HOP 0334

abstract of observational proposal

Main Objective:
We propose an IRIS-SUMER(SOHO)-Hinode, GBOs observation campaign, with the possibility of observing with SUMER, perhaps for the last time, in lines (e.g., Lyman alpha) which complement those of IRIS.

Scientific Justification:
Background: The hydrogen Lyman α doublet at 121.6 nm (Vial 2006) along with the Mg II doublet at 279.6 and 280. 3 nm are strong resonance lines which play a major role from both viewpoints of chromosphere diagnostic and energetics (see e.g. VAL and FAL models; Vernazza et al. 1981 ; Fontenla et al. 1991). This major role is also valid in other various solar structures such as active regions, sunspots and filaments/prominences (in this last case, see e.g. Heinzel et al. 2014, Vial et al. 2016). Whatever the solar structure is, the Lyman α line is formed at a temperature no lower than 10 000 K (except of course in the corona where it is about one million K) while the Mg II doublet is formed at much lower temperatures no higher than 15 000 K (at which Mg II is ionized into Mg III). This implies that the Lyman α and Mg II k and h lines are complementary, e.g. in terms of sounding the low to high chromosphere (and other structures). Moreover, the photons at different positions in the line profiles are formed at different altitudes (or depths) in such a way that the photons in the Lyman α wing are formed in the same region as the photons from the core of the Mg II lines.

Motivation: The latest opportunity for observing simultaneously Mg II h and k with hydrogen Lyman α traces back to the seventies (OSO8 )! During the whole lifetime of SOHO, only a few observations in the Lyman α line have been performed with SUMER for instrumental reasons. They are even more scarce after the launch of IRIS and the only dedicated effort of coordination has been attempted during the first week of December 2016 more as a technical rehearsal (from SUMER standpoint) than as a science endeavour. However, useful data have been obtained and some lessons drawn, such as the need of very simple and robust programs.

Another motivation lies in the fact that although the H and Mg II lines are optically thick and formed in NonLTE, it is now possible to compute the coupled equations of statistical equilibrium, ionization and radiative transfer with 1D and 2D codes with 20 atomic levels (for Hydrogen) which run on PCs with a computing time less than one minute (see e.g. https://idoc.ias.upsud.fr/MEDOC/Radiative transfer codes/).

It is proposed to rely upon simultaneous Hinode observations which concern two domains/instruments: SP, in order to map the magnetic field and its variations (including flux emergence) for all observations performed on the solar disk; EIS, for all observations on and offdisk where the main lines are required, first-of-all the 256 A of He II which will be analyzed jointly with Lyman alpha of H (see HOP105).

remarks

Dates: March 27 to April 4 in 2017 (approx.), during SUMER campaign observations run from GSFC

Time window:
The daily SUMER observing time depends on the DSN schedule and GSFC daytime. Specifically, SUMER will be operated from NASA/GSFC (EDT= UTC-04) and commands be uploaded during the DNS windows (Madrid 08-10 UT, Goldstone 15-17 UT, Canberra 22-24 UT). Therefore, the observations must be run after (not before) these windows, preferably during or after the GSFC daytime window (roughly 13-21 UT) and during the daytime of coordinating GBOs.

Target(s) of interest:
The targets will range from quiescent filaments/prominences, coronal rain, to eruptive prominences, flares, and spicules. We propose a dedicated HOP for the campaign which relies upon existing HOPs for a variety of targets:

A) Prominences/filaments: refer to HOP 73 (Berger et al., Quiescent Prominence Dynamics), HOP 139 (Okamoto et al., Filament Formation and Evolution by Emerging Flux), HOP 269 (Liu et al. Prominence-Coronal Cavity Systems).
B) Spicules: HOPS 113 and 144.
C) Other disk observations: refer to HOP 323.

Previous HOP information:
None (but previous SUMER campaigns--HOPs 93, 104, 193, 205, 211)

Additional Remarks:
In general, pointing will be jointly selected the day before, within the constraints of the operation modes of all participating instruments. Specifically keep in mind that Hinode needs initial plans on
Sunday, Tuesday and Thursday evenings GSFC time; and final pointing coordinates on Monday, Wednesday & Friday evenings, while IRIS makes its final plan every weekday by ~4 PM GSFC time, and both missions make a 3-day weekend plan on Friday.

For each observation run, an image with a substantial FOV from each instrument is requested for the purpose of co-alignment across instruments.