C. Catala

Asteroseismology of solar-type stars with Kepler: III. Ground-based data

We report on the ground-based follow-up program of spectroscopic and photometric observations of solar-like asteroseismic targets for the Kepler space mission. These stars constitute a large group of more than a thousand objects which are the subject of an intensive study by the Kepler Asteroseismic Science Consortium Working Group 1 (KASC WG-1). In the current work we will discuss the methods we use to determine the fundamental stellar atmospheric parameters using high-quality stellar spectra. These provide essential constraints for the asteroseismic modelling and make it possible to verify the parameters in the Kepler Input Catalogue (KIC) (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

PLATO: a multiple telescope spacecraft for exo-planets hunting

PLATO stands for PLAnetary Transits and Oscillation of stars and is a Medium sized mission selected as M3 by the European Space Agency as part of the Cosmic Vision program. The strategy behind is to scrutinize a large fraction of the sky collecting lightcurves of a large number of stars and detecting transits of exo-planets whose apparent orbit allow for the transit to be visible from the Earth. Furthermore, as the transit is basically able to provide the ratio of the size of the transiting planet to the host star, the latter is being characterized by asteroseismology, allowing to provide accurate masses, radii and hence density of a large sample of extra solar bodies. In order to be able to then follow up from the ground via spectroscopy radial velocity measurements these candidates the search must be confined to rather bright stars. To comply with the statistical rate of the occurrence of such transits around these kind of stars one needs a telescope with a moderate aperture of the order of one meter but with a Field of View that is of the order of 50 degrees in diameter. This is achieved by splitting the optical aperture into a few dozens identical telescopes with partially overlapping Field of View to build up a mixed ensemble of differently covered area of the sky to comply with various classes of magnitude stars. The single telescopes are refractive optical systems with an internally located pupil defined by a CaF2 lens, and comprising an aspheric front lens and a strong field flattener optical element close to the detectors mosaic. In order to continuously monitor for a few years with the aim to detect planetary transits similar to an hypothetical twin of the Earth, with the same revolution period, the spacecraft is going to be operated while orbiting around the L2 Lagrangian point of the Earth-Sun system so that the Earth disk is no longer a constraints potentially interfering with such a wide field continuous uninterrupted survey.

The PLATO opto-mechanical unit prototyping and AIV phase

PLATO is the acronym of PLAnetary Transits and Oscillations of stars, and it is a mission proposed for the ESA Cosmic Vision program in the Medium size program, with the target to detect and characterize exoplanets by the means of their transit on a bright star. The instrumental overall layout proposed by the Plato Payload Consortium consists in a multitelescope concept instrument, composed by several tens of telescope units, for which we are developing an all refractive optical solution. These devices are characterized by a very large Field of View (more than 20 degrees on one side) with an optical quality that fits most of the energy into a single CCD pixel. Such a goal can be achieved in a variety of solutions, some including aspheric elements as well. A complete prototype of one telescope unit is foreseen to be built initially (during phase B1) to show the alignment feasibility and, only in a second moment (Phase B2), to perform full environmental and functional test. The aim of this article is to describe the alignment, integration and verification strategy of the opto-mechanics of the prototype. Both the approaches of testing the telescope at the target working temperature or to test it at ambient temperature around a displaced zero point, taking into account the effects of thermal deformations, are considered and briefly sketched in this work.