Proposal #113

We propose AAVSOnet observations of the bright variable star Zeta Andromedae. We are planning observations of the star to directly measure differential rotation on the star’s surface by resolving individual spot patterns on the disk of the star interferometrically with the CHARA observatory, which has never been done before. Those observations are being planned to overlap with the time that the star will be observed by the NASA TESS mission from 7 Oct 2019 through 2 Nov 2019. In order to obtain long time-baseline measurements of the spot evolution of the star, we are also conducting ground-based photometric observations of the star from Fairborn Observatory in Arizona with the APT telescopes for several months before and after the TESS and CHARA observations. Although the TESS photometry will provide much higher precision, it is limited to the 27-day duration of the TESS sectors, less than 2 rotational cycles, which is why the ground-based photometry will be so useful. These observations will clarify whether the spots evolution timescale is shorter than expected, which will add reliability to the interferometric results. However, our monitoring facilities will be offline in July and August 2019 for the annual monsoon season, and we are looking for other facilities to conduct monitoring.
We would like to obtain nightly observations of the star via the AAVSOnet Bright Star Monitoring network across the visible spectrum. B band will provide the best spot contrast, V band will be the most similar to the APT observations (allowing us to cross-calibrate), and I band will be closest to the CHARA bandpass. The brightness modulation of the star ranges from +3.92 to +4.14 in V band, so we would like to obtain observations with the best available SNR. We would ideally like a set of BVI observations between one and three times per night from July 1 – Sept 15, 2019. The estimated exposure times are 8 seconds in B, 4 seconds in V, and 3 seconds in I. The reason for the requested cadence is that while the star has a known rotation period of 17.7 days, we want to explore whether there are significant changes due to spot evolution on shorter timescales, and if so, to calibrate them.
We realize that these observations will be challenging, given the brightness of the target star and the faintness of any comparison stars within the potential FOVs of the BSM telescopes. We still believe that the campaign would be valuable if we can monitor the stellar variability to within 0.05 mag. Our scientific goal is to obtain maximal SNR in any available filters, with the key objective being relative photometry.
The results of the observations will be reduced and analyzed by our team, and the data will be included in resulting journal publications. We will also be happy to include the results in the AAVSO database.