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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).

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Photometric monitoring by amateurs in support of a yy gem professional observing session

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
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
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
Can Amateurs ProvidethisSupport?

  • 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
The Team


All sky calibration needed
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
Typical Light Curve from Amateur Observer


Observers at shorter wavelengths find larger flare amplitude
Observers at Shorter Wavelengths Find Larger Flare Amplitude



Flare amplitude has well defined spectral index
Flare Amplitude Has Well-Defined Spectral Index


This flare occurs during secondary transit
This Flare Occurs During Secondary Transit


Combining light curves produces primary secondary transit shapes
Combining Light Curves Produces Primary & Secondary Transit Shapes


Transit depths vary with wavelength but secondary is deeper than primary
Transit Depths Vary With Wavelength, But Secondary is Deeper Than Primary


An explanation for secondary depth to be greater than primary today
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 amplitude vs wavelength
OOT Variation Amplitude Primary Todayvs. Wavelength


Cfht preliminary results
CFHT Preliminary Results Primary Today

  • 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
Summary of Amateur Observations Primary Today

  • 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
Summary of Amateur Findings Primary Today

  • 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
Final Thoughts Primary Today

  • 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


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