Transiting Disintegrating Planetary Debris around WD 1145+017

More than a decade after astronomers realized that disrupted planetary material likely pollutes the surfaces of many white dwarf stars, the discovery of transiting debris orbiting the white dwarf WD 1145+017 has opened the door to new explorations of this process. We describe the observational evidence for transiting planetary material and the current theoretical understanding (and in some cases lack thereof) of the phenomenon.Comment: Invited review chapter. Accepted March 23, 2017 and published October 7, 2017 in the Handbook of Exoplanets. 15 pages, 10 figure

Quantifying the challenges of detecting unseen planetary companions with transit timing variations

Both ground and space-based transit observatories are poised to significantly increase the number of known transiting planets and the number of precisely measured transit times. The variation in a planet's transit times may be used to infer the presence of additional planets. Deducing the masses and orbital parameters of such planets from transit time variations (TTVs) alone is a rich and increasingly relevant dynamical problem. In this work, we evaluate the extent of the degeneracies in this process, systematically explore the dependence of TTV signals on several parameters and provide phase space plots that could aid observers in planning future observations. Our explorations are focused on a likely-to-be prevalent situation: a known transiting short-period Neptune or Jupiter-sized planet and a suspected external low-mass perturber on a nearly-coplanar orbit. Through approximately 10^7 N-body simulations, we demonstrate how TTV signal amplitudes may vary by orders of magnitude due to slight variations in any one orbital parameter (0.001 AU in semimajor axis, 0.005 in eccentricity, or a few degrees in orbital angles), and quantify the number of consecutive transit observations necessary in order to obtain a reasonable opportunity to characterize the unseen planet (approximately greater or equal to 50 observations). Planets in or near period commensurabilities of the form p:q, where p < 21 and q < 4, produce distinct TTV signatures, regardless of whether the planets are actually locked in a mean motion resonance. We distinguish these systems from the secular systems in our explorations. Additionally, we find that computing the autocorrelation function of a TTV signal can provide a useful diagnostic for identifying possible orbits for additional planets and suggest that this method could aid integration of TTV signals in future studies of particular exosystems.Comment: 53 pages total, including 18 figures, 1 table, and 1 appendix. Accepted for publication in ApJ. Better resolution plots will appear in online journa

Identifying Non-Resonant Kepler Planetary Systems

The Kepler mission has discovered a plethora of multiple transiting planet candidate exosystems, many of which feature putative pairs of planets near mean motion resonance commensurabilities. Identifying potentially resonant systems could help guide future observations and enhance our understanding of planetary formation scenarios. We develop and apply an algebraic method to determine which Kepler 2-planet systems cannot be in a 1st-4th order resonance, given the current, publicly available data. This method identifies when any potentially resonant angle of a system must circulate. We identify and list 70 near-resonant systems which cannot actually reside in resonance, assuming a widely-used formulation for deriving planetary masses from their observed radii and that these systems do not contain unseen bodies that affect the interactions of the observed planets. This work strengthens the argument that a high fraction of exoplanetary systems may be near resonance but not actually in resonance.Comment: 6 pages, 2 figures, 1 table, accepted for publication in MNRAS Letter

A Bayesian Surrogate Model for Rapid Time Series Analysis and Application to Exoplanet Observations

We present a Bayesian surrogate model for the analysis of periodic or quasi-periodic time series data. We describe a computationally efficient implementation that enables Bayesian model comparison. We apply this model to simulated and real exoplanet observations. We discuss the results and demonstrate some of the challenges for applying our surrogate model to realistic exoplanet data sets. In particular, we find that analyses of real world data should pay careful attention to the effects of uneven spacing of observations and the choice of prior for the "jitter" parameter.Comment: 25 pages, 4 figures, accepted to Bayesian Analysis , special issue for Ninth Valencia International Conference on Bayesian Statistic

Mass and eccentricity constraints on the planetary debris orbiting the white dwarf WD 1145+017

Being the first of its kind, the white dwarf WD 1145+017 exhibits a complex system of disintegrating debris which offers a unique opportunity to study its disruption process in real time. Even with plenty of transit observations there are no clear constraints on the masses or eccentricities of such debris. Using N-body simulations, we show that masses greater than ≃1020 kg (a tenth of the mass of Ceres) or orbits that are not nearly circular (eccentricity > 10−3) dramatically increase the chances of the system becoming unstable within 2 yr, which would contrast with the observational data over this timespan. We also provide a direct comparison between transit phase shifts detected in the observations and by our numerical simulations

The unstable fate of the planet orbiting the A-star in the HD 131399 triple stellar system

Validated planet candidates need not lie on long-term stable orbits, and instability triggered by post-main-sequence stellar evolution can generate architectures which transport rocky material to white dwarfs, polluting them. The giant planet HD 131399Ab orbits its parent A star at a projected separation of about 50-100 au. The host star, HD131399A, is part of a hierarchical triple with HD131399BC being a close binary separated by a few hundred au from the A star. Here, we determine the fate of this system, and find that (i) stability along the main sequence is achieved only for a favourable choice of parameters within the errors, and (ii) even for this choice, in almost every instance the planet is ejected during the transition between the giant branch and white dwarf phases of HD 131399A. This result provides an example of both how the free-floating planet population may be enhanced by similar systems, and how instability can manifest in the polluted white dwarf progenitor population

Efeitos de Diferentes Terapias de Reposição Hormonal Sobre a Pressão Arterial e Balanço Mineral Ósseo de Ratas Castradas

O estrogênio tem um importante papel na regulação homeostática de vários tecidos do organismo, bem ilustrados pelas alterações fisiopatológicas que ocorrem na sua deficiência, na menopausa. Com o objetivo de amenizar estas alterações, tem-se estudado o uso da terapia de reposição hormonal (TRH) na pós-menopausa, em função de seus benefícios na prevenção da osteoporose e doenças cardiovasculares. Entretanto, a TRH tradicional com estrogênio está associada a uma maior incidência no desenvolvimento de câncer de mama e endométrio. Uma das alternativas para a reposição hormonal são as isoflavonas (fitoestrogênios derivados da soja) e o raloxifeno (SERM). Este estudo tem como objetivo avaliar os possíveis efeitos do 17-&#946;-estradiol, isoflavonas e raloxifeno sobre ratas castradas por meio da medida da pressão arterial, concentração de cálcio e fósforo ósseo e sérico, peso corpóreo, da câmara ventricular esquerda e uterino. Ratas Wistar adultas foram divididas em cinco grupos (n=8). Um grupo controle (C), um grupo castrado (CC) e os grupos castrados e tratados com estrogênio (CE), isoflavona (CI) e raloxifeno (CR). Dez semanas após a ovariectomia, iniciou-se o tratamento dos grupos CE, CI e CR que durou 12 semanas. No final do tratamento, foi feita a medida direta da pressão arterial e coletadas amostras de sangue, cuja concentração de cálcio e fósforo foram medidas. Os animais foram, então, sacrificados para se analisar o peso úmido e seco dos fêmures direito e esquerdo, ventrículo esquerdo e útero, além da análise da concentração de cálcio e fósforo dos fêmures. O tratamento com a 17-&#946;-estradiol, isoflavonas e raloxifeno não alterou os níveis pressóricos das ratas. Os grupos CE e CR obtiveram os menores níveis plasmáticos e os maiores níveis ósseos de cálcio. O grupo CR apresentou o menor nível de fósforo sérico e os grupos CE e CR apresentaram os menores níveis de fósforo ósseo. O grupo CE obteve o menor ganho de peso corporal. Quanto ao peso dos fêmures, os grupos CE e CR obtiveram os maiores ganho de massa óssea. O ventrículo esquerdo apresentou peso maior no grupo CE, assim como o peso do útrero. Com base nos resultados obtidos, concluímos que os tratamentos com a isoflavona e o raloxifeno apresentaram maiores benefícios, quando comparados ao tratamento com o 17-&#946;-estradiol, pois aumentaram a concentração de cálcio e a massa óssea sem alterar a pressão arterial e nem o trofismo das células cardíacas e uterinas