Disentangling protoplanetary disk gas mass and carbon depletion through combined atomic and molecular tracers

Abstract

The total disk gas mass and elemental C, N, O composition of protoplanetary disks are crucial ingredients for our understanding of planet formation. Measuring the gas mass is complicated, since H${}_2$ cannot be detected in the cold bulk of the disk and the elemental abundances with respect to hydrogen are degenerate with gas mass in all disk models. We present new NOEMA observations of CO, ${}^{13}$CO, C${}^{18}$O and optically thin C${}^{17}$O $J$=2-1 lines, and use additional high angular resolution Atacama Large Millimeter Array millimeter continuum and CO data to construct a representative model of LkCa 15. The transitions that constrain the gas mass and carbon abundance most are C${}^{17}$O 2-1, N${}_2$H${}^{+}$ 3-2 and HD 1-0. Using these three molecules we find that the gas mass in the LkCa 15 disk is $M_{\mathrm{g}}=0.01_{-0.004}^{+0.01}{M}_{\odot }$, a factor of six lower than estimated before. The carbon abundance is C/H = ($3\pm 1.5)\times 10^{-5}$, implying a moderate depletion of elemental carbon by a factor of 3-9. All other analyzed transitions also agree with these numbers, within a modeling uncertainty of a factor of two. Using the resolved \ce{C2H} image we find a C/O ratio of $\sim$1, which is consistent with literature values of H${}_2$O depletion in this disk. The lack of severe carbon depletion in the LkCa 15 disk is consistent with the young age of the disk, but contrasts with the higher depletions seen in older cold transition disks. Combining optically thin CO isotopologue lines with N${}_2$H${}^{+}$ is promising to break the degeneracy between gas mass and CO abundance. The moderate level of depletion for this source with a cold, but young disk, suggests that long carbon transformation timescales contribute to the evolutionary trend seen in the level of carbon depletion among disk populations, rather than evolving temperature effects and presence of dust traps alone.

arXiv comment16 pages, 8 figures. Accepted for publication in A&A

References in corpus (87)

• The Gaia mission
• Dust Grain Size Distributions and Extinction in the Milky Way, LMC, and SMC
• The effects of snowlines on C/O in planetary atmospheres
• The Cologne Database for Molecular Spectroscopy, CDMS, in the Virtual Atomic and Molecular Data Centre, VAMDC
• The Mass Dependence Between Protoplanetary Disks and their Stellar Hosts
• Resolved Images of Large Cavities in Protoplanetary Transition Disks
• ALMA Survey of Lupus Protoplanetary Disks I: Dust and Gas Masses
• Ring shaped dust accumulation in transition disks
• Effects of Dust Growth and Settling in T Tauri Disks
• An Old Disk That Can Still Form a Planetary System
• Extrasolar planet population synthesis IV. Correlations with disk metallicity, mass and lifetime
• ALMA Survey of Lupus Protoplanetary Disks II: Gas Disk Radii
• The Definitive Abundance of Interstellar Oxygen
• Exoplanetary Atmospheres: Key Insights, Challenges and Prospects
• LkCa 15: A Young Exoplanet Caught at Formation?
• Detection of the Water Reservoir in a Forming Planetary System
• Dust Evolution and the Formation of Planetesimals
• Accreting Protoplanets in the LkCa 15 Transition Disk
• A Parametric Modeling Approach to Measuring the Gas Masses of Circumstellar Disks
• Unveiling the Structure of Pre-Transitional Disks
• The warm gas atmosphere of the HD 100546 disk seen by Herschel (Evidence of a gas-rich, carbon-poor atmosphere?)
• Chemical enrichment of giant planets and discs due to pebble drift
• Survival of molecular gas in cavities of transition disks (I. CO)
• Desorption rates and sticking coefficients for CO and N2 interstellar ices
• Tracing the Ingredients for a Habitable Earth from Interstellar Space through Planet Formation
• Volatile carbon locking and release in protoplanetary disks. A study of TW Hya and HD 100546
• Protoplanetary disk masses from CO isotopologues line emission
• Lupus disks with faint CO isotopologues: low gas/dust or large carbon depletion?
• A Significantly Low CO Abundance Toward the TW Hya Protoplanetary Disk: A Path to Active Carbon Chemistry?
• Hydrocarbon emission rings in protoplanetary disks induced by dust evolution
• Mass measurements in protoplanetary disks from hydrogen deuteride
• Setting the volatile composition of (exo)planet-building material. Does chemical evolution in disk midplanes matter?
• The Effect of the Radial Pressure Gradient in Protoplanetary Disks on Planetesimal Formation
• Gas density drops inside dust cavities of transitional disks around young stars observed with ALMA
• Water in star-forming regions (WISH): Physics and chemistry from clouds to disks as probed by Herschel spectroscopy
• Submillimeter lines from circumstellar disks around pre-main sequence stars
• Resolving the inner dust disks surrounding LkCa 15 and MWC 480 at mm wavelengths
• Disk Imaging Survey of Chemistry with SMA: II. Southern Sky Protoplanetary Disk Data and Full Sample Statistics
• Disk Imaging Survey of Chemistry with SMA (DISCS): I. Taurus Protoplanetary Disk Data
• Scaling Relations Associated with Millimeter Continuum Sizes in Protoplanetary Disks
• Determining protoplanetary disk gas masses from CO isotopologues line observations
• CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing
• Transport of CO in Protoplanetary Disks: Consequences of Pebble Formation, Settling, and Radial Drift
• An ALMA Survey of CO isotopologue emission from Protoplanetary Disks in Chamaeleon I
• CO destruction in protoplanetary disk midplanes: inside versus outside the CO snow surface
• Unlocking CO Depletion in Protoplanetary Disks I. The Warm Molecular Layer
• Disks around CQ Tau and MWC 758: dense PDR or gas dispersal?
• Detecting Weak Spectral Lines in Interferometric Data through Matched Filtering
• Systematic Variations of CO Gas Abundance with Radius in Gas-rich Protoplanetary Disks
• Robustness of N2H+ as tracer of the CO snowline
• No Clear, Direct Evidence for Multiple Protoplanets Orbiting LkCa 15: LkCa 15 bcd are Likely Inner Disk Signals
• A survey of C2H, HCN, and C18O in protoplanetary disks
• Bright C2H emission in protoplanetary disks in Lupus: high volatile C/O>1 ratios
• Constraining Gas-Phase Carbon, Oxygen, and Nitrogen in the IM Lup Protoplanetary Disk
• Sensitive limits on the abundance of cold water vapor in the DM Tau protoplanetary disk
• Molecules with ALMA at Planet-forming Scales (MAPS). VII. Sub-stellar O/H and C/H and super-stellar C/O in planet feeding gas
• HD far infrared emission as a measure of protoplanetary disk mass
• CN rings in full protoplanetary disks around young stars as probes of disk structure
• Nitrogen isotope fractionation in protoplanetary disks
• Survey of cold water lines in protoplanetary disks: indications of systematic volatile depletion
• Resolving the planet-hosting inner regions of the LkCa 15 disk
• Grain growth signatures in the protoplanetary discs of Chamaeleon and Lupus
• On the nature of the transition disk around LkCa 15
• Rapid Evolution of Volatile CO from the Protostellar Disk Stage to the Protoplanetary Disk Stage
• Probing CO and N${}_2$ Snow Surfaces in Protoplanetary Disks with N${}_2$H${}^{+}$ Emission
• L1521E: the first starless core with no molecular depletion
• Annular substructures in the transition disks around LkCa 15 and J1610
• CO2 infrared emission as a diagnostic of planet-forming regions of disks
• An ALMA Survey of H${}_2$CO in Protoplanetary Disks
• Molecules with ALMA at Planet-forming Scales (MAPS). IX. Distribution and Properties of the Large Organic Molecules HC${}_3$N, CH${}_3$CN, and $c$-C${}_3$H${}_2$
• The First Detection of 13C17O in a Protoplanetary Disk: a Robust Tracer of Disk Gas Mass
• Variable H${}^{13}$CO${}^{+}$ Emission in the IM Lup Disk: X-ray Driven Time-Dependent Chemistry?
• An unbiased ALMA spectral survey of the LkCa 15 and MWC 480 protoplanetary disks
• An evolutionary study of volatile chemistry in protoplanetary disks
• Exoplanet Chemistry
• Mass constraints for 15 protoplanetary disks from HD 1-0
• Excess C/H in Protoplanetary Disk Gas from Icy Pebble Drift across the CO Snowline
• A novel way of measuring the gas disk mass of protoplanetary disks using N2H+ and C18O
• Gas temperature structure across transition disk cavities
• The role of C/O in nitrile astrochemistry in PDRs and planet-forming disks
• Destruction of refractory carbon grains drives the final stage of proto-planetary disk chemistry
• Tracing pebble drift and trapping using radial carbon depletion profiles in protoplanetary disks
• New Constraints on Protoplanetary Disk Gas Masses in Lupus
• If you like C/O variations, you should have put a ring on it
• New constraints on the dust and gas distribution in the LkCa 15 disk from ALMA
• Near-Infrared Imaging Polarimetry of LkCa 15: A Possible Warped Inner Disk
• H${}_2$O distribution in the disc of HD 100546 and HD 163296: the role of dust dynamics and planet--disc interaction

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