An ALMA Survey of Chemistry in Disks around M4-M5 Stars

Abstract

M-stars are the most common hosts of planetary systems in the Galaxy. Protoplanetary disks around M-stars thus offer a prime opportunity to study the chemistry of planet-forming environments. We present an ALMA survey of molecular line emission toward a sample of five protoplanetary disks around M4-M5 stars (FP Tau, J0432+1827, J1100-7619, J1545-3417, and Sz 69). These observations can resolve chemical structures down to tens of AU. Molecular lines of ${}^{12}$CO, ${}^{13}$CO, C${}^{18}$O, C${}_2$H, and HCN are detected toward all five disks. Lines of H${}_2$CO and DCN are detected toward 2/5 and 1/5 disks, respectively. For disks with resolved C${}^{18}$O, C${}_2$H, HCN, and H${}_2$CO emission, we observe substructures similar to those previously found in disks around solar-type stars (e.g., rings, holes, and plateaus). C${}_2$H and HCN excitation conditions estimated interior to the pebble disk edge for the bright disk J1100-7619 are consistent with previous measurements around solar-type stars. The correlation previously found between C${}_2$H and HCN fluxes for solar-type disks extends to our M4-M5 disk sample, but the typical C${}_2$H/HCN ratio is higher for the M4-M5 disk sample. This latter finding is reminiscent of the hydrocarbon enhancements found by previous observational infrared surveys in the innermost ($<$10AU) regions of M-star disks, which is intriguing since our disk-averaged fluxes are heavily influenced by flux levels in the outermost disk, exterior to the pebble disk edge. Overall, most of the observable chemistry at 10-100AU appears similar for solar-type and M4-M5 disks, but hydrocarbons may be more abundant around the cooler stars.

46 pages (20 pages in the main document, 26 pages in the appendix), 48 figures, 7 tables. Accepted in ApJ (February 2021)

References in corpus (23)

• The Gaia mission
• The Solar Neighborhood XVII: Parallax Results from the CTIOPI 0.9m Program -- Twenty New Members of the RECONS 10 Parsec Sample
• X-Shooter spectroscopy of young stellar objects in Lupus: Accretion properties of class II and transitional objects
• A Steeper than Linear Disk Mass-Stellar Mass Scaling Relation
• Observations of Protoplanetary Disk Structures
• Complex organic molecules in protoplanetary disks
• Direct mapping of the temperature and velocity gradients in discs. Imaging the vertical CO snow line around IM Lupi
• Hydrocarbon emission rings in protoplanetary disks induced by dust evolution
• An ALMA Survey of CO isotopologue emission from Protoplanetary Disks in Chamaeleon I
• A survey of C2H, HCN, and C18O in protoplanetary disks
• An ALMA survey of DCN/H${}^{13}$CN and DCO${}^{+}$/H${}^{13}$CO${}^{+}$ in protoplanetary disks
• Brown dwarf disks with ALMA
• An ALMA Survey of H${}_2$CO in Protoplanetary Disks
• Stacking Spectra in Protoplanetary Disks: Detecting Intensity Profiles from Hidden Molecular Lines in HD 163296
• DCO${}^{+}$, DCN and N${}_2$D${}^{+}$ reveal three different deuteration regimes in the disk around the Herbig Ae star HD163296
• An evolutionary study of volatile chemistry in protoplanetary disks
• Increased H${}_2$CO production in the outer disk around HD 163296
• The Taurus Boundary of Stellar/Substellar (TBOSS) Survey II. Disk Masses from ALMA Continuum Observations
• The Taurus Boundary of Stellar/Substellar (TBOSS) Survey I: far-IR disk emission measured with Herschel
• HfS, Hyperfine Structure Fitting Tool
• Dynamical Masses and Stellar Evolutionary Model Predictions of M-Stars
• Sensitive survey for 13CO, CN, H2CO, and SO in the disks of T Tauri and Herbig Ae stars II: Stars in $\rho$ Oph and upper Scorpius
• Vacuum ultraviolet photodesorption and photofragmentation of formaldehyde-containing ices

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• Dancing on the Grain: Variety of CO and its isotopologue fluxes as a result of surface chemistry and T Tauri disk properties
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