# # Program information file # PROGRAM_ID 2021B033 PROGRAM_TITLE A Changing-Look AGN in the Making PROGRAM_INV1 Hermine Landt PROGRAM_INV2 Junjie Mao PROGRAM_INV3 Missagh Mehdipour PROGRAM_INV4 Dan Stern PROGRAM_INV5 Mike Brotherton PROGRAM_SCICAT extra-galactic PROGRAM_ABSTRACT_BEG Outflows from active galactic nuclei [AGN] limit the rate of black hole growth and can significantly influence star formation in their host galaxy. The outflowing ions producing the blue-shifted absorption lines have been found in a variety of ionisation states implying a diversity of ionising environments both within and between objects. The obscuring wind is a new breed of AGN winds discovered in a large X-ray observing campaign on NGC 5548 in 2013 and subsequently found also in a few other AGN. It is thought to be an accretion disk wind, which, if dense enough, could be responsible for the 'changing-look' AGN state. For the first time, we have a case in hand where we can witness exactly how this is happening. In late 2020, we detected an X-ray obscuring event in the bright quasar MR 2251-178, which was accompanied by a declining UV/optical luminosity and broad troughs in the He I 1.08 broad emission line. Here we propose to observe MR 2251-178 with near-IR spectroscopy in regular intervals [about once a month] in order to catch the on-set of the changing-look AGN state, understand how it happens and what its relationship is to the X-ray obscuring events. We ask for SpeX in the short cross-dispersed [SXD] mode equipped with the 0.3 arcsec slit, which gives a spectral resolution of FWHM~150 km/s. This resolution is sufficient to study the He I absorbers and profile changes in the broad emission lines. PROGRAM_ABSTRACT_END