Exoplanets and Stellar Physics

Abstract:

We describe the current status of the HARMONI instrument design, which will form the basis for the first-light integral field spectrograph on the European Extremely Large Telescope. We review the phase A design, and highlight current on-going work to evolve the design in-line changing telescope requirements and lessons learned during the Phase A work. We also outline the key science drivers for the instrument, and describe briefly the requirements for the laser tomographic adaptive optics system which is expected to feed HARMONI.

Abstract:

ATLAS is a generic Laser Tomographic AO (LTAO) system for the E-ELT. Based on modular, relatively simple, and yet innovative concepts, it aims at providing diffraction-limited images in the near infra-red for a close to 100 percent sky coverage.

Abstract:

CoRoT-7 is an 11 th magnitude K-star whose light curve shows transits with a depth of 0.3mmag and a period of 0.854d, superimposed on variability at the 1 per cent level, due to the modulation of evolving active regions with the star's 23-d rotation period. In this paper, we revisit the published HARPS radial-velocity (RV) measurements of the object, which were previously used to estimate the companion mass, but have been the subject of ongoing debate. We build a realistic model of the star's activity during the HARPS observations, by fitting simultaneously the linewidth (as measured by the width of the cross-correlation function) and the line bisector, and use it to evaluate the contribution of activity to the RV variations. The data show clear evidence of errors above the level of the formal uncertainties, which are accounted for neither by activity nor by any plausible planet model and which increase rapidly with a decreasing signal-to-noise ratio (S/N) of the spectra. We cite evidence of similar systematics in mid-S/N spectra of other targets obtained with HARPS and other high-precision RV spectrographs, and discuss possible sources. Allowing for these, we re-evaluate the semi-amplitude of the CoRoT-7b signal, finding Kb= 1.6 ± 1.3ms-1, a tentative detection with a much reduced significance (1.2σ) compared to previous estimates. We also argue that the combined presence of activity and additional errors precludes a meaningful search for additional low-mass companions, despite previous claims to the contrary. Taken at face value, our analysis points to a lower density for CoRoT-7b, the 1σ mass range spanning 1-4 M ⊕ and allowing for a wide range of bulk compositions. In particular, an ice-rich composition is compatible with the RV constraints. More generally, this study highlights the importance of a realistic treatment of both activity and uncertainties, particularly in the medium S/N regime, which applies to most small planet candidates from CoRoT and Kepler. © 2010 The Authors Monthly Notices of the Royal Astronomical Society © 2010 RAS.

Abstract:

Many of the proposed science cases for extremely large telescopes (ELT) are only possible because of the unprecedented sensitivity and spatial resolution due to advanced, e.g. tomographic and multi conjugate, adaptive optic (AO) systems. Current AO systems on 8-10 m telescopes work best at wavelengths longward of 1 μm with Strehl ratios ≥ 15%. At red-optical wavelengths, e.g. in the I band (0.8 μm), the Strehl ratio is at best a few percent. The AO point spread function (PSF) typically has a diffraction-limited core superimposed on the seeing halo, however, for a 5% Strehl ratio the core has a very low intensity above the seeing halo. At an ELT, due to a 3-4 times higher angular resolution, the diffraction limited PSF core of only 5% Strehl ratio stands more prominently atop the shallow seeing halo leading to almost diffraction limited image quality even at low Strehl ratios. Prominent ELT science cases that use the Calcium triplet can exploit this gain in spatial resolution in the red-optical: stellar populations in dense environments or crowded fields; and the case of intermediate mass black holes in nuclear and globular stellar clusters, as well as (super-) massive black holes in galaxies.