1,796 research outputs found
Supernovae in the nuclear regions of starburst galaxies
The feasibility of using near-infrared observations to discover supernovae in
the nuclear and circumnuclear regions of nearby starburst galaxies is
investigated. We provide updated estimates of the intrinsic core-collapse
supernova rates in these regions. We discuss the problem of extinction, and
present new estimates of the extinction towards 33 supernova remnants in the
starburst galaxy M 82. This is done using H I and H_2 column density
measurements. We estimate the molecular to atomic hydrogen mass ratio to be 7.4
+- 1.0 in M 82. We have assembled near-infrared photometric data for a total of
13 core-collapse supernovae, some unpublished hitherto. This constitutes the
largest database of IR light curves for such events. We show that the IR light
curves fall into two classes, ``ordinary'' and ``slow-declining''. Template
JHKL light curves are derived for both classes. For ordinary core-collapse
supernovae, the average peak JHKL absolute magnitudes are -18.4, -18.6, -18.6,
and -19.0 respectively. The slow-declining core-collapse SNe are found to be
significantly more luminous than the ordinary events, even at early times,
having average peak JHKL absolute magnitudes of -19.9, -20.0, -20.0, and -20.4
respectively. We investigate the efficiency of a computerised image subtraction
method in supernova detection. We then carry out a Monte Carlo simulation of a
supernova search using K-band images of NGC 5962. The effects of extinction and
observing strategy are discussed. We conclude that a modest observational
programme will be able to discover a number of nuclear supernovae.Comment: 19 pages, 7 figures; accepted in MNRA
56Ni dredge-up in Supernova 1987A
We use early-time observations of He I 10830 \AA to measure the extent of
upward mixing of radioactive material in SN 1987A. This work develops and
extends the work of Graham (1988), and places constraints on actual explosion
models. The presence of the He I 10830 \AA (2s^{3}S--2p^{3}P) line at
days post-explosion implies re-ionisation by -rays from upwardly-mixed
radioactive material produced during the explosion. Using the unmixed explosion
model 10H (Woosley 1988) as well as mixed versions of it, we estimated the
-ray energy deposition by applying a purely absorptive radiative
transfer calculation. The deposition energy was used to find the ionisation
balance as a function of radius, and hence the 2sS population density
profile. This was then applied to a spectral synthesis model and the synthetic
spectra were compared with the observations. Neither model 10H nor the mixed
version, 10HMM, succeeded in reproducing the observed He I 10830 \AA line. The
discrepancy with the data found for 10HMM is particularly significant, as this
model has successfully reproduced the X-ray and -ray observations and
the UVOIR light curve. We find that a match to the He I line profile is
achieved by reducing the extent of mixing in 10HMM. Our reduced-mixing models
also reproduce the observed -ray line light curves and the iron-group
velocities deduced from late-time infrared line profiles. We suggest that the
He I line method provides a more sensitive measure of the extent of mixing in a
type II supernova explosion.Comment: 18 pages, 5 figures, accepted for publication in MNRAS (uses epsf.sty
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Measuring the competitiveness of the UK construction industry. Volume 1
EBSâs estimates of relative productivity in construction are as follows:
1.
The US is about 25-35% ahead of the UK and Germany in terms of average labour productivity (ALP).
2.
The UK is ahead of Germany in ALP on an output per worker basis, but not on an output per hour worked basis (this is due to Germans working fewer hours per week on average).
These results are largely unchanged under various sensitivity tests, for example, using GDP PPP exchange rates instead of construction PPP exchange rates to convert national currencies to a common currency.
The EBS estimate for the US-UK comparison is supported by UCL/DL (who estimate a US lead in ALP of 42% in 1999).
UCL/DLâs estimates for the Germany-UK comparison are also similar to those of EBS, since they show Germany level with the UK in ALP on an output per worker basis, but ahead on an output per hour worked basis.
Productivity comparisons of the UK with France are subject to difficulties. Depending on the exchange rates they use for conversion purposes, EBS find that France is well ahead of Britain on some measures of ALP (and indeed is close to the US) but on other measures French ALP is much the same as in Britain.
UCL/DL argue strongly for using an exchange rate, which shows French construction ALP to be well ahead of the UK. They state that: âThe French construction PPPs have been controversial for some timeâŠ.[and tend to lead to] underestimates of French construction outputâ.
There are difficulties in conducting this type of analysis that are hard to surmount, for example it is unlikely that labour inputs are well measured in any country because of illegal immigration, â the hidden economyâ, etc. However, unless there is reason to think that the proportion of uncounted construction workers is significantly higher or lower in Britain as compared to, say, the United States, then it seems reasonable to accept that ALP in the US construction industry is some way ahead of the UK.
In many ways cross-country comparisons of productivity levels across the whole construction industry are not comparing like with like since the composition of construction output differs greatly from country to country. It is therefore hard to construct reliable national rankings based on aggregated data for construction given the present state of the data
Early-time Spitzer observations of the type II-Plateau supernova, 2004dj
We present mid-infrared observations with the Spitzer Space Telescope of the
nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have
obtained the first mid-IR spectra of any supernova apart from SN 1987A. A
prominent [NiII] 6.64 micron line is observed, from which we deduce that the
mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red
wing of the CO-fundamental band. We relate our findings to possible progenitors
and favour an evolved star, most likely a red supergiant, with a probable
initial mass between ~10 and 15 Msun.Comment: ApJ Letters (accepted
Spectroscopically Peculiar Type Ia Supernovae and Implications for Progenitors
In a recent paper Li et al. (2000) reported that 36 percent of 45 Type Ia
supernovae (SNe Ia) discovered since 1997 in two volume-limited supernova
searches were spectroscopically peculiar, and they suggested that because this
peculiarity rate is higher than that reported for an earlier observational
sample by Branch et al. (1993), it is now more likely that SNe Ia are produced
by more than one kind of progenitor. In this paper I discuss and clarify the
differences between the results of Li et al. and Branch et al. and I suggest
that multiple progenitor systems are now less likely than they were before.Comment: 11 pages; accepted by PASP; several minor changes, 2 references
added, main conclusions unchange
A Spitzer Space Telescope study of SN 2002hh: an infrared echo from a Type IIP supernova
We present late-time (590-994 d) mid-IR photometry of the normal, but
highly-reddened Type IIP supernova SN 2002hh. Bright, cool, slowly-fading
emission is detected from the direction of the supernova. Most of this flux
appears not to be driven by the supernova event but instead probably originates
in a cool, obscured star-formation region or molecular cloud along the
line-of-sight. We also show, however, that the declining component of the flux
is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR
emission could also be coming from newly-condensed dust and/or an ejecta/CSM
impact but their contributions are likely to be small. For the case of a CSM-IR
echo, we infer a dust mass of as little as 0.036 M(solar) with a corresponding
CSM mass of 3.6(0.01/r(dg))M(solar) where r(dg) is the dust-to-gas mass ratio.
Such a CSM would have resulted from episodic mass loss whose rate declined
significantly about 28,000 years ago. Alternatively, an IR echo from a
surrounding, dense, dusty molecular cloud might also have been responsible for
the fading component. Either way, this is the first time that an IR echo has
been clearly identified in a Type IIP supernova. We find no evidence for or
against the proposal that Type IIP supernovae produce large amounts of dust via
grain condensation in the ejecta. However, within the CSM-IR echo scenario, the
mass of dust derived implies that the progenitors of the most common of
core-collapse supernovae may make an important contribution to the universal
dust content.Comment: 41 pages, 11 figures, 4 tables, accepted for publication in
Astrophysical Journal (References corrected
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