66 research outputs found
Characterization of Planetary Atmospheres
After the discovery of the first exoplanet in 1990’s and a fast growing number of discoveries since then, there have been many attempts to observe and characterize their atmospheres. In particular, water and methane have been the focus of many investigations due to their relevance to the origin of life and habitability, as well as their major roles to shape the structure of planetary atmospheres. Abundances retrieved for these species can be also used as a tracer of carbon-to-oxygen ratio (C/O) and metallicity of these atmospheres; hence potentially linking the formation scenarios with the observations. Water’s spectral signature is everywhere, but despite many efforts, there has been only one robust detection of methane and only recently. The question is,
“where is methane?”.
By applying a hierarchical modelling approach (utilising more than 177,000 thermochemical equilibrium cloud-free, disequilibrium cloud-free, and thermochemical equilibrium cloudy models) we predict that there are four classes of irradiated gaseous planets; two of them (Class-I and Class-II; Teff<1650 K) likely to show signatures of CH4 in their transmission spectra, if cloudy-free and C/O above a certain threshold (aka the “Methane Valley”). The effect of disequilibrium processes on the classification found to be modest with a more continuous transition between Class-II and III planets. Clouds, however, heat-up the deeper parts of Class-I and Class-II planets; removing CH4 from the photosphere. Simultaneously, clouds obscure any molecular features; hence making the observation of methane even more challenging
Presence of liquid water during the evolution of exomoons orbiting ejected free-floating planets
Free-floating planets (FFPs) can result from dynamical scattering processes
happening in the first few million years of a planetary system's life. Several
models predict the possibility, for these isolated planetary-mass objects, to
retain exomoons after their ejection. The tidal heating mechanism and the
presence of an atmosphere with a relatively high optical thickness may support
the formation and maintenance of oceans of liquid water on the surface of these
satellites. In order to study the timescales over which liquid water can be
maintained, we perform dynamical simulations of the ejection process and infer
the resulting statistics of the population of surviving exomoons around
free-floating planets. The subsequent tidal evolution of the moons' orbital
parameters is a pivotal step to determine when the orbits will circularize,
with a consequential decay of the tidal heating. We find that close-in (R) Earth-mass moons with CO-dominated atmospheres
could retain liquid water on their surfaces for long timescales, depending on
the mass of the atmospheric envelope and the surface pressure assumed. Massive
atmospheres are needed to trap the heat produced by tidal friction that makes
these moons habitable. For Earth-like pressure conditions ( = 1 bar),
satellites could sustain liquid water on their surfaces up to 52 Myr. For
higher surface pressures (10 and 100 bar), moons could be habitable up to 276
Myr and 1.6 Gyr, respectively. Close-in satellites experience habitable
conditions for long timescales, and during the ejection of the FFP remain bound
with the escaping planet, being less affected by the close encounter.Comment: 21 pages, 12 figures, accepted for publication on International
Journal of Astrobiolog
A Pilot Survey of an M Dwarf Flare Star with Swift's UV Grism
The near-ultraviolet (NUV) spectral region is a useful diagnostic for stellar
flare physics and assessing the energy environment of young exoplanets,
especially as relates to prebiotic chemistry. We conducted a pilot NUV
spectroscopic flare survey of the young M dwarf AU Mic with the Neil Gehrels
Swift Observatory's UltraViolet and Optical Telescope. We detected four flares
and three other epochs of significantly elevated count rates during the 9.6
hours of total exposure time, consistent with a NUV flare rate of 0.5
hour. The largest flare we observed released a minimum energy of
610 erg between 1730-5000 \r{A}. All flares had durations longer
than the 14-17 minute duration of each Swift visit, making measuring
total flare energy and duration infeasible.Comment: Published in Research Notes of the AAS (RNAAS
Ground-based detection of an extended helium atmosphere in the Saturn-mass exoplanet WASP-69b
Hot gas giant exoplanets can lose part of their atmosphere due to strong
stellar irradiation, affecting their physical and chemical evolution. Studies
of atmospheric escape from exoplanets have mostly relied on space-based
observations of the hydrogen Lyman-{\alpha} line in the far ultraviolet which
is strongly affected by interstellar absorption. Using ground-based
high-resolution spectroscopy we detect excess absorption in the helium triplet
at 1083 nm during the transit of the Saturn-mass exoplanet WASP-69b, at a
signal-to-noise ratio of 18. We measure line blue shifts of several km/s and
post transit absorption, which we interpret as the escape of part of the
atmosphere trailing behind the planet in comet-like form.
[Additional notes by authors: Furthermore, we provide upper limits for helium
signals in the atmospheres of the exoplanets HD 209458b, KELT-9b, and GJ 436b.
We investigate the host stars of all planets with detected helium signals and
those of the three planets we derive upper limits for. In each case we
calculate the X-ray and extreme ultraviolet flux received by these planets. We
find that helium is detected in the atmospheres of planets (orbiting the more
active stars and) receiving the larger amount of irradiation from their host
stars.]Comment: Submitted to Science on 14 March 2018; Accepted by Science on 16
November 2018; Published by Science on 6 December 2018. This is the author's
version of the work. It is posted here by permission of the AAAS for personal
use. The definitive version was published in Science, on 6 December 2018 -
Report: pages 21 (preprint), 4 figures - Supplementary materials: 22 pages,
10 figures, 3 table
Stellar Astrophysics and Exoplanet Science with the Maunakea Spectroscopic Explorer (MSE)
The Maunakea Spectroscopic Explorer (MSE) is a planned 11.25-m aperture
facility with a 1.5 square degree field of view that will be fully dedicated to
multi-object spectroscopy. A rebirth of the 3.6m Canada-France-Hawaii Telescope
on Maunakea, MSE will use 4332 fibers operating at three different resolving
powers (R ~ 2500, 6000, 40000) across a wavelength range of 0.36-1.8mum, with
dynamical fiber positioning that allows fibers to match the exposure times of
individual objects. MSE will enable spectroscopic surveys with unprecedented
scale and sensitivity by collecting millions of spectra per year down to
limiting magnitudes of g ~ 20-24 mag, with a nominal velocity precision of ~100
m/s in high-resolution mode. This white paper describes science cases for
stellar astrophysics and exoplanet science using MSE, including the discovery
and atmospheric characterization of exoplanets and substellar objects, stellar
physics with star clusters, asteroseismology of solar-like oscillators and
opacity-driven pulsators, studies of stellar rotation, activity, and
multiplicity, as well as the chemical characterization of AGB and extremely
metal-poor stars.Comment: 31 pages, 11 figures; To appear as a chapter for the Detailed Science
Case of the Maunakea Spectroscopic Explore
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