Abstract
The BRightest Target Explorer (BRITE) is the pioneering nanosatellite mission dedicated for photometric observations of the brightest stars in the sky. The BRITE charge coupled device (CCD) sensors are poorly shielded against extensive flux of energetic particles which constantly induce defects in the silicon lattice. In this paper we investigate the temporal evolution of the generation of the dark current in the BRITE CCDs over almost four years after launch. Utilizing several steps of image processing and employing normalization of the results, it was possible to obtain useful information about the progress of thermal activity in the sensors. The outcomes show a clear and consistent linear increase of induced damage despite the fact that only about 0.14% of CCD pixels were probed. By performing the analysis of temperature dependencies of the dark current, we identified the observed defects as phosphorus-vacancy (PV) pairs, which are common in proton irradiated CCD matrices. Moreover, the Meyer-Neldel empirical rule was confirmed in our dark current data, yielding meV for proton-induced PV defects.
Highlights
The BRightest Target Explorer (BRITE) is the pioneering nanosatellite mission dedicated for photometric observations of the brightest stars in the sky
The pioneering mission of the BRITE nanosatellites allows one to perform photometric measurements of stars with very high precision, the charge coupled device (CCD) sensors installed onboard are exposed to strong irradiation and experience gradual degradation
In this paper we present a detailed analysis of the progress of the dark current generation in the BRITE CCDs
Summary
The BRight Target Explorer (BRITE) is a constellation of six nanosatelites launched in 2013–2014, which are dedicated to high-precise photometry of the brightest stars in blue (b) and red (r) filters. The mission is a collaboration between Canada, Austria and Poland Each of these countries has two satellites: UniBRITE (UBr) and BRITE Austria (BAb) are Austrian satellites, BRITE Toronto (BTr) and BRITE Montreal (failed to communicate after launch) are Canadian satellties, BRITE Lem (BLb) and BRITE Heweliusz (BHr) are Polish. The combination of large-area image sensor and a dedicated lens system allowed for maximizing the number of stars measured simultaneously in a single field. Due to the lack of thermal stabilization and varying exposure times (1–5 s, depending on the intensities of stars included in the field), such analysis is not a trivial task and it requires applying several steps of image processing and proper normalization of the data. The analysis can utilize information only from a very small portion of the CCD arrays (i.e., only several tiny subrasters per field) and at unstabilized temperatures, which are dependent on the observed field
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