HOP 0026

abstract of observational proposal

1. OBJECTIVE: To study the differences between both photospheric and chromospheric oscillations associated with granules and intergranular lanes.
SCIENCE JUSTIFICATION: Analysis of coarse-resolution TRACE UV imaging time series has shown that oscillations are present in the solar magnetic network at frequencies below the cutoff predicted by standard acoustic wave theory (see, e.g., Krijger et al. 2001). In this scenario such low-frequency waves should not propagate beyond the temperature minimum, but the phase behaviour associated with upward-propagating waves is observed in the outer atmosphere. The recent work of
Bloomfield et al. (2006), comparing the variation of phase behaviour with the underlying magnetic field, suggests that these waves are magneto-acoustic slow modes while Jefferies et al. (2006) propose that they are transmitted through "magneto-acoustic portals" -- regions at the edge of supergranular convective cells where the acoustic cutoff frequency is reduced by the presence of inclined
magnetic fields (Bel & Leroy 1977). We aim to search for the locations where differing forms of waves enter the outer atmosphere through the investigation at high spatial resolution of both oscillation frequencies and amplitudes, in addition to the phase relations observed between the photosphere and chromosphere.

2. OBJECTIVE: To study the distribution of field inclinations in both bright and
dark penumbral structures, any associated spatial differences in wave behaviour, and the centre-to-limb variation of these effects.
SCIENCE JUSTIFICATION: Recent work using high spatial resolution ground-based imaging (Langhans et al. 2005) indicates that the dark cores of bright filaments harbour the most inclined fields in sunspot penumbrae while bright filaments have much less inclined fields. Currently, two competing theories exist to explain the observed fine structure of sunspot penumbrae: 1) the "uncombed" model of Solanki & Montavon (1993), and 2) the "gappy" model of Spruit & Scharmer (2006). The
first theory proposes that the penumbral atmosphere contains flux tubes of nearly horizontal magnetic field with a less inclined magnetic field surrounding it, while the second proposes that the near-horizontal fields are located at magnetic cusp points lying above field-free regions of the atmosphere. These two theories should yield differing speeds and preferred directions of wave propagation associated with bright penumbral filaments, due to the different nature of the atmosphere underlying these structures (i.e., magnetic or non-magnetic). It is such behaviour that we aim to study in a sunspot at differing positions across the solar disk, using the technique of wave detection from full-Stokes spectropolarimetry of Bloomfield et al. (2007).

request to SOT

1. 1) SOT-SP: Complete cycle (I->III) to be run.
I) Context (deep magnetogram) SP map of surrounding
quiet-Sun region:
Time per exposure: 19.2 s (12 waveplate rotations),
FOV along slit: 164 arcsec,
Slit scan sampling: 0.16 arcsec,
Time for map area: 1940 s (101 steps=16 arcsec).
II) Fixed slit (normal mode) SP observations at map centre:
Time per exposure: 4.8 s (3 waveplate rotations),
FOV along slit: 164 arcsec,
Slit scan sampling: 0 arcsec,
Time for map area: 10800 s (2250 exposures).
III) Context (deep magnetogram) SP map of surrounding
quiet-Sun region: (same as run I).
2) SOT-BFI: Complete cycle (I->III) to be run. If data rate permits:
Co-temporal with SP time series:
I) Ca II H imaging at high cadence (~3-6 s?),
II) CN-band imaging at high cadence (~3-6 s?),
III) G-band imaging at high cadence (~3-6 s?).
However, if data rate is already large, then:
I) Context CN-band and G-band images,
II) Ca II H imaging at high cadence (~2-6 s?) co-temporal
with SP time series,
III) Context CN-band and G-band images.
OPTIONAL (Data rate permitting)
3) SOT-NFI: Photospheric dopplergrams in Fe I 5567.1 \AA +/- 0.045
\AA at high cadence (~4-6 s?).

2. 1) SOT-SP: Complete cycle (I->III) to be run once a day (at the
very least, once every other day) as a sunspot transits
the solar disk.
I) Fixed slit (normal mode) SP observations halfway
through leading penumbra (with rotation compensation
applied):
Time per exposure: 4.8 s (3 waveplate rotations),
FOV along slit: 164 arcsec,
Slit scan sampling: 0 arcsec,
Time for map area: 10800 s (2250 exposures).
II) Context (normal mode) SP map of whole sunspot:
Time per exposure: 4.8 s (3 waveplate rotations),
FOV along slit: 164 arcsec,
Slit scan sampling: 0.16 arcsec,
Time for map area: 2500 s (500 steps = 80 arcsec).
III) Fixed slit (normal mode) SP observations halfway
through trailing penumbra: (same as run I).
OPTIONAL (Data rate permitting)
2) SOT-BFI: Ca II H imaging at high cadence (~4-6 s?) including the
entire sunspot and some surrounding quiet sun in FOV.
3) SOT-NFI: Photospheric dopplergrams in Fe I 5567.1 \AA +/- 0.045
\AA at high cadence (~4-6 s?) including the entire
sunspot and some surrounding quiet sun in FOV.

remarks

Main observing window: 8-11 UT

1. POINTING REQUIREMENTS: The chosen region should sample a quiet region of the solar disk, preferably close to disk centre (so that the difference in sampling
heights between photospheric and chromospheric observations does not manifest itself in radially-orientated features being displaced horizontally).

2. POINTING REQUIREMENTS: The SP slit should be located about halfway through the leading penumbra (for the first time series run) and halfway through the trailing penumbra (for the second time series) in order for the slit to sample both bright and dark penumbral structures. Both penumbrae need observing as they provide information from differing magnetic geometries with respect to the LOS when away from disk centre. The context map should record the sunspot and some nearby quiet
sun. If the sunspot is very large (i.e., >~80 arcsec between the penumbra/QS boundaries) and the scan-time required is too long, then two smaller maps of 251 steps (i.e., 40 arcsec) centred on each of the time series slit locations will instead be suitable.

1) SMALL SUNSPOT:
POS 2 POS 1
| QUIET SUN |
| _____________ |
|/ \|
| PENUMBRA |
/| _____ |\
/ | / \ | \
| | / \ | |
| | | UMBRA | | |
| | | | | |
| | \ / | |
\ | \_____/ | /
\| |/
| |
|\_____________/|
| |
| |
|<-------------|------------->|
SLIT SCAN RANGE FOR CONTEXT MAP

2) LARGE SUNSPOT:
POS 2 POS 1
| QUIET SUN |
| ___________________ |
| / \ |
|/ \|
| PENUMBRA |
/| |\
/ | _______ | \
/ | / \ | \
| | / \ | |
| | / \ | |
| | | | | |
| | | UMBRA | | |
| | | | | |
| | \ / | |
| | \ / | |
\ | \_______/ | /
\ | | /
\| |/
| |
|\ /|
| \___________________/ |
| |
|<-----|----->| |<-----|----->|
SLIT SCAN RANGES FOR CONTEXT MAPS