MSC RESEARCH PROJECT-II
PRESENTATION ON : IMAGING POLARIMETRY OF
SOME COMETS
Presented by: Anushka Dey
Roll-042523 No:2013900312
Semester: 4th semester
Paper: Research Project-II
Under the supervision of : Prof.Himadri
Sekhar Das
WHY STUDY COMETS?
MOTIVATION
• Comets are the icy remnants from the early solar
system. Often called dirty snowball (Fred Whipple)
• They carry primordial dust and organic material
• Studying them help us understand solar system
form,ation and dust properties.
• Imaging polarimetry provides insight into:
• Grain size, shape, and composition
• jets, asymmetries, and outflows
Image credit: Comet Lovejoy
(NASA)
STRUCTURE OF COMET
Main components:
Nucleus:
• Solid core made of ice, dust and organic
compounds
• Typically 1-10 km in size
Coma
• Formed by sublimination of ices near the sun
• Can extend up to hundreds of thousands of
kilometers
Tails
• Dust Tail( Type II)
• Curved, yellow-white, made of small dust
grains
• Formed by solar radiation pressure
• Ion tail( Type I)
• Straight, bluish, made of ionized gases
• Formed by solar interaction
TYPES AND ORIGIN OF COMETS
Type Period(P) Origin Example
Short Period P< 200 years Kuiper Belt 2P/Encke
Comets
Jupiter Family P< 20 years Kuiper belt 9p/Temple 1
Comets
Halley-Type 20<P<200 years Outer edges of 1P/Halley
Comets Kuiper belt
Long-period P>200 years Oort cloud C/1996 B2
Comets (Hyakutake)
Non-Periodic Hyperbolic orbits Oort cloud C/2023 H5
Comets (e>1) (Lemmon)
OBJECTIVES OF MY PROJECT:
(1) Review of Cometary Properties and Structure: To conduct a detailed review of the physical and
chemical properties of comets, including their nucleus, coma, and tail structures, and to summarize their
role in understanding the early solar system.
(2) Study of Imaging Polarimetry of Comets: To perform imaging polarimetric observations of selected
comets, focusing on understanding the scattering properties of cometary dust and its dependence on factors
such as phase angle and distance from the Sun.
(3) Analysis of Intensity Profiles and Polarization Maps: To analyze the intensity distribution and
polarization maps of cometary comae, aiming to derive insights into the spatial variation of dust properties,
grain size distribution, and the composition of the cometary environment.
COMET SELECTED TO WORK WITH: C/2023 H5( Comet Lemmon)
Comet C/2023 H5, commonly known as comet Lemmon,
was discovered on April 19, 2023, by the Mount
Lemmon Survey using a 1.5-meter reflector telescope.
The orbital elements of C/2023 H5 (Lemmon) are as
follows:
e (Eccentricity): 1.0004350
q (Perihelion distance): 4.3126220 (AU)
i (Inclination): 97.85560
Epoch of Perihelion Passage: June 30, 2025, 06:15
UTC
Classification(s): Nearly isotropic; New (a > 10000
AU)
Category: Non- periodic comet
Image Credit: F. Kugel
METHODOLOGY
• Unpublished raw data was utilized from the polarimetric observation data of comet C/2023 H5, carried out on
05/03/2025 at 1:25 LT at phase angle=10.3493 by the 104cm Sampuranand Telescope of Aryabhatta Research
Institute of Observational sciences (ARIES), Nainital using R filter.
• First of all, To correct for the electronic offset in CCD images, a master bias frame was created by loading the
necessary IRAF packages: imred, ccdred and zerocombine and the following parameters were set:
• All the observational frames were then bias-subtracted to remove electronic noise and create clean images for each
frames by loading the package: epar ccdproc
• To increase the signal to noise ratio, the data images were then combined to obtain the four final
images of the rotations by loading the IRAF package: epar imcombine.
• Then the center shift for each of the images were done by loading the packages: digiphot, apphot, centerpars,
epar center, and epar imshift which created a shifted log file for all the images.
• After the creation of the center co-ordinate file of the combined images using the package: epar center, aperture
photometry was performed on the ordinary and extraordinary beams using epar phot allowing the measurement
of the total intensity in each beam by generation of .mag1 files.
• Finally after the creation of output ordinary and extraordinary intensity files. Average of the sky value was taken
which was found to be 396 with moffat value 3.11 and calculation were performed using a custom FORTRAN
program( newpolinput.in).
• Cmt.out file was created that contained all the necessary data containing aperture, polarization
angle, polarization %, etc. From here one of suitable value of Polarization % was selected based
on Moffat value
RESULT : Polarization % was calculated by selecting a value of polarization angle value from the cmt.out table
And using the formula:
Pr= (Pobs ep) x cos 2
Where, obs = 180- 2.754=177.246
r= obs- (
Pobs 3.838- Poffset
=3.838-0.85
=2.9
And then, Pr = 2.9 x cos (2x 68)= -2.14%
Value of Polarization angle selected
from here
CREATION OF INTENSITY MAP
• Then the final intensity map with contours was created with python script,
these contours in intensity map helps in identifying intensity gradients and
morphological features such as jets or asymmetries. The resulting plot
provided a clear and informative representation of the comet's intensity
structure for further analysis
Fig 1: Intensity Map with contours-Intensity image of Comet C/2023 H5 with overlaid contours
showing brightness distribution and coma asymmetry
CREATION OF POLARIZATION MAP
• Now, to investigate the spatial distribution of dust polarization in
Comet C/2023 H5 (Lemmon), a Polarization map was constructed
using images obtained at four orientations using python script.The map
presents the degree of linear polarization across the coma, derived
from the Stokes parameters, and is overlaid with vectors indicating the
direction of polarization at each point.
Fig 2: Polarization Map of Comet C/2023 H5- Spatial distribution of
linear polarization across the cometary coma, with overlaid sun-
comet radius vector to indicate illumination geometry.
Radial Intensity Profiling
• A one-dimensional intensity (brightness) profile was extracted along the sunward–antisunward direction in order to
examine the spatial variation in the comet's coma using python script . A cometary coma's brightness profile in
various directions is a useful tool for examining the physical characteristics of dust grains.
Fig 4: Comet Intensity Map with directional arrows-Intensity image of Fig 5: Log-Log Intensity Profiles-Radial Intensity Profiles plotted in log-log scale along the sunward and
Comet C/2023 H5(Lemmon) showing the sunward and tailward tailward directions, indicating slopes in inner, middle, and outer coma regions. Dashed Vertical line
directions, overlaid with North and East orientations. marks the seeing radius
Morphological Enhancement
• An enhancement technique was used to draw attention to the low contrast cometary
coma structures in order to examine the comets' morphology. By using azimuthal
average and azimuthal renormalization filtering, we have employed a rotational gradient
approach. The azimuthal average and azimuthal renormalization filter was processed
through a comet enhancement program, available at the link: https://cie.psi.edu/
Figure 6: Azimuthal average filter (left) and Azimuthal renormalization filter(right) used on the FITS
image.
RESULT AND CONCLUSION
• The calculated polarization Pr=−2.14% at a phase angle of 10.3493 indicates that comet C/2023 H5 exhibits negative polarization, which is typical for
comets observed at small phase angles (generally < 20°). This negative polarization at a phase angle of 10.35° is consistent with expected scattering
behavior for dust-rich comets at low phase angles. Similar polarization values have been observed in comets such as 32P/Comas Solà and 290P/Jager
under comparable conditions, reinforcing that C/2023 H5 is likely a dust-rich comet with submicron, fluffy dust grains.
• The intensity map with overlaid contours shows a central peak (yellow
region at 1955.2 flux) around (25, 15) in pixel coordinates, indicating
the brightest part of the comet, likely the nucleus or the inner coma.
The intensity decreases outward, as seen by the transition from
yellow to green, blue, and purple, with contours marking specific
intensity levels .
• The intensity distribution is not perfectly circular. There’s a slight
elongation or asymmetry, particularly toward the lower-left direction
which could suggest a dust tail or jet activity in that direction,
influenced by solar radiation pressure or the comet's rotation.
• Such intensity asymmetries are characteristic of comets with non-
isotropic dust emission, consistent with observations in comets like
C/2015 V2 (Johnson), where similar tailward enhancements were
observed (Mazarbhuiya et al. 2022).
• The polarization map (Figure 11) shows the degree of linear polarization in
the coma, ranging from -1% to -7%. The highest negative polarization (red, -
7%) is near the center, around (21, 18) in pixel coordinates, and the
Polarization decreases outward to -1% (blue regions). At lower phase angles,
this negative polarization is expected. This trend is typical of dusty comets
observed at small phase angles, where submicron grains produce strong
backscattering effects near the nucleus (Kolokolova et al. 2007).
• The uniformity in negative polarization across apertures also supports the
classification of C/2023 H5 as a dust-rich comet, since gas-rich comets
typically show a steep polarization drop-off with increasing aperture size
( Kolokolova et al. 2015).
Fig 7: POLARIZATION MAP
Figure 12: Intensity image of comet C/2023 H5 with applied Figure 13: Intensity image of comet C/2023 H5 with applied
azimuthally average Filter azimuthally average Filter
• To analyze the morphology of the comet, we have used a rotational gradient technique to highlight the low contrast structure of the cometary coma- the azimuthal average
filtering which provides a clear radial intensity profile, showing how brightness decreases with distance from the nucleus and azimuthally renormalization filter, the
azimuthally renormalized filter, by removing the radial gradient, highlights any deviations from symmetry.
• The presence of some asymmetry indicates directional features, likely a dust tail, consistent with the previous intensity map's elongation in the anti-solar direction.
• The symmetric nature of this map suggests that, on average, the coma is circularly symmetric, which is typical for comets when azimuthal variations are averaged out. A
strong dust jet feature seems to be Present in the antisolar direction and a asymmetric jet feature seems to be present in the anti solar direction as seen in the azimuthally
renormalization feature. A L-shaped structure appears as radial outflow of dust from the nucleus. This morphology parallels the findings in comet 32P/Comas Solà, where a
V-shaped antisolar feature was attributed to radial dust outflows (Mazarbhuiya et al. 2022).
• In the sunward direction, the inner region exhibited a slope of -0.160
with a high coefficient of determination (R² = 0.979, P-value =
1.740×10⁻¹¹), indicating a robust fit and a steep decline in intensity
with distance. This suggests significant dust or gas concentration
close to the nucleus, likely driven by solar radiation pressure.
• The middle region showed a shallower slope of -0.064 (R² = 0.834, P-
value = 1.204×10⁻¹¹), reflecting a more gradual decrease in intensity
as the distance increases, possibly due to the dispersion of material.
• In the outer region, insufficient or invalid data prevented slope
calculation, likely due to low signal-to-noise ratios at larger distances.
• In the tailward direction, the inner region had a slope of -0.116 (R² =
0.979, P-value = 1.958×10⁻¹¹), indicating a slightly less steep decline
compared to the sunward direction, which may suggest differences
in material composition or dynamics in the tail.
• The middle region yielded a slope of -0.091 (R² = 0.989, P-value =
6.146×10⁻²⁷), demonstrating an excellent fit and a continued gradual
decline in intensity. The outer region provided a slope of -0.049 (R² =
0.972, P-value = 4.330×10⁻⁴⁵), with a high statistical significance,
indicating a very slow decrease in intensity at larger distances,
Figure 10: log-log intensity profile showing cuts through the coma the sunward and tailward consistent with the expected behavior of a comet’s tail where dust
profile for the comet.Verical dashed line represents the seeing radius limit for the observed and gas are more diffuse.
line.
• These findings highlight distinct radial intensity profiles in the
sunward and tailward directions, reflecting the influence of solar
radiation and cometary activity on material distribution. The steeper
slopes in the inner regions suggest concentrated outgassing near the
nucleus, while the shallower slopes at greater distances indicate
dispersion of material, particularly in the tailward direction where
the outer region data remain reliable.
CONCLUSION:
• The observed negative polarization value of −2.14%, together with morphological features and intensity profiles, suggests that the coma
is primarily composed of submicron-sized, irregular, and porous dust grains which is consistent with characteristics seen in other dust-
rich comets observed at similar phase angles.
• The polarization map revealed spatial variations within the coma, with the most pronounced negative polarization found near the
comet’s nucleus. This phenomenon typically occurs at small phase angles and provides valuable clues about the nature and structure of
cometary dust. The findings closely mirror those reported by Mazarbhuiya et al. (2022) for comets 32P/Comas Solà and C/2015 V2
(Johnson), which also exhibited negative polarization values below 22°, with relatively uniform distributions across different aperture
sizes.
• Further insights emerged from the intensity and filtered images, which revealed structural asymmetries and hints of jet-like features,
particularly in the antisolar direction. Techniques such as azimuthal averaging and renormalization helped bring out these low-contrast
details, pointing to anisotropic dust emission—an effect similarly noted in 32P/Comas Solà, where V-shaped features were linked to radial
outflows of dust.
• Radial intensity profiles extracted in both sunward and tailward directions showed notable differences in slope across various regions of
the coma. The inner coma exhibited steeper slopes, suggesting higher dust production close to the nucleus, while the outer regions
appeared more diffuse—likely shaped by the effects of solar radiation pressure. These slope variations, deviating from the typical -1
canonical slope, support observations by Mazarbhuiya et al., who attributed such changes to non-uniform emission, dust grain
fragmentation, and evolving grain properties.
• Overall, Comet C/2023 H5 (Lemmon) clearly falls into the category of dust-rich, low-Pmax comets, where light scattering behavior is
heavily influenced by small, loosely bound dust particles. The results of this study not only strengthen our understanding of this comet’s
dust
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• Web : https://ssd.jpl.nasa.gov/horizons/app.html#/
• Web : https://astro.vanbuitenen.nl/comet/2023H5
• Web : https://www.Cobs.si/comet/
• Web : https://cie.psi.edu/
THANK YOU
