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 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 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} feet (approx 39 km) over a period of approx 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) 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 1.0pm 0.3 MK and a flow speed of approx 260 km s−1 with a large uncertainty interval.
Highlights
The primary instrument of the Balloon-borne Investigation of Temperature and Speed of Electrons in the corona (BITSE) mission is an optical telescope fitted with an external occulter that blocks the direct sunlight so the faint emission from the corona can be observed
The BITSE COR mechanical design consists of the following primary components: a modular aluminum structure for the telescope tube, external occulter, aperture door mechanism, lens group assembly, filter wheel, polarization camera, thermal radiator system, heat rejection mirror, base plate, the BITSE electronics box (BEB), and the power distribution unit (PDU)
The middleware consists of (i) the operating system (OS) abstraction layer that isolates the FSW from the OS, (ii) the platform support package (PSP) that adapts FSW to the specific hardware, and OS platform, and (iii) the core Flight Executive, which is a set of mission-independent, reusable, core flight software services, and operating environment. cFE provides common services such as time, executive, event, and table services along with the software bus to FSW
Summary
The primary instrument of the Balloon-borne Investigation of Temperature and Speed of Electrons in the corona (BITSE) mission is an optical telescope fitted with an external occulter that blocks the direct sunlight so the faint emission from the corona can be observed. Ichimoto et al (1996) obtained coronal spectra in the range 3700 to 4729 Å at two heights (1.1 and 2 Rs) during the November 3, 1994, total solar eclipse, compared them with the expected spectra for a given coronal electron density distribution, and obtained an electron temperature of 1.6 MK in a streamer They estimated the bulk flow speed of the electrons as ≈ 80 km s−1 from the change in the intensity ratios at 3990 and 4218 Å. Reginald and Davila (2000) and Reginald et al (2003) used the Multiaperture Coronal Spectrometer (MACS) to measure white-light Kcoronal intensities simultaneously at several locations in the corona during the total solar eclipse of June 21, 2001 They obtained an electron temperatures of 0.96 ± 0.05 and 1.2 ± 0.2 MK in two streamers at a heliocentric distance of 1.1 Rs. The corresponding flow speeds were 72 km s−1 and 257 km s−1 with large uncertainties. We present images obtained by BITSE and preliminary results on the temperature and flow speed of electrons
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