%0 Journal Article
%T Warm CO in evolved stars from the THROES catalogue - I. Herschel-PACS spectroscopy of O-rich envelopes
%A C. S芍nchez Contreras
%A J. M. da Silva Santos
%A J. Ramos-Medina
%A P. Garc赤a-Lario
%J -
%D 2018
%R 10.1051/0004-6361/201833177
%X In this work (Paper I), we analyse <i>Herschel<i/>-PACS spectroscopy for a subsample of 23 O-rich and 3 S-type evolved stars, in different evolutionary stages from the asymptotic giant branch (AGB) to the planetary nebula (PN) phase, from the THROES catalogue. (C-rich targets are separately studied in Paper II). The broad spectral range covered by PACS (‵55每210 <i>米<i/>m) includes a large number of high-<i>J<i/> CO lines, from <i>J<i/> = 14 ˋ 13 to <i>J<i/> = 45 ˋ 44 (<i>v<i/> = 0), that allow us to study the warm inner layers of the circumstellar envelopes (CSEs) of these objects, at typical distances from the star of ＞10<sup>14<sup/>每10<sup>15<sup/> cm and ＞10<sup>16<sup/> cm for AGBs and post-AGB-PNe, respectively. We have generated CO rotational diagrams for each object to derive the rotational temperature, total mass within the CO-emitting region and average mass-loss rate during the ejection of these layers. We present first order estimations of these basic physical parameters using a large number of high-<i>J<i/> CO rotational lines, with upper-level energies from <i>E<i/><sub>up<sub/> ‵ 580 to 5000 K, for a relatively big set of evolved low-to-intermediate mass stars in different AGB-to-PN evolutionary stages. We derive rotational temperatures ranging from <i>T<i/><sub>rot<sub/> ‵ 200 to 700 K, with typical values around 500 K for AGBs and systematically lower, ‵200 K, for objects in more advanced evolutionary stages (post-AGBs and PNe). Our values of <i>T<i/><sub>rot<sub/> are one order or magnitude higher than the temperatures of the outer CSE layers derived from low-<i>J<i/> CO line studies. The total mass of the inner CSE regions where the PACS CO lines arise is found to range from <i>M<i/><sub>H<sub>2<sub/><sub/> ‵ 10<sup>ˋ6<sup/> to ＞10<sup>ˋ2<sup/> <i>M<i/><sub>×<sub/>, which is expected to represent a small fraction of the total CSE mass. The mass-loss rates estimated are in the range <i>ˋ<i/> ‵ 10<sup>ˋ7<sup/> ˋ 10<sup>ˋ4<sup/> <i>M<i/><sub>×<sub/>yr<sup>ˋ1<sup/>, in agreement (within uncertainties) with values found in the literature. We find a clear anticorrelation between <i>M<i/><sub>H<sub>2<sub/><sub/> and <i>ˋ<i/> vs. <i>T<i/><sub>rot<sub/> that probably results from a combination of most efficient line cooling and higher line opacities in high mass-loss rate objects. For some strong CO emitters in our sample, a double temperature (hot and warm) component is inferred. The temperatures of the warm and hot components are ‵400每500 K and ‵600每900 K, respectively. The mass of the warm component (‵10<sup>ˋ5<sup/>每8 ℅ 10<sup>ˋ2<sup/>
%U https://www.aanda.org/articles/aa/full_html/2018/10/aa33177-18/aa33177-18.html