IA/U.Porto Seminar - Star formation across different scales. Bridging the gap through accretion - 20 abril 2018

The accretion rate drives the formation, growth and early evolution of young stars, also bridging the gap between different physical systems across various scales. During the first part of the talk I will focus on intermediate -stellar- scales, describing observational evidence that suggests that the accretion mechanism could change from “magnetospheric accretion” in low-mass T-Tauri and Herbig Ae stars to direct disk-to-star “boundary layer” accretion in Herbig Be and more massive young stellar objects. Smaller -planetary- scales will be the topic of the second part of the talk. Despite of the fact that the number of known exoplanets around stars different than the Sun has increased exponentially during the last decades, the detection of forming -accreting- planets in protoplanetary disks around young stars remains merely anecdotal, with only a few candidates proposed to date. The pre-main sequence stars HD 100546 and LkCa 15 are two of the most representative candidates, given that their circumstellar disks may host (proto-) planetary systems with several planets each. I will summarize some of the main properties of HD 100546 as inferred from spectrometry, spectro-interferometry and high-resolution polarized imaging with X-SHOOTER, AMBER and SPHERE on the VLTs at Cerro Paranal. I will also discuss the potential of spectro-astrometry to detect planets in formation based on recently obtained ISIS/WHT data of LkCa 15. Finally, the third part of the talk will be devoted to link individual young stars with larger scales. We have recently found a statistically significant, roughly linear correlation between the rate of gas transformed into stars and the mass of dense gas directly involved on star formation, ranging 16 orders of magnitude and encompassing au-size circumstellar disks, pc-size protostellar-hosting clouds within our Galaxy, and kpc-size cloud-hosting galaxies. I will describe the “bottom-up” hypothesis we propose to explain this finding, according to which the protostellar accreting population drives the correlation for all scales.