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

MAGSAT data processing: A report for investigators

The in-flight attitude and vector magnetometer data bias recovery techniques and results are described. The attitude bias recoveries are based on comparisons with a magnetic field model and are thought to be accurate to 20 arcsec. The vector magnetometer bias recoveries are based on comparisons with the scalar magnetometer data and are thought to be accurate to 3 nT or better. The MAGSAT position accuracy goals of 60 m radially and 300 m horizontally were achieved for all but the last 3 weeks of Magsat lifetime. This claim is supported by ephemeris overlap statistics and by comparisons with ephemerides computed with an independent orbit program using data from an independent tracking network. MAGSAT time determination accuracy is estimated at 1 ms. Several errors in prelaunch assumptions regarding data time tags, which escaped detection in prelaunch data tests, and were discovered and corrected postlaunch are described. Data formats and products, especially the Investigator-B tapes, which contain auxiliary parameters in addition to the basic magnetometer and ephemeris data, are described

Predictors of discordance among Chilean families

Parent-youth agreement on parental behaviors can characterize effective parenting. Although discordance in families may be developmentally salient and harmful to youth outcomes, predictors of discordance have been understudied, and existing research in this field has been mostly limited to North American samples. This paper addressed this literature gap by using data from a community-based study of Chilean adolescents. Analysis was based on 1,068 adolescents in Santiago, Chile. The dependent variable was discordance which was measured by the difference between parent and youth’s assessment of parental monitoring. Major independent variables for this study were selected based on previous research findings that underscore youth’s developmental factors, positive parental and familial factors and demographic factors. Descriptive and multivariate analyses were conducted to examine the prevalence and associations between youth, parental and familial measures with parent-youth discordance. There was a sizable level of discordance between parent and youth’s report of parental monitoring. Youth’s gender and externalizing behavior were significant predictors of discordance. Warm parenting and family involvement were met with decreases in discordance. The negative interaction coefficients between parental warmth and youth’s gender indicated that positive parental and familial measures have a greater effect on reducing parent-youth discordance among male youths. Results support the significance of positive family interactions in healthy family dynamics. Findings from this study inform the importance of services and interventions for families that aim to reduce youth’s problem behavior and to create a warm and interactive family environment.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4181713/Accepted manuscrip

Thermodynamic description of a dynamical glassy transition

For the dynamical glassy transition in the $p$-spin mean field spin glass model a thermodynamic description is given. The often considered marginal states are not the relevant ones for this purpose. This leads to consider a cooling experiment on exponential timescales, where lower states are accessed. The very slow configurational modes are at quasi-equilibrium at an effective temperature. A system independent law is derived that expresses their contribution to the specific heat. $t/t_w$-scaling in the aging regime of two-time quantities is explained.Comment: 5 pages revte

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 New Kinematic Distance Estimator to the LMC

The distance to the Large Magellanic Cloud (LMC) can be directly determined by measuring three of its properties, its radial-velocity field, its mean proper motion, and the position angle \phi_ph of its photometric line of nodes. Statistical errors of 2% are feasible based on proper motions obtained with any of several proposed astrometry satellites, the first possibility being the Full-Sky Astrometric Mapping Explorer (FAME). The largest source of systematic error is likely to be in the determination of \phi_ph. I suggest two independent methods to measure \phi_ph, one based on counts of clump giants and the other on photometry of clump giants. I briefly discuss a variety of methods to test for other sources of systematic errors.Comment: submitted to ApJ, 13 page

A dynamical analysis of the proposed HU Aquarii planetary system

It has recently been suggested that the eclipsing polar HU Aquarii is host to at least two giant planets. We have performed highly detailed dynamical analysis of the orbits of those planets and show that the proposed system is highly unstable on timescales of < 5\times 10$^3$ years. For the coplanar orbits suggested in the discovery letter, we find stable orbital solutions for the planetary system only if the outer body moves on an orbit that brings it no closer to the host star than ~ 6 AU. The required periastron distance for the outer planet lies approximately 5 Hill radii beyond the orbit of the inner planet, and well beyond the 1-{\sigma} error bars placed on the orbit of the outer planet in the discovery letter. If the orbits of the proposed planets are significantly inclined with respect to one another, the median stability increases slightly, but such systems still become destabilised on astronomically minute timescales (typically within a few 10$^4$ years). Only in the highly improbable scenario where the outer planet follows a retrograde but coplanar orbit (i.e. inclined by 180 degrees to the orbit of the inner planet) is there any significant region of stability within the original 1-{\sigma} orbital uncertainties. Our results suggest that, if there is a second (and potentially, a third planet) in the HU Aquarii system, its orbit is dramatically different to that suggested in the discovery paper, and that more observations are critically required in order to constrain the nature of the suggested orbital bodies.Comment: 2 figures, 1 table, accepted to MNRAS Letter

Winds of Planet Hosting Stars

The field of exoplanetary science is one of the most rapidly growing areas of astrophysical research. As more planets are discovered around other stars, new techniques have been developed that have allowed astronomers to begin to characterise them. Two of the most important factors in understanding the evolution of these planets, and potentially determining whether they are habitable, are the behaviour of the winds of the host star and the way in which they interact with the planet. The purpose of this project is to reconstruct the magnetic fields of planet hosting stars from spectropolarimetric observations, and to use these magnetic field maps to inform simulations of the stellar winds in those systems using the Block Adaptive Tree Solar-wind Roe Upwind Scheme (BATS-R-US) code. The BATS-R-US code was originally written to investigate the behaviour of the Solar wind, and so has been altered to be used in the context of other stellar systems. These simulations will give information about the velocity, pressure and density of the wind outward from the host star. They will also allow us to determine what influence the winds will have on the space weather environment of the planet. This paper presents the preliminary results of these simulations for the star $\tau$ Bo\"otis, using a newly reconstructed magnetic field map based on previously published observations. These simulations show interesting structures in the wind velocity around the star, consistent with the complex topology of its magnetic field.Comment: 8 pages, 2 figures, accepted for publication in the peer-reviewed proceedings of the 14th Australian Space Research Conference, held at the University of South Australia, 29th September - 1st October 201

The Origin of Mercury

Mercury's unusually high mean density has always been attributed to special circumstances that occurred during the formation of the planet or shortly thereafter, and due to the planet's close proximity to the Sun. The nature of these special circumstances is still being debated and several scenarios, all proposed more than 20 years ago, have been suggested. In all scenarios, the high mean density is the result of severe fractionation occurring between silicates and iron. It is the origin of this fractionation that is at the centre of the debate: is it due to differences in condensation temperature and/or in material characteristics (e.g. density, strength)? Is it because of mantle evaporation due to the close proximity to the Sun? Or is it due to the blasting off of the mantle during a giant impact? In this paper we investigate, in some detail, the fractionation induced by a giant impact on a proto-Mercury having roughly chondritic elemental abundances. We have extended the previous work on this hypothesis in two significant directions. First, we have considerably increased the resolution of the simulation of the collision itself. Second, we have addressed the fate of the ejecta following the impact by computing the expected reaccretion timescale and comparing it to the removal timescale from gravitational interactions with other planets (essentially Venus) and the Poynting-Robertson effect. To compute the latter, we have determined the expected size distribution of the condensates formed during the cooling of the expanding vapor cloud generated by the impact. We find that, even though some ejected material will be reaccreted, the removal of the mantle of proto-Mercury following a giant impact can indeed lead to the required long-term fractionation between silicates and iron and therefore account for the anomalously high mean density of the planet. Detailed coupled dynamical-chemical modeling of this formation mechanism should be carried out in such a way as to allow explicit testing of the giant impact hypothesis by forthcoming space missions (e.g. MESSENGER and BepiColombo