Rotation in the Pleiades With K2. I. Data and First Results

Abstract

Young (125 Myr), populous (>1000 members), and relatively nearby, the Pleiades has provided an anchor for stellar angular momentum models for both younger and older stars. We used K2 to explore the distribution of rotation periods in the Pleiades. With more than 500 new periods for Pleiades members, we are vastly expanding the number of Pleiads with periods, particularly at the low mass end. About 92% of the members in our sample have at least one measured spot-modulated rotation period. For the ∼8% of the members without periods, non-astrophysical effects often dominate (saturation, etc.), such that periodic signals might have been detectable, all other things being equal. We now have an unusually complete view of the rotation distribution in the Pleiades. The relationship between P and (V − K s ) 0 follows the overall trends found in other Pleiades studies. There is a slowly rotating sequence for 1.1 (V − K s ) 0 3.7, and a primarily rapidly rotating population for (V − K s ) 0 5.0. There is a region in which there seems to be a disorganized relationship between P and (V − K s ) 0 for 3.7 (V − K s ) 0 5.0. Paper II continues the discussion, focusing on multi-period structures, and Paper III speculates about the origin and evolution of the period distribution in the Pleiades.

NGTS clusters survey – I. Rotation in the young benchmark open cluster Blanco 1

“…We attribute this to the emergence of sufficiently deep convective envelopes (Wilson 1966), which drive the magnetic dynamos that in turn give rise to surface starspot distributions (whose longitudinal inhomogeneity drives the observed rotational modulation patterns). This increase in modulation amplitude around F5 spectral type was also noted in the Pleiades (Rebull et al 2016a). Once convective envelopes become sufficiently deep ((G -K s ) 0 ∼ 1.4, early G spectral type), there is no clear trend between modulation amplitude and stellar mass.…”

“…Nielsen et al 2013) as well as open clusters (e.g. Cargile et al 2014;Rebull et al 2016a). LS models the observed variability as a sine wave with a given period.…”

“…B18); this motivated us to use a flexible non-parametric model. For each CMD, we iteratively fit the whole cluster sequence using a GP with a stochastically-driven damped simple harmonic oscillator (SHO) kernel, as implemented in Celerite and exoplanet, and fixed the quality factor at Q = 1/2, which approximates the well-known Matern-3/2 kernel (Rasmussen & Williams 2006). At each step, we perform a running median filter on the residuals of the fit and reject 3σ outliers above the GP model in the next iteration, with this process typically converging towards a maximum a posteriori (MAP) fit to the single star cluster sequence within ∼5 iterations.…”

“…Given the very similar age estimates for these clusters, we compare their rotation period distributions to understand the level to which mass-dependent angular momentum loss mechanisms are imprinted on stars at ∼110-115 Myr. We cross-matched the Gaia-DR2 Pleiades membership list with stars from Rebull et al (2016a), which resulted in 589 Pleiads with measured rotation periods 9 . We also performed our CMD fitting technique on the Pleiades to identify likely multiple systems.…”

“…Observational studies of rotation in young open clusters date back to the 1960s, but rapidly expanded as large-scale photometric surveys arose using wide-field cameras on small-to-medium class telescopes, e.g. : the Monitor Survey (Irwin et al 2006), HATNet (Hartman et al 2010), SuperWASP (Delorme et al 2011), KELT (Cargile et al 2014), PTF (Covey et al 2016a) and K2 (Rebull et al 2016a(Rebull et al ,b, 2017Stauffer et al 2016;Douglas et al 2017Douglas et al , 2019…”