The search and characterization of extrasolar planets is one of the main topics of current astronomy, with the ultimate goals of understanding the formation and evolution of planetary systems, the general conditions for the formation of life-friendly environments, and possibly detecting signature of extra-solar life. In the last decades the research of extrasolar planets underwent a steep increase of interest and different methods of detection were developed. Each of them has its own merit and lack in studying the extrasolar system architecture and the characteristics of extrasolar planets. Stars and their planetary entourage form and grow together, at least in most cases, tied by the circumstellar disk. A unique theory that can describe all the processes that happen between the protostellar cloud collapse and the final system stabilization is not available at the moment. Indirect methods are very useful to study more evolved systems, where the protoplanetary disk contribution is negligible, in their innermost regions. On the other hand, direct imaging with high-contrast instruments offers the possibility to study the early phases of the planet formation, that are not accessible to other indirect methods of planets detection, and plays a key role in current planet formation theories. This thesis focuses on the capabilities of direct imaging with SPHERE, the new high-contrast imager of VLT, in detecting planets at different stages of their evolution, coupled with radial velocities observations of old systems obtained from SARG, the old TNG echelle spectrograph. Chapter 1 briefly introduces the planet formation and evolution theories with the most important exoplanets research methods. Chapter 2 describes the SPHERE instrument used for the majority of the results presented in this thesis. In Chapter 3 I present the case of four young objects. I exploit the SPHERE visible channel to study Z CMa jets, and the near-IR channel for HD 100546 and T Cha, looking for the presence of planets. At the same time, I was able to study in detail the circumplanetary disk of HD 100546 in a quite wide spectral range: in the dedicated Section I show that the system brightest structures suggest the presence of at least three gaps in the inner regions of the disk, coupled with other structures, such as spiral arms. I detected a diffuse source at the location of the claimed planet HD 100546 b, but the nature of this emission is, however, still unknown. Lastly, LkCa15 was studied both in the visible and in the near-IR of SPHERE. In Chapter 4 I present the study of the accretion signature in a few objects. GQ Lup b accretion was observed both in H_alpha and in Paschen beta, exploiting all three SPHERE subsystems. Two systems that have already cleaned out their surroundings from gas and dust are presented in Chapter 5: HIP 80591 and HD 65426. In the latter, I first found out that one companion candidate had high probability to be bound to the star due to its position and it spectral features. These findings were later confirmed by a deeper analysis and follow up observations that demonstrate HD 65426 b, the companion I studied, is a warm Jupiter-like planet with mass between 6 and 12 M_J. In Chapter 6, I study the chromospheric activity in older binary stars in order to detect a radial velocity signal hidden by the Doppler shift induced by the activity. I found out that Ha-excess, an index based on the Halpha line, is a good indicator of the star activity when the log_RHK' index is not available and can be used also to infer stellar ages in case of stars younger then 1.5 Gyr. Moreover, HD 76073 B shows a high radial velocities scatter that can be explained by the presence of a low-mass companion (Sissa et al. 2016). Finally, in Chapter 7 I give the conclusions and explain future prospects. Appendixes are dedicated to the more technical aspects of my work, that were needed to improve instrument capabilities and data reduction, and to better defining the instrument set-ups needed to achieve different scientific aims.

Observation of extrasolar planets at various ages / Sissa, Elena. - (2017 Jun 30).

### Observation of extrasolar planets at various ages

#### Abstract

The search and characterization of extrasolar planets is one of the main topics of current astronomy, with the ultimate goals of understanding the formation and evolution of planetary systems, the general conditions for the formation of life-friendly environments, and possibly detecting signature of extra-solar life. In the last decades the research of extrasolar planets underwent a steep increase of interest and different methods of detection were developed. Each of them has its own merit and lack in studying the extrasolar system architecture and the characteristics of extrasolar planets. Stars and their planetary entourage form and grow together, at least in most cases, tied by the circumstellar disk. A unique theory that can describe all the processes that happen between the protostellar cloud collapse and the final system stabilization is not available at the moment. Indirect methods are very useful to study more evolved systems, where the protoplanetary disk contribution is negligible, in their innermost regions. On the other hand, direct imaging with high-contrast instruments offers the possibility to study the early phases of the planet formation, that are not accessible to other indirect methods of planets detection, and plays a key role in current planet formation theories. This thesis focuses on the capabilities of direct imaging with SPHERE, the new high-contrast imager of VLT, in detecting planets at different stages of their evolution, coupled with radial velocities observations of old systems obtained from SARG, the old TNG echelle spectrograph. Chapter 1 briefly introduces the planet formation and evolution theories with the most important exoplanets research methods. Chapter 2 describes the SPHERE instrument used for the majority of the results presented in this thesis. In Chapter 3 I present the case of four young objects. I exploit the SPHERE visible channel to study Z CMa jets, and the near-IR channel for HD 100546 and T Cha, looking for the presence of planets. At the same time, I was able to study in detail the circumplanetary disk of HD 100546 in a quite wide spectral range: in the dedicated Section I show that the system brightest structures suggest the presence of at least three gaps in the inner regions of the disk, coupled with other structures, such as spiral arms. I detected a diffuse source at the location of the claimed planet HD 100546 b, but the nature of this emission is, however, still unknown. Lastly, LkCa15 was studied both in the visible and in the near-IR of SPHERE. In Chapter 4 I present the study of the accretion signature in a few objects. GQ Lup b accretion was observed both in H_alpha and in Paschen beta, exploiting all three SPHERE subsystems. Two systems that have already cleaned out their surroundings from gas and dust are presented in Chapter 5: HIP 80591 and HD 65426. In the latter, I first found out that one companion candidate had high probability to be bound to the star due to its position and it spectral features. These findings were later confirmed by a deeper analysis and follow up observations that demonstrate HD 65426 b, the companion I studied, is a warm Jupiter-like planet with mass between 6 and 12 M_J. In Chapter 6, I study the chromospheric activity in older binary stars in order to detect a radial velocity signal hidden by the Doppler shift induced by the activity. I found out that Ha-excess, an index based on the Halpha line, is a good indicator of the star activity when the log_RHK' index is not available and can be used also to infer stellar ages in case of stars younger then 1.5 Gyr. Moreover, HD 76073 B shows a high radial velocities scatter that can be explained by the presence of a low-mass companion (Sissa et al. 2016). Finally, in Chapter 7 I give the conclusions and explain future prospects. Appendixes are dedicated to the more technical aspects of my work, that were needed to improve instrument capabilities and data reduction, and to better defining the instrument set-ups needed to achieve different scientific aims.
##### Scheda breve Scheda completa Scheda completa (DC)
protoplanetary disks, planetary systems, methods: data analysis, stars: individual: T Cha, stars: individual: HD100546, stars: individual: Lk Ca 15, stars: individual: GQ Lup,stars: individual: HIP80591, stars: individual: HIP65426, techniques: high angular resolution, techniques: image processing, techniques: spectroscopic, binaries: visual, stars: activity, techniques: radial velocities
Observation of extrasolar planets at various ages / Sissa, Elena. - (2017 Jun 30).
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11577/3426311