2022/04/19 by Merel L. R. van ’t Hoff, Merel L. R. van 't Hoff, Margot Leemker +13 · 1 citation
Chemistry · Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #Atmospheric Ozone and Climate #Earth and Planetary Astrophysics (astro-ph.EP) #FOS: Physical sciences #Molecular Spectroscopy and Structure #Solar and Stellar Astrophysics (astro-ph.SR) #astro-ph.EP #astro-ph.GA #astro-ph.SR
paper · pdf · doi:10.48550/arxiv.2204.08622
Accepted for publication in ApJ, 15 pages, 6 figures and appendix
arxiv created 2022/04/19 · openalex publication_date 2022/04/19 · arxiv updated 2022/04/20 · openalex created_date 2022/04/27 · openalex updated_date 2026/07/28
The water snowline in circumstellar disks is a crucial component in planet formation, but direct observational constraints on its location remain sparse due to the difficulty of observing water in both young embedded and mature protoplanetary disks. Chemical imaging provides an alternative route to locate the snowline, and HCO+ isotopologues have been shown to be good tracers in protostellar envelopes and Herbig disks. Here we present ∼0.5′′ resolution (∼35 au radius) Atacama Large Millimeter/submillimeter Array (ALMA) observations of HCO+ J=4-3 and H13CO+ J=3-2 toward the young (Class 0/I) disk L1527 IRS. Using a source-specific physical model with the midplane snowline at 3.4 au and a small chemical network, we are able to reproduce the HCO+ and H13CO+ emission, but for HCO+ only when the cosmic ray ionization rate is lowered to 10-18 s-1. Even though the observations are not sensitive to the expected HCO+ abundance drop across the snowline, the reduction in HCO+ above the snow surface and the global temperature structure allow us to constrain a snowline location between 1.8 and 4.1 au. Deep observations are required to eliminate the envelope contribution to the emission and to derive more stringent constraints on the snowline location. Locating the snowline in young disks directly with observations of H2O isotopologues may therefore still be an alternative option. With a direct snowline measurement, HCO+ will be able to provide constraints on the ionization rate.