SPW5 Ascona

ChromosphericMagnetographAndreas Lagg, Achim Gandorfer, Davina InnesMPI for Solar System ResearchKatlenburg-Lindau, Germanylagg@mps.mpg.de

UCL M-Class meeting, Aug 31 2010MotivationWishlist:Provide reliable chromospheric magnetic field measurementsSimple interpretationFor all solar activity levels (QS sunspot)spatial resolution TBDHigh temporal resolutionReliable and simple instrumentstand alone science2UCL M-Class meeting, Aug 31 2010CandidatesHe 10830 Near-IR lines: He 10830

Successfully used by ground based observatories (e.g. TIP-2, VTT)Purely chromosphericB-range 1 G to several kGideal for coupling scienceheight diagnostic tool!off-limb AND on-disk easy to interpret(Asensio Ramos et al. 2008, Lagg et al., 2009)3UCL M-Class meeting, Aug 31 2010

He 10830 VTT / TIP-24Photosphere: Si 10827 UCL M-Class meeting, Aug 31 2010

He 10830 VTT / TIP-25Chromosphere: He 10830 UCL M-Class meeting, Aug 31 2010He 10830:problemsIR wavelength: need large aperture to achieve good spatial resolutionFormation: coronal illumination required low sensitivity for QS regions

Well suited for large ground-based telescopes (Gregor, ATST, good IR seeing)or large space-borne telescopes6UCL M-Class meeting, Aug 31 2010Candidate:Ca IR linesCa IR lines (8542 )

Complex non-LTE modeling requiredSpatial resolution similar to He 10830

Leave it for ATST & Co7UCL M-Class meeting, Aug 31 2010Candidate:Na D / Mg IbNa I D2 (5896 ), Mg Ib (5173 )

Probe only upper photosphere / lower chromosphere

8UCL M-Class meeting, Aug 31 2010Candidate:Ca II H&KCa II H (3933 ), Ca II K (3968 )

Good lines for chromospheric diagnosticComplex non-LTE analysis required(chromospheric information hidden in strong wings)

9UCL M-Class meeting, Aug 31 2010Candidate:Mg II h&kIRIS Science Summary:

The Mg II resonance doublet lines have superior qualities over the visible chromospheric diagnostics. The Mg+ ion does not have a meta-stable upper state (as does Ca+ associated with its infrared triplet) which simplifies its radiative transfer; Mg+ is not significantly affected by excitation through absorption of coronal emission (unlike He 10830; except during major flares); and the range of formation for Mg II h&k is much narrower than for H. In effect, the Mg II h&k lines are formed under effectively thin conditions (emitted photons escape, albeit subject to scattering) while having a ~20-fold higher opacity (mostly because of the higher abundance). Consequently, the Mg II h&k lines have a much higher contrast relative to the Ca II H&K doublet for small structures higher in the atmosphere, while being revealing such small structures over a larger range in optical depth because the lines are effectively thin. In addition, we note that the broad wings of Mg II enable tracing of perturbations from the upper photosphere into the upper chromosphere.10UCL M-Class meeting, Aug 31 2010Mg II h&kHeritageRocket & Balloon Experiments: e.g. Lemaire & Skumanich (1973), Morrill et al. (2001, HRTS flights 1975-1997), Samain & Lemaire (1982)IRIS (Interface Region Imaging Spectrograph)LMSAL, LMS&ES, SAO, ARC, MSU, LSJU, ITA/UiOSolar-C Plan BModelling: Uitenbroek (1996), Boccialini (1996), Lemaire et al. (1981)

11UCL M-Class meeting, Aug 31 2010Mg II h&kspectra12

LPSP instrument on OSO-8Lemaire et al. (1981)Quiet SunUCL M-Class meeting, Aug 31 2010Mg II h&kspectra13LPSP instrument on OSO-8Lemaire et al. (1981)Plage

UCL M-Class meeting, Aug 31 2010Mg II h&kspectra14LPSP instrument on OSO-8Lemaire et al. (1981)Plage Flux Levels

400055018003500UCL M-Class meeting, Aug 31 2010Mg II h&kInstrumentFull Stokes Imaging PolarimeterLyot Prefilter and one or two etalonsOptics/CCD: no showstoppers for 280 nm rangeSize? (30cm aperture = 0.235 diff. limit resolution)Diffraction limited performance (yes/no?) with option to increase S/N by on-board binningFOV: ~240 (2K detector)15UCL M-Class meeting, Aug 31 2010Mg II h&kphoton budgetIRIS instrument (diff. limited):16

UCL M-Class meeting, Aug 31 2010Mg II h&knoise level17

Mg II KQuiet SunActive RegionFlareIntensity(counts/s/spectral pixel/spatial pixel)25 m spectral pixel1100450010000Polarimeter (33% eff.)5s integration time(counts/spectral pixel/spatial pixel) 40 m spectral pixel29001200026500Polarimetric accuracy(noise level) for Q, U, Vdiff. limited1.85%0.92%0.62%Polarimetric accuracy(noise level) for Q, U, V3x diff. limit0.62%0.3%0.2%UCL M-Class meeting, Aug 31 2010SummaryMg II h&k imaging polarimeter``ideal chromospheric magnetographnew stand-alonesupport science for coronal measurementsphotospheric channel?

theoretical modelling: A. Pietarila18UCL M-Class meeting, Aug 31 2010