* TITLE: Multi-wavelength observations of coronal hole plumes at solar minimum. * AUTHORS: Giulio Del Zanna (P.I.) UCL / Mullard Space Science Laboratory, UK gdz[at]mssl.ucl.ac.uk Vincenzo Andretta INAF / Osservatorio Astronomico di Capodimonte, Italy andretta[at]oacn.inaf.it Yuan-Kuen Ko Harvard-Smithsonian Center for Astrophysics, USA yko[at]cfa.harvard.edu Giannina Poletto INAF / Osservatorio Astrofisico di Arcetri, Italy poletto[at]arcetri.astro.it Luca Teriaca Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany teriaca[at]mps.mpg.de Angelos Vourlidas Naval Research Laboratory mailto:vourlidas[at]nrl.navy.mil * PARTICIPATING INSTRUMENTS: SOHO/SUMER SOHO/CDS SOHO/UVCS Hinode/EIS Hinode/SOT Hinode/XRT TRACE STEREO/SECCHI-EUVI/COR1 N.B.: A Hinode Operation Plan (HOP) has been set up for this campaign; it has been assigned number 44 (http://www.isas.jaxa.jp/home/solar/hinode_op/hop.php?hop=0044) * SCIENTIFIC OBJECTIVE: To characterize the physical parameters (densities, temperatures, abundances, flows) of coronal hole plumes with coordinated multi-spacecraft observations, and relate changes in the photospheric magnetic fields with changes in the observed plasma properties in order to understand understand the physical processess that lead to the formation of these stable structures. * SCIENTIFIC JUSTIFICATION: ** ABSTRACT: 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. ** MAIN TEXT: Plumes are ray-like structures ubiquitous in coronal holes, in particular during solar minimum. Despite many observations from SOHO and other instruments, the contribution of plumes to the fast solar wind is still controversial. Also, the heating, acceleration mechanisms, and the role of the observed waves are not known. With SOHO/CDS we were able to measure temperatures, densities and chemical abundances near the footpoints (see Del Zanna et al. 2003). However the limited spatial resolution of CDS did not allow accurate measurements across plumes. Line-of-sight measurements of line shifts with SOHO/SUMER suggest outflow speeds of the order of 10-20 km/s at the base of the coronal holes (see, e.g. Wilhelm et al 2000), and even lower at the base of polar plumes. Doppler dimming techniques applied to SOHO/SUMER and UVCS spectra taken at larger heights have produced contradictory results (see, e.g. Gabriel et al. 2003, Teriaca et al., 2003), with similar outflows speeds in interplumes but completely different results in plumes. Quasi-periodic 10-minutes fluctuations in intensity have been observed in plumes (cf. DeForest and Gurman 1998) and have been interpreted as slow magnetoacustic waves propagating at 75-150 km/s. However, detailed spectroscopic observations have been lacking. The origin of the formation of plumes might be related to magnetic reconnection processes occurring in the low atmosphere, but SOHO/MDI measurements have not provided conclusive evidence. ** DETAILS ON THE OBSERVATIONAL STRATEGY: 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. Outflow speed: off-limb; UVCS will observe the H lyman alpha line (and possibly OVI doublet lines at 1032-1037 Angstrom) to provide via Doppler dimming techniques an estimate of the outflow speed in plume/interplume plasma. Intensity fluctuations and origin of plumes: High-temporal spectroscopic EIS observations with high-cadence TRACE imaging and Hinode/SOT magnetograms. ** REFERENCES Deforest, C. E., & Gurman, J. B. 1998, ApJL, 501, L217 Del Zanna, G., Bromage, B. J. I., & Mason, H. E., 2003, A&A, 398, 743 Del Zanna, G., Mason, H.E., 2005a, Adv. Space Res., 36, 1503-1511 Del Zanna, G., Mason, H.E., 2005b, A&A, 433, 731-744 Gabriel, A. H., Bely-Dubau, F., & Lemaire, P., 2003, ApJ, 589, 623 Teriaca, L. et al., 2003, ApJ, 588, 566 Wilhelm, K., Dammasch, I. E., Marsch, E., & Hassler, D. M. 2000, A&A, 353, 749 * DETAILED OBSERVING SEQUENCES PER INSTRUMENT: ** SOHO/SUMER [POC: W. Curdt] 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. Currently, the SUMER observations for this campaign are scheduled for the period Fri, Nov. 2, 12:00 UT - Sat, Nov. 3, 24:00 UT (see also: http://www.mps.mpg.de/homes/theissen/scr/planning/mktoptable.cgi?print=no) ** SOHO/UVCS [POC: Y.-K. Ko, G. Poletto]: The UVCS spectrometer will observe at increasing heliocentric distances the Hydrogen Lyman alpha line, acquiring values of the line intensity both in plumes and in the interplume ambient. We expect to acquire data from about 1.6 to 4-5 solar radii. At the lower altitude we may be able to observe also the OVI lines at 1032 and 1037 A: this will allow us to derive the outflow speed of the OVI ion, which is different from the H outflow speed. Because of the long exposure time required by OVI line observations this analysis will probably be limited to one or two heliocentric distances. Currently, the UVCS observations will cover the full period of the campaign: Tue, Oct. 30, 16:00 UT - Mon, Nov. 5, 16:00 UT. ** SOHO/CDS [POC: P. Young, G. Del Zanna]: on-disk: a 4'x4' (or smaller) raster which would mainly include transition region lines, to be repeated a few times (4-5 hours). Possible studies: STRONGLI (To be confirmed): takes about 60 min and covers most of the strong CDS lines. off-limb: one observation of about 4-5 hours each day, with a FOV of about 300''x 240''. This could be a series of pointings of the NISAT_S6/v24 (26m 15s, 40"x240"). On the day of the large SUMER raster, the sequence should be repeated at least at the beginning, middle and end. ** HINODE/EIS [POC: L. Culhane]: EIS count rates and studies: On-disk: previous EIS observations of coronal holes 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 such time cadence will be used. Off-limb: a previous off-limb campaign (in May 2007, for the Ulysses quadrature: HOP 7 [http://www.isas.jaxa.jp/home/solar/hinode_op/hop.php?hop=0007]) has shown that EIS can successfully observe off-limb, with adequate count rates. We plan to run a study to cover a large 300"x512" area in about 1h10m, to be repeated 4 times each day, and as many times as possible during the SUMER observation. Hinode/SOT pointing should be close to the limb, so almost half of the EIS FOV will be off-limb. ** HINODE/SOT [POC: TBD]: Full-resolution NFI magnetograms (if operational) and SP scans of the photospheric magnetic fields as they evolve during the formation of plumes are essential to understand the role of magnetic reconnection in heting these structures. Ca II H observations. ** HINODE/XRT [POC: TBD]: High cadence (20s exposure?) observations in a single filter (Al-poly) with a 512"x512" field of view, to characterise the evolution of hotter plasma. ** TRACE [POC: Dawn Myers(?)]: High cadence 171 768"x768" images with 195 and WL in context. ** STEREO/SECCHI [POC: A. Vourlidas]: COR1: Synoptic observations will be sufficient to provide electron densities at the heights observed by SOHO/UVCS. EUVI: Non-compressed, deep exposures (TBD) in the 171 band, for morphology and 3-D reconstruction of the plume geometry. Note: A similar program has already run in the campaign of April 2007. * OPERATIONAL CONSIDERATIONS AND TARGET SELECTION: ** TARGET: 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. ** MODES OF COORDINATED OBSERVATIONS: 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. 128"x128") 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"x512" (SOT pointed near the limb) On the day that SUMER will run the off-limb observation, it is important to have at least three repetitions of these 4 hours studies at SUMER beginning, centre and end of observation. * PROPOSED OBSERVATION DATES The timing of this observation is important: in November 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. The upcoming period of availability of SUMER will last about two weeks, starting on 2 November, possibly even a few days earlier; the observations should take place during the period 30 October - 5 November (inclusive). ** NOTES: TRACE is are already committed to a THEMIS campaign on 30 October.