Optical investigation of cometary nuclei

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1987.Includes bibliographies.by Karen Jean Meech.Ph.D

Isotopic ratios in outbursting comet C/2015 ER61

Isotopic ratios in comets are critical to understanding the origin of cometary material and the physical and chemical conditions in the early solar nebula. Comet C/2015 ER61 (PANSTARRS) underwent an outburst with a total brightness increase of 2 magnitudes on the night of 2017 April 4. The sharp increase in brightness offered a rare opportunity to measure the isotopic ratios of the light elements in the coma of this comet. We obtained two high-resolution spectra of C/2015 ER61 with UVES/VLT on the nights of 2017 April 13 and 17. At the time of our observations, the comet was fading gradually following the outburst. We measured the nitrogen and carbon isotopic ratios from the CN violet (0,0) band and found that $^{12}$C/$^{13}$C=100 $\pm$ 15, $^{14}$N/$^{15}$N=130 $\pm$ 15. In addition, we determined the $^{14}$N/$^{15}$N ratio from four pairs of NH$_2$ isotopolog lines and measured $^{14}$N/$^{15}$N=140 $\pm$ 28. The measured isotopic ratios of C/2015 ER61 do not deviate significantly from those of other comets.Comment: 4 pages, 4 figures, accepted to be published by A&

The impact and rotational lightcurves of Comet 9P/Tempel 1

UVES and HIRES high-resolution spectra of comet 9P/Tempel 1 are used to investigate the impact and rotational light curves of various species with a view toward building a simple model of the distribution and activity of the sources. The emission by OH, NH, CN, C3, CH, C2, NH2 and OI, are analyzed, as well as the light scattered by the dust. It is found that a simple model reproduces fairly well the impact lightcurves of all species combining the production of the observed molecules and the expansion of the material throughout the slit. The rotational light curve for each species is explained in terms of a single model with three sources.Comment: 34 pages, 11 figures Accepted for publication in the special issue of Icarus associated with the Deep Impact mission to Comet 9P/Tempel

Monitoring of the optical spectrum of comet 2I/Borisov at the VLT

2I/Borisov is the first active interstellar comet observed in the Solar Sytem, allowing for the first time to sample the composition of a planetary building block from an extrasolar system. We report on the monitoring of 2I with the FORS low resolution spectrograph of the ESO VLT at Paranal during four months, from November 19, 2019 to March 20, 2020. We collected a dozen spectra at 8 different epochs allowing to follow the evolution of the comet activity and composition around perihelion. We also observed with the same instrumental setup an Oort Cloud comet, C/2019 U6 (Lemmon), at about the same heliocentric and geocentric distance than 2I/Borisov at perihelion (rh=Delta=2 au) and with similar AfRho value and Q(CN) in order to use it as a reference for the Solar System. The usual species are detected in the optical spectrum of 2I (CN, C3, C2, and NH2) and their production rates and abundance ratios are computed. The dust production rate and colors are also derived, compared to C/2019 U6 and other comets of the Solar System, and their evolutions are followed with the heliocentric distance. Fig1. Comparison of the optical spectra of the interstellar comet 2I/Borisov at perihelion (rh=Delta=2,0 au) and the Oort Could comet C/2019 U6 (Lemmon) observed with FORS at the ESO VLT (Paranal Observatory). C/2019/U6 was chosen for comparison as a Solar System comet with a typical composition. It was also at the about the same distances to the Sun and Earth, and it had about the same dust and CN production rates as 2I/Borisov as measured by the TRAPPIST-South telescope

High resolution optical spectroscopy of 2I/Borisov: a surprising similarity to solar system comets

2I/Borisov - hereafter 2I - is the first visibly active interstellar comet observed in the solar system. It was discovered on August 20, 2019 and remained visible for several months, permitting observations with various telescopes around the world and in space. We observed 2I with UVES, the high-resolution optical spectrograph mounted on the UT2 telescope at Paranal observatory in Chile, with the objective to characterize its composition. We collected spectra at 12 different epochs between November 15, 2019, and March 16, 2020, covering a heliocentric distance range from 2.1 au pre-perihelion to 2.6 au post-perihelion.Our observations allowed us to make several key measurements, some being made for the first time in the coma of an interstellar comet. We detected emissions from the radicals OH, NH, CN, CH, C2, and NH2, the [OI]forbidden oxygen lines at 557.73, 630.03, and 636.37 nm, as well as several FeI and NiI lines. We derived the abundance of FeI and NiI in the coma using the model described in [1] and find log Q(NiI)=21.88±0.07 molecules/s and Q(FeI)=21.67±0.16 molecules/s, corresponding to log(NiI/FeI)=0.21±0.18. This ratio agrees with the value recently found in solar system comets [1], as shown in Fig. 1.NH2 ortho and para lines from the ro-vibronic (0,8,0) and (0,9,0) bands were measured and allowed us to derive a NH2 ortho-to-para ratio (OPR) of 3.21±0.15, corresponding to an OPR and spin temperature of ammonia of 1.11±0.08 and 31+10/-5 K, respectively. These values are consistent with measurements in solar system comets and likely reflect the physico-chemical conditions in the comet inner coma.We measured the three forbidden oxygen lines and determined the ratio between the intensity of the green [OI] line and the red doublet. We obtained a rather high value G/R=0.31±0.05 close to perihelion, with possibly an increasing trend while the comet moved away from the Sun. This is consistent with the high CO abundance in the coma of 2I and the increase of the CO/H2O ratio with the heliocentric distance [2,3].Finally, from the OH (0-0) emission band around 309 nm we derived a water production rate of (2.2±0.2) x 1026 molecules/s close to perihelion on December 24 and 26, 2019.In conclusion, high spectral resolution observations of 2I/Borisov and the associated measurements of the NH2OPR and the Ni/Fe abundance ratio are remarkably similar to solar system comets. The measured G/R ratio is unusually high but consistent with the high abundance ratio of CO/H2O found by other investigators [2,3] and potentially suggesting formation in a colder environment. Figure 1: Comparison between the log(Ni/Fe) ratio of 2I and the values measured by [1] for a sample of solar system comets (Jupiter Family Comets (JFC), Oort Cloud Comets (OC), and Halley Type Comets (HTC)). The horizontal line represents the average value for solar system comets from [1]. References:[1] Manfroid, J., Hutsemékers, D., & Jehin, E. 2021, Nature, 593, 372[2] Cordiner, M. A., Milam, S. N., Biver, N., et al. 2020, Nature Astronomy, 4, 861[3] Bodewits, D., Noonan, J. W., Feldman, P. D., et al. 2020, Nature Astronomy, 4,8

The perihelion activity of comet 67P/Churyumov-Gerasimenko as seen by robotic telescopes

Around the time of its perihelion passage the observability of 67P/Churyumov-Gerasimenko from Earth was limited to very short windows each morning from any given site, due to the low solar elongation of the comet. The peak in the comet's activity was therefore difficult to observe with conventionally scheduled telescopes, but was possible where service/queue scheduled mode was possible, and with robotic telescopes. We describe the robotic observations that allowed us to measure the total activity of the comet around perihelion, via photometry (dust) and spectroscopy (gas), and compare these results with the measurements at this time by Rosetta's instruments. The peak of activity occurred approximately two weeks after perihelion. The total brightness (dust) largely followed the predictions from Snodgrass et al. (2013), with no significant change in total activity levels from previous apparitions. The CN gas production rate matched previous orbits near perihelion, but appeared to be relatively low later in the year

Outgassing Behavior of C/2012 S1 (ISON) From September 2011 to June 2013

We report photometric observations for comet C/2012 S1 (ISON) obtained during the time period immediately after discovery (r=6.28 AU) until it moved into solar conjunction in mid-2013 June using the UH2.2m, and Gemini North 8-m telescopes on Mauna Kea, the Lowell 1.8m in Flagstaff, the Calar Alto 1.2m telescope in Spain, the VYSOS-5 telescopes on Mauna Loa Hawaii and data from the CARA network. Additional pre-discovery data from the Pan STARRS1 survey extends the light curve back to 2011 September 30 (r=9.4 AU). The images showed a similar tail morphology due to small micron sized particles throughout 2013. Observations at sub-mm wavelengths using the JCMT on 15 nights between 2013 March 9 (r=4.52 AU) and June 16 (r=3.35 AU) were used to search for CO and HCN rotation lines. No gas was detected, with upper limits for CO ranging between (3.5-4.5)E27 molec/s. Combined with published water production rate estimates we have generated ice sublimation models consistent with the photometric light curve. The inbound light curve is likely controlled by sublimation of CO2. At these distances water is not a strong contributor to the outgassing. We also infer that there was a long slow outburst of activity beginning in late 2011 peaking in mid-2013 January (r~5 AU) at which point the activity decreased again through 2013 June. We suggest that this outburst was driven by CO injecting large water ice grains into the coma. Observations as the comet came out of solar conjunction seem to confirm our models.Comment: 8 pages, 2 figures, 3 table

Isotopic Ratios in a Peculiar Outbursting Comet

Isotopic ratios in comets provide keys for the understanding of the origin of cometary material, and the physical and chemical conditions in the early Solar Nebula. A newly discovered peculiar comet, C/2015 ER61, underwent an outburst with a total brightness increase of 2 magnitudes on the night of April 4th, 2017. The sharp increase in brightness offers a rare opportunity to measure the isotopic ratios of the light elements of this comet. We obtained two high-resolution spectra of C/2015 ER61 with UVES on Apr. 13 and Apr. 17 respectively. At the time of our observations, the comet was fading gradually since the outburst. We measured the 12C/13C and 14N/15N isotopic ratios from the CN Violet (0,0) band. In addition, we determined the 14N/15N ratio in NH2 for C/2015 ER61 from four pairs of NH2 isotopologue lines. Some 18OH lines were detected but the S/N of these lines is too low to derive a reliable 18O/16O estimate. We will present our UVES spectra of C/2015 ER61, obtained shortly after the outburst. We will also present the comparison of the Isotopic ratios of C/2015 ER61 with those of other comets