Can gas in young debris disks be constrained by their radial brightness profiles?

Abstract

Disks around young stars are known to evolve from optically thick, gas-dominated protoplanetary disks to optically thin, almost gas-free debris disks. It is thought that the primordial gas is largely removed at ages of ~10 Myr, but it is difficult to discern the true gas densities from gas observations. This suggests using observations of dust: it has been argued that gas, if present with higher densities, would lead to flatter radial profiles of the dust density and surface brightness than those actually observed. However, here we show that these profiles are surprisingly insensitive to variation of the parameters of a central star, location of the dust-producing planetesimal belt, dustiness of the disk and - most importantly - the parameters of the ambient gas. This result holds for a wide range of gas densities (three orders of magnitude), for different radial distributions of the gas temperature, and different gas compositions. The brightness profile slopes of -3...-4 we find are the same that were theoretically found for gas-free debris disks, and they are the same as actually retrieved from observations of many debris disks. Our specific results for three young (10-30 Myr old), spatially resolved, edge-on debris disks (beta Pic, HD 32297, and AU Mic) show that the observed radial profiles of the surface brightness do not pose any stringent constraints on the gas component of the disk. We cannot exclude that outer parts of the systems may have retained substantial amounts of primordial gas which is not evident in the gas observations (e.g. as much as 50 Earth masses for beta Pic). However, the possibility that gas, most likely secondary, is only present in little to moderate amounts, as deduced from gas detections (e.g. ~0.05 Earth masses in the beta Pic disk), remains open, too.

Accepted for publication in Astronomy and Astrophysics

References in corpus (19)

• Dust dynamics during protoplanetary disc clearing
• Demographics of Transition Objects
• HST/ACS Multiband Coronagraphic Imaging of the Debris Disk around Beta Pictoris
• Collisional processes and size distribution in spatially extended debris discs
• The Carbon-Rich Gas in the Beta Pictoris Circumstellar Disk
• Outer edges of debris discs: how sharp is sharp?
• A Resolved Molecular Gas Disk around the Nearby A Star 49 Ceti
• The AU Microscopii Debris Disk: Multiwavelength Imaging and Modeling
• Disk Dispersal and Planet Formation Time Scales
• Collisional and Thermal Emission Models of Debris Disks: Towards Planetesimal Population Properties
• The Masses of Transition Circumstellar Disks: Observational Support for Photoevaporation Models
• The Dust and Gas Around beta Pictoris
• From discs to planetesimals I: evolution of gas and dust discs
• Formation of Narrow Dust Rings in Circumstellar Debris Disks
• CARMA Millimeter-Wave Aperture Synthesis Imaging of the HD 32297 Debris Disk
• 12 and 18 micron images of dust surrounding HD 32297
• A Low-Mass H2 Component to the AU Microscopii Circumstellar Disk
• A Ring of Warm Dust in the HD 32297 Debris Disk
• Effects of photophoresis on the evolution of transitional circumstellar disks

Cited by in corpus (21)

• Debris Disks: Seeing Dust, Thinking of Planetesimals and Planets
• ALMA observations of the molecular gas in the debris disk of the 30 Myr old star HD 21997
• Molecular gas in young debris disks
• Stirring in massive, young debris discs from spatially resolved Herschel images
• Modeling the HD32297 Debris Disk with Far-IR Herschel Data
• A resolved debris disk around the candidate planet-hosting star HD95086
• ALMA continuum observations of a 30 Myr old gaseous debris disk around HD 21997
• The vertical structure of debris disks and the impact of gas
• Resolved Imaging of the HD191089 Debris Disc
• Debris discs in binaries: a numerical study
• Primordial or Secondary? Testing models of debris disk gas with ALMA
• The interplay between radiation pressure and the photoelectric instability in optically thin disks of gas and dust
• Vertical evolution of exocometary gas: I. How vertical diffusion shortens the CO lifetime
• VLT imaging of the β Pictoris gas disk
• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) I: Motivation, sample, data reduction, and results overview
• Morphology of the gas-rich debris disk around HD 121617 with SPHERE observations in polarized light
• A multi-wavelength study of the debris disc around 49 Cet
• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) V: Comparison between scattered light and thermal emission
• Submillimetre observations of RX J1856.5--3754
• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS). X. Interpreting the peculiar dust rings around HD 131835
• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) XI: Gas-dust interactions and radial offsets between micron and millimetre-sized grains