Vanko, M., Torres, G., Hambálek, L., Pribulla, T., Buchhave, L. A., Budaj, J., Dubovský, P., Garai, Z., Ginski, C., Grankin, K., Komzík, R., Krushevska, V., Kundra, E., Marka, C., Mugrauer, M., Neuhäuser, R., Ohlert, J., Parimucha, S., Perdelwitz, V., Raetz, St, and Shugarov, S. Yu. 2017. "On the nature of the candidate T-Tauri star V501 Aurigae?" Monthly Notices of the Royal Astronomical Society, 467 4902–4913. https://doi.org/10.1093/mnras/stx407.
We report new multicolour photometry and high-resolution spectroscopic observations of the long-period variable V501 Aur, previously considered to be a weak-lined T-Tauri star belonging to the Taurus-Auriga star-forming region. The spectroscopic observations reveal that V501 Aur is a single-lined spectroscopic binary system with a 68.8-d orbital period, a slightly eccentric orbit (e ~ 0.03), and a systemic velocity discrepant from the mean of Taurus-Auriga. The photometry shows quasi-periodic variations on a different, ~55-d time-scale that we attribute to rotational modulation by spots. No eclipses are seen. The visible object is a rapidly rotating (vsin i ? 25 km s-1) early K star, which along with the rotation period implies it must be large (R > 26.3 R?), as suggested also by spectroscopic estimates indicating a low surface gravity. The parallax from the Gaia mission and other independent estimates imply a distance much greater than the Taurus-Auriga region, consistent with the giant interpretation. Taken together, this evidence together with a re-evaluation of the Li i ?6707 and H? lines shows that V501 Aur is not a T-Tauri star, but is instead a field binary with a giant primary far behind the Taurus-Auriga star-forming region. The large mass function from the spectroscopic orbit and a comparison with stellar evolution models suggest the secondary may be an early-type main-sequence star.
