Coordinated observations with the Swedish 1-m Solar Telescope and Solar Orbiter

(Solar Orbiter Nugget #36 by Sanja Danilovic¹)

Introduction

The Swedish 1-m Solar Telescope (SST) has been operated by the Institute for Solar Physics (ISP) since 2002 [1]. The current instrumental setup includes two Fabry–Pérot (FP) interferometers called CRISP and CHROMIS and the microlensed hyperspectral imager Helium Spectropolarimeter (HeSP). The CRISP instrument currently covers a circular field-of-view (FOV) with a diameter of 88 arcsec and a sampling of 0.044 arcsec/pixel. It takes polarisation-sensitive,  quasi-monochromatic images while tuning through spectral lines. The temporal resolution depends on observational programs where the number of spectral lines and the number of wavelength points per line can be adjusted. Sampling through the multiple spectral lines enables us to retrieve the stratification of the solar atmosphere [2,3]. The photospheric and chromospheric magnetic field vectors are retrieved with ten times higher spatial resolution than with SO/HMI [4].  These magnetic field maps can be either embedded in SO/HMI maps or can be taken in mosaic mode and used for magnetic field extrapolation methods [5,6]. The combination of magnetic field information at two layers improves the field extrapolations [7] and higher spatial sampling allows retrieving magnetic field topology in the lower solar atmosphere. The SST provides information about the chromospheric dynamics and thus fills in the gap between the photosphere and transition region and corona covered by solar space instrumentation. In combination with Solar Orbiter, it can provide stereoscopic observations of the solar atmosphere, as illustrated by last year’s coordinated campaign.

October 2024 Campaign

The coordinated observations with Solar Orbiter took place in the period from October 12th to October 24th, 2023. Due to local seeing conditions and daily solar elevation in October, the observations were scheduled at 9 UT over 11 days in total. The weather conditions permitted observations on 7 of those 11 days. On 4 of these 7 days the seeing was good to excellent. The captured targets are two active regions, a sunspot and a coronal hole, from the different Solar Orbiter Observing Plans (SOOPs – see here, such as the Long Term AR SOOP and the Fast Wind SOOP).

An example of data collected on October 17th is shown in Fig. 1. Solar Orbiter was at 0.36 AU with a separation angle of 54 deg to the Sun-Earth line (panel a).

Figure 1 - Overview of the observations obtained on October 17th 2023. a) Solar Orbiter position with respect to the Sun-Earth line (credit Solar-MACH), b) Field-of-view of Solar Obiter EUI/HRI (purple) and SST/CRISP plotted over SDO/AIA 171 image, c) Mosaic taken with SST/CRISP shows the Ca II 854.2 nm line core, d) Solar Obiter EUI/HRI image, e) line-of-sight component of photospheric magnetic field obtained in Fe I 617.3 nm spectral line observed with SST/CRISP and f) SST/CRISP image of the Halpha line core.

This enabled stereoscopic observations of a decaying active region close to the disc center for Earth-based facilities (panel b). The mosaic (panel c) was taken at the beginning and the end of an hour-long observation. It shows fine structures in the solar chromosphere visible in the Ca II 854.2 nm line. The evolution of the photospheric and chromospheric dynamics was recorded with the CRISP instrument (panels e and f).

The attached movie shows the evolution in the combined data that cover 30 min at the temporal sampling of SST/CRISP. Top row shows chromosphere in the core of the Ca II 854.2 nm line with the line-of-sight magnetic field in chromosphere and photosphere. The high-resolution images obtained with the EUI/HRI instrument on board Solar Orbiter show dynamic fibrils which are interpreted as shock waves that lift the cold chromospheric material upwards. The bright areas (coronal bright points) visible in SDO/AIA 171 appear smaller and fragmented in EUI/HRI images.

More details of the whole campaign can be found in the recorded talk and presentation material on the ESPOS webpage (https://espos.stream/2024/05/02/Danilovic/).

Future

The instruments at the SST will undergo an upgrade next year. The CRISP and CROMIS FOV will be increased to 120 arcsec in diameter. The capabilities of CHROMIS will be expanded to allow spectropolarimetric observations in the Ca II H&K lines. This means that we will be able to obtain magnetic field properties in a wide range of heights, from the photosphere to the upper chromosphere with a spatial resolution of 100 km and a cadence of 30 sec.

The SST observational schedule for the whole season is being made early in the year. To be able to secure co-observations with Solar Orbiter or any other instrumentation, requests for coordinated observations need to be sent to jorrit.leenaarts@astro.su.se in January of the same year. The next planned coordinated observations will take place in the period 2-16 October 2024 during the R_SMALL_MRES_MCAD_AR-Long-Term SOOP.

Acknowledgements

The Swedish 1-m Solar Telescope is operated on the island of La Palma by the Institute for Solar Physics of Stockholm University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The Institute for Solar Physics is supported by a grant for research infrastructures of national importance from the Swedish Research Council (registration number 2017-00625).

Affiliations

1 Institute for Solar Physics, Stockholm University, Sweden

References

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