Observations of the RRc variable LINEAR 1169665 with the robotic telescope TAROT.

LINEAR 1169665 is a RR Lyrae of sub-type c discovered by the asteroid survey LINEAR. The robotic telescope TAROT at Calern Observatory has observed it between the years 2006 and 2015. The present study of TAROT data as well as those from the surveys ASAS-SN (2012-2019) and LINEAR (2002-2008) shows that this star presents a period modulation with a period of 1800.1 days (4.9 years) but with no significant variation of magnitude at maximum. This phenomenon is similar to the one found in KEPLER data for the RRc KIC 2831097 (Sodor et al., 2017) which was suspected to be the result of a light time effect in a double stellar system. The large modulation period and the lack of amplitude modulation exclude it to be attributed to a Blazhko effect. But alternatively to the light time effect this phenomenon might be due to a new modulation phenomenon with long period affecting at least RRc stars.