Non-LTE radiative transfer for sub-millimeter water lines in Comet 67P/Churyumov-Gerasimenko

Lee, Seungwon; Allmen, Paul von; Kamp, L. W.; Gulkis, S.; Davidsson, B.

doi:10.1016/j.icarus.2011.07.007

Cited by 17 publications

(15 citation statements)

References 19 publications

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“…This parameterization was also inspired by a DSMC simulation of the coma structure (Lee et al 2011;Davidsson et al 2010). The resulting temperature profile shows a rapid monotonic decrease initially followed by a slow asymptotic approach to the terminal temperature (the minimum value).…”

Section: Models and Data Analysesmentioning

confidence: 99%

“…The rate equation for the ortho H 16 2 O rotational population levels includes radiative coupling, collisions with neutral water molecules, collisions with electrons, and infrared radiative pumping. The rate equation is described in detail in Lee et al (2011). The average radiation intensity that is needed in the rate equation can be accurately calculated with a direct ray transfer sampling approach such as the accelerated Monte Carlo method (Hogerheijde & van der Tak 2000).…”

Section: Models and Data Analysesmentioning

confidence: 99%

“…The synthetic power received by the MIRO radiometer was converted to antenna temperature to compare with the calibrated line spectra of the MIRO measurement. The details of the line spectrum calculation are described in Lee et al (2011).…”

Section: Models and Data Analysesmentioning

confidence: 99%

See 2 more Smart Citations

Spatial and diurnal variation of water outgassing on comet 67P/Churyumov-Gerasimenko observed from Rosetta/MIRO in August 2014

Lee

Allmen

Allen

et al. 2015

A&A

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Aims. We present the spatial and diurnal variation of water outgassing on comet 67P/Churyumov-Gerasimenko using the H 16 2 O rotational transition line at 556.936 GHz observed from Rosetta/MIRO in August 2014. Methods. The water line was analyzed with a non-LTE radiative transfer model and an optimal estimation method to retrieve the H 16 2 O outgassing intensity, expansion velocity, and gas kinetic temperature. On August 7−9, 2014 and August 18−19, 2014, MIRO performed long steady nadir-pointing observations of the nucleus while it was rotating around its spin axis. The ground track of the MIRO beam during the observation was mostly on the northern hemisphere of comet 67P, covering its three distinct parts: the so-called head, body, and neck areas. Results. The MIRO spectral observation data show that the water-outgassing intensity varies by a factor of 30, from 0.1 × 10 25 molecules s −1 sr −1 to 3.0 × 10 25 molecules s −1 sr −1 , the terminal gas expansion velocity varies by 0.17 km s −1 from 0.61 km s −1 to 0.78 km s −1 , and the terminal gas temperature varies by 27 K from 47 K to 74 K. The retrieved coma parameters are co-registered with local environment variables such as the subsurface temperatures, measured in the MIRO continuum bands, the local solar time, illumination condition, and beam location on nucleus. The spatial variation of the outgassing activity is very noticeable, and the largest outgassing activity in August 2014 occurs near the neck region of the nucleus. The outgassing activity in the neck region is also found to be correlated with the local solar hour, which is related to the local illumination condition.

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Section: Models and Data Analysesmentioning

confidence: 99%

Section: Models and Data Analysesmentioning

confidence: 99%

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Spatial and diurnal variation of water outgassing on comet 67P/Churyumov-Gerasimenko observed from Rosetta/MIRO in August 2014

Lee

Allmen

Allen

et al. 2015

A&A

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“…Since large uncertainties still exist for the electron density and temperature profile in cometary comae, we used the same method as Biver (1997), which was also used in more recent studies (Bensch and Bergin, 2004;Zakharov et al, 2007;Hartogh et al, 2010;Paganini et al, 2010;Lee et al, 2011), where the positions of the contact surface and the recombination surface (outside of which the recombination rate of electrons with ions is negligible) are determined by two scaling factors respectively referred to as R cs and R rec hereafter. This approach matches the location of the contact surface for 1P/Halley during the Giotto encounter with R cs $ 3750 km and R rec $ 7150 km.…”

Section: The Effect Of Electron Collisions On the Rotational Temperaturementioning

confidence: 99%

Understanding measured water rotational temperatures and column densities in the very innermost coma of Comet 73P/Schwassmann–Wachmann 3 B

Fougere

Combi

Tenishev

et al. 2012

Icarus

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“…In this work we use the same ortho-H 2 O non-LTE model with seven levels and nine transitions as used in previous work (Gulkis et al, 2015;Lee et al, 2015). In our nominal model, following the formalism as in (Lee et al, 2011), the water-electron collisional excitation may also play a role at larger distance from the nucleus. Nevertheless, the measurements of electron density around 67P during an early activity (July-August 2014) (Edberg et al, 2015) is too low to strongly influence the simulated line amplitudes.…”

Section: D Non-lte and Beam Synthesis Modelmentioning

confidence: 99%

Constraining spatial pattern of early activity of comet 67P/C–G with 3D modelling of the MIRO observations

Zhao

Rezac

Hartogh

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Our aim is to investigate early activity (July 2014) of 67P/CG with 3D coma and radiative transfer modeling of MIRO measurements, accounting for nucleus shape, illumination, and orientation of the comet. We investigate MIRO line shape information for spatial distribution of water activity on the nucleus during the onset of activity. During this period we show that MIRO line shape have enough information to clearly isolate contribution from Hapi and Inhotep independently, and compare it to the nominal case of activity from the entire illuminated surface. We also demonstrate that spectral line shapes differ from the 1D model for different viewing geometries and coma conditions relevant to this study. Specifically, line shapes are somewhat sensitive to the location of the terminator in the coma. At last, fitting the MIRO observations we show that the Imhotep region (possible extended source of H 2 O due to CO 2 activity) contributes only a small fraction of the total number of water molecules into MIRO beam in the early activity. On the other hand, a strong enhancement of water activity from the Hapi region seems required to fit the MIRO line shapes. This is consistent with earlier Rosetta A PREPRINT -FEBRUARY 28, 2019 results. Nevertheless, within the assumption of our coma and surface boundary conditions we cannot get a reasonable fit to all MIRO mapping observations in July 2014, which may illustrate that a more sophisticated coma model or more accurate temperature/velocity distribution is needed.

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Non-LTE radiative transfer for sub-millimeter water lines in Comet 67P/Churyumov-Gerasimenko

Cited by 17 publications

References 19 publications

Spatial and diurnal variation of water outgassing on comet 67P/Churyumov-Gerasimenko observed from Rosetta/MIRO in August 2014

Spatial and diurnal variation of water outgassing on comet 67P/Churyumov-Gerasimenko observed from Rosetta/MIRO in August 2014

Understanding measured water rotational temperatures and column densities in the very innermost coma of Comet 73P/Schwassmann–Wachmann 3 B

Constraining spatial pattern of early activity of comet 67P/C–G with 3D modelling of the MIRO observations

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