265 research outputs found
The Lyman-alpha Forest at z~4: Keck HIRES Observations of Q 0000-26
This paper describes a study of the Lyman-alpha forest absorption clouds
along the quasar sightline Q0000-26 (zem=4.1). The spectrum was obtained with
the High Resolution Spectrometer on the 10m Keck telescope. We derive accurate
H I column density and Doppler width distributions for the clouds from Voigt
profile fitting. We also analyze simulated Lyman-alpha forest spectra of
matching characteristics in order to gauge the effects of line
blending/blanketing and noise in the data. The results are compared with
similar studies at lower redshifts in order to study any possible evolution in
the clouds' properties. We also estimate the mean intensity of the UV
background at z=4 from an analysis of the proximity effect.Comment: plain TeX containing 23 PS pages, 3 PS tables, and 9 PS figures, ApJ,
Dec 1, 1996 issue replacing an earlier version which contains an corrupted
table
The Del1 deposition domain can immobilize 3α-hydroxysteroid dehydrogenase in the extracellular matrix without interfering with enzymatic activity
Developing methods that result in targeting of therapeutic molecules in gene therapies to target tissues has importance, as targeting can increase efficacy and decrease off target-side-effects. Work from my laboratory previously showed that the extracellular matrix protein Del1 is organized in the extracellular matrix (ECM) via the Del1 deposition domain (DDD). In this work, a fusion protein with DDD was made to assay the ability to immobilize an enzyme without disrupting enzymatic function. A prostatic cancer-derived cell line LNCap that grows in an androgen-dependent manner was used with 3α-hydroxysteroid dehydrogenase (3 αHD), which catalyzes dihydrotestosterone (DHT). Plasmids encoding a 3αHD:DDD fusion were generated and transfected into cultured cells. The effects of 3αHD immobilized in the ECM by the DDD were evaluated by monitoring growth of LNCap cells and DHT concentrations. It was demonstrated that the DDD could immobilize an enzyme in the ECM without interfering with function
The Aspherical Properties of the Energetic Type Ic SN 2002ap as Inferred from its Nebular Spectra
The nebular spectra of the broad-lined, SN 1998bw-like Type Ic SN 2002ap are
studied by means of synthetic spectra. Two different modelling techniques are
employed. In one technique, the SN ejecta are treated as a single zone, while
in the other a density and abundance distribution in velocity is used from an
explosion model. In both cases, heating caused by gamma-ray and positron
deposition is computed (in the latter case using a Monte Carlo technique to
describe the propagation of gamma-rays and positrons), as is cooling via
forbidden-line emission. The results are compared, and although general
agreement is found, the stratified models are shown to reproduce the observed
line profiles much more accurately than the single-zone model. The explosion
produced ~ 0.1 Msun of 56Ni. The distribution in velocity of the various
elements is in agreement with that obtained from the early-time models, which
indicated an ejected mass of ~ 2.5 Msun with a kinetic energy of 4 x 10^{51}
erg. Nebular spectroscopy confirms that most of the ejected mass (~ 1.2 Msun)
was oxygen. The presence of an oxygen-rich inner core, combined with that of
56Ni at high velocities as deduced from early-time models, suggests that the
explosion was asymmetric, especially in the inner part.Comment: 24 pages, 6 figures, 2 Tables. Accepted by the Astrophysical Journa
The Optical/Near-Infrared Light Curves of SN 2002ap for the First 140 Days after Discovery
Supernova (SN) 2002ap in M74 was observed in the bands for the
first 40 days following its discovery (2002 January 29) until it disappeared
because of solar conjunction, and then in June after it reappeared. The
magnitudes and dates of peak brightness in each band were determined. While the
rate of increase of the brightness before the peak is almost independent of
wavelength, the subsequent rate of decrease becomes smaller with wavelength
from the to the band, and is constant at wavelengths beyond . The
photometric evolution is faster than in the well-known ``hypernovae''
SNe~1998bw and 1997ef, indicating that SN 2002ap ejected less mass. The
bolometric light curve of SN 2002ap for the full period of observations was
constructed. The absolute magnitude is found to be much fainter than that of SN
1998bw, but is similar to that of SN 1997ef, which lies at the faint end of the
hypernova population. The bolometric light curve at the early epochs was best
reproduced with the explosion of a C+O star that ejects 2.5~M_\sun with
kinetic energy . A comparison of the
predicted brightness of SN 2002ap with that observed after solar conjunction
may imply that -ray deposition at the later epochs was more efficient
than in the model. This may be due to an asymmetric explosion.Comment: 15 pages, 6 figures, quality of figure1 is reduced for smaller
filesize, accepted for publication in Ap
A low upper-limit on the lithium isotope ratio in HD140283
We have obtained a high-S/N (900-1100), high-resolving-power (R=95000)
spectrum of the metal-poor subgiant HD 140283 in an effort to measure its
6Li/7Li isotope ratio. From a 1-D atmospheric analysis, we find a value
consistent with zero, 6Li/7Li = 0.001, with an upper limit of 6Li/7Li < 0.026.
This measurement supersedes an earlier detection (0.040 +/- 0.015(1sigma)) by
one of the authors. HD 140283 provides no support for the suggestion that
Population II stars may preserve their 6Li on the portion of the subgiant
branch where 7Li is preserved. However, this star does not defeat the
suggestion either; being at the cool end of subgiant branch of the Spite
plateau, it may be sufficiently cool that 6Li depletion has already set in, or
the star may be sufficiently metal poor that little Galactic production of 6Li
had occurred. Continued investigation of other subgiants is necessary to test
the idea. We also consider the implications of the HD 140283 upper limit in
conjunction with other measurements for models of 6Li production by cosmic rays
from supernovae and structure formation shocks.Comment: 8 pages, 4 figures; accepted for publication in Astronomy and
Astrophysic
Chemical composition of carbon-rich, very metal-poor subgiant LP625-44 observed with the Subaru/HDS
We have obtained a high resolution (R~90,000) spectrum of the carbon- and
s-process-element-rich, very metal-poor ([Fe/H]=-2.7) subgiant LP625-44, as
well as that of HD140283 (a metal-poor subgiant with normal abundance ratio)
for comparison, with the High Dispersion Spectrograph (HDS) for the Subaru
Telescope for detailed abundance study. The oxygen abundance derived from the O
I triplet around 7770A is uncertain, but the excess of oxygen in LP625-44 seems
remarkable (perhaps by nearly a factor 10), in comparison with that of HD140283
derived from the same lines. The Na enhancement in LP625-44 is by about a
factor 50, suggesting hydrogen burning in the 22Ne-rich layer in an asymptotic
giant branch star which produces the abundance pattern of this object. In our
new spectrum of LP625-44, the Pb I lambda 3683A line has been detected, as well
as the Pb I lambda 4057A line which has already been studied, confirming the Pb
abundance (log epsilon(Pb)~1.9) derived by the previous work. The abundance
ratio of s-process elements at the second peak (e.g., La, Ce and Nd) to that at
the third peak (Pb) in LP 625-44 is significantly higher (by a factor 5) than
that in other three s-process element-rich objects recently studied by van Eck
et al.. Recent theoretical works have modeled the s-process nucleosynthesis in
the radiative layer of asymptotic giant branch stars in the inter-pulse phase,
and the above results means that these processes produced a large scatter in
the abundance ratios. Another possiblity is that different processes (e.g.,
s-process nucleosynthesis during thermal pulses) have contributed to heavy
elements in the early Galaxy.Comment: 65 pages, 11 figures, to appear in PAS
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