Fabry-Perot Approach to SPRING Sanjay Gosain NSO

Why do we need a network? Solar synoptic observations with good duty cycle are essential for space weather research, as well as important research topics such as helioseismology. Examples: (i)Continuous magnetogram data are required for realtime characterization of non-potentiality (helicity, shear, netcurrents etc.) in Active Region (AR), which is key to flare/CME forecasting, and to make coronal field models. (ii)Long span of continuous observations are essential to provide high frequency resolution in power spectra of solar oscillations (key to successful inversion of oscillation data) without spurious periodicities due to observing gaps such as due to diurnal cycle. 93% annual mean duty cycle needs 6 site network, and 82% with 5 site network (Hill et al. 1985)

Observational Requirements for SPRING Space weather research requirements: Fulldisk Vector Magnetograms : at photospheric and chromospheric heights (to observe magnetic field evolution in ARs and filaments, and to build better coronal field models). Field-of-View:Fulldisk Ang. resolution: 1” (4k x 4k) or 2”? Temp. Resolution:5-10 minutes Fulldisk Dopplergrams : at multiple heights to study wave propagation and infer energy transport, study acoustic wave interactions with surface magnetic fields and to characterize systematics in local helioseismology. Field-of-View:Fulldisk Ang. resolution: 1” (4k x 4k) or 2”? Temp. Resolution:at least 1 minute

Filtergraph Approach to SPRING 1. Michelson Interferometer : Examples: GONG, MDI, HMI Advantage: large FoV, stable, compact Disadvantage: Not suitable for multi-wavelength work as proposed in SPRING 2. Lyot type filters: Examples: UBF, Chromag Advantage: large FoV, high contrast Disadvantage: Requires lot of Calcite, Dual beam polarimetry not possible, slow tunability, low transmission for narrow passbands 3. Magneto-optical-filter : Examples : MOTH, GOLF Advantage: stability, large FoV Disadvantage: Not suitable for multi-wavelength work as required in SPRING 4. Fabry-Perot Interferometer: Examples: IBIS, CRISP Advantage: Large wavelength range, rapid tunability, high transmission Disadvantage: Field dependent passband shift, ghost reflections, long term drifts.

Helioseismic Large Region Interferometric Device (HELLRIDE) Instrument, VTT Multiline Imaging Spectrometer Dual Etalon system Several lines (10-15) per minute FoV 100 arcsec Fast prefilter changing stage Staiger, J. in A&A, 5353, 83, 2011

HELLRIDE instrument in Fulldisk Mode Simulation Parameters: R 0.95 No Absorption No surface defects Etalon Aper. 7.5 cm Telescope 20 cm Ang. Magn. 3 Prefilt FWHM 1.4 A Prefilter T max 80% Simulations were done to evaluate the performance of single FP for fulldisk observations with HELLRIDE instrument. Single FP can be used for fulldisk velocity measurements when D Tel /D FP is 3 or 4. For FP aperture 5cm maximum Telescope Dia: 20cm, for 7.5 cm aperture etalon, upto 30 cm is acceptable. For large telescope : e.g. 1m with FP aperture 5 cm Passband shift across the disk is large (comparable or more than FSR). In such case tandem etalon configuration is required.

Simulation with SOLIS data SOLIS is a Fulldisk Slit-spectrograph (2k x 2k x 128 x 4) Long-slit scans the full solar image in N-S direction Fe I 630.2nm : Stokes-I,V observations are done in 12 min. Stokes I,Q,U,V observations in 25 min. Ca II 854.2nm : Stokes-I,V in 45 minutes Stokes-I,Q,U,V in 45 minutes

Simulation with SOLIS data Disk CenterSolar Limb Angular shift of FP and prefilter are not same. Prefilter coatings may be optimized for angular shift matching or similar to etalon

HELLRIDE Fulldisk Tests During 2015 test fulldisk multi-line dopplergrams were obtained.  long time series possible: Instrument stable enough. Future tests  Implement a diffuser + lens system to obtain Flat-fields  Online spectral drift monitoring system: using Laser  Simultaneous white-light camera for image restoration.  Polychromatic Polarimeter: to obtain LOS/vector magnetic and velocity maps in various lines.

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