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Probing CO and N_2 Snow Surfaces in Protoplanetary Disks with N_2H^+ Emission

Qi, Chunhua and Öberg, Karin I. and Espaillat, Catherine C. and Robinson, Connor E. and Andrews, Sean M. and Wilner, David J. and Blake, Geoffrey A. and Bergin, Edwin A. and Cleeves, L. Ilsedore (2019) Probing CO and N_2 Snow Surfaces in Protoplanetary Disks with N_2H^+ Emission. Astrophysical Journal, 882 (2). Art. No. 160. ISSN 1538-4357. doi:10.3847/1538-4357/ab35d3.

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Snowlines of major volatiles regulate the gas and solid C/N/O ratios in the planet-forming midplanes of protoplanetary disks. Snow surfaces are the 2D extensions of snowlines in the outer disk regions, where radiative heating results in an increasing temperature with disk height. CO and N_2 are two of the most abundant carriers of C, N, and O. N_2H^+ can be used to probe the snow surfaces of both molecules, because it is destroyed by CO and formed from N_2. Here we present Atacama Large Millimeter/submillimeter Array (ALMA) observations of N_2H^+ at ~0.”2–0.”4 resolution in the disks around LkCa 15, GM Aur, DM Tau, V4046 Sgr, AS 209, and IM Lup. We find two distinctive emission morphologies: N_2H^+ is either present in a bright, narrow ring surrounded by extended tenuous emission, or in a broad ring. These emission patterns can be explained by two different kinds of vertical temperature structures. Bright, narrow N_2H^+ rings are expected in disks with a thick Vertically Isothermal Region above the Midplane (VIRaM) layer (LkCa 15, GM Aur, DM Tau) where the N_2H^+ emission peaks between the CO and N_2 snowlines. Broad N_2H^+ rings come from disks with a thin VIRaM layer (V4046 Sgr, AS 209, IM Lup). We use a simple model to extract the first sets of CO and N_2 snowline pairs and corresponding freeze-out temperatures toward the disks with a thick VIRaM layer. The results reveal a range of N_2 and CO snowline radii toward stars of similar spectral type, demonstrating the need for empirically determined snowlines in disks.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Qi, Chunhua0000-0001-8642-1786
Öberg, Karin I.0000-0001-8798-1347
Espaillat, Catherine C.0000-0001-9227-5949
Robinson, Connor E.0000-0003-1639-510X
Andrews, Sean M.0000-0003-2253-2270
Wilner, David J.0000-0003-1526-7587
Blake, Geoffrey A.0000-0003-0787-1610
Bergin, Edwin A.0000-0003-4179-6394
Cleeves, L. Ilsedore0000-0003-2076-8001
Alternate Title:Probing CO and N2 Snow Surfaces in Protoplanetary Disks with N2H+ Emission
Additional Information:© 2019 The American Astronomical Society. Received 2019 June 10; revised 2019 July 17; accepted 2019 July 24; published 2019 September 13. We thank Ryan Loomis, Jane Huang, and Romane Le Gal for useful discussions. This paper makes use of ALMA data ADS/JAO. ALMA#2015.1.00678.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This paper utilizes the D'Alessio Irradiated Accretion Disk (DIAD) code. We wish to recognize the work of Paola D'Alessio, who passed away in 2013. Her legacy and pioneering work live on through her substantial contributions to the field. C.C.E. acknowledges support from the National Science Foundation under career grant AST-1455042. Facility: ALMA. - Software: CASA (McMullin et al. 2007), MIRIAD (Sault et al. 1995), DIAD (D'Alessio et al. 1998, 1999, 2001, 2005, 2006), RATRAN (Hogerheijde & van der Tak 2000).
Group:Astronomy Department
Funding AgencyGrant Number
Subject Keywords:Astrochemistry; Interstellar molecules; Protoplanetary disks
Issue or Number:2
Classification Code:Astrochemistry (75); Interstellar molecules (849); Protoplanetary disks (1300)
Record Number:CaltechAUTHORS:20190916-140415605
Persistent URL:
Official Citation:Chunhua Qi et al 2019 ApJ 882 160
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:98659
Deposited By: Tony Diaz
Deposited On:16 Sep 2019 21:16
Last Modified:16 Nov 2021 17:40

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