Photometric Monitoring by Amateurs in Support of a YY Gem Professional Observing Session

B. Gary (AZ), Dr. L. Hebb (TN), J. Foote (UT), C. Foote (UT),

R. Zambelli (Italy), J. Gregorio (Portugal), J. Garlitz (OR), G. Srdoc (Croatia),

T. Yada (Japan), A. Ayiomamitis (Greece)

Professional Astronomer’s Goal

• M dwarf star radii & temperatures can’t be modeled: 5-10% larger than models & cooler than models

• Might be due to magnetic fields that: 1) affect convection, 2) produce starspots, 3) produce polar starspots that mislead transit shape interpretation (wrong radii)

• Dr. Leslie Hebb funded to measure polarization vs. orbital motion & locked stellar rotation w/ spectropolarimeter on 3.6-meter CFHT (Hawaii) during January 4-13, 2012

• Will create polarization maps versus phase

Support Needed That Might be Met by Amateurs

• Need to know precise eclipse shapes vs. wavelength for accurate size solution

• Need to know precise Out-of-Transit (OOT) shape vs. wavelength to constrain star-spot solution

• Need to know level of flare activity during CFHT observations to assess representativeness of CFHT magnetic field measurements

Can Amateurs Provide this Support?

• YY Gem is bright, so small telescopes OK• Orbital period = 19.5 hrs; so long observing sessions

needed (coordinated to overlap)• Light curve creation & combining same as for

exoplanets• Many amateurs are experienced exoplanet observers• Coordinated amateur observing already

demonstrated• Professional observatories too expensive

The Team

All-Sky Calibration Needed

All-sky magnitudes for reference star (“1”) are used to combine LCs.

Other nearby stars used for reference to improve precision.

Typical Light Curve from Amateur Observer

Observers at Shorter Wavelengths Find Larger Flare Amplitude

Combining All Observers Shows that Flare Amplitude Decreases

with Wavelength

Flare Amplitude Has Well-Defined Spectral Index

This Flare Occurs During Secondary Transit

Combining Light Curves Produces Primary & Secondary Transit Shapes

Transit Depths Vary With Wavelength,But Secondary is Deeper Than Primary

An Explanation for Secondary Depth to be Greater Than Primary Today

• Starspots are believed to exist on both YY Gem stars

• Starspots are caused by magnetic field concentrations (inhibiting stellar atmosphere movement)

• Changes in starspots are likely

• A starspot location change can change transit depth, conceivably causing secondary to be deeper

• Is there evidence for presence of starspots?

• Yes, notice out-of-transit (OOT) variation in following sequence (going from g’- to z’-band)

OOT Variation at g’-Band

OOT Variation at r’-Band (Smaller)

OOT Variation at i’-Band (Smaller)

OOT Variation at z’-Band (Almost Gone)

OOT Variation Amplitude vs. Wavelength

CFHT Preliminary Results

• 34 averaged I & V Stokes parameter velocity profiles obtained for all phases during 10 nights

• Data quality is good (high SNR)• Preliminary starspot maps for both stars look good • There are 2 spot complexes on both stars; no polar

spots• Field strength maps for both stars look good. • Analysis still underway

Summary of Amateur Observations

• 9 observers with 8 band coverage: B,V,Rc,Ic,g’,r’,i’,z’• 127 light curves obtained• 93 of these during the 10-day CFHT observations;

almost continuous temporal coverage• 44 complete transits, most with multi-band coverage• Prior to 10-day CFHT, 56 non-overlapping hours of

observations (only one small flare) • During 10-day CFHT, 180 non-overlapping hours of

observations (20 flares)

Summary of Amateur Findings

• During the 10-day CFHT observations flare activity was elevated, implying that at least one star was undergoing magnetic field disturbances

• Star spots were present but at different locations on at least one star compared to 1971 observations

• Accurate transit shapes and depths for primary and secondary transits were obtained from B- to z’-band, and these will provide useful constraint for size solution

Final Thoughts

• This photometry monitoring support was provided by a coordinated network of amateurs, which would have been prohibitively expensive for professionals

• This is one more illustration of how professional/amateur collaborations can contribute to science when professional budgets are constrained