Extension of Tycho catalog for low-extinction windows in the galactic bulge

We present in this work secondary catalogs up to $m_{Val} \sim 13$ based on the Tycho reference frame (ESA, 1997) for 12 selected low-extinction fields towards the galactic bulge. The observations have been performed with the Askania-Zeiss Meridian Circle equiped with a CCD camera, located at the Abrah\~ao de Moraes Observatory (Valinhos, Brazil) and operated by the Institute of Astronomy and Geophysics, S\~ao Paulo University. The presented catalog, though not complete, has been designed to help in intensive search programmes (e.g. microlensing and variable searches) and therefore the selected standards have a high astrometric and photometric ($V$ band, approximately) quality. The mean precisions obtained were $0.0018^{s}$ in $\alpha$, 0.013'' in $\delta$, 0.030 for the standard deviation in magnitude and 0.0042 for the magnitude when weighted with the error bars in each night (in the mean, 42 stars for the catalog of each window). Tables B.1 to B.12 are also available in eletronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.Comment: 16 pages, 6 figures, A&A Latex style. Published in A&A

Stellar variability in low-extinction regions towards the Galactic Bulge

Intensive monitoring of low-extinction windows towards the galactic bulge has provided in the last years valuable information for studies about the dynamics, kinematics and formation history of this part of the galaxy, mainly by characterizing the bulge stellar populations (Paczy\'nski, 1996). Since 1997, we have been conducting an intensive photometric-astrometric survey of the galactic bulge, with the monitoring of about 120000 stars in 12 windows uniformly distributed in galactic latitude and longitude (Blanco & Terndrup, 1989 e Blanco, 1988) never before submitted to this kind of survey. For this purpose, we have used the IAG/USP CCD Meridian Circle of the Abrah\~ao de Moraes Observatory. The main objective of this work is the identification and classification of variable objects. In this work we present the set up and development of the necessary tools for a project like this and the posterior analysis of our data. We briefly describe the construction of a program to organize and detect variables among the observed stars, including real time alerts (for variations greater than 0.3 magnitudes). The preliminary analysis after the processing of 76 nights of observation yielded 479 variable stars, from which 96.7 % of them are new. We discuss the preliminary classification of this variables, based on: a) the observed amplitude of variation; b) the shape of light curve; c) the expected variable classes among our data and d) the calculated periods, whenever possible. Finally, we discuss the future perspectives for the project and for the applications and analysis of the discovered variable stars.Comment: 10 pages, 14 figures. Accepted by A&A

Hybrid confinement of optical and mechanical modes in a bullseye optomechanical resonator

Optomechanical cavities have proven to be an exceptional tool to explore fundamental and technological aspects of the interaction between mechanical and optical waves. Such interactions strongly benefit from cavities with large optomechanical coupling, high mechanical and optical quality factors, and mechanical frequencies larger than the optical mode linewidth, the so called resolved sideband limit. Here we demonstrate a novel optomechanical cavity based on a disk with a radial mechanical bandgap. This design confines light and mechanical waves through distinct physical mechanisms which allows for independent control of the mechanical and optical properties. Our device design is not limited by unique material properties and could be easily adapted to allow large optomechanical coupling and high mechanical quality factors with other promising materials. Finally, our demonstration is based on devices fabricated on a commercial silicon photonics facility, demonstrating that our approach can be easily scalable.Comment: 16 pages, 11 figure

Exploring the use of classification uncertainty to improve classification accuracy

Moraes, D., Benevides, P., Moreira, F. D., Costa, H., & Caetano, M. (2021). Exploring the use of classification uncertainty to improve classification accuracy. In The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLIII-B3-2021, XXIV ISPRS Congress (2021 edition), (pp. 81-86). https://doi.org/10.5194/isprs-archives-XLIII-B3-2021-81-2021Supervised classification of remotely sensed images has been widely used to map land cover and land use. Since the performance of supervised methods depends on the quality of the training data, it is essential to develop methods to generate an enhanced training dataset. Active learning represents an alternative for such purpose as it proposes to create a dataset of optimized samples, normally collected based on classification uncertainty. However, it is heavily dependent on human interaction, since the user has to label selected samples over a number of iterations. In this paper, we explore the use of uncertainty to improve classification accuracy through a single iteration. We conducted experiments in a region of Portugal (Trás-os-Montes), using multioral Sentinel-2 images. The proposed approach consisted in computing the classification uncertainty of a Random Forest to collect additional training data from areas of high uncertainty and perform a new classification. An accuracy assessment was performed to compare the overall accuracy of the initial and new classifications. The results exhibited an increase in accuracy, though considered not statistically significant. Obstacles related to labelling additional sampling units resulted in a lack of additional training data for various classes, which might have limited the accuracy improvement. Additionally, an uneven proportion of additional training sampling units per class and the collection of new sample data from a limited number of uncertainty regions might also have prevented a higher increase in accuracy. Nevertheless, visual inspection of the maps revealed that the new classification reduced the confusion between some classes.publishe

Ar/Cl-2 etching of GaAs optomechanical microdisks fabricated with positive electroresist

FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESA method to fabricate GaAs microcavities using only a soft mask with an electrolithographic pattern in an inductively coupled plasma etching is presented. A careful characterization of the fabrication process pinpointing the main routes for a smooth devic1015767FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES2012/17610-32012/17765-72016/18308-02018/15577-52018/15580-62019/01402-100