Cyanogen jets in comet Halley

A’Hearn, Michael F.; Hoban, S.; Birch, P. V.; Bowers, Craig; Martin, R.; Klinglesmith, Daniel A.

doi:10.1038/324649a0

Cited by 215 publications

(56 citation statements)

References 15 publications

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“…-Coma structures: The cometary images were analyzed for the presence of coma structures applying two different numerical enhancement procedures to the flux calibrated data, 1) adaptive Laplace filtering (Richter 1978(Richter , 1991Boehnhardt & Birkle 1994) and 2) radial renormalization (A'Hearn et al 1986). The former method is sensitive to gradient changes on different scales depending on the width of the spatial filter applied.…”

Section: Analysis and Resultsmentioning

confidence: 99%

Imaging and spectroscopy of comet C/2001 Q4 (NEAT) at 8.6 AU from the Sun

Tozzi

Boehnhardt²,

Curto³

2003

A&A

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Abstract. Comet C/2001 Q4 (NEAT) was observed inbound at an heliocentric distance of 8.6 AU. Broadband filter images in the visible and long slit spectroscopy in the 3500-7000 Å range was recorded. No sign of CN emission was detected and an upper limit for CN production rate of 1.4 × 10 25 molecules s −1 is estimated. The color of the dust in the inner coma is very red with a spectral index of 29%/1000 Å. The radial profile of the dust coma displays steep gradients of 1.7 (inner part) to 2.4 (outer part). The afρ value, a proxy for the dust production, is measured to be 1500 cm. The coma shows a weak and short conic structure in the northern hemisphere that is interpreted as dust fan produced by an active region on the nuclear surface.

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Section: Analysis and Resultsmentioning

confidence: 99%

Imaging and spectroscopy of comet C/2001 Q4 (NEAT) at 8.6 AU from the Sun

Tozzi

Boehnhardt²,

Curto³

2003

A&A

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“…This can be seen in video clip Animation2, where we have applied a technique similar to ring-masking (A'Hearn et al 1986) to the residual images, to enhance the contrast in the central region (from the individual pixel values, our method subtracts the smoothed radial profile of the azimuthal minimum). The features in the outer coma weakly correlate with their progenitors visible during the earlier cycles, which can be caused by the postulated excitation of the rotation state.…”

Section: Cn and C 3 Transient Structuresmentioning

confidence: 99%

Rotation-stimulated structures in the CN and C₃comae of comet 103P/Hartley 2 close to the EPOXI encounter

Waniak

Borisov

Drahus

et al. 2012

A&A

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Context. In late 2010, a Jupiter family comet 103P/Hartley 2 was the subject of an intensive world-wide investigation. On UT October 20.7, the comet approached the Earth within only 0.12 AU, and on UT November 4.6 it was visited by the NASA EPOXI spacecraft. Aims. We joined this international effort and organized a ground-based observing campaign with three key goals to: (1) measure the parameters of the nucleus rotation in a time series of CN; (2) investigate the compositional structure of the coma by comparing the CN images with nightly snapshots of C 3 ; and (3) investigate the photochemical relation of CN to HCN, using the HCN data collected nearly simultaneously with our images. Methods. The images were obtained through narrowband filters using the two-meter telescope of the Rozhen National Astronomical Observatory. They were taken over four nights about the moment of the EPOXI encounter. Image processing methods and periodicity analysis techniques were used to identify transient coma structures and investigate their repeatability and kinematics. Results. We observe shells, arc-, jet-and spiral-like patterns that are very similar for the CN and C 3 comae. The CN features expanded outwards with the sky-plane projected velocities of between 0.1 to 0.3 km s −1 . A corkscrew structure, observed on November 6, evolved with a much higher velocity of 0.66 km s −1 . The photometry of the inner coma of CN shows variability with a period of 18.32 ± 0.30 h (valid for the middle moment of our run, UT 2010 Nov 5.0835), which we attribute to the nucleus rotation. This result is fully consistent with independent determinations around the same time by other teams. The pattern of repeatability is, however, imperfect, which is understendable given the suggested excitation of the rotation state, and the variability detected in CN correlates well with the cyclic changes in HCN, but only in the active phases. The identified coma structures, along with the snapshot of the nucleus orientation obtained by EPOXI, enable us to estimate the spin axis orientation. We obtain RA = 122 • , Dec = +16 • (epoch J2000.0), neglecting at this point the rotational excitation.

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“…To enhance the existing asymmetries and/or features, two different methods were applied: 1) adaptive Laplace filtering (Richter 1978(Richter , 1991Boehnhardt & Birkle 1994) and 2) radial renormalization (A'Hearn et al 1986). The former method does not depend on the accuracy of the comet nucleus centering by a 2D Gaussian, and it is more sensitive to gradient changes on different scales depending on the width of the spatial filtering applied.…”

Section: D Morphologymentioning

confidence: 99%

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

Lara¹,

Rodrigo²,

Tozzi³

et al. 2004

A&A

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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.

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Cyanogen jets in comet Halley

Cited by 215 publications

References 15 publications

Imaging and spectroscopy of comet C/2001 Q4 (NEAT) at 8.6 AU from the Sun

Imaging and spectroscopy of comet C/2001 Q4 (NEAT) at 8.6 AU from the Sun

Rotation-stimulated structures in the CN and C₃comae of comet 103P/Hartley 2 close to the EPOXI encounter

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

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Cyanogen jets in comet Halley

Cited by 215 publications

References 15 publications

Imaging and spectroscopy of comet C/2001 Q4 (NEAT) at 8.6 AU from the Sun

Imaging and spectroscopy of comet C/2001 Q4 (NEAT) at 8.6 AU from the Sun

Rotation-stimulated structures in the CN and C3comae of comet 103P/Hartley 2 close to the EPOXI encounter

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

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Rotation-stimulated structures in the CN and C₃comae of comet 103P/Hartley 2 close to the EPOXI encounter