Helioseismology with PICARD

PICARD is a CNES micro-satellite launched in June 2010 (Thuillier at al. 2006). Its main goal is to measure the solar shape, total and spectral irradiance during the ascending phase of the activity cycle. The SODISM telescope onboard PICARD also allows us to conduct a program for helioseismology in intensity at 535.7 nm (Corbard et al. 2008). One-minute cadence low-resolution full images are available for a so-called medium-$l$ program, and high-resolution images of the limb recorded every 2 minutes are used to study mode amplification near the limb in the perspective of g-mode search. First analyses and results from these two programs are presented here.Comment: 6 pages, 6 figures, Eclipse on the Coral Sea: Cycle 24 Ascending, GONG 2012 / LWS/SDO-5 / SOHO 27, November 12 - 16, 2012, Palm Cove, Queensland. Accepted for publication in Journal of Physics Conference Series on March 1st 201

Site testing in summer at Dome C, Antarctica

We present summer site testing results based on DIMM data obtained at Dome C, Antarctica. These data have been collected on the bright star Canopus during two 3-months summer campaigns in 2003-2004 and 2004-2005. We performed continuous monitoring of the seeing a nd the isoplanatic angle in the visible. We found a median seeing of 0.54 \arcsec and a median isoplanatic angle of 6.8 \arcsec. The seeing appears to have a deep minimum around 0.4 \arcsec almost every day in late afternoon

Transient HCl in the atmosphere of Mars

A major quest in Mars’ exploration has been the hunt for atmospheric gases, potentially unveiling ongoing activity of geophysical or biological origin. Here, we report the first detection of a halogen gas, HCl, which could, in theory, originate from contemporary volcanic degassing or chlorine released from gas-solid reactions. Our detections made at ~3.2 to 3.8 μm with the Atmospheric Chemistry Suite and confirmed with Nadir and Occultation for Mars Discovery instruments onboard the ExoMars Trace Gas Orbiter, reveal widely distributed HCl in the 1- to 4-ppbv range, 20 times greater than previously reported upper limits. HCl increased during the 2018 global dust storm and declined soon after its end, pointing to the exchange between the dust and the atmosphere. Understanding the origin and variability of HCl shall constitute a major advance in our appraisal of martian geo- and photochemistry

Simulation of pupil-plane observation of angle-of-arrival fluctuations in daytime turbulence

Optics in Atmospheric Propagation and Adaptative Systems VI, eds. J. D. Gonglewski and K. Stein, Proccedings of SPIE, Bellingham, WA 5237, pp. 238-248 (2004)International audienc

Error due to atmospheric turbulence effects on solar diameter measurements performed with an astrolabe

Diameter measurements performed with the solar astrolabe are affected by instrumental and atmospheric effects. The problem is to know how these effects contribute to the error on diameter measurements. Thus, a numerical simulation is developed to bring some responses to this problem. For this purpose, synthetic images of the Sun similar to the ones obtained by the instrument through the Earth atmosphere are simulated. A fractal model is used to generate randomly perturbed wavefronts and therefore optical response of the whole system, atmosphere and instrument. Many sequences of solar images are then simulated for various observation conditions (Fried's parameter r0, spatial coherence outer scale $\mathit{L}_{0}$ and atmospheric characteristic times). They are used to define the time of contact of the direct and reflected solar images which is fundamental in the solar astrolabe experiment. It is then studied as a function of the observation conditions relatively to the experimental characteristics (exposure time)

New data analysis technique developed for the determination of the solar limb position in measurements of the solar diameter and oblateness, and application to observations obtained with the balloon-borne Solar Disk Sextant (SDS) experiment.

Solar diameter measurements performed from ground by several instruments during these last decades show variations which are not in agreement. In relation with solar activity, these measurements do not reveal consistent results. These results can be either attributed to Earth atmosphere effects or to instrumental ones especially in presence of noise. Noise affects directly the determination of the solar diameter defined as the zero crossing of the second derivative of the solar limb. Furthermore, presence of noise in data causes additional problems requiring appropriate data filtering without changing the solar limb slope. Several methods have been developed and used for a correct inflexion point position determination, among them, is the Fast Fourier Transform Definition (FFTD). We first present a complete description of the FFTD tool and in particular a new method to choose the filtering parameter (a) to be determined for applying FFDT. An alternative method by filtering using the wavelet analysis is also shown. The Solar Disk Sextant (SDS) is an instrument which has been flown on stratospheric balloons from 1992 to 1998 at 37 km altitude preventing all atmospheric effects. SDS uses a prism as angular reference. We present and discuss results obtained from SDS data analysis and compare them using others methods of inflexion point position detection. Finally, we discuss all other SDS experimental parameters able to cause solar diameter measurement variations.We show the relationship between the diameter variation and solar variability

Design of an optical sun sensor for a space application: a reliable passive sun tracking device for the SOLAR/SOLSPEC instrument

International audienceSOLAR/SOLSPEC, a spectroradiometer measuring solar spectral irradiance is an instruments of the SOLAR payload mounted on the zenith external platform of the European Columbus module of the International Space Station. Solar flux is received by the SOLAR instruments thanks to the Coarse Pointing Device (CPD). A complementary Sun position tracking module, the Position Sensitive Device (PSD), is integrated in SOLAR/SOLSPEC. The PSD module has been a useful tool to monitor for misalignments between the CPD and the SOLAR payload. It is used in SOLAR/SOLSPEC's operations to follow the quality of the Sun tracking. The PSD module is also valuable to monitor for SOLAR/SOLSPEC's three spectrometers (ultraviolet, visible, infrared) angular response in orbit. We first give a detailed description of the PSD's functionalities. We then present the results of the PSD data analysis. We will show that the PSD module has, despite working in a severe space environment, preserved its full potential from 2008 up to 2017 thanks to its design and appropriate selection of components. We conclude that its robustness makes of the PSD module a simple, yet reliable, instrument useful for future long term space-based missions