m d warf v ariability & t ransits i n t he n ear i nfrared ropacs meeting lisbon 2010 niall...
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M DWARF VARIABILITY & TRANSITS IN THE NEAR INFRAREDRoPACS Meeting Lisbon 2010
Niall Goudling ([email protected])
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OVERVIEW
Introduction
Selecting candidate M dwarfs
Identifying variable stars
Light curve manipulation
Some results
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INTRODUCTION
Variability of M dwarfs has a wide impact: Understanding magnetic activity and variability
of M dwarfs Implications of transit surveys Implications for astrobiology
Up to 80% of later M dwarfs are active.
Spot coverage can be over 50% and up to ~70%.
S. Sciortino et al. (1998)A. Reiners (2006)
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SELECTING M DWARFS Using relations from Covey et al (2007)
(Plots used: r-i vs g-r; z-J vs i-z; J-H vs z-J; H-Ks vs J-H; i-Ks vs g-i)
Luminosity class tracks on colour colour plots
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SELECTING M DWARFS Using relations from Covey at al (2007)
(Plots used: r-i vs g-r; z-J vs i-z; J-H vs z-J; H-Ks vs J-H; i-Ks vs g-i)
Luminosity class tracks on colour colour plots+
Polynomials fitted to standard spectral positions in 7D colour space
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ESTIMATING SPECTRAL TYPE/LUM. CLASS
Using 2MASS (JHKs) and SDSS (ugriz) filters
Each colour-colour plot estimates a class for a star.
Each colour-type plot estimates a type.
Modal class found.
Resistant mean of spectral types found to give “average” spectral type.
Sample of ~3800 potential M dwarfs in total.
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19HR FIELD SPECTRAL TYPES
Spectral Type
Frequency
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PERIODOGRAMS
M Dwarf candidate → Periodogram + folding code
Periods found in light curves with Lomb-Scargle Periodogram.
Least squares sinusoid fitting.
Generally good with intrinsic variations and deep EBs.
Not good with transits or shallow EBs.
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19.55+36.60-3_3751
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PERIODOGRAM
Period (days)
Pow
er
Peak at 7.08 days
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Periodograms have only limited use:Po
wer
Period (days)
Peak corresponding to EB period p=0.83 days
19.55+36.60-2_1819
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PROBLEMS...
Aliasing with observational period...
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PROBLEMS...
Aliasing with observational period...
Periods at 1.000, 0.500, 0.333, 0.250, 0.200 (±0.0005) days
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PROBLEMS...
Aliasing with observational period...
Periods at 1.000, 0.500, 0.333, 0.250, 0.200 (±0.0005) days
Follow up?
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SOME EXAMPLES
Spectral Type=M2.5±1.21Period= 3.82 days
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SOME EXAMPLES
Spectral Type=M2±0.61Period= 2.45 days
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SOME EXAMPLES
Spectral Type=M2±0.61Period= 2.45 days
Second period?
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SOME EXAMPLES
Spectral Type=M1±1.18Period= 17.48 days
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SOME EXAMPLES
Spectral Type=M0±2.07Period= 35.58 days
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A FEW EBS...
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A FEW EBS...
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A FEW EBS...
But only 33 variable stars so far....
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SOME RESULTS...
Spectral Type
Am
plitu
de
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SOME RESULTS...
Spectral Type
Peri
od
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SOME RESULTS...
Amplitude
Peri
od
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IMPACT OF NEARBY STARS?
90%
83%
57%
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FUTURE WORK
Improve stellar classification.
More thorough period search; follow up for longer periods.
Gain an idea of the fraction of M dwarfs that are periodically variable.
Period search in 03hr, 07hr and 17hr fields.
Can flaring events be detected in WTS light curves?
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SUMMARY
Understanding activity of M dwarfs is important for better transit models and transit identification.
M dwarf variability seems to be low level (~ ±0.01 Mag)
More periodicity needs to be found to identify p, A, and Spectral Type relations (if any).
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Thank you!