Image enhancement techniques for quantitative investigations of morphological features in cometary comae: A comparative study

Samarasinha, Nalin H.; Larson, S. M.

doi:10.1016/j.icarus.2014.05.028

Cited by 65 publications

(76 citation statements)

References 23 publications

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“…As discussed in Section 4, the gas morphology did not affect the centroiding but dust images had a strong tail which may have biased the dust centroids slightly tailward. We applied various enhancement techniques (e.g., Schleicher & Farnham 2004;Samarasinha & Larson 2014) to explore faint structures in the coma morphology. Numerous enhancement techniques were applied to confirm the validity of structures in the coma, but analyses discussed herein primarily utilized removal of an azimuthal median profile.…”

Section: Ccd Observations and Reductionsmentioning

confidence: 99%

Observations of Comet Ison (C/2012 S1) From Lowell Observatory

Knight

Schleicher

2014

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We observed the dynamically new sungrazing comet ISON (C/2012 S1) extensively at Lowell Observatory throughout 2013 in order to characterize its behavior prior to perihelion. ISON had "typical" abundances for an Oort Cloud comet. Its dust production, as measured by r Af , remained nearly constant during the apparition but its CN gas production increased by ∼50 ×. The minimum active area necessary to support observed water production rates exceeded the likely surface area of the nucleus and suggests a population of icy grains in the coma. Together with the flattening of the dust radial profile over time, this is consistant with ejection of a large quantity of slow moving dust and icy grains in the coma at large heliocentric distance. The dust morphology was dominated by the tail, but a faint sunward dust fan was detected in March, April, May, and September. We imaged multiple gas species in September, October, and November. All gas species were more extended than the dust coma, although only CN had sufficient signal-to-noise for detailed morphological study. Excess CN signal was observed in the sunward hemisphere in September and early October. In November the excess CN signal was in the tailward hemisphere and two faint CN features appeared approximately orthogonal to the tail with position angles varying by about ±20°from night to night. Using numerical modeling, we best reproduced the orientation and shape of these features as well as the bulk brightness with a pole oriented approximately toward the Sun and a single source located within ∼35°of the equator. Variations in position angle and relative brightness of the CN features from night to night suggest a rotation period shorter than 24 hr. The production rates and coma morphology suggest a nucleus that was active over nearly its entire sunward facing hemisphere in September and October but which underwent a significant mass loss event, potentially including fragmentation, shortly before November 1. Significant subsequent mass loss likely continued at the same site over subsequent days/weeks and may have catastrophically weakened the nucleus prior to perihelion.

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Section: Ccd Observations and Reductionsmentioning

confidence: 99%

Observations of Comet Ison (C/2012 S1) From Lowell Observatory

Knight

Schleicher

2014

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“…at 4.8 AU no high activity is expected, at least no H2O sublimation, only activity triggered by CO or CO2 sublimation). With all this in mind, we finally found the aperture that gave the lowest dispersion in the photometry of the comet and of the stars with similar (Samarasinha & Larson 2014). Green circles mark the comet photocentre.…”

Section: Photometrymentioning

confidence: 93%

“…The seeing during this observing night was 1.63 . The image was processed and filtered with different digital techniques (Samarasinha & Larson 2014) in order to enhance structures in the inner coma; the results of this processing are shown in the four upper panels of Fig. 1.…”

Section: Photometrymentioning

confidence: 99%

Short-term variability of comet C/2012 S1 (ISON) at 4.8 AU from the Sun

Santos-Sanz

Ortiz

Morales

et al. 2015

A&A

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Context. We observed comet C/2012 S1 (ISON) during six nights in February 2013 when it was at 4.8 AU from the Sun. At this distance and time the comet was not very active and it was theoretically possible to detect photometric variations likely due to the rotation of the cometary nucleus. Aims. The goal of this work is to obtain differential photometry of the comet inner coma using different aperture radii in order to derive a possible rotational period. Methods. Large field of view images were obtained with a 4 k × 4 k CCD at the f/3 0.77 m telescope of La Hita Observatory in Spain. Aperture photometry was performed in order to get relative magnitude variation versus time. Using calibrated star fields we also obtained ISON's R-magnitudes versus time. We applied a Lomb-Scargle periodogram analysis to get possible periodicities for the observed brightness variations, directly related with the rotation of the cometary nucleus. Results. The comet light curve obtained is very shallow, with a peak-to-peak amplitude of 0.03 ± 0.02 mag. A tentative synodic rotational period (single-peaked) of 14.4 ± 1.2 h for ISON's nucleus is obtained from our analysis, but there are other possibilities. We studied the possible effect of the seeing variations in the obtained periodicities during the same night, and from night to night. These seeing variations had no effect on the derived periodicity. We discuss and interpret all possible solutions for the rotational period of ISON's nucleus.

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“…In order to enhance the structures observed in the coma, images are filtered using different digital techniques (Low Pass, Larson-Sekanina, and Laplacian), following the guidelines of Samarasinha & Larson (2014). The best results are obtained for the Laplacian filter.…”

Section: Observed Featuresmentioning

confidence: 99%

“…The best results are obtained for the Laplacian filter. The final images (individual and master) are filtered using the Laplacian filtering technique (Boehnhardt & Birkle 1994; Kidger et al 1996;Samarasinha & Larson 2014). The filtering process does not conserve flux; only the morphology and position of the features can be obtained from the filtered images.…”

Section: Observed Featuresmentioning

confidence: 99%

The Rotation Period of C/2014 Q2 (Lovejoy)

Serra

Licandro

2015

ApJ

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C/2014 Q2 (Lovejoy) was observed around perihelion (2015 January 30) on 15 nights between 2015 January 21 and February 11 using the TADer 0.3-m astrograph telescope at Teide Observatory (IAC, Tenerife, Spain). Two large spiral jet structures were observed over several cometary rotations. A new method of searching for periodicities in the PA of spiral jets in the coma region at a fixed distance (20,624 km) from the cometary optocenter is presented and used to determine a nuclear rotation period of 17.89 ± 0.17 hr.

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Image enhancement techniques for quantitative investigations of morphological features in cometary comae: A comparative study

Cited by 65 publications

References 23 publications

Observations of Comet Ison (C/2012 S1) From Lowell Observatory

Observations of Comet Ison (C/2012 S1) From Lowell Observatory

Short-term variability of comet C/2012 S1 (ISON) at 4.8 AU from the Sun

The Rotation Period of C/2014 Q2 (Lovejoy)

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