Development of the opto-mechanical design for ICE-T

ICE-T (International Concordia Explorer Telescope) is a double 60 cm f/1.1 photometric robotic telescope, on a parallactic mount, which will operate at Dome C, in the long Antarctic night, aiming to investigate exoplanets and activity of the hosting stars. Antarctic Plateau site is well known to be one of the best in the world for observations because of sky transparency in all wavelengths and low scintillation noise. Due to the extremely harsh environmental conditions (the lowest average temperature is -80$^\circ$C) the criteria adopted for an optimal design are really challenging. Here we present the strategies we have adopted so far to fulfill the mechanical and optical requirements.Comment: 7 pages, 2 figures, contributed talk at 'An astronomical Observatory at Concordia (Dome C, Antarctica) for the next decade', 11-15 May, Rome (Italy

Three years of experience with the STELLA robotic observatory

Since May 2006, the two STELLA robotic telescopes at the Izaa observatory in Tenerife, Spain, delivered an almost uninterrupted stream of scientific data. To achieve such a high level of autonomous operation, the replacement of all troubleshooting skills of a regular observer in software was required. Care must be taken on error handling issues and on robustness of the algorithms used. In the current paper, we summarize the approaches we followed in the STELLA observatory. Copyright © 2010 Thomas Granzer et al

Solar Physics and the Solar-Stellar Connection at Dome C

Solar magnetic fields evolve on many time-scales, e.g., the generation, migration, and dissipation of magnetic flux during the 22-year magnetic cycle of the Sun. Active regions develop and decay over periods of weeks. The build-up of magnetic shear in active regions can occur within less than a day. At the shortest time-scales, the magnetic field topology can change rapidly within a few minutes as the result of eruptive events such as flares, filament eruptions, and coronal mass ejections. The unique daytime seeing characteristics at Dome C, i.e., continuous periods of very good to excellent seeing during almost the entire Antarctic summer, allow us to address many of the top science cases related to the evolution of solar magnetic fields. We introduce the Advanced Solar Photometric Imager and Radiation Experiment and present the science cases for synoptic solar observations at Dome C. Furthermore, common science cases concerning the solar-stellar connection are discussed in the context of the proposed International Concordia Explorer Telescope.Comment: 8 pages, 2 b/w figures, submitted to 2nd ARENA Conference on "The Astrophysical Science Cases at Dome C'', H. Zinnecker, H. Rauer, and N. Epchtein (eds.), EAS Publications Serie

Broad-band spectrophotometry of HAT-P-32 b: search for a scattering signature in the planetary spectrum

Multicolour broad-band transit observations offer the opportunity to characterize the atmosphere of an extrasolar planet with small- to medium-sized telescopes. One of the most favourable targets is the hot Jupiter HAT-P-32 b. We combined 21 new transit observations of this planet with 36 previously published light curves for a homogeneous analysis of the broad-band transmission spectrum from the Sloan u′ band to the Sloan z′ band. Our results rule out cloud-free planetary atmosphere models of solar metallicity. Furthermore, a discrepancy at reddest wavelengths to previously published results makes a recent tentative detection of a scattering feature less likely. Instead, the available spectral measurements of HAT-P-32 b favour a completely flat spectrum from the near-UV to the near-IR. A plausible interpretation is a thick cloud cover at high altitudes

Noise Sources in Photometry and Radial Velocities

The quest for Earth-like, extrasolar planets (exoplanets), especially those located inside the habitable zone of their host stars, requires techniques sensitive enough to detect the faint signals produced by those planets. The radial velocity (RV) and photometric transit methods are the most widely used and also the most efficient methods for detecting and characterizing exoplanets. However, presence of astrophysical "noise" makes it difficult to detect and accurately characterize exoplanets. It is important to note that the amplitude of such astrophysical noise is larger than both the signal of Earth-like exoplanets and state-of-the-art instrumentation limit precision, making this a pressing topic that needs to be addressed. In this chapter, I present a general review of the main sources of noise in photometric and RV observations, namely, stellar oscillations, granulation, and magnetic activity. Moreover, for each noise source I discuss the techniques and observational strategies which allow us to mitigate their impact.Comment: 11 pages, 2 tables, Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

Atmospheric Heating and Wind Acceleration: Results for Cool Evolved Stars based on Proposed Processes

A chromosphere is a universal attribute of stars of spectral type later than ~F5. Evolved (K and M) giants and supergiants (including the zeta Aurigae binaries) show extended and highly turbulent chromospheres, which develop into slow massive winds. The associated continuous mass loss has a significant impact on stellar evolution, and thence on the chemical evolution of galaxies. Yet despite the fundamental importance of those winds in astrophysics, the question of their origin(s) remains unsolved. What sources heat a chromosphere? What is the role of the chromosphere in the formation of stellar winds? This chapter provides a review of the observational requirements and theoretical approaches for modeling chromospheric heating and the acceleration of winds in single cool, evolved stars and in eclipsing binary stars, including physical models that have recently been proposed. It describes the successes that have been achieved so far by invoking acoustic and MHD waves to provide a physical description of plasma heating and wind acceleration, and discusses the challenges that still remain.Comment: 46 pages, 9 figures, 1 table; modified and unedited manuscript; accepted version to appear in: Giants of Eclipse, eds. E. Griffin and T. Ake (Berlin: Springer

Searching for star-planet magnetic interaction in CoRoT observations

Close-in massive planets interact with their host stars through tidal and magnetic mechanisms. In this paper, we review circumstantial evidence for star-planet interaction as revealed by the photospheric magnetic activity in some of the CoRoT planet-hosting stars, notably CoRoT-2, CoRoT-4, and CoRoT-6. The phenomena are discussed in the general framework of activity-induced features in stars accompanied by hot Jupiters. The theoretical mechanisms proposed to explain the activity enhancements possibly related with hot Jupiter are also briefly reviewed with an emphasis on the possible effects at photospheric level. The unique advantages of CoRoT and Kepler observations to test these models are pointed out.Comment: Invited review paper accepted by Astrophysics and Space Science, 13 pages, 5 figure

Astrobiologically Interesting Stars within 10 parsecs of the Sun

The existence of life based on carbon chemistry and water oceans relies upon planetary properties, chiefly climate stability, and stellar properties, such as mass, age, metallicity and Galactic orbits. The latter can be well constrained with present knowledge. We present a detailed, up-to-date compilation of the atmospheric parameters, chemical composition, multiplicity and degree of chromospheric activity for the astrobiologically interesting solar-type stars within 10 parsecs of the Sun. We determine their state of evolution, masses, ages and space velocities, and produce an optimized list of candidates that merit serious scientific consideration by the future space-based interferometry probes aimed at directly detecting Earth-sized extrasolar planets and seeking spectroscopic infrared biomarkers as evidence of photosynthetic life. The initially selected stars number 33 solar-type within the population of 182 stars (excluding late M-dwarfs) closer than 10 pc. A comprehensive and detailed data compilation for these objects is still essentially lacking: a considerable amount of recent data has so far gone unexplored in this context. We present 13 objects as the nearest "biostars", after eliminating multiple stars, young, chromospherically active, hard X-ray emitting stars, and low metallicity objects. Three of these "biostars", HD 1581, 109358 and 115617, closely reproduce most of the solar properties and are considered as premier targets. We show that approximately 7% of the nearby stars are optimally interesting targets for exobiology.Comment: 36 pages, recommended for publication in Astrobiolog