1 / 25

NRH and LOFAR Scientific and technical aspects

NRH and LOFAR Scientific and technical aspects. A. Kerdraon Observatoire de Paris - LESIA - USN. 4th LOFAR KSP meeting Potsdam 2010 November 8-9. NRH - LOFAR. Comparisons / differences UV coverage Software and data formats Science requirements Solar activity and bursts.

percy
Download Presentation

NRH and LOFAR Scientific and technical aspects

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. NRH and LOFARScientific and technical aspects A. Kerdraon Observatoire de Paris - LESIA - USN 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9 4th LOFAR KSP meeting Potsdam 2010 November 8-9

  2. NRH - LOFAR • Comparisons / differences • UV coverage • Software and data formats • Science requirements • Solar activity and bursts. • Quiet sun thermal emission. 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9 4th LOFAR KSP meeting Potsdam 2010 November 8-9

  3. Nançay Radioheliograph vs LOFAR General characteristics (Lofar is red) Frequency range: 150 - 450 MHz ( 30 - 250 MHz) 648 baselines from 50 to 3200m (25 to 4,800 l) (< 30 to > 10000 l) Spatial resolution: ~4 to 0.3 arcmin (depending on frequency, declination, snapshot/synthesis) ( better than 0.2 arcmin at 150 MHz) Field of view: from 10 to 3 degrees (> 3 degrees at 150 MHz)) Stokes I and V (4 Stokes) Time resolution: 0.1 to 0.2 typ. ( could be < 0.1s ? Depending on the frequency range ?) Works in progress on NRH: Realtime computer: will need a > 1 month stop in 2011 (when?) Correlator: will be changes in 2012. We consider a move to a more standard data format after. Observations will stop a few month

  4. NRH -> LOFAR KSP: Interferometry U-V coverage The solar corona is a broad complex source: u-v min < 30 l. Main problem: negative bowl due to poor uv sampling around the origin. Strong impact on quiet Sun TB. Different size scales ( from 1 degree to a fraction of arcmin) A dense coverage is needed at D < 1000m Diffusion of radio waves in the corona broadens sources: baselines > 10-20 km may not useful (probably, but…) Field of view: Inverse of UV min -> largest structure observed, > 3 degrees Primary beam: > 6 degrees -> field of view around the sun. CMEs, ejectas, may be observed at very high altitudes To a lesser extent, type III also 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  5. NRH - LOFAR Centre of UV plan Lofar: orange NRH= brown Snapshot uv coverage: at common frequencies, cross-calibration should be easy. LOFAR alone has not so many visibilities ! 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9 4th LOFAR KSP meeting Potsdam 2010 November 8-9

  6. NRH - LOFAR NRH Light blue: snapshot coverage Blue: denser uv coverage Will LOFAR increase the spatial resolution on snapshots? Is it possible to have more baselines in the core ? Currently, the uv sampling is low at U,V > 1000m 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  7. NRH - LOFAR NRH Light blue: rotationnal synthesis UV coverage Dark blue: snapshot UV coverage With rotationnal synthesis (not shown explicitly, let us imagine a 7h rotation), LOFAR has a much greater UV coverage then NRH -> images of the quiet sun Again: the snapshot uv coverage is very sparse. 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  8. NRH - LOFAR • Software aspects: • LOFAR: Casa or any Aips-like software. MS or uvfits formats: • Lot of work to get 1 image. Solutions may be: • Write python scripts • Export to Uvfits • In any case, we have to make utilities to handle large numbers of images. • NRH: proprietary visiblities files format. May export FITS images files. • Has a lot of utilities to merge with other solar observations • Cannot export MS or uvfits format (to do ?) • Some capabilities to merge with other radiotelescopes (namely: GMRT) with an uvfits import. 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  9. NRH – LOFARSolar activity • Expected science (from previous NRH observations): • T III bursts (electrons beams) • In relation ship with flares and CMEs: they seem to be reasonnably connected to Interplanetary medium at 150 MHz • Low frequency spectras • Direction finding in space • Comparisons with space coronagraphs, B extrapolations etc. • But positions at higher altitudes may help ( 100 – 30 MHz range). Also an increase in spatial resolution and sensitivity. • For type IIIs storms,( typ. < 80 MHz), and any particles acceleration high in the corona, everything has to be done 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9 4th LOFAR KSP meeting Potsdam 2010 November 8-9

  10. NRH – LOFARSolar activity • Shocks Type II radio bursts: • Sometimes at meter l, often at decameter l. • At meter wavelength • Often emission at 2nd or 3rd harmonic at a time. • Seams to be located on the CMEs sides. • May be difficult to compare with decameter, or interplanetary shocks. • With LOFAR: • Much more bursts. • More frequencies for a better understanding. • Connection with interplanetary shocks (?) 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9 4th LOFAR KSP meeting Potsdam 2010 November 8-9

  11. NRH - LOFAR • Quiet sun emission: what benefits ? • We are speaking of the slowly varying thermal emission, on which we can apply rotationnal synthesis • We think now that increased spatial resolution make sense at 150 MHz: features are not spatially resolved, like bright lanes or small holes. • Features (magnetic ?) are symplifying when the wavelength (i.e. the altitude) increases, probably this evolutionwith the altitude will continue in the 150 – 50 MHz range -> solar wind. • All examples are from Mercier, C. and Chambe, G. • (to be published in Solar Phys. end of 2010) 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9 4th LOFAR KSP meeting Potsdam 2010 November 8-9

  12. 2005 Aug 15 : 432 410 327 226 164 151 MHz. Typical with central coronal hole 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  13. 2008 Jun 6: very quiet sun445 432 408 360 327 298 270 228 173 150 MHz. 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  14. 2008 Jul 14 hole and large bright/dark features445 432 408 360 327 298 270 228 173 150 MHz. 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  15. 2010 may 15 holes and NS large features445 432 408 361 327 299 271 228 173 151 MHz. 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  16. NRH - LOFAR • Models of quiet corona • 2 components: • Corona ( Ne, T) isothermal, vertically stratified. • Transition region: fitted to EUV emission measure. • TB < Tc at 400 MHz, TB = Tc at 100 (?) MHz • Parameters may differ in different structures (holes, bright structures, “mean” quiet sun…) • TB = TC (optically thick) may be reached in the meter range, but not everywhere on the sun. • Optically thin regime is expected at f < 66 MHz 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9 4th LOFAR KSP meeting Potsdam 2010 November 8-9

  17. 2004 jun 27: no saturation at Tc in the hole, the hole is not visible at 150 MHz 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  18. 2007 may 23: No saturation at Tc in the hole, still cold at 150 MHz 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  19. 2007 jun 10: bright feature spectrum needs a different model (structuration by B) 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  20. 2008 jun 8: mean quiet sun is too hot at 450 MHz, the small « pore » can be fitted. 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  21. NRH - LOFAR • Quiet sun programm • Increase the frequency coverage at low frequencies: • Better models: effect of the magnetic field on the stratification, non isothermal models, solar wind acceleration… • Increase the spatial resolution: • Better measurement of TB (there are a lot of samll scale structures) 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  22. NRH - LOFAR • Some conclusions • Quiet sun: daily observations > 1 week in spring/summer, with at least a common frequency (150.9 MHz) with NRH and > 2 lower frequencies • Active sun: on a good candidate region, a good set of frequencies and high time resolution (better than 1 sec). • Small scale spectral features: high time resolution, what set of frequencies ? (zebra, pulsations and more at LF) 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  23. NRH -> LOFAR KSP : time/frequency sampling for solar radio bursts 0.1 sec, 200 kHz bandwidth, 5 to 20 frequencies With 20 frequencies, it is possible to have a raw spectrum of different sources. With the 200 kHz bandwidth, only I and V are required In a spectrograph mode (one or a few stations), 4 Stokes make sense if the bandwidth is <10 kHz. Ability to obtain a large observing time: This is mandatory to « get something ». If its possible only in the LF band of Lofar, it is still OK, assuming that NRH is observing at the same time (calibration ?) 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  24. NRH - LOFAR Thank you 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9

  25. 4th LOFAR solar KSP meeting Potsdam4th LOFAR KSP meeting Potsdam 2010 November 8-9 Bastian et al. (2001)

More Related