HOP 0044

abstract of observational proposal

Objective: To characterize the physical parameters (densities,
temperatures, abundances flows) of coronal hole plumes with coordinated
multi-spacecraft observations, and relate changes of the photospheric
magnetic fields to understand the physical processess that lead to the
formation of these stable structures.

Scientific Justification: Despite many previous observations, mostly
from SOHO, the contribution of coronal hole plumes to the fast solar
wind is still a matter of debate. The_ heating, acceleration
mechanisms, and the role of the observed waves are not known. We have an unique opportunity to coordinate SUMER, CDS and UVCS (SOHO), TRACE and STEREO observations with Hinode to provide detailed measurements of these features during solar minimum.

request to EIS

DETAILS:
Electron temperature:

on-disk: The Hinode/EIS study will include a large number of lines from different ionization stages.

off-limb: The ratio of the strong forbidden [Fe XII] 1242,1359 A and [Fe XI] 1467 A observed by SUMER with any of the bright dipole-allowed Fe XII, Fe XI lines observed by Hinode/EIS [cf._ Del Zanna \& Mason, 2005a,b] is strongly temperature-sensitive. With these measurements we will be able to check the results obtained from the SUMER Mg IX temerature-sensitive ratio, the only direct measurements obtained so far for plumes.

Electron density:
on-disk: Hinode/EIS_ provides_ excellent line ratios for plume observations, in particular Mg VII, strong at the base of plumes (see Del Zanna et al., 2003 for SOHO/CDS measurements).

off-limb: Hinode/EIS has a wide range of coronal line ratios that can be used to accurately measure the electron density.

Chemical composition:

on-disk: Hinode/EIS upper transition region lines from low-FIP elements (e.g. Mg, Si, Fe) will be matched to SOHO/CDS-NIS2 high-FIP neon lines.

off-limb:_ Hinode/EIS low-FIP lines (e.g. Mg, Si, Fe) will be matched to _high-FIP lines observed by SOHO/SUMER (oxigen, neon), together with Ly-series lines, which will provide absolute measurement against the hydrogen abundance.

EIS count rates and studies:

on-disk: previous EIS observations of coronal holes clearly show that exposures of the order of 50s are sufficient. Polar plumes are as bright as the quiet Sun (or more) in upper transition region lines, and a study with a faster time cadence will be used.

off-limb: a previous off-limb campaign (in May 2007 for the Ulysses quadrature) has shown that EIS can succesfully observe off-limb, with adequate count rates. For the off-limb May campaign a special engeneering study that returned the bottom 512" was designed. A similar study will be designed to observe the south coronal hole, so EIS can obtain off-limb spectra up to 500" off-limb while the
Hinode/SOT is still pointed within the Sun (the existing EIS study is also a possibility). 50 pointing positions with a step size of 6'' can cover a large_ 302''x 512'' area in about 4h.

other participating instruments

SoHO/UVCS/SUMER/CDS, TRACE, STEREO

SOHO/UVCS will provide measurements of chemical abundances and flows higher up in the corona during_ 30 October - 5 November.

SUMER will start observing on Nov 2.
SUMER will acquire a series of spectra including lines suitable for electron temperature and density diagnostics, for the determination of the speed along the plane of sky (Doppler Dimming) and for abundance studies. The SUMER sequence is_ based on the experience acquired from a study run during the April 2007 campaign (see
<http://www.mps.mpg.de/homes/curdt/hinode/res7.htm>), sampling a 280"x300" FOV just above the limb, in order to obtain representative plume and inter-plume observations. Note that the SUMER study will run over more than one day.

We are also seeking support from SOHO/CDS, TRACE.
CDS will provide complementary information to EIS, TRACE will provide
high-cadence imaging.

The timing of this observation is important: in October we will have the unique possibility to have Hinode observations in conjunction with SOHO/SUMER. Also, the angular separation of the STEREO satellites is optimal. It is only now in solar minimum that we can clearly observe plumes in fully developed coronal holes.

remarks

TARGETS

The south_ or north coronal hole. The north coronal hole will be slightly (4 degrees) more tilted towards Earth. However, we shall recommend the hole that has larger spatial extent. on-disk: one sequence of observations on disk each day lasting 3 hours.

A first set will consist of a mosaic of 40" slot images with emission lines that will allow measurements of density and radiance variations with high cadence. A second set will consist of a repetition of a 2" step raster covering _a relatively small area (e.g. 128x128) centred on the base of a plume. Normally, plumes are long-lasting (days) recurrent features, so any SOHO or

STEREO image of the previous day should be sufficient for the pointing. off-limb: one EIS observation of about 4-5 hours each day during the period_ 30 October - 5 November, with a FOV of 300''x 512''_ (SOT pointed near the limb)

On the day that SUMER will run the off-limb observation (between Nov. 2nd and 5th), it is important to have at least three repetitions of these 4 hours studies at SUMER beginning, centre and end of observation.