UCL Discovery
UCL home » Library Services » Electronic resources » UCL Discovery

ISO-LWS observations of rotational CO lines from C-rich objects: AFGL 2688, AFGL 618 and NGC 7027

Justtanont, K; Barlow, MJ; Tielens, AGGM; Hollenbach, D; Latter, WB; Liu, XW; Sylvester, RJ; ... Skinner, CJ; + view all (2000) ISO-LWS observations of rotational CO lines from C-rich objects: AFGL 2688, AFGL 618 and NGC 7027. Astronomy & Astrophysics , 360 pp. 1117-1125. Green open access

[thumbnail of justtanont00_co_AA360_1117.pdf]
Preview
Text
justtanont00_co_AA360_1117.pdf - Published Version

Download (304kB) | Preview

Abstract

We present ISO-LWS full scan observations of CO rotational emission lines (J=14-13 up to J=37- 36) from two C-rich post-AGB objects, AFGL 2688; AFGL 618, and one C-rich PN, NGC 7027. The presence of high rotational lines cannot be explained by a spherical, constant velocity wind during the previous AGB phase, but indicates a layer of warm, dense gas with a substantial beam filling factor (Ω > 10-10 sr). By simple optically thin calculations, we estimate the total mass of gas cooled through CO rotational lines to be typically ~ 0.1 Msun. We also consider the physical processes responsible for heating and cooling the warm gas in these objects. Energy sources for the gas could include FUV photons, resulting in a PhotoDissociation Region (PDR), as well as shocks driven by the interacting winds during this evolutionary phase. We have calculated detailed models for the heating and cooling in C-rich PDRs and shocks in order to explain the CO spectra observed. In both models, the gas is cooled radiatively by molecular rotational lines as well as by atomic fine structure lines. Both models can produce warm gas of >500 K at a density of 106 - 107 cm-3. We conclude that the source of heating for the young PN, NGC 7027, is FUV photons from the central star. For the least evolved post-AGB star, AFGL 2688, the effective temperature is too cool to produce many FUV photons to heat the gas. However, there is evidence of a fast wind developing and hence the most likely heating mechanism for the envelope is shocks. For AFGL 618, the central star is hot enough to provide copious amounts of FUV photons but fast outflows have also been observed and both processes may be operational. However, in view of [O I] 63 μm high resolution observations, the heating mechanism is more likely to be a PDR. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) with the participation of ISAS and NASA.

Type: Article
Title: ISO-LWS observations of rotational CO lines from C-rich objects: AFGL 2688, AFGL 618 and NGC 7027
Open access status: An open access version is available from UCL Discovery
Publisher version: https://ui.adsabs.harvard.edu/abs/2000A%26A...360....
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Science & Technology, Physical Sciences, Astronomy & Astrophysics, stars : circumstellar matter, stars : evolution, stars : individual : NGC 7027, AFGL 618, AFGL 2688, stars : late-type, stars : mass-loss, infrared : stars, LONG-WAVELENGTH SPECTROMETER, PLANETARY-NEBULA NGC-7027, PHOTODISSOCIATION REGIONS, INTERSTELLAR SHOCKS, CARBON-MONOXIDE, EGG NEBULA, EMISSION, AFGL-2688, SPECTRUM, IRC+10216
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10096059
Downloads since deposit
13Downloads
Download activity - last month
Download activity - last 12 months
Downloads by country - last 12 months

Archive Staff Only

View Item View Item