Increased Heat Transport in Ultra-Hot Jupiter Atmospheres Through H$_2$ Dissociation/Recombination [EPA]

A new class of exoplanets is beginning to emerge: planets whose dayside atmospheres more closely resemble stellar atmospheres as most of their molecular constituents dissociate. The effects of the dissociation of these species will be varied and must be carefully accounted for. Here we take the first steps towards understanding the thermodynamical consequences of dissociation and recombination of molecular hydrogen (H$_2$). Using a simple energy balance model with eastward winds, we demonstrate that H$_2$ dissociation/recombination can significantly increase the day-night heat transport on ultra-hot Jupiters: gas giant exoplanets where the temperature is $\gtrsim$ 2200 K somewhere on the planet. For these planets, significant H$_2$ dissociation should occur on their highly irradiated daysides, transporting some of the energy deposited on the dayside towards the nightside of the planet where the H atoms recombine into H$_2$; this mechanism bears similarities to latent heat. Given a fixed wind speed, this will act to increase the heat recirculation efficiency; alternatively, a measured heat recirculation efficiency will require slower wind speeds after accounting for H$_2$ dissociation/recombination.

Read this paper on arXiv…

T. Bell and N. Cowan
Fri, 23 Feb 18

Comments: 8 pages, 5 figures, submitted to ApJL, comments welcome

A semi-analytical model of the Galilean satellites' dynamics [EPA]

The Galilean satellites’ dynamics has been studied extensively during the last century. In the past it was common to use analytical expansions in order to get simple models to integrate, but with the new generation computers it became prevalent the numerical integration of very sophisticated and almost complete equations of motion. In this article we aim to describe the resonant and secular motion of the Galilean satellites through a Hamiltonian, depending on the slow angles only, obtained with an analytical expansion of the perturbing functions and an averaging operation. In order to have a model as near as possible to the actual dynamics, we added perturbations and we considered terms that in similar studies of the past were neglected, such as the terms involving the inclinations and the Sun’s perturbation. Moreover, we added the tidal dissipation into the equations, in order to investigate how well the model captures the evolution of the system.

Read this paper on arXiv…

G. Lari
Fri, 23 Feb 18

Comments: N/A

ALICE Data Release: A revaluation of HST-NICMOS coronagraphic images [EPA]

The Hubble Space Telescope (HST) NICMOS instrument has been used from 1997 to 2008 to perform coronagraphic observations of about 400 targets. Most of them were part of surveys looking for substellar companions or resolved circumstellar disks to young nearby stars, making the NICMOS coronagraphic archive a valuable database for exoplanets and disks studies. As part of the Archival Legacy Investigations of Circumstellar Environments (ALICE) program, we have consistently re-processed a large fraction of the NICMOS coronagrahic archive using advanced PSF subtraction methods. We present here the high-level science products of these re-analyzed data, which we delivered back to the community through the Mikulski Archive for Space Telescopes (MAST) this http URL . We also present the second version of the HCI-FITS format (for High-Contrast Imaging FITS format), which we developed as a standard format for data exchange of imaging reduced science products. These re-analyzed products are openly available for population statistics studies, characterization of specific targets, or detected point source identification.

Read this paper on arXiv…

J. Hagan, E. Choquet, R. Soummer, et. al.
Fri, 23 Feb 18

Comments: Accepted for publication in AJ. 11 pages

Possible Photometric Signatures of Moderately Advanced Civilizations: The Clarke Exobelt [EPA]

This paper puts forward a possible new indicator for the presence of moderately advanced civilizations on transiting exoplanets. The idea is to examine the region of space around a planet where potential geostationary or geosynchronous satellites would orbit (herafter, the Clarke exobelt). Civilizations with a high density of devices and/or space junk in that region, but otherwise similar to ours in terms of space technology (our working definition of “moderately advanced”), may leave a noticeable imprint on the light curve of the parent star. The main contribution to such signature comes from the exobelt edge, where its opacity is maximum due to geometrical projection. Numerical simulations have been conducted for a variety of possible scenarios. In some cases, a Clarke exobelt with a fractional face-on opacity of ~1E-4 would be easily observable with existing instrumentation. Simulations of Clarke exobelts and natural rings are used to quantify how they can be distinguished by their light curve.

Read this paper on arXiv…

H. Socas-Navarro
Fri, 23 Feb 18

Comments: Accepted for publication in ApJ

Modal Decomposition of TTV – Inferring Planet Masses and Eccentricities [EPA]

Transit timing variations (TTVs) are a powerful tool for characterizing the properties of transiting exoplanets. However, inferring planet properties from the observed timing variations is a challenging task, which is usually addressed by extensive numerical searches. We propose a new, computationally inexpensive method for inverting TTV signals in a planetary system of two transiting planets. To the lowest order in planetary masses and eccentricities, TTVs can be expressed as a linear combination of 3 functions, which we call the \textit{TTV modes}. These functions depend only on the planets’ linear ephemerides, and can be either constructed analytically, or by performing 3 orbital integrations of the three-body system. Given a TTV signal, the underlying physical parameters are found by decomposing the data as a sum of the TTV modes. We demonstrate the use of this method by inferring the mass and eccentricity of 6 \textit{Kepler} planets that were previously characterized in other studies. Finally we discuss the implications and future prospects of our new method.

Read this paper on arXiv…

I. Linial, S. Gilbaum and R. Sari
Fri, 23 Feb 18

Comments: 10 pages, 7 figures, submitted to ApJ

The frequency of window damage caused by bolide airbursts: a quarter century case study [EPA]

We have empirically estimated how often fireball shocks produce overpressure at the ground sufficient to damage windows. Our study used a numerical entry model to estimate the energy deposition and shock production for a suite of 23 energetic fireballs reported by US Government sensors over the last quarter century. For each of these events we estimated the peak overpressure on the ground and the ground area above overpressure thresholds of 200 and 500 Pa where light and heavy window damage, respectively, is expected. Our results suggest that at the highest overpressure it is the rare, large fireballs (such as the Chelyabinsk fireball) which dominate the long-term areal ground footprints for heavy window damage. The height at the fireball peak brightness and the fireball entry angle contribute to the variance in ground overpressure, with lower heights and shallower angles producing larger ground footprints and more potential damage. The effective threshold energy for fireballs to produce heavy window damage is ~5 – 10 kT; such fireballs occur globally once every one to two years. These largest annual bolide events, should they occur over a major urban centre with large numbers of windows, can be expected to produce economically significant window damage. However, the mean frequency of heavy window damage (overpressure above 500 Pa) from fireball shock waves occurring over urban areas is estimated to be approximately once every 5000 years. Light window damage (overpressure above 200 Pa) is expected every ~600 years.

Read this paper on arXiv…

N. Gi, P. Brown and M. Aftosmis
Thu, 22 Feb 18

Comments: 37 pages, 9 figures, Accepted for publication in MAPS

Comets in UV [EPA]

Comets are important “eyewitnesses” of Solar System formation and evolution. Important tests to determine the chemical composition and to study the physical processes in cometary nuclei and coma need data in the UV range of the electromagnetic spectrum. Comprehensive and complete studies require for additional ground-based observations and in-situ experiments. We briefly review observations of comets in the ultraviolet (UV) and discuss the prospects of UV observations of comets and exocomets with space-born instruments. A special refer is made to the World Space Observatory-Ultraviolet (WSO-UV) project.

Read this paper on arXiv…

B. Shustov, M. Sachkov, A. Castro, et. al.
Wed, 21 Feb 18

Comments: International symposium “Ultraviolet Sky Surveys: the need and the means” 10 – 14 July 2017, Tel Aviv University, Israel