COSMO K-COR ONAGRAPH SCIENCE GOALS

The COronal Solar Magnetism Observatory (COSMO) is a proposed facility dedicated to studying coronal and chromospheric magnetic fields and their role in driving solar activity such as coronal mass ejections (CMEs). COSMO is comprised of 3 instruments: 1) a 1.5 m coronagraph dedicated to the study of coronal magnetic fields; 2) a chromospheric and prominence magnetometer ; and 3) a K-coronagraph. The National Center for Atmospheric Research (NCAR), via the National Science Foundation (NSF), provided full funding for the COSMO K-coronagraph, which was recently deployed to the Mauna Loa Solar Observatory (MLSO) in Hawaii. It will measure the polarization brightness (pB) of the K-corona formed by Thomson scattering of photospheric light by coronal free electrons. With a field-of-view of 1.05 to 3.0 solar radii and an image cadence of 15 seconds, it is ideally suited for studying the formation and propagation of CMEs which are the primary driver of space weather at Earth. It replaces the aging MLSO K-coronameter ( currently known as Mk4) which had been in operation since 1980.

COSMO K-CORONAGRAPH SCIENCE GOALS• Understand the formation of CMEs and their relation to other forms of solar activity

• Identify Earth-directed CMEs (halos) in real time

• Determine the density distribution of the corona over solar cycle time scales

• Measure the radial brightness profiles from 1.05 Rּס to beyond 1.5 Rּס in magnetically open regions.

The objective lens is made of fused silica, which is extraordinarily pure and has very low levels of birefringence. K-cor observes at a wavelength of 735 nm with a 30 nm pass band filter. The corona is recorded using two modified Photon Focus MV-D1024E-160 1024 x 1024 cameras with frame rates of 140Hz, full well depth of 185,000 photoelectrons and full CameraLink interface. The instrument uses a 4-state Stokes definition scheme to record the Stokes vectors I, Q, and U, where I is the total intensity and Q and U are the linear polarization states. A pair of 2-state Ferroelectric Liquid Crystals change the state of the modulator. A calibration diffuser provides flat-field and absolute intensity of coronal gain.

The COSMO K-CoronagraphAn instrument designed to study CME formation, evolution and acceleration … coming this fall! (2013)

Joan Burkepile(1), Alfred deWijn(1), Steve Tomczyk(1), Scott Sewell(1), Dennis Gallagher(1), Greg Card(1), Alice Lecinski(1), Brandon Larson(1), Lee Sutherland(1), Pete Nelson(2), Pei Huang(3), Rich Summers(1), Don Kolinski(1), Leonard Sitongia(1), Allen Stueben(1), Ben Berkey(1) 1=National Center for Atmospheric Res.; (2) = Sierra Scientific Solutions (3) = Huang Assoc. CONTACT INFO: Joan Burkepile, Principal Investigator: [email protected] Alfred deWijn, Instrument Scientist: [email protected]

OPTICAL DESIGN

2 5 2 5 - S P - 3 0 0 0 ( Z e m a x M o d e l ) _ G a l l a g h e r _ 1 _ 9 _ 2 0 1 2 d . Z M XC o n f i g u r a t i o n : A l l 2

3 D L a y o u tK - C o r o n a g r a p h P o s t - P D R B a s e l i n e1 / 9 / 2 0 1 2

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2734 mm total optical track

High Quality Fuse Silica Objective Lens

AFT OPTICS

2 5 2 5 - S P - 3 0 0 0 ( Z e m a x M o d e l ) _ G a l l a g h e r _ K _ C O R _ F I N A L _ M u l i t i C o n f i g . z m xC o n f i g u r a t i o n : A l l 2

3 D L a y o u tK - C o r o n a g r a p h P o s t - P D R B a s e l i n e5 / 1 8 / 2 0 1 2

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Color Corrector LensCemented doublet

1st imaging lens group- Two element lens common to both optical paths.One plano concave. one plano-convex lens

Common GlassesS-LAL-7S-NPH1S-LAL14SF1

50X50mmBeam splitterSF1

Lyot Stop 0.92X(85%)

Lyot Spot

F/1.93385 mm EFL

IMAGING ASSEMBLY (ZOOMED)

AFT OPTICS (ZOOMED)

2 5 2 5 - S P - 3 0 0 0 ( Z e m a x M o d e l ) _ G a l l a g h e r _ K _ C O R _ F I N A L _ M u l i t i C o n f i g . z m xC o n f i g u r a t i o n : A l l 2

3 D L a y o u tK - C o r o n a g r a p h P o s t - P D R B a s e l i n e5 / 1 8 / 2 0 1 2

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Plano BK7 field lens from OptoSigma 011-4575

Band pass filter and vignettingdisk.

FLC Modulator

Color Corrector optics

Beam splittercamera lens assembly

Occulter Station

IMAGING ASSEMBLY

2nd imaging lens group 2X – 2 lensesOne plano-convex, one plano-concave

Calibration optics

Objective Lens

Occulter and Field Lens

Aft Optics:

Modulator

Beam Splitter

Imaging Assembly

Mechanical Layout of K-coronagraph

WHY BUILD A GROUND-BASED CORONAGRAPH?Information of the very low corona is needed to study the formation of CMEs . The 1-2 million degree corona has a scale height of order a tenth of a solar radius (~60,000 km). Most of the mass and magnetic free energy resides in this first scale height. Most CMEs form in this region. Space-based coronagraphs have provided spectacular images and invaluable information about the outer corona and CME properties that are impossible to attain from the ground. These coronagraphs are externally occulted to attain very low stray light levels needed to see the outer corona. The price paid is to over-occult the solar disk blocking the inner corona. LASCO C2 blocks the corona up to 2.0 solar radii and STEREO COR2 up to 2.5 solar radii. Internally occulted coronagraphs can view the very low corona. STEREO COR1 is such a coronagraph and views down to 1.50 solar radii, but still 4 scale heights above where most of the coronal material resides.

The COSMO K-coronagraph is specifically designed to view the corona into the first scale height (down to 1.05 solar radii) with a high enough cadence (15 seconds) to study the birth and evolution of CMEs from the ground at a fraction of the cost (5%) of a space-based coronagraph. The Mauna Loa site provides pristine sky conditions needed to view the corona.

DESIGN HIGHLIGHTS:

• Field-of-view: 1.05 to 3 solar radii• Temporal cadence: 15 seconds with goal of 8 seconds ( vs. 3 minutes for the MLSO Mk4 K-coronameter)• 20 cm aperture• Internally occulted• Pass band: ~720 to 750 nm• Out-of-band rejection <= 1 part in a million (factor of 10 better signal – to – noise than the MLSO Mk4 K-coronameter• Minimization of scattered light through use of unocated, ultra-high quality singlet objective lens, Hepa clean air system, baffles, coatings, and

out-of-band rejection filters.

STATUS

The K-coronagraph installation at MLSO was completed in September 2013. The instrument is currently operating in engineering mode while it undergoes final systems checks and calibration verification. Qualitative movies and images will be provided in the last two weeks of November. The goal is to provide fully calibrated data by the end of 2013 from the Mauna Loa web site: http://mlso.hao.ucar.edu

We are grateful to design panel members Clarence Korendyke (NRL), David Elmore (NSO) and Scott Spuler (NCAR / Earth Observing Lab) for their time, expertise and constructive insights on the K-coronagraph design. NCAR science is supported in part by the National Science Foundation (NSF)

A K-cor image composited with a SDO AIA 171 image both from October 31, 2013. K-cor is the first white light coronagraph able routinely view into the first scale height of the corona (1.05 Rsun) outside of an eclipse.