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We present two transits of the hot-Jupiter exoplanet XO-2b using the Gran Telescopio Canarias (GTC). The time series observations were performed using long-slit spectroscopy of XO-2 and a nearby reference star with the OSIRIS instrument, enabling differential specrophotometric transit lightcurves capable of measuring the exoplanets transmission spectrum. Two optical low-resolution grisms were used to cover the optical wavelength range from 3800 to 9300{AA}. We find that sub-mmag level slit losses between the target and reference star prevent full optical transmission spectra from being constructed, limiting our analysis to differential absorption depths over ~1000{AA} regions. Wider long slits or multi-object grism spectroscopy with wide masks will likely prove effective in minimising the observed slit-loss trends. During both transits, we detect significant absorption in the planetary atmosphere of XO-2b using a 50{AA} bandpass centred on the Na I doublet, with absorption depths of Delta(R_pl/R_star)^2=0.049+/-0.017 % using the R500R grism and 0.047+/-0.011 % using the R500B grism (combined 5.2-sigma significance from both transits). The sodium feature is unresolved in our low-resolution spectra, with detailed modelling also likely ruling out significant line-wing absorption over an ~800{AA} region surrounding the doublet. Combined with narrowband photometric measurements, XO-2b is the first hot Jupiter with evidence for both sodium and potassium present in the planets atmosphere.
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We present Gran Telescopio Canarias (GTC) optical transit narrow-band photometry of the hot-Jupiter exoplanet XO-2b using the OSIRIS instrument. This unique instrument has the capabilities to deliver high cadence narrow-band photometric lightcurves, allowing us to probe the atmospheric composition of hot Jupiters from the ground. The observations were taken during three transit events which cover four wavelengths at spectral resolutions near 500, necessary for observing atmospheric features, and have near-photon limited sub-mmag precisions. Precision narrow-band photometry on a large aperture telescope allows for atmospheric transmission spectral features to be observed for exoplanets around much fainter stars than those of the well studied targets HD209458b and HD189733b, providing access to the majority of known transiting planets. For XO-2b, we measure planet-to-star radius contrasts of R_pl/R_star=0.10508+/-0.00052 at 6792 Ang, 0.10640+/-0.00058 at 7582 Ang, and 0.10686+/-0.00060 at 7664.9 Ang, and 0.10362+/-0.00051 at 8839 Ang. These measurements reveal significant spectral features at two wavelengths, with an absorption level of 0.067+/-0.016% at 7664.9 Ang due to atmospheric potassium in the line core (a 4.1-sigma significance level), and an absorption level of 0.058+/-0.016% at 7582 Ang, (a 3.6-sigma significance level). When comparing our measurements to hot-Jupiter atmospheric models, we find good agreement with models which are dominated in the optical by alkali metals. This is the first evidence for potassium in an extrasolar planet, an element that has long been theorized along with sodium to be a dominant source of opacity at optical wavelengths for hot Jupiters.
We used GTC instrument OSIRIS to obtain long-slit spectra in the optical range (520-1040 nm) of the planetary host star WASP-43 (and a reference star) during a full primary transit event and four partial transit observations. We integrated the stellar flux of both stars in different wavelength regions producing several light curves. We fitted transit models to these curves to measure the star-to-planet radius ratio, Rp/Rs, across wavelength among other physical parameters. We measure a Rp/Rs in the white light curve of 0.15988^{+0.00133}_{-0.00145}. We present a tentative detection of an excess in the planet-to-star radius ratio around the Na I doublet (588.9 nm, 589.5 nm) when compared to the nearby continuum at the 2.9-sigma level. We find no significant excess of the measured planet-to-star radius ratio around the K I doublet (766.5 nm, 769.9 nm) when compared to the nearby continuum. Combining our observations with previous published epochs, we refine the estimation of the orbital period. Using a linear ephemeris, we obtained a period of P=0.81347385 +/- 1.5 x 10^{-7} days. Using a quadratic ephemeris, we obtained a period of 0.81347688 +/- 8.6 x 10^{-7} days, and a change in this parameter of dP/dt = -0.15 +/- 0.06 sec/year. As previous results, this hints to the orbital decay of this planet although a timing analysis over several years needs to be made in order to confirm this.
We here present the ages of four compact stellar clusters (CSCs) in the nearby spiral galaxy M81, using long-slit optical spectra obtained with the 10.4-m Gran Telescopio Canarias (GTC). All the four CSCs, including the brightest in this galaxy, are found to have ages between 5 to 6 Myr, with one of them showing Wolf-Rayet spectral features. The photometric masses of these clusters, calculated using their spectroscopically-derived ages, lie between 3000 and 18000 Msun. The observed clusters are among the brightest objects, and hence the most massive, in the entire disk of M81. This implies the absence of massive (1.0e5 Msun) compact stellar clusters in M81.
We report photometric and radial velocity observations of the XO-4 transiting planetary system, conducted with the FLWO 1.2m telescope and the 8.2m Subaru Telescope. Based on the new light curves, the refined transit ephemeris of XO-4b is $P = 4.1250828 pm 0.0000040$ days and $T_c [BJD_TDB] = 2454485.93323 pm 0.00039$. We measured the Rossiter-McLaughlin effect of XO-4b and estimated the sky-projected angle between the stellar spin axis and the planetary orbital axis to be $lambda = -46.7^{circ} ^{+8.1^{circ}}_{-6.1^{circ}}$. This measurement of $lambda$ is less robust than in some other cases because the impact parameter of the transit is small, causing a strong degeneracy between $lambda$ and the projected stellar rotational velocity. Nevertheless, our finding of a spin-orbit misalignment suggests that the migration process for XO-4b involved few-body dynamics rather than interaction with a gaseous disk. In addition, our result conforms with the pattern reported by Winn et al. (2010, ApJL, 718, L145) that high obliquities are preferentially found for stars with effective temperatures hotter than 6250~K.
Context. The launch of the exoplanet space missions obtaining exquisite photometry from space has resulted in the discovery of thousands of planetary systems with very different physical properties and architectures. Among them, the exoplanet CoRoT-29b was identified in the light curves the mission obtained in summer 2011, and presented an asymmetric transit light curve, which was tentatively explained via the effects of gravity darkening. Aims. Transits of CoRoT-29b are measured with precision photometry, to characterize the reported asymmetry in their transit shape. Methods. Using the OSIRIS spectrograph at the 10-m GTC telescope, we perform spectro-photometric differential observations, which allow us to both calculate a high-accuracy photometric light curve, and a study of the color-dependence of the transit. Results. After careful data analysis, we find that the previously reported asymmetry is not present in either of two transits, observed in July 2014 and July 2015 with high photometric precisions of 300ppm over 5 minutes. Due to the relative faintness of the star, we do not reach the precision necessary to perform transmission spectroscopy of its atmosphere, but we see no signs of color-dependency of the transit depth or duration. Conclusions. We conclude that the previously reported asymmetry may have been a time-dependent phenomenon, which did not occur in more recent epochs. Alternatively, instrumental effects in the discovery data may need to be reconsidered.
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