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Near-Sun Photometric Follow-up of the Rapidly-Fading Sun-like Star ASASSN-21qj

ATel #14900; D. D. Balam (DAO/National Research Council of Canada), C. E. Spratt (UVic-Ret), D. W. E. Green (CBAT) and Tyler Hrynyk (Canadian Space Agency)
on 6 Sep 2021; 17:28 UT
Credential Certification: David D. Balam (cosmos@uvic.ca)

Subjects: Optical, Star, Transient, Variables

We have taken advantage of the near-sun capabilities of the Canadian NEOSSat orbiting telescope (https://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/neossat/) to perform follow-up photometry of the optical transient ASASSN-21qj (#14879), reported as under-going a rapid dimming event by the ASSASN survey, Shappee et al. 2014,(https://ui.adsabs.harvard.edu/abs/2017PASP..129j4502K/abstract) at relatively small solar elongation. The spacecraft was tasked to obtain a series of 60 second duration images over three orbits of the spacecraft that were co-added to yield image stacks of 2640, 3480 and 2460 seconds duration. We have performed differential aperture photometry using an aperture of 30 seconds of arc using the Gaia catalogue star Gaia DR2 5539975927391545344 (http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%407439336&Name=TYC%207660-897-1&submit=submit) as a secondary standard in the field. The NEOSSat is an un-filtered detector, however, the sensitivity curve of the back illuminated E2V 47-20 CCD is similar to the Gaia G filter response curve. Our measurements yield the following magnitudes: UT 2021 Sept. 3.037 G_NEOSSat = 14.27(+/- 0.07), Sept. 3.169 G_NEOSSat = 14.15 (+/- 0.06) and Sept. 3.236 G_NEOSSat = 13.85 (+/- 0.07). ASASSN-21qj was 0.4 magnitudes fainter than its quiescent brightness before the field became Sun constrained on UT 2021-06-29. On UT Aug. 26 the ASSASN team reported the object as 1.5 magnitudes fainter and 24 hours later 2.2 magnitudes fainter than it quiescent brightness and dimming. Our measurements show that the star has brightened in the week since the ASASSN measurements. In addition, we have seen a brightening trend over the 7 hours of coverage of our orbiting sensor.