Cinemática galáctica local y constante de precesión

La distribución de las velocidades residuales y los parámetros cinemáticos en el entorno solar han sido calculados por diversos autores (DELHAYE, 1965). Sin embargo, las diferencias significativas que aparecen entre las distintas determinaciones nos animaron a profundizar en este tema. El método estadístico aplicado y los datos utilizados son las principales causas de tales discrepancias. Por ello, hemos dedicado el primer Capítulo a analizar los datos disponibles, para tratar de encontrar las causas de dichas discrepancias y obtener una fuente de datos que (con la misma muestra de estrellas) nos permitiese atacar el estudio de la distribución de las velocidades residuales y de los parámetros cinemáticos del movimiento macroscópico de la Galaxia en el entorno del Sol. En cuanto se refiere al estudio de la distribución de las velocidades residuales, en el Capítulo segundo se han calculado los momentos centrados hasta el cuarto orden. Hasta hace poco, únicamente se consideraban los momentos de segundo orden y sólo CHARLIER (1926) había estimado los momentos hasta el cuarto orden, si bien los datos entonces disponibles eran de menor calidad. Recientemente, ERICKSON (1975) ha publicado momentos hasta el cuarto orden para el Catálogo de GLIESE (1969), y ello nos ha animado a atacar el problema por otro método de cálculo obteniendo plena coincidencia al aplicarlo a su muestra de estrellas, lo cual nos ha permitido extender estos cálculos al Catálogo FK4. Al desarrollo del modelo tridimensional de OGORODNIKOV-MILNE para calcular el gradiente del campo galáctico de velocidades hemos dedicado el Capítulo tercero, sin más hipótesis que la de la aproximación lineal. Para interpretar los valores hallados en función de los parámetros cinemáticos de la Galaxia, necesitarnos separar la parte hemisimétrica de dicho gradiente de las correcciones de precesión con las cuales aparece mezclada. Para ello, en lugar de admitir hipótesis de dudosa justificación, hemos preferido adoptar un modelo galáctico. El modelo galáctico elegido con el fin de paliar el problema expuesto ha sido un modelo isotermo, el cual se justifica perfectamente en las proximidades del Sol. Dicho modelo se ha desarrollado en el cuarto Capítulo, planteándose las ecuaciones hidrodinámicas que de él se deducen y que nos han permitido cerrar el problema y calcular los parámetros cinemáticos de la Galaxia en el entorno del Sol, así corno las correcciones a la constante de la precesión. La concordancia con otros autores y la coherencia interna de los resultados obtenidos pone de manifiesto la bondad del método de cálculo empleado y la necesidad de atacar los problemas de dinámica galáctica mediante modelos tridimensionales, así como al propio tiempo justifica la adopción del citado modelo isotermo

Cinemática galáctica local y constante de precesión

[spa] La distribución de las velocidades residuales y los parámetros cinemáticos en el entorno solar han sido calculados por diversos autores (DELHAYE, 1965). Sin embargo, las diferencias significativas que aparecen entre las distintas determinaciones nos animaron a profundizar en este tema. El método estadístico aplicado y los datos utilizados son las principales causas de tales discrepancias. Por ello, hemos dedicado el primer Capítulo a analizar los datos disponibles, para tratar de encontrar las causas de dichas discrepancias y obtener una fuente de datos que (con la misma muestra de estrellas) nos permitiese atacar el estudio de la distribución de las velocidades residuales y de los parámetros cinemáticos del movimiento macroscópico de la Galaxia en el entorno del Sol. En cuanto se refiere al estudio de la distribución de las velocidades residuales, en el Capítulo segundo se han calculado los momentos centrados hasta el cuarto orden. Hasta hace poco, únicamente se consideraban los momentos de segundo orden y sólo CHARLIER (1926) había estimado los momentos hasta el cuarto orden, si bien los datos entonces disponibles eran de menor calidad. Recientemente, ERICKSON (1975) ha publicado momentos hasta el cuarto orden para el Catálogo de GLIESE (1969), y ello nos ha animado a atacar el problema por otro método de cálculo obteniendo plena coincidencia al aplicarlo a su muestra de estrellas, lo cual nos ha permitido extender estos cálculos al Catálogo FK4. Al desarrollo del modelo tridimensional de OGORODNIKOV-MILNE para calcular el gradiente del campo galáctico de velocidades hemos dedicado el Capítulo tercero, sin más hipótesis que la de la aproximación lineal. Para interpretar los valores hallados en función de los parámetros cinemáticos de la Galaxia, necesitarnos separar la parte hemisimétrica de dicho gradiente de las correcciones de precesión con las cuales aparece mezclada. Para ello, en lugar de admitir hipótesis de dudosa justificación, hemos preferido adoptar un modelo galáctico. El modelo galáctico elegido con el fin de paliar el problema expuesto ha sido un modelo isotermo, el cual se justifica perfectamente en las proximidades del Sol. Dicho modelo se ha desarrollado en el cuarto Capítulo, planteándose las ecuaciones hidrodinámicas que de él se deducen y que nos han permitido cerrar el problema y calcular los parámetros cinemáticos de la Galaxia en el entorno del Sol, así corno las correcciones a la constante de la precesión. La concordancia con otros autores y la coherencia interna de los resultados obtenidos pone de manifiesto la bondad del método de cálculo empleado y la necesidad de atacar los problemas de dinámica galáctica mediante modelos tridimensionales, así como al propio tiempo justifica la adopción del citado modelo isotermo

CCD drift-scan imaging lunar occultations: a feasible approach for submeter class telescopes

A CCD drift-scanning technique for lunar occultation (LO) observations is presented. While this approach has been addressed before by Sturmann (\cite{laszlo94}) for the case of large telescopes, the technical validity has never been discussed for sub-meter class telescopes. In contrast to Sturmann's scheme, the proposed technique places the CCD in the image plane of the telescope. This does not represent a problem in the case of small telescopes, where the practical angular resolution attainable by LO is not limited by aperture smoothing. Photon-generated charge is read out at millisecond rates on a column by column basis, as the diffraction pattern of the occulted star is being tracked. Two LO events (SAO 79031 and SAO 77911) were observed to demonstrate the feasibility of the method. Data analysis was carried out, yielding unresolved angular diameters for both objects. We show, however, that the technique could be useful for close binary detections with small telescopes. A discussion of the limiting resolution and magnitude imposed by our instrumentation is carried out, showing that the drift-scanning technique could be extended to 1-2 m telescopes for stellar diameter determination purposes. Finally, we point out that the technical demands required by this technique can be easily met by most small professional observatories and advanced amateurs

Application of fast CCD drift scanning to speckle imaging of binary stars

A new application of a fast CCD drift scanning technique that allows us to perform speckle imaging of binary stars is presented. For each observation, an arbitrary number of speckle frames is periodically stored on a computer disk, each with an appropriate exposure time given both atmospheric and instrumental considerations. The CCD charge is shifted towards the serial register and read out sufficiently rapidly to avoid an excessive amount of interframe dead time. Four well-known binary systems (ADS 755, ADS 2616, ADS 3711 and ADS 16836) are observed in to show the feasibility of the proposed technique.Bispectral data analysis and power spectrum fitting is carried out for each observation, yielding relative astrometry and photometry. A new approach for self-calibrating this analysis is also presented and validated.The proposed scheme does not require any additional electronic or optical hardware, so it should allow most small professional observatories and advanced amateurs to enjoy the benefits of diffraction-limited imaging

TFAW: Wavelet-based signal reconstruction to reduce photometric noise in time-domain surveys

Context. There have been many efforts to correct systematic effects in astronomical light curves to improve the detection and characterization of planetary transits and astrophysical variability. Algorithms such as the trend filtering algorithm (TFA) use simultaneously-observed stars to measure and remove systematic effects, and binning is used to reduce high-frequency random noise. Aims: We present TFAW, a wavelet-based modified version of TFA. First, TFAW aims to increase the periodic signal detection and second, to return a detrended and denoised signal without modifying its intrinsic characteristics. Methods: We modified TFA's frequency analysis step adding a stationary wavelet transform filter to perform an initial noise and outlier removal and increase the detection of variable signals. A wavelet-based filter was added to TFA's signal reconstruction to perform an adaptive characterization of the noise- and trend-free signal and the underlying noise contribution at each iteration while preserving astrophysical signals. We carried out tests over simulated sinusoidal and transit-like signals to assess the effectiveness of the method and applied TFAW to real light curves from TFRM. We also studied TFAW's application to simulated multiperiodic signals. Results: TFAW improves the signal detection rate by increasing the signal detection efficiency (SDE) up to a factor ̃2.5× for low S/R light curves. For simulated transits, the transit detection rate improves by a factor ̃2 - 5× in the low-S/R regime compared to TFA. TFAW signal approximation performs up to a factor ̃2× better than bin averaging for planetary transits. The standard deviations of simulated and real TFAW light curves are ̃40% better compared to TFA. TFAW yields better MCMC posterior distributions and returns lower uncertainties, less biased transit parameters and narrower (by approximately ten times) credibility intervals for simulated transits. TFAW is also able to improve the characterization of multiperiodic signals. We present a newly-discovered variable star from TFRM

Els dos telescopis refractors més grans de Catalunya

[cat] Entre 1886 i 1904 varen aparèixer a Catalunya dos telescopis refractors dobles (amb dos tubs, un visual i un altre fotogràfic) de grans dimensions. El primer fou un telescopi de la firma francesa Mailhat amb una obertura de 22 cm en ambdós tubs, que finalment va ser donat a la Facultat de Ciències de la Universitat de Barcelona. L'altre telescopi refractor fou també doble, de la mateixa firma, però amb 38 cm d'obertura, i va anar a l'Observatori Fabra. Aquesta comunicació, fa un estudi històric i tècnic d'aquestos telescopis.[eng] Two double refracting large telescopes (with two tubes, one for observations and another for photography) appeared in Catalonia between 1886 and 1904. The first was from the French firm Mailhat, a telescope with an aperture of 22 cm in both tubes that eventually was given to the Faculty of Sciences of the University of Barcelona in 1923 as a donation. The other refractor telescope was also made by the same firm but with an aperture of 38 cm and was designed for the Fabra Observatory project. In this communication a historical and technical study of these telescopes is carried out

A New Wavelet-based Approach for the Automated Treatment of Large Sets of Lunar Occultation Data

Context: The introduction of infrared arrays for lunar occultations (LO) work and the improvement of predictions based on new deep IR catalogues have resulted in a large increase in sensitivity and in the number of observable occultations.Aims: We provide the means for an automated reduction of large sets of LO data. This frees the user from the tedious task of estimating first-guess parameters for the fit of each LO lightcurve. At the end of the process, ready-made plots and statistics enable the user to identify sources that appear to be resolved or binary, and to initiate their detailed interactive analysis.Methods: The pipeline is tailored to array data, including the extraction of the lightcurves from FITS cubes. Because of its robustness and efficiency, the wavelet transform has been chosen to compute the initial guess of the parameters of the lightcurve fit.Results: We illustrate and discuss our automatic reduction pipeline by analyzing a large volume of novel occultation data recorded at Calar Alto Observatory. The automated pipeline package is available from the authors.Algorithm tested with observations collected at Calar Alto Observatory (Spain). Calar Alto is operated by the German-Spanish Astronomical Center (CAHA)

Optical Photometric Monitoring of LS i +61 303

Three gamma-ray binaries, namely PSR B1259 63, HESS J0632+057 and LS I +61 303, contain compact objects orbiting around massive Be stars. Around periastron passage the compact objects should produce significant changes in the structure of the Be disks due to gravitational forces and eventually by ram pressure from the putative pulsar wind. Indeed, variability in the Hα emission line has been detected in all these systems, and optical periodic variability has been detected in one of them. However, there is lack of a systematic monitoring with accurate photometry, which could be used to constrain the shape of the disk during the periastron passage. This information is important to build accurate physical models to explain the broadband spectral energy distribution of these sources. Here we present an ongoing program to monitor the optical photometry of gamma-ray binaries and show preliminary results for the case of LS I +61 303

Wavelet-based Image deconvolution for Wide Field CCD Imagery

We show how a wavelet-based image adaptive deconvolution algorithm can provide significant improvements in the analysis of wide-field CCD images. To illustrate it, we apply our deconvolution protocol to a set of images from a Baker-Nunn telescope. This f/1 instrument has an outstanding field of view of 4.4°x4.4° with high optical quality offering unique properties to study our deconvolution process and results. In particular, we obtain an estimated gain in limiting magnitude of ΔR∼0.6 mag and in limiting resolution of Δρ∼3.9 arcsec. These results increase the number of targets and the efficiency of the underlying scientific project

Evidence of coupling between the thermal and nonthermal emission in the gamma-ray binary LS I +61 303

The gamma-ray binary LS I +61 303 is composed of a Be star and a compact companion orbiting in an eccentric orbit. Variable flux modulated with the orbital period of ~26.5 d has been detected from radio to very high-energy gamma rays. In addition, the system presents a superorbital variability of the phase and amplitude of the radio outbursts with a period of ~4.6 yr. We present optical photometric observations of LS I +61 303 spanning ~1.5 yr and contemporaneous Hα equivalent width (EWHα) data. The optical photometry shows, for the first time, that the known orbital modulation suffers a positive orbital phase shift and an increase in flux for data obtained 1-yr apart. This behavior is similar to that already known at radio wavelengths, indicating that the optical flux follows the superorbital variability as well. The orbital modulation of the EWHα presents the already known superorbital flux variability but shows, also for the first time, a positive orbital phase shift. In addition, the optical photometry exhibits a lag of ~0.1-0.2 in orbital phase with respect to the EWHα measurements at similar superorbital phases, and presents a lag of ~0.1 and ~0.3 orbital phases with respect noncontemperaneous radio and X-ray outbursts, respectively. The phase shifts detected in the orbital modulation of thermal indicators, such as the optical flux and the EWHα, are in line with the observed behavior for nonthermal indicators, such as X-ray or radio emission. This shows that there is a strong coupling between the thermal and nonthermal emission processes in the gamma-ray binary LS I +61 303. The orbital phase lag between the optical flux and the EWHα is naturally explained considering different emitting regions in the circumstellar disk, whereas the secular evolution might be caused by the presence of a moving one-armed spiral density wave in the disk