We present new results from the Parallaxes of Southern Extremely Cool dwarfs program to measure parallaxes, proper motions and multi-epoch photometry of L and early T dwarfs. The observations were made on 108 nights over the course of 8 years using the Wide Field Imager on the ESO 2.2m telescope. We present 118 new parallaxes of L & T dwarfs of which 52 have no published values and 24 of the 66 published values are preliminary estimates from this program. The parallax precision varies from 1.0 to 15.5 mas with a median of 3.8 mas. We find evidence for 2 objects with long term photometric variation and 24 new moving group candidates. We cross-match our sample to published photometric catalogues and find standard magnitudes in up to 16 pass-bands from which we build spectral energy distributions and H-R diagrams. This allows us to confirm the theoretically anticipated minimum in radius between stars and brown dwarfs across the hydrogen burning minimum mass. We find the minimum occurs between L2 and L6 and verify the predicted steep dependence of radius in the hydrogen burning regime and the gentle rise into the degenerate brown dwarf regime. We find a relatively young age of ∼2 Gyr from the kinematics of our sample.

We present results from the PARallaxes of Southern Extremely Cool objects (PARSEC) program, an observational program begun in April 2007 to determine parallaxes for 122 L and 28 T southern hemisphere dwarfs using the Wide Field Imager on the ESO 2.2m telescope. The results presented here include parallaxes of 10 targets from observations over 18 months and a first version proper motion catalog.The proper motions were obtained by combining PARSEC observations astrometrically reduced with respect to the Second US Naval Observatory CCD Astrograph Catalog, and the Two Micron All Sky Survey Point Source Catalogue. The resulting median proper motion precision is 5mas/yr for 195,700 sources. The 140 0.3deg 2 fields sample the southern hemisphere in an unbiased fashion with the exception of the galactic plane due to the small number of targets in that region. The proper motion distributions are shown to be statistically well behaved. External comparisons are also fully consistent. We will continue to update this catalog until the end of the program and we plan to improve it including also observations from the GSC2.3 database.We present preliminary parallaxes with a 4.2 mas median precision for 10 brown dwarfs, 2 of which are within 10pc. These increase by 20% the present number of L dwarfs with published parallaxes. Of the 10 targets, 7 have been previously discussed in the literature: two were thought to be binary but the PARSEC observations show them to be single, one has been confirmed as a binary companion and another has been found to be part of a binary system, both of which will make good benchmark systems. These results confirm that the foreseen precision of PARSEC can be achieved and that the large field of view will allow us to identify wide binary systems.Observations for the PARSEC program will end in early 2011 providing 3-4 years of coverage for all targets. The main expected outputs are: more than a 100% increase of the number of L dwarfs with parallaxes; to increment -in conjuction with published results -to at least 10 the number of objects per spectral subclass up to L9, and; to put sensible limits on the general binary fraction of brown dwarfs. We aim to contribute significantly to the understanding of the faint end of the H-R diagram and of the L/T transition region.

Rapizo, H.; d'Avila, V.; Violante-Carvalho, N.; Pinho, U.; Parente C.E., and Nascimento, F., 0000. Simple techniques for retrieval of wind wave periods and directions from optical images sequences in wave tanks. Journal of Coastal Research, 00(0), 000-000. Coconut Creek (Florida), ISSN 0749-0208.Optical techniques are potentially suitable for overcoming some of the limitations faced by single-point sensors, like buoys, in retrieving spatial properties of wind-generated waves. However, most of the approaches that have been addressed in the literature employ complex configurations that use a coupling system between cameras, making its implementation difficult. This article describes simple techniques for measuring the period and direction of multimodal, regular waves, employing a single, commonly available camera. Furthermore, there is no special requirement for light conditions, making its implementation feasible, in both indoor and outdoor environments. Several tests were conducted in a multidirectional tank, varying the steepness and direction of the waves. The optical measurements were in good agreement, especially for waves from moderate to greater steepness. The techniques described here could be employed as a preliminary step before tackling more-complex configurations, for instance, as a priori information on the main wave modes.

No abstract

Abstract. Here we derive a formulation connecting the observed variations of the solar diameter to the heliophysics of the photosphere, in particular in connection to the granulation pattern and morphology. The results from the measurements are next used to correlate the variations of the semi-diameter and of estimators of the solar activity along the solar cycle 23. The values obtained strongly support a broader physical description of the photosphere, intertwining the diameter variations with the irradiance, the sunspots, the 10.7 cm radio emission, and to a lesser degree with the integrated magnetic field and with the flares count.Keywords. Sun: fundamental parameters, granulation, flares, activity, radio radiation Searching for long time behavior of solar granulationWe have obtained the images of the full solar disc from the Big Bear Solar Observatory. These images cover the beginning, the peak, and the post-peak of the solar cycle 23. They are densely distributed between 2000 to 2006. The images are all of 1364 × 1035 pxs. The same telescope, the same camera and the same orientation were used. The exposition time varies from 50 to 80 ms. We have examined two kinds of images: Fl imagessubtracted from dark and from flat field (1261 images), and Fr images -subtracted from limb darkening (1341 images)To avoid limb darkening influences, we took only the central part of the images. Thus, we considered only the central part from each original image up to 0, 35 of the solar radius. In this way only 2% of intensity variation remains even for Fl images. The central portion of the Sun was next divided in 10 × 10 collateral sectors. Each sector has 30 × 30 pxs. In each sector the statistics described below have been independently applied, and sectors deviating from the average by 3σ or more were removed from all the final analyses. This strategy seeks to discard the presence of sunspots from the solar granulation description.Three estimators are here used as first assessment to the granulation state. For each estimator the average of the sectors is calculated (after removing the deviating ones).(a) standard deviation of counts (S) as probe of the grains' mean size. (b) difference between the uppermost and lowest counts tenths (Q) as probe of the grains' brightness.(c) degree of the better adjusted polynomial along lines and columns (N) as probe of the grains' number.The model then assumes a patch of grains formed by bright centers and dark intergrain contours. Through large number statistics the balance between the two structures along the solar cycle is assessed. After all Fl and Fr images have been treated, and the three statistics obtained for each one, a final filter was applied removing within each year the 72 at https://www.cambridge.org/core/terms. https://doi

No abstract

Abstract. The measurements of the solar photospheric diameter rank among the most difficult astronomic observations. Reasons for this are the fuzzy definition of the limb, the SNR excess, and the adverse daytime seeing condition. As a consequence there are very few lengthy and consistent time series of such measurements. Using modern techniques, just the series from the IAG/USP and from Calern/OCA span more than one solar cycle. The Rio de Janeiro Group observations started in 1997, and therefore in 2008 one complete solar cycle time span can be analyzed. The series shares common principles of observation and analysis with the ones afore mentioned, and it is complementary on time to them. The distinctive features are the larger number of individual points and the improved precision. The series contains about 25,000 single observations, evenly distributed on a day-by-day basis. The typical error of a single observation is half an arc-second, enabling us to investigate variations at the expected level of tens of arc-second on a weekly basis. These features prompted to develop a new methodology for the investigation of the heliophysical scenarios leading to the observed variations, both on time and on heliolatitude. The algorithms rely on running averages and time shifts to derive the correlation and statistical incertitude for the comparison of the long term and major episodes variations of the solar diameter against activity markers. The results bring support to the correlation between the diameter variation and the solar activity, but evidentiating two different regimens for the long term trend and the major solar events.

Abstract. The Observatório Nacional at Rio de Janeiro has developed a new heliometer to perform accurate measurements of the solar diameter. The equipment makes use of split parabolic mirrors, rather than split achromatic lenses as objective. In its first campaign this reflector heliometer generated a few thousands of images of the Sun through which we evaluate the precision of the solar diameter measurements as been 5 mas. The mechanical and thermal stability of the instrument is guaranteed by the use of a telescope tube manufactured in carbon fiber. The tube firmly holds the heliometric mirrors and the CCD camera that collects the images. The perfect lodging between the two half-mirrors over its supporting plate defines the angular instrumental separation between the two images of the sun. The heliometric mirrors and supporting plate have been made in ceramic material in order to ensure the stability of the optical configuration and to maintain the two images of the solar disk displaced by a fixed angle in relation to each other. To verify the stability of the instrument we designed the procedures of collimation and comparison. The collimation consists of using the heliometer for measuring the diameter of an artificial solar image specifically created for this purpose. The comparison is performed by measuring the residual unfold of a punctual image after been unfold by two opposed heliometers. The heliometric approach allows the measurement of the solar diameter at any heliolatitude and can be undertaken as often as desired. Computer programs have been developed for automated image acquisition and analysis. The optical and mechanical design has been performed by using 3D computer aided design software.