16903

We ask for 3 WFC3-UVIS orbits to obtain F438W comma F555W comma and F814W images of the location of the Type Ia supernova (SN) 2017erp. We recently discovered a point source at the location of the SN in WFC3-IR observations taken during Feb. and Sep. 2021. We rule out the SN itself or a light echo. Instead comma the object is consistent with a subgiant or red giant at a temperature of virgul5000 K comma but with an abnormally high luminosity of virgul33 comma 000 Solar luminosities. It may be a clump of red giants or a globular cluster at or behind the location of the SN. No other SN Ia has ever been directly associated with such a stellar group. A more exciting possibility is that this object is the shock-heated surviving companion of SN 2017erp.s progenitor. If so comma this will be the first-ever detection of a surviving companion in a normal SN Ia. It would also provide direct evidence of the d_commasingle degenerated_comma channel whereby a white dwarf explodes after accreting matter from a main sequence or evolved star. WFC3-UVIS has a higher resolution than WFC3-IR comma which will allow us to precisely test the object.s coincidence with the SN and determine whether it is resolved or not. The images will also flesh out the object.s spectral energy distribution comma for a more accurate classification comma temperature comma and luminosity. We ask for DD time so that these observations will be scheduled during 3-10 January 2022 or 14-28 February 2022 comma when one last infrared visit to this field is planned. By obtaining optical and infrared images at the same time comma we will gain a complete snapshot of the object at a single moment in time comma providing a baseline for comparison with any future observations to test the object.s variability.