J/AJ/157/186 r'-band photometry of comet 96P/Machholz 1 (Eisner+, 2019)
Properties of the bare nucleus of comet 96P/Machholz 1.
Eisner N.L., Knight M.M., Snodgrass C., Kelley M.S.P., Fitzsimmons A.,
Kokotanekova R.
<Astron. J., 157, 186 (2019)>
=2019AJ....157..186E 2019AJ....157..186E (SIMBAD/NED BibCode)
ADC_Keywords: Solar system ; Comets ; Photometry, ugriz
Keywords: comets: individual (96P/Machholz 1) - methods: data analysis -
methods: observational
Abstract:
We 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.
Description:
Images were obtained on a total of nine nights during the 2017/2018
apparition, primarily using the broadband r' filter. The observations
were always tracked at the ephemeris rate of the comet, with the exception
of the images obtained on 2018 July 11/12 with the New Technology
Telescope, which were taken with sidereal tracking and short-enough
exposures to prevent the comet from moving more than the seeing disk.
Images taken on 2017 April 7 were obtained using the 4.2 m Southern
Astrophysical Research (SOAR) telescope on Cerro Pachon in Chile using
the Goodman Spectrograph Red Camera, which utilizes an e2v 231-84 CCD
(Clemens et al. 2004SPIE.5492..331C 2004SPIE.5492..331C). Images taken on 2017 July 2 and 3
were obtained at SOAR with the SOAR Optical Imager (SOI), which uses
a mosaic of two e2v 2048x4096 pixel CCDs (Walker et al.
2003SPIE.4841..286W 2003SPIE.4841..286W). The observations on 2018 June 25 and July 10/11
made use of the Goodman Spectrograph Red camera at the SOAR telescope.
Snapshot r'-band images were obtained on 2018 July 12 using the 3.54 m
New Technology Telescope (NTT) at La Silla, Chile, with the ESO Faint
Object Spectrograph and Camera (EFOSC2), which employs a 2048x2048 pixel
Loral/Lesser CCD (Buzzoni et al. 1984Msngr..38....9B 1984Msngr..38....9B). Our final images
were acquired using the 4.2 m William Herschel Telescope (WHT), in
La Palma, Spain, on 2018 July 31 through August 2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 47 697 All observed r'-band magnitudes and their
statistical uncertainties
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See also:
J/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)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 20 A20 --- Obs.Date UT date of the observation and time of exposure
midpoint (YYYY-MMM-DDThh:mm:ss)
22- 34 F13.5 d JD [2457850.84866/2458333.45212] Julian Date
36- 41 F6.3 mag rmag [18.114/20.683] Apparent r' band magnitude
43- 47 F5.3 mag e_rmag [0.003/0.245] Statistical uncertainty in rmag
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 01-Aug-2019