The gas and dust coma of Comet C/1999 H1 (Lee)

Abstract

Abstract. Comet Lee (C/1999 H1) was observed on June 6, 1999 when it was at r h = 0.98 AU and ∆ = 1.195 AU. The spectrophotometric observations, between 0.6 and 1 µm, were aimed at the detection of the CI( 1 D) doublet λλ 9823/9850 Å. The non-detection of these lines, with a 3σ flux upper limit of the order of 4.6 × 10 −17 erg cm −2 s −1 , confirms the CO depletion already noted by other authors. Several CN and NH 2 emission bands lie in that spectral range, making it possible to derive production rates for both species as ∼3.1 × 10 26 s −1 and 1.2 × 10 27 s −1 , respectively. The oxygen forbidden line at 6300 Å was used to obtain Q H 2 O = (1.22 ± 0.7) × 10 29 s −1 . Assuming that CN and NH 2 are directly produced by HCN and NH 3 , Comet Lee has a HCN/H 2 O ≈ 0.25% and NH 3 /H 2 O ≈ 1% at r h = 0.98 AU, in reasonable agreement with what has been found in other long-period comets. The structural analysis carried out on cometary images acquired with broad band R Bessel filter clearly displays two pairs of ion rays likely produced by the H 2 O + doublet at 6198 and 6200 Å, wavelengths covered by the bandpass filter. Identical features are found in the images acquired with the Gunn i filter. The dust brightness profiles in the east-west direction do not deviate from a ρ −m law (with 0.7 < m ≤ 1.2) as expected for a steady state model coma with a constant dust production rate and expanding at constant velocity. The dust production rate, as obtained from the A f ρ parameter, is ∼500 cm, which compared with the gas production rate classifies this comet as a dust poor one with relatively high (6.5-11.7) gas-to-dust mass ratio. Analysis of the normalized reflectivity gradient (i.e. continuum color) as a function of ρ indicates a slight reddening of the solid component in the coma at large cometocentric distances, whereas the average dust color within an aperture of 20 000 km, centered at the nucleus, is ∼9% per 1000 Å. Mie scattering computations applied to an ensemble of particles indicate that the dust coma is characterised by a relative broad size distribution with a typical mean size of 1 µm. These grains might be composed of a mixture of silicates and icy material.

Ammonium sulfate on Titan: Possible origin and role in cryovolcanism

“…Mousis et al (2002) presented a new turbulent evolutionary model which indicates that the yield of CH 4 and NH 3 would actually have been insignificant even in the warmer, dense saturnian subnebula, concluding that the materials which went to form the saturnian satellites probably contained only small quantities of primordial CH 4 and NH 3 from the Primitive Solar Nebula (PSN); i.e., CO/CH 4 ≈ 5 and N 2 /NH 3 ≈ 3. This being the case, the mass fraction of NH 3 in Titan's mantle would have been just 1.6 wt% NH 3 , a value which is essentially identical to that found in comets (e.g., Meier et al, 1994;Bird et al, 1997;Lara et al, 2004). The turbulent evolutionary model does not account for the catalytic effect of iron grains in the PSN and the possibility that other grain surface reactions could yield N 2 /NH 3 < 1 (e.g., Ruffle and Herbst, 2000).…”

Solar and Heliospheric Observatory/Solar Wind Anisotropies Observations of Five Moderately Bright Comets: 1999-2002

“…Other water production rates covering limited ranges of heliocentric distance have been reported by Weaver et al (2002), Mumma et al (2001b), Neufeld et al (2000), Feldman et al (1999), Lara et al (2004a), and Dello Russo et al (2005). These, as well as those discussed above from Chiu et al and Biver et al, are plotted in Figure 2 along with the TRM dailyaveraged deconvolved water production rates from SWAN, which are given in Table 3.…”

Activity evolution, outbursts, and splitting events of comet 73P/Schwassmann-Wachmann 3

“…During the 4-night run close to perigee in , it was impossible to acquire any spectra because the comet moved too rapidly across the sky and, consequently, the optocenter slowly drifted outside the field of view of the slit. Details of the spectroscopic data reduction and calibration can be found in Lara et al (2001Lara et al ( , 2004a and are not repeated here. Since the gas emission of 73P does not cover the entire length of the slit, apart from CN on the spectra obtained in May 2, it is possible to measure the sky contamination by extracting spectra directly from the edges of the frame.…”