Upper limits on CH${}_3$OH in the HD 163296 protoplanetary disk: evidence for a low gas-phase CH${}_3$OH/H${}_2$CO ratio

Abstract

Methanol (CH${}_3$OH) is at the root of organic ice chemistry in protoplanetary disks. However, its weak emission has made detections difficult. To date, gas-phase CH${}_3$OH has been detected in only one Class II disk, TW Hya. We use the Atacama Large Millimeter/submillimeter Array (ALMA) to search for a total of four CH${}_3$OH emission lines in bands 6 and 7 toward the disk around the young Herbig Ae star HD 163296. The disk-averaged column density of methanol and its related species formaldehyde (H${}_2$CO) are estimated assuming optically thin emission in local thermodynamic equilibrium. We compare these results to the gas-phase column densities of the TW Hya disk. No targeted methanol lines were detected individually nor after line stacking. The 3$\sigma$ disk-integrated intensity upper limits are $<51$ mJy km s${}^{-1}$ for the band 6 lines and $<26$ mJy km s${}^{-1}$ for the band 7 lines. The band 7 lines provide the strictest 3$\sigma$ upper limit on disk-averaged column density with $N_{\mathrm{avg}}<5.0\times 10^{11}$ cm${}^{-2}$. The methanol-to-formaldehyde ratio is CH${}_3$OH/H${}_2$CO $<0.24$ in the HD 163296 disk compared to a ratio of $1.27$ in the TW Hya disk. Differences in the stellar irradiation of Herbig disks compared to T Tauri disks likely influence the gaseous methanol and formaldehyde content. Possible reasons for the lower HD 163296 methanol-to-formaldehyde ratio include: a higher than expected gas-phase formation of H${}_2$CO in the HD 163296 disk, uncertainties in the grain surface formation efficiency of CH${}_3$OH and H${}_2$CO, and differences in the disk structure and/or CH${}_3$OH and H${}_2$CO desorption processes that release the molecules from ice mantles back into the gas phase. These results provide observational evidence that the gas-phase chemical complexity found in disks may be strongly influenced by the spectral type of the host star.

Accepted to Astronomy & Astrophysics, 11 pages, 3 figures

References in corpus (12)

• Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores
• A Three-Dimensional View of Turbulence: Constraints on Turbulent Motions in the HD 163296 Protoplanetary Disk using DCO${}^{+}$
• Complex organic molecules in protoplanetary disks
• H2O and OH gas in the terrestrial planet-forming zones of protoplanetary disks
• Three radial gaps in the disk of TW Hydrae imaged with SPHERE
• Reprocessing of Ices in Turbulent Protoplanetary Disks: Carbon and Nitrogen Chemistry
• Formation and Atmosphere of Complex Organic Molecules of the HH 212 Protostellar Disk
• Chemistry in Protoplanetary Disks: A Sensitivity Analysis
• Methanol Along the Path from Envelope to Protoplanetary Disc
• DCO${}^{+}$, DCN and N${}_2$D${}^{+}$ reveal three different deuteration regimes in the disk around the Herbig Ae star HD163296
• Increased H${}_2$CO production in the outer disk around HD 163296
• Gas mass tracers in protoplanetary disks: CO is still the best

Cited by in corpus (28)

• Molecules with ALMA at Planet-forming Scales (MAPS) I: Program Overview and Highlights
• Molecules with ALMA at Planet-forming Scales (MAPS) VI: Distribution of the small organics HCN, C2H, and H2CO
• 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${}_2$
• A major asymmetric ice trap in a planet-forming disk: III. First detection of dimethyl ether
• An unbiased ALMA spectral survey of the LkCa 15 and MWC 480 protoplanetary disks
• Sulphur monoxide emission tracing an embedded planet in the HD 100546 protoplanetary disk
• ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) V: Sample, overview, and demography of disk molecular emission
• Tracing snowlines and C/O ratio in a planet-hosting disk: ALMA molecular line observations towards the HD169142 disk
• Organic molecules in the protoplanetary disk of DG Tau revealed by ALMA
• Herbig Stars: A Quarter Century of Progress
• Dust continuum emission and the upper limit fluxes of sub-millimeter water lines of the protoplanetary disk around HD 163296 observed by ALMA
• The TW Hya Rosetta Stone Project II: Spatially resolved emission of formaldehyde hints at low-temperature gas-phase formation
• Exploring the link between star and planet formation with Ariel
• Chemical survey of Class I protostars with the IRAM-30m
• Investigating the asymmetric chemistry in the disk around the young star HD 142527
• Resolved molecular line observations reveal an inherited molecular layer in the young disk around TMC1A
• Complex organic molecules in protoplanetary disks : X-ray photodesorption from methanol-containing ices. Part I -- Pure methanol ices
• Photodesorption of acetonitrile CH3CN in UV-irradiated regions of the Interstellar Medium: an experimental evidence
• ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) III: The interplay between gas and dust in the protoplanetary disk of DG Tau
• The Molecular Composition of Shadowed Protosolar Disk Midplanes beyond the Water Snowline
• Complex organic molecules in protoplanetary disks: X-ray photodesorption from methanol-containing ices. Part II -- Mixed methanol-CO and methanol-H2O ices
• Radial and vertical constraints on the icy origin of H${}_2$CO in the HD 163296 Protoplanetary Disk
• ALMA reveals thermal and non-thermal desorption of methanol ice in the HD 100546 protoplanetary disk
• Vacuum ultraviolet photodesorption and photofragmentation of formaldehyde-containing ices
• Evidence for a Sharp CO Snowline Transition in a Protoplanetary Disk and Implications for Millimeter-wave Observations of CO Isotopologues
• Spatial distribution of organics in the Horsehead nebula: Signposts of chemistry driven by atomic carbon
• Impact of Size-dependent Grain Temperature on Gas-Grain Chemistry in Protoplanetary Disks: the case of low mass star disks
• Hunting for methanol in the water rich, planet forming disk around HL Tau