2,075 research outputs found
Can rates of ocean primary production and biological carbon export be related through their probability distributions?
© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Global Biogeochemical Cycles 32 (2018): 954-970, doi:10.1029/2017GB005797.We describe the basis of a theory for interpreting measurements of two key biogeochemical fluxesâprimary production by phytoplankton (p, ÎŒg C · Lâ1 · dayâ1) and biological carbon export from the surface ocean by sinking particles (f, mg C · mâ2 · dayâ1)âin terms of their probability distributions. Given that p and f are mechanistically linked but variable and effectively measured on different scales, we hypothesize that a quantitative relationship emerges between collections of the two measurements. Motivated by the many subprocesses driving production and export, we take as a null model that largeâscale distributions of p and f are lognormal. We then show that compilations of p and f measurements are consistent with this hypothesis. The compilation of p measurements is extensive enough to subregion by biome, basin, depth, or season; these subsets are also well described by lognormals, whose logâmoments sort predictably. Informed by the lognormality of both p and f we infer a statistical scaling relationship between the two quantities and derive a linear relationship between the logâmoments of their distributions. We find agreement between two independent estimates of the slope and intercept of this line and show that the distribution of f measurements is consistent with predictions made from the moments of the p distribution. These results illustrate the utility of a distributional approach to biogeochemical fluxes. We close by describing potential uses and challenges for the further development of such an approach.National Science Foundation Grant Number: OCE-1315201;
Simons Foundation Grant Numbers: 329108, 553242;
National Aeronautics and Space Administration Grant Numbers: NNX16AR47G, NNX16AR49
Using binary stars to bound the mass of the graviton
Interacting white dwarf binary star systems, including helium cataclysmic
variable (HeCV) systems, are expected to be strong sources of gravitational
radiation, and should be detectable by proposed space-based laser
interferometer gravitational wave observatories such as LISA. Several HeCV star
systems are presently known and can be studied optically, which will allow
electromagnetic and gravitational wave observations to be correlated.
Comparisons of the phases of a gravitational wave signal and the orbital light
curve from an interacting binary white dwarf star system can be used to bound
the mass of the graviton. Observations of typical HeCV systems by LISA could
potentially yield an upper bound on the inverse mass of the graviton as strong
as km (
eV), more than two orders of magnitude better than present solar system derived
bounds.Comment: 21 pages plus 4 figures; ReVTe
Double Neutron Star Systems and Natal Neutron Star Kicks
We study the four double neutron star systems found in the Galactic disk in
terms of the orbital characteristics of their immediate progenitors and the
natal kicks imparted to neutron stars. Analysis of the effect of the second
supernova explosion on the orbital dynamics, combined with recent results from
simulations of rapid accretion onto neutron stars lead us to conclude that the
observed systems could not have been formed had the explosion been symmetric.
Their formation becomes possible if kicks are imparted to the radio-pulsar
companions at birth. We identify the constraints imposed on the immediate
progenitors of the observed double neutron stars and calculate the ranges
within which their binary characteristics (orbital separations and masses of
the exploding stars) are restricted. We also study the dependence of these
limits on the magnitude of the kick velocity and the time elapsed since the
second explosion. For each of the double neutron stars, we derive a minimum
kick magnitude required for their formation, and for the two systems in close
orbits we find it to exceed 200km/s. Lower limits are also set to the
center-of-mass velocities of double neutron stars, and we find them to be
consistent with the current proper motion observations.Comment: 25 pages, 6 figs (9 parts), 4 tables, AASTeX, Accepted in Ap
An evolvable space telescope for future astronomical missions
Astronomical flagship missions after JWST will require affordable space telescopes and science instruments. Innovative spacecraft-electro-opto-mechanical system architectures matched to the science requirements are needed for observations for exoplanet characterization, cosmology, dark energy, galactic evolution formation of stars and planets, and many other research areas. The needs and requirements to perform this science will continue to drive us toward larger and larger apertures. Recent technology developments in precision station keeping of spacecraft, interplanetary transfer orbits, wavefront/sensing and control, laser engineering, macroscopic application of nano-technology, lossless optical designs, deployed structures, thermal management, interferometry, detectors and signal processing enable innovative telescope/system architectures with break-through performance. Unfortunately, NASAâs budget for Astrophysics is unlikely to be able to support the funding required for the 8 m to 16 m telescopes that have been studied as a follow-on to JWST using similar development/assembly approaches without decimating the rest of the Astrophysics Divisionâs budget. Consequently, we have been examining the feasibility of developing an âEvolvable Space Telescopeâ that would begin as a 3 to 4 m telescope when placed on orbit and then periodically be augmented with additional mirror segments, structures, and newer instruments to evolve the telescope and achieve the performance of a 16 m or larger space telescope. This paper reviews the approach for such a mission and identifies and discusses candidate architectures
Pulsar Kicks and Spin Tilts in the Close Double Neutron Stars PSR J0737-3039, PSR B1534+12 and PSR B1913+16
In view of the recent measurement of the scintillation velocity for PSR
J0737-3039, we examine the complete set of constraints imposed on the pulsar B
natal kicks (magnitude and orientation) and predict the most favorable pulsar
kick velocity and spin tilt for both isotropic and polar kicks. Our analysis
takes into account both currently unknown parameters: the orientation of the
orbital plane on the sky (Omega) and the radial component of the systemic
velocity (V_r). Assuming that the system's peculiar velocity is entirely due to
the second supernova explosion, we find that the system may have crossed the
Galactic plane multiple times since the birth of the second neutron star and
that the post-supernova peculiar velocity could have been as high as 1200km/s.
We also confirm the absolute lower and upper limits on the physical parameters
derived in our earlier study. For specific combinations of the two unknown
parameters Omega and V_r, however, we find much tighter constraints on the
pre-supernova binary configuration and natal kicks imparted to pulsar B, as
well as on the age of system. Once Omega is measured in the coming year, it
will be straightforward to use the results presented here to further constrain
the natal kicks and the spin-tilt predictions. We complete our comprehensive
study and derive similar constraints and spin-tilt predictions for PSR
B1534+12, where the only free parameter is V_r. Lastly, for PSR B1913+16, we
update the progenitor and kick constraints using the measured pulsar spin tilt
and allowing for Roche-lobe overflow from the progenitor of the pulsar
companion.Comment: Replaced Fig. 16 with corrected version. See ApJ 616, p. 414 for
high-resolution figures and notes added in proo
Gravitational waveforms with controlled accuracy
A partially first-order form of the characteristic formulation is introduced
to control the accuracy in the computation of gravitational waveforms produced
by highly distorted single black hole spacetimes. Our approach is to reduce the
system of equations to first-order differential form on the angular
derivatives, while retaining the proven radial and time integration schemes of
the standard characteristic formulation. This results in significantly improved
accuracy over the standard mixed-order approach in the extremely nonlinear
post-merger regime of binary black hole collisions.Comment: Revised version, published in Phys. Rev. D, RevTeX, 16 pages, 4
figure
From X-ray dips to eclipse: Witnessing disk reformation in the recurrent nova USco
The 10th recorded outburst of the recurrent eclipsing nova USco was observed
simultaneously in X-ray, UV, and optical by XMM-Newton on days 22.9 and 34.9
after outburst. Two full passages of the companion in front of the nova ejecta
were observed, witnessing the reformation of the accretion disk. On day 22.9,
we observed smooth eclipses in UV and optical but deep dips in the X-ray light
curve which disappeared by day 34.9, then yielding clean eclipses in all bands.
X-ray dips can be caused by clumpy absorbing material that intersects the line
of sight while moving along highly elliptical trajectories. Cold material from
the companion could explain the absence of dips in UV and optical light. The
disappearance of X-ray dips before day 34.9 implies significant progress in the
formation of the disk. The X-ray spectra contain photospheric continuum
emission plus strong emission lines, but no clear absorption lines. Both
continuum and emission lines in the X-ray spectra indicate a temperature
increase from day 22.9 to day 34.9. We find clear evidence in the spectra and
light curves for Thompson scattering of the photospheric emission from the
white dwarf. Photospheric absorption lines can be smeared out during scattering
in a plasma of fast electrons. We also find spectral signatures of resonant
line scattering that lead to the observation of the strong emission lines.
Their dominance could be a general phenomenon in high-inclination systems such
as Cal87.Comment: Submitted to ApJ. 16 pages, 16 figure
N-Methylimidazole Promotes The Reaction Of Homophthalic Anhydride With Imines
The addition of N-methylimidazole (NMI) to the reaction of homophthalic anhydride with imines such as pyridine-3-carboxaldehyde-N-trifluoroethylimine (9) reduces the amount of elimination byproduct and improves the yield of the formal cycloadduct, tetrahydroisoquinolonic carboxylate 10. Carboxanilides of such compounds are of interest as potential antimalarial agents. A mechanism that rationalizes the role of NMI is proposed, and a gram-scale procedure for the synthesis and resolution of 10 is also described
Sub-Subgiants in the Old Open Cluster M67?
We report the discovery of two spectroscopic binaries in the field of the old
open cluster M67 -- S1063 and S1113 -- whose positions in the color-magnitude
diagram place them approximately 1 mag below the subgiant branch. A ROSAT study
of M67 independently discovered these stars to be X-ray sources. Both have
proper-motion membership probabilities greater than 97%; precise center-of-mass
velocities are consistent with the cluster mean radial velocity. S1063 is also
projected within one core radius of the cluster center. S1063 is a single-lined
binary with a period of 18.396 days and an orbital eccentricity of 0.206. S1113
is a double-lined system with a circular orbit having a period of 2.823094
days. The primary stars of both binaries are subgiants. The secondary of S1113
is likely a 0.9 Mo main-sequence star, which implies a 1.3 Mo primary star. We
have been unable to explain securely the low apparent luminosities of the
primary stars; neither binary contain stars presently limited in radius by
their Roche lobes. We speculate that S1063 and S1113 may be the products of
close stellar encounters involving binaries in the cluster environment, and may
define alternative stellar evolutionary tracks associated with mass-transfer
episodes, mergers, and/or dynamical stellar exchanges
An evolvable space telescope for future astronomical missions 2015 update
In 2014 we presented a concept for an Evolvable Space Telescope (EST) that was assembled on orbit in 3 stages, growing from a 4x12 meter telescope in Stage 1, to a 12-meter filled aperture in Stage 2, and then to a 20-meter filled aperture in Stage 3. Stage 1 is launched as a fully functional telescope and begins gathering science data immediately after checkout on orbit. This observatory is then periodically augmented in space with additional mirror segments, structures, and newer instruments to evolve the telescope over the years to a 20-meter space telescope. In this 2015 update of EST we focus upon three items: 1) a restructured Stage 1 EST with three mirror segments forming an off-axis telescope (half a 12-meter filled aperture); 2) more details on the value and architecture of the prime focus instrument accommodation; and 3) a more in depth discussion of the essential in-space infrastructure, early ground testing and a concept for an International Space Station testbed called MoDEST. In addition to the EST discussions we introduce a different alternative telescope architecture: a Rotating Synthetic Aperture (RSA). This is a rectangular primary mirror that can be rotated to fill the UV-plane. The original concept was developed by Raytheon Space and Airborne Systems for non-astronomical applications. In collaboration with Raytheon we have begun to explore the RSA approach as an astronomical space telescope and have initiated studies of science and cost performance
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