FAR-ULTRAVIOLET OBSERVATIONS OF COMET C/2012 S1 (ISON) FROM FORTIS

We have used the unique far-UV imaging capability offered by a sounding rocket borne instrument to acquire observations of C/2012 S1 (ISON) when its angular separation with respect to the sun was 26.3deg, on 2013 November 20.49. At the time of observation the comet's heliocentric distance and velocity relative to the sun were rh = 0.43 AU and rh_dot = -62.7 km s^-1. Images dominated by C I 1657 A and H I 1216 A were acquired over a 1e6 x 1e6 km^2 region. The water production rate implied by the Lyman alpha observations is constrained to be Q_H2O approximately 8e29 s^-1 while the neutral carbon production rate was Q_C approximately 4e28 s^-1. The radial profile of C I was consistent with it being a dissociation product of a parent molecule with a lifetime approximately 5e4 seconds, favoring a parent other than CO. We constrain the Q_CO production rate to 5(+1.5, -7.5)e28 s^-1 with 1sigma errors derived from photon statistics. The upper limit on the Q_CO/Q_H2O < 6%.

[1]  I. S. Bowen.  EXCITATION BY LINE COINCIDENCE , 1947 .

[2]  Kevin France,et al.  FORTIS: pathfinder to the Lyman continuum , 2004, SPIE Astronomical Telescopes + Instrumentation.

[4]  Jason McPhate,et al.  Rocket-borne Long-Slit Ultraviolet Spectroscopy of Comet Hale-Bopp , 1999 .

[5]  David A. Rapchun,et al.  Fabrication and calibration of FORTIS , 2011, Optical Engineering + Applications.

[6]  P. Feldman,et al.  Solar Flux Variability and the Lifetimes of Cometary H2O and OH , 1994 .

[7]  J. Bertaux,et al.  Pre- and Post-Perihelion Activity of Comet Hyakutake (1996 B2) , 2005 .

[8]  Massimo Stiavelli,et al.  Project Lyman , 2008, Astronomical Telescopes + Instrumentation.

[9]  N. Biver,et al.  The compositional evolution of C/2012 S1 (ISON) from ground-based high-resolution infrared spectroscopy as part of a worldwide observing campaign , 2016 .

[10]  P. Feldman,et al.  GALEX FUV OBSERVATIONS OF COMET C/2004 Q2 (MACHHOLZ): THE IONIZATION LIFETIME OF CARBON , 2010, 1011.4313.

[11]  Mary J. Li,et al.  Calibration and flight qualification of FORTIS , 2013, Optics & Photonics - Optical Engineering + Applications.

[12]  G. Blake,et al.  EN ROUTE TO DESTRUCTION: THE EVOLUTION IN COMPOSITION OF ICES IN COMET D/2012 S1 (ISON) BETWEEN 1.2 AND 0.34 AU FROM THE SUN AS REVEALED AT INFRARED WAVELENGTHS , 2016 .

[13]  D. E. Kerr,et al.  Spectroradiometric calibration techniques in the far ultraviolet: a stable emission source for the Lyman bands of molecular hydrogen. , 1975, Applied optics.

[14]  Fred L. Whipple,et al.  A comet model. I. The acceleration of Comet Encke , 1950 .

[15]  Fred L. Whipple,et al.  A Comet Model. II. Physical Relations for Comets and Meteors. , 1950 .

[16]  Leo Haser,et al.  Distribution d’intensité dans la tête d’une comète , 1957, Bulletin de la Classe des sciences.

[17]  Mary J. Li,et al.  Fabrication of FORTIS , 2010, Astronomical Telescopes + Instrumentation.

[18]  David A. Rapchun,et al.  Microshutter array development for the James Webb space telescope , 2005, SPIE Micro + Nano Materials, Devices, and Applications.

[19]  J.-L. Bertaux,et al.  UNUSUAL WATER PRODUCTION ACTIVITY OF COMET C/2012 S1 (ISON): OUTBURSTS AND CONTINUOUS FRAGMENTATION , 2014 .

[20]  Martin J. L. Turner,et al.  UV and Gamma-Ray Space Telescope Systems , 2004 .

[21]  J. Greenstein.  High-resolution spectra of Comet MRKOS (1957d) , 1958 .

[22]  F. Whipple.  Cometary brightness variation and nucleus structure , 1978 .

[23]  P. Feldman,et al.  FAR-ULTRAVIOLET OBSERVATIONS OF COMET C/2001 Q4 (NEAT) WITH FIMS/SPEAR , 2014 .

[24]  Zdenek Sekanina,et al.  Disintegration of Comet C/2012 S1 (ISON) Shortly Before Perihelion: Evidence from Independent Data Sets , 2014, 1404.5968.

[25]  P. Swings.  Complex structure of cometary bands tentatively ascribed to the contour of the solar spectrum , 1941 .