Exoplanet atmospheres

Abstract:

As a demonstration of the capabilities of the new Oxford SWIFT integral field spectrograph, we present first observations for a set of 14 early-type galaxies in the core of the Coma cluster. Our data consist of I- and z-band spatially resolved spectroscopy obtained with the Oxford SWIFT spectrograph, combined with r-band photometry from the SDSS archive for 14 early- type galaxies. We derive spatially resolved kinematics for all objects from observations of the calcium triplet absorption features at \sim 8500 {AA} . Using this kinematic information we classify galaxies as either Fast Rotators or Slow Rotators. We compare the fraction of fast and slow rotators in our sample, representing the densest environment in the nearby Universe, to results from the ATLAS3D survey, finding the slow rotator fraction is \sim 50 per cent larger in the core of the Coma cluster than in the Virgo cluster or field, a 1.2 {\sigma} increase given our selection criteria. Comparing our sample to the Virgo cluster core only (which is 24 times less dense than the Coma core) we find no evidence of an increase in the slow rotator fraction. Combining measurements of the effective velocity dispersion {\sigma_e} with the photometric data we determine the Fundamental Plane for our sample of galaxies. We find the use of the average velocity dispersion within 1 effective radius, {\sigma_e}, reduces the residuals by 13 per cent with respect to comparable studies using central velocity dispersions, consistent with other recent integral field Fundamental Plane determinations.

Abstract:

Thunderstorm activity has been observed on Saturn via radio emissions from lightning discharges and optical detections of the lightning flashes on the planets nightside. Thunderstorms provide extreme environments in which specific atmospheric chemistry can be induced - namely through energy release via lightning discharges, and fast vertical transport resulting in rapid advection of tropospheric species. It is thus theorised that certain atmospheric trace species such as C 2H 2, HCN, and CO can be generated in the troposphere by large bursts of energy in the form of lightning, and transported upward towards the upper troposphere by the extreme dynamics of thunderstorms, where they should be observable by satellite instruments. In this work, high-spectral-resolution Cassini/CIRS observations from October 2005 through April 2009 are used to study whether there is an observable increase in upper tropospheric acetylene in regions of known normal thunderstorm activity. Using both individual measurements in which there is known thunderstorm activity, as well as large coadditions of data to study latitudinal-dependencies over the full disc, no systematic enhancement in upper tropospheric (100 mbar) C 2H 2 was detected around regions in which there are known occurrences of normally sized (2000 km) thunderstorms, or in normally sized thunderstorm-prone regions such as 40°S. It is likely that the magnitude of the enhancement theorised is too generous or that enhancements are not advected into the upper troposphere as vertical mixing rates in models would suggest, since Cassini/CIRS can only detect C 2H 2 above the 200 mbar level - although the massive northern hemisphere thunderstorm of 2010/2011 seems able to decrease stratospheric concentrations of C 2H 2. From this, it can be asserted that lightning from normal thunderstorm activity cannot be the key source for upper tropospheric C 2H 2 on Saturn, since the upper-tropospheric concentrations retrieved agree with the concentrations stemming from the photolysis of CH 4 (23 ppbv) from solar radiation penetrating through the Saturnian atmosphere, with an upper limit for lightning-induced C 2H 2 volume mixing ratio of 10 -9. © 2012 Elsevier Ltd. All rights reserved.

Abstract:

The existence of methane in Titan's atmosphere (∼6% level at the surface) presents a unique enigma, as photochemical models predict that the current inventory will be entirely depleted by photochemistry in a timescale of ∼20Myr. In this paper, we examine the clues available from isotopic ratios (12C/13C and D/H) in Titan's methane as to the past atmosphere history of this species. We first analyze recent infrared spectra of CH4 collected by the Cassini Composite Infrared Spectrometer, measuring simultaneously for the first time the abundances of all three detected minor isotopologues: 13CH4, 12CH3D, and 13CH3D. From these we compute estimates of 12C/13C= 86.5 ± 8.2 and D/H= (1.59 ± 0.33) × 10-4, in agreement with recent results from the Huygens GCMS and Cassini INMS instruments. We also use the transition state theory to estimate the fractionation that occurs in carbon and hydrogen during a critical reaction that plays a key role in the chemical depletion of Titan's methane: CH4+ C2H→ CH3+ C2H2. Using these new measurements and predictions we proceed to model the time evolution of 12C/13C and D/H in Titan's methane under several prototypical replenishment scenarios. In our Model1 (no resupply of CH4), we find that the present-day 12C/13C implies that the CH4 entered the atmosphere 60-1600Myr ago if methane is depleted by chemistry and photolysis alone, but much more recently - most likely less than 10Myr ago - if hydrodynamic escape is also occurring. On the other hand, if methane has been continuously supplied at the replenishment rate then the isotopic ratios provide no constraints, and likewise for the case where atmospheric methane is increasing. We conclude by discussing how these findings may be combined with other evidence to constrain the overall history of the atmospheric methane. © 2012 The American Astronomical Society. All rights reserved.