4,170 research outputs found
Revised Orbit and Transit Exclusion for HD 114762b
Transiting planets around bright stars have allowed the detailed follow-up
and characterization of exoplanets, such as the study of exoplanetary
atmospheres. The Transit Ephemeris Refinement and Monitoring Survey (TERMS) is
refining the orbits of the known exoplanets to confirm or rule out both transit
signatures and the presence of additional companions. Here we present results
for the companion orbiting HD 114762 in an eccentric 84 day orbit. Radial
velocity analysis performed on 19 years of Lick Observatory data constrain the
uncertainty in the predicted time of mid-transit to ~5 hours, which is less
than the predicted one-half day transit duration. We find no evidence of
additional companions in this system. New photometric observations with one of
our Automated Photoelectric Telescopes (APTs) at Fairborn Observatory taken
during a revised transit time for companion b, along with 23 years of nightly
automated observations, allow us to rule out on-time central transits to a
limit of ~0.001 mag. Early or late central transits are ruled out to a limit of
~0.002 mag, and transits with half the duration of a central transit are ruled
out to a limit of ~0.003 mag.Comment: 5 pages, 2 figures, accepted for publication in ApJ
Femoroacetabular Impingement as a Complication of Acetabular Fracture Fixation
Case We present the case of a thirteen-year-old female who sustained a posterior wall acetabular fracture dislocation. She underwent urgent closed reduction and subsequent uncomplicated open reduction and internal fixation. Post reduction computed tomography demonstrated a concentrically reduced hip joint with no evidence of femoroacetabular impingement (FAI). She subsequently healed her fracture and returned to running activities; however, one year later presented with aching pain in her thigh. Radiographs demonstrated the development of a large osseous prominence on her anterolateral femoral neck consistent with femoroacetabular impingement. Based on these findings she was evaluated by a hip preservation specialist. She subsequently underwent successful hip arthroscopy for labral repair and femoral osteochondroplasty. She was eventually able to return to running sports with little pain. Summary We present a case of FAI presenting as a complication of acetabular fracture fixation. This should be discussed with patients presenting with traumatic hip dislocations as a possible complication of surgical fixation or possibly of the injury itself
Limits on Stellar Companions to Exoplanet Host Stars With Eccentric Planets
Though there are now many hundreds of confirmed exoplanets known, the
binarity of exoplanet host stars is not well understood. This is particularly
true of host stars which harbor a giant planet in a highly eccentric orbit
since these are more likely to have had a dramatic dynamical history which
transferred angular momentum to the planet. Here we present observations of
four exoplanet host stars which utilize the excellent resolving power of the
Differential Speckle Survey Instrument (DSSI) on the Gemini North telescope.
Two of the stars are giants and two are dwarfs. Each star is host to a giant
planet with an orbital eccentricity > 0.5 and whose radial velocity data
contain a trend in the residuals to the Keplerian orbit fit. These observations
rule out stellar companions 4-8 magnitudes fainter than the host star at
passbands of 692nm and 880nm. The resolution and field-of-view of the
instrument result in exclusion radii of 0.05-1.4 arcsecs which excludes stellar
companions within several AU of the host star in most cases. We further provide
new radial velocities for the HD 4203 system which confirm that the linear
trend previously observed in the residuals is due to an additional planet.
These results place dynamical constraints on the source of the planet's
eccentricities, constraints on additional planetary companions, and informs the
known distribution of multiplicity amongst exoplanet host stars.Comment: 10 pages, 7 figures, 2 tables, accepted to Ap
Two Jupiter-Mass Planets Orbiting HD 154672 and HD 205739
We report the detection of the first two planets from the N2K Doppler planet
search program at the Magellan telescopes. The first planet has a mass of M sin
i = 4.96 M_Jup and is orbiting the G3 IV star HD154672 with an orbital period
of 163.9 days. The second planet is orbiting the F7 V star HD205739 with an
orbital period of 279.8 days and has a mass of M sin i = 1.37 M_Jup. Both
planets are in eccentric orbits, with eccentricities e = 0.61 and e = 0.27,
respectively. Both stars are metal rich and appear to be chromospherically
inactive, based on inspection of their Ca II H and K lines. Finally, the best
Keplerian model fit to HD205739b shows a trend of 0.0649 m/s/day, suggesting
the presence of an additional outer body in that system.Comment: 16 pages, 5 figures, accepted for publication on A
The Habitable-Zone Planet Finder: A Stabilized Fiber-Fed NIR Spectrograph for the Hobby-Eberly Telescope
We present the scientific motivation and conceptual design for the recently
funded Habitable-zone Planet Finder (HPF), a stabilized fiber-fed near-infrared
(NIR) spectrograph for the 10 meter class Hobby-Eberly Telescope (HET) that
will be capable of discovering low mass planets around M dwarfs. The HPF will
cover the NIR Y & J bands to enable precise radial velocities to be obtained on
mid M dwarfs, and enable the detection of low mass planets around these stars.
The conceptual design is comprised of a cryostat cooled to 200K, a dual
fiber-feed with a science and calibration fiber, a gold coated mosaic echelle
grating, and a Teledyne Hawaii-2RG (H2RG) NIR detector with a 1.7m cutoff.
A uranium-neon hollow-cathode lamp is the baseline wavelength calibration
source, and we are actively testing laser frequency combs to enable even higher
radial velocity precision. We will present the overall instrument system design
and integration with the HET, and discuss major system challenges, key choices,
and ongoing research and development projects to mitigate risk. We also discuss
the ongoing process of target selection for the HPF survey.Comment: 14 pages, 9 figures. To appear in the proceedings of the SPIE 2012
Astronomical Instrumentation and Telescopes conferenc
Performance of second order particle-in-cell methods on modern many-core architectures
The emergence of modern many-core architectures that offer an extreme level of parallelism makes methods that were previously infeasible due to computational expense now achievable. Particle-in-Cell (PIC) codes often fail to fully leverage this increased performance
potential due to their high use of memory bandwidth. The use of higher order PIC methods may offer a solution to this by improving simulation accuracy significantly for an increase in computational intensity when compared to their first order counterparts. This greater expense is accompanied with only a minor increase in the amount of memory throughput required during the simulation.
In this presentation we will show the performance of a second order PIC algorithm. Our implementation uses second order finite elements and particles that are represented with a collection of surrounding ghost particles. These ghost particles each have associated weights
and offsets around the true particle position and therefore represent a charge distribution.
We test our PIC implementation against a first order algorithm on various modern compute architectures including Intel’s Knights Landing (KNL) and NVIDIA’s Tesla P100.
Our preliminary results show the viability of second order methods for PIC applications on these architectures when compared to previous generations of many-core hardware.
Specifically, we see an order of magnitude improvement in performance for second order methods between the Pascal and Kepler GPU architectures, despite only a 4× improvement in theoretical peak performance between the architectures. Although these initial results
show a large increase in runtime over first order methods, we hope to be able to show improved scaling behaviour and increased simulation accuracy in the future
The roles of transcription and genotoxins underlying p53 mutagenesis in vivo
Transcription drives supercoiling which forms and stabilizes single-stranded (ss) DNA secondary structures with loops exposing G and C bases that are intrinsically mutable and vulnerable to non-enzymatic hydrolytic reactions. Since many studies in prokaryotes have shown direct correlations between the frequencies of transcription and mutation, we conducted in silico analyses using the computer program, mfg, which simulates transcription and predicts the location of known mutable bases in loops of high-stability secondary structures. Mfg analyses of the p53 tumor suppressor gene predicted the location of mutable bases and mutation frequencies correlated with the extent to which these mutable bases were exposed in secondary structures. In vitro analyses have now confirmed that the 12 most mutable bases in p53 are in fact located in predicted ssDNA loops of these structures. Data show that genotoxins have two independent effects on mutagenesis and the incidence of cancer: Firstly, they activate p53 transcription, which increases the number of exposed mutable bases and also increases mutation frequency. Secondly, genotoxins increase the frequency of G-to-T transversions resulting in a decrease in G-to-A and C mutations. This precise compensatory shift in the \u27fate\u27 of G mutations has no impact on mutation frequency. Moreover, it is consistent with our proposed mechanism of mutagenesis in which the frequency of G exposure in ssDNA via transcription is rate limiting for mutation frequency in vivo
Climate-driven changes in the predictability of seasonal precipitation
Climate-driven changes in precipitation amounts and their seasonal variability are expected in many continental-scale regions during the remainder of the 21st century. However, much less is known about future changes in the predictability of seasonal precipitation, an important earth system property relevant for climate adaptation. Here, on the basis of CMIP6 models that capture the present-day teleconnections between seasonal precipitation and previous-season sea surface temperature (SST), we show that climate change is expected to alter the SST-precipitation relationships and thus our ability to predict seasonal precipitation by 2100. Specifically, in the tropics, seasonal precipitation predictability from SSTs is projected to increase throughout the year, except the northern Amazonia during boreal winter. Concurrently, in the extra-tropics predictability is likely to increase in central Asia during boreal spring and winter. The altered predictability, together with enhanced interannual variability of seasonal precipitation, poses new opportunities and challenges for regional water management
Improved Orbital Parameters and Transit Monitoring for HD 156846b
HD 156846b is a Jovian planet in a highly eccentric orbit (e = 0.85) with a
period of 359.55 days. The pericenter passage at a distance of 0.16 AU is
nearly aligned to our line of sight, offering an enhanced transit probability
of 5.4% and a potentially rich probe of the dynamics of a cool planetary
atmosphere impulsively heated during close approach to a bright star (V = 6.5).
We present new radial velocity (RV) and photometric measurements of this star
as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). The
RV measurements from Keck-HIRES reduce the predicted transit time uncertainty
to 20 minutes, an order of magnitude improvement over the ephemeris from the
discovery paper. We photometrically monitored a predicted transit window under
relatively poor photometric conditions, from which our non-detection does not
rule out a transiting geometry. We also present photometry that demonstrates
stability at the millimag level over its rotational timescale.Comment: 7 pages, 4 figures, accepted for publication in Ap
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