HOP 0475

abstract of observational proposal

Main Objective: Hinode support request for SO/PHI cross-calibration with Hinode/SP

Scientific Justification: Perform coordinated observations with the Polarimetric and Helioseismic Imager (PHI) instrument on board the Solar Orbiter (SO) spacecraft and the Hinode spectropolarimeter (Hinode/SP) during the 13th Remote Sensing Window (RSW) of the SO science mission phase that will take place between March 13 and March 24, 2024. The main goal of this HOP is to acquire co-spatial and co-temporal SO/PHI and Hinode/SP data to perform a detailed inter-calibration with the SO/PHI instrument, including both telescopes, the Full Disk Telescope (FDT) and the High Resolution Telescope (HRT). These observations will help us bring the full capabilities of the SO/PHI instrument for science, as well as to acquire additional calibration data.

In the nominal mode SO/PHI provides maps of the vector magnetic field and line-of-sight velocities with both telescopes by observing the Fe 617 nm line at 5 points inside the line plus another point in the nearby continuum. In addition, an alternative mode, where 11 points are acquired inside the line, resulting in a twice as high spectral sampling, is available. This mode is used for better cross calibration for parts of this proposal. In order to fully test the capabilities of SO/PHI and monitor any possible degradation of the instruments, it is important to complement these observations with the Hinode/SP, as long as such co-observations are possible. These observations need to be taken while SO is crossing the Sun-Earth line, while SO sees the Sun from the same point of view as Hinode. In this way, a full characterization of the imaging and polarimetric properties of the SO/PHI instrument with respect to Hinode/SP is possible. As SO will leave the ecliptic at the beginning of 2025, this is the last chance to get real co-aligned
observations from a vantage point on or close to Earth.

The SO/PHI observations that will be used for cross-calibration will be taken on March 19 and 20, 2024, when SO is at a distance of about 0.45 au from the Sun, and at less than 2 degrees separation with Earth. At those times, the pixel scale is about 157 km for HRT and 1400 km for FDT.

The SO/PHI-FDT observations will take place during the Solar Orbiter Observation Plan (SOOP) called COORD_CALIBRATION (CC1_111) led by M. Romoli. The SO pointing at this time will be the disk center.

The SO/PHI-HRT observations will take place during the Solar Orbiter Observation Plan (SOOP) called COORD_CALIBRATION (CC1_115) led by J. Hirzberger. These SO/PHI-HRT observations will be taken at locations decided about three days in advance. The pointing for Hinode should be adapted to that decision.

request to SOT

In support of the FDT observations on March 19, 2024: We request one 320"x164" fast map during the requested time interval (13:50 to 14:50 UT) covering an AR, possibly close to the central meridian and anyway not too close to the limb.

In support of the HRT co-observations on March 20, 2024: We request three 20" x 164" deep maps, during the requested time interval (00:58 to 02:00 UT). Each scan is expected to take about 20 minutes to complete, please extend the time interval if the scans are a bit longer. Each scan should start at a different position in the slit-scanning axis, such that for the first scan the starting point would coincide with the provided SO nominal pointing, the second scan should be offset to start at +50 arcsec in the slit-scanning direction with respect to the nominal pointing, and the third scan should be offset to start at -50 arscec.
The exact pointing will be provided about three days in advance.

remarks

Dates:
Co-observation with FDT:
March 19, 2024, FDT will observe from 13:53 UT to 13:58 UT with a 12-point scan of the line, followed by standard (6 points) observations from 13:59 UT to 14:59 UT.

Co-observation with HRT:
20 March 2024, HRT will observe from 01:00 UT to 01:05 UT with a 12-point scan of the line, followed by standard (6 points) observations from 01:06 UT to 02:06 UT.

Time window:
For the FDT observations on March 19, 2024 co-observations should be performed in the time interval from 13:50 UT to 14:50 UT.

For the HRT observations on March 20, 2024 co-observations should be performed in the time interval from 00:58 UT to 02:00 UT.

Target(s) of interest:
For the FDT observations on March 19, 2024: Active region, possibly close to central meridian and anyway not too close to the limb

For the HRT observations on March 20, 2024: Active region, same nominal pointing of the SOOP COORD_CALIBRATION (CC1_115), to be published in the late afternoon of 17/03/2024 on the dedicated web page
https://s2e2.cosmos.esa.int/confluence/display/SOSP/Solar+Orbiter+Planning+-+for+coordination+with+e
xternal+parties

We request three scans, each starting at a different position with respect to the pointing during the CC1_115 SOOP: i) start at the published nominal pointing as SO; ii) start with an offset of +50 arcsec in the slit-scanning direction with respect to the published nominal pointing; iii) start with an offset of -50 arcsec in the slit-scanning direction with respect to the published nominal pointing.

Previous HOPs: Several successful HOPs have already been run to address the SO/PHI - Hinode-SP cross-calibration.
HOP 0397 was run during SO commissioning (data has been successfully analyzed and pending for publication), HOP 0431 and HOP 0452 were run during the science mission phase in 2022 and 2023 (data analysis is ongoing). Unfortunately, co-observations with SO/PHI-FDT could not be performed, as part of HOP 0452, in 2023, due to a failure on board the SO spacecraft. SO will leave the ecliptic at the beginning of 2025, making this the last chance to get real co-aligned observations from a vantage point on or close to Earth. This HOP is important to continue monitoring and cross-calibrating SO/PHI and to perform detailed studies about the temporal evolution of its performance.

Additional remarks:
It is important to take into account that the above specific times (UT) are still to be confirmed. Exact times of observations will be provided well in advance, probably two weeks before the observations.