Refined physical properties and g',r',i',z',J,H,K transmission spectrum of WASP-23b from the ground

Multi-band observations of planetary transits using the telescope defocus technique may yield high-quality light curves suitable for refining the physical properties of exoplanets even with small or medium size telescopes. Such observations can be used to construct a broad-band transmission spectrum of transiting planets and search for the presence of strong absorbers. We have thoroughly characterised the orbital ephemeris and physical properties of the transiting planet and host star in the WASP-23b system, constructed a broad-band transmission spectrum of WASP-23b and performed a comparative analysis with theoretical models of hot Jupiters. We observed a complete transit of WASP-23b in seven bands simultaneously, using the GROND instrument on the MPG/ESO 2.2m telescope at La Silla Observatory and telescope defocussing. The optical data were taken in the Sloan g',r',i' and z' bands. The resulting light curves are of high quality, with a root-mean-square scatter of the residual as low as 330ppm in the z'-band, with a cadence of 90s. Near-infrared data were obtained in the JHK bands. We performed MCMC analysis of our photometry plus existing radial velocity data to refine measurements of the ephemeris and physical properties of the WASP-23. We constructed a broad-band transmission spectrum of WASP-23b and compared it with a theoretical transmission spectrum of a Hot Jupiter. We measured the central transit time with a precision about 8s. From this and earlier observations we obtain an orbital period of P=2.9444300+/-0.0000011d. Our analysis also yielded a larger radius and mass for the planet (Rp=1.067+0.045-0.038 RJup and, Mp=0.917+0.040-0.039MJup). The transmission spectrum is marginally flat, given the limited precision of the measurements for the planet radius and poor spectral resolution of the data.Comment: 8 pages, 5 figures, accepted for publication in Astronomy & Astrophysic

Very Low-Mass Objects in the Coronet Cluster: The Realm of the Transition Disks

We present optical and IR spectra of a set of low-mass stars and brown dwarfs in the Coronet cluster (aged ~1Myr), obtained with the multifiber spectrograph FLAMES/VLT and IRS/Spitzer. The optical spectra reveal spectral types between M1 and M7.5, confirm the youth of the objects (via Li 6708 A absorption), and show the presence of accretion (via Halpha) and shocks (via forbidden line emission). The IRS spectra, together with IR photometry from the IRAC/MIPS instruments on Spitzer and 2MASS, confirm the presence of IR excesses characteristic of disks around ~70% of the objects. Half of the disks do not exhibit any silicate emission, or present flat features characteristic of large grains. The rest of the disks show silicate emission typical of amorphous and crystalline silicate grains a few microns in size. About 50% of the objects with disks do not show near-IR excess emission, having "transitional" disks, according to their classical definition. This is a very high fraction for such a young cluster. The large number of "transitional" disks suggests lifetimes comparable to the lifetimes of typical optically thick disks. Therefore, these disks may not be in a short-lived phase, intermediate between Class II and Class III objects. The median spectral energy distribution of the disks in the Coronet cluster is also closer to a flat disk than observed for the disks around solar-type stars in regions with similar age. The differences in the disk morphology and evolution in the Coronet cluster could be related to fact that these objects have very late spectral types compared to the solar-type stars in other cluster studies. Finally, the optical spectroscopy reveals that one of the X-ray sources is produced by a Herbig Haro object in the cloud.Comment: 51 pages, 13 figures, 10 table

The Herschel/PACS view of disks around low-mass stars in Chamaleon-I

Circumstellar disks are expected to be the birthplaces of planets. The potential for forming one or more planets of various masses is essentially driven by the initial mass of the disks. We present and analyze Herschel/PACS observations of disk-bearing M-type stars that belong to the young ~2 Myr old Chamaleon-I star forming region. We used the radiative transfer code RADMC to successfully model the SED of 17 M-type stars detected at PACS wavelengths. We first discuss the relatively low detection rates of M5 and later spectral type stars with respect to the PACS sensitivity, and argue their disks masses, or flaring indices, are likely to be low. For M0 to M3 stars, we find a relatively broad range of disk masses, scale heights, and flaring indices. Via a parametrization of dust stratification, we can reproduce the peak fluxes of the 10 $\mu$m emission feature observed with Spitzer/IRS, and find that disks around M-type stars may display signs of dust sedimentation. The Herschel/PACS observations of low-mass stars in Cha-I provide new constraints on their disk properties, overall suggesting that disk parameters for early M-type stars are comparable to those for more massive stars (e.g., comparable scale height and flaring angles). However, regions of the disks emitting at about 100 $\mu$m may still be in the optically thick regime, preventing direct determination of disk masses. Thus the modeled disk masses should be considered as lower limits. Still, we are able to extend the wavelength coverage of SED models and start characterizing effects such as dust sedimentation, an effort leading the way towards ALMA observations of these low-mass stars

ATCA and Spitzer Observations of the Binary Protostellar Systems CG30 and BHR71

We present interferometric observations with resolution of ~3 arcsecs of the isolated, low-mass protostellar double cores CG30 and BHR71 in the N2$H+(1-0) line and at 3mm dust continuum, using the Australian Telescope Compact Array (ATCA). The results are complemented by infrared data from the Spitzer Space Telescope. In CG30, the 3mm dust continuum images resolve two compact sources with a separation of ~21.7 arcsecs (~8700 AU). In BHR71, strong dust continuum emission is detected at the position of the mid-infrared source IRS1, while only weak emission is detected from the secondary mid-infrared source IRS2. Assuming optically thin 3mm dust continuum emission, we derive hydrogen gas masses of 0.05--2.1$M_\odot$for the four sub-cores. N2H+(1-0) line emission is detected in both CG30 and BHR71, and is spatially associated with the thermal dust continuum emission. We derive the velocity fields and find symmetric velocity gradients in both sources. Assuming that these gradients are due to core rotation, we estimate the specific angular momenta and ratios of rotational energy to gravitational energy for all cores. We also find that the N2H+ emission is strongly affected by the outflows, both in terms of entrainment and molecule destruction.$Spitzer$images show the mid-infrared emission from all four sub-cores. All four sources appear to drive their own outflows. Based on the ATCA and$Spitzer$ observations, we construct spectral energy distributions (SEDs) and derive temperatures and luminosities for all cores. Based on the morphology and velocity structure, we suggest that the sub-cores in CG30 were formed by initial fragmentation of a filamentary prestellar core, while those in BHR71 could originate from rotational fragmentation of a single collapsing protostellar core.Comment: 31 pages, 10 figures, to be published by ApJ in Sep. 200

Kepler-539: a young extrasolar system with two giant planets on wide orbits and in gravitational interaction

We confirm the planetary nature of Kepler-539b (aka Kepler object of interest K00372.01), a giant transiting exoplanet orbiting a solar-analogue G2 V star. The mass of Kepler-539b was accurately derived thanks to a series of precise radial velocity measurements obtained with the CAFE spectrograph mounted on the CAHA 2.2m telescope. A simultaneous fit of the radial-velocity data and Kepler photometry revealed that Kepler-539b is a dense Jupiter-like planet with a mass of Mp = 0.97 Mjup and a radius of Rp = 0.747 Rjup, making a complete circular revolution around its parent star in 125.6 days. The semi-major axis of the orbit is roughly 0.5 au, implying that the planet is at roughly 0.45 au from the habitable zone. By analysing the mid-transit times of the 12 transit events of Kepler-539b recorded by the Kepler spacecraft, we found a clear modulated transit time variation (TTV), which is attributable to the presence of a planet c in a wider orbit. The few timings available do not allow us to precisely estimate the properties of Kepler-539c and our analysis suggests that it has a mass between 1.2 and 3.6 Mjup, revolving on a very eccentric orbit (0.4<e<0.6) with a period larger than 1000 days. The high eccentricity of planet c is the probable cause of the TTV modulation of planet b. The analysis of the CAFE spectra revealed a relatively high photospheric lithium content, A(Li)=2.48 dex, which, together with both a gyrochronological and isochronal analysis, suggests that the parent star is relatively young.Comment: 11 pages, 14 figures, accepted for publication in Astronomy & Astrophysic

Bistability patterns and nonlinear switching with very high contrast ratio in a 1550 nm quantum dash semiconductor laser

We report on the experimental observation of optical bistability (OB) and nonlinear switching (NS) in a nanostructure laser; specifically a 1550 nm quantum dash Fabry-Perot laser subject to external optical injection and operated in reflection. Different shapes of optical bistability and nonlinear switching, anticlockwise and clockwise, with very high on-off contrast ratio (up to 180:1) between output states were experimentally measured. These results added to the potential of nanostructure lasers for enhanced performance offer promise for use in fast all-optical signal processing applications in optical networks. © 2012 American Institute of Physics

Physical properties of the WASP-44 planetary system from simultaneous multi-colour photometry

We present ground-based broad-band photometry of two transits in the WASP-44 planetary system obtained simultaneously through four optical (Sloan g', r', i', z') and three near-infrared (NIR; J, H, K) filters. We achieved low scatters of 1-2 mmag per observation in the optical bands with a cadence of 48 s, but the NIR-band light curves present much greater scatter. We also observed another transit of WASP-44 b by using a Gunn-r filter and telescope defocussing, with a scatter of 0.37 mmag per point and an observing cadence around 135 s. We used these data to improve measurements of the time of mid-transit and the physical properties of the system. In particular, we improved the radius measurements of the star and planet by factors of 3 and 4, respectively. We find that the radius of WASP-44 b is 1.002 R_Jup, which is slightly smaller than previously thought and differs from that expected for a core-free planet. In addition, with the help of a synthetic spectrum, we investigated the theoretically-predicted variation of the planetary radius as a function of wavelength, covering the range 370-2440 nm. We can rule out extreme variations at optical wavelengths, but unfortunately our data are not precise enough (especially in the NIR bands) to differentiate between the theoretical spectrum and a radius which does not change with wavelength.Comment: 13 pages, 6 figures, to appear in Monthly Notices of the Royal Astronomical Societ

Eclipsing binaries and fast rotators in the Kepler sample. Characterization via radial velocity analysis from Calar Alto

The Kepler mission has provided high-accurate photometric data in a long time span for more than two hundred thousands stars, looking for planetary transits. Among the detected candidates, the planetary nature of around 15% has been established or validated by different techniques. But additional data is needed to characterize the rest of the candidates and reject other possible configurations. We started a follow-up program to validate, confirm, and characterize some of the planet candidates. In this paper we present the radial velocity analysis (RV) of those presenting large variations, compatible with being eclipsing binaries. We also study those showing large rotational velocities, which prevents us from obtaining the necessary precision to detect planetary-like objects. We present new RV results for 13 Kepler objects of interest (KOIs) obtained with the CAFE spectrograph at the Calar Alto Observatory, and analyze their high-spatial resolution images and the Kepler light curves of some interesting cases. We have found five spectroscopic and eclipsing binaries. Among them, the case of KOI-3853 is of particular interest. This system is a new example of the so-called heartbeat stars, showing dynamic tidal distortions in the Kepler light curve. We have also detected duration and depth variations of the eclipse. We suggest possible scenarios to explain such effect, including the presence of a third substellar body possibly detected in our RV analysis. We also provide upper mass limits to the transiting companions of other six KOIs with large rotational velocities. This property prevents the RV method to obtain the necessary precision to detect planetary-like masses. Finally, we analyze the large RV variations of other two KOIs, incompatible with the presence of planetary-mass objects. These objects are likely to be stellar binaries but a longer timespan is still needed.Comment: Accepted for publication in A&A. 18 pages, 9 figures, 17 tables. This version fixes an error affecting the values of tables A.1-A.13. The text remains unaltere