DeSSpOt: an instrument for stellar spin orientation determination

Abstract

We designed and constructed a special instrument to enable the determination of the stellar's spin orientation. The Differential image rotator for Stellar Spin Orientation, DeSSpOt, allows the simultaneous observations of two anti-parallel orientations of the star on the spectrum. On a high resolution ´echelle spectrum, the stellar rotation causes a slight line tilt visible in the spatial direction which is comparable to a rotation curve. We developed a new method, which exploits the variations in these tilts, to estimate the absolute position angle of the rotation axis. The line tilt is retrieved by a spectroastrometric extraction of the spectrum. In order to validate the method, we observed spectroscopic binaries with known orbital parameters. The determination of the orbital position angle is equivalent to the determination of the stellar position angle, but is easier to to detect. DeSSpOt was successfully implemented on the high resolution Coud´e spectrograph of the Th¨uringer Landessternwarte Tautenburg. The observations of Capella led to the determination of the orbital position angle. Our value of 37.2° is in agreement with the values previously found in the literature. As such we verified that both method and instrument are valid.