The Balloon-Borne Investigation of Temperature and Speed of Electrons in the Corona (BITSE): Mission Description and Preliminary Results

Abstract

We report on the Balloon-borne Investigation of Temperature and Speed of Electrons in the corona (BITSE) mission launched recently to observe the solar corona from $\approx 3$ ≈ 3 Rs to 15 Rs at four wavelengths (393.5, 405.0, 398.7, and 423.4 nm). The BITSE instrument is an externally occulted single stage coronagraph developed at NASA’s Goddard Space Flight Center in collaboration with the Korea Astronomy and Space Science Institute (KASI). BITSE used a polarization camera that provided polarization and total brightness images of size $1024 \times 1024$ 1024 × 1024 pixels. The Wallops Arc Second Pointer (WASP) system developed at NASA’s Wallops Flight Facility (WFF) was used for Sun pointing. The coronagraph and WASP were mounted on a gondola provided by WFF and launched from the Fort Sumner, New Mexico station of Columbia Scientific Balloon Facility (CSBF) on September 18, 2019. BITSE obtained 17,060 coronal images at a float altitude of $\approx \mbox{128,000}$ ≈ 128,000 feet ($\approx 39$ ≈ 39 km) over a period of $\approx 4$ ≈ 4 hrs. BITSE flight software was based on NASA’s core Flight System, which was designed to help develop flight quality software. We used EVTM (Ethernet Via Telemetry) to download science data during operations; all images were stored on board using flash storage. At the end of the mission, all data were recovered and analyzed. Preliminary analysis shows that BITSE imaged the solar minimum corona with the equatorial streamers on the east and west limbs. The narrow streamers observed by BITSE are in good agreement with the geometric properties obtained by the Solar and Heliospheric Observatory (SOHO) coronagraphs in the overlapping physical domain. In spite of the small signal-to-noise ratio ($\approx 14$ ≈ 14 ) we were able to obtain the temperature and flow speed of the western steamer. In the heliocentric distance range 4 – 7 Rs on the western streamer, we obtained a temperature of $\approx 1.0\pm 0.3$ ≈ 1.0 ± 0.3 MK and a flow speed of $\approx 260$ ≈ 260 km s−1 with a large uncertainty interval.

First light observations of the solar wind in the outer corona with the Metis coronagraph

“…The present data, extending previous results out to 6 R , indicate that the neutral hydrogen/proton component in proximity of the current sheet reaches a speed of ≈ 160 km s −1 at 4 R and this maintains a fairly constant value out to 6 R . It is interesting to note that if the hydrogen kinetic temperature is assumed to be isotropic in the computation of Doppler dimming, the wind speed derived from Metis data is higher by ≈ 40 km s −1 , but still lower than the value, 260 km s −1 (with large uncertainties as reported by the authors), measured during a balloon experiment along a streamer by Gopalswamy et al (2021) in 2019.…”

“…The assumed electron temperature is decreasing from 0.7 MK to 0.5 MK from 4 R to 6 R (see, Dolei, 2018). Recently, in a balloon-borne investigation of a coronal streamer within 4 and 7 R , Gopalswamy et al (2021) found a higher electron temperature, 1.0 ± 0.3 MK, close to the value found for streamers by Fineschi et al (1998), 1.1 ± 0.3 MK, but at a lower heliodistance, 2.7 R . Across the radial direction, T H i,⊥ is assumed to be equal to 1.6 MK, value determined by UVCS observations of the equatorial belt during solar minimum (Dolei et al 2016).…”

First light observations of the solar wind in the outer corona with the Metis coronagraph

“…The present data, extending previous results out to 6 R , indicate that the neutral hydrogen-proton component in the proximity of the current sheet reaches a speed of ≈160 km s −1 at 4 R and this maintains a fairly constant value out to 6 R . It is interesting to note that if the hydrogen kinetic temperature is assumed to be isotropic in the computation of Doppler dimming, the wind speed derived from Metis data is higher by ≈40 km s −1 , but still lower than the value of 260 km s −1 (with large uncertainties as reported by the authors) that was measured during a balloon experiment along a streamer by Gopalswamy et al (2021) in 2019.…”

Space Missions for Astronomy and Astrophysics in Korea: Past, Present, and Future

“…The second one is the polarization camera that can directly collect polarized light without an extra mechanism for rotating polarization wheels as done by the traditional detector. Regions outside the streamers were masked out due to no signal there [117].…”

“…The NASA-KASI coronagraph team achieved TRL 6 or higher in all technologies for NGC through the BITSE mission. More detailed description on the mission and preliminary results can be found in Goplaswamy et al [117].…”