J/AJ/157/186ivo://CDS.VizieR/J/AJ/157/186doi:10.26093/cds/vizier.51570186CDSEisner N.L.Knight M.M.Snodgrass C.Kelley M.S.P.Fitzsimmons A.,Kokotanekova R.2019-11-22T13:54:16Z2019-08-06T12:49:05ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frsolar-systemcometsinfrared-photometryvisible-astronomybroad-band-photometryWe observed comet 96P/Machholz 1 on a total of nine 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 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'=0.17+/-0.03, and i'-z'=0.06+/-0.04. 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 hr and 4.096+/-0.002 hr 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 s. 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.2019AJ....157..186Ehttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/157/186CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+A/444/287 : The nuclei of 3 comets (Snodgrass+, 2005)J/A+A/546/A115 : Colors of minor bodies in outer solar system (Hainaut+, 2012)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/157/186https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/157/186http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/157/186https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/157/186https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/157/186http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/157/186GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticalInfrareddefaultJ/AJ/157/186/table2All observed r'-band magnitudes and their statistical uncertaintiesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObs.DateUT date of the observation and time of exposure midpoint (YYYY-MMM-DDThh:mm:ss)time.epoch;obscharJD[2457850.84866/2458333.45212] Julian Datedtime.epochdoublermag[18.114/20.683] Apparent r' band magnitudemagphot.mag;em.opt.Rfloate_rmag[0.003/0.245] Statistical uncertainty in rmagmagstat.error;phot.mag;em.opt.Rfloat