Simultaneous Multicolor Observations of Starlink's Darksat by the Murikabushi Telescope with MITSuME

In this paper, we present the SDSS g'-, the Cousins R_c-, and I_c-band magnitudes and associated colors of Starlink's STARLINK-1113 (one of the standard Starlink satellites) and 1130 (Darksat) with a darkening treatment to its surface. Using the 105 cm Murikabushi telescope/MITSuME, simultaneous multicolor observations for the above satellites were conducted four times: on 2020 April 10 and May 18 (for Darksat), and 2020 June 11 (for Darksat and STARLINK-1113). We found that (1) the SDSS g'-band apparent magnitudes of Darksat (6.95 ± 0.11-7.65 ± 0.11 mag) are comparable to or brighter than that of STARLINK-1113 (7.69 ± 0.16 mag), (2) the shorter the observed wavelength is, the fainter the satellite magnitudes tend to become, (3) the reflected flux by STARLINK-1113 is extremely (>1.0 mag) redder than that of Darksat, (4) there is no clear correlation between the solar phase angle and orbital altitude-scaled magnitude, and (5) by flux model fitting of the satellite trails with the blackbody radiation, it is found that the albedo of Darksat is about half that of STARLINK-1113. In particular, result (1) is inconsistent with previous studies. However, considering both solar and observer phase angles and atmospheric extinction, the brightness of STARLINK-1113 can be drastically reduced in the SDSS g' and the Cousins R_c band. Simultaneous multicolor-multispot observations of more than three colors would give us more detailed information regarding the impact of low-Earth-orbit satellite constellations.