Research

Positions, light & small bodies

My work connects the geometry of the celestial sphere with the practical challenge of measuring moving objects in crowded astronomical images.

Undergraduate work Master's research Doctoral direction

Positional astronomy · undergraduate work

Licenciatura in Physics · Universidade Estadual Vale do Acaraú · Sobral · 2018 thesis

My undergraduate thesis, Astronomia de Posição (Positional Astronomy), brings together celestial reference systems, spherical trigonometry, and transformations between astronomical coordinates. It also discusses apparent celestial motion and uses Stellarium to illustrate astronomical situations.

This work addresses a basic question behind astrometry: how do we define and relate the coordinates used to describe a position in the sky?

Supervisor: Prof. Dr. Antônio Fernandes Siqueira.

A celestial sphere with the horizon plane in blue and arcs indicating altitude and azimuth. — **Horizontal coordinates.** Altitude and azimuth locate an object relative to an observer's horizon. Original diagram from *Astronomia de Posição*. Figure 5, p. 24.

Spherical position triangle connecting the zenith, the elevated celestial pole and a star, with angular relationships marked. — **The position triangle.** Spherical geometry connects the observer's latitude with horizontal and equatorial coordinates. Original diagram from the undergraduate thesis. Figure 12, p. 34.

Small bodies in crowded fields · master's research

Master's in Astronomy · Observatório Nacional · Rio de Janeiro · 2025 thesis

My master's thesis, Astrometria e fotometria de pequenos corpos do Sistema Solar em imagens com campos estelares densos, studies how neighboring stars affect the measured position and brightness of a moving Solar System body.

Supervisor: Dr. Julio I. Bueno de Camargo. Co-supervisor: Dr. Adriano Pieres. Read the full thesis (PDF, Portuguese).

Separating the target from the background

I first compared PRAIA and DAOPHOT measurements of reference-star positions in a simulated dense field. I then applied difference image analysis (DIA), using DIAPL2, to a sequence of SOAR/SOI observations of the centaur (10199) Chariklo.

A reference image models the stellar background without the moving target. Subtracting that model from aligned science images makes it possible to measure Chariklo with less contamination. Reference stars are measured with PRAIA on the resampled science images.

Science, template, resampled science and difference images of a dense stellar field. Red arrows indicate Chariklo in the science images. — **Removing the stellar background.** From left to right: the science image, reference template, resampled science image, and difference image. The red arrows identify Chariklo in the science frames. Figure 4.5, p. 43.

Astrometric results

The analysis found smaller scatter in position residuals relative to the NIMA ephemeris after image subtraction. The table below reproduces the scatter values and sample sizes reported in the thesis.

Chariklo astrometry · thesis, Table 4.1
Reduction	Measurements	Scatter in Δα cos δ	Scatter in Δδ
Without DIA	95	0.066″	0.075″
With DIA	129	0.018″	0.017″

The reductions contain different numbers of accepted measurements. These results describe this observing sequence. See Table 4.1 and its discussion, p. 45.

Recovering the light curve

Photometry on the difference images also recovered Chariklo's rotational brightness variation. Cleaner position and brightness measurements can support stellar-occultation predictions and the physical study of small bodies.

Two plots of instrumental magnitude against time: original-image PSF photometry on the left and difference-image aperture photometry on the right. The vertical scales differ. — **Photometry before and after subtraction.** Original-image PSF photometry (left) and difference-image aperture photometry (right). The panels use different vertical scales; the comparison illustrates the effect of stellar contamination. Figure 5.2, p. 57.

Doctoral research direction

I am beginning doctoral studies in small-body astrometry and photometry, with an emphasis on measurement software that incorporates machine learning and artificial intelligence. My interests include detection and centroid estimation under crowding, robust treatment of moving sources, and reproducible processing of astronomical images.