Deep Impact: High-Resolution Optical Spectroscopy with the ESO VLT and the Keck I Telescope

We report on observations of comet 9P/Tempel 1 carried out before, during, and after the NASA Deep Impact event (UT July 4), with the optical spectrometers UVES and HIRES mounted on the telescopes Kueyen of the ESO VLT (Chile) and Keck I on Mauna Kea (Hawaii), respectively. A total observing time of about 60 hr, distributed over 15 nights around the impact date, allowed us (1) to find a periodic variation of 1.709 ± 0.009 days in the CN and NH flux, explained by the presence of two major active regions; (2) to derive a lifetime ≳5 × 10⁴ s (at 1.5 AU) for the parent of the CN radical from a simple modeling of the CN light curve after the impact; (3) to follow the gas and dust spatial profiles' evolution during the 4 hr following the impact and derive the projected velocities (400 and 150 m s^-1, respectively); and (4) to show that the material released by the impact has the same carbon and nitrogen isotopic composition as the surface material (¹²C/ ¹³C = 95 ± 15 and ¹⁴N/¹⁵N = 145 ± 20).