Alguns projetos científicos


TESS lightcurves as a new chronometer through solar twins

Geisa Ponte, Diego Lorenzo-Oliveira, Adriana Valio, and Jorge Melendez

We investigate the impact of chromospheric activity on NASA/TESS lightcurves of solar twins with well-determined ages. We show that the TESS photometric amplitudes are strongly correlated with the mean chromospheric activity level of our sample stars, and also with rotational periods and stellar ages, being, thus, an important diagnostic of stellar ages.

  • Paper in preparation


Searching for solar twin candidates in distant open clusters with Gemini/GMOS

Geisa Ponte & Diego Lorenzo-Oliveira

In this work, we performed a search for the stars of NGC188 and M67 more similar to the Sun, from low-resolution spectroscopic observations (R=2500, λλ3850-5000) using the GMOS/Gemini multi-object spectrograph. We initially identified 21 candidates for solar twins in NGC 188 and 3 in M67. This new list of candidates will optimize the high-resolution spectroscopic search for solar twins in these clusters. Besides, this sample has the potential to provide essential links for building stellar chronometers based on chromospheric activity and for chemicals such as Li, [Y/Mg] and [Y/Al].

  • Paper in preparation

Mapping biases in the empirical spectroscopic analysis of solar twin stars

Geisa Ponte & Gustavo Porto de Mello

This study aims to compare characterizations of entwinement between solar twin candidate stars and the Sun, in addition to the well-known 18 Sco. Besides, we aim to map possible biases in the empirical analyses of this class of stars. We report the results of comparing manual and automatic measurements, as well as comparing different spectrographs, different resolutions, and using Ganymede and Vesta as solar proxies.

  • Paper in preparation

Photometric variability in TESS lightcurves of FGK stars due to magnetic activity: an analysis through machine learning

Geisa Ponte & Roberta Duarte

We investigated the impact of flux modulation on the lightcurves from TESS/NASA mission to find magnetic activity indices linked to stellar age by gyrochronology. To train our machine learning algorithm, we used a well-known sample of 448 FGK stars with a known level of magnetic activity. These stars were monitored over at least one rotation period. The ultimate goal is to be able to classify as many stars as possible in bins of ages, and chromospheric activity, taking into account only their apparent photometric behavior.

  • Paper in preparation


The ancient main-sequence solar proxy HIP 102152 unveils the activity and rotational fate of our Sun

Diego Lorenzo-Oliveira, Jorge Meléndez, Geisa Ponte, Jhon Yana Galarza

MNRAS 495.1 (Jun. 2020), pp.L61–L65

The effect of stellar activity on the spectroscopic stellar parameters of the young solar twin HIP 36515

Jhon Yana Galarza, Jorge Meléndez, Diego Lorenzo-Oliveira, Adriana Valio, Henrique Reggiani, Marilia Carlos, Geisa Ponte, Lorenzo Spina, Raphaëlle D. Haywood, Davide Gandolfi

MNRAS 490.1 (Nov. 2019), pp.L86–L90


Constraining the evolution of stellar rotation using solar twins

Diego Lorenzo-Oliveira, Jorge Meléndez, Jhon Yana Galarza, Geisa Ponte, Leonardo A. dos Santos, Lorenzo Spina, Megan Bedell, Iván Ramírez, Jacob L. Bean, Martin Asplund

MNRAS Letters 485 (May 2019), pp. L68–L72.