Differential Rotation of the Active G5 V Star κ¹Ceti: Photometry from theMOSTSatellite

Abstract

ABSTRACT. About 30.5 days of nearly uninterrupted broadband photometry of the solar-type star k 1 Ceti, obtained with the MOST (Microvariability and Oscillations of Stars) satellite, shows evidence for two large starspots with different rotation periods of 8.9 and ∼9.3 days ( ). Ground-based measurements of Ca ii H and K emission DQ/Q Ӎ 4% in 2002 and 2003 reveal variations in chromospheric activity with a period of about 9.3 days. The data were obtained during the MOST commissioning phase. When the data are combined with historical observations, they indicate that the 9.3 day spot has been stable in its period for over 30 yr. The photometry, with a sampling rate of approximately once per minute, was also used to search for acoustic (p-mode) oscillations in the star. We detect no clear evidence for p-modes in the k 1 Ceti photometry, with a noise level around 7-9 mmag at frequencies in the range of 0.5-4 mHz (3 j detection limit of 21-27 mmag). There were no flares or planetary transits during 30.5 days of MOST monitoring with light amplitudes greater than 2 mmag (durations 1200 minutes) and 3 mmag (2-200 minute durations). While this rules out any close-in planets with Jupiter diameters ≥0.5 and orbital inclinations close to 90Њ, the scatter in differential radial velocities permit a close giant planet in a more highly inclined orbit.On-line material: machine-readable table

Multi-season optical modulation phased with the orbit of the super-Earth 55 Cancri e

“…These variations illustrate a need to treat MOST observations on a similar timescale. Traditional techniques (Rucinski et al 2004;Rowe et al 2008;Dragomir et al 2013) consist in correcting these stray-light systematics on short sequences (e.g., of two-day length). Typically, the short time series are phase folded at the satellite orbital period and a moving average filter is iteratively removed for each of them.…”

The Solar Wind in Time II: 3D stellar wind structure and radio emission

“…κ 1 Ceti is estimated to be the second youngest star in our selected sample, with an age of 0.65 Gyr (Rosén et al 2016). The observed rotation period from photometry is 9.2 days (Messina & Guinan 2003;Rucinski et al 2004, ground and space respectively). The higher levels of activity in this star are apparent when we examine the ZDI map, with nondipolar geometry and relatively strong B field (B r,max ≈ 35 G, do Nascimento, Jr. et al 2016).…”

Investigating stellar surface rotation using observations of starspots

“…With the recent launch of several photometric space missions, the high accuracy, high cadence, stellar light-curves are now also revolutionising the active star research. These missions include the Canadian micro-satellite MOST (for results on active stars see, e.g., Rucinski et al 2004 andSiwak et al 2011) and the French CoRoT satellite (e.g., Lanza et al 2009;Silva-Valio et al 2010;Huber et al 2010). The real break-through happened, though, with the launch of the NASA's Kepler satellite.…”