|Unraveling the unexpected wind deceleration in the envelopes around evolved stars
|At the end of their lives, low and intermediate mass stars lose a significant fraction of their mass via a copious mass loss through cool, low-velocity winds (v virgul 10 km-s). After several decades of study, the exact mechanisms triggering this mass loss are still not understood in all detail, but it is generally accepted that pulsations and dust formation play a crucial role. Using these two ingredients, the wind acceleration in the envelope surrounding the stars can be predicted. Herschel-HIFI has the unique capability to study the line profiles of many molecules excited in the circumstellar envelopes, hence enabling us to assess the wind velocity profile in evolved stars. While the HIFI data indeed show for some targets an acceleration of the wind, the widths of the lines in 2 oxygen-rich evolved stars are larger for the high-excitation lines compared to the low-excitation ones, suggesting a deceleration of the wind. This wind profile is completely unexpected, and can currently not be explained. However, the current dataset at hand is too scarce and not well sampled in terms of excitation energy levels. We therefore request Herschel-HIFI observing time to gather a series of SiO rotational lines in both the ground and first vibrational state to deduce with high accuracy the wind acceleration-deceleration in two oxygen-rich evolved stars. This will enable us to clarify the role of dust formation and pulsations in the onset of the stellar wind around low and intermediate mass stars.
|Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Doradus. Non-LTE abundance analysis of CO, SiO, and HCN . Van de Sande M. et al. . Astronomy & Astrophysics, Volume 609, id.A63, 16 pp. . 609 . 10.1051/0004-6361/201731298 . 2018A&A...609A..63V ,
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2012, GT2_ldecin_3, SPG v14.1.0. https://doi.org/10.5270/esa-1ps6bmx