Comet 2P/Encke

 

2013/08/09    2013/10/08

 

2013 Aug 09
Mouseover to browse the image in BGRY color sequels version. Both images are asinh stretched. I noticed a diffuse "halo" around the bright stellar nucleus, probably its coma? However I could not find any evidence from obserations from other observers. In order to rule out the possibility of it being the effect from the imperfect flatfield image, I generated a minimum image from all of the image sequence with background centered around the nucleus normalized, with which the image sequence was subtracted. The resulting individual images were stacked both in average and median method, and the "halo" was found in both, albeit the SNR in the median combined image appeared poorer. Nevertheless, when I performed photometry in IDL, I regarded the comet as a bare nucleus. The photometric aperture was merely 2x its FWHM, which was ~1" greater than surrounding sidereal stars of similar magnitude.
 

MPC observation computed with Astrometrica using both UCAC-4 and CMC-14 star catalogs -- the former for astrometric reduction and the latter for photometric work:

COD C42
OBS M.-T. Hui, X. Gao
MEA M.-T. Hui
TEL 0.36-m f/6.9 Schmidt-Cassegrain + CCD
NET UCAC-4
COM Possible diffuse faint coma detected around the bright stellar nucleus in,
COM the stacked image, size round 29" x 32".
0002P        KC2013 08 09.83434 03 09 46.38 +27 26 11.7          18.0 N      C42
0002P        KC2013 08 09.83588 03 09 46.64 +27 26 13.0          18.2 N      C42
0002P        KC2013 08 09.83742 03 09 46.75 +27 26 13.8          18.2 N      C42
0002P        KC2013 08 09.83897 03 09 46.95 +27 26 15.9          18.4 N      C42
0002P        KC2013 08 09.84051 03 09 47.14 +27 26 16.9          18.2 N      C42
0002P        KC2013 08 09.84205 03 09 47.28 +27 26 17.9                      C42
0002P        KC2013 08 09.84360 03 09 47.48 +27 26 19.2          18.3 N      C42
0002P        KC2013 08 09.84514 03 09 47.65 +27 26 20.7          18.1 N      C42
0002P        KC2013 08 09.84668 03 09 47.80 +27 26 22.2          18.2 N      C42
0002P        KC2013 08 09.84823 03 09 48.09 +27 26 23.8          18.2 N      C42
0002P        KC2013 08 09.84977 03 09 48.13 +27 26 24.9          18.4 N      C42
0002P        KC2013 08 09.85132 03 09 48.32 +27 26 26.1                      C42
0002P        KC2013 08 09.85287 03 09 48.43 +27 26 26.8          18.4 N      C42
0002P        KC2013 08 09.85441 03 09 48.83 +27 26 28.6          18.3 N      C42
0002P        KC2013 08 09.85596 03 09 48.93 +27 26 30.0          18.3 N      C42
0002P        KC2013 08 09.85750 03 09 49.09 +27 26 31.0          18.2 N      C42
0002P        KC2013 08 09.85905 03 09 49.32 +27 26 32.9          18.2 N      C42
0002P        KC2013 08 09.86059 03 09 49.46 +27 26 34.0          18.2 N      C42
0002P        KC2013 08 09.86213 03 09 49.69 +27 26 35.5          18.1 N      C42
0002P        KC2013 08 09.86368 03 09 49.85 +27 26 36.8          18.3 N      C42
0002P        KC2013 08 09.86524 03 09 50.02 +27 26 38.2          18.3 N      C42
0002P        KC2013 08 09.86698 03 09 50.22 +27 26 39.0          18.1 N      C42
0002P        KC2013 08 09.86872 03 09 50.38 +27 26 40.3          18.1 N      C42
0002P        KC2013 08 09.87030 03 09 50.56 +27 26 42.1          18.4 N      C42
0002P        KC2013 08 09.87188 03 09 50.77 +27 26 43.9          18.4 N      C42
0002P        KC2013 08 09.87344 03 09 50.96 +27 26 44.6          18.3 N      C42
0002P        KC2013 08 09.87501 03 09 51.13 +27 26 46.4          18.4 N      C42
0002P        KC2013 08 09.87659 03 09 51.32 +27 26 47.5          18.5 N      C42
0002P        KC2013 08 09.87816 03 09 51.50 +27 26 49.1          18.4 N      C42
0002P        KC2013 08 09.87973 03 09 51.67 +27 26 50.4          18.2 N      C42
0002P        KC2013 08 09.88130 03 09 51.88 +27 26 51.6          18.2 N      C42
0002P        KC2013 08 09.88286 03 09 52.14 +27 26 53.5          18.2 N      C42
0002P        KC2013 08 09.88442 03 09 52.27 +27 26 54.5          18.2 N      C42
0002P        KC2013 08 09.88598 03 09 52.42 +27 26 56.1          18.2 N      C42
0002P        KC2013 08 09.88757 03 09 52.61 +27 26 57.2          18.2 N      C42
0002P        KC2013 08 09.88913 03 09 52.79 +27 26 58.8          18.1 N      C42
0002P        KC2013 08 09.89068 03 09 52.98 +27 26 59.7          18.2 N      C42
0002P        KC2013 08 09.89222 03 09 53.18 +27 27 01.0          18.4 N      C42
0002P        KC2013 08 09.89377 03 09 53.36 +27 27 02.4          18.3 N      C42
0002P        KC2013 08 09.89531 03 09 53.55 +27 27 03.6          18.5 N      C42

Photometry result computed with FOCAS, which processes images based upon the .LOG file of Astrometrica, by means of Multibox method:

COD C42
OBS M.-T. Hui, X. Gao
CATALOG: USNO A2.0 / CMC-14 - BAND: R

                                   10x10  20x20  30x30  40x40  50x50  60x60   SNR   SB   COD
COMET         UTC                    +/-    +/-    +/-    +/-    +/-    +/-     N  FWHM  CAT
------------  -------------------  -----  -----  -----  -----  -----  -----  ----  ----  ---
2P            09/08/2013 20:46:35  18.26  17.83  17.53  17.28  17.09  16.97   7.8  20.2  C42
2P            09/08/2013 20:46:35*  0.11   0.15   0.25   0.33   0.41   0.49    38   4.0  CMC

                                                                     AFRHO         LOG
COMET         UTC                   DELTA    r    BOX "   MAG   RSR    CM    +/-  AFRHO  OBS
------------  -------------------   -----  -----  -----  -----  ---  -----  ----  -----  ---
2P            09/08/2013 20:46:35    1.64   1.85  16.82  17.92    8      6     1  0.779  C42

FoCAs 3.42
www.astrosurf.com/cometas-obs
es.groups.yahoo.com/group/Cometas_Obs

Interpretation for FOCAS table headings:

The upper section:
Fisrt line:
COMET, UTC: refering to their original meanings respectively
10x10, 20x20 ... 60x60: the aperture sizes of photometry in term of rectangle in arcsec that are used to measure an object's magnitude
SNR: the Signal-to-Noise Ratio for aperture photometry
SB: stars of faintest magnitude on the images used in data reduction with the used star catalog in Astrometrica, rather than the stars of faintest magnitude in the images
COD: MPC Code of the observatory

Second line:
+/-: precisions of measurement
N: the number of used images for measurement
FWHM: Full-Width-Half-Maximum of total PSF, relevant to degree of seeing
CAT: the used star catalog in Astrometrica
The lower section:
DELTA: cometocentric distance of the Earth
r: heliocentric distance of the comet
BOX: dimension of the box aperture, always equivalent to a spatial dimension of 2E+04 km enclosing the comet
MAG: magnitude of the comet enclosed by the box
RSR: SNR expressed in integer
AFRHO CM: Afrho value in centimeter
+/-: precision of Afrho
LOG AFRHO: equal to alog10(Afrho)
OBS: MPC code of the observatory

Please note that the FOCAS also calculated Af$\rho $ for the comet. However, since the morphological appearance of the comet greatly differentiated from the 1/$\rho$ coma model, I would instead regard the value as meaningless.

As the observation lasted over 1-hr, I attempted to utilize the data to see if there would be any brightness change during the monitor. Unfortunately the tracking of the system was extremely poor that even a 60-sec exposure would lead to trailed images. In order to improve the SNR of the comet, I stacked every continuous 10 images respectively according to the background stars as well as the motion of the comet, which resulted in overall 8 datasets to be measured. (Frankly speaking I had attempted to stack every 2 and 4 images, however, the SNR was still found poor.) The images of untrailed stars were later fed into MaxImDL for registration on stars and were stored. Subsequently I typed command lines to crop the corresponding untrailed comet images centered on the optocenter, substituted the upper left corner with the cropped comet images and saved them in the working directory. As there was paper which proved the robustness and reliability of photometry in MaxImDL, I applied the software for photometry for saving time. Totally 6 comparison stars around the comet taken from NOMAD catalog were used, along with neighboring three check stars, showed in the following image. The photometric aperture radius was set to 8-pixel, with a gap of 4-pixel and a sky annulus of 8-pixel.

The faint streak in the image is trailed 2P/Encke. MaxImDL computed photometry as follows:

'+' label the comet, squares label comparison stars whereas triangles label check stars.

The graphic shows some variation in the brightness of the comet. Unfortunately MaxImDL did not show uncertainties so I had to perform extra computation in IDL. By taking counting statistics of electrons and the uncertainties from the zeropoints of each dataset I obtained the following graphic.

Yet as the number of the data was insufficient, I could not draw any conclusion about the lightcurve. It is likely that the change in brightness was seen. Weather permitting I will keep monitoring this comet.

 

Copyright @ Man-To Hui 2013/08/25

 

2013 Oct 08
 

MPC observation computed with Astrometrica using NOMAD star catalogs:

COD C42
OBS X.Gao, M.-T. Hui
MEA M.-T. Hui
TEL 0.11-m f/5.0 refractor + CCD
NET NOMAD
0002P        KC2013 10 08.83965 08 25 11.46 +42 14 43.8          14.4 N      C42
0002P        KC2013 10 08.85146 08 25 20.76 +42 14 21.6          14.5 N      C42
0002P        KC2013 10 08.86339 08 25 30.34 +42 13 58.1          14.5 N      C42
0002P        KC2013 10 08.87531 08 25 39.99 +42 13 38.6          14.2 N      C42

Photometric measurements were performed in IDL. 15 stars whose V mag were taken from APASS catalog with color index similar to the sun were used to solve the zeropoint of the stacked image.

ZP = 23.1793+-0.0304691

aper mag emag
  4.5   13.663+-0.033
  9.0   12.469+-0.032
 13.5   11.820+-0.031
 18.0   11.379+-0.031
 22.5   11.055+-0.031
 27.0   10.805+-0.031
 31.5   10.606+-0.031
 36.0   10.443+-0.031
 40.5   10.307+-0.031
 45.0   10.190+-0.031
 49.5   10.091+-0.031
 54.0   10.005+-0.031
 58.5    9.929+-0.031
 63.0    9.863+-0.031
 67.5    9.803+-0.031
 72.0    9.749+-0.031
 76.5    9.701+-0.031
 81.0    9.660+-0.031
 85.5    9.623+-0.031
 90.0    9.590+-0.031
 94.5    9.561+-0.031
 99.0    9.535+-0.031
103.5    9.510+-0.031
108.0    9.487+-0.031
112.5    9.467+-0.031
117.0    9.448+-0.031
121.5    9.429+-0.031
126.0    9.412+-0.031
130.5    9.397+-0.031
135.0    9.384+-0.031
139.5    9.374+-0.031
144.0    9.365+-0.031
148.5    9.357+-0.031
153.0    9.350+-0.031
157.5    9.343+-0.031
162.0    9.337+-0.031

The aperture sizes are all in pixel.

Afrho data were derived as well:

However, I must warn that there must be contamination from gas emission due to the inappropriate bandpass used.

 

Copyright @ Man-To Hui 2013/11/12

Feel free to e-mail me with any doubts or questions.

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