4,096 research outputs found
Thermal Emission and Albedo Spectra of Super Earths with Flat Transmission Spectra
Planets larger than Earth and smaller than Neptune are some of the most
numerous in the galaxy, but observational efforts to understand this population
have proved challenging because optically thick clouds or hazes at high
altitudes obscure molecular features (Kreidberg et al. 2014b). We present
models of super Earths that include thick clouds and hazes and predict their
transmission, thermal emission, and reflected light spectra. Very thick, lofted
clouds of salts or sulfides in high metallicity (1000x solar) atmospheres
create featureless transmission spectra in the near-infrared. Photochemical
hazes with a range of particle sizes also create featureless transmission
spectra at lower metallicities. Cloudy thermal emission spectra have muted
features more like blackbodies, and hazy thermal emission spectra have emission
features caused by an inversion layer at altitudes where the haze forms. Close
analysis of reflected light from warm (~400-800 K) planets can distinguish
cloudy spectra, which have moderate albedos (0.05-0.20), from hazy models,
which are very dark (0.0-0.03). Reflected light spectra of cold planets (~200
K) accessible to a space-based visible light coronagraph will have high albedos
and large molecular features that will allow them to be more easily
characterized than the warmer transiting planets. We suggest a number of
complementary observations to characterize this population of planets,
including transmission spectra of hot (>1000 K) targets, thermal emission
spectra of warm targets using the James Webb Space Telescope (JWST), high
spectral resolution (R~10^5) observations of cloudy targets, and reflected
light spectral observations of directly-imaged cold targets. Despite the dearth
of features observed in super Earth transmission spectra to date, different
observations will provide rich diagnostics of their atmospheres.Comment: 23 pages, 23 figures. Revised for publication in The Astrophysical
Journa
Vertical Atmospheric Structure in a Variable Brown Dwarf: Pressure-dependent Phase Shifts in Simultaneous Hubble Space Telescope-Spitzer Light Curves
Heterogeneous clouds or temperature perturbations in rotating brown dwarfs
produce variability in the observed flux. We report time-resolved simultaneous
observations of the variable T6.5 brown dwarf 2MASSJ22282889-431026 over the
wavelength ranges 1.1-1.7 microns and broadband 4.5 microns. Spectroscopic
observations were taken with Wide Field Camera 3 on board the Hubble Space
Telescope and photometry with the Spitzer Space Telescope. The object shows
sinusoidal infrared variability with a period of 1.4 hr at most wavelengths
with peak-to-peak amplitudes between 1.45% and 5.3% of the mean flux. While the
light curve shapes are similar at all wavelengths, their phases differ from
wavelength to wavelength with a maximum difference of more than half of a
rotational period. We compare the spectra with atmospheric models of different
cloud prescriptions, from which we determine the pressure levels probed at
different wavelengths. We find that the phase lag increases with decreasing
pressure level, or higher altitude. We discuss a number of plausible scenarios
that could cause this trend of light curve phase with probed pressure level.
These observations are the first to probe heterogeneity in an ultracool
atmosphere in both horizontal and vertical directions, and thus are an ideal
test case for realistic three dimensional simulations of the atmospheric
structure with clouds in brown dwarfs and extrasolar planets.Comment: Accepted to ApJL, 6 pages, 3 figures. Minor language updates from v1
to match published versio
Practice tests improve performance, increase engagement and protect from psychological distress
The increasing prevalence of high levels of distress in university student populations has led academic and support staff to investigate options to help students cope with academic stress. Our research focused on investigating the benefit of early academic interventions for content engagement and feedback. In a 1st year psychology student sample of 547 we collected data on psychological measures (motivation and distress), practice test engagement and performance on assessment tasks. Assessment data from a baseline phase (practice tests were available) were compared to assessment data from an intervention  (reward for undertaking practice tests). Our experiment also allowed an investigation of the type of benefit gained from practice tests engagement (content specific benefit vs general engagement effects). Results show that undertaking practice tests ahead of assessment quizzes is associated with significantly higher assessment performance.  Practice test uptake significantly increased when an incentive was in place resulting in much higher assessment scores for students. Students who showed high levels of distress on the DASS performed significantly lower on assessments. However, highly distressed students who undertook practice testing showed performance at the same level as non-distressed students.Marlin, S.; English, T.; Morley, L.; O'keefe-Quinn, T.; Whitfield, P. (2020). Practice tests improve performance, increase engagement and protect from psychological distress. En 6th International Conference on Higher Education Advances (HEAd'20). Editorial Universitat Politècnica de València. (30-05-2020):811-818. https://doi.org/10.4995/HEAd20.2020.11151OCS81181830-05-202
Effect of Longitude-Dependent Cloud Coverage on Exoplanet Visible Wavelength Reflected-Light Phase Curves
We use a planetary albedo model to investigate variations in visible wavelength phase curves of exoplanets. Thermal and cloud properties for these exoplanets are derived using one-dimensional radiative-convective and cloud simulations. The presence of clouds on these exoplanets significantly alters their planetary albedo spectra. We confirm that non-uniform cloud coverage on the dayside of tidally locked exoplanets will manifest as changes to the magnitude and shift of the phase curve. In this work, we first investigate a test case of our model using a Jupiter-like planet, at temperatures consistent to 2.0 AU insolation from a solar type star, to consider the effect of H2O clouds. We then extend our application of the model to the exoplanet Kepler-7b and consider the effect of varying cloud species, sedimentation efficiency, particle size, and cloud altitude. We show that, depending on the observational filter, the largest possible shift of the phase curve maximum will be similar to 2 degrees-10 degrees for a Jupiter-like planet, and up to similar to 30 degrees (similar to 0.08 in fractional orbital phase) for hot-Jupiter exoplanets at visible wavelengths as a function of dayside cloud distribution with a uniformly averaged thermal profile. The models presented in this work can be adapted for a variety of planetary cases at visible wavelengths to include variations in planet-star separation, gravity, metallicity, and source-observer geometry. Finally, we tailor our model for comparison with, and confirmation of, the recent optical phase-curve observations of Kepler-7b with the Kepler space telescope. The average planetary albedo can vary between 0.1 and 0.6 for the 1300 cloud scenarios that were compared to the observations. Many of these cases cannot produce a high enough albedo to match the observations. We observe that smaller particle size and increasing cloud altitude have a strong effect on increasing albedo. In particular, we show that a set of models where Kepler-7b has roughly half of its dayside covered in small-particle clouds high in the atmosphere, made of bright minerals like MgSiO3 and Mg2SiO4, provide the best fits to the observed offset and magnitude of the phase-curve, whereas Fe clouds are found to be too dark to fit the observations
EFFECT OF LONGITUDE-DEPENDENT CLOUD COVERAGE ON EXOPLANET VISIBLE WAVELENGTH REFLECTED-LIGHT PHASE CURVES
We use a planetary albedo model to investigate variations in visible wavelength phase curves of exoplanets. Thermal and cloud properties for these exoplanets are derived using one-dimensional radiative-convective and cloud simulations. The presence of clouds on these exoplanets significantly alters their planetary albedo spectra. We confirm that non-uniform cloud coverage on the dayside of tidally locked exoplanets will manifest as changes to the magnitude and shift of the phase curve. In this work, we first investigate a test case of our model using a Jupiter-like planet, at temperatures consistent to 2.0 AU insolation from a solar type star, to consider the effect of H[subscript 2]O clouds. We then extend our application of the model to the exoplanet Kepler-7b and consider the effect of varying cloud species, sedimentation efficiency, particle size, and cloud altitude. We show that, depending on the observational filter, the largest possible shift of the phase curve maximum will be ~2°–10° for a Jupiter-like planet, and up to ~30° (~0.08 in fractional orbital phase) for hot-Jupiter exoplanets at visible wavelengths as a function of dayside cloud distribution with a uniformly averaged thermal profile. The models presented in this work can be adapted for a variety of planetary cases at visible wavelengths to include variations in planet–star separation, gravity, metallicity, and source-observer geometry. Finally, we tailor our model for comparison with, and confirmation of, the recent optical phase-curve observations of Kepler-7b with the Kepler space telescope. The average planetary albedo can vary between 0.1 and 0.6 for the 1300 cloud scenarios that were compared to the observations. Many of these cases cannot produce a high enough albedo to match the observations. We observe that smaller particle size and increasing cloud altitude have a strong effect on increasing albedo. In particular, we show that a set of models where Kepler-7b has roughly half of its dayside covered in small-particle clouds high in the atmosphere, made of bright minerals like MgSiO[subscript 3] and Mg[subscript 2]SiO[subscript 4], provide the best fits to the observed offset and magnitude of the phase-curve, whereas Fe clouds are found to be too dark to fit the observations
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