Next Gen VLA Observations of Protoplanetary Disks A. Meredith Hughes Wesleyan University ALMA (NRAO/ESO/NAOJ); C. Brogan, B. Saxton (NRAO/AUI/NSF)

What can a Next-Gen VLA give us? 3. Access to terrestrial planet- forming regions 1. Pebbles and rocks throughout the disk 2. Low optical depth across disk radii

Why Pebbles and Rocks? 1cm – 1m is VERY interesting grain size for theory of planet formation. Radial Drift Meter size barrier Time evolution: -Planet formation is quick after meter-size barrier crossed, but when/how does this happen? Brauer et al. (2007) C. Dullemond Modified from Fu et al. (2014)

Seeing Pebbles and Rocks Log [Emission Efficiency (Q)] Log λ 1 Turnover at 2πa a At a given wavelength, large grains (a>λ) are the most efficient emitters Log [Grain Size (a)] Log [Number of Grains (N)] dN/da ∞ a -3.5 Many more small grains than large. Small grains dominate surf area Net effect: Smallest grain that can emit efficiently will dominate flux at a given wavelength. Grain size ≈ Wavelength of observation Need long wavelengths to see pebbles

Seeing Pebbles and Rocks One more piece of the puzzle: κ ν ∞ λ -1 (opacity) (Surface density) Millimeter flux (optically thin): F ν ∞ Σ * κ ν * B ν (T) ∞ λ -3 (Planck function ∞ λ -2 ) The bottom line: Flux drops off like crazy with wavelength. Need LOTS of sensitivity to image pebbles.

Low Optical Depth Optical Depth: τ = Σ κ ν Longer wavelengths have lower optical depth, but only until surface density gets high. Andrews et al. (2009) Surface density profile in outer disk similar to MMSN: Σ ∞ R -1 At λ = 1mm, τ = 1 at 10 AU Radius at which τ=1 is inversely proportional to wavelength of observation!

Why Low Optical Depth? τ = 1 at λ = 1mm (ALMA) τ = 1 at λ = 3cm (NGVLA) We can only trace underlying mass distribution of solids where τ < 1 Want to know when, where, how much mass in pebbles exists

Terrestrial Planet-Forming Regions ALMA (ESO/NAOJ/NRAO), T. Sawada ALMA Band 9, 15km baselines -> 6mas resolution 0.9 AU at distance of Taurus, 2.5 AU in Orion But disk is optically thick at this radius/wavelength! NGVLA will allow us to see inside terrestrial planet-forming regions Time domain: changes on ~1 year! Don’t need to improve over ALMA resolution; need to make sensitivity/resolution of VLA comparable

Chemistry Lots of exciting chemistry: volatiles in planet-forming regions, complex organics, etc. Most exciting to me: Ammonia! Nitrogen chemistry & TEMPERATURE One example: turbulence in protoplanetary disks Degeneracy between temperature and turbulence Simon, Hughes et al. (submitted)

Low optical depth, which is necessary to trace dust mass distribution within 10 AU NGVLA will provide: Views of pebbles and rocks in protoplanetary disks Radial drift, meter-size barrier Access to terrestrial planet-forming regions: mass distribution, changes on ~1yr timescales Chemistry, particularly ammonia for accurate temperature determination