The Young Embedded Disk L1527 IRS: Constraints on the Water Snowline and Cosmic-Ray Ionization Rate from HCO+ Observations

Abstract The water snowline in circumstellar disks is a crucial component planet formation, but direct observational constraints on its location remain sparse owing to the difficulty of observing both young embedded and mature protoplanetary disks. Chemical imaging provides an alternative route locate snowline, HCO + isotopologues have been shown be good tracers protostellar envelopes Herbig Here we present ∼0.″5 resolution (∼35 au radius) Atacama Large Millimeter/submillimeter Array (ALMA) observations J = 4 − 3 H 13 CO 2 toward (Class 0/I) disk L1527 IRS. Using source-specific physical model with midplane at 3.4 small chemical network, are able reproduce emission, for only when cosmic-ray ionization rate lowered 10 −18 s −1 . Even though not sensitive expected abundance drop across reduction above snow surface global temperature structure allow us constrain between 1.8 4.1 au. Deep required eliminate envelope contribution emission derive more stringent location. Locating directly O may therefore still option. With measurement, will provide rate.