On changes in the spectra of Comet C/1999 S4 (LINEAR) on July 22−28, 2002

Abstract

Some spectra of Comet C/1999 S4 (LINEAR) are obtained with the UAGS spectrograph (long slit and CCD) installed on the 1-m Zeiss reflector of the SAO RAS (the Northern Caucasus, Nizhny Arkhyz) on July 23/24, 26/27, and 27/28, 2000. Sophisticated identification of emission lines in the spectra of Comet C/1999 S4 (LINEAR) is made. Emission lines of the molecules C₂, C₃, CN, NH, CH, NH₂, CO⁺, H₂O⁺, and others were identified in the spectra of Comet C/1999 S4 (LINEAR) derived on July 22/23, 2000 before splitting the cometary nucleus. Analysis of the CCD spectra obtained on July 27/28, 2000 reveals very weak emission lines superposed on the solar reflection spectrum, unlike the case of spectra obtained with the same instrument on July 22/23. From analysis of the surface brightness profile of C₂ along the slit, the velocity of expansion of two secondary fragments (V = 10 km/hr) and energy of fragment expansion (E = 8.7 · 10¹⁵ erg) are estimated. The luminescence cometary continuum is detected by a level of 26% at 5000 Å in the spectra of the comet. Possible mechanisms of nucleus splitting are discussed.