arXiv subjects

C. V. Morley

Publications and source records attributed to C. V. Morley.

9 recordsLinked to original sources

arXiv2026

Clouds with a silicate lining: Using JWST spectra to probe atmospheric diversity in young AB Dor L dwarfs

We present the first full JWST NIRSpec Prism and MIRI LRS 0.6 - 14 $μ$m (R ~ 100) spectra and analysis of five ~ 133 Myr L dwarf members of the AB Doradus moving group and one probable $\sim 500$ Myr T dwarf of the Oceanus moving group with known inclination angles between ~ $23 - 90^{\circ}$: W0047+68, 2M0355+11, 2M0642+41, W1741-46, 2M2206-42, and 2M2244+20. We construct near-complete spectral energy distributions of each of our objects to measure their bolometric luminosities, and estimate their fundamental parameters ($T_{\text{eff}}$, radius, $M$ and $\log g$). We use cross-sections of relevant gases to identify the species that are present in each atmosphere. Of particular interest is the silicate absorption feature at 8 - 11 $μ$m, which provides insight into the complex cloud structure of brown dwarfs. We examine this silicate absorption feature in detail and also test whether there exists a latitudinal dependence in the silicate absorption feature within a coeval sample of brown dwarfs. Various molecular absorption bands are visible in our spectra, including H$_2$O, CH$_4$, CO and CO$_2$. The shape of the silicate absorption feature varies within our sample, and we find that 4/5 of our L type objects agree with previously observed trends stating that objects viewed equator-on have deeper silicate absorption. We highlight W1741-46 as an outlier in our sample with an unusually strong silicate absorption given its near pole-on orientation. We also present a tentative correlation between the wavelength of peak silicate absorption and inclination, which may suggest variations in cloud chemical composition or physical properties. We find an unexpected spectral diversity within our sample, which motivates future studies on these objects through atmospheric retrievals, which will determine the silicate cloud composition and reveal whether there exists a trend with inclination.

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arXiv2025

Cold day-side winds shape large leading streams in evaporating exoplanet atmospheres

Recent observations of planetary atmospheres in HAT-P-32 b and HAT-P-67 b reveal extensive outflows reaching up to hundreds of planetary radii. The helium 1083 nm light curves for these planets, captured across their full orbits, show notable asymmetries: both planets display more pronounced pre-transit than post-transit absorptions, with HAT-P-67 b being the more extreme case of that geometry. Using three-dimensional (3D) hydrodynamic simulations, we identify key factors influencing the formation of a dense leading outflow stream and characterize its morphology. Our models suggest that such a geometry of escaped material is caused by a relatively cold outflow of high mass-loss rate, launched preferentially from the planet's day side. From the simulations we calculate synthetic He I 1083 nm spectra that show large absorption depths and irregular line profiles due to complex gas kinematics. We find that the measurements of the He I 1083 nm equivalent width and the velocity shift relative to the planet's rest frame, observed over a significant portion of the planet's orbital phase, can provide important constraints on the outflow properties and its interaction with the stellar wind.

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arXiv2025

A temperate super-Jupiter imaged with JWST in the mid-infrared

Of the ~25 directly imaged planets to date, all are younger than 500Myr and all but 6 are younger than 100Myr. Eps Ind A (HD209100, HIP108870) is a K5V star of roughly solar age (recently derived as 3.7-5.7Gyr and 3.5$^{+0.8}_{-1.3}$Gyr). A long-term radial velocity trend as well as an astrometric acceleration led to claims of a giant planet orbiting the nearby star (3.6384$\pm$0.0013pc). Here we report JWST coronagraphic images that reveal a giant exoplanet which is consistent with these radial and astrometric measurements, but inconsistent with the previously claimed planet properties. The new planet has temperature ~275K, and is remarkably bright at 10.65um and 15.50um. Non-detections between 3.5-5um indicate an unknown opacity source in the atmosphere, possibly suggesting a high metallicity, high carbon-to-oxygen ratio planet. The best-fit temperature of the planet is consistent with theoretical thermal evolution models, which are previously untested at this temperature range. The data indicates that this is likely the only giant planet in the system and we therefore refer to it as ``b", despite it having significantly different orbital properties than the previously claimed planet ``b".

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arXiv2015

Discovery and spectroscopy of the young Jovian planet 51 Eri b with the Gemini Planet Imager

Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric composition and luminosity, which is influenced by their formation mechanism. Using the Gemini Planet Imager, we discovered a planet orbiting the \$sim$20 Myr-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water vapor absorption. Modeling of the spectra and photometry yields a luminosity of L/LS=1.6-4.0 x 10-6 and an effective temperature of 600-750 K. For this age and luminosity, "hot-start" formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the "cold- start" core accretion process that may have formed Jupiter.

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arXiv2014

Near-infrared Detection of WD 0806-661 B with the Hubble Space Telescope

WD 0806-661 B is one of the coldest known brown dwarfs (T=300-345 K) based on previous mid-infrared photometry from the Spitzer Space Telescope. In addition, it is a benchmark for testing theoretical models of brown dwarfs because its age and distance are well-constrained via its primary star (2+/-0.5 Gyr, 19.2+/-0.6 pc). We present the first near-infrared detection of this object, which has been achieved through F110W imaging (~Y+J) with the Wide Field Camera 3 on board the Hubble Space Telescope. We measure a Vega magnitude of m110=25.70+/-0.08, which implies J~25.0. When combined with the Spitzer photometry, our estimate of J helps to better define the empirical sequence of the coldest brown dwarfs in M4.5 versus J-[4.5]. The positions of WD 0806-661 B and other Y dwarfs in that diagram are best matched by the cloudy models of Burrows et al. and the cloudless models of Saumon et al., both of which employ chemical equilibrium. The calculations by Morley et al. for 50% cloud coverage differ only modestly from the data. Spectroscopy would enable a more stringent test of the models, but based on our F110W measurement, such observations are currently possible only with Hubble, and would require at least ~10 orbits to reach a signal-to-noise ratio of ~5.

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arXiv2014

Discovery of a new Y dwarf: WISE J030449.03-270508.3

We present a new Y dwarf, WISE J030449.03-270508.3, confirmed from a candidate sample designed to pick out low temperature objects from the WISE database. The new object is typed Y0pec following a visual comparison with spectral standards, and lies at a likely distance of 10-17 pc. Its tangential velocity suggests thin disk membership, but it shows some spectral characteristics that suggest it may be metal-poor and/or older than previously identified Y0 dwarfs. Based on trends seen for warmer late type T dwarfs, the Y-band flux peak morphology is indicative of sub-solar metallicity, and the enhanced red wing of the J-band flux peak offers evidence for high gravity and/or low metallicity (with associated model trends suggesting an age closer to ~10 Gyr and mass in the range 0.02-0.03 Mo). This object may thus be extending the population parameter-space of the known Y0 dwarfs.

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arXiv2013

A Search for Methane in the Atmosphere of GJ 1214b via GTC Narrow-Band Transmission Spectrophotometry

We present narrow-band photometric measurements of the exoplanet GJ 1214b using the 10.4 m Gran Telescopio Canarias (GTC) and the OSIRIS instrument. Using tuneable filters we observed a total of five transits, three of which were observed at two wavelengths nearly simultaneously, producing a total of eight individual light curves, six of these probed the possible existence of a methane absorption feature in the 8770 - 8850 Å region at high resolution. We detect no increase in the planet-to-star radius ratio across the methane feature with a change in radius ratio of $Δ$R = -0.0007 $\pm$ 0.0017 corresponding to a scale height (H) change of -0.5 $\pm$ 1.2 H across the methane feature, assuming a hydrogen dominated atmosphere. We find a variety of water and cloudy atmospheric models fit the data well, but find that cloud-free models provide poor fits. These observations support a flat transmission spectrum resulting from the presence of a high-altitude haze or a water-rich atmosphere, in agreement with previous studies. In this study the observations are predominantly limited by the photometric quality and the limited number of data points (resulting from a long observing cadence), which make the determination of the systematic noise challenging. With tuneable filters capable of high resolution measurements (R ~ 600 - 750) of narrow absorption features, the interpretation of our results are also limited by the absence of high resolution methane models below 1 $μ$m.

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arXiv2013

Fundamental properties of T dwarfs from model fits to FIRE spectra

We fit a sample of 49 R=6000 NIR (0.9 - 2.5 micron) T dwarf spectra obtained with Magellan's FIRE spectrograph with two different atmospheric model sets to compare the derived physical parameters such as Teff, log g, cloud opacity, and rotational velocity between the models, as well as their reliability. Many of our T dwarfs have distance measurements, which allows us to calculate their radii during the fitting, which can be compared to evolutionary models to determine age, mass and potentially the presence of unseen companions. We present our spectral sample and model fits, and comment on the measured fundamental properties of these T dwarfs. Our analysis allows us to identify global deviations between models and observed spectra, and hence provides important feedback for the next generation of substellar atmospheric models.

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arXiv2012

A lower radius and mass for the transiting extrasolar planet HAT-P-8b

Context. The extrasolar planet HAT-P-8 b was thought to be one of the more inflated transiting hot Jupiters. Aims. By using new and existing photometric data, we computed precise estimates of the physical properties of the system. Methods. We present photometric observations comprising eleven light curves covering six transit events, obtained using five medium-class telescopes and telescope-defocussing technique. One transit was simultaneously obtained through four optical filters, and two transits were followed contemporaneously from two observatories. We modelled these and seven published datasets using the jktebop code. The physical parameters of the system were obtained from these results and from published spectroscopic measurements. In addition, we investigated the theoretically-predicted variation of the apparent planetary radius as a function of wavelength, covering the range 330-960 nm. Results. We find that HAT-P-8 b has a significantly lower radius (1.321 R_Jup) and mass (1.275 M_Jup) compared to previous estimates (1.50 R_Jup and 1.52 M_Jup respectively). We also detect a radius variation in the optical bands that, when compared with synthetic spectra of the planet, may indicate the presence of a strong optical absorber, perhaps TiO and VO gases, near the terminator of HAT-P-8 b. Conclusions. These new results imply that HAT-P-8 b is not significantly inflated, and that its position in the planetary mass-radius diagram is congruent with those of many other transiting extrasolar planets.

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