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Survey of Cold Water Lines in Protoplanetary Disks: Indications of Systematic Volatile Depletion

Du, Fujun and Bergin, Edwin Anthony and Hogerheijde, Michiel and van Dishoeck, Ewine F. and Blake, Geoff and Bruderer, Simon and Cleeves, Ilse and Dominik, Carsten and Fedele, Davide and Lis, Dariusz C. and Melnick, Gary and Neufeld, David and Pearson, John and Yildiz, Umut (2017) Survey of Cold Water Lines in Protoplanetary Disks: Indications of Systematic Volatile Depletion. Astrophysical Journal, 842 (2). Art. No. 98. ISSN 1538-4357. http://resolver.caltech.edu/CaltechAUTHORS:20170619-104851391

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Abstract

We performed very deep searches for 2 ground-state water transitions in 13 protoplanetary disks with the HIFI instrument on board the Herschel Space Observatory, with integration times up to 12 hr per line. We also searched for, with shallower integrations, two other water transitions that sample warmer gas. The detection rate is low, and the upper limits provided by the observations are generally much lower than predictions of thermo-chemical models with canonical inputs. One ground-state transition is newly detected in the stacked spectrum of AA Tau, DM Tau, LkCa 15, and MWC 480. We run a grid of models to show that the abundance of gas-phase oxygen needs to be reduced by a factor of at least ~100 to be consistent with the observational upper limits (and positive detections) if a dust-to-gas mass ratio of 0.01 were to be assumed. As a continuation of previous ideas, we propose that the underlying reason for the depletion of oxygen (hence the low detection rate) is the freeze-out of volatiles such as water and CO onto dust grains followed by grain growth and settling/migration, which permanently removes these gas-phase molecules from the emissive upper layers of the outer disk. Such depletion of volatiles is likely ubiquitous among different disks, though not necessarily to the same degree. The volatiles might be returned back to the gas phase in the inner disk (≾15 au), which is consistent with current constraints. Comparison with studies on disk dispersal due to photoevaporation indicates that the timescale for volatile depletion is shorter than that of photoevaporation.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/aa70eeDOIArticle
http://iopscience.iop.org/article/10.3847/1538-4357/aa70ee/metaPublisherArticle
https://arxiv.org/abs/1705.00799arXivDiscussion Paper
ORCID:
AuthorORCID
van Dishoeck, Ewine F.0000-0001-7591-1907
Blake, Geoff0000-0003-0787-1610
Lis, Dariusz C.0000-0002-0500-4700
Additional Information:© 2017 The American Astronomical Society. Received 2016 October 7; revised 2017 April 27; accepted 2017 May 1; published 2017 June 19. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada, and the United States (NASA) under the leadership of SRON, Netherlands Institute for Space Research, Groningen, The Netherlands, and with major contributions from Germany, France, and the United States. Support for this work was provided by NASA through an award issued by JPL/Caltech. E.A.B. acknowledges support from NASA XRP grant NNX16AB48G. M.H. and E.v.D. acknowledge support from the Netherlands Research School for Astronomy (NOVA) and European Union A-ERC grant 291141 CHEMPLAN. D.F. acknowledges support from the Italian Ministry of Education, Universities and Research project SIR (RBSI14ZRHR).
Funders:
Funding AgencyGrant Number
NASA/JPL/CaltechUNSPECIFIED
NASANNX16AB48G
Nederlandse Onderzoekschool Voor Astronomie (NOVA)UNSPECIFIED
European Research Council (ERC)291141 CHEMPLAN
Ministero dell'Istruzione, dell'Università e della Ricerca (MIUR)RBSI14ZRHR
Subject Keywords:strochemistry – circumstellar matter – molecular processes – planet–disk interactions – planetary systems – planets and satellites: atmospheres
Record Number:CaltechAUTHORS:20170619-104851391
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170619-104851391
Official Citation:Fujun Du et al 2017 ApJ 842 98
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78329
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:19 Jun 2017 18:07
Last Modified:30 Aug 2017 20:52

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