ALMA continuum observations of a 30 Myr old gaseous debris disk around HD 21997

Abstract

Circumstellar disks around stars older than 10 Myr are expected to be gas-poor. There are, however, two examples of old (30-40 Myr) debris-like disks containing a detectable amount of cold CO gas. Here we present ALMA and Herschel Space Observatory observations of one of these disks, around HD 21997, and study the distribution and origin of the dust and its connection to the gas. Our ALMA continuum images at 886um clearly resolve a broad ring of emission within a diameter of ~4.5 arcsec, adding HD 21997 to the dozen debris disks resolved at (sub)millimeter wavelengths. Modeling the morphology of the ALMA image with a radiative transfer code suggests inner and outer radii of ~55 and ~150 AU, and a dust mass of 0.09 M_Earth. Our data and modeling hints at an extended cold outskirt of the ring. Comparison with the morphology of the CO gas in the disk reveals an inner dust-free hole where gas nevertheless can be detected. Based on dust grain lifetimes, we propose that the dust content of this gaseous disk is of secondary origin produced by planetesimals. Since the gas component is probably primordial, HD 21997 is one of the first known examples of a hybrid circumstellar disk, a so-far little studied late phase of circumstellar disk evolution.

Accepted for publication in ApJ Letters, 6 pages, 3 figures, 1 tables (emulateapj style)

References in corpus (8)

• Variations on Debris Disks: Icy Planet Formation at 30-150 AU for 1-3 Solar Mass Main Sequence Stars
• Nearby debris disk systems with high fractional luminosity reconsidered
• ALMA observations of the molecular gas in the debris disk of the 30 Myr old star HD 21997
• Flux calibration of the Herschel-SPIRE photometer
• Survival of icy grains in debris discs. The role of photosputtering
• A Resolved Molecular Gas Disk around the Nearby A Star 49 Ceti
• The Dust Properties of Eight Debris Disk Candidates as Determined by Submillimeter Photometry
• Herschel Observations of Gas and Dust in the Unusual 49 Ceti Debris Disk

Cited by in corpus (37)

• Probing for Exoplanets Hiding in Dusty Debris Disks: Disk Imaging, Characterization, and Exploration with HST/STIS Multi-Roll Coronagraphy
• SONS: The JCMT legacy survey of debris discs in the submillimetre
• Debris Disks in the Scorpius-Centaurus OB Association Resolved by ALMA
• Dynamical evolution of an eccentric planet and a less massive debris disc
• A Comprehensive Census of Nearby Infrared Excess Stars
• An Empirical Planetesimal Belt Radius - Stellar Luminosity Relation
• Stirring in massive, young debris discs from spatially resolved Herschel images
• Radial Surface Density Profiles of Gas and Dust in the Debris Disk around 49 Ceti
• ALMA observations of the debris disk around the young Solar Analog HD 107146
• The SEEDS High Contrast Imaging Survey of Exoplanets around Young Stellar Objects
• Planet populations inferred from debris discs: insights from 178 debris systems in the ISPY, LEECH and LIStEN planet-hunting surveys
• Gas and dust around A-type stars at tens of Myr:signatures of cometary breakup
• Imaging [CI] around HD 131835: reinterpreting young debris discs with protoplanetary disc levels of CO gas as shielded secondary discs
• The hybrid disks: a search and study to better understand evolution of disks
• Resolved Millimeter-Wavelength Observations of Debris Disks around Solar-Type Stars
• Discovery of an Inner Disk Component around HD 141569 A
• ISPY -- NACO Imaging Survey for Planets around Young stars: Survey description and results from the first 2.5 years of observations
• Detection of submillimeter-wave [C I] emission in gaseous debris disks of 49 Ceti and Beta Pictoris
• The co-existence of hot and cold gas in debris discs
• Photoevaporation of Grain-Depleted Protoplanetary Disks around Intermediate-Mass Stars: Investigating Possibility of Gas-Rich Debris Disks as Protoplanetary Remnants
• Lack of other molecules in CO-rich debris discs: is it primordial or secondary gas?
• Effects of inclined star-disk encounter on protoplanetary disk size
• Primordial or Secondary? Testing models of debris disk gas with ALMA
• Unlocking the secrets of the midplane gas and dust distribution in the young hybrid disc HD 141569
• MAMBO image of the debris disk around epsilon Eridani : robustness of the azimuthal structure
• Deep ALMA Search for CO Gas in the HD 95086 Debris Disc
• First sub-arcsecond submillimeter-wave [C I] image of 49 Ceti with ALMA
• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) I: Motivation, sample, data reduction, and results overview
• Insights into planet formation from debris disks: I. The solar system as an archetype for planetesimal evolution
• Mass accretion rates from multi-band photometry in the Carina Nebula: the case of Trumpler 14
• Physical conditions of gas components in debris disks of 49 Ceti and HD 21997
• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS) IV: CO gas imaging and overview
• Stellar winds can affect gas dynamics in debris disks and create observable belt winds
• An Incipient Debris Disk in the Chamaeleon I Cloud
• Abundance analysis of stars hosting gas-rich debris disks
• Debris Disks in Nearby Young Moving Groups in the ALMA Era
• HD 44892: The youngest (or oldest?) gas-harbouring debris disc around an intermediate mass star