Gavin Ramsay, J. Gerry Doyle

The view from K2: Questioning the traditional view of flaring on early dM stars

Figure 5. The cumulative flare frequency (in seconds) versus U-band flare energy (in erg) for different classes of dwarf stars and TYC1330 and RXJ0626. Data is taken from Hilton (2011): Active M3-M5, 332 hours on 4 stars observing 157 flares; Active M6-M8, 59 hours on 4 stars observing 39 flares; Less Active M3–M5, 147 hrs on 8 stars observing 28 flares; Inactive M0-M2, 256 hours on 16 stars observing 9 flares; Inactive M3-M5, 153 hours on 6 stars observing 3 flares; Active M0-M1, data from Moffett (1974), Doyle & Mathiouidakis (1990) and Dal & Evren (2011), 156 hours on 2 stars observing 63 flares. In addition, we include from Shibayama (2013) a line for solar maximum and minimum which used a bolometric/GOES X-ray flux relation derived from work by Kretzschmar (2011). Data for active G dwarfs are taken from Shibayama et al (2013) which took 46,000 hrs of observations on 4 stars observing 116 flares.


We use K2 short cadence data obtained over a duration of 50 days during Campaign 0 to observe two M1V dwarf stars, TYC 1330-879-1 and RXJ 0626+2349. We provide an overview of our data analysis, in particular, making a comparison between using a fixed set of pixels and an aperture which follows the position of the source. We find that this moving aperture approach can give fewer non-astrophysical features compared to a fixed aperture. Both sources shows flares as energetic as observed from several M4V stars using both Kepler and ground based telescopes. We find that the flare energy distribution of the sources shown here are very similar to the less active M3–M5 stars but are ∼8 times less likely to produce a flare of a comparable energy to the more active M0–M5 stars. We discuss the biases and sources of systematic errors when comparing the activity of stars derived from different instruments. We conclude that K2 observations will provide an excellent opportunity to perform a census of flare activity across the full range of M dwarf spectral class and hence the physical mechanisms which power them.

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Last Revised: 2015 March 10th