v410tau_rotated.pdf (452.99 kB)

Lightcurve for the 'young Sun' V410 Tau from Super-WASP

figure

posted on 2012-08-16, 16:37 authored by Aleks ScholzAleks Scholz

The star V410 Tau is one of the best-studied young, magnetically active objects and a young analogue to the Sun. It has a well-established rotation period of 1.87 days, visible in the lightcurve due to the presence of cool surface spots (analogous to the Sun spots) which are co-rotating with the star. The figure shows the lightcurve for V410 Tau from the public archive of the Super-WASP project (Butters et al. 2010, see link). Super-WASP is a systematic search for transiting exoplanets; it also provides an excellent database to study other types of variability. The 3659 datapoints for two seasons are plotted in phase to the best-fitting period of 1.91 days and are offset from each other for clarity. The period search and lightcurve analysis was part of a summer project by Donna Rodgers-Lee at the Dublin Institute for Advanced Studies.

The figure reveals the following:

1. The lightcurve in each season has two maxima, marked by the red dashed line and the arrows. This has been observed before for this object and is well-explained by the existence of two spots, a large and a small one, at different latitudes (Herbst 1989). The phase shift in the second maxima by 0.2 (see red arrows) means that the small spot shifted in longitude with respect to the large spot between 2004/5 and 2006/7.

2. The entire lightcurve from 2006/7 is shifted by a phase difference of 0.35 with respect to 2004/5, which indicates that the large spot shifted in longitude as well.

3. The amplitude of the variations is much larger in 2004/5 compared with 2006/7. This is in line with an earlier tentative detection of a magnetic cycle - a periodic modulation of the activity strength, similar to the 11 yr cycle in the Sun. For V410 Tau, Stelzer et al. (2003) find a possible cycle of 5.4 yr with a maximum in 1999. Thus, the next maximum would be expected for 2004/5, as observed.

4. Our best period of 1.911 days is longer than the known value of 1.87 days. In fact, a period of 1.87 days does not match the Super-WASP lightcurve. This could be explained by differential rotation as in the Sun - we could be observing spots at high latitudes which have longer rotation periods than at the equator, except that surface maps for V410 Tau show no evidence for substantial differential rotation (Rice & Strassmeier 1996).