Missing water in Class I protostellar disks

Astronomy and Astrophysics, vol. 636, pp. A26

Abstract

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.

Authors 13

1. D. Harsono Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, Niels Bohrweg 2, 2300 RA Leiden, The Netherlands

2. Magnus V. Persson

   Chalmers University of Technology

   Affiliation as printed

   Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden

3. A. Ramos

   The University of Texas at Austin

   Affiliation as printed

   Department of Astronomy, University of Texas, Austin, TX, USA

4. Nadia M. Murillo Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, Niels Bohrweg 2, 2300 RA Leiden, The Netherlands

5. Luke T. Maud Aachen Leiden Observatory

   Leiden University · European Southern Observatory · Leiden Observatory

   Affiliation as printed

   European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany

   Leiden Observatory, Leiden University, Niels Bohrweg 2, 2300 RA Leiden, The Netherlands

6. M. R. Hogerheijde Aachen Leiden Observatory

   Leiden University · Leiden Observatory · University of Amsterdam

   Affiliation as printed

   Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

   Leiden Observatory, Leiden University, Niels Bohrweg 2, 2300 RA Leiden, The Netherlands

7. Arthur D. Bosman Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, Niels Bohrweg 2, 2300 RA Leiden, The Netherlands

8. Lars Erik Kristensen

   University of Copenhagen

   Affiliation as printed

   Niels Bohr Institute & Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K, Denmark

9. Jes Kristian Jørgensen

   University of Copenhagen

   Affiliation as printed

   Niels Bohr Institute & Centre for Star and Planet Formation, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen K, Denmark

10. Edwin A. Bergin

    University of Michigan

    Affiliation as printed

    Department of Astronomy, The University of Michigan, 500 Church St., 830 Dennison Bldg., Ann Arbor, MI 48109, USA

11. R. Visser

    European Southern Observatory

    Affiliation as printed

    European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany

12. J. C. Mottram

    Max Planck Institute for Astronomy

    Affiliation as printed

    Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany

13. Ewine F. van Dishoeck Aachen Leiden Observatory

    Leiden University · Max Planck Institute for Extraterrestrial Physics · Leiden Observatory

    Affiliation as printed

    Leiden Observatory, Leiden University, Niels Bohrweg 2, 2300 RA Leiden, The Netherlands

    Max Planck Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany