Observatoire De La Cote d'Azur Research Articles

The AMBRE project: Parameterisation of FGK-type stars from the ESO:HARPS archived spectra

The AMBRE project is a collaboration between the European Southern Observatory (ESO) and the Observatoire de la Cote d'Azur (OCA). It has been established to determine the stellar atmospheric parameters (effective temperature, surface gravity, global metallicities and abundance of alpha-elements over iron) of the archived spectra of four ESO spectrographs. The analysis of the ESO:HARPS archived spectra is presented. The sample being analysed (AMBRE:HARPS) covers the period from 2003 to 2010 and is comprised of 126688 scientific spectra corresponding to 17218 different stars. For the analysis of the spectral sample, the automated pipeline developed for the analysis of the AMBRE:FEROS archived spectra has been adapted to the characteristics of the HARPS spectra. Within the pipeline, the stellar parameters are determined by the MATISSE algorithm, developed at OCA for the analysis of large samples of stellar spectra in the framework of galactic archaeology. In the present application, MATISSE uses the AMBRE grid of synthetic spectra, which covers FGKM-type stars for a range of gravities and metallicities. We first determined the radial velocity and its associated error for the ~15% of the AMBRE:HARPS spectra, for which this velocity had not been derived by the ESO:HARPS reduction pipeline. The stellar atmospheric parameters and the associated chemical index [alpha/Fe] with their associated errors have then been estimated for all the spectra of the AMBRE:HARPS archived sample. Based on quality criteria, we accepted and delivered the parameterisation of ~71% of the total sample to ESO. These spectra correspond to ~10706 stars; each are observed between one and several hundred times. This automatic parameterisation of the AMBRE:HARPS spectra shows that the large majority of these stars are cool main-sequence dwarfs with metallicities greater than -0.5 dex.

Ground-based measurements of the solar diameter during the rising phase of solar cycle 24

For the past thirty years, modern ground-based time-series of the solar radius have shown different apparent variations according to different instruments. The origins of these variations may result from the observer, the instrument, the atmosphere, or the Sun. Solar radius measurements have been made for a very long time and in different ways. Yet we see inconsistencies in the measurements. Numerous studies of solar radius variation appear in the literature, but with conflicting results. These measurement differences are certainly related to instrumental effects or atmospheric effects. Use of different methods (determination of the solar radius), instruments, and effects of Earth's atmosphere could explain the lack of consistency on the past measurements. A survey of the solar radius has been initiated in 1975 by Francis Laclare, at the Calern site of the Observatoire de la Cote d'Azur (OCA). Several efforts are currently made from space missions to obtain accurate solar astrometric measurements, for example, to probe the long-term variations of solar radius, their link with solar irradiance variations, and their influence on the Earth climate. Aims. The program includes a ground-based observatory consisting of different instruments based at the Calern site (OCA, France). This set of instruments has been named Picard and consists of a Ritchey-Chretien telescope providing full-disk images of the Sun in five narrow-wavelength bandpasses (centered on 393.37, 535.7, 607.1, 782.2, and 1025.0 nm), a Sun-photometer that measures the properties of atmospheric aerosol, a pyranometer for estimating a global sky-quality index, a wide-field camera that detects the location of clouds, and a generalized daytime seeing monitor allowing us to measure the spatio-temporal parameters of the local turbulence. Sol is meant to perpetuate valuable historical series of the solar radius and to initiate new time-series, in particular during solar cycle 24. Methods. We defined the solar radius by the inflection-point position of the solar-limb profiles taken at different angular positions of the image. Our results were corrected for the effects of refraction and turbulence by numerical methods. Results. From a dataset of more than 20 000 observations carried out between 2011 and 2013, we find a solar radius of 959.78 ± 0.19 arcsec (696 113 ± 138 km) at 535.7 nm after making all necessary corrections. For the other wavelengths in the solar continuum, we derive very similar results. The solar radius observed with the Solar Diameter Imager and Surface Mapper II during the period 2011-2013 shows variations shorter than 50 milli-arcsec that are out of phase with solar activity.

The AMBRE Project: Stellar parameterisation of the ESO:FEROS archived spectra

The AMBRE Project is a collaboration between the European Southern Observatory (ESO) and the Observatoire de la Cote d'Azur (OCA) that has been established in order to carry out the determination of stellar atmospheric parameters for the archived spectra of four ESO spectrographs. The analysis of the FEROS archived spectra for their stellar parameters (effective temperatures, surface gravities, global metallicities, alpha element to iron ratios and radial velocities) has been completed in the first phase of the AMBRE Project. From the complete ESO:FEROS archive dataset that was received, a total of 21551 scientific spectra have been identified, covering the period 2005 to 2010. These spectra correspond to ~6285 stars. The determination of the stellar parameters was carried out using the stellar parameterisation algorithm, MATISSE (MATrix Inversion for Spectral SynthEsis), which has been developed at OCA to be used in the analysis of large scale spectroscopic studies in galactic archaeology. An analysis pipeline has been constructed that integrates spectral reduction and radial velocity correction procedures with MATISSE in order to automatically determine the stellar parameters of the FEROS spectra. Stellar atmospheric parameters (Teff, log g, [M/H] and [alpha/Fe]) were determined for 6508 (30.2%) of the FEROS archived spectra (~3087 stars). Radial velocities were determined for 11963 (56%) of the archived spectra. 2370 (11%) spectra could not be analysed within the pipeline. 12673 spectra (58.8%) were analysed in the pipeline but their parameters were discarded based on quality criteria and error analysis determined within the automated process. The majority of these rejected spectra were found to have broad spectral features indicating that they may be hot and/or fast rotating stars, which are not considered within the adopted reference synthetic spectra grid of FGKM stars.

The AMBRE project: Results from the MATISSE analysis of the ESO-FEROS archived spectra

The goal of AMBRE, a joint project between ESO and the Observatoire de la Cote d'Azur, is to provide a homogeneous determination of the stellar parameters (including mean metallicity and some chemical abundances) for the archived spectra of the FEROS, HARPS, UVES and Flames/GIRAFFE spectrographs. We present here a preliminary analysis of the FEROS stellar sample. The stellar parameters, derived using the stellar classification algorithm MATISSE, have been combined with distances and radial velocities in order to explore current theories regarding galactic stellar populations. We have reviewed the sample for potential disk stars with which we can explore kinematic and chemical signatures of the thin and thick disk. We present here a comparison of the potential disk stellar sample to the analysis of 66 disk stars that was carried out in. Under a contract between the European Southern Observatory (ESO) and the Observatoire de la Cote d'Azur (OCA), the AMBRE Project is tasked with determining the stellar parameters for the archived spectra of four of ESO's spectrographs: FEROS, HARPS, UVES & FLAMES/GIRAFFE, which will be made available to the astronomical community via the ESO Archive. The analysis of the FEROS spectra is now complete and the analysis of the UVES and HARPS spectra is underway. This project presents a unique opportunity to exploit a large pre-existing spectral dataset (∼250,000 spectra) for global information outside the original goals of the individual observing programmes. Despite the inherent programme biases, the FEROS dataset (as for the remaining archived datasets) is a homogeneous determination of stellar parameters for a large spectral sample. An analysis pipeline has been built which futher treats the archived spectra in order that they may be fed into the stellar parametrisation algorithm, MATISSE, which has been developed at OCA (1). An indepth discussion of the analysis pipeline and validation of the FEROS results will be presented in Worley et al. (2011), in preparation.

Mesures du rayon solaire avec l'instrument DORAYSOL (1999–2006) sur le site de Calern (observatoire de la Côte d'Azur)

La série d'observations du rayon solaire sur le site de CALERN à l'Observatoire de la Côte d'Azur s'étend sur près de 30 ans. Les mesures d'abord visuelles, faites par le même observateur, sont devenues progressivement impersonnelles par l'usage de capteurs CCD. Pour améliorer encore le rendement et la qualité des observations du demi-diamètre nous avons réalisé un nouvel instrument : DORAYSOL. Le principe de l'instrument est toujours basé sur le passage du Soleil à hauteur constante mais il permet un plus grand nombre d'observations le même jour par l'emploi d' un prisme d'angle variable. Un système d'acquisition numérique CCD des images du Soleil rend les mesures plus crédibles et l'instrument est semi-automatique par la motorisation de ses principales fonctions. Les résultats présentés ici couvrent huit années d'observations et comptent près de 20 000 mesures obtenues entre 1999 et 2006. Une analyse des principaux biais de mesures instrumentaux montre en particulier que l'écart entre les mesures des passages à l'est et à l'ouest est systématique, ce qui justifie notamment l'utilisation de moyennes pour le calcul du rayon. Ainsi, les mesures obtenues par DORAYSOL sont en bon accord avec celles acquises sur la série antérieure avec l'Astrolabe solaire, qu'il s'agisse de la valeur moyenne du rayon (959,48″±0,01″), de son caractère variable dans le temps ou encore de l'éventuelle dissymétrie apparente de la photosphère observée. Nous souhaitons que ce programme, interrompu depuis 2007 par manque de personnel, soit à nouveau repris pour que les observations du rayon solaire faites au sol soient simultanées à celles obtenues depuis l'espace par la mission PICARD. Nous développons également sur le site de CALERN l'instrument MISOLFA, destiné à évaluer les paramètres qui caractérisent la turbulence au sol et le télescope SODISM 2, réplique du télescope embarqué sur le satellite. Notons que les travaux d'étude, de réalisation et de mise au point de ces deux instruments ont retardé l'analyse des résultats obtenus par DORAYSOL et donc leur exposé dans la présente note. Il convient enfin de souligner que seule, la poursuite de ces mesures pendant une longue durée, permettra la recherche de variations à long terme de la géométrie globale du Soleil. The series of measurements of the Solar radius at CALERN site of the observatoire de la Côte d'Azur (OCA) spans about 30 years. Measurements of the Sun were first achieved visually by the same single observer, then gradually grew more man-independent with the use of CCD acquisitions. The DORAYSOL instrument was designed and built up to keep improving the number and the quality of these semi-diameter measurements. The principle of this instrument remains the same as that of the Solar Astrolabe (timing the crossing of a parallel of altitude by the Sun) but a varying prism enables larger numbers of daily measurements. Digital CCD acquisition of images improves the credibility of the data and five computer-driven motors are giving a better control of the attitude of the instrument. The results for eight years and nearly 20,000 measurements are presented. Analysis of instrumental biases shows that differences between East and West measurements are systematic and then allow one to choose the mean values to calculate the Solar radius. This results display a good agreement with the Solar Astrolabe series, namely the mean value of the Sun radius (959.48″±0.01″), its time-dependence and the apparent dissymmetry of the photosphere. In the framework of the PICARD CNES Space mission, Solar radius ground measurements at CALERN simultaneously with the onboard SODISM telescope were projected. It appeared in 2007 that the maintenance of the DORAYSOL program was not possible alongside the development of the atmospheric turbulence monitor MISOLFA and the preparation for setting up the model of the SODISM 2 telescope, the staff at hand becoming insufficient. We do hope that it will be resumed, in a fully automated way. A continuation of the ground-based series would permit one to detect possible long time variations of the global geometry of the Sun.

Time Transfer by Laser Link (T2L2) experiment on Mir

The experiment on Time Transfer by Laser Link (T2L2) under development at the OCA (Observatoire de la Cote d'Azur) and the CNES (Centre National d'Etudes Spatiales) will permit the synchronization of remote clocks. To perform a T2L2 time transfer, laser stations and a satellite are needed, all equipped with a clock and a time-tagging unit. We have the opportunity to put a T2L2 payload on the Russian space station Mir in 1999. The T2L2 is based on the propagation of light pulses in space. It will make it possible to synchronize remote ground clocks, several thousand kilometres apart, with an uncertainty of about 100 ps, and to measure the performance of ground clocks having a relative frequency stability of about 3 × 10-15 over the station visibility period (around 200 s). Accumulation of the data from several successive passages of Mir will allow a stability of about 3 × 10-17 over ten days to be reached. The uncertainty budget of the T2L2 time transfer is analysed, and the on-board optical equipment that will allow us to achieve these time-transfer performances is presented.