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

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 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 H 2 column density ranges from 1.7 × 10 18 to 4.2 × 10 21 cm −2 and the molecular mass ranges from 2.7 × 10 −4 to 1.7 × 10 −1 M .

The MUSE view of the planetary nebula NGC 3132

“…In (Storey 1984) and CO (Sahai et al 1990) emission, both peaked on the shell where [O i] is strong. In addition, mid-infrared rotational H 2 lines have been detected (Mata et al 2016) as well as CO (J=3-2) emission (Guzman-Ramirez et al 2018). These neutral gas indicators suggest that there may be a photodissociation region (PDR) at the outer shell of the nebula.…”

A search for cool molecular gas in GK Persei and other classical novae

“…As we have shown, it does not possess a molecular component, which is common among genuine PNe of various types and ages (e.g. Bublitz et al 2019;Guzman-Ramirez et al 2018). The material filling the bipolar shell may be interacting with the inner nova ejecta, as suggest in earlier studies (e.g., Harvey et al 2016).…”

Lessons from the Ionised and Molecular Mass of Post-CE PNe

“…The sample was later extended to 21 post-CE PNe, including objects with molecular observations published in the literature [14][15][16][17]. Note that only 3 of these 21 objects, NGC 6778, NGC 2346, and NGC 7293, show molecular emission at all; hence, the molecular masses computed below are upper limits in most cases.…”

“…We assumed an excitation temperature of T ex = 50 K and a CO abundance X = 2×10 −4 for every object in our calculations and primarily used the 12 CO J = 2−1 transition, which is more ubiquous and better detected in the literature. In order to overcome the clear limitation that this transition (as well as the 12 CO J = 3−2 one) is usually not optically thin, we introduce a correction factor for the underestimated masses resulting from J = 2−1 (and J = 3−2) transitions in order to match masses found via the J = 1−0 transition in a sample of PNe in which both transitions are available in the literature [14][15][16][17]. These resulted in a factor of 3.65 to calculations using 12 CO J = 2−1 and a factor 5.0 for those using 12 CO J = 3−2.…”