Properties of the Bare Nucleus of Comet 96P/Machholz 1. (arXiv:1903.10500v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Eisner_N/0/1/0/all/0/1">Nora L. Eisner</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Knight_M/0/1/0/all/0/1">Matthew M. Knight</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Snodgrass_C/0/1/0/all/0/1">Colin Snodgrass</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kelley_M/0/1/0/all/0/1">Michael S.P. Kelley</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:+Kokotanekova_R/0/1/0/all/0/1">Rosita Kokotanekova</a>
We observed comet 96P/Machholz 1 on a total of 9 nights before and after
perihelion during its 2017/2018 apparition. Both its unusually small perihelion
distance and the observed fragmentation during multiple apparitions make 96P an
object of great interest. Our observations show no evidence of a detectable
dust coma, implying that we are observing a bare nucleus at distances ranging
from 2.3 AU to 3.8 AU. Based on this assumption we calculated its color, and
found average values of g’-r’ = 0.50 +/- 0.04, r’-i’ = 0.037 +/- 0.34, and
i’-z’ = 0.10 +/- 0.08. These are notably more blue than those of the nuclei of
other Jupiter family and long period comets. Furthermore, assuming a bare
nucleus, we found an equivalent nuclear radius of 3.4 +/- 0.2 km with an axial
ratio of at least 1.6 +/- 0.1. The lightcurve clearly displays one large peak,
one broad flat peak, and two distinct troughs, with a clear asymmetry that
suggests that the shape of the nucleus deviates from that of a simple triaxial
ellipsoid. This asymmetry in the lightcurve allowed us to constrain the nuclear
rotation period to 4.10 +/- 0.03 hours and 4.096 +/- 0.002 hours before and
after perihelion, respectively. Within the uncertainties, 96P’s rotation period
does not appear to have changed throughout the apparition, and we conclude a
maximum possible change in rotation period of 130 seconds. The observed
properties were compared to those of comet 322P and interstellar object
1I/’Oumuamua in an attempt to study the effects of close perihelion passages on
cometary surfaces and their internal structure, and the potential interstellar
origin of 96P.
We observed comet 96P/Machholz 1 on a total of 9 nights before and after
perihelion during its 2017/2018 apparition. Both its unusually small perihelion
distance and the observed fragmentation during multiple apparitions make 96P an
object of great interest. Our observations show no evidence of a detectable
dust coma, implying that we are observing a bare nucleus at distances ranging
from 2.3 AU to 3.8 AU. Based on this assumption we calculated its color, and
found average values of g’-r’ = 0.50 +/- 0.04, r’-i’ = 0.037 +/- 0.34, and
i’-z’ = 0.10 +/- 0.08. These are notably more blue than those of the nuclei of
other Jupiter family and long period comets. Furthermore, assuming a bare
nucleus, we found an equivalent nuclear radius of 3.4 +/- 0.2 km with an axial
ratio of at least 1.6 +/- 0.1. The lightcurve clearly displays one large peak,
one broad flat peak, and two distinct troughs, with a clear asymmetry that
suggests that the shape of the nucleus deviates from that of a simple triaxial
ellipsoid. This asymmetry in the lightcurve allowed us to constrain the nuclear
rotation period to 4.10 +/- 0.03 hours and 4.096 +/- 0.002 hours before and
after perihelion, respectively. Within the uncertainties, 96P’s rotation period
does not appear to have changed throughout the apparition, and we conclude a
maximum possible change in rotation period of 130 seconds. The observed
properties were compared to those of comet 322P and interstellar object
1I/’Oumuamua in an attempt to study the effects of close perihelion passages on
cometary surfaces and their internal structure, and the potential interstellar
origin of 96P.
http://arxiv.org/icons/sfx.gif
