“Caracterização Instrumental e do Céu no Observatório Astronômico do Sertão de Itaparica (OASI)”

Abstract

The instrumental and night-sky characterization of an astronomical observatory are essential for efficient observation planning, appropriate of new instrument selection, and the application of photometric corrections, thereby enabling more accurate determination of the physical parameters of observed objects. This work presents a detailed description of the instrumentation currently available at the Observatório Astronômico do Sertão de Itaparica (OASI), with comments on recent acquisitions, planned equipment, identified operational limitations, and proposed mitigation strategies.

On the other hand, the characterization of the sky was carried out, determining the seeing distribution for 30- and 40-second exposures, both peaking at a mode of $1.35''$. The mean seeing was $1.48''$ (30 s) and $1.36''$ (40 s), with standard deviations of $0.55''$ and $0.47''$, respectively. The annual analysis showed no apparent correlation between seeing and seasonality, indicating the presence of photometric nights throughout most of the year. No correlation were found between seeing and meteorological parameters such as humidity, atmospheric pressure, and temperature. Nevertheless, the possibility of a correlation in multivariate analyses that consider combinations of meteorological parameters cannot be ruled out.

Another parameter studied was the atmospheric extinction coefficient in the R filter, using data from 2011 to 2018. The distribution of this parameter showed a mode at $0.318$, median of $0.236$, and mean of $0.261$. These values are consistent with OASI’s local characteristics, including its low elevation, proximity to a river, and the presence of dust, which contribute to increased aerosol scattering.

Finally, an analysis of light pollution was conducted using All-Sky camera images. A progressive increase in light pollution was observed up to 2018, followed by a reduction during the COVID-19 pandemic, and a sharp rise from 2021 onward, linked to urban infrastructure projects and the replacement of sodium lamps with LEDs. The main emission sources were identified in nearby cities, with a newly detected hotspot located in in Coité, only 5.5 km from OASI. Light pollution imposes significant observational constraints, especially for low-altitude targets ($<20^\circ$), such as Atira-type asteroids and Sungrazers, primarily affecting the western sky. In contrast, the eastern sky remains with low light pollution, providing more favorable conditions for observing these objects at sunrise.