Lower limit for differential rotation in members of young loose stellar associations

Abstract

Context. Surface differential rotation (SDR) plays a key role in dynamo models and determines a lower limit on the accuracy of stellar rotation period measurements. SDR estimates are therefore essential to constrain theoretical models and infer realistic rotation period uncertainties. Aims. We measure a lower limit to SDR in a sample of solar-like stars belonging to young loose stellar associations with the aim of investigating how SDR depends on global stellar parameters in the age range (4−95 Myr). Methods. The rotation period of a solar-like star can be recovered by analyzing the flux modulation caused by dark spots and stellar rotation. The SDR and the latitude migration of dark-spots induce a modulation of the detected rotation period. We employed longterm photometry to measure the amplitude of such a modulation and to compute the quantity ∆Ω phot = 2π P min − 2π Pmax that is a lower limit to SDR. Results. We find that ∆Ω phot increases with the stellar effective temperature and with the global convective turn-over timescale τ c , which is the characteristic time for the rise of a convective element through the stellar convection zone. We find that ∆Ω phot is proportional to T 2.18±0.65 eff in stars recently settled on the ZAMS. This power law is less steep than those found by previous authors, but closest to recent theoretical models. We investigate how ∆Ω phot changes in time in a ∼1 M star. We find that ∆Ω phot steeply increases between 4 and 30 Myr and that it is almost constant between 30 and 95 Myr. We find also that the relative shear increases with the Rossby number Ro. Although our results are qualitatively in agreement with hydrodynamical mean-field models, our measurements are systematically higher than the values predicted by these models. The discrepancy between ∆Ω phot measurements and theoretical models is particularly large in stars with periods between 0.7 and 2 d. Such a discrepancy, together with the anomalous SDR measured by other authors for HD 171488 (rotating in 1.31 d), suggests that the rotation period could influence SDR more than predicted by the models.

CARMENES input catalogue of M dwarfs

“…For this, we carefully selected 47 single, inactive M dwarfs with previous published P cycle and P rot (Savanov 2012;Robertson et al 2013;Suárez Mascareño et al 2016, 2018Wargelin et al 2017;Küker et al 2019) and the stars of our sample for which we have found P cycle and P rot (see Table 2). In our sample of field M dwarfs we did not include fast-rotating, probably very young M dwarfs tabulated by Vida et al (2013Vida et al ( , 2014 and Distefano et al (2016Distefano et al ( , 2017. Figure 8 shows the plot P cycle /P rot vs. 1/P rot in log-log scale.…”

Activity cycles in members of young loose stellar associations

“…In Distefano et al (2016) (hereafter Paper I) we investigated the rotational properties of these stars and we determined a lower limit for their SDR (Surface Differential Rotation). In the present paper we focused in their magnetic activity.…”

Evidence of radius inflation in stars approaching the slow-rotator sequence

“…Data may also come from inhomogeneous estimates, like those in which v sin i upper and lower limits are obtained from different analyses and instrumentation, as long as they are not affected by significant biases. Uncertainties due to surface differential rotation (SDR) are also estimated, with the most likely values derived from the recent work of Distefano et al (2016). The method is applied for the first time to the rich dataset available for the Pleiades.…”