296 research outputs found
A Dynamical Analysis of the Proposed Circumbinary HW Virginis Planetary System
In 2009, the discovery of two planets orbiting the evolved binary star system
HW Virginis was announced, based on systematic variations in the timing of
eclipses between the two stars. The planets invoked in that work were
significantly more massive than Jupiter, and moved on orbits that were mutually
crossing - an architecture which suggests that mutual encounters and strong
gravitational interactions are almost guaranteed. In this work, we perform a
highly detailed analysis of the proposed HW Vir planetary system. First, we
consider the dynamical stability of the system as proposed in the discovery
work. Through a mapping process involving 91,125 individual simulations, we
find that the system is so unstable that the planets proposed simply cannot
exist, due to mean lifetimes of less than a thousand years across the whole
parameter space. We then present a detailed re-analysis of the observational
data on HW Vir, deriving a new orbital solution that provides a very good fit
to the observational data. Our new analysis yields a system with planets more
widely spaced, and of lower mass, than that proposed in the discovery work, and
yields a significantly greater (and more realistic) estimate of the uncertainty
in the orbit of the outermost body. Despite this, a detailed dynamical analysis
of this new solution similarly reveals that it also requires the planets to
move on orbits that are simply not dynamically feasible. Our results imply that
some mechanism other than the influence of planetary companions must be the
principal cause of the observed eclipse timing variations for HW Vir. If the
sys- tem does host exoplanets, they must move on orbits differing greatly from
those previously proposed. Our results illustrate the critical importance of
performing dynamical analyses as a part of the discovery process for
multiple-planet exoplanetary systems.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
A Detailed Investigation of the Proposed NN Serpentis Planetary System
The post-main sequence eclipsing binary NN Serpentis was recently announced
as the potential host of at least two massive planetary companions. In that
work, the authors put forward two potential architectures that fit the
observations of the eclipsing binary with almost identical precision. In this
work, we present the results of a dynamical investigation of the orbital
stability of both proposed system architectures, finding that they are only
stable for scenarios in which the planets are locked in mutual mean motion
resonance. In the discovery work, the authors artificially fixed the orbital
eccentricity of the more massive planet, NN Ser(AB) c, at 0. Here, we reanalyse
the observational data on NN Serpentis without this artificial constraint, and
derive a new orbital solution for the two proposed planets. We detail the
results of further dynamical simulations investigating the stability of our new
orbital solution, and find that allowing a small non-zero eccentricity for the
outer planet renders the system unstable. We conclude that, although the
original orbits proposed for the NN Serpentis planetary system prove
dynamically feasible, further observations of the system are vital in order to
better constrain the system's true architecture.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society; 5 figures, 2 table
Departure from the constant-period ephemeris for the transiting exoplanet WASP-12 b
Most hot Jupiters are expected to spiral in towards their host stars due to
transfering of the angular momentum of the orbital motion to the stellar spin.
Their orbits can also precess due to planet-star interactions. Calculations
show that both effects could be detected for the very-hot exoplanet WASP-12 b
using the method of precise transit timing over a timespan of the order of 10
yr. We acquired new precise light curves for 29 transits of WASP-12 b,
spannning 4 observing seasons from November 2012 to February 2016. New
mid-transit times, together with literature ones, were used to refine the
transit ephemeris and analyse the timing residuals. We find that the transit
times of WASP-12 b do not follow a linear ephemeris with a 5 sigma confidence
level. They may be approximated with a quadratic ephemeris that gives a rate of
change in the orbital period of -2.56 +/- 0.40 x 10^{-2} s/yr. The tidal
quality parameter of the host star was found to be equal to 2.5 x 10^5 that is
comparable to theoretical predictions for Sun-like stars. We also consider a
model, in which the observed timing residuals are interpreted as a result of
the apsidal precession. We find, however, that this model is statistically less
probable than the orbital decay.Comment: Accepted for publication in A&A Letter
Discarding orbital decay in WASP-19b after one decade of transit observations
We present an empirical study of orbital decay for the exoplanet WASP-19b, based on mid-time measurements of 74 complete transits (12 newly obtained by our team and 62 from the literature), covering a 10-yr baseline. A linear ephemeris best represents the mid-transit times as a function of epoch. Thus, we detect no evidence of the shortening of WASP-19b's orbital period and establish an upper limit of its steady changing rate, P' = −2.294 ms yr−1, and a lower limit for the modified tidal quality factor Q'* = (1.23 ± 0.231) × 106. Both are in agreement with previous works. This is the first estimation of Q' directly derived from the mid-times of WASP-19b obtained through homogeneously analysed transit measurements. Additionally, we do not detect periodic variations in the transit timings within the measured uncertainties in the mid-times of transit. We are therefore able to discard the existence of planetary companions in the system down to a few M in the first-order mean-motion resonances 1:2 and 2:1 with WASP-19b, in the most conservative case of circular orbits. Finally, we measure the empirical Q'* values of 15 exoplanet host stars, which suggest that stars with Teff ≲ 5600 K dissipate tidal energy more efficiently than hotter stars. This tentative trend needs to be confirmed with a larger sample of empirically measured Q'*.Fil: Petrucci, Romina Paola. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Departamento de Astrofísica Estelar; ArgentinaFil: Jofre, Jorge Emiliano. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Departamento de Astrofísica Estelar; Argentina. Universidad Nacional Autónoma de México; México. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gómez Maqueo Chew, Y.. Universidad Nacional Autónoma de México; MéxicoFil: Hinse, T. C.. Chungnam National University; Corea del SurFil: Mazek, M.. Institute Of Physics Czech Academy Of Sciences; República ChecaFil: Tan, T. -G.. Perth Exoplanet Survey Telescope; AustraliaFil: Gomez, Mercedes Nieves. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Departamento de Astrofísica Estelar; Argentin
Testing proposed planetary systems - to destruction
The authors examine the dynamics of exoplanet systems and find that some of them don't last long. The stability of planetary systems offers a check on the likelihood of proposed multiple-exoplanet systems
Modelling the inner debris disc of HR 8799
In many ways, the HR 8799 planetary system strongly resembles our own. It features four giant planets and two debris belts, analogues to the Asteroid and Edgeworth-Kuiper belts. Here, we present the results of dynamical simulations of HR8799’s inner debris belt, to study its structure and collisional environment. Our results suggest that HR 8799’s inner belt is highly structured, with gaps between regions of dynamical stability. The belt is likely constrained between sharp inner and outer edges, located at ∼6 and ∼8 au, respectively. Its inner edge coincides with a broad gap cleared by the 4:1 mean-motion resonance with HR 8799e. Within the belt, planetesimals are undergoing a process of collisional attrition like that observed in the Asteroid belt. However, whilst the mean collision velocity in the Asteroid belt exceeds 5 km s−1, the majority of collisions within HR 8799’s inner belt occur with velocities of order 1.2 km s−1, or less. Despite this, they remain sufficiently energetic to be destructive – giving a source for the warm dust detected in the system. Interior to the inner belt, test particles remain dynamically unstirred, aside from narrow bands excited by distant high-order resonances with HR 8799e. This lack of stirring is consistent with earlier thermal modelling of HR 8799’s infrared excess, which predicted little dust inside 6 au. The inner system is sufficiently stable and unstirred that the formation of telluric planets is feasible, although such planets would doubtless be subject to a punitive impact regime, given the intense collisional grinding required in the inner belt to generate the observed infrared excess
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