Proposal #287

AAVSONet proposal for TU Tau, submitted by Robert Buchheim (BHU)
Target name: TU Tau (aka WDS J05452+2425AB, aka 000-BBK-105) = 000-BBK-105
RA= 05 45 13.73 = 86.30721
Dec= +24 25 12.4 = +24.42011
Min mag≈ 8.8 (V) Max mag≈ 7.7 (V) per VSX

Proposal form:
Why this target? TU Tau is listed as a semi-regular variable. The primary star is a Carbon star (see spectra in AVSpec from BHU, IDG and STIB). There are only sporadic photometric observations in the AAVSO database, but the ASAS record (2002 – 2009) shows a pretty chaotic cycle of brightening and fading.
TU Tau is also a visual double star, where the secondary is an A-type star (WDS J05452+2425AB), with a separation of about 0.2 arc-sec. There is only one astrometric measurement, so it isn’t clear whether this is an optical double or a binary.
Supporting comment received from Dr. Richard Gray (App. State Univ): “TU Tau is an interesting binary system consisting of a variable carbon giant and an A-type dwarf. Nothing is known to date about the period of this binary. While we don't have any evidence that it is an eclipsing binary, it does appear that at certain phases we are seeing the A dwarf through the extended atmosphere of the giant, which may give us insights into the extended atmospheres of carbon giants. Photometry (BVR) and spectroscopy, especially in the blue-violet (380 - 500nm) where the A star is visible would be valuable.”

Goal: I (along with other participants in our Spectroscopy discussion group) plan to monitor the star for any spectral changes during this observing season. Contemporaneous photometry will allow us to flux-calibrate the spectra, thereby correlating spectral changes with brightness changes.

Requested observations: I request B-V-R observations of this star approximately every seven to ten days, from now through April 15, 2023. There are no time-critical events on this semi-regular variable star (SRB), so you can adjust the observing schedule as needed for weather or other higher-priority targets, or to avoid the Moon (which can pass close to TU Tau).