Missing water in Class i protostellar disks
Journal article, 2020

Context. Water is a key volatile that provides insight into the initial stages of planet formation. The low water abundances inferred from water observations toward low-mass protostellar objects may point to a rapid locking of water as ice by large dust grains during star and planet formation. However, little is known about the water vapor abundance in newly formed planet-forming disks. Aims. We aim to determine the water abundance in embedded Keplerian disks through spatially-resolved observations of H218O lines to understand the evolution of water during star and planet formation. Methods. We present H218O line observations with ALMA and NOEMA millimeter interferometers toward five young stellar objects. NOEMA observed the 31,3-22,0 line (Eup? kB = 203.7 K) while ALMA targeted the 41,4-32,1 line (Eup? kB = 322.0 K). Water column densities were derived considering optically thin and thermalized emission. Our observations were sensitive to the emission from the known Keplerian disks around three out of the five Class I objects in the sample. Results. No H218O emission is detected toward any of our five Class I disks. We report upper limits to the integrated line intensities. The inferred water column densities in Class I disks are NH218O < 1015 cm-2 on 100 au scales, which include both the disk and envelope. The upper limits imply a disk-averaged water abundance of ? 10-6 with respect to H2 for Class I objects. After taking the physical structure of the disk into account, the upper limit to the water abundance averaged over the inner warm disk with T > 100 K is between ~10-7 and 10-5. Conclusions. Water vapor is not abundant in warm protostellar envelopes around Class I protostars. Upper limits to the water vapor column densities in Class I disks are at least two orders of magnitude lower than values found in Class 0 disk-like structures.

ISM: abundances


Protoplanetary disks

Stars: protostars

Stars: formation


D. Harsono

Leiden University

Magnus V. Persson

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Galactic Astrophysics

A. Ramos

The University of Texas at Austin

N. M. Murillo

Leiden University

Luke T. Maud

European Southern Observatory (ESO)

Leiden University

M. Hogerheijde

Leiden University

University of Amsterdam

A. D. Bosman

Leiden University

L. E. Kristensen

Niels Bohr Institute

Jes K. Jørgensen

Niels Bohr Institute

E. A. Bergin

University of Michigan

R. Visser

European Southern Observatory (ESO)

J. C. Mottram

Max Planck Society

E. F. van Dishoeck

Leiden University

Max Planck Society

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 636 1935994

Subject Categories

Astronomy, Astrophysics and Cosmology

Oceanography, Hydrology, Water Resources

Geosciences, Multidisciplinary



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