Banca de DEFESA: FRANCISCO DE ASSIS CHAVES DE BRITO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : FRANCISCO DE ASSIS CHAVES DE BRITO
DATE: 21/12/2021
TIME: 15:00
LOCAL: Plataforma Google Meet
TITLE:

Infrared Excess and Debris Discs in M67 Cluster Stars

KEY WORDS:

Excess infrared radiation, Debris Disk, M67 Cluster.

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

The search for circumstellar material orbiting different star families is one of the most studied topics in Stellar
Astronomy, mainly because the presence of this material indicates the existence of exoplanets. In addition, their physical
properties can tell us how much a planetary system may resemble the Solar System, indicating how this system may evolve.
Current studies show the presence of circumstellar material with temperatures close to those found in the asteroid belt of the
Solar System, but with widely varying dimensions and compositions. Although most studies of circumstellar dust and disks
reveal that this material tends to disappear for stellar ages exceeding 300-400 million years, there are research showing that
debris disks can be found orbiting stars with ages on the order of the solar age, i.e., 4 to 5 billion years. The main objective of
this doctoral thesis is to search for debris disks that orbit stars of the Open Cluster M67, which is close to the age of the Sun.
From this point of view M67 Cluster may contain stars at different evolutionary stages and may offer unique conditions to
search for debris disks. It should be noted that this aspect will offer conditions to better understand how circumstellar debris
disks evolve with age. This study adopted the strategy of searching for infrared excess in M67 stars, using observations
collected by the WISE Mission, which provides fluxes at wavelengths corresponding to the bands 3.3 - 4.7 - 12 and 22 μm. O diagnóstico para identificação do excesso consistiu na comparação entre distribuições espectrais de energia, m.
The diagnostics to identify the excess in M67 stars compared the spectral distributions of energy, built from theoretical models, and observational fluxes obtained at different wavelengths, extending from about 0.5 to 22 μm. O diagnóstico para identificação do excesso consistiu na comparação entre distribuições espectrais de energia, m, covering observations made by
the Gaia Mission, 2MASS Project and WISE Mission. From an initial sample of 1520 stars, members of M67, 1380 stars were
identified, presenting observations at WISE wavelengths 3.3 - 4.7 - 12 and 22 μm. O diagnóstico para identificação do excesso consistiu na comparação entre distribuições espectrais de energia, m, defined as bands W1, W2, W3 and W4
respectively. These stars with WISE measurements also showed observations in the G, G RP and G BP bands of Gaia, as well
as in the J, H and K bands of 2MASS. From the sample of 1380 stars, three objects designated J085103.24+114547.3,
J085202.94+105932.7 and J085116.70+114529.6 show excesses with physical meaning (SNR > 3), absence of contamination
by other sources or artifacts and circular images. These results point to a fraction of 0.2% of M67 stars with an excess at 22
μm. O diagnóstico para identificação do excesso consistiu na comparação entre distribuições espectrais de energia, m, a value far below that cited in the literature for stars on the order of or with greater ages than the solar age, which is about
4%. Considering that this excess is associated with the presence of circumstellar material, defined as debris disk, we used
standard models to estimate the physical parameters associated with the disks: luminosity fraction, radius, mass and
temperature. Although the temperatures of the material, between 225 and 300 K, are on the order of the temperatures known
for the solar Zodiacal Cloud, the values obtained for the luminosity fraction and the mass, respectively 10 4 and 10 5 times
higher than the Zodiacal Cloud values, show that the material around the stars J085103.24+114547.3, J085202.94+105932.7
and J085116.70+114529.6 is brighter and denser than what is expected at the age of M67. Such material must also be
composed of second-generation dust and debris and no longer be composed of material from the planetary formation phase.
This unusual characteristic, that is, brighter and denser material, seems to indicate the presence of one or more replenishment
mechanisms in these regions, through violent collisions between asteroids, planetesimals and planets.

BANKING MEMBERS:
Externo à Instituição - HELIO JAQUES ROCHA PINTO - UFRJ
Interno - 1675216 - BRUNO LEONARDO CANTO MARTINS
Externa à Instituição - HELOISA MARIA BOECHAT-ROBERTY - UFRJ
Interno - 3060853 - IZAN DE CASTRO LEÃO
Presidente - 346785 - JOSE RENAN DE MEDEIROS