Herschel/HIFI Spectral Scans


Improved baseline quality in two examples of Spectral Scan observations: left is the original SPG deconvolved spectrum, while the baseline-corrected product is shown on the right


The main purpose of these Highly Processed Data Products (HPDP) is to improve the quality of the spectral baseline of the Level 2.5 deconvolved products generated by the Standard Pipeline (SPG) for HIFI Spectral Scan observations. Residual artefacts in the form of standing waves and other baseline distortion may indeed still exist in some of those, and their cleaning involves treatment on the individual Level 2 products used to feed the deconvolution algorithm.

We provide here baseline-corrected versions of those products for about 2/3 of the ~500 Spectral Scan observations performed by HIFI. The main product of the delivered data-set will therefore be a continuum-subtracted spectrum with baseline artefacts removed to the best of our knowledge. The removed baseline, however, is also provided as an stand-alone products, to allow users to inspect the flux component we decided to remove, but also as a proxy of the intrinsic continuum of the source, which can then be used to e.g. model this continuum and add it back to the baseline-subtracted spectrum. Each product is provided separately for the respective H and V polarisation spectra. Those products will be served by the Herschel Science Archive, but they can also be fetched from this local Data repository, together with their Postcards.

Owing to the semi-automatic data processing approach used to perform the baseline subtraction, there exist cases where complicated line profiles, or high line density circumstances, may lead to imperfect baseline correction, essentially because of sub-optimal line masking by the involved algorithm. It is recommended to inspect the detailed baseline shape around any line of particular interest by e.g. overlaying it on top of the original SPG spectrum (which is also part of the delivered data-set for the record). We strongly encourage any user of these products to carefully read the associated release notes.

Herschel Science Centre, July 2017