HOP 0419

abstract of observational proposal

Main Objective:
The main goal is to investigate the effects and energetics of solar flares on the lower atmosphere, by analyzing how the magnetic field geometry changes during flares at different heights and also the evolution of the continuum emission, which may indicate energy dissipation via recombination e.g., Balmer continuum or via enhanced H- emission.

Scientific Justification: In the standard flare model, electrons are accelerated in the corona and precipitate into the lower solar atmosphere, where they are assumed to be halted at chromospheric heights due to enhanced atmospheric densities. The electron beam completely ionizes the hydrogen within this layer, leading to hydrogen recombination and Balmer continuum emission that is visible within the NUV channel of IRIS (Heinzel & Kleint, 2014). The irradiation of the photosphere from the upper layers is termed "backwarming", and provides a possible additional mechanism for the enhancement of the continuum due to the large populations of H- below the temperate minimum. One can distinguish between these two process and their relative contributions to flare energy dissipation, by taking spectral measurements over a wide range of wavelengths. The energy that goes into radiation can then be calculated and compared to the input energy of accelerated electrons derived from X-ray observations. Magnetic field measurements, both at photospheric and at chromospheric levels, will allow us to investigate the magnetic restructuring during flares in 3D.

With IRIS, the NUV band can be covered to search for Balmer continuum emission. Hinode’s SP adds valuable points around 6302 A to study both the magnetic field, line, and continuum emission. SST will be used for the near-IR obtaining magnetic field measurements in Ca II 8542 and additionally several points at blue wavelengths with CHROMIS. These data will be additionally combined with data from HMI, XRT and STIX. Compared to our first study of an X-flare (Kleint et al 2016), we would like to improve the coverage in the visible, with Hinode, to better constrain the blackbody-type enhancement and we would like to improve the cadence in IRIS to determine the onset and decay time of the continuum emission. The improved cadence will also allow us to capture the evolution of transient Mg II flare-ribbon-spectra (Panos et al 2018) as well as capturing signs of possible optically thick Si IV line formation (Kerr et al. 2019).

request to EIS

We request to run the following EIS study: HH_Flare_raster_v3 (EIS Study 461), which includes a good set of coronal lines for studying flares. In addition, the large FOV will increase the chance of catching flares and improve the overlap with IRIS. If we successfully catch a flare, we will try a different study, by increasing the cadence at the cost of the FOV. Hence, if possible, we would request to switch to the following EIS study: qub_hi-cad_flare_v2 (EIS Study 530). For each study, the EIS pointing should be centered on the IRIS pointing.

other participating instruments

IRIS requests: Proposal has bee submitted to the IRIS team (Bart and Milan) and they will try to support the observations

- Sit-and-stare for high spectral cadence
- Max 8 second integration time
- AEC and rotation tracking on
- SJI 1400 and 2832 , please make sure this does not compromise the AEC
- Center slit on neutral line, or at least crossing the neutral line
- Full linelist

Please do not select the flare linelist since this is missing the Si IV 1394 A which we would like to capture

High data rate option (preferable):
3600258603 | Large sit-and-stare 0.3x120 1s Si IV Mg II w s Deep x 8 FUV spectr | 56.72 |85.27 | 1.02 | 9.5+/-0.1 | 9.5+/-0.1 | 0.0+/-0.0 | 11.6+/-4.2 | 0.0+/-0.0 | 56.7+/-0.0

If this data rate is too high, then please run for as long as possible before switching to the low data rate option:
3680108603 | Large sit-and-stare 0.3x120 1s Si IV Mg II w s Deep x 8 Spatial x 2 | 55.69 |47.78 | 0.58 | 9.3+/-0.1 | 9.3+/-0.1 | 0.0+/-0.0 | 11.3+/-4.2 | 0.0+/-0.0 | 55.6+/-0.0

If an opportunity arises, and a flare is eminent, the following full linelist zero summing high telemetry mode would be beneficial for our research goals:
3680258603 | Large sit-and-stare 0.3x120 1s Si IV Mg II w s Deep x 8 FUV spectr | 57.81 |138.36 | 1.63 | 9.6+/-0.1 | 9.6+/-0.1 | 0.0+/-0.0 | 11.8+/-4.3 | 0.0+/-0.0 | 57.8+/-0.0

remarks

Dates: 1. ToO program from Aug 11 to Aug 19, since we have observing time with SST
2-3. We will alert the planners if a suitable target is available and propose pointing coordinates. Supersonic downflows are a backup program in case only non-flaring active regions are available

Time window: Good seeing at SST most often occurs from 7.30-11.30 UT. Please schedule observations for this time range and in case of telemetry issues, prioritize 8-10 UT. SST will carry out a flare-watch program from 11.30-17 UT. Should a promising active region be available, we would very much appreciate any co-observations (even low data rate) that may be possible also from 11.30-17 UT. Short synoptic interruptions are allowed.

Target(s) of interest: Flares, i.e. complex active regions. ToO, we will alert planners if a suitable AR is available. Ideally, please position the slit across the neutral line or at leased crossing it (IRIS). Our backup program are supersonic AR downflows, for which we would ask to target the ends of AR loops that are visible in AIA 171.

Additional remarks:
Time window for good seeing at SST: 7.30-11.30 UT.

SST will do a flare watch program from 11.30-17 UT, any low-data rate co-observation of IRIS and Hinodewould be very appreciated in case flaring active regions are present.

Hinode planners: please start the observation at the end of orbital night, and finish at the beginning of orbital night to maximize telemetry.

Previous HOPs: None from current PI
from Co-Is: HOP 251 (several publications seen below), HOP 310 (lack of solar flares)

Publications:
- L. Kleint et al., ApJ, 816, 88, 2016
- W. Liu, et al., SoPh, 290, 3235, 2015
- P. Judge, L. Kleint, A. Sainz Dalda, ApJ, 814, 100, 2015
- M. Battaglia et al., ApJ 813, 113, 2015
- L. Kleint, et al., ApJ 806, 9, 2015
- P. Judge, et al., ApJ 796, 85, 2014
- P. Heinzel & L. Kleint, ApJ 794, 23, 2014