Detection and Characterization of Extrasolar Planets through Planet-Disk Dynamical Interactions

Structures observed in circumstellar disks may be caused by gravitational interaction with planetary or stellar companions. These perturbed disks are often signposts of planet birth in exoplanetary systems, and offer insights into the properties of both the disk and the perturbing planets. Therefore, structures observed in these disks provide a powerful tool for detecting and studying extrasolar planetary systems. In this work, we examine the link between disk structures and nearby/embedded planets using numerical simulations of both hypothetical and observed disk systems. We demonstrate that gaps can be opened in dynamically cold debris disks at the mean-motion resonances (MMRs) of an orbiting planet. These gaps are opened away from the orbit of the planet itself, revealing that not all disk gaps need contain a planetary body. These gaps are large and deep enough to be detectable in resolved disk images for a wide range of reasonable disk-planet parameters. The gap location, shape, and size are diagnostic of the planet location, eccentricity and mass, and allow one to infer the existence of unseen planets, as well as calculate many important parameters of both seen and unseen planets in these systems. We suggest that the widths, locations, and shapes of the two most prominent resonances, the 2:1 and 3:1 MMRs, could be used to determine: 1) the position of any unseen planets for more efficient targeted searches, and 2) the mass, semimajor axis and eccentricity of the planetary perturber, and present an algorithm for doing so. We apply our dynamical model of planet-disk interactions to the protoplanetary disk around the young pre-main sequence star HL Tauri which was observed recently in unprecedented detail by the \textit{Atacama Large Millimeter/submillimeter Array} (ALMA). We determine that the disk structures that are likely sculpted by yet-to-be detected planets embedded in this gas-rich disk can be reproduced to a large extent using a simple particle-only model. For example, the number of planets in the HL Tau system remains a matter of debate; however, our results show that at least 5 of the observed gaps could be produced with only 3 planets in the system, where the additional gaps are due to mean-motion resonances. Our fitting of planetary masses and distances are also consistent with those in the literature. Therefore, we conclude that a particle-only treatment of gas-rich disks may be useful in understanding disk-planet dynamical interactions in some cases, and provide `low-cost\u27 initial parameter determinations which can ultimately be used as a starting point for investigating protoplanetary disks more thoroughly using computationally expensive hydrodynamic models. In the present study, we show that numerical simulations of circumstellar disks provide a powerful tool for the study of planets and planetary systems which can ultimately help in understanding their formation and evolution

Asteroid (3200) Phaethon: colors, phase curve, limits on cometary activity and fragmentation

We report on a multi-observatory campaign to examine asteroid 3200 Phaethon during its December 2017 close approach to Earth, in order to improve our measurements of its fundamental parameters, and to search for surface variations, cometary activity and fragmentation. The mean colors of Phaethon are B-V = 0.702 +/- 0.004, V-R = 0.309 +/- 0.003, R-I = 0.266 +/- 0.004, neutral to slightly blue, consistent with previous classifications of Phaethon as a F-type or B-type asteroid. Variations in Phaethon's B-V colors (but not V-R or R-I) with observer sub-latitude are seen and may be associated with craters observed by the Arecibo radar. High cadence photometry over phases from 20 to 100 degrees allows a fit to the values of the HG photometric parameters; H = 14.57 +/- 0.02, 13.63 +/- 0.02, 13.28 +/- 0.02, 13.07 +/- 0.02; G = 0.00 +/- 0.01, -0.09 +/- 0.01, -0.10 +/- 0.01, -0.08 +/- 0.01 in the BVRI filters respectively; the negative G values are consistent with other observations of F type asteroids. Light curve variations were seen that are also consistent with concavities reported by Arecibo, indicative of large craters on Phaethon's surface whose ejecta may be the source of the Geminid meteoroid stream. A search for gas/dust production set an upper limit of 0.06 +/- 0.02 kg/s when Phaethon was 1.449 AU from the Sun, and 0.2 +/- 0.1 kg/s at 1.067 AU. A search for meter-class fragments accompanying Phaethon did not find any whose on-sky motion was not also consistent with background main belt asteroids.Comment: Accepted by the Astronomical Journal, 15 pages, 8 figures, 1 animated figur

Asteroid (3200) Phaethon: Colors, Phase Curve, Limits on Cometary Activity, and Fragmentation

We report on a multiobservatory campaign to examine asteroid 3200 Phaethon during its 2017 December close approach to Earth, in order to improve our measurements of its fundamental parameters, and to search for surface variations, cometary activity, and fragmentation. The mean colors of Phaethon are B – V = 0.702 ± 0.004, V – R = 0.309 ± 0.003, and R – I = 0.266 ± 0.004, neutral to slightly blue, consistent with previous classifications of Phaethon as a F-type or B-type asteroid. Variations in Phaethon's B – V colors (but not V – R or R – I) with observer sublatitude are seen and may be associated with craters observed by the Arecibo radar. High-cadence photometry over phases from 20° to 100° allows a fit to the values of the HG photometric parameters; H = 14.57 ± 0.02, 13.63 ± 0.02, 13.28 ± 0.02, 13.07 ± 0.02; G = 0.00 ± 0.01, −0.09 ± 0.01, −0.10 ± 0.01, −0.08 ± 0.01 in the BVRI filters respectively; the negative G values are consistent with other observations of F-type asteroids. Light-curve variations were seen that are also consistent with concavities reported by Arecibo, indicative of large craters on Phaethon's surface whose ejecta may be the source of the Geminid meteoroid stream. A search for gas/dust production sets an upper limit of 0.06 ± 0.02 kg s^(−1) when Phaethon was 1.449 au from the Sun, and 0.2 ± 0.1 kg s^(−1) at 1.067 au. A search for meter-class fragments accompanying Phaethon did not find any whose on-sky motion was not also consistent with background main-belt asteroids

Debris Disks: Probing Planet Formation

Debris disks are the dust disks found around ~20% of nearby main sequence stars in far-IR surveys. They can be considered as descendants of protoplanetary disks or components of planetary systems, providing valuable information on circumstellar disk evolution and the outcome of planet formation. The debris disk population can be explained by the steady collisional erosion of planetesimal belts; population models constrain where (10-100au) and in what quantity (>1Mearth) planetesimals (>10km in size) typically form in protoplanetary disks. Gas is now seen long into the debris disk phase. Some of this is secondary implying planetesimals have a Solar System comet-like composition, but some systems may retain primordial gas. Ongoing planet formation processes are invoked for some debris disks, such as the continued growth of dwarf planets in an unstirred disk, or the growth of terrestrial planets through giant impacts. Planets imprint structure on debris disks in many ways; images of gaps, clumps, warps, eccentricities and other disk asymmetries, are readily explained by planets at >>5au. Hot dust in the region planets are commonly found (<5au) is seen for a growing number of stars. This dust usually originates in an outer belt (e.g., from exocomets), although an asteroid belt or recent collision is sometimes inferred.Comment: Invited review, accepted for publication in the 'Handbook of Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018

Modeling non-motorized travel demand at intersections based on traffic counts and GIS data in Calgary, Canada

In September 2009 the City of Calgary Council approved Plan It Calgary, which proposes policies that focus on the development of resilient neighborhoods through the intensification and diversification of urban activities around transit stations and routes. More intensive development and mixed land use encourage non-motorized trips and reinforce comfortable, safe and walkable streets. The development of high-density, mixed-use and transit- and pedestrian-oriented communities has the potential to generate trips with shorter destinations, which are expected to result in a higher share of active travel modes, such as biking and walking. Thus, there is a growing need to estimate the impact of land-use development scenarios and transportation policies on bicycle and pedestrian demand to predict future non-motorized trip volumes and adequately design the related infrastructure. This study calibrates multiple linear and Poisson regression models to estimate non-motorized travel demand based on GIS, transportation data and road characteristics. The empirical models that have been developed in this research can be used to assess the impacts of urban design and built environments, such as developing high-density and mix-land-use areas, and building complete streets in the middle ring communities of the City of Calgary in influencing the demand for active travel modes. The developed models show the benefits of improved pedestrian infrastructure, such as improved network connectivity and increases in the length of pedestrian pathways, as well as the integration of transit and walking modes and transit and bicycle modes in encouraging more non-motorized travel demand. The method employed herein is a straightforward statistical analysis method, and the needed data are relatively easy to access