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Chromospheric Magnetograph. Andreas Lagg , Achim Gandorfer , Davina Innes MPI for Solar System Research Katlenburg -Lindau, Germany Motivation. Wishlist : Provide reliable chromospheric magnetic field measurements Simple interpretation

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chromospheric magnetograph


Andreas Lagg, Achim Gandorfer, DavinaInnes

MPI for Solar System Research




  • Providereliablechromosphericmagneticfieldmeasurements
    • Simple interpretation
    • For all solar activitylevels (QS  sunspot)
    • spatialresolution TBD
    • High temporal resolution
  • Reliableand „simple“ instrument
  • stand alonescience
candidates he 10830
CandidatesHe 10830 Å

Near-IR lines: He 10830 Å

Successfullyusedbygroundbasedobservatories (e.g. TIP-2, VTT)


B-range 1 G to several kG

ideal for coupling science

height diagnostic tool!

off-limb AND on-disk ‘easy’ to interpret(Asensio Ramos et al. 2008, Lagg et al., 2009)

he 10830 vtt tip 2
He 10830 ÅVTT / TIP-2

Photosphere: Si 10827 Å

he 10830 vtt tip 21
He 10830 ÅVTT / TIP-2

Chromosphere: He 10830 Å

he 10830 problems
He 10830:problems

IR – wavelength: need large aperturetoachievegoodspatialresolution

Formation: coronalilluminationrequired lowsensitivityfor QS regions

 Well suitedfor large ground-basedtelescopes (Gregor, ATST, good IR seeing)or large space-bornetelescopes

candidate ca ir lines
Candidate:Ca IR lines

Ca IR lines (8542 Å)

Complex non-LTE modelingrequired

Spatialresolutionsimilarto He 10830

 Leaveitfor ATST & Co

candidate ca ii h k
Candidate:Ca II H&K

Ca II H (3933 Å), Ca II K (3968 Å)


Complex non-LTE analysisrequired(chromosphericinformation „hidden“ in strong wings)

candidate mg ii h k
Candidate:Mg II h&k

IRIS 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 10830Å; except during major flares); and the range of formation for Mg II h&k is much narrower than for Hα. In effect, the Mg II h&k lines are formed under effectively thin conditions (emittedphotonsescape, albeitsubjectto 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 upperchromosphere.“

mg ii h k heritage
Mg II h&kHeritage

Rocket & 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/UiO

Solar-C Plan B

Modelling: Uitenbroek (1996), Boccialini (1996), Lemaire et al. (1981)

mg ii h k spectra
Mg II h&kspectra

Quiet Sun

LPSP instrument on OSO-8Lemaire et al. (1981)

mg ii h k spectra1
Mg II h&kspectra


LPSP instrument on OSO-8Lemaire et al. (1981)

mg ii h k spectra2
Mg II h&kspectra

Plage – Flux Levels

LPSP instrument on OSO-8Lemaire et al. (1981)





mg ii h k instrument
Mg II h&kInstrument

Full Stokes Imaging PolarimeterLyotPrefilterandoneortwoetalons

Optics/CCD: noshowstoppersfor 280 nmrange

Size? (30cm aperture = 0.235´´diff. limitresolution)

Diffraction limited performance (yes/no?) withoptiontoincrease S/N by on-boardbinning

FOV: ~240´´ (2K detector)

mg ii h k photon budget
Mg II h&kphotonbudget

IRIS instrument (diff. limited):


Mg II h&kimagingpolarimeter

``ideal´´ chromosphericmagnetograph

new stand-alone



theoreticalmodelling: A. Pietarila