath? The role of informal and hidden networks in the management of crises
Crisis management research traditionally focuses on the role of formal communication networks in the escalation and management of organisational crises. Here, we consider instead informal and unobservable networks. The paper explores how hidden informal exchanges can impact upon organisational decision-making and performance, particularly around inter-agency working, as knowledge distributed across organisations and shared between organisations is often shared through informal means and not captured effectively through the formal decision-making processes. Early warnings and weak signals about potential risks and crises are therefore often missed. We consider the implications of these dynamics in terms of crisis avoidance and crisis management
An Extremely Bright Echo Associated With SN 2002hh
We present new, very late-time optical photometry and spectroscopy of the
interesting Type II-P supernova, SN 2002hh, in NGC 6946. Gemini/GMOS-N has been
used to acquire visible spectra at six epochs between 2004 August and 2006
July, following the evolution of the SN from age 661 to 1358 days. Few optical
spectra of Type II supernovae with ages greater than one year exist. In
addition, g'r'i' images were acquired at all six epochs. The spectral and
photometric evolution of SN 2002hh has been very unusual. Measures of the
brightness of this SN, both in the R and I bands as well as in the H-alpha
emission flux, show no significant fading over an interval of nearly two years.
The most straightforward explanation for this behavior is that the light being
measured comes not only from the SN itself but also from an echo off of nearby
dust. Echoes have been detected previously around several SNe but these echoes,
at their brightest, were ~8 mag below the maximum brightness of the SN. At V~21
mag, the putative echo dominates the light of SN 2002hh and is only ~4 mag
below the outburst's peak brightness. There is an estimated 6 magnitudes of
total extinction in V towards SN 2002hh. The proposed explanation of a
differential echo/SN absorption is inconsistent with the observed BVRI colors.Comment: 24 pages, 6 figures. Accepted for publication in the Ap
Low Carbon Abundance in Type Ia Supernovae
We investigate the quantity and composition of unburned material in the outer
layers of three normal Type Ia supernovae (SNe Ia): 2000dn, 2002cr and 20 04bw.
Pristine matter from a white dwarf progenitor is expected to be a mixture of
oxygen and carbon in approximately equal abundance. Using near-infrared (NIR,
0.7-2.5 microns) spectra, we find that oxygen is abundant while carbon is
severely depleted with low upper limits in the outer third of the ejected mass.
Strong features from the OI line at rest wavelength = 0.7773 microns are
observed through a wide range of expansion velocities approx. 9,000 - 18,000
km/s. This large velocity domain corresponds to a physical region of the
supernova with a large radial depth. We show that the ionization of C and O
will be substantially the same in this region. CI lines in the NIR are expected
to be 7-50 times stronger than those from OI but there is only marginal
evidence of CI in the spectra and none of CII. We deduce that for these three
normal SNe Ia, oxygen is more abundant than carbon by factors of 100 - 1,000.
MgII is also detected in a velocity range similar to that of OI. The presence
of O and Mg combined with the absence of C indicates that for these SNe Ia,
nuclear burning has reached all but the extreme outer layers; any unburned
material must have expansion velocities greater than 18,000 km/s. This result
favors deflagration to detonation transition (DD) models over pure deflagration
models for SNe Ia.Comment: accepted for publication in Ap
Detection of CO and Dust Emission in Near-Infrared Spectra of SN 1998S
Near-infrared spectra (0.95 -- 2.4 micron) of the peculiar Type IIn supernova
1998S in NGC 3877 from 95 to 355 days after maximum light are presented. K-band
data taken at days 95 and 225 show the presence of the first overtone of CO
emission near 2.3 micron, which is gone by day 355. An apparent extended blue
wing on the CO profile in the day 95 spectrum could indicate a large CO
expansion velocity (~2000 -- 3000 km/s). This is the third detection of
infrared CO emission in nearly as many Type II supernovae studied, implying
that molecule formation may be fairly common in Type II events, and that the
early formation of molecules in SN 1987A may be typical rather than
exceptional. Multi-peak hydrogen and helium lines suggest that SN 1998S is
interacting with a circumstellar disk, and the fading of the red side of this
profile with time is suggestive of dust formation in the ejecta, perhaps
induced by CO cooling. Continuum emission that rises towards longer wavelengths
(J -> K) is seen after day 225 with an estimated near-infrared luminosity >~
10^40 erg/s. This may be related to the near-infrared excesses seen in a number
of other supernovae. If this continuum is due to free-free emission, it
requires an exceptionally shallow density profile. On the other hand, the shape
of the continuum is well fit by a 1200 +- 150 K blackbody spectrum possibly due
to thermal emission from dust. Interestingly, we observe a similar 1200 K
blackbody-like, near-infrared continuum in SN 1997ab, another Type IIn
supernova at an even later post-maximum epoch (day 1064+). A number of dust
emission scenarios are discussed, and we conclude that the NIR dust continuum
is likely powered by the interaction of SN 1998S with the circumstellar medium.Comment: 38 Pages, 12 Figures, Submitted to The Astronomical Journa
A Search for Isolated Microwave Pulses from the Perseus Cluster of Galaxies
The paper describes a search for prompt
microwave emissions from supernovae in the central
region of the Perseus cluster of galaxies, using a
coincidence technique involving five tracking radiometers
located at widely spaced sites. No coincidences
were found between January and December, 1973, and no supernovae were reported during this period
from the optical surveys, in that region of sky
Reflections on the Evolution of Smart Polymers
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Since Staudinger\u27s recognition that polymers were long chain molecules with covalent bonds between repeating units, the field has evolved tremendously. In addition to their many structural roles, polymers have been developed to exhibit âsmartâ stimuli-responsive behavior. This article will describe the evolution of selected classes of smart polymers including those responsive to changes in pH, temperature, light, and mechanical stimuli, as well as self-immolative polymers and their application in drug delivery, sensors, and actuators. It will also highlight key advancements in polymer chemistry that enabled rapid progress over the past âŒ20 years. Whether the key achievements were predictable will be discussed, and the extent to which polymer science remains an independent science versus a service tool will be addressed. Finally, some possibilities for the evolution of the field over the next 20â30 years will be described
An Upper Limit to Microwave Pulse Emission at the Onset of a Supernova
This paper reports an upper limit at 10 GHz of 4 x 10^(43) erg in a 40 MHz bandwidth for the microwave pulse emission at the onset of an optically observed supernova
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