The dispersal of circumstellar disks is crucial to set the time available for the formation of planetary systems around young stars. Observations of young clusters with solar metallicity show that optically-thick circumstellar disks disappear in ~1-3 Myr around approximately half of young low-mass stars and are almost absent around members of ~8-10 Myr old associations, which approximately corresponds to the shutdown of mass accretion. This general trend might in fact be an exception, not the norm: feedback mechanisms, like photoevaporation, and other environmental properties, such as metallicity and density, might strongly affect the timescale over which the accretion tapers off and protoplanetary disks are dispersed. With the majority of stars in the Universe having formed at Cosmic Noon, with similar characteristics (e.g., stellar density, metallicity) as those of distant clusters of our Galaxy and Magellanic Clouds, it is clear how it is important to investigate the star formation process in different environmental conditions.

Indeed, metallicity appears to have an effect on the lifetime of circumstellar disks, but it is not clear whether we understand the implications. Infrared studies of young metal-poor stars (Z~0.2 Zsun) in star forming regions (SFRs) of the outer Galaxy indicate that their disks dissolve significantly faster than nearby solar metallicity young stars. At the same time, analysis of HST photometry and very recent JWST spectra of pre-main sequence stars in young dense clusters of the Magellanic Clouds (Z down to ~0.1 Zsun), demonstrate that mass accretion rates decrease more slowly with time than what is observed in solar-metallicity SFRs. These two findings are in apparent contradiction, because the former would imply shorter timescales for the disk dispersal, while the latter would result in longer timescales for the decrease of mass accretion rate (and in principle longer disk timescale). Recently, the possibility has been explored that low metallicity might increase the effectiveness of photoevaporation in removing gas and small dust grains from circumstellar disks and therefore impacting on disk erosion. On the other hand, recent observations hint at the effect of stellar density in low metallicity regions as an additional mechanism that regulates the intensity of the accretion process. A clear picture is therefore still missing.

In this Special Section, scientific communities working on the effects of the environment on accretion and disk properties both from observations and theoretical modeling will join with the final aim to understand the very nature of mass accretion process and disk survival. The discussion will focus on distant clusters of our Galaxy and of the Local Group and regions with characteristics akin to those in place at Cosmic Noon, and will try to answer the following main questions:

- How do environmental conditions like metallicity, density, and intense UV local fields affect accretion properties, disk lifetime, initial mass function, and possible planetary formation?

- Are star forming regions in the outer Galaxy a sort of bridge between nearby young clusters and very distant clusters in the Magellanic Clouds?

- Are current JWST instruments, and next-coming facilities (e.g., MOONS@VLT, MAVIS@VLT, CUBES@VLT) going to revolutionize our understanding of the star formation processes, especially in distant star forming regions?

Programme

• Observations of accretion and disk properties across different star-forming environments
• Environment effects on star (and planet) formation
• Disk dispersal in different environmental conditions: theory confronts observations

Invited speakers

• Agata Karska (Nicolaus Copernicus University, Poland; MPI for Radio Astronomy, Germany)
• Barbara Ercolano (University Observatory Muenchen, Germany)
• Chikako Yasui (National Astronomical Observatory of Japan)
• Elena Sabbi (Gemini Observatory, USA)
• Germano Sacco (INAF - Arcetri Astrophysical Observatory, Italy)
• Thomas Haworth (Queen Mary University of London, UK)
• Venu Kalari (Gemini Observatory/NSF's NOIRLab, Chile)

Scientific organisers

• Katia Biazzo (INAF - Astronomical Observatory of Rome, Italy; chair)
• Cathie Clarke (University of Cambridge, UK; co-chair)
• Guido De Marchi (European Space Agency, The Netherlands; co-chair)
• Mario Giuseppe Guarcello (INAF - Astronomical Observatory of Palermo, Italy; co-chair)
• Megan Reiter (Rice University, USA; co-chair)

Contact

• Katia Biazzo (katia.biazzo @ inaf.it)
• Guido De Marchi (Guido.De.Marchi @ esa.int)