174P/Echeclus and its Blue Coma Observed Post-Outburst. (arXiv:1811.11220v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Seccull_T/0/1/0/all/0/1">Tom Seccull</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fraser_W/0/1/0/all/0/1">Wesley C. Fraser</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Puzia_T/0/1/0/all/0/1">Thomas H. Puzia</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fitzsimmons_A/0/1/0/all/0/1">Alan Fitzsimmons</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cupani_G/0/1/0/all/0/1">Guido Cupani</a>
It has been suggested that centaurs may lose their red surfaces and become
bluer due to the onset of cometary activity, but the way in which cometary
outbursts affect the surface composition and albedo of active centaurs is
poorly understood. We obtained consistent visual-NIR reflectance spectra of the
sporadically active centaur 174P/Echeclus during a period of inactivity in 2014
and six weeks after its outburst in 2016 to see if activity had observably
changed the surface properties of the nucleus. We observed no change in
Echeclus’ surface reflectance properties following the outburst compared to
before, indicating that, in this case, any surface changes due to cometary
activity were not sufficiently large to be observable from Earth. Our spectra
and post-outburst imaging have revealed, however, that the remaining dust coma
is not only blue compared to Echeclus, but also bluer than Solar, with a
spectral gradient of -7.7+/-0.6% per 0.1 micron measured through the 0.61-0.88
micron wavelength range that appears to continue up to a wavelength of ~1.3
micron before becoming neutral. We conclude that the blue visual colour of the
dust is likely not a scattering effect, and instead may be indicative of the
dust’s carbon-rich composition. Deposition of such blue, carbon-rich, comatic
dust onto a red active centaur may be a mechanism by which its surface colour
could be neutralised.
It has been suggested that centaurs may lose their red surfaces and become
bluer due to the onset of cometary activity, but the way in which cometary
outbursts affect the surface composition and albedo of active centaurs is
poorly understood. We obtained consistent visual-NIR reflectance spectra of the
sporadically active centaur 174P/Echeclus during a period of inactivity in 2014
and six weeks after its outburst in 2016 to see if activity had observably
changed the surface properties of the nucleus. We observed no change in
Echeclus’ surface reflectance properties following the outburst compared to
before, indicating that, in this case, any surface changes due to cometary
activity were not sufficiently large to be observable from Earth. Our spectra
and post-outburst imaging have revealed, however, that the remaining dust coma
is not only blue compared to Echeclus, but also bluer than Solar, with a
spectral gradient of -7.7+/-0.6% per 0.1 micron measured through the 0.61-0.88
micron wavelength range that appears to continue up to a wavelength of ~1.3
micron before becoming neutral. We conclude that the blue visual colour of the
dust is likely not a scattering effect, and instead may be indicative of the
dust’s carbon-rich composition. Deposition of such blue, carbon-rich, comatic
dust onto a red active centaur may be a mechanism by which its surface colour
could be neutralised.
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