4/7/21

 Given some brown dwarfs and their associated light curves,what are we looking at when we want to decide whether the objectis “variable” or not? Some answers:(a) What “data quality class” is it in?(1) (How many of its datapoints are ‘good’ vs ‘info’ vs ‘warn’vs ‘severe’)?(b) Is the star “variable”?(1) What’s its Stetson index?(2) What’s its reduced chi-squared in each band?(3) Does the star show significant periodicity, according tothe Lomb-Scargle diagram?(c) Does the star show significantcolorvariability? (What arethe rchi2 values for its J-H and H-K colors? Is there periodicitydetectable in these “differenced” channels?)(d) If the star is variable, how would we classify its variability?Some possible answers:(1) nonvariable / flat (this is a “null hypothesis” answer)(2) rotators, including:(A) sinusoidal periodic, like a perfect rotator(B) differential rotator (sinusoidal with some drift in thephase and/or amplitude)(C) sinusoidal plus linear/secular drift(3) other periodic stars:(A) AA Tau / periodic disk dipper variables(B) eclipsing binaries of any sort (unlikely in our sample)(C) f95 types (including, like, the actual f95): periodicdisk brighteners(4) non-periodic variables:(A) short timescale, irregular accretion “bursty” activity(B) long timescale, changes in disk geometry(C) one-off “dipper” events(D) also, consider classifying this kind of variability byits color change behavior(E) sometimes we’ll see “compound color variability”,i.e. a star having clear “dust reddening” but then switch to“blueing disk geometry changes” and back, etc (as describedby Rice et al. (2015)).(5) other weird cases, which we can handle as they arise...