HOP 0287

abstract of observational proposal

The flow and magnetic fields surrounding an active region (AR) filament play an important role in filament formation, their evolution and disruption. AR filament eruptions are often related to coronal mass ejections (CMEs) (e.g., Low et al. 2001, JGR 106, 25141; Gopalswamy et al. 2003, ApJ 286, 562). CMEs are the most energetic events in the solar system expelling up to 1013 kg of coronal material from the Sun at speeds of several hundreds to thousands of kilometers per second. Since AR filaments and CMEs are closely connected and the primary cause of space weather disturbances, we need to understand their properties, especially their ultimate origin, precursors, and near-Sun evolution in order to predict them. Filaments are embedded in magnetic fields. Their plasma is sustained against gravity by magnetic field lines. There are several models which aim to explain this phenomenon. The sheared arcade models show sheared field lines below an unsheared coronal arcade (Antiochos et al. 1994, APJL 420, 41) where plasma can be stored. Eventually, reconnection can happen between the sheared and overlying unsheared field lines producing helical field lines (DeVore and Antiochos 2000, APJ 539, 954-963) which are typically called flux ropes. The well-know flux-rope model from van Ballegooijen and Martens (1989, APJ 343, 971-984) attempts to explain how these helical structures are formed in the chromosphere or corona when combining photospheric converging flows and shearing motions at the magnetic neutral line producing reconnection processes. So far, there are only few observations of active region filaments to support the aforementioned models (e.g., Okamoto et al. 2008, APJ 673, L215-L218; Lites et al. 2010, APJ 718, 474-487; Kuckein et al. 2012, A&A 539, A131; Kuckein et al. 2012, A&A 542, A112; Xu et al. 2012, APJ 749, 138). Furthermore, such a study requires simultaneous and coordinated observations of several layers of the Sun, including spectropolarimetry.

mproved measurements of the photospheric and chromospheric three-dimensional magnetic and flow fields are crucial for a precise determination of the origin and evolution of AR filaments. We will carry out such measurements based on high-resolution vector magnetograms and three-dimensional flow field observations. Transverse flow field measurements will be based on speckle reconstructed intensity images. This provides a more realistic approximation of the real plasma velocity fields rather than velocity measurements derived from longitudinal magnetograms. Combining photospheric and chromospheric vector magnetograms (e.g., Yelles Chaouche et al. 2012, APJ 748, 23) will make it possible to understand how AR filaments are formed and how they eventually evolve towards a CME.

request to SOT

SOT G-band and Ca II H images will be used to provide the evolution of horizontal-flow fields in photosphere and near chromoshpere.

SP data will furnish the information about the photospheric magnetic field for the region by using the two magnetically sensitive Fe I λ630.15 nm and λ630.25 nm lines and the nearby continuum to obtain Stokes IQUV spectral profiles.

SOT ~1140 Mbits/day
Combination of SP and FG observation with SP as first priority. The observing procedure is the same for every day during the coordinated observing run.

SP ~400 Mbits/hr, ~800 Mbits/day
Context SP IQUV scan (fast map, for 64'' x 123'', 0.32'' slit, 14 min) at the beginning and end of the coordinated high cadence observing run. Continuous high cadence SP IQUV scans (fast 32''x 123'', 0.32'' slit, 7 min cadence) centered on the magnetic neutral line during the coordinated observation.

FG ~170 Mbits/hr, ~340 Mbits/day
Ca II H and G-band image sequence during coordinated observation (2-minute cadence, 111'' x 111'' FOV, 2 x 2 pixel binning).

other participating instruments

GREGOR:
Blue imaging channel (BIC) Sequences of G-band (λ430.7 nm) images will be used to investigate horizontal proper motions, to find associations with small-scale magnetic fields (proxy-magnetometry), and to match the spectroscopic data to observations from space (Hinode and SDO). Along with it we will be taking image sequences in blue continuum (λ450.6 nm). Images will cover a field-of-view (FOV) of 75'' x 93'' and with a cadence of 30 s.

GREGOR Fabry-Pérot Interferometer (GFPI) We will acquire spectropolarimetric data in the spectral lines Fe I (λ630.2 nm) and Fe I (λ617.34 nm). The choice of Fe I (λ630.2 nm) will enable us to cross-calibrate GFPI data with Hinode SP data. GFPI data will cover a FOV of 50'' x 38'' and have a cadence of 30- 90 s depending on the setting chose to scan the spectral line (GFPI, Puschmann et al. 2012, AN 333, Issue 9, 880).

GREGOR Infrared Spectrograph (GRIS) We will use the spectrograph in the 1μm window to obtain all four Stokes IQUV spectral profiles in Si I λ1082.7 nm (photosphere) together with He I λ1083.0 nm (chromosphere) scanning a field of view 60'' x 60'' (GRIS, Collados et al. 2012, AN 333, Issue 9, 872).

VTT:
ChroTel Chromospheric full-disk images (Ca II K, Hα, He I λ1083 nm, 2k x 2k pixels) will be provided by ChroTel (Kentischer et al. 2008, Proc SPIE, 7014, 701413).

COMP-S:
Coronal Multichannel Polarimeter for Slovakia (CoMP-S) operated at Lomnicky Peak Observatory (COMP) is a 2D multi-channel spectro-polarimeter. It is attached to a 200/3000 ZEISS coronagraph, but with a neutral filter, measurements on the solar disk are also possible. The observations will cover areas large enough to enclose the filament; and three spectral lines (Hα λ656.3 nm, He D3 λ587.5 nm and Ca II λ854.2 nm) that probe different temperature regimes in the filament will be used (Kucera et al. 2010, Contrib. Astron. Obs. Skalnaté Pleso 40, 135; Schwartz 2012, Contrib. Astron. Obs. Skalnaté Pleso 42, 135)

SST:
SST observations will be carried out by Adur Pastor Yabar (PI). The CRISP instrument will acquire the full Stokes vector at two different wavelengths: Fe I λ617.3 nm and Ca II λ854.2 nm.

IRIS:
With IRIS we selected OBS-ID 3860108092. This will provide slitjaw images in spectral lines C II, Si IV, Mg II h/k, and Mg II h/k wing with FOV 120" x 120" and cadence of 36.3s. Large sparse 64-step raster scan will cover FOV of 64" x 120" with an exposure time of 8s and a repeat cadence of 581s. Because flares could be related to active region filaments, we will be using flare linelist. The resulting data rate will be ~0.5 Mbit/s.

SDO:
We will use SDO/HMI and SDO/AIA images for the global overview.

remarks

Time period of proposed observations: 10 days from 10 August - 19 August 2015
We request Hinode support for 2 hours of observing time on 10 days during the time window specified below. Observations on consecutive days are desired, but not necessary. Like other ground-based HOPs, it requires fairly high priority until some good data is obtained at Tenerife, then priority can drop down. We will inform the Hinode teams well in advance about the local weather condition.

Time window in day: The best seeing conditions at Tenerife are from 8:30-10:30 UT in August. Continuous observations within that time window are requested to cover the temporal evolution of magnetic and flow fields. However, the time window and its duration are not rigid. We highly appreciate suggestions from Hinode team and will be able to adjust accordingly.

Target of interest: An active region with a filament and well define magnetic neutral line would be the preferred target. We would prefer to follow the same region for the whole observing campaign, if it matches the above criteria. Observer on site will specify detailed pointing and inform Hinode team every day.

Dr. Meetu Verma
Post-doctoral researcher
Leibniz-Institut für Astrophysik Potsdam (AIP) An der Sternwarte 16, Potsdam, Germany
phone: +49 331 7499 450 (office in Potsdam, Germany)
+34 922 329 142 (VTT Tenerife)