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Low-degree Helioseismology with AIA R. HoweF. Hill, R. Komm, A.-M. Broomhall, W. J. Chaplin, Y. Elsworth
Introduction • AIA aboard SDO is best known for spectacular coronal images, BUT … • AIA’s 4500 (Visible continuum), 1700 (UV continuum), 1600 (CIV) bands are sensitive to helioseismic modes. • We can use the DATAMEAN keyword to form an l=0 time series without exporting the images. • Results can be compared with HMI and BiSON observations.
Data: Sample Images 1700 4500 1600
Data series • Available data series for AIA are: • aia_test.synoptic: May 1-11, 18-20. 10242 images, mean cadence 90s for 1600, 1700, 4500. • aia_test.synoptic2 has slower cadence (mean 120s for 1600, 110s for 1700, 103s for 4500) from May 20. • Series aia_test.lev1 has full cadence from June 09. • 4500 only at 1h from June 5. • For HMI we use hmi_test.V_45s and hmi_test.Ic_45s from May 1. • BiSON 0-d time series, 40s cadence, May 1-11. • Concentrate on May 1-11 (“Period 1”) and June 10-26 (“Period 2”).
Issues for the analysis • The data release is still in “beta testing” phase: coverage and cadence are irregular. • Ultraviolet channels are sensitive to flares. • HMI data have strong diurnal variation (mostly observer motion, with contribution from non-linear calibration.) • Data are interpolated to regular cadence (60s for AIA, 45s for HMI), detrended with 15-minute moving mean, and have spikes rejected.
Discussion and Conclusions • AIA 1600 and 1700 bands (at full cadence) look promising for helioseismology, though slightly noisier than HMI velocity. • Slight phase difference from velocity signal. • May have slightly less power in low-frequency modes, more in high-frequency, than velocity data. • Little or no granulation noise. • HMI velocity has very good signal/noise. • Longer stretches of high-cadence data will be needed to establish the detailed characteristics of the ultraviolet acoustic power spectrum.
Acknowledgments • SDO data courtesy SDO (NASA) and the AIA and HMI consortia. • BiSON is operated by the High Resolution Optical Spectroscopy group of the School of Physics and Astronomy at the University of Birmingham, UK, in collaboration with Sheffield Hallam University, UK. It is funded by the Science and Technology Facilities Council (STFC).
About the logo Thanks to Pete Marenfield of NOAO for the artistic finishing touches.