Adaptive optics parameters connection to wind speed at the Teide Observatory

Current projects for large telescopes demand a proper knowledge of atmospheric turbulence to design efficient adaptive optics systems in order to reach large Strehl ratios. However, the proper characterization of the turbulence above a particular site requires long-term monitoring. Because of the lack of long-term information on turbulence, high-altitude winds (in particular winds at the 200 mbar pressure level) were proposed as a parameter for estimating the total turbulence at a particular site, with the advantage of records of winds going back several decades. We present the first complete study of atmospheric adaptive optics parameters above the Teide Observatory (Canary Islands, Spain) in relation to wind speed. On-site measurements of   C ² _N ( h )  profiles (more than 20 200 turbulence profiles) from G-SCIDAR (Generalized Scintillation Detection and Ranging) observations and wind vertical profiles from balloons have been used to calculate the seeing, the isoplanatic angle and the coherence time. The connection of these parameters to wind speeds at ground and at 200 mbar pressure level are shown and discussed. Our results confirm the well-known high quality of the Canary Islands astronomical observatories.     

Diurnal photometric conditions at Teide observatory and long-term solar irradiance variations

Monochromatic extinction coefficients at four wavelengths have been obtained over a period of more than two years at the Observatorio del Teide (Izaña Tenerife) using a full disc, direct sunlight, quadruple photometer devoted to the detection of integral luminosity oscillations of the Sun. The mean extinction coefficients (0.13 at 500 nm) show a seasonal variation of about 15%, the best atmospheric conditions being in winter and autumn. Moreover, in anyone day the extinction coefficient in the afternoon is always lower than the one in the morning by 7%. A one-year period fluctuation, with an amplitude of 0.035 mag, has been identified in the instrumental magnitudes outside the atmosphere, and is interpreted as the variation produced by the different Sun-Earth distance from winter to summer. Finally, the study made to detect periodic time fluctuations in both, Sun's magnitude and extinction coefficients, has given null results at levels of 0.04 and 1.8%, respectively.     

Stray-light correction in magnetograph observations using the maximum entropy method

We have developed a method of stray-light correction which is applicable to filter-based magnetograph observations. Stray-light-corrected Stokes images are obtained by performing the deconvolution of observed Stokes images by the point spread function which is determined from the Stokes I image. For image deconvolution, the maximum entropy principle is used to guarantee that intensity should be positive and polarization degrees should be less than unity. We present an iterative algorithm for the maximum entropy method, which seeks the solution in Fourier space and thus accomplishes fast convergence. We find that our method is effective in correcting stray light which has a spread angle greater than the full width at half maximum of the point spread function. We also discuss the effect of stray light on magnetograph calibration.     

Analysis of the Spectra of Two Pleiades Brown Dwarfs: Teide 1 and Calar 3

Results of the numerical simulation of spectra of the Pleiades brown dwarfs Calar 3 and Teide 1 are discussed. Synthetical spectra were computed for several model atmospheres from a grid of Allard and Hauschildt (1995). From the comparison of computed and observed spectra we have found that: – the spectrum of Teide 1 may be reasonably well fitted by JOLA in the visible region, including the spectral regions around the Li I lines at λλ 670.8 and 812.6 nm. – The structure of absorption bands observed in the spectrum of Teide 1 and Calar 3 depends mainly on T_eff. The dependence on gravity is much weaker. – A comparison of observed and computed spectra shows that effective temperatures of these Pleiades brown dwarfs is T_eff ≈ 2900 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Solar rotation measurements at Mount Wilson

We examine the background velocity fields of the Sun as observed at Mount Wilson. The method of velocity reduction of the full-disk Mount Wilson data is outlined. We describe a number of tests that have been carried out in order to find an instrumental origin for short-term rotation variations and a large-scale background line-shift - the ears. No instrumental cause can be found for this ear effect, although such a cause cannot yet be ruled out.Operated jointly by the Carnegie Institution of Washington and the California Institute of Technology.     

Solar rotation measurements at Mount Wilson

The ears velocity pattern described in Paper I (Howard et al., 1980) had no physical explanation. A reanalysis shows that the large scale solar velocity patterns are better described by a nonmonotonic limbshift and a meridional flow. The results of the new analysis imply that the study of solar velocity pattern at the level of a few ms^–1 required that magnetic regions be treated separately from nonmagnetic regions.Now at: Institute for Astronomy, University of Hawaii, Honolulu, Hawaii 96822, U.S.A.     

Solar rotation measurements at Mount Wilson

This paper describes a thorough reevaluation of the procedures for reducing the data acquired at the Mt. Wilson Observatory synoptic program of solar observations at the 150-foot tower. We also describe a new program of acquiring as many scans per day as possible of the solar magnetic and velocity fields. We give a new fitting formula which removes the background velocity field from each scan. An important new feature of our reduction algorithm is our treatment of the limb shift which permits time variation in this function. We identify the difference between the limb shift along the north-south axis and the east-west axis as potentially being a result of meridional circulation. Our analysis interprets the time variation in the east-west limb shift as being the result of changes in a vertical component of the meridional circulation.The performance of the system improved in 1982 as a result of the installation of a new exit slit assembly. The amplitude of the limb shift variations found prior to 1982 is larger than is easily explained with simple ideas of meridional circulation. However, we have not been able to firmly identify instrumental causes for the variations although small changes in the band-pass of the exit slit assembly could have contributed.We have established a correlation between the observed stray light in the system and a component of the velocity field which is antisymmetric with respect to the solar central meridian. We remove this stray light effect by adding an additional term to the fitting function.Finally, we show that the inclusion of the above improvements allows us to study the torsional oscillations at high latitude using a procedure which can retain the longitude dependent information about the velocity pattern.     

Solar rotation measurements at Mount Wilson

Possible sources of systematic error in solar Doppler rotational velocities are examined. Scattered light is shown to affect the Mount Wilson solar rotation results, but this effect is not enough to bring the spectroscopic results in coincidence with the sunspot rotation. Interference fringes at the spectrograph focus at Mount Wilson have in two intervals affected the rotation results. It has been possible to correlate this error with temperature and thus correct for it. A misalignment between the entrance and exit slits is a possible source of error, but for the Mount Wilson slit configuration the amplitude of this effect is negligibly small. Rapid scanning of the solar image also produces no measurable effect.     

Gasdynamic interpretation of ice measurements at the Giacobini-Zinner encounter

Plasma measurements of the ICE spacecraft at its encounter with comet Giacobini-Zinner are found to be in qualitative agreement with corresponding predictions of a gasdynamic model on the solar wind interaction with the cometary neutral gas.     

Modelling of magnetic field measurements at Mercury

Mapping Mercury's internal magnetic field with a magnetometer in closed orbit around the planet will provide valuable information about its internal structure. By measuring magnetic field multipoles of order higher than the dipole we could, in principle, determine some properties, such as size and location, of the internal source. Here we try to quantify these expectations. Using conceptual models, we simulate the actual measurement during the BepiColombo mission, and then we analyze the simulated data in order to estimate the measurement errors due to the limited spatial sampling. We also investigate our ability to locate the field generating current system within the planet. Finally, we address the main limitation of our model, due to the presence of time-varying external magnetospheric currents.     

A comparison of cosmic ray composition measurements at the highest energies

In recent years the Fly's Eye and Akeno groups have presented analyses of the cosmic ray mass composition at energies above 10¹⁷ eV. While the analysis of the Fly's Eye group points to a likely change in mass composition from heavy to light at energies above 10¹⁸ eV, the Akeno analysis favours an unchanging composition. However, the two groups base their conclusions on simulations using quite different hadronic models. Here we present a comparison of the experiments using the same hadronic model and find that the agreement between the experiments is much improved. Under this model, both experiments measure a composition rich in iron around 10¹⁷ eV which becomes lighter at higher energies. However, the agreement is not complete, which indicates scope for improvement of the interaction model, or perhaps the need for a re-examination of the experimental results.     

Absolute brightness temperature measurements at 2.1-mm wavelength

Absolute measurements of the brightness temperatures of the Sun, new Moon, Venus, Mars, Jupiter, Saturn, and Uranus, and of the flux density of DR21 at 2.1-mm wavelength are reported. Relative measurements at 3.5-mm wavelength are also presented which resolve the absolute calibration discrepancy between The University of Texas 16-ft radio telescope and the Aerospace Corporation 15-ft antenna. The use of the bright planets and DR21 as absolute calibration sources at millimeter wavelengths is discussed in the light of recent observations.     

Planetary brightness temperature measurements at 1.4-mm wavelength

Precise relative measurements of the disk brightness temperatures of Venus, Mars, Jupiter, and Saturn have been made at a mean wavelength of 1.4 mm. The rings of Saturn contribute significantly to the observed total emission. Other results include a better understanding of the properties of the NRAO 11-m antenna near its high frequency limit and of atmospheric degradation of observations in this wavelength range.     

Lunar temperature measurements at 3200 Mc/s

The measured effective black-body temperature at the lunar equator is 220 °K, with an estimated probable error of 5 per cent. No variation with lunar phase was detected; if present, and obscured by the random scatter of the observations, it is less than 5 per cent at this frequency.     

Interstellar scintillation measurements of pulsars at 326.5 MHz

We have measured the decorrelation frequency (f _v ) and decorrelation time (t _v ) for 15 pulsars. We show by combining our data with those of others thatfv∫ DM^-1.79±0.14 andt _v ∫ DM^-0.80±0.15 up to a dispersion measure (DM) of about 60 cm³ pc. The combined data set does not form a complete sample, but the relations obtained from our measurements on 14 pulsars, which form almost a complete sample up to 41 cm³ pc, are consistent with the above relations, suggesting that these relations are not seriously affected by selection effects. The relations are broadly in agreement with those expected from a homogeneous interstellar medium and are in disagreement with earlier conclusions by others that these relations steepen even for low-DM pulsars. The agreement suggests that the local interstellar medium is homogeneous at least up to a distance of about 2 kpc.     

Atmospheric emission measurements at 85 to 118 GHz

Measurements have been made of the atmospheric gaseous emission spectrum in the region from 85–118 GHz (wavelength range 3·5–2·5 mm), and the results have been used to estimate the attenuation in the zenith direction over this range, which includes the low frequency side of the oxygen absorption line centered at 118·75 GHz. The results are compared with theoretical predictions based on line shape models in current use, and the discrepancies between experiment and theory are discussed.     

Global oscillation measurements at Kumbel station in frame of the IRIS programme

The second of the IRIS network instruments was commissioned in August 1988 at Kumbel mountain, located 75 km from Tashkent (U.S.S.R.). Atmospheric and operating conditions on Kumbel are discussed, as well as preliminary results derived from this station's global solar oscillation measurements.     

Solar diameter measurements at São Paulo Observatory

In this work we describe solar radius measurements made from 1972 with the São Paulo astrolabe. We find values of  959.52 ± 0.03 arcsec  for the visual data and  959.61 ± 0.05 arcsec  for the CCD data using a modified data acquisition system. We compare our results with other astrolabe measurements and with SOHO –MDI. Observations of the solar radius show contradictory results when we try to correlate changes in the diameter with the solar cycle. Our series is not correlated with the solar cycle but it shows a period of  13.4 ± 2.2 yr  . We have also compared our time series with other long-term measurements of solar radius along solar cycle 21 and analysed our measurements as a function of heliographic latitude. We do not find a significant solar oblateness.