48 research outputs found
Strong XUV irradiation of the Earth-sized exoplanets orbiting the ultracool dwarf TRAPPIST-1
We present an XMM-Newton X-ray observation of TRAPPIST-1, which is an
ultracool dwarf star recently discovered to host three transiting and temperate
Earth-sized planets. We find the star is a relatively strong and variable
coronal X-ray source with an X-ray luminosity similar to that of the quiet Sun,
despite its much lower bolometric luminosity. We find L_x/L_bol=2-4x10^-4, with
the total XUV emission in the range L_xuv/L_bol=6-9x10^-4, and XUV irradiation
of the planets that is many times stronger than experienced by the present-day
Earth. Using a simple energy-limited model we show that the relatively close-in
Earth-sized planets, which span the classical habitable zone of the star, are
subject to sufficient X-ray and EUV irradiation to significantly alter their
primary and any secondary atmospheres. Understanding whether this high-energy
irradiation makes the planets more or less habitable is a complex question, but
our measured fluxes will be an important input to the necessary models of
atmospheric evolution.Comment: 5 pages, published as a letter in MNRAS (accepted 16 September 2016
A precise optical transmission spectrum of the inflated exoplanet WASP-52b
We have measured a precise optical transmission spectrum for WASP-52b, a
highly inflated hot Jupiter with an equilibrium temperature of 1300 K. Two
transits of the planet were observed spectroscopically at low resolution with
the auxiliary-port camera (ACAM) on the William Herschel Telescope (WHT),
covering a wide range of 4000-8750 \AA. We use a Gaussian process approach to
model the correlated noise in the multi-wavelength light curves, resulting in a
high precision relative transmission spectrum with errors on the order of a
pressure scale height. We attempted to fit a variety of different
representative model atmospheres to the transmission spectrum, but did not find
a satisfactory match to the entire spectral range. For the majority of the
covered wavelength range (4000-7750 \AA) the spectrum is flat, and can be
explained by an optically thick and grey cloud layer at 0.1 mbar, but this is
inconsistent with a slightly deeper transit at wavelengths \AA. We
were not able to find an obvious systematic source for this feature, so this
opacity may be the result of an additional unknown absorber.Comment: Submitted to MNRAS 17 Jan 2017, revised version after comments from
reviewer, 12 pages, 10 figure
The composition and dynamics of exoplanet atmospheres.
The study of exoplanets has rapidly developed in the last twenty years, and the detailed characterization of planetary atmospheres has become a key area of research.
For transiting planets around bright stars, atmospheric features can be detected with transmission spectroscopy. I will present a low resolution transmission spectrum of WASP-52b, and show that the most likely interpretation is that the planet is shrouded with an opaque cloud layer.
By using transmission spectroscopy at much higher resolution, in this thesis I will present the first spatially resolved measurements of a weather system in an exoplanet. By modeling the absorption profile of sodium on HD189733b, I show that the planet atmosphere has an excess velocity not explained by planetary rotation.
HD209458b is evaporating under intense irradiation from its star, and may lose as much as 1010 g s-1. Mechanisms of mass loss are poorly understood, in particular the efficiency. To calculate this rate for HD209458b a key component is missing - the high energy flux of the star. I will demonstrate that it is possible to recover this flux by building a coronal model for the star, using constraints for different temperatures of plasma from UV and X-ray sources.
I will present commissioning data gathered with NGTS that are the most precise ever gathered with a ground based wide field transit survey. Simulations of the performance of NGTS in this thesis show that the survey can be expected to detect ~200 low mass planets.
The simulations of NGTS also show that a sample of bright super-Earths and hot-Neptunes can be expected to be detected, which would be sensitive to the same techniques performed on hot Jupiters in this thesis. One day, these same techniques could be important tools for characterizing the atmospheres of Earth analogs
Transit Signatures of Inhomogeneous Clouds on Hot Jupiters: Insights From Microphysical Cloud Modeling
We determine the observability in transmission of inhomogeneous cloud cover
on the limbs of hot Jupiters through post processing a general circulation
model to include cloud distributions computed using a cloud microphysics model.
We find that both the east and west limb often form clouds, but that the
different properties of these clouds enhances the limb to limb differences
compared to the clear case. Using JWST it should be possible to detect the
presence of cloud inhomogeneities by comparing the shape of the transit
lightcurve at multiple wavelengths because inhomogeneous clouds impart a
characteristic, wavelength dependent signature. This method is statistically
robust even with limited wavelength coverage, uncertainty on limb darkening
coefficients, and imprecise transit times. We predict that the short wavelength
slope varies strongly with temperature. The hot limb of the hottest planets
form higher altitude clouds composed of smaller particles leading to a strong
rayleigh slope. The near infrared spectral features of clouds are almost always
detectable, even when no spectral slope is visible in the optical. In some of
our models a spectral window between 5 and 9 microns can be used to probe
through the clouds and detect chemical spectral features. Our cloud particle
size distributions are not log-normal and differ from species to species. Using
the area or mass weighted particle size significantly alters the relative
strength of the cloud spectral features compared to using the predicted size
distribution. Finally, the cloud content of a given planet is sensitive to a
species' desorption energy and contact angle, two parameters that could be
constrained experimentally in the future.Comment: 21 pages, 17 figures, submitted to ApJ, revised following comments
from refere
Moyo Vol. X N 1
Million, Chris. Coming Around to Reality: Former Cult Member Turned Editor Uses You for His Own Therapeutic Purposes . 4.
Louden, Annie. A Disciple of Mr. Dewey, and All His Dirty Little Decimals: Confession of a Book-Hoarding Monomaniac . 5.
Soucy, Kate. 14 Days in Dumay: Reflections After a Trip to Haiti . 6.
Frieberg, Alicia. Foreign Hostel Encounters:Ireland, Land of Ire . 8.
Fisher, Dan. Open the Road Wider. Open The Road Wider. The Girft of the Reverend Jusan Fudo William Frank Parker . 10.
Barrett, Laura. Requiem for An Okay Cat . Cinema Annex Formerly Home to One Heck of an Adequate Feline . 11.
The Editors. Late-Night Delivery Frightens Editors into Submission . 12.
2nd Chief Angel of the Quill. A Statement from the Mystic and Calorific Band of the Wingless Angels . 13.
Miller, Jeremy. Rapunzel, Rapunzel, Let Down Your Keycard! Denison man Struggles to Reach Girlfriend at Medium Security Prison... er... University . 15.
Mallinger, Adam. Cult-Invated Taste: Pop Cult Vs. Pop Culture . 16.; Million, Chris. A Day in the Lights. A Ballet Boy\u27s Continued Search for masculinity . 18.
Newitt, Heidi. Show Us Your Tits! A Feminist Glimpse Into the Overt Misogyny in Popular Culture Today . 20.
Woods, Lindsay. Stuck in the Doledrums. Attempted Seduction of U.S. Senator Strikes Out . 22.
Hankinson, Tom. Wingless Angels Just a Bunch of Dorks: Denison\u27s Secret Society-Watch Out, They Might Hit You With a Pocket Protector . 20.
Silverstein, Illana. First Contact: Improvisational Dance on Campus . 32.
Dunson, Jim. Philosophy of Pecan Pie: The Culmination of a Grand Tradition of Cu-lino-Epistemological Thought .
Kovach, Steve. Empirical Test Goes Horribly Awry: Frozen Yogurt Proves Less Philosophically Fruitful than Pie . 34
The XUV environments of exoplanets from Jupiter-size to super-Earth
Planets that reside close-in to their host star are subject to intense high-energy irradiation. Extreme-ultraviolet (EUV) and X-ray radiation (together, XUV) is thought to drive mass-loss from planets with volatile envelopes. We present XMM–Newton observations of six nearby stars hosting transiting planets in tight orbits (with orbital period, Porb < 10 d), wherein we characterize the XUV emission from the stars and subsequent irradiation levels at the planets. In order to reconstruct the unobservable EUV emission, we derive a new set of relations from Solar TIMED/SEE data that are applicable to the standard bands of the current generation of X-ray instruments. From our sample, WASP-80b and HD 149026b experience the highest irradiation level, but HAT-P-11b is probably the best candidate for Ly α evaporation investigations because of the system’s proximity to the Solar system. The four smallest planets have likely lost a greater percentage of their mass over their lives than their larger counterparts. We also detect the transit of WASP-80b in the near-ultraviolet with the optical monitor on XMM–Newton
Single transit candidates from K2 : detection and period estimation
Photometric surveys such as Kepler have the precision to identify exoplanet and eclipsing binary candidates from only a single transit. K2, with its 75 d campaign duration, is ideally suited to detect significant numbers of single-eclipsing objects. Here we develop a Bayesian transit-fitting tool (‘Namaste: An Mcmc Analysis of Single Transit Exoplanets’) to extract orbital information from single transit events. We achieve favourable results testing this technique on known Kepler planets, and apply the technique to seven candidates identified from a targeted search of K2 campaigns 1, 2 and 3. We find EPIC203311200 to host an excellent exoplanet candidate with a period, assuming zero eccentricity, of 540+410 −230 d and a radius of 0.51 ± 0.05RJup. We also find six further transit candidates for which more follow-up is required to determine a planetary origin. Such a technique could be used in the future with TESS, PLATO and ground-based photometric surveys such as NGTS, potentially allowing the detection of planets in reach of confirmation by Gaia
Global Climate and Atmospheric Composition of the Ultra-Hot Jupiter WASP-103b from HST and Spitzer Phase Curve Observations
We present thermal phase curve measurements for the hot Jupiter WASP-103b
observed with Hubble/WFC3 and Spitzer/IRAC. The phase curves have large
amplitudes and negligible hotspot offsets, indicative of poor heat
redistribution to the nightside. We fit the phase variation with a range of
climate maps and find that a spherical harmonics model generally provides the
best fit. The phase-resolved spectra are consistent with blackbodies in the
WFC3 bandpass, with brightness temperatures ranging from K on the
nightside to K on the dayside. The dayside spectrum has a
significantly higher brightness temperature in the Spitzer bands, likely due to
CO emission and a thermal inversion. The inversion is not present on the
nightside. We retrieved the atmospheric composition and found the composition
is moderately metal-enriched ( solar)
and the carbon-to-oxygen ratio is below 0.9 at confidence. In
contrast to cooler hot Jupiters, we do not detect spectral features from water,
which we attribute to partial HO dissociation. We compare the phase curves
to 3D general circulation models and find magnetic drag effects are needed to
match the data. We also compare the WASP-103b spectra to brown dwarfs and young
directly imaged companions and find these objects have significantly larger
water features, indicating that surface gravity and irradiation environment
play an important role in shaping the spectra of hot Jupiters. These results
highlight the 3D structure of exoplanet atmospheres and illustrate the
importance of phase curve observations for understanding their complex
chemistry and physics.Comment: 25 pages, 17 figures, 7 tables; accepted to A
ACCESS & LRG-BEASTS: a precise new optical transmission spectrum of the ultrahot Jupiter WASP-103b
We present a new ground-based optical transmission spectrum of the ultrahot
Jupiter WASP-103b (K). Our transmission spectrum is the result
of combining five new transits from the ACCESS survey and two new transits from
the LRG-BEASTS survey with a reanalysis of three archival Gemini/GMOS transits
and one VLT/FORS2 transit. Our combined 11-transit transmission spectrum covers
a wavelength range of 3900--9450A with a median uncertainty in the transit
depth of 148 parts-per-million, which is less than one atmospheric scale height
of the planet. In our retrieval analysis of WASP-103b's combined optical and
infrared transmission spectrum, we find strong evidence for unocculted bright
regions () and weak evidence for HO (), HCN
(), and TiO (), which could be responsible for
WASP-103b's observed temperature inversion. Our optical transmission spectrum
shows significant structure that is in excellent agreement with the extensively
studied ultrahot Jupiter WASP-121b, for which the presence of VO has been
inferred. For WASP-103b, we find that VO can only provide a reasonable fit to
the data if its abundance is implausibly high and we do not account for stellar
activity. Our results highlight the precision that can be achieved by
ground-based observations and the impacts that stellar activity from F-type
stars can have on the interpretation of exoplanet transmission spectra.Comment: 33 pages, 17 figures, 7 tables. Accepted for publication in A