Molecules with ALMA at Planet-forming Scales (MAPS). XIII. HCO+ and disk ionization structure

Yuri Aikawa, Gianni Cataldi, Yoshihide Yamato, Ke Zhang, Alice S. Booth, Kenji Furuya, Sean M. Andrews, Jaehan Bae, Edwin A. Bergin, Jennifer B. Bergner, Arthur D. Bosman, L. Ilsedore Cleeves, Ian Czekala, Viviana V. Guzmán, Jane Huang, John D. Ilee, Charles J. Law, Romane Le Gal, Ryan A. Loomis, François MénardHideko Nomura, Karin I. Öberg, Chunhua Qi, Kamber R. Schwarz, Richard Teague, Takashi Tsukagoshi, Catherine Walsh, David J. Wilner

Research output: Contribution to journalArticlepeer-review


We observed HCO+ J = 1 - 0 and H13CO+ J = 1 - 0 emission toward the five protoplanetary disks around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480 as part of the MAPS project. HCO+ is detected and mapped at 0"3 resolution in all five disks, while H13CO+ is detected (S/N > 6σ) toward GM Aur and HD 163296 and tentatively detected (S/N > 3σ) toward the other disks by a matched filter analysis. Inside a radius of R ~ 100 au, the HCO+ column density is flat or shows a central dip. At outer radii (≳100 au), the HCO+ column density decreases outward, while the column density ratio of HCO+/CO is mostly in the range of ~10-5-10-4. We derived the HCO+ abundance in the warm CO-rich layer, where HCO+ is expected to be the dominant molecular ion. At R ≳ 100 au, the HCO+ abundance is ~3 × 10-11 - 3 × 10-10, which is consistent with a template disk model with X-ray ionization. At the smaller radii, the abundance decreases inward, which indicates that the ionization degree is lower in denser gas, especially inside the CO snow line, where the CO-rich layer is in the midplane. Comparison of template disk models with the column densities of HCO+, N2H+, and N2D+ indicates that the midplane ionization rate is ≳10-18 s-1 for the disks around IM Lup, AS 209, and HD 163296. We also find hints of an increased HCO+ abundance around the location of dust continuum gaps in AS 209, HD 163296, and MWC 480. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.
Original languageEnglish
Article number13
Number of pages22
JournalAstrophysical Journal Supplement Series
Issue number1
Early online date3 Nov 2021
Publication statusPublished - Nov 2021


  • Astrochemistry
  • Planetary system formation
  • Protoplanetary disks


Dive into the research topics of 'Molecules with ALMA at Planet-forming Scales (MAPS). XIII. HCO+ and disk ionization structure'. Together they form a unique fingerprint.

Cite this