Banca de QUALIFICAÇÃO: DASAEV OLIVEIRA FONTINELE

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : DASAEV OLIVEIRA FONTINELE
DATE: 03/09/2025
TIME: 15:30
LOCAL: Plataforma Zoom
TITLE:

ON THE NATURE OF PHOTOMETRIC VARIABILITY IN ULTRA-COLD DWARF STARS

KEY WORDS:

Stellar rotation, Brown dwarfs, Stellar photometry

PAGES: 104
BIG AREA: Ciências Exatas e da Terra
AREA: Física
SUMMARY:

Fully convective M dwarfs exhibit a variety of magnetic phenomena, raising numerous questions about how these
stars generate and sustain large-scale coherent magnetic fields. In this work, we present an initial search for rotation signatures
in 250 ultra-cool dwarfs (UCDs) from the Gaia DR3 catalog, using light curves obtained by TESS. We identified 71 targets
with unambiguous periodicities, of which 61 present rotation signatures and a single source behavior, with periods between
0.133 and 5.81 days. Five UCDs show double-dip features, namely variations with two periods, one approximately double or
half the other. The remaining ten UCDs with unambiguous variability present a likely non-single behavior. We also found 20
UCDs showing complex behavior in their light curves, with noticeable fluctuations and irregular structure, with a few
exhibiting apparent changes in their temporal structure. The remaining 159 targets show noisy light curves corresponding to
low-amplitude signals, whose temporal variation cannot be easily identified. The distribution of the UCDs with rotation
signature in the CMD diagram points to a lack of rotating objects within about 11.5 < 𝑀! < 12.5 and 𝐺 − 𝐺"# < 1.5
separating them into two regimes, one mainly composed of less massive late-M stars with 𝑃$%& ≥ 1.0 d, and another mainly
composed of more massive early-M stars with 𝑃$%& < 1.0 d. bf It is important to emphasize that by separating stars into age
intervals, one observes that UCDs with 𝑃$%& ≥ 1.0 d tend to be located in regions of younger objects, and, in contrast, those
with 𝑃$%& < 1.0 d are mainly concentrated in regions of older objects.

 

COMMITTEE MEMBERS:
Externo ao Programa - 1675216 - BRUNO LEONARDO CANTO MARTINS - nullExterno à Instituição - CARLOS EDUARDO FERREIRA LOPES
Presidente - 346785 - JOSE RENAN DE MEDEIROS