# # Program information file # PROGRAM_ID 2021B087 PROGRAM_TITLE The first near-IR spectroscopic campaign in conjunction with an approved Hubble Space Telescope UV campaign to map the dust in the torus and accretion disk in the AGN Mrk 817 PROGRAM_INV1 Jake Mitchell PROGRAM_INV2 Hermine Landt PROGRAM_INV3 Martin Ward PROGRAM_INV4 Daniel Kynoch PROGRAM_INV5 Keith Horne PROGRAM_SCICAT extra-galactic PROGRAM_ABSTRACT_BEG Reverberation is a powerful technique that has been extensively used to study the properties of the broad emission line regions in AGN. Recently it has also been applied to investigate the detailed properties of the dusty region within the nucleus, which cannot be spatially resolved except with great difficulty in a few cases. This proposal would complete our campaign on Mrk 817 by extending it into Semester 2021B. It builds on our past success [on NGC 5548] of the first near-IR spectroscopic campaign, which resulted in new insights on the dust properties and its distribution. This offers us a rare opportunity since Mrk 817 is currently the target of an intensive Hubble Space Telescope UV campaign. Only one such HST campaign has been carried out previously [on NGC 5548]. Near-IR spectroscopy, unlike photometry, can explore several signatures of the hot dust, such as its flux and temperature, measurement of the dust response at different frequencies and also the variability of associated emission lines, e.g., the coronal lines and Paschen lines, and the outer radii of the accretion disc. Importantly, only a spectroscopic monitoring campaign can constrain the astrochemistry of the dust surrounding supermassive black holes by measuring the luminosity-based radius simultaneously with the lag times. Besides the lags of various emission lines, the HST data will provide an exquisitely sampled UV continuum light-curve as the input driver, which is more variable than the optical light-curve and so is a direct measure of the accretion disk heating the dust. We propose to observe using SpeX at a cadence of three days for about a month. This request completes our campaign on Mrk 817. PROGRAM_ABSTRACT_END