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Beyond the Limb

Explore the feasibility of observing background objects using AIA beyond the solar limb. This study compares solar and stellar measurements, detects stars with AIA, and proposes methods for tracking and modeling stellar emission. The research aims to determine if observations of background objects are possible and presents findings on potential targets and observational techniques. Challenges such as path correction and off-limb intensity decay are addressed, along with future work recommendations.

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Beyond the Limb

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  1. A Narrow Band EUV search for Background Objects with the AIA Beyond the Limb Sam Schonfeld Advisors: Paola Testa and Steve Saar

  2. Contents • Motivation • Cross calibrating solar measurements • Methods: Finding Targets • Tracking targets • Modeling stellar emission • Estimating Signal • Methods: Preparing Observations • Off-Limb Intensity Decay • Satellite Path Correction • Conclusions AIA 171Å AIA 193Å

  3. Motivation: Comparing Sun and Stars • Sun is a Star at 1 AU • Spatial resolution • Test stellar models • This proximity is also a problem • Difficult to measure the Sun and anything else with the same instrument • Different telescopes use different techniques • Possible discrepancies between instruments

  4. Motivation: The AIA • Constant full sun imaging from SDO • Narrow band EUV telescopes • High resolution and cadence • Chance to observe Sun and stars together • Objectives: • Primary: Determine whether possible to observe background objects • Secondary: If possible, make observations

  5. Methods: Can AIA Detect Stars? • Pros • Star is point a source • Sun is relatively dim • AIA is sensitive • Dynamic range ≈ 104 DN • Object must be ≈103more Luminous than Sun! • Cons • Star is > 107 farther • Flux=L / (4πD2) • Extinction due to ISM

  6. Methods: Candidate Objects Selected from ROSAT x-ray observations

  7. Methods: Path Elimination 1 pixel ≈ 0.6 arc seconds

  8. Methods: Remaining Objects • 4 Stars, 3 Galaxies, 2 Galaxy Clusters, 2 Unknown

  9. Methods: Stellar EM Models PZ Tel • Emission Measure • Differential Emission Measure • Amount of emitting material • P(T)=emissivity • Use models of similar stars • Scale with distance and luminosity • AIA Temperature response functions • Based on atomic models Argiroffi et al. 2004 94 131 171 193 211 335

  10. Methods: Predicted Count Rates AIA exposure ≈ 2.9 sec

  11. Methods: Observational Techniques • Track Single pixel across field for hours • Integrate signal • Acts like a longer exposure • Takes advantage of point source • Subtract out background • Off-limb coronal emissions AIA 171Å

  12. Methods: Off-limb Coronal Emission AIA 171Å

  13. Methods: Exponential Decay 171 Å Consistent with exponential decay of coronal density 94 Å Suggests AIA noise ≈3 DN

  14. Methods: Image Offset Problem SDO is in Orbit! Earth Geostationary Geosynchronous Corrected Earth Geostationary Geosynchronous Corrected April 2011 June 2010 Dr. Bart De Pontieu

  15. Conclusion • Observation appears possible but… • Stellar sources produce count rates within the noise level • Future Work: to make observations • Finish orbit corrections • Longer exposures would allow observations • Off pointing from disk would increase number of targets • Include non-stellar targets

  16. Supplemental • HD 199143 • PMS AeFe • HD 206301 • Variable RS CVn type • HD 210803 • PMS • HD 245924 • T-Tau type

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