Sirius: a prototype astronomical intensity interferometer using avalanche photodiodes in linear mode

ABSTRACT Optical intensity interferometry, developed in the 1950s, is a simple and inexpensive method for achieving angular resolutions on microarcsecond scales. Its low sensitivity has limited intensity interferometric observations to bright stars so far. Substantial improvements are possible by using avalanche photodiodes (APDs) as light detectors. Several recent experiments used APDs in single-photon detection mode; however, these either provide low electronic bandwidths (few MHz) or require very narrow optical bandpasses. We present here the results of laboratory measurements with a prototype astronomical intensity interferometer using two APDs observing an artificial star in continuous (‘linear’) detection mode with an electronic bandwidth of 100 MHz. We find a photon–photon correlation of about 10−6, as expected from the ratio of the coherence times of the light source and the detectors. In a configuration where both detectors are on the optical axis (zero baseline), we achieve a signal-to-noise ratio of ∼2700 after 10 min of integration. When measuring the correlation as a function of baseline, we find a Gaussian correlation profile with a standard deviation corresponding to an angular half-width of the artificial star of 0.55 arcsec, in agreement with the estimate by the manufacturer. Our results demonstrate the possibility to construct large astronomical intensity interferometers using linear-mode APDs.

Sprint pattern analysis of professional female soccer players on artificial and natural turf (Análisis del patrón de carrera en jugadoras de fútbol femenino en césped artificial y natural)

Introduction: There is few evidence that details the behavior of each spatiotemporal variable of the running pattern of female soccer players using different surfaces. Objective: To describe the spatiotemporal variables of the sprint pattern developed on natural and artificial turf by professional female soccer players. Methods: A cross-sectional study was conducted on nineteen (n=19) professional athletes with an average age of 22.3 years, who´s sprint spatiotemporal variables were evaluated in a natural (Bermuda 419) and artificial (Star 2) playing field through an optical measurement system (Opto Gait, Italy). The analysis of the differences of the space and time variables by turf was done with the Wilcoxon test for paired data and the differences in speed and acceleration by playing position was done using the Kruskal–Wallis test. The Spearman test was used to compare the correlation between speed, acceleration and anthropometric variables. Finally, an alpha level of 5% was considered for the whole analysis. Results: On the natural turf, the speed and cadence of the players were higher; on the artificial turf, the energy, flight time, contact phase and step angle were higher (p<0.05). On the other hand, an indirect relationship was observed between speed, contact time, percentage and fat weight (p=0.01). Conclusion: Our results suggest that the natural turf, Bermuda 419, allows for a faster sprinting patterns, characterized by lower energy use, flight time, contact phase and step angle. Resumen. Introducción: Existe poca evidencia que detalle el comportamiento de cada variable espaciotemporal del patrón de carrera de mujeres futbolistas utilizando diferentes superficies. Objetivo: describir las variables espacio temporales del patrón de carrera desarrollado en superficie natural y artificial por mujeres futbolistas profesionales. Métodos: se realizó un estudio de corte transversal en diecinueve (n=19) deportistas profesionales con un promedio de edad de 22.3 años, a quienes se les evaluaron las variables espacio temporales de la carrera en césped natural (Bermuda 419) y artificial (Star 2) a través de un sistema de medición óptico (Opto Gait). El análisis de las diferencias de las variables espacio temporales fue realizado con el test de Wilcoxon para datos pareados y las diferencias en la velocidad y aceleración fue realizados usando el test Kruskal-Wallis. El test de Spearman se usó para comparar la correlación entre las variables de velocidad, aceleración y antropométricas. Finalmente, un nivel de alpha de 5% fue considerado para el análisis total. Resultados: en la superficie natural, la velocidad y cadencia de las futbolistas fueron superiores; sobre superficie artificial, la energía, el tiempo de vuelo, la fase de contacto y el ángulo de paso fueron más altas (p<0.05). De otra parte, se observó una relación indirecta entre la velocidad, tiempo de contacto, porcentaje y peso graso (p=0.01). Conclusión: nuestros resultados sugieren que la superficie natural, Bermuda 419, permite un patrón de carrera más rápido, caracterizado por un menor uso de energía, tiempo de vuelo, fase de contacto y ángulo de paso.

Mapping the stellar age of the Milky Way bulge with the VVV

Context. The bulge represents the best compromise between old and massive Galactic components, and as such its study is a valuable opportunity to understand how the bulk of the Milky Way formed and evolved. In addition, being the only bulge in which we can individually resolve stars in all evolutionary sequences, the properties of its stellar content provide crucial insights into the formation of bulges. Aims. We are providing a detailed and comprehensive census of the Milky Way bulge stellar populations by producing deep and accurate photometric catalogs of the inner ∼300 deg2 of the Galaxy. Methods. We performed DAOPHOT/ALLFRAME point spread function (PSF) fitting photometry of multi-epochs J and Ks images provided by the VISTA Variables in the Vía Láctea (VVV) survey to obtain deep photometric catalogs. Artificial star experiments have been conducted on all images to properly assess the completeness and the accuracy of the photometric measurements. Results. We present a photometric database containing nearly 600 million stars across the bulge area surveyed by the VVV. Through the comparison of derived color-magnitude diagrams of selected fields representative of different levels of extinction and crowding, we show the quality, completeness and depth of the new catalogs. With the exception of the fields located along the plane, this new photometry samples stars down to ∼1–2 mag below the old main sequence turnoff with unprecedented accuracy. To demonstrate the tremendous potential inherent to this new dataset, we give a few examples of possible applications, including (i) star count studies through the dataset completeness map; (ii) surface brightness map; and (iii) cross-correlation with Gaia DR2. Conclusions. The database presented here represents an invaluable collection for the whole community, and we encourage its exploitation. The photometric catalogs including completeness information are publicly available through the ESO Science Archive as part of the MW-BULGE-PSPHOT release.

Distances from the tip of the red giant branch to the dwarf galaxies dw1335-29 and dw1340-30 in the Centaurus group

Context. The abundance and spatial distribution of dwarf galaxies are excellent empirical benchmarks against which to test models of structure formation on small scales. The nearby Centaurus group, with its two subgroups centered on Cen A and M 83, stands out as an important alternative to the Local Group for scrutinizing cosmological model predictions in a group of galaxies context. Aims. We have obtained deep optical images of three recently discovered M 83 satellite galaxy candidates with the FORS2 instrument mounted on the Very Large Telescope. We aim to confirm their group membership and study their stellar population. Methods. Deep V I-band photometry was used to resolve the brightest stars in our targets. Artificial star tests are performed to estimate the completeness and uncertainties of the photometry. The color-magnitude diagrams reveal the red giant branch (RGB) stars, allowing us to use the Sobel edge detection method to measure the magnitude of the RGB tip and thus derive distances and group membership for our targets. The mean metallicity of the dwarf galaxies were further determined by fitting BASTI model isochrones to the mean RGB locus. Results. We confirm the two candidates, dw1335-29 and dw1340-30, to be dwarf satellites of the M 83 subgroup, with estimated distances of 5.03 ± 0.24 Mpc and 5.06 ± 0.24 Mpc, respectively. Their respective mean metallicities of ⟨[Fe/H]⟩ = −1.79 ± 0.4 and ⟨[Fe/H]⟩ = −2.27 ± 0.4 are consistent with the metallicity–luminosity relation for dwarf galaxies. The third candidate, dw1325-33, could not be resolved into stars due to insufficiently deep images, implying its distance must be larger than 5.3 Mpc. Using the two newly derived distances we assess the spatial distribution of the galaxies in the M 83 subgroup and discuss a potential plane-of-satellites around M 83.

Artificial Star Test for Crowded Field CCD Photometry

A new method of performing an artificial star test (AST) for crowded field stellar CCD photometry is proposed. This AST method is superior in the cases when it is necessary to account for varying photometric quality across the study field, arising due to crowding variations. For this purpose, the color-magnitude diagrams (CMDs) of AST stars with statistically reliable error estimates, as well as completeness maps, can be generated at a required spatial resolution.

Maximum-likelihood implementation of the tip-of-the-red-giant-branch method

The luminosity of the tip of the red giant branch (TRGB) provides an excellent measure of galaxy distances and is easily determined in the resolved images of nearby galaxies observed with the Hubble Space Telescope (HST). We use a maximum-likelihood algorithm to locate the TRGB in galaxy colour–magnitude diagrams. The algorithm is optimized by introducing reliable photometric errors and a completeness characterization determined based on artificial-star experiments. The program has been tested extensively using Monte Carlo simulations, artificial galaxies, and a sample of nearby dwarf galaxies observed with the HST's WFPC2 and ACS cameras. Our procedure is shown to be reliable, yield good accuracy, and does not introduce any systematic errors. The methodology is especially useful in cases in which the TRGB approaches the photometric limit and/or the RGB is poorly populated.