Do chromospheric polar spots exist? (Observations at the Calar Alto observatory)
Final Report Abstract
The proposed observations could be carried out as planned for one of the two available observing nights at CAHA, the other night was largely lost due to poor weather. This time sampling would still allow to study the polar regions of one of the two components of ER Vul. However, the instrumental problems described above, partially also in combination with the moderate weather conditions, significantly inhibit our intendended analysis: it requires a detailed modelling of the chromospheric excess flux on top of the photospheric emission for the rather shallow (e.g. Hα ) line profiles encountered in ER Vul due to their rotational broadening. Such an analysis needs the information of a spectrally well-resolved central interval of the line cores and it has to be carried out during one or several continously observed eclipses to minimize the influence of intrinsic short-term time variations in the activity of both binary components. We strongly believe that the given unexpectedly poor signal level will not allow our intended analysis – actually our preliminary estimates support this assessment. Nevertheless, we intend to attempt some further modelling of our CAFE spectra of 21 August 2015. We plan to do this in the framework of a publication on ER Vul that we are currently working on. However, the main focus of this publication will be our observations of the same target which made use of several instruments of the XMM-Newton satellite. Based on that modelling of our CAFE data presented here, we will decide whether we will re-attempt similar observations of ER Vul with a hopefully refurbished CAFE spectrograph.
