SDSS J172102.48+273301.2 (AM CVn star) https://www.aavso.org/vsx/index.php?view=detail.top&oid=233123 The second part of the current double superoutburst began on (or shortly before) September 3, according to ZTF (and ATLAS) data: https://lasair.roe.ac.uk/object/ZTF21abvdxkq/ The 2012 superoutburst had started between May 27 and June 5 (Denis Denisenko, vsnet-alert 14657). Time-resolved photometry during the current superoutburst is required. Clear skies, Patrick -------------------- Naoto Kojiguchi wrote on Friday, 3 September 2021 at 17:22:22 UTC: SDSS J172102.48+273301.2: AM CVn object with double superoutburst Taguchi-san has reported the latest outburst of this object detected by ZTF alert. This object will soon show a second superoutburst. SC ~ 9.3 yr. Time-resolved photometry is required. YYYYMMDD(UT)   mag  observer comment 20210825.323 <16.677g ASN 20210826.196 15.852zr ZLR Start of outburst 20210826.217 15.659g ASN 20210827.277 16.078o ATF 20210827.319 15.813g ASN 20210828.195 15.757zg ZLR 20210828.211 15.764g ASN 20210828.258 16.124zr ZLR 20210829.044 15.935g ASN 20210829.275 16.140cy ATF 20210830.751 <16.748g ASN Start of dip 20210831.208 19.372zg ZLR 20210831.333 19.748o ATF ATF (ATLAS Forced Photometry (Tonry et al. 2018)) ASN (ASAS-SN survey (Shappee+ 2014; Kochanek+ 2017)) ZLR (Zwicky Transient Facility Lasair (Masci+ 2019))