Gemini/GMOS Transmission Spectral Survey: Complete Optical Transmission Spectrum of the hot Jupiter WASP-4b

We present the complete optical transmission spectrum of the hot Jupiter WASP-4b from 440-940 nm at R ~ 400-1500 obtained with the Gemini Multi-Object Spectrometers (GMOS); this is the first result from a comparative exoplanetology survey program of close-in gas giants conducted with GMOS. WASP-4b has an equilibrium temperature of 1700 K and is favorable to study in transmission due to a large scale height (370 km). We derive the transmission spectrum of WASP-4b using 4 transits observed with the MOS technique. We demonstrate repeatable results across multiple epochs with GMOS, and derive a combined transmission spectrum at a precision about twice above photon noise, which is roughly equal to to one atmospheric scale height. The transmission spectrum is well fitted with a uniform opacity as a function of wavelength. The uniform opacity and absence of a Rayleigh slope from molecular hydrogen suggest that the atmosphere is dominated by clouds with condensate grain size of ~1 um. This result is consistent with previous observations of hot Jupiters since clouds have been seen in planets with similar equilibrium temperatures to WASP-4b. We describe a custom pipeline that we have written to reduce GMOS time-series data of exoplanet transits, and present a thorough analysis of the dominant noise sources in GMOS, which primarily consist of wavelength- and time- dependent displacements of the spectra on the detector, mainly due to a lack of atmospheric dispersion correction.Comment: 23 pages, 12 figures, accepted for publication in AJ, 2017 July

Retrieving planet formation parameters of WASP-77Ab using SimAb

Context. The atmospheric compositions of planets offer a unique view into their respective formation processes. State-of-the-art observatories and techniques are finally able to provide high-precision data on atmospheric composition that can be used to constrain planet formation. Aims. In this context, we focus on the formation of WASP-77Ab based on previous observations of its atmosphere, which have provided precise C/O and metallicity measurements. Methods. We use the SimAb planet formation simulation to model the formation of WASP-77Ab. We assume two compositions for the disk WASP-77Ab was formed within: one of a solar composition and one that represents the composition of WASP-77A. In addition, we consider two different scenarios regarding the migration of the planet and we study the possible planet formation paths that reproduce the composition of WASP-77Ab. Result. This work shows that the planet is expected to have formed in a disk where not many planetesimals could be accreted. Moreover, we demonstrate that the most likely migration scenario is disk-free migration, whereby the planet initiates its Type II migration within the CO ice line and ends it beyond the water ice line

Exoplanet HD 209458b : Evaporation strengthened

Following re-analysis of Hubble Space Telescope observations of primary transits of the extrasolar planet HD209458b at Lyman-alpha, Ben-Jaffel (2007, BJ007) claims that no sign of evaporation is observed. Here we show that, in fact, this new analysis is consistent with the one of Vidal-Madjar et al. (2003, VM003) and supports the detection of evaporation. The apparent disagreement is mainly due to the disparate wavelength ranges that are used to derive the transit absorption depth. VM003 derives a (15+/-4)% absorption depth during transit over the core of the stellar Lyman-alpha line (from -130 km/s to +100 km/s), and this result agrees with the (8.9+/-2.1)% absorption depth reported by BJ007 from a slightly expanded dataset but over a larger wavelength range (+/-200 km/s). These measurements agree also with the (5+/-2)% absorption reported by Vidal-Madjar et al. (2004) over the whole Lyman-alpha line from independent, lower-resolution data. We show that stellar Lyman-alpha variability is unlikely to significantly affect those detections. The HI atoms must necessarily have velocities above the escape velocities and/or be outside the Roche lobe, given the lobe shape and orientation. Absorption by HI in HD209458b's atmosphere has thus been detected with different datasets, and now with independent analyses. All these results strengthen the concept of evaporating hot-Jupiters, as well as the modelization of this phenomenon.Comment: To be published in ApJ

The Embedded Super Star Cluster of SBS0335-052

We analyze the infrared (6-100 micron) spectral energy distribution of the blue compact dwarf and metal-poor (Z=Z_solar/41) galaxy SBS0335-052. With the help of DUSTY (Ivezic et al. 1999), a program that solves the radiation transfer equations in a spherical environment, we evaluate that the infrared (IR) emission of SBS0335-052 is produced by an embedded super-star cluster (SSC) hidden under 10^5 M_solar of dust, causing 30 mag of visual extinction. This implies that one cannot detect any stellar emission from the 2x10^6 M_solar stellar cluster even at near-infrared (NIR) wavelengths. The derived grain size distribution departs markedly from the widely accepted size distribution inferred for dust in our galaxy (the so-called MRN distribution, Mathis et al. 1977), but resembles what is seen around AGNs, namely an absence of PAH and smaller grains, and grains that grow to larger sizes (around 1 micron). The fact that a significant amount of dust is present in such a low-metallicity galaxy, hiding from UV and optical view most of the star formation activity in the galaxy, and that the dust size distribution cannot be reproduced by a standard galactic law, should be borne in mind when interpreting the spectrum of primeval galaxies.Comment: 32 pages, 3 figures,accepted for publication in A

The Diabolo photometer and the future of ground-based millimetric bolometer devices

The millimetric atmospheric windows at 1 and 2 mm are interesting targets for cosmological studies. Two broad areas appear leading this field: 1) the search for high redshift star-forming galaxies and 2) the measurement of Sunyaev-Zel'dovich (SZ) effect in clusters of galaxies at all redshifts. The Diabolo photometer is a dual-channel photometer working at 1.2 and 2.1 mm and dedicated to high angular resolution measurements of the Sunyaev--Zel'dovich effect towards distant clusters. It uses 2 by 3 bolometers cooled down to 0.1 K with a compact open dilution cryostat. The high resolution is provided by the IRAM 30 m telescope. The result of several Winter campaigns are reported here, including the first millimetric map of the SZ effect that was obtained by Pointecouteau et al. (2001) on RXJ1347-1145, the non-detection of a millimetric counterpart to the radio decrement towards PC1643+4631 and 2 mm number count upper limits. We discuss limitations in ground-based single-dish millimetre observations, namely sky noise and the number of detectors. We advocate the use of fully sampled arrays of (100 to 1000) bolometers as a big step forward in the millimetre continuum science. Efforts in France are briefly mentionned.Comment: 7 pages, 6 figures, to appear in the Proceedings of the 2K1BC ``Experimental Astronomy at millimeter wavelengths'', Breuil-Cervinia (AO) Italy - July 9 - 13, 2001, Eds. M. De Petris et a

Observations of the Sunyaev-Zel'dovich effect at high angular resolution towards the galaxy clusters A665, A2163 and CL0016+16

We report on the first observation of the Sunyaev-Zel'dovich effect with the Diabolo experiment at the IRAM 30 metre telescope. A significant brightness decrement is detected in the direction of three clusters (Abell 665, Abell 2163 and CL0016+16). With a 30 arcsecond beam and 3 arcminute beamthrow, this is the highest angular resolution observation to date of the SZ effect.Comment: 23 pages, 8 figures, 6 tables, accepted to New Astronom

An infrared study of the double nucleus in NGC3256

We present new resolved near and mid-IR imaging and N-band spectroscopy of the two nuclei in the merger system NGCA3256, the most IR luminous galaxy in the nearby universe. The results from the SED fit to the data are consistent with previous estimates of the amount of obscuration towards the nuclei and the nuclear star formation rates. However, we also find substantial differences in the infrared emission from the two nuclei which cannot be explained by obscuration alone. We conclude that the northern nucleus requires an additional component of warm dust in order to explain its properties. This suggests that local starforming conditions can vary significantly within the environment of a single system.Comment: Accepted for publication (MNRAS