More Rapidly Rotating PMS M Dwarfs with Light Curves Suggestive of Orbiting Clouds of Material

Abstract

In a previous paper, using data from K2 Campaign 2, we identified 11 very low mass members of the ρ Oph and Upper Scorpius star-forming region as having periodic photometric variability and phased light curves showing multiple scallops or undulations. All of the stars with the "scallop-shell" light curve morphology are mid-to-late M dwarfs without evidence of active accretion and with photometric periods generally <1 day. Their phased light curves have too much structure to be attributed to non-axisymmetrically distributed photospheric spots and rotational modulation. We have now identified an additional eight probable members of the same star-forming region plus three stars in the Taurus star-forming region with this same light curve morphology and sharing the same period and spectral type range as the previous group. We describe the light curves of these new stars in detail and present their general physical characteristics. We also examine the properties of the overall set of stars in order to identify common features that might help elucidate the causes of their photometric variability.

Rotation of Low-mass Stars in Upper Scorpius and ρ Ophiuchus with K2

“…Furthermore, only young stars have been found to exhibit these LC morphologies. We have discussed many of these stars in two previous papers (Stauffer et al , 2018. Although there is no detailed physical model to explain these LC morphologies, their photometric variability almost certainly must be due to gas and dust orbiting the star in a stable configuration at the star's Keplerian co-rotation radius.…”

“…In Table 5, we list all of the USco and ρ Oph stars identified as belonging to this category in Stauffer et al (2017Stauffer et al ( , 2018. We also list 10 additional stars whose phased LCs have features that may fall in this category, but where the features are less obvious or the signal-to-noise ratio of the LC is relatively poor or where other K2 artifacts make interpretation of the LC difficult.…”

“…The observed distributions of those quantities for the early M stars show similar trends, but not at a statistically significant level. The correlation between rotation and binarity for USco and our other K2 clusters will be discussed at greater length in a future paper (J. R. Stauffer et al 2018, in preparation).…”

“…David et al (2016b) discuss one of these stars in detail. Stauffer et al (2018) identify an additional eight stars in USco and ρ Oph with similar LC morphologies, as well as three additional similar stars in Taurus using K2 Campaign 13 data.…”

“…10. Scallops and flux dips-narrow flux dips, unusual but repeatable shapes in their phased LCs, some of which change shape slightly after a flare; interpreted as arising from orbiting clouds of material and/or dusty debris near the Keplerian co-rotation radius (see Stauffer et al 2017Stauffer et al , 2018. 11.…”