Opening PANDORA’s box: APEX observations of CO in PNe^★

¹ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
e-mail: guzmanl@strw.leidenuniv.nl
² European Southern Observatory, Alonso de Córdova 3107, Santiago, Chile
³ CONACYT Instituto Nacional de Astrofísica, Óptica y Electrónica, Luis E. Erro 1, 72840 Tonantzintla, Puebla, Mexico
⁴ European Southern Observatory, Karl-Schwarzschild-str. 2, 85748 Garching, Germany
⁵ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁶ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁷ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁸ Jodrell Bank Centre for Astrophysics, University of Manchester, Manchester, UK
⁹ Department of Physics & Laboratory for Space Research, University of Hong Kong, Pok Fu Lam Road, Hong Kong
¹⁰ Centre for Research in Earth and Space Sciences, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada
¹¹ Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile

Received: 7 September 2017
Accepted: 16 March 2018

Abstract

Context. Observations of molecular gas have played a key role in developing the current understanding of the late stages of stellar evolution.

Aims. The survey Planetary nebulae AND their cO Reservoir with APEX (PANDORA) was designed to study the circumstellar shells of evolved stars with the aim to estimate their physical parameters.

Methods. Millimetre carbon monoxide (CO) emission is the most useful probe of the warm molecular component ejected by low- to intermediate-mass stars. CO is the second-most abundant molecule in the Universe, and the millimetre transitions are easily excited, thus making it particularly useful to study the mass, structure, and kinematics of the molecular gas. We present a large survey of the CO (J = 3−2) line using the Atacama Pathfinder EXperiment (APEX) telescope in a sample of 93 proto-planetary nebulae and planetary nebulae.

Results. CO (J = 3−2) was detected in 21 of the 93 objects. Only two objects (IRC+10216 and PN M2-9) had previous CO (J = 3−2) detections, therefore we present the first detection of CO (J = 3−2) in the following 19 objects: Frosty Leo, HD 101584, IRAS 19475+3119, PN M1-11, V* V852 Cen, IC 4406, Hen 2-113, Hen 2-133, PN Fg 3, PN Cn 3-1, PN M2-43, PN M1-63, PN M1-65, BD+30 3639, Hen 2-447, Hen 2-459, PN M3-35, NGC 3132, and NGC 6326.

Conclusions. CO (J = 3−2) was detected in all 4 observed pPNe (100%), 15 of the 75 PNe (20%), one of the 4 wide binaries (25%), and in 1 of the 10 close binaries (10%). Using the CO (J = 3−2) line, we estimated the column density and mass of each source. The H₂ column density ranges from 1.7 × 10¹⁸ to 4.2 × 10²¹ cm⁻² and the molecular mass ranges from 2.7 × 10⁻⁴ to 1.7 × 10⁻¹ M_⊙.