228 research outputs found
13C-Methyl isocyanide as an NMR probe for cytochrome P450 active site
The cytochromes P450 (CYPs) play a central role in many biologically important oxidation reactions, including the metabolism of drugs and other xenobiotic compounds. Because they are often assayed as both drug targets and anti-targets, any tools that provide: (a) confirmation of active site binding and (b) structural data, would be of great utility, especially if data could be obtained in reasonably high throughput. To this end, we have developed an analog of the promiscuous heme ligand, cyanide,with a 13CH3-reporter attached. This 13C-methyl isocyanide ligand binds to bacterial (P450cam) and membrane-bound mammalian (CYP2B4) CYPs. It can be used in a rapid 1D experiment to identify binders, and provides a qualitative measure of structural changes in the active site
The XO Planetary Survey Project - Astrophysical False Positives
Searches for planetary transits find many astrophysical false positives as a
by-product. There are four main types analyzed in the literature: a
grazing-incidence eclipsing binary star, an eclipsing binary star with a small
radius companion star, a blend of one or more stars with an unrelated eclipsing
binary star, and a physical triple star system. We present a list of 69
astrophysical false positives that had been identified as candidates of
transiting planets of the on-going XO survey. This list may be useful in order
to avoid redundant observation and characterization of these particular
candidates independently identified by other wide-field searches for transiting
planets. The list may be useful for those modeling the yield of the XO survey
and surveys similar to it. Subsequent observations of some of the listed stars
may improve mass-radius relations, especially for low-mass stars. From the
candidates exhibiting eclipses, we report three new spectroscopic double-line
binaries and give mass function estimations for 15 single lined spectroscopic
binaries.Comment: 13 pages, 4 figures, accepted to ApJ
Current management of children with acute otitis media: a feasibility survey for a pragmatic study
NICMOS Observations of the Transiting Hot Jupiter XO-1b
We refine the physical parameters of the transiting hot Jupiter planet XO-1b
and its stellar host XO-1 using HST NICMOS observations. XO-1b has a radius
Rp=1.21+/-0.03 RJup, and XO-1 has a radius Rs=0.94+/-0.02 RSun, where the
uncertainty in the mass of XO-1 dominates the uncertainty of Rp and Rs. There
are no significant differences in the XO-1 system properties between these
broad-band NIR observations and previous determinations based upon ground-based
optical observations. We measure two transit timings from these observations
with 9 s and 15 s precision. As a residual to a linear ephemeris model, there
is a 2.0 sigma timing difference between the two HST visits that are separated
by 3 transit events (11.8 days). These two transit timings and additional
timings from the literature are sufficient to rule out the presence of an Earth
mass planet orbiting in 2:1 mean motion resonance coplanar with XO-1b. We
identify and correct for poorly understood gain-like variations present in
NICMOS time series data. This correction reduces the effective noise in time
series photometry by a factor of two, for the case of XO-1.Comment: 13 pages, 8 figures, submitted to Ap
XO-5b: A Transiting Jupiter-sized Planet With A Four Day Period
The star XO-5 (GSC 02959-00729, V=12.1, G8V) hosts a Jupiter-sized,
Rp=1.15+/-0.12 Rjup, transiting extrasolar planet, XO-5b, with an orbital
period of P=4.187732+/-0.00002 days. The planet mass (Mp=1.15+/-0.08 Mjup) and
surface gravity (gp=22+/-5 m/s^2) are significantly larger than expected by
empirical Mp-P and Mp-P-[Fe/H] relationships. However, the deviation from the
Mp-P relationship for XO-5b is not large enough to suggest a distinct type of
planet as is suggested for GJ 436b, HAT-P-2b, and XO-3b. By coincidence XO-5
overlies the extreme H I plume that emanates from the interacting galaxy pair
NGC 2444/NGC 2445 (Arp 143).Comment: 10 pages, 9 Figures, Submitted to Ap
XO-3b: A Massive Planet in an Eccentric Orbit Transiting an F5V Star
We report the discovery of a massive (Mpsini = 13.02 +/- 0.64 Mjup; total
mass 13.25 +/- 0.64 Mjup), large (1.95 +/- 0.16 Rjup) planet in a transiting,
eccentric orbit (e = 0.260 +/- 0.017) around a 10th magnitude F5V star in the
constellation Camelopardalis. We designate the planet XO-3b, and the star XO-3,
also known as GSC 03727-01064. The orbital period of XO-3b is 3.1915426 +/-
0.00014 days. XO-3 lacks a trigonometric distance; we estimate its distance to
be 260 +/- 23 pc. The radius of XO-3 is 2.13 +/- 0.21 Rsun, its mass is 1.41
+/- 0.08 Msun, its vsini = 18.54 +/- 0.17 km/s, and its metallicity is [Fe/H] =
-0.177 +/- 0.027. This system is unusual for a number of reasons. XO-3b is one
of the most massive planets discovered around any star for which the orbital
period is less than 10 days. The mass is near the deuterium burning limit of 13
Mjup, which is a proposed boundary between planets and brown dwarfs. Although
Burrows et al. (2001) propose that formation in a disk or formation in the
interstellar medium in a manner similar to stars is a more logical way to
differentiate planets and brown dwarfs, our current observations are not
adequate to address this distinction. XO-3b is also unusual in that its
eccentricity is large given its relatively short orbital period. Both the
planetary radius and the inclination are functions of the spectroscopically
determined stellar radius. Analysis of the transit light curve of XO-3b
suggests that the spectroscopically derived parameters may be over estimated.
Though relatively noisy, the light curves favor a smaller radius in order to
better match the steepness of the ingress and egress. The light curve fits
imply a planetary radius of 1.25 +/- 0.15 Rjup, which would correspond to a
mass of 12.03 +/- 0.46 Mjup.Comment: 26 pages, 10 figures. Accepted by ApJ. Current version has several
small corrections as a result of a bug in the fitting softwar
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