1,721,171 research outputs found
Polarimetric & Spectropolarimetric Properties of FGK Type Stars and Extrasolar Systems
No full textMost of the results on extrasolar planets are obtained with Doppler surveys. Here we suggest a different approach aimed
to study the polarimetric properties of the residual interplanetary dust
The astroclimatological comparison of the Paranal Observatory and El Roque de Los Muchachos Observatory
No full textThe new extremely large telescope projects need accurate evaluation of the candidate sites. In this paper, we present the astroclimatological comparison between the Paranal Observatory, located on the coast of the Atacama Desert (Chile), and the Observatorio del Roque de Los Muchachos (ORM), located in La Palma (Canary Islands). We apply a statistical analysis using long-term data bases from Paranal and Carlsberg Automatic Meridian Circle (CAMC) weather stations. The monthly, seasonal and annual averages of the main synoptical parameters in the two sites are computed. We compare the long-term trends in order to understand the main differences between the two sites. Significant differences between the two analysed sites have been found. Temperature has increasing trends in both observatories with somewhat higher evidence at the ORM. Seasonal variations of pressure at Paranal have been highly decreasing since 1989, and we do not see the same phenomenon at the ORM. The two sites are dominated by high pressure. In cold seasons, relative humidity (RH) is lower than 60 per cent at CAMC and 15 per cent at Paranal. In warm seasons, RH is lower than 40 per cent at CAMC and 20 per cent at Paranal. The analysis of the dew point has shown better conditions at Paranal with respect to CAMC in winter, autumn and spring before 2001, while the two sites are becoming similar afterwards. Winds at the ORM are subject to pronounced local variations
Bright Stars and Metallicity Spread in the Globular Cluster omega Centauri
Full text linkThe globular cluster omega Centauri (NGC~5139) is the most massive and brightest cluster in our Galaxy. It has also a moderately high mass to light ratio (3.6) and an anomalous flattening (0.83) for a globular cluster. This cluster is also very interesting because it is one of a few examples of globular clusters with a measurable spread in the metal abundance (see Da Costa & Willumsen 1981, Norris et al. 1996, and Suntzeff and Kraft 1996 and references therein) and then it offers a unique, big sample of nearby stars having all the same distance and reddening but showing different metallicity (and age ?) effects. A recent paper by Norris et al. (1997) shows also an interesting correlation between kinematics and metal abundance
Long-term analysis of clear sky at astronomical sites: A comparison between polar and geostationary satellites
No full textAnalysis of the fraction of clear sky at the La Palma and Mt Graham sites
No full textThe amount of available telescope time is one of the most important requirements when selecting astronomical sites, as it affects the performance of ground-based telescopes. We present a quantitative survey of cloud coverage at La Palma and Mt Graham using both ground- and satellite-based data. The aim of this work is to derive clear nights for the satellite infrared channels and to verify the results using ground-based observations. At La Palma, we found a mean percentage of clear nights of 62.6 per cent from ground-based data and 71.9 per cent from satellite-based data. Taking into account the fraction of common nights, we found a concordance of 80.7 per cent of clear nights for ground- and satellite-based data. At Mt Graham, we found a 97 per cent agreement between the Columbine heliograph and the night-time observing log. From the Columbine heliograph and the Total Ozone Mapping Spectrometer-Ozone Monitoring Instrument (TOMS-OMI) satellite, we found that about 45 per cent of nights were clear, while satellite data (GOES, TOMS) are much more dispersed than those of La Palma. Setting a statistical threshold, we retried a comparable seasonal trend between the heliograph and satellite
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