116 research outputs found
PEXO : a global modeling framework for nanosecond timing, microsecond astrometry, and μm/s radial velocities
54 pages, 2 tables, 19 figures, accepted for publication in ApJS, PEXO is available at https://github.com/phillippro/pexoThe ability to make independent detections of the signatures of exoplanets with complementary telescopes and instruments brings a new potential for robust identification of exoplanets and precision characterization. We introduce PEXO, a package for Precise EXOplanetology to facilitate the efficient modeling of timing, astrometry, and radial velocity data, which will benefit not only exoplanet science but also various astrophysical studies in general. PEXO is general enough to account for binary motion and stellar reflex motions induced by planetary companions and is precise enough to treat various relativistic effects both in the solar system and in the target system. We also model the post-Newtonian barycentric motion for future tests of general relativity in extrasolar systems. We benchmark PEXO with the pulsar timing package TEMPO2 and find that PEXO produces numerically similar results with timing precision of about 1 ns, space-based astrometry to a precision of 1{\mu}as, and radial velocity of 1 {\mu}m/s and improves on TEMPO2 for decade-long timing data of nearby targets, due to its consideration of third-order terms of Roemer delay. PEXO is able to avoid the bias introduced by decoupling the target system and the solar system and to account for the atmospheric effects which set a practical limit for ground-based radial velocities close to 1 cm/s. Considering the various caveats in barycentric correction and ancillary data required to realize cm/s modeling, we recommend the preservation of original observational data. The PEXO modeling package is available at GitHub (https://github.com/phillippro/pexo).Peer reviewe
First-Year Spectroscopy for the SDSS-II Supernova Survey
This paper presents spectroscopy of supernovae discovered in the first season
of the Sloan Digital Sky Survey-II Supernova Survey. This program searches for
and measures multi-band light curves of supernovae in the redshift range z =
0.05 - 0.4, complementing existing surveys at lower and higher redshifts. Our
goal is to better characterize the supernova population, with a particular
focus on SNe Ia, improving their utility as cosmological distance indicators
and as probes of dark energy. Our supernova spectroscopy program features
rapid-response observations using telescopes of a range of apertures, and
provides confirmation of the supernova and host-galaxy types as well as precise
redshifts. We describe here the target identification and prioritization, data
reduction, redshift measurement, and classification of 129 SNe Ia, 16
spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first
season. We also describe our efforts to measure and remove the substantial host
galaxy contamination existing in the majority of our SN spectra.Comment: Accepted for publication in The Astronomical Journal(47pages, 9
figures
Constant light enhances synchrony among circadian clock cells and promotes behavioral rhythms in VPAC(2)-signaling deficient mice
Individual neurons in the suprachiasmatic nuclei (SCN) contain an intracellular molecular clock and use intercellular signaling to synchronize their timekeeping activities so that the SCN can coordinate brain physiology and behavior. The neuropeptide vasoactive intestinal polypeptide (VIP) and its VPAC2 receptor form a key component of intercellular signaling systems in the SCN and critically control cellular coupling. Targeted mutations in either the intracellular clock or intercellular neuropeptide signaling mechanisms, such as VIP-VPAC2 signaling, can lead to desynchronization of SCN neuronal clocks and loss of behavioral rhythms. An important goal in chronobiology is to develop interventions to correct deficiencies in circadian timekeeping. Here we show that extended exposure to constant light promotes synchrony among SCN clock cells and the expression of ~24 h rhythms in behavior in mice in which intercellular signaling is disrupted through loss of VIP-VPAC2 signaling. This study highlights the importance of SCN synchrony for the expression of rhythms in behavior and reveals how non-invasive manipulations in the external environment can be used to overcome neurochemical communication deficits in this important brain system
A critical review of mathematical models and data used in diabetology
The literature dealing with mathematical modelling for diabetes is abundant. During the last decades, a variety of models have been devoted to different aspects of diabetes, including glucose and insulin dynamics, management and complications prevention, cost and cost-effectiveness of strategies and epidemiology of diabetes in general. Several reviews are published regularly on mathematical models used for specific aspects of diabetes. In the present paper we propose a global overview of mathematical models dealing with many aspects of diabetes and using various tools. The review includes, side by side, models which are simple and/or comprehensive; deterministic and/or stochastic; continuous and/or discrete; using ordinary differential equations, partial differential equations, optimal control theory, integral equations, matrix analysis and computer algorithms
The Orbit and Mass of the Third Planet in the Kepler-56 System
While the vast majority of multiple-planet systems have their orbital angular
momentum axes aligned with the spin axis of their host star, Kepler-56 is an
exception: its two transiting planets are coplanar yet misaligned by at least
40 degrees with respect to their host star. Additional follow-up observations
of Kepler-56 suggest the presence of a massive, non-transiting companion that
may help explain this misalignment. We model the transit data along with
Keck/HIRES and HARPS-N radial velocity data to update the masses of the two
transiting planets and infer the physical properties of the third,
non-transiting planet. We employ a Markov Chain Monte Carlo sampler to
calculate the best-fitting orbital parameters and their uncertainties for each
planet. We find the outer planet has a period of 1002 5 days and minimum
mass of 5.61 0.38 Jupiter masses. We also place a 95% upper limit of 0.80
m/s/yr on long-term trends caused by additional, more distant companions.Comment: 7 pages, 1 figure, 2 tables; accepted for publication in AJ. Minor
edits made after referee repor
Magnetic Inflation and Stellar Mass. I. Revised Parameters for the Component Stars of the Kepler
Precise Masses in the WASP-47 System
We present precise radial velocity observations of WASP-47, a star known to
host a hot Jupiter, a distant Jovian companion, and, uniquely, two additional
transiting planets in short-period orbits: a super-Earth in a ~19 hour orbit,
and a Neptune in a ~9 day orbit. We analyze our observations from the HARPS-N
spectrograph along with previously published data to measure the most precise
planet masses yet for this system. When combined with new stellar parameters
and reanalyzed transit photometry, our mass measurements place strong
constraints on the compositions of the two small planets. We find unlike most
other ultra-short-period planets, the inner planet, WASP-47 e, has a mass (6.83
+/- 0.66 Me) and radius (1.810 +/- 0.027 Re) inconsistent with an Earth-like
composition. Instead, WASP-47 e likely has a volatile-rich envelope surrounding
an Earth-like core and mantle. We also perform a dynamical analysis to
constrain the orbital inclination of WASP-47 c, the outer Jovian planet. This
planet likely orbits close to the plane of the inner three planets, suggesting
a quiet dynamical history for the system. Our dynamical constraints also imply
that WASP-47 c is much more likely to transit than a geometric calculation
would suggest. We calculate a transit probability for WASP-47 c of about 10%,
more than an order of magnitude larger than the geometric transit probability
of 0.6%.Comment: 15 pages, 3 figures, 3 tables. Accepted in A
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