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Title: ON THE ABSENCE OF EUV EMISSION FROM COMET C/2012 S1 (ISON)

Abstract

When the sungrazing comet C/2012 S1 (ISON) made its perihelion passage within two solar radii of the Sun’s surface, it was expected to be a bright emitter at extreme ultraviolet (EUV) wavelengths. However, despite solar EUV telescopes repointing to track the orbit of the comet, no emission was detected. This “null result” is interesting in its own right, offering the possibility of placing limits on the size and composition of the nucleus. We explain the lack of detection by considering the properties of the comet and the solar atmosphere that determine the intensity of EUV emission from sungrazing comets. By comparing these properties with those of sungrazing comet C/2011 W3 (Lovejoy), which did emit in the EUV, we conclude that the primary factor resulting in non-detectable EUV emission from C/2012 S1 (ISON) was an insufficiently large nucleus. We conclude that the radius of C/2012 S1 (ISON) was at least a factor of four less than that of C/2011 W3 (Lovejoy). This is consistent with white-light observations in the days before perihelion that suggested the comet was dramatically reducing in size on approach.

Authors:
 [1];  [2]
  1. High Altitude Observatory, NCAR, Boulder CO 80301 (United States)
  2. NASA Goddard Space Flight Center, Code 671, Greenbelt MD 20771 (United States)
Publication Date:
OSTI Identifier:
22663051
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 822; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMETS; COMPARATIVE EVALUATIONS; DETECTION; EMISSION; EXTREME ULTRAVIOLET RADIATION; ORBITS; SOLAR ATMOSPHERE; SUN; SURFACES; TELESCOPES; VISIBLE RADIATION; WAVELENGTHS

Citation Formats

Bryans, Paul, and Pesnell, W. Dean. ON THE ABSENCE OF EUV EMISSION FROM COMET C/2012 S1 (ISON). United States: N. p., 2016. Web. doi:10.3847/0004-637X/822/2/77.
Bryans, Paul, & Pesnell, W. Dean. ON THE ABSENCE OF EUV EMISSION FROM COMET C/2012 S1 (ISON). United States. doi:10.3847/0004-637X/822/2/77.
Bryans, Paul, and Pesnell, W. Dean. Tue . "ON THE ABSENCE OF EUV EMISSION FROM COMET C/2012 S1 (ISON)". United States. doi:10.3847/0004-637X/822/2/77.
@article{osti_22663051,
title = {ON THE ABSENCE OF EUV EMISSION FROM COMET C/2012 S1 (ISON)},
author = {Bryans, Paul and Pesnell, W. Dean},
abstractNote = {When the sungrazing comet C/2012 S1 (ISON) made its perihelion passage within two solar radii of the Sun’s surface, it was expected to be a bright emitter at extreme ultraviolet (EUV) wavelengths. However, despite solar EUV telescopes repointing to track the orbit of the comet, no emission was detected. This “null result” is interesting in its own right, offering the possibility of placing limits on the size and composition of the nucleus. We explain the lack of detection by considering the properties of the comet and the solar atmosphere that determine the intensity of EUV emission from sungrazing comets. By comparing these properties with those of sungrazing comet C/2011 W3 (Lovejoy), which did emit in the EUV, we conclude that the primary factor resulting in non-detectable EUV emission from C/2012 S1 (ISON) was an insufficiently large nucleus. We conclude that the radius of C/2012 S1 (ISON) was at least a factor of four less than that of C/2011 W3 (Lovejoy). This is consistent with white-light observations in the days before perihelion that suggested the comet was dramatically reducing in size on approach.},
doi = {10.3847/0004-637X/822/2/77},
journal = {Astrophysical Journal},
number = 2,
volume = 822,
place = {United States},
year = {Tue May 10 00:00:00 EDT 2016},
month = {Tue May 10 00:00:00 EDT 2016}
}