PACS and SPIRE range spectroscopy of cool, evolved stars⋆
Koninklijke Sterrenwacht van België, Ringlaan 3, 1180 Brussel, Belgium
2 Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
3 Onsala Space Observatory, Department of Earth and Space Sciences, Chalmers University of Technology, 439 92 Onsala, Sweden
Accepted: 20 July 2018
Context. At the end of their lives AGB stars are prolific producers of dust and gas. The details of this mass-loss process are still not understood very well. Herschel PACS and SPIRE spectra which cover the wavelength range from ∼55 to 670 μm almost continuously, offer a unique way of investigating properties of AGB stars in general and the mass-loss process in particular as this is the wavelength region where dust emission is prominent and molecules have many emission lines.
Aims. We present the community with a catalogue of AGB stars and red supergiants (RSGs) with PACS and/or SPIRE spectra reduced according to the current state of the art.
Methods. The Herschel interactive processing environment (HIPE) software with the latest calibration is used to process the available PACS and SPIRE spectra of 40 evolved stars. The SPIRE spectra of some objects close to the Galactic plane require special treatment because of the weaker fluxes in combination with the strong and complex background emission at those wavelengths. The spectra are convolved with the response curves of the PACS and SPIRE bolometers and compared to the fluxes measured in imaging data of these sources. Custom software is used to identify lines in the spectra, and to determine the central wavelengths and line intensities. Standard molecular line databases are used to associate the observed lines. Because of the limited spectral resolution of the PACS and SPIRE spectrometers (∼1500), several known lines are typically potential counterparts to any observed line. To help identifications in follow-up studies the relative contributions in line intensity of the potential counterpart lines are listed for three characteristic temperatures based on local thermodynamic equilibrium (LTE) calculations and assuming optically thin emission.
Results. The following data products are released: the reduced spectra, the lines that are measured in the spectra with wavelength, intensity, potential identifications, and the continuum spectra, i.e. the full spectra with all identified lines removed. As simple examples of how this data can be used in future studies we have fitted the continuum spectra with three power laws (two wavelength regimes covering PACS, and one covering SPIRE) and find that the few OH/IR stars seem to have significantly steeper slopes than the other oxygen- and carbon-rich objects in the sample, possibly related to a recent increase in mass-loss rate. As another example we constructed rotational diagrams for CO (and HCN for the carbon stars) and fitted a two-component model to derive rotational temperatures.
Key words: stars: AGB and post-AGB / stars: mass-loss / infrared: stars
The reduced spectra and the line subtracted spectra as well as Table E.1 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/618/A143
© ESO 2018