Summary on Option-A
H. Hara (NAOJ)
2010 Mar 11

Prime Mission Description• Explore the origin of solar magnetic activity
cycle from out-of-ecliptic observations(observations: helioseismic, total irradiance,
TR & coronal imaging/spectroscopy, andheliospheric, and in-situ observations)Option-A related Sub-WG Activity• Helioseismology and Dynamo sub-WG– Reported by Sekii, Brun, Kosovichev,
Appourchaux(Solar Orbiter), Finsterle (TSI)• Engineering (Orbit and Spacecraft) sub-WG– reported by Kawakatsu
Important steps given from the previous science
meeting. Orbit & S/C are becoming feasible.

• UV/EUV sub-WG– Reported byTeriaca• X-ray telescope sub-WG– Reported by Korreck• Other (heliospheric physics)– Reported by Isobe, Hara

Can we send S/C to the vantage point ?
Orbit & Spacecraft• Two orbit candidates shown with investigations of S/Cfeasibility.
• Final orbit: 1 yr period, 1.0 AU circular
40 deg max heliosphehic-latitude
rotating the Sun synchronized with Earth– SEP Option: technical challenges driven by presenceof ion engines. Maybe limited observing opportunity inthe first few years.
– Jupiter Option: probably conservative orbit
methodology. Limited data rate in the first 4 years.
• Which will be preferable from various points including thetechnical readiness? This is an important input toengineering group.

Helioseismology & Dynamo• Expected outcome– Meridional flow
• where and how the flow sinks• How it evolves in the 11-yr activity cycle– Differential rotation• all latitudes covered– Convective structures and its evolution in highlatitudes– Motions of magnetic structures in highlatitudes– Polar field evolution

Discussions (1)• Will it really work for advancing theresolution of the dynamo problem?
– No question! Selection of the final S/C orbit isappropriate for the dynamo issues.
– If the signature of magnetic flux tube in CZ isfound, it will be an additional big jump.

Discussion (2)• Multi-instrument helioseismology to first see thedeep convection zone in a good accuracy.
Possible?
– Timing is not a problem [ done by SOHO + obs. at Earth ]– Spatial co-registration (knowledge of geometry for twospacecrafts) not a problem.
– Minimize instrumental effects by using the sameobservables and the same line

• Can we use an imaging photometer for
helioseismology? [ not preferred ]– S/N is about 10 times lower in intensity– More modes observed in velocity

Discussion (3)• Can a huge telescope in ecliptic be replaced
regarding the Option-A science?
– Short time coverage near polar regions– Field-of-view is small to see the deep CZ• Solution of spacecraft at L5 (L4) reasonable todo helioseismology?
[ for some specific problem ]– Large angle helioseismology limited nearequatorial tachocline, no gain in high latitude
regions

Discussion (4)• Why 40 deg?
– Latitude of 0-60 deg covered with MDI– 30 deg appears to be the minimum number, but
not correct (see Sekii’s presentation)– For spatial integration, 30+α deg required inhelioseismology– What α is actually needed?
α=10 deg is a value from helioseismology

Discussion (5)• Difference with Solar Orbiter– Continuous observations at any orbital phase in thefinal orbit– Fast arrival at high inclination orbit for a S/C mission life
– Duration of observations at inclination above 30 deg:
>60 days for each hemisphere vs ~20 days in SO– Higher telemetry rate by a factor of >7 at least for
helioseismic observations. Much higher rate is possible
when S/C approaching to the Earth at lower latitudes– Contain TSI observation– Thermally stable observing conditions at 1 AU
– Complementary mission

Discussion (6)• Difference with SDO– Polar regions covered– Complementary mission

Discussion (7)• Other science topics– Thank you for inputs by Luca Teriaca on solarwind, by Kelly Korreck on the coronal imaging– But some topics are raised from Option-Asupporters• Heliospheric imaging observations by H. Hara and
H. Isobe who inspired by STEREO-HI observations• Cosmic ray observations by Hiroaki Isobe whoinspired by Ulysses results– Need to define the role of in-situ measurements
more clearlyToward Mission Proposal forOption-A• Prime description of the Mission– Science goals• Payload to achieve the science goals• Technical feasibility and readiness• International Option-A Team framework