Contact Binaries: A Study of the Proximity Effects and Gravity Darkening Based on Kopal’s Fourier Method

A new method for the determination of the proximity effects and gravity darkening exponents in contact binaries of W UMa type is presented. The method is based on Kopal’s method of Fourier analysis of the light changes of eclipsing variables in the Frequency Domain. The method was applied to 36 W UMa systems for which geometric and photometric elements have been derived by the most powerful techniques. The derived values are very close to those predicted by the existing theory of radiative transfer or convective equilibrium.     

Neutrino Tomography – Learning About The Earth’s Interior Using The Propagation Of Neutrinos

Because the propagation of neutrinos is affected by the presence of Earth matter, it opens new possibilities to probe the Earth’s interior. Different approaches range from techniques based upon the interaction of high energy (above TeV) neutrinos with Earth matter, to methods using the MSW effect on the oscillations of low energy (MeV to GeV) neutrinos. In principle, neutrinos from many different sources (sun, atmosphere, supernovae, beams etc.) can be used. In this talk, we summarize and compare different approaches with an emphasis on more recent developments. In addition, we point out other geophysical aspects relevant for neutrino oscillations.     

Model of optical turbulence profile at Cerro Pachón

New measurements of optical turbulence profile at the Cerro Pachón observatory in Chile are analysed jointly with previously published data to model the variations of the intensity and thickness of the ground layer and free atmosphere under a variety of observing conditions. This work is motivated by the need to predict statistically the performance of ground-layer adaptice optics. We find that the ground-layer profile can be represented by a decaying exponent with a scale height of 20–40 m, increasing to 100 m under bad conditions. The zone from 6 to 500 m contributes typically about 61 per cent to the total integral, the latter causing a median seeing of 0.77 arcsec. Turbulence integrals in the ground layer and in free atmosphere vary independently of each other, in 50 per cent of cases they deviate by less than 1.8 times from their respective median values. The existence of periods with low turbulence in the free atmosphere and their importance for adaptive optics is stressed.     

Neutral sodium atoms release from the surface of the Moon induced by meteoroid impacts

In this work, we calculate the vapour and neutral Na production rates on the Moon, as due to the impacts of meteoroids in the radius range of 10⁻⁸–0.15 m. We limit our calculations to this size range, since meteoroids with radius larger than 0.15 m have not been found to be important for the production of the exosphere in a time interval comparable with that of the observations.
We have considered a new dynamical model of the flux of meteoroids at the heliocentric distance of the Moon, regarding objects in the radius range of 10⁻²–0.15 m. Instead, the flux of smaller meteoroids (radius range 10⁻⁸–10⁻² m) has been calculated using the two distributions adopted by Cintala and Love & Brownlee.
The results of our model are that (i) the neutral Na production rate is  ∼3–4.9 × 10⁴ atoms cm⁻² s⁻¹  , slightly larger than the previous estimates  (∼2–3 × 10⁴ atoms cm⁻² s⁻¹)  , and (ii) only about 6 per cent of neutral Na is produced by the impacts of meteoroids in the size range 10⁻³–0.15 m, whereas about 94 per cent of the Na comes from the  10⁻⁵–10⁻³ m  size range.     

Astronomical Image Co-adding Method based on Wide-field Image Deconvolution

Due to the atmospheric turbulence, the static aberration, tracking and pointing errors of telescopes, the point spread functions (PSFs) in different fields of view are different. Meanwhile, there are different PSFs in the images obtained by different telescopes. The quality of co-adding image is limited by the image with the poorest quality, and finally the resolution and sensitivity of the quad-channel telescope will also be affected. Dividing the image into some regions with the same type of PSF, and deconvolving these regions can improve the quality of the co-adding image. According to this theory, an image restoration algorithm based on the PSF clustering is proposed. Firstly, this paper makes the PSF clustering analysis by using Self-Organizing Maps, and makes the image segmentation based on the result of the PSF clustering analysis, then using the clustered PSFs to make deconvolutions on the sub-images. Then, the restored sub-images after deconvolution are joined together. Finally, by through the image registration and co-adding, the image with a high signal to noise ratio can be obtained. The result shows that the signal to noise ratio of the astronomical images are improved with our method, and the detection capability on faint stars is also improved.     

Potential of the VLTI for linking stellar frames to ICRF

The question of positioning the optical counterparts of the ICRF quasars is outlined in the perspective of future space astrometry missions, which ultimately will bring a new realization of the ICRS in the optical range. Ground-based interferometry with a dual-field observing mode (PRIMA/VLTI),together with the missions DIVA and FAME, will have a key role in building an extragalactic reference frame in the optical/near-IR range with about the same accuracy as that of the present (VLBI) primary frame. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sodium beacon tip–tilt determination with Rayleigh-aided auxiliary telescope technique

The usefulness of tracking the Rayleigh portion of a mesospheric sodium laser guide star as reference for absolute tip–tilt recovery in the frame of the auxiliary telescopes technique is shown. This approach leads to the reduction of the ground occupation needed to attain a given sky coverage by more than one order of magnitude. Speed, tracking precision, and the number of auxiliary telescopes are also reduced, making this new approach a more attractive one. The use of a low-altitude Rayleigh spot reinforces the fundamental limitations affecting this and other techniques, thus degrading significantly the quality of the recovered tip–tilt. However, it is shown that, provided adequate care is taken in the collection and treatment of data, an interesting tilt signal can still be retrieved.     

The astroclimatological comparison of the Paranal Observatory and El Roque de Los Muchachos Observatory

The 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.