JOP050: The Smallest Observable Category of Eruptive Filaments Author(s): A. H. McAllister, S. F. Martin, K. L. Harvey, B. Lites, J. Zirker, P. Judge, J. B. Gurman (EIT), D. Zarro (CDS), D. Hassler, U. Schuehle (SUMER), T. Brown (MDI) Progress: Draft Scheme July 1996 Updated observing programs and observing schedule May 1997 Objectives: (1) define in physical terms the smallest class of filament eruption events as distinguished from other types of macrospicules. (2) understand the processes leading to the formation and eruption of these filaments. (3) investigate their role in the transport of mass, magnetic flux, and energy up into the solar corona, including interactions with large-scale overlying coronal structure. Scientific Background: --------------------- Several authors have noted that many macro-spicules observed at the solar limb have the form of small arches or erupting loops (eg. Moore, Tang, Bohlin, and Golub 1977; LaBonte 1979; Habbal and Gonzalez, 1991). Hermans and Martin (1986) made a detailed study of the smallest (10"-20") filaments on the disk. Comparing the results with the literature on macro-spicules it is clear that these filaments are the same as the erupting loop-like class of macro-spicules. The Hermans and Martin (1986) study showed that the mini-filaments form and erupt with many of the same characteristics as larger filaments. These include their location between opposite polarity fields, and frequent associations with small flares and cancelling magnetic flux. The difference is that these tiny filaments do not seem to have an extended stable phase; they form and erupt, over intervals of 15 to 200 minutes. Although they are small in scale, the large numbers of the tiny active filaments merit quantitative investigation. Hermans and Martin (1986) made a conservative estimate of 600 mini-erupting filaments per day on the whole sun, while LaBonte (1979) estimated 1400 macro-spicules per day. The large numbers and rapid evolution of these filaments also provide a key opportunity to study the filament formation and eruption processes in detail. Science Questions: ----------------- On this topic we suggest that there are at least three areas of study that could be profitably explored in collaboration with EIT, SUMER, and CDS: (1) Formation. Current theories of filament formation vary in ideas about the source of the filament mass. Obtaining data at several wavelengths, corresponding to different temperatures in the range of 10^4 to 10^5 K, might allow discrimination between scenarios, eg. cool mass being raised from the photosphere/chromosphere, or hot mass condensing out of the corona. (2) Global mass flux and energy transport. A rough estimate shows that the cumulative mass in the smallest filaments maybe on the order of 10^16 g/day, which is equivalent to a sizable fraction of the net daily outflow from the corona. Although not all of their mass is necessarily expelled into the upper corona, they might play a role in the mass loading of closed streamer regions and thus in providing mass for coronal mass ejections (CMEs). (3) Magnetic Context. The known relationship of many of these events to magnetic inversion lines and cancelling magnetic flux (Hermans and Martin, 1986) suggest that they form a link in the general evolution of the small-scale magnetic fields on the quiet sun. The study of these filaments may therefore also provide a tool for investigating the transport of magnetic flux through the photosphere and up into the corona. Targets of Opportunity: ---------------------- The Hermans and Martin study revealed that micro-filaments can be observed anywhere on the quiet sun unlike some other categories of macro-spicules which are best observed in coronal holes (Habbal and Gonzalez, 1991). During the current solar minimum, areas to target are unipolar, or mixed polarity network, under closed coronal structures. Near solar minimum polar coronal holes are not choice targets for this program. We note that the interaction of these erupting filaments with the upper corona might vary for these targets. Coordinated Observations: Ha Doppler images - Helio Research He I (1083 nm) images - NSO/Kitt Peak Filtergraph Mg, He I D3, He I 1083 nm, and other wavelengths - NSO/Sacramento Peak UBF Ly a images - SUMER Ly a, He, C, Doppler shifts and line ratios - SUMER He I (58.4 nm),O III, O IV, Si IV, Ne IV, and Ne VI, line ratios - CDS He II (30.4 nm) and Fe XI/X images - EIT Soft X-ray images - Yohkoh SXT Photospheric Magnetograms - NSO/Kitt Peak Vacuum Tel. Photospheric Vector Magnetograms - HAO Advanced Stokes Polarimeter at NSO/Sacramento Peak Chromospheric Magnetograms (854.2 nm) - Kitt Peak Vacuum Tel. High resolution Magnetograms - MDI Needed for alignment of SOHO and GBO images. Guideline parameters: FOV, 5x5 arc min; resolution, ~1"; temperature range, 10x4 K on up, with most emphasis on 1-5 x 10x4 K; time cadence target 5-10 min; duration, two 1 week campaigns, SW US daylight hours (8 a day). Detailed Programs for the groundbased sites: ------------------------------------------- Helio Research: Using an ultra narrow band Fabry-Perot etalon in a new 25cm solar telescope Sara Martin of Helio Research will observe at H-alpha over an 8 X 8 arc min field of view to be certain of encompassing all the SOHO fields, in particular the 7 X 7 field of EIT with 1" margin for pointing error. The filter has a half-width of 0.1A at H$\alpha$ and is tunable in the range of H$\alpha$ + and - 2.8 Angstroms by applying high voltage bias. For this campaign images will be taken in 0.2A steps from about Ha-0.6A to Ha+0.6A. Images at each wavelength will be recorded at 1 min. intervals. The etalon is also a universal filter in the range of 5000 to 7000 Angstroms. In a few seconds, a alternative prefilter can be rotated into the beam and the voltage changed to observe another spectral line. The observing program will include taking images in a photospheric line or low chromospheric line such as the Ca line near 6103A. These images will be taken about once an hour or at the cadence of magnetograms from MDI, and used mainly for alignment purposes. NSO/Kitt Peak: At NSO/Kitt Peak K. Harvey will acquire photospheric magnetograms (Fe I 868.8 nm), or chromospheric magnetograms (Ca II 854.2 nm) along with velocitygrams over an 8 X 8 arc min FOV at a 5 or 10 minute cadence. The magnetograms and velocity grams can be acquired at the same time, but only at one wavelength. The goal is to observe the relatively small intracell (internetwork) magnetic fields within supergranules in addition to the network and ephemeral region magnetic fields. For limb observations He 10830 line profiles can be made, yielding velocity and magnetic information in post-processing. NSO/Sac Peak and ASP: Using a 1.5 (fixed) x 4 (maximum) arc min. FOV. The time cadence is typically 10 min, for a 1.5"x 1.5" FOV, and so would be ~25 min for this large FOV. Using the ASP, B. Lites will record weak both vertial and horizontal internetwork fields. It can also observe somewhat higher using MgI b-lines, but signals there are quite weak and there is little chance of seeing IN fields. Jack Zirker will coordinate a complementary observing program taking concurrent Mg b and H$\alpha$ filtergrams using the Universal Birefringent Filter. The a 2.5" centered FOV will be used for the UBF. The Tower telescope light will be shared between the two benches. Detailed Programs for the SOHO instruments: ------------------------------------------ CDS: Using the Normal Incidence Spectrometer (NIS), observe O III, O IV, Si IV, Ne IV, Ne VI, and He I to obtain coverage in the 10-50,000 K range. Optionally add the higher-temperature sensitive lines: Mg IX, and Fe XVI. The FOV is nominally 4x4 arcmins, i.e, raster the NIS 2x240" slit in the E-W direction at 120 locations. The total raster duration is about 30 minutes, with 10 sec exposures at each location. The cadence can be increased to 15 mins, by using exposures of <5 sec, but this will reduce the S/N. A sequence called O_FFLOWS has been designed. Versions with different exposures have been produced so that fine tuning of the exposure times can be done in the first several days of the June run. SUMER: Due to the loss of the east-west tracking ability SUMER will make north-south scans at a fixed longitude. This severely limits its potential for this JOP. However it can be run along a N/S slit in the main FOV. The lines will be selected to include at least one low temperature line. Optimally a spectral region will be selected that includes several relatively strong lines that form at temperatures from the chromosphere, the transition region and the lower corona. A good pair of relatively strong lines with the required temperature characteristics are He I (58.4 nm) and O I (115.2 nm). The width and strength of these lines should yield acceptable count rates. C III is a hotter line in the same window, whose use may be explored in preliminary runs. EIT: Images will be taken in a 5 x 5 block (~ 7 x 7 arc min) subfield. 304 A images every 10 minutes, probably for < 8 hours, but as close to that as can be done, plus 195 A images every 20 minutes during the same period (i.e., stretching out the CME watch cadence somewhat to accommodate the 304's). MDI: Matched high-resolution (~ 7 x 7 arc min) subfields, for use in aligning the SOHO and ground based data sets. When available high cadence will be used to help map magnetic field and velocity evolution. The standard observing mode in which continuum and paired doppler grams are taken each minute will suit this proposal. Observing runs: -------------- Two week long runs have been scheduled, one for June 9-15, 1997 and a second for September 18-24, 1997. Each day we will observe for as much of the window from 15:00 UT to 23:00 UT as is possible at each site. June: During the first run the ASP and Sac Peak will join in at the discretion of B. Lites, who has time booked for another program. Helio Research will not take calcium images for this first run and MDI will be in Helioseismology mode but will provide full disk magnetograms at a 90 min cadence. During this run we will focus near a segment of the west limb, which we hope will allow SUMER to work within the target FOV. September: This run will certainly include the Sac Peak instruments and be able to make use of the high resolution MDI FOV. There will also be coordinated observations taken at Big Bear Solar Observatory. The target region has not yet been selected but will probably be on the disk, and should be coordinated with the MDI FOV. References: ---------- Habbal, S. R. and Gonzalez, R. D., 1991, Ap. J., 376, L25. Hermans, L. M. and Martin, S. F., 1986, in Coronal and Prominence Plasmas, ed. A. Poland, NASA Conference Publication 2442. LaBonte, B. J., 1979, Solar Phys. 61, 238. Moore, R. L., Tang F., Bohlin J. D., and Golub L., 1977, Ap. J., 218, 286.