Star and Planet Formation

Dear Colleagues,

There has been rapid growth in research on star and planet formation and evolution in recent years. In particular, thanks to the increasing quality of disk observations around Young Stellar Objects (YSOs), provided by new facilities at high spatial resolution from the optical to the radio domain, there has been increasing recognition of the importance of disk evolution in setting the initial conditions for the formation of planetary systems. As recently demonstrated, planet formation occurs in the early phases of disk evolution. In fact, it has been demonstrated that disks quickly lose their homogeneous structure, already developing gaps, rings, and spirals during the pre-main-sequence phase.

In this Special Issue, we focus on the formation and evolution of disks in YSOs, together with related phenomena (accretion, jets, and winds) and their relationships with the properties of the central star. On the one hand, mass accretion is one of the main drivers for the evolution of disks. Studies of the evolution of disk mass accretion, from the early protostellar phase to protoplanetary disk dispersal, mainly involve multi-wavelength observations obtained through spectroscopic and photometric surveys using different facilities (e.g., VLT/X-shooter, FLAMES, ESPRESSO, KMOS, TNG/GIARPS, HST, and VST/OmegaCam). These surveys enable the investigation of YSOs (<= 10-30 Myr) from solar-mass stars to very low-mass stars down to the brown dwarf limit, which actively accrete mass from planet-forming disks. On the other hand, the ejection of matter through collimated and high-velocity jets and from slow and compact winds during protostellar evolution is an important ingredient in removing angular momentum from the star–disk system; it allows the material to accrete on the star, to shape the disk surface density, and to define the environment for planet formation. This kind of research is mainly conducted through optical/IR high-contrast imaging (e.g., SPHERE and HST) and high-resolution spectroscopy, but also via ALMA and JWST observations, which allow us to study jet acceleration and the collimation region during the first phases of stellar evolution.

In this volume, we aim to highlight the key roles of recent (e.g., TNG/GIARPS) and new (e.g., JWST) facilities in enriching our knowledge on the accretion and ejection properties of stars in young clusters in different environments and with different metallicity (particularly those within our Galaxy and the Magellanic Clouds); moreover, we aim to discuss the opportunities and challenges of the next generation of multi- (e.g., VLT/MOONS, VISTA/4MOST, WHT/WEAVE, and MSE) and single- (e.g., NTT/SOXS and VLT/CUBES) object spectrographs, but also through photometric surveys (such as those within the Rubin-LSST facility). In addition, we welcome papers on high-angular-resolution investigation of YSOs based on active instruments such as VLT/SPHERE and MUSE. Soon, this research  will also benefit from the availability of new-generation high-angular-resolution instruments such as the very recent VLT/ERIS and the upcoming LBT/SHARK-VIS/NIR. Our final aim is to understand the mechanisms at the origin of the disk structures and if/how they are connected to the presence and/or formation of protoplanets.

We invite colleagues to submit articles on the broad subject of "Star and Planet Formation". We welcome reviews and new results in this field covering the current state-of-the-art, but also addressing ongoing observations and future developments. The main subjects are:

• Accretion and disk–star interactions in different environmental conditions;
• The ejection of matter through jets and winds;
• Disk dispersal and planet Formation;
• Properties of Young Stellar Objects.

Dr. Katia Biazzo
Dr. Simone Antoniucci
Guest Editors

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• accretion
• jets
• winds
• star and planet formation
• young stellar objects