[Paper Review] Demographics of young stars and their protoplanetary disks: lessons learned on disk evolution and its connection to planet formation

C. F. Manara, M. Ansdell+5 more|arXiv (Cornell University)|Mar 18, 2022

Astrophysics and Star Formation StudiesPhysics and Astronomy68 citations

TL;DR

Reviews the latest survey-era demographics of young stars and their disks, showing how stellar mass and age influence disk mass and size, and how debris disks relate to planet formation.

ABSTRACT

Since Protostars and Planets VI (PPVI), our knowledge of the global properties of protoplanetary and debris disks, as well as of young stars, has dramatically improved. At the time of PPVI, mm-observations and optical to near-infrared spectroscopic surveys were largely limited to the Taurus star-forming region, especially of its most massive disk and stellar population. Now, near-complete surveys of multiple star-forming regions cover both spectroscopy of young stars and mm interferometry of their protoplanetary disks. This provides an unprecedented statistical sample of stellar masses and mass accretion rates, as well as disk masses and radii, for almost 1000 young stellar objects within 300 pc from us, while also sampling different evolutionary stages, ages, and environments. At the same time, surveys of debris disks are revealing the bulk properties of this class of more evolved objects. This chapter reviews the statistics of these measured global star and disk properties and discusses their constraints on theoretical models describing global disk evolution. Our comparisons of observations to theoretical model predictions extends beyond the traditional viscous evolution framework to include analytical descriptions of magnetic wind effects. Finally, we discuss how recent observational results can provide a framework for models of planet population synthesis and planet formation.

Motivation & Objective

• Summarize how surveys of young stellar objects and disks have advanced since PPVI.
• Quantify global stellar and disk properties (mass, accretion rate, disk mass, disk size) across different regions and ages.
• Evaluate disk evolution models (viscous vs disk winds) against observational constraints.
• Discuss implications for planet population synthesis and formation timelines.

Proposed method

• Synthesize results from optical spectroscopy and mm interferometry surveys across multiple star-forming regions.
• Compare observed stellar masses, ages, and accretion rates with evolutionary models and dynamical mass estimates.
• Analyze disk dust masses and sizes derived from ALMA continuum observations, noting caveats (gas masses, dust opacity, gas-to-dust ratio).
• Contrast debris disk demographics and transitional indicators with protoplanetary disk evolution.
• Incorporate findings on disk radii from CO and dust tracers and discuss implications for radial drift and disk structure.

Experimental results

Research questions

• RQ1 What do global properties of young stars and disks tell us about disk evolution mechanisms and timescales?
• RQ2 How do disk masses and sizes scale with stellar mass and age across regions?
• RQ3 What is the relationship between protoplanetary disk dissipation and the emergence of debris disks?
• RQ4 How do observations constrain viscous versus disk-wind driven evolution models and their role in planet formation?
• RQ5 What implications do disk demographics have for planet population synthesis and formation efficiency?

Key findings

• Higher mass stars tend to host more massive dust disks.
• Disk dust masses decline rapidly with age on timescales of a few Myr.
• CO lines often appear CO-depleted, making them unreliable as total gas mass tracers; continuum remains the primary mass proxy.
• Disk radii measured in gas (CO) are generally larger than dust radii, suggesting radial drift of mm-sized grains.
• Evidence supports rapid transitions from protoplanetary to debris disks, with infrared excess gaps around ~8x10^-3 as a delineation benchmark.
• Debris disk structure reveals belts and gaps, with vertical structure indicating multiple dynamical populations; multiplicity affects debris disk fractions.