A Broadband Scalar Vortex Coronagraph

Broadband coronagraphy with deep nulling and small inner working angle has the potential of delivering images and spectra of exoplanets and other faint objects. In recent years, many coronagraphic schemes have been proposed, the most promising being the optical vortex phase mask coronagraphs. In this paper, a new scheme of broadband optical scalar vortex coronagraph is proposed and characterized experimentally in the laboratory. Our setup employs a pair of computer generated phase gratings (one of them containing a singularity) to control the chromatic dispersion of phase plates and achieves a constant peak-to-peak attenuation below $1\cdot 10^{-3}$ over a bandwidth of 120 nm centered at 700 nm. An inner working angle of ~\lambda/D is demonstrated along with a raw contrast of 11.5 magnitudes at 2\lambda/D.Comment: Accepted, 6 pages, 6 image

Investigation of a transiting planet candidate in Trumpler 37: An astro-physical false positive eclipsing spectroscopic binary star

We report our investigation of the first transiting planet candidate from the YETI project in the young (∼4 Myr old) open cluster Trumpler 37. The transit-like signal detected in the lightcurve of F8V star 2M21385603+5711345 repeats every 1.364894 + 0.000015 days, and has a depth of 54.5 + 0.8 mmag in R. Membership in the cluster is supported by its mean radial velocity and location in the color-magnitude diagram, while the Li diagnostic and proper motion are inconclusive in this regard. Follow-up photometric monitoring and adaptive optics imaging allow us to rule out many possible blend scenarios, but our radial-velocity measurements show it to be an eclipsing single-lined spectroscopic binary with a late-type (mid-M) stellar companion, rather than one of planetary nature. The estimated mass of the companion is 0.15–0.44 M⊙. The search for planets around very young stars such as those targeted by the YETI survey remains of critical importance to understand the early stages of planet formation and evolution

A search for transit timing variation

Photometric follow-ups of transiting exoplanets (TEPs) may lead to discoveries of additional, less massive bodies in extrasolar systems. This is possible by detecting and then analysing variations in transit timing of transiting exoplanets. In 2009 we launched an international observing campaign, the aim of which is to detect and characterise signals of transit timing variation (TTV) in selected TEPs. The programme is realised by collecting data from 0.6--2.2-m telescopes spread worldwide at different longitudes. We present our observing strategy and summarise first results for WASP-3b with evidence for a 15 Earth-mass perturber in an outer 2:1 orbital resonance.Comment: Poster contribution to Detection and Dynamics of Transiting Exoplanets (Haute Provence Observatory Colloquium, 23-27 August 2010

A Possible Detection of Occultation by a Proto-planetary Clump in GM Cephei

GM Cep in the young (~ 4 Myr) open cluster Trumpler 37 has been known to be an abrupt variable and to have a circumstellar disk with very active accretion. Our monitoring observations in 2009–2011 revealed the star to show sporadic ?are events, each with brightening of . 0.5 mag lasting for days. These brightening events, associated with a color change toward the blue, should originate from an increased accretion activity. Moreover, the star also underwent a brightness drop of ~ 1 mag lasting for about a month, during which the star became bluer when fainter. Such brightness drops seem to have a recurrence time scale of a year, as evidenced in our data and the photometric behavior of GM Cep over a century. Between consecutive drops, the star brightened gradually by about 1 mag and became blue at peak luminosity. We propose that the drop is caused by obscuration of the central star by an orbiting dust concentration. The UX Orionis type of activity in GM Cep therefore exemplifies the disk inhomogeneity process in transition between grain coagulation and planetesimal formation in a young circumstellar disk

A small actively-controlled high-resolution spectrograph based on off-the-shelf components

We present the design and testing of a prototype in-plane echelle spectrograph based on an actively controlled fibre-fed double-pass design. This system aims to be small and efficient with the minimum number of optical surfaces - currently a collimator/camera lens, cross-dispersing prism, grating and a reflector to send light to the detector. It is built from catalogue optical components and has dimensions of approximately 20x30 cm. It works in the optical regime with a resolution of >70,000. The spectrograph is fed by a bifurcated fibre with one fibre to a telescope and the other used to provide simultaneous Thorium Argon light illumination for wavelength calibration. The positions of the arc lines on the detector are processed in real time and commercial auto-guiding software is used to treat the positions of the arc lines as guide stars. The guiding software sends any required adjustments to mechanical piezo-electric actuators which move the mirror sending light to the camera removing any drift in the position of the arc lines. The current configuration using an sCMOS detector provides a precision of 3.5 milli-pixels equivalent to 4 m/s in a standard laboratory environment.Comment: 21 pages, 9 figures, 2 tables, accepted PAS

Near-Earth asteroids spectroscopic survey at Isaac Newton Telescope

The population of near-Earth asteroids (NEAs) shows a large variety of objects in terms of physical and dynamical properties. They are subject to planetary encounters and to strong solar wind and radiation effects. Their study is also motivated by practical reasons regarding space exploration and long-term probability of impact with the Earth. We aim to spectrally characterize a significant sample of NEAs with sizes in the range of $\sim$0.25 - 5.5 km (categorized as large), and search for connections between their spectral types and the orbital parameters. Optical spectra of NEAs were obtained using the Isaac Newton Telescope (INT) equipped with the IDS spectrograph. These observations are analyzed using taxonomic classification and by comparison with laboratory spectra of meteorites. A total number of 76 NEAs were observed. We classified 44 of them as Q/S-complex, 16 as B/C-complex, eight as V-types, and another eight belong to the remaining taxonomic classes. Our sample contains 27 asteroids categorized as potentially hazardous and 31 possible targets for space missions including (459872) 2014 EK24, (436724) 2011 UW158, and (67367) 2000 LY27. The spectral data corresponding to (276049) 2002 CE26 and (385186) 1994 AW1 shows the 0.7 $\mu$m feature which indicates the presence of hydrated minerals on their surface. We report that Q-types have the lowest perihelia (a median value and absolute deviation of $0.797\pm0.244$ AU) and are systematically larger than the S-type asteroids observed in our sample. We explain these observational evidences by thermal fatigue fragmentation as the main process for the rejuvenation of NEA surfaces. In general terms, the taxonomic distribution of our sample is similar to the previous studies and matches the broad groups of the inner main belt asteroids. Nevertheless, we found a wide diversity of spectra compared to the standard taxonomic types.Comment: Accepted in Astronomy & Astrophysics (A&A