2,961 research outputs found
Photon-weighted barycentric correction and its importance for precise radial velocities
When applying the barycentric correction to a precise radial velocity
measurement, it is common practice to calculate its value only at the
photon-weighted midpoint time of the observation instead of integrating over
the entire exposure. However, since the barycentric correction does not change
linearly with time, this leads to systematic errors in the derived radial
velocities. The typical magnitude of this second-order effect is of order 10 cm
s, but it depends on several parameters, e.g. the latitude of the
observatory, the position of the target on the sky, and the exposure time. We
show that there are realistic observing scenarios, where the errors can amount
to more than 1 ms. We therefore recommend that instruments operating in
this regime always record and store the exposure meter flux curve (or a similar
measure) to be used as photon-weights for the barycentric correction. In
existing data, if the flux curve is no longer available, we argue that
second-order errors in the barycentric correction can be mitigated by adding a
correction term assuming constant flux.Comment: 9 pages, 7 figures, accepted to MNRA
Controlling trapping potentials and stray electric fields in a microfabricated ion trap through design and compensation
Recent advances in quantum information processing with trapped ions have
demonstrated the need for new ion trap architectures capable of holding and
manipulating chains of many (>10) ions. Here we present the design and detailed
characterization of a new linear trap, microfabricated with scalable
complementary metal-oxide-semiconductor (CMOS) techniques, that is well-suited
to this challenge. Forty-four individually controlled DC electrodes provide the
many degrees of freedom required to construct anharmonic potential wells,
shuttle ions, merge and split ion chains, precisely tune secular mode
frequencies, and adjust the orientation of trap axes. Microfabricated
capacitors on DC electrodes suppress radio-frequency pickup and excess
micromotion, while a top-level ground layer simplifies modeling of electric
fields and protects trap structures underneath. A localized aperture in the
substrate provides access to the trapping region from an oven below, permitting
deterministic loading of particular isotopic/elemental sequences via
species-selective photoionization. The shapes of the aperture and
radio-frequency electrodes are optimized to minimize perturbation of the
trapping pseudopotential. Laboratory experiments verify simulated potentials
and characterize trapping lifetimes, stray electric fields, and ion heating
rates, while measurement and cancellation of spatially-varying stray electric
fields permits the formation of nearly-equally spaced ion chains.Comment: 17 pages (including references), 7 figure
DuraSeal Exact is a safe adjunctive treatment for durotomy in spine: Postapproval study
Study designA nonrandomized, two-armed prospective study.ObjectiveWater-tight dural closure is paramount to the prevention of cerebrospinal fluid (CSF) leakage and associated complications. Synthetic polyethylene glycol (PEG) hydrogel has been used as an adjunct to sutured dural repair; however, its expansion postoperatively is a concern for neurological complications. A low-swell formulation of PEG sealant was introduced as DuraSeal Exact Spine Sealant System (DESS). A Post-Approval Study was performed primarily to evaluate the safety and efficacy of DESS for spinal dural repair compared to current alternatives, in a large patient population, reflecting a real-world practice.MethodsA total of 36 sites in the United States enrolled 429 patients treated with DESS as an adjunct to dural repair in the spinal sealant group and 406 patients treated with all other modalities in the control arm, from October 2011 to June 2016. The primary endpoint was the incidence of CSF leak within 90 days of operation. The secondary endpoints evaluated were deep surgical site infection and neurological serious adverse events.ResultsThe CSF leakage in the DESS group (6.6%) was not significantly different from the control group (6.5%) (p = .83), and there was no significant difference in the time to first leak. The two groups had no significant differences in deep surgical site infection (1.6% versus control 2.1%, p = .61) or proportion of subjects with neurological serious adverse events (2.9% versus control 1.6%, p = .516).ConclusionsDuraSeal Exact Spinal Sealant is safe when compared to current alternatives for spinal dural repair
Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants
We report precision Doppler measurements of three intermediate-mass subgiants
from Lick and Keck Observatories. All three stars show variability in their
radial velocities consistent with planet-mass companions in Keplerian orbits.
We find a planet with a minimum mass of 2.5 Mjup in a 351.5 day orbit around HD
192699, a planet with a minimum mass of 2.0 Mjup in a 341.1 day orbit around HD
210702, and a planet with a minimum mass of 0.61 Mjup in a 297.3 day orbit
around HD 175541. Stellar mass estimates from evolutionary models indicate that
all of these stars were formerly A-type dwarfs with masses ranging from 1.65 to
1.85 Msun. These three long-period planets would not have been detectable
during their stars' main-sequence phases due to the large rotational velocities
and stellar jitter exhibited by early-type dwarfs. There are now 9 "retired"
(evolved) A-type stars (Mstar > 1.6 Msun) with known planets. All 9 planets
orbit at distances a \geq 0.78 AU, which is significantly different than the
semimajor axis distribution of planets around lower-mass stars. We examine the
possibility that the observed lack of close-in planets is due to engulfment by
their expanding host stars, but we find that this explanation is inadequate
given the relatively small stellar radii of K giants (Rstar < 32 Rsun = 0.15
AU) and subgiants (Rstar < 7 Rsun = 0.03 AU). Instead, we conclude that planets
around intermediate-mass stars reside preferentially beyond ~0.8 AU, which may
be a reflection of different formation and migration histories of planets
around A-type stars.Comment: 31 pages, 9 figures, 6 tables, ApJ accepted, corrected minor typo
Retired A Stars: The Effect of Stellar Evolution on the Mass Estimates of Subgiants
Doppler surveys have shown that the occurrence rate of Jupiter-mass planets
appears to increase as a function of stellar mass. However, this result depends
on the ability to accurately measure the masses of evolved stars. Recently,
Lloyd (2011) called into question the masses of subgiant stars targeted by
Doppler surveys. Lloyd argues that very few observable subgiants have masses
greater than 1.5 Msun, and that most of them have masses in the range 1.0-1.2
Msun. To investigate this claim, we use Galactic stellar population models to
generate an all-sky distribution of stars. We incorporate the effects that make
massive subgiants less numerous, such as the initial mass function and
differences in stellar evolution timescales. We find that these effects lead to
negligibly small systematic errors in stellar mass estimates, in contrast to
the roughly 50% errors predicted by Lloyd. Additionally, our simulated target
sample does in fact include a significant fraction of stars with masses greater
than 1.5 Msun, primarily because the inclusion of an apparent magnitude limit
results in a Malmquist-like bias toward more massive stars, in contrast to the
volume-limited simulations of Lloyd. The magnitude limit shifts the mean of our
simulated distribution toward higher masses and results in a relatively smaller
number of evolved stars with masses in the range 1.0-1.2 Msun. We conclude
that, within the context of our present-day understanding of stellar structure
and evolution, many of the subgiants observed in Doppler surveys are indeed as
massive as main-sequence A stars.Comment: Accepted to ApJ, 5 pages, 3 figures; changed title, reworded
introduction and conclusion
An Eccentric Hot Jupiter Orbiting the Subgiant HD 185269
We report the detection of a Jupiter-mass planet in a 6.838 day orbit around
the 1.28 solar mass subgiant HD 185269. The eccentricity of HD 185269b (e =
0.30) is unusually large compared to other planets within 0.1 AU of their
stars. Photometric observations demonstrate that the star is constant to
+/-0.0001 mag on the radial velocity period, strengthening our interpretation
of a planetary companion. This planet was detected as part of our radial
velocity survey of evolved stars located on the subgiant branch of the H-R
diagram--also known as the Hertzsprung Gap. These stars, which have masses
between 1.2 and 2.5 solar masses, play an important role in the investigation
of the frequency of extrasolar planets as a function of stellar mass.Comment: 18 pages, 4 figures, 3 tables, ApJ in press (scheduled for Dec 2006,
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