601 research outputs found
Evolution of the Reverse Shock Emission from SNR 1987A
We present new (2004 July) G750L and G140L Space Telescope Imaging
Spectrograph (STIS) data of the H-alpha and Ly-alpha emission from supernova
remnant (SNR) 1987A. With the aid of earlier data, from Oct 1997 to Oct 2002,
we track the local evolution of Ly-alpha emission and both the local and global
evolution of H-alpha emission. In addition to emission which we can clearly
attribute to the surface of the reverse shock, we also measure comparable
emission, in both H-alpha and Ly-alpha, which appears to emerge from supernova
debris interior to the surface. New observations taken through slits positioned
slightly eastward and westward of a central slit show a departure from
cylindrical symmetry in the H-alpha surface emission. Using a combination of
old and new observations, we construct a light curve of the total H-alpha flux,
F, from the reverse shock, which has increased by a factor ~ 4 over about 8
years. However, due to large systematic uncertainties, we are unable to discern
between the two limiting behaviours of the flux - F ~ t (self-similar
expansion) and F ~ t^5 (halting of the reverse shock). Such a determination is
relevant to the question of whether the reverse shock emission will vanish in
less than about 7 years (Smith et al. 2005). Future deep, low- or
moderate-resolution spectra are essential for accomplishing this task.Comment: 28 pages, 12 figures. Accepted by Ap
The Hubble Ultra Deep Field
This paper presents the Hubble Ultra Deep Field (HUDF), a one million second
exposure of an 11 square minute-of-arc region in the southern sky with the
Hubble Space Telescope. The exposure time was divided among four filters, F435W
(B435), F606W (V606), F775W (i775), and F850LP (z850), to give approximately
uniform limiting magnitudes mAB~29 for point sources. The image contains at
least 10,000 objects presented here as a catalog. Few if any galaxies at
redshifts greater than ~4 resemble present day spiral or elliptical galaxies.
Using the Lyman break dropout method, we find 504 B-dropouts, 204 V-dropouts,
and 54 i-dropouts. Using these samples that are at different redshifts but
derived from the same data, we find no evidence for a change in the
characteristic luminosity of galaxies but some evidence for a decrease in their
number densities between redshifts of 4 and 7. The ultraviolet luminosity
density of these samples is dominated by galaxies fainter than the
characteristic luminosity, and the HUDF reveals considerably more luminosity
than shallower surveys. The apparent ultraviolet luminosity density of galaxies
appears to decrease from redshifts of a few to redshifts greater than 6. The
highest redshift samples show that star formation was already vigorous at the
earliest epochs that galaxies have been observed, less than one billion years
after the Big Bang.Comment: 44 pages, 18 figures, to appear in the Astronomical Journal October
200
Preliminary Spectral Analysis of the Type II Supernova 1999em
We have calculated fast direct spectral model fits to two early-time spectra
of the Type-II plateau SN 1999em, using the SYNOW synthetic spectrum code. The
first is an extremely early blue optical spectrum and the second a combined HST
and optical spectrum obtained one week later. Spectroscopically this supernova
appears to be a normal Type II and these fits are in excellent agreement with
the observed spectra. Our direct analysis suggests the presence of enhanced
nitrogen. We have further studied these spectra with the full NLTE general
model atmosphere code PHOENIX. While we do not find confirmation for enhanced
nitrogen (nor do we rule it out), we do require enhanced helium. An even more
intriguing possible line identification is complicated Balmer and He I lines,
which we show falls naturally out of the detailed calculations with a shallow
density gradient. We also show that very early spectra such as those presented
here combined with sophisticated spectral modeling allows an independent
estimate of the total reddening to the supernova, since when the spectrum is
very blue, dereddening leads to changes in the blue flux that cannot be
reproduced by altering the ``temperature'' of the emitted radiation. These
results are extremely encouraging since they imply that detailed modeling of
early spectra can shed light on both the abundances and total extinction of SNe
II, the latter improving their utility and reliability as distance indicators.Comment: to appear in ApJ, 2000, 54
Analysis of the Type IIn Supernova 1998S: Effects of Circumstellar Interaction on Observed Spectra
We present spectral analysis of early observations of the Type IIn supernova
1998S using the general non-local thermodynamic equilibrium atmosphere code \tt
PHOENIX}. We model both the underlying supernova spectrum and the overlying
circumstellar interaction region and produce spectra in good agreement with
observations. The early spectra are well fit by lines produced primarily in the
circumstellar region itself, and later spectra are due primarily to the
supernova ejecta. Intermediate spectra are affected by both regions. A
mass-loss rate of order \msol yr is inferred
for a wind speed of 100-1000 \kmps. We discuss how future self-consistent
models will better clarify the underlying progenitor structure.Comment: to appear in ApJ, 2001, 54
Recuperação de plantas de batata `macaca´ contaminadas in vitro por meio da desinfestação com fegatex.
Novel Regioselective Synthesis of 1,3,4,5-Tetrasubstituted Pyrazoles and Biochemical Valuation on F1FO-ATPase and Mitochondrial Permeability Transition Pore Formation
An efficient, eco-compatible, and very cheap method for the construction of fully substituted pyrazoles (Pzs) via eliminative nitrilimine-alkene 1,3-dipolar cycloaddition (ENAC) reaction was developed in excellent yield and high regioselectivity. Enaminones and nitrilimines generated in situ were selected as dipolarophiles and dipoles, respectively. A deep screening of the employed base, solvent, and temperature was carried out to optimize reaction conditions. Recycling tests of ionic liquid were performed, furnishing efficient performance until six cycles. Finally, a plausible mechanism of cycloaddition was proposed. Then, the effect of three different structures of Pzs was evaluated on the F1FO-ATPase activity and mitochondrial permeability transition pore (mPTP) opening. The Pz derivatives’ titration curves of 6a, 6h, and 6o on the F1FO-ATPase showed a reduced activity of 86%, 35%, and 31%, respectively. Enzyme inhibition analysis depicted an uncompetitive mechanism with the typical formation of the tertiary complex enzyme-substrate-inhibitor (ESI). The dissociation constant of the ESI complex (Ki’) in the presence of the 6a had a lower order of magnitude than other Pzs. The pyrazole core might set the specific mechanism of inhibition with the F1FO-ATPase, whereas specific functional groups of Pzs might modulate the binding affinity. The mPTP opening decreased in Pz-treated mitochondria and the Pzs’ inhibitory effect on the mPTP was concentration-dependent with 6a and 6o. Indeed, the mPTP was more efficiently blocked with 0.1 mM 6a than with 1 mM 6a. On the contrary, 1 mM 6o had stronger desensitization of mPTP formation than 0.1 mM 6o. The F1FO-ATPase is a target of Pzs blocking mPTP formation
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