Clouds play a significant role for the energy budget in planetary atmospheres. They can scatter incident stellar radiation back to space, effectively cooling the surface of terrestrial planets. On the other hand, they may contribute to the atmospheric greenhouse effect by trapping outgoing thermal radiation. For exoplanets near the outer boundary of the habitable zone, condensation of CO2 can occur due to the low atmospheric temperatures. These CO2 ice clouds may play an important role for the surface temperature and, therefore, for the question of habitability of those planets. However, the optical properties of CO2 ice crystals differ significantly from those of water droplets or water ice particles. Except for a small number of strong absorption bands, they are almost transparent with respect to absorption. Instead, they are highly effective scatterers at long and short wavelengths. Therefore, the climatic effect of a CO2 ice cloud will depend on how much incident stellar radiation is scattered to space in comparison to the amount of thermal radiation scattered back towards the planetary surface. This contribution aims at the potential greenhouse effect of CO2 ice particles. Their scattering and absorption properties are calculated for assumed particle size distributions with different effective radii and particle densities. An accurate radiative transfer model is used to determine the atmospheric radiation field affected by such CO2 particles. These results are compared to less detailed radiative transfer schemes employed in previous studies.

ASTEP (Antarctic Search for Transiting Exo Planets) is a research program funded mainly by French ANR grants and by the French Polar Institute (IPEV), dedicated to the photometric study of exoplanetary transits from Antarctica.

The preliminary “pathfinder” instrument ASTEP–South is described in another communication (Crouzet et al., these proceedings), and we focus in this presentation on the main instrument of the ASTEP program: “ASTEP–400”, a 40 cm robotized and thermally-controlled photometric telescope operated from the French-Italian Concordia station (Dome C, Antarctica).

ASTEP–400 has been installed at Concordia during the 2009-2010 summer campaign. Since, the telescope has been operated in nominal conditions during 2010 and 2011 winters, and the 2012 winterover is presently in progress. Data from the first two winter campaigns are available and processed. We give a description of the ASTEP–400 telescope from the mechanical, optical and thermal point of view. Control and software issues are also addressed. We end with a discussion of some astronomical results obtained with ASTEP–400.

We summarize the current discussions towards astronomical time-series observations at Dome C and emphasize some near-future projects. We define time-series as the continuous process of data taking that takes advantage of the unique time windows and observing conditions at Dome C. We emphasize that most of the current approaches to time-series astrophysics require a dedicated flux collector. In addition, some specific scientific topics may proceed with significant fractions of time on multi-purpose facilities. We consider only on those ideas and projects that were presented at least once during the various ARENA workshops and conferences. Topics of solar science are not considered in detail here.

The unexpected diversity of exoplanets includes a growing number of super Earth-planets, i.e. exoplanets with masses smaller than 10 Earth masses and a similar chemical and mineralogicalcomposition like Earth. We present a thermal evolution model for a super-Earth to calculate the sourcesand sinks of atmospheric carbon dioxide. The photosynthesis-sustaining habitable zone (pHZ) isdetermined by the limits of biological productivity on the planetary surface. We apply the model tocalculate the habitability of super-Earths in Gliese 581. The super-Earth Gl 581c is clearly outside thepHZ while Gl 581d at the outer edge of the pHZ could at least harbor some primitive life forms.

The Wide-field High-resolution Infrared TElescope (WHITE) that we propose for Dome Cwill be dedicated in the first years of its life to carry out a few legacy surveys (well-focused in terms of science objectives and time).
WHITE would have an angular resolution of ~0.3'' uniform over ~0.7 sq. deg. in the wavelength range 1 µm to 5 µm, which means that we will very efficiently use all the available observational time during night time and day time. Moreover, the deepest observations will be performed by summing up shorter individual frames. We will obtain temporal information that can be used to study variable objects.
The three key science objectives of WHITE are: 1) A survey of the Magellanic Clouds to make a complete census of young stellar objects in the Clouds and in the Bridge and to study their star formation history and the link with the Milky Way. The interaction of the two Clouds with our Galaxy might be the closest example of a minor merging event that could be the main driver of galaxy evolution in the last 5 Gyrs. 2) Establishing of the first sample of dusty supernovae at z < 1.2 in the near infrared range (1.0 - 5.0 µm) to constrain the equation of state of these obscured objects, study the formation of dust in galaxies, and build the first high resolution sample of high-redshift galaxies observed in their optical frame 3) A very wide weak lensing survey that would allow to estimate the equation of state of dark energy in a way that would favourably compete with space projects.

Dome Fuji is potentially one of the best astronomical sites in Antarctic plateau. We have a plan to build a 2-m class infrared telescope at Dome Fuji, and have been evaluating the site since the 2006/2007 Antarctic summer. We present the outline of a 2-m class telescope project and some results of our SODAR measurements.

Solar magnetic fields evolve on many time-scales, e.g., thegeneration, migration, and dissipation of magnetic flux during the 22-yearmagnetic cycle of the Sun. Active regions develop and decay over periods ofweeks. The build-up of magnetic shear in active regions can occur within lessthan a day. At the shortest time-scales, the magnetic field topology can changerapidly within a few minutes as the result of eruptive events such as flares,filament eruptions, and coronal mass ejections. The unique daytime seeingcharacteristics at Dome C, i.e., continuous periods of verygood to excellent seeing during almost the entire Antarctic summer, allow us toaddress many of the top science cases related to the evolution of solarmagnetic fields. We introduce the Advanced Solar Photometric Imager andRadiation Experiment and present the science cases for synoptic solarobservations at Dome C. Furthermore, common science cases concerningthe solar-stellar connection are discussed in the context of the proposedInternational Concordia Explorer Telescope.

Near-infrared spectro-photometry, at a spectral resolution of ~100, allows to characterize a great variety of stellar sources, from late-typegiants to emission line stars. Various components of the inter-stellar medium can also be traced. This technique can therefore be very fruitful, in addition, for studies of star forming regions, the Milky Way and external galaxies.The outstanding environmental conditions that are expected at Dome C should be favorable to carry out spectro-photometric surveys in the 1 to 2.5 μm region, that would usefully complement space-borne projects.

We present the science case for ICE-T, the International Concordia Explorer Telescope, a double telescope optimized for ultra-high and ultra wide field optical time-series photometry fromDome C. ICE-T consists of two 60 cm 8°×8°-FOV Schmidt telescopes for Sloan g and i photometry and one independent 25 cm, solar, full-disk, Ca ii-K imagingtelescope on a single mount. ICE-T is therefore operable during night and day. A 28 cm narrow-field Maksutov spectrophotometric telescope for night-time aerosol measurements (TAVERN-SP) will beprovided by AWI early on and operated in parallel with IRAIT and later with ICE-T. The low scintillation noise and the long continuous darkness are among the unique properties for highprecision optical time-series photometry.

In a first part the paper reviews some of the major Spitzer legacy imagingsurveys to show the quantity of data available, and the subsequent need forspectroscopic follow-up surveys on equivalent wide fields. They arerequired for many science cases, as giant star forming regions, youngplanetary nebulea, the Galactic Centre, nearby galaxies, distant galaxyclusters. This capability of wide, integral field spectroscopy, missing inall the existing and planned astronomical facilities, thus, appears amongthe most pertinent choice for the future of astronomy at Dome C. For theinstrumental solution, aflexibility in the choice of spectral resolution and spectral domain on abroad infrared range is desirable to be able to undertake a large variety of study, onextragalactic and galactic fields as well. This capability can be only offered byan Imaging FTS. It fully benefits from the low thermal backgroundemission of Dome C, particularly in the 1.8 to 5.5 μm range, and reachan optimum sensitivity by imaging emission lines. In a difficult site asDome C, a dedicated, medium-size telescope would be the most effective wayof exploiting such an instrument.

This is a brief summary of the 2nd ARENA conference, including statistical information and a short review of the talks. The conference ended up with the creation of 6 working groups aimed at preparing the final ARENA roadmap in the fields of astronomy and astrophysics where Antarctic atmospheric conditions at Dome C could lead to compelling scientific breakthroughs. The results of their reflections and recommendations will be presented at the third and final ARENA conference to be held in May 2009.

Antarctica offers unique conditions for ground-based observations, such as low sky background in the infrared, improved seeing, and low turbulence and scintillation noise. These properties are particularly beneficial to imaging, precision photometry, and infrared observations. It may be less clear if Antarctica offers equally compelling advantages for spectroscopy, in particular in the optical domain. However, scientific programmes that make use of imaging (or 3D) spectroscopy for selected follow-up studies of IR surveys, long-termmonitoring of extended targets and resolved stellar population studies in crowded fields, also benefit from the site conditions at Dome C.

Dome A, the summit of the Antarctic plateau, is expected to have even better atmospheric conditions for ground-based astronomy than Dome C.Instruments to evaluate and exploit Dome A's astronomical potentialmust operate within logistical constraints, which are currentlyvery stringent. Instrumentation now at Dome A exemplifies the techniques and solutions required by this environment. Future instrumentation and infrastructure will allow the qualities of the siteto be exploited much more fully.

We have entered the phase of extrasolar planets characterization, probing theiratmospheres for molecules, constraining their horizontal and vertical temperature profiles and estimating the contribution of clouds and hazes. We report here a short review of the current situation using ground based andspace based observations. What are the future challenges and how can we better address them? Is there a nichefor DOME C observations?

Many problems in time domain astronomy are bestapproached with continuous,high frequency (<1 minute) observations over a large area of the sky, because event rates are generally less than 0.01 detections per sq. degree in a year. For GRBs and theearliest stages of SNe, follow-up spectroscopy, multiband photometry andpolarization measurements need to be triggered in seconds or minutes.Plateau sites in Antarctica are optimal for a new survey, Xian(eXtreme Imaging Antarctic Network), for which the scientific motivation is presented.

I describe aspects of the non-solar astronomyuse of Dome C telescopes under daytime/summerconditions. In the thermal IR (TIR) wavelengthregion, where scattered sunlight is dwarfed bysky and facility radiation, astronomy benefitsfrom the better seeing, continuous sky coverage,a more than doubling of the observing time andthe improved site accessibility and logistics.Na-Laser Guide Stars (LGSs) can be used forwavefront sensing in daytime using very narrowband filters to suppress the sky background atvisible wavelengths. It enables the use ofAdaptive Optics for diffraction limited imagingin the TIR during daytime at Dome C.

The proposed design for PILOT is a general-purpose, wide-field (1°) 2.4 m, f/10 Ritchey-Chrétien telescope, with fast tip-tilt guiding, for 0.5-25 µm. The design allows both wide-field and diffraction-limited use at these wavelengths. The expected overall image quality, including median seeing, is 0.28-0.3'' FWHM from 0.8-2.4 µm. Point source sensitivities are estimated.

Excellent seeing, coronal conditions, and very low IR thermal background are qualities of the Dome C/Concordia station site that will allow unique solar astrophysics science. We review the science case for inner corona observations (onset of the coronal heating mechanism still poorly understood) and the promises of high angular resolution to disentangle the possible mechanisms at work between waves, convection, and reconnection in this particularly magnetically structured solar atmosphere between the high chromosphere and inner corona. For coronagraphy, IR and high resolution possibilities, Dome C is a case by itself between classical ground-based sites and space opportunities. Telescopes from 50 cm (coronagraphy oriented) to 4 m (full high resolution advantage including IR access) are proposed to benefit from these remarkable observing capabilities. Using 3 × Ø50 cm off-axis telescopes, we first propose a medium size facility (1.4 m equivalent telescope) for very high resolution access, ADSIIC (Antarctica Demonstrator of Solar Interferometric Imaging & Coronagraphy), before the ultimate 9-telescope Solar Facility equivalent to a 4 m diameter telescope: A-FOURMI (Antarctica 4 m Interferometer). Finally, 30 m tower designs and their logistics using standard containers and elementary elements of 6 m maximum length, are presented and discussed. These towers are indeed of general interest also for the other optical and IR telescopes intended for Dome C/Concordia, allowing to get over most of the turbulent ground layer and to reach the best possible permanent seeing conditions (better than half an arcsec).

We have developed a Wide Field Cryogenic Telescope II (WFCT-II), which containsa whole telescope-optics in a cryostat to suppress thermal emission from the whole telescope.The cryostat is of a cylindrical shape of 800 mm length and 300 mm diameter.The telescope inside is a Ritchey-Chretien system with the primary mirror of 231 mm in diameterand a focal length of 1500 mm.
The InSb 1k × 1k infrared array detector (Aladdin II) has a FoV of 1 square degreeand a resolution of 3'' × 3''/pixel.
We can install 5 filters whose wavelengths range from 1 μm to 5 μm.