7,334 research outputs found
On the Fundamental Mass-Period Functions of Extrasolar Planets
Employing a catalog of 175 extrasolar planets (exoplanets) detected by the
Doppler-shift method, we constructed the independent and coupled mass-period
functions. It is the first time in this field that the selection effect is
considered in the coupled mass-period functions. Our results are consistent
with those in Tabachnik and Tremaine (2002) with the major differences that we
obtain a flatter mass function but a steeper period function. Moreover, our
coupled mass-period functions show that about 2.5 percent of stars would have a
planet with mass between Earth Mass and Neptune Mass, and about 3 percent of
stars would have a planet with mass between Neptune Mass and Jupiter Mass.Comment: Accepted by ApJ Supplement Series in Nov. 2009, Acknowledgment added
in Dec. 2009, a Reference-Based Catalog of Exoplanets can be obtained
electronically from Appendix A of the latex file or from the authors for
further studies
A Super-Earth Transiting a Naked-Eye Star
We have detected transits of the innermost planet "e" orbiting 55 Cnc
(V=6.0), based on two weeks of nearly continuous photometric monitoring with
the MOST space telescope. The transits occur with the period (0.74 d) and phase
that had been predicted by Dawson & Fabrycky, and with the expected duration
and depth for the crossing of a Sun-like star by a hot super-Earth. Assuming
the star's mass and radius to be 0.963_{-0.029}^{+0.051} M_sun and 0.943 +/-
0.010 R_sun, the planet's mass, radius, and mean density are 8.63 +/- 0.35
Mearth, 2.00 +/- 0.14 Rearth, and 5.9_{-1.1}^{+1.5} g/cm^3. The mean density is
comparable to that of Earth, despite the greater mass and consequently greater
compression of the interior of 55 Cnc e. This suggests a rock-iron composition
supplemented by a significant mass of water, gas, or other light elements.
Outside of transits, we detected a sinusoidal signal resembling the expected
signal due to the changing illuminated phase of the planet, but with a full
range (168 +/- 70 ppm) too large to be reflected light or thermal emission.
This signal has no straightforward interpretation and should be checked with
further observations. The host star of 55 Cnc e is brighter than that of any
other known transiting planet, which will facilitate future investigations.Comment: ApJ Letters, in press (v3) Minor changes/clarifications; (v2) Revised
after fixing an error in the data reduction pipeline; for details see
http://web.mit.edu/~jwinn/www/55cnc_response.tx
Fundamental Performance of a Dispersed Fixed Delay Interferometer In Searching For Planets Around M Dwarfs
We present a new method to calculate fundamental Doppler measurement limits
with a dispersed fixed-delay interferometer (DFDI) in the near infrared
wavelength region for searching for exoplanets around M dwarfs in the coming
decade. It is based on calculating the Q factor, a measure of flux-normalized
Doppler sensitivity in the fringing spectra created with DFDI. We calculate the
Q factor as a function of spectral resolution R, stellar projected rotational
velocity V sini, stellar effective temperature T_eff and optical path
difference (OPD) of the interferometer. We also compare the DFDI Q factor to
that for the popular cross-dispersed echelle spectrograph method (the direct
echelle (DE) method). Given the IR Doppler measurement is likely to be
detector-limited for a while, we introduce new merit functions, which is
directly related to photon-limited RV uncertainty, to evaluate Doppler
performance with the DFDI and DE methods. We find that DFDI has strength in
wavelength coverage and multi-object capability over the DE for a limited
detector resource. We simulate the performance of the InfraRed Exoplanet
Tracker (IRET) based on the DFDI design, being considered for the next
generation IR Doppler measurements. The predicted photon-limited RV uncertainty
suggests that IRET is capable of detecting Earth-like exoplanets in habitable
zone around nearby bright M dwarfs if they exist. A new method is developed to
quantitatively estimate the influence of telluric lines on RV uncertainty. Our
study shows that photon-limited RV uncertainty can be reached if 99% of the
strength of telluric lines can be removed from the measured stellar spectra. At
low to moderate levels of telluric line strength removal (50% to 90%), the
optimal RV uncertainty is typically a factor of 2-3 times larger than
photon-limited RV uncertainty.Comment: 43 pages, 20 figures, 6 tables. Accepted by Ap
R-parity Violation and Semileptonic Decays of B-meson
We investigate the effects of R-parity violation on the semileptonic decays
of B-meson in the minimal supersymmetric standard model with explicit R-parity
violation and discuss its physical implications. We find that the semileptonic
decays of B-meson can be largely affected by the R-parity violation.Comment: 10 pages, LaTex file, no figure. References and a table are added.
Tables are improve
JPSS-1 VIIRS Radiometric Characterization and Calibration Based on Pre-Launch Testing
The Visible Infrared Imaging Radiometer Suite (VIIRS) on-board the first Joint Polar Satellite System (JPSS) completed its sensor level testing on December 2014. The JPSS-1 (J1) mission is scheduled to launch in December 2016, and will be very similar to the Suomi-National Polar-orbiting Partnership (SNPP) mission. VIIRS instrument has 22 spectral bands covering the spectrum between 0.4 and 12.6 m. It is a cross-track scanning radiometer capable of providing global measurements twice daily, through observations at two spatial resolutions, 375 m and 750 m at nadir for the imaging and moderate bands, respectively. This paper will briefly describe J1 VIIRS characterization and calibration performance and methodologies executed during the pre-launch testing phases by the government independent team to generate the at-launch baseline radiometric performance and the metrics needed to populate the sensor data record (SDR) Look-Up-Tables (LUTs). This paper will also provide an assessment of the sensor pre-launch radiometric performance, such as the sensor signal to noise ratios (SNRs), radiance dynamic range, reflective and emissive bands calibration performance, polarization sensitivity, spectral performance, response-vs-scan (RVS), and scattered light response. A set of performance metrics generated during the pre-launch testing program will be compared to both the VIIRS sensor specification and the SNPP VIIRS pre-launch performance
A Novel Non-Intrusive Method to Resolve the Thermal-Dome-Effect of Pyranometers: Radiometric Calibration and Implications
Traditionally the calibration equation for pyranometers assumes that the measured solar irradiance is solely proportional to the thermopile's output voltage; therefore only a single calibration factor is derived. This causes additional measurement uncertainties because it does not capture sufficient information to correctly account for a pyranometer's thermal effect. In our updated calibration equation, temperatures from the pyranometer's dome and case are incorporated to describe the instrument's thermal behavior, and a new set of calibration constants are determined, thereby reducing measurement uncertainties. In this paper, we demonstrate why a pyranometer's uncertainty using the traditional calibration equation is always larger than a-few-percent, but with the new approach can become much less than 1% after the thermal issue is resolved. The highlighted calibration results are based on NIST-traceable light sources under controlled laboratory conditions. The significance of the new approach lends itself to not only avoiding the uncertainty caused by a pyranometer's thermal effect but also the opportunity to better isolate and characterize other instrumental artifacts, such as angular response and non-linearity of the thermopile, to further reduce additional uncertainties. We also discuss some of the implications, including an example of how the thermal issue can potentially impact climate studies by evaluating aerosol's direct-radiative effect using field measurements with and without considering the pyranometer's thermal effect. The results of radiative transfer model simulation show that a pyranometer's thermal effect on solar irradiance measurements at the surface can be translated into a significant alteration of the calculated distribution of solar energy inside the column atmosphere
Evolution of Planetary Systems in Resonance
We study the time evolution of two protoplanets still embedded in a
protoplanetary disk. The results of two different numerical approaches are
presented and compared. In the first approach, the motion of the disk material
is computed with viscous hydrodynamical simulations, and the planetary motion
is determined by N-body calculations including exactly the gravitational forces
exerted by the disk material. In the second approach, only the N-body
integration is performed but with additional dissipative forces included such
as to mimic the effect of the disk torques acting on the disk. This type of
modeling is much faster than the full hydrodynamical simulations, and gives
comparative results provided that parameters are adjusted properly.
Resonant capture of the planets is seen in both approaches, where the order
of the resonance depends on the properties of the disk and the planets.
Resonant capture leads to a rise in the eccentricity and to an alignment of the
spatial orientation of orbits. The numerical results are compared with the
observed planetary systems in mean motion resonance (Gl 867, HD 82943, and 55
Cnc). We find that the forcing together of two planets by their parent disk
produces resonant configurations similar to those observed, but that
eccentricity damping greater than that obtained in our hydrodynamic simulations
is required to match the GJ 876 observations.Comment: Latex, 14 pages, 13 figures, A&A accepte
Hydrodynamic stability and mode coupling in Keplerian flows: local strato-rotational analysis
Aims. Qualitative analysis of key (but yet unappreciated) linear phenomena in
stratified hydrodynamic Keplerian flows: (i) the occurrence of a vortex mode,
as a consequence of strato-rotational balance, with its transient dynamics;
(ii) the generation of spiral-density waves (also called inertia-gravity or
waves) by the vortex mode through linear mode coupling in shear
flows. Methods. Non-modal analysis of linearized Boussinesq equations written
in the shearing sheet approximation of accretion disk flows. Results. It is
shown that the combined action of rotation and stratification introduces a new
degree of freedom -- vortex mode perturbation -- which is linearly coupled with
the spiral-density waves. These two modes are jointly able to extract energy
from the background flow and they govern the disk dynamics in the small-scale
range. The transient behavior of these modes is determined by the non-normality
of the Keplerian shear flow. Tightly leading vortex mode perturbations undergo
substantial transient growth, then, becoming trailing, inevitably generate
trailing spiral-density waves by linear mode coupling. This course of events --
transient growth plus coupling -- is particularly pronounced for perturbation
harmonics with comparable azimuthal and vertical scales and it renders the
energy dynamics similar to the 3D unbounded plane Couette flow case.
Conclusions. Our investigation strongly suggests that the so-called bypass
concept of turbulence, which has been recently developed by the hydrodynamic
community for spectrally stable shear flows, can also be applied to Keplerian
disks. This conjecture may be confirmed by appropriate numerical simulations
that take in account the vertical stratification and consequent mode coupling
in the high Reynolds number regime.Comment: A&A (accepted
Equilibria in the secular, non-coplanar two-planet problem
We investigate the secular dynamics of a planetary system composed of the
parent star and two massive planets in mutually inclined orbits. The dynamics
are investigated in wide ranges of semi-major axes ratios (0.1-0.667), and
planetary masses ratios (0.25-2) as well as in the whole permitted ranges of
the energy and total angular momentum. The secular model is constructed by
semi-analytic averaging of the three-body system. We focus on equilibria of the
secular Hamiltonian (periodic solutions of the full system), and we analyze
their stability. We attempt to classify families of these solutions in terms of
the angular momentum integral. We identified new equilibria, yet unknown in the
literature. Our results are general and may be applied to a wide class of
three-body systems, including configurations with a star and brown dwarfs and
sub-stellar objects. We also describe some technical aspects of the
semi-numerical averaging. The HD 12661 planetary system is investigated as an
example configuration.Comment: 18 pages, 17 figures, accepted to Monthly Notices of the Royal
Astronomical Societ
{2,2′-[Ethylenebis(nitrilomethylidyne)]diphenolato-κ4 O,N,N′,O′}oxidovanadium(IV)
The title compound, [V(C16H14N2O2)O], was synthesized by the reaction of vanadyl(IV) sulfate and N,N′-bis(salicylidene)ethylenediamine under hydrothermal conditions. The asymmetric unit contains two molecules. Each VIV atom is coordinated in a square-pyramidal geometry by two N atoms and two O atoms from a ligand in the basal plane and by an oxide O atom in the apical position. Weak C—H⋯O hydrogen bonds lead to a three-dimensional supramolecular structure
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