No large population of unbound or wide-orbit Jupiter-mass planets [EPA]

Gravitational microlensing is the only method capable of exploring the entire population of free-floating planets down to Mars-mass objects, because the microlensing signal does not depend on the brightness of the lensing object. A characteristic timescale of microlensing events depends on the mass of the lens: the less massive the lens, the shorter the microlensing event. A previous analysis of 474 microlensing events found an excess of very short events (1-2 days) – more than known stellar populations would suggest – indicating the existence of a large population of unbound or wide-orbit Jupiter-mass planets (reported to be almost twice as common as main-sequence stars). These results, however, do not match predictions of planet formation theories and are in conflict with surveys of young clusters. Here we report the analysis of a six times larger sample of microlensing events discovered during the years 2010-2015. Although our survey has very high sensitivity (detection efficiency) to short-timescale (1–2 days) microlensing events, we found no excess of events with timescales in this range, with a 95% upper limit on the frequency of Jupiter-mass free-floating or wide-orbit planets of 0.25 planet per main-sequence star. We detected a few possible ultrashort-timescale events (with timescales of less than 0.5 day), which may indicate the existence of Earth- and super-Earth-mass free-floating planets, as predicted by planet-formation theories. [abridged]

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P. Mroz, A. Udalski, J. Skowron, et. al.
Tue, 25 Jul 17

Comments: published in Nature, authors’ version (see for the published version)

Extrasolar Planets and Their Host Stars [EPA]

In order to understand the exoplanet, you need to understand its parent star. Astrophysical parameters of extrasolar planets are directly and indirectly dependent on the properties of their respective host stars. These host stars are very frequently the only visible component in the systems. This book describes our work in the field of characterization of exoplanet host stars using interferometry to determine angular diameters, trigonometric parallax to determine physical radii, and SED fitting to determine effective temperatures and luminosities. The interferometry data are based on our decade-long survey using the CHARA Array. We describe our methods and give an update on the status of the field, including a table with the astrophysical properties of all stars with high-precision interferometric diameters out to 150 pc (status Nov 2016). In addition, we elaborate in more detail on a number of particularly significant or important exoplanet systems, particularly with respect to (1) insights gained from transiting exoplanets, (2) the determination of system habitable zones, and (3) the discrepancy between directly determined and model-based stellar radii. Finally, we discuss current and future work including the calibration of semi-empirical methods based on interferometric data.

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K. Braun and T. Boyajian
Tue, 25 Jul 17

Comments: 80 pages in SpringerBrief format containing a few blank pages, 16 figures, 1 table of all stars with high-precision interferometric diameters, glossary of commonly encountered terms, SpringerBrief 2017, ISBN 978-3-319-61198-3

VLA observations of the disk around the young brown dwarf 2MASS J044427+2512 [EPA]

We present multi-wavelength radio observations obtained with the VLA of the protoplanetary disk surrounding the young brown dwarf 2MASS J04442713+2512164 (2M0444) in the Taurus star forming region. 2M0444 is the brightest known brown dwarf disk at millimeter wavelengths, making this an ideal target to probe radio emission from a young brown dwarf. Thermal emission from dust in the disk is detected at 6.8 and 9.1 mm, whereas the 1.36 cm measured flux is dominated by ionized gas emission. We combine these data with previous observations at shorter sub-mm and mm wavelengths to test the predictions of dust evolution models in gas-rich disks after adapting their parameters to the case of 2M0444. These models show that the radial drift mechanism affecting solids in a gaseous environment has to be either completely made inefficient, or significantly slowed down by very strong gas pressure bumps in order to explain the presence of mm/cm-sized grains in the outer regions of the 2M0444 disk. We also discuss the possible mechanisms for the origin of the ionized gas emission detected at 1.36 cm. The inferred radio luminosity for this emission is in line with the relation between radio and bolometric luminosity valid for for more massive and luminous young stellar objects, and extrapolated down to the very low luminosity of the 2M0444 brown dwarf.

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L. Ricci, H. Rome, P. Pinilla, et. al.
Tue, 25 Jul 17

Comments: 9 pages, 5 figures, accepted for publication in ApJ

Planet formation and disk-planet interactions [EPA]

This review is based on lectures given at the 45th Saas-Fee Advanced Course ‘From Protoplanetary Disks to Planet Formation’ held in March 2015 in Les Diablerets, Switzerland. Starting with an overview of the main characterictics of the Solar System and extrasolar planets, we describe the planet formation process in terms of the sequential accretion scenario. First the growth processes of dust particles to planetesimals and subsequently to terrestrial planets or planetary cores are presented. This is followed by the formation process of the giant planets either by core accretion or gravitational instability. Finally, the dynamical evolution of the orbital elements as driven by disk-planet interaction and the overall evolution of multi-object systems is presented.

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W. Kley
Tue, 25 Jul 17

Comments: Lecture Notes of the 45th Saas-Fee Advanced Course ‘From Protoplanetary Disks to Planet Formation’, March 2015, 111 Pages

On the use of the autonomous Birkhoff equations in Lie series perturbation theory [EPA]

In this article, we present the Lie transformation algorithm for autonomous Birkhoff systems. Here, we are referring to Hamiltonian systems that obey a symplectic structure of the general form. Two examples of normalization in the restricted three-body problem are given to illustrate the application of the algorithm in perturbation theory. The efficiency of this algorithm for problems of asymptotic integration in dynamics is discussed for the case where there is a need to use non-canonical variables in the phase space.

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T. Boronenko
Tue, 25 Jul 17

Comments: 27 pages

A novel strategy to seek bio-signatures at Enceladus and Europa [EPA]

A laboratory experiment is suggested in which conditions similar to those in the plume ejecta from Enceladus and, perhaps, Europa are established. Using infrared spectroscopy and polarimetry, the experiment might identify possible bio-markers in differential measurements of water from the open-ocean, from hydrothermal vents, and abiotic water samples. Should the experiment succeed, large telescopes could be used to acquire sensitive infrared spectra of the plumes of Enceladus and Europa, as the satellites transit the bright planetary disks. The extreme technical challenges encountered in so doing are similar to those of solar imaging spectropolarimetry. The desired signals are buried in noisy data in the presence of seeing-induced image motion and a changing natural source. Some differential measurements used for solar spectropolarimetry can achieve S/N ratios of $10^5$ even in the presence of systematic errors two orders of magnitude larger. We review the techniques and likelihood of success of such an observing campaign with some of the world’s largest ground-based telescopes, as well as the long anticipated James Webb Space Telescope. We discuss the relative merits of the new 4m Daniel K. Inouye Solar Telescope, as well as the James Webb Space Telescope and larger ground-based observatories, for observing the satellites of giant planets. As seen from near Earth, transits of Europa occur regularly, but transits of Enceladus will begin again only in 2022.

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P. Judge
Tue, 25 Jul 17

Comments: Accepted for publication in Astrobiology

Developing a Method to Determine Electrical Conductivity in Meteoritic Materials with Applications to Induction Heating Theory (2008 Student Thesis) [EPA]

Magnetic induction was first proposed as a planetary heating mechanism by Sonett and Colburn in 1968, in recent years this theory has lost favor as a plausible source of heating in the early solar system. However, new models of proto-planetary disk evolution suggest that magnetic fields play an important role in solar system formation. In particular, the magneto-hydrodynamic behavior of proto-planetary disks is believed to be responsible for the net outward flow of angular momentum in the solar system. It is important to re-evaluate the plausibility of magnetic induction based on the intense magnetic field environments described by the most recent models of proto-planetary disk evolution.
In order to re-evaluate electromagnetic induction theory the electrical conductivity of meteorites must be determined. To develop a technique capable of making these measurements, a time-varying magnetic field was generated to inductively heat metallic control samples. The thermal response of each sample, which depends on electrical conductivity, was monitored until a thermal steady state was achieved. The relationship between conductivity and thermal response can be exploited to estimate the electrical conductivity of unknown samples. After applying the technique to various metals it was recognized that this method is not capable of making precise electrical conductivity measurements. However, this method can constrain the product of the electrical conductivity and the square of the magnetic permeability, or ${\sigma}{{\mu}^2}$, for meteoritic and metallic samples alike. The results also illustrate that along with electrical conductivity {\sigma}, the magnetic permeability {\mu} of a substance has an important effect on induction heating phenomena for paramagnetic ({\mu}/{\mu}0 > 1) and especially ferromagnetic materials ({\mu}/{\mu}0 >> 1).

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D. DellaGiustina
Tue, 25 Jul 17

Comments: N/A