Kreutz Sungrazing Comet

C/2011 W3 (Lovejoy)

2011/12/04

CBET 2930, issued on Dec 02 2011, announced the discovery of a new comet of 13^m by Terry Lovejoy from Thornlands, Australia, on three images taken each on Nov 27.7 and Nov 29.7 UT, through a Celestron 0.20-m f/2.1 Schimdt-Cassegrain reflector + QHY9 CCD in the course of his normal comet-search program. The comet appears as a clearly diffuse circular object with an approximate 1' coma in diameter. The central condensation is of around 16^m and no tail is seen. T. Lovejoy found that the comet had increased in brightness by around a magnitude and the coma turned well-condensed by Dec 1.7 UT. The new comet has been designated C/2011 W3 (Lovejoy).

The most exciting aspect of the comet is that with astrometric observations it is an inbound Kreutz sungrazing comet, which is the first ground-based discovery of a Kreutz sungrazing comet since comet C/1970 K1 (White-Ortiz-Bolelli)! Compared to those Kreutz sungrazers observed by LASCO and STEREO imagers, it is likely C/2011 W3 will become the brightest one amongst them. However, since it is intrinsically faint, possibilities of becoming a broad daylight comet as C/1965 S1 (Ikeya-Seki) and survival after perihelion seem implausible. Anyway, it surely will convey precious information before its final destruction to researchers for close studies. I wish a brilliant performance within the FOV of STEREO and SOHO/LASCO cameras.

2011 Dec 04

Images remotely obtained from Golden Stars Observatory, Australia, owned by Angus Lau from Hong Kong.

Mouseover to see the version in pseudo color.

Images remotely obtained from Golden Stars Observatory, converted from bin 1x1 to bin 2x2. The comet appears evidently trailed in bin 1x1 images due to a longer exposure, yet the SNR of the comet rises as a result advantageously.

Mouseover to see the version in pseudo color.

The following MPC observations were compiled with coordinates measured in Astrometrica by UCAC-3 star catalog and photometry by USNO-A 2.0 star catalog in R band. The first quadruplet is measured from images with exposure of 30-sec each whilst the last quadruplet from images with exposure of 120-sec each:

COD XXX
OBS A. Lau, M.-T. Hui
MEA M.-T. Hui
TEL 0.18-m f/7.1 refractor + CCD
NET UCAC-3
    CK11W030 IC2011 12 04.73307 15 11 43.22 -49 35 51.3          13.8 N      XXX
    CK11W030 C2011 12 04.73398 15 11 44.51 -49 35 43.3          14.1 N      XXX
    CK11W030 C2011 12 04.73502 15 11 45.64 -49 35 39.8          13.9 N      XXX
    CK11W030 C2011 12 04.73608 15 11 46.98 -49 35 37.8          14.0 N      XXX
    CK11W030 C2011 12 04.73924 15 11 51.41 -49 35 19.5          14.3 N      XXX
    CK11W030 C2011 12 04.74144 15 11 53.73 -49 35 11.5          14.3 N      XXX
    CK11W030 C2011 12 04.74341 15 11 55.92 -49 35 02.7          14.4 N      XXX
    CK11W030 C2011 12 04.74529 15 11 58.65 -49 34 54.3          14.4 N      XXX
----- end -----

PSF with one of the images with an exposure of 30-sec.

PSF with one of the images with an exposure of 120-sec.

Gauss curve produced by Astrometrica with USNO-A 2.0. The total PSF is using an aperture circle with a radius of 5-pixel around the brightest pixel. We can see the Gauss curve in the right is as the computed ideal line and the real pixels contributed around the ideal line. The Fit RMS, which inlays under the Gauss curve, is the deviation from the ideal line. Because of the SNR being still very low both in images of 30-sec and 120-sec, as well as the fragile appearance of the comet, the peak of ADU is merely above the noise level. The enhancement in images of 120-sec is not as obvious as expected.

Photometry result computed with FOCAS II, which processes images based upon the .LOG file of Astrometrica, by means of Multibox method. The first two rows are the results measured from images of 30-sec each, whereas the last two lines from images of 120-sec each.

COD XXX
CATALOG: USNO A2.0 / CMC-14 - BAND: R
                                   10x10 20x20 30x30 40x40 50x50 60x60 SNR SB COD
OBJECT        DATE       TIME        +/-    +/-    +/-    +/-    +/-    +/-     N FWHM CAT
------------ ---------- -------- ----- ----- ----- ----- ----- ----- ---- ---- ---
C/2011 W3     04/12/2011 17:37:44 13.97 12.93 12.35 11.93 11.62 11.39 4.3 16.9 XXX
C/2011 W3     04/12/2011 17:37:44* 0.09 0.11 0.11 0.13 0.12 0.13     4 5.9 USN
C/2011 W3     04/12/2011 17:48:58 14.34 13.22 12.68 12.35 12.12 11.96 6.4 16.4 XXX
C/2011 W3     04/12/2011 17:48:58* 0.03 0.06 0.06 0.06 0.06 0.04 4 5.4 USN

FoCAs II - 17/03/2010
www.astrosurf.com/cometas-obs
es.groups.yahoo.com/group/Cometas_Obs

Interpretation of the FOCAS II table headings:

Fisrt line:

OBJECT, DATE, TIME: 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

Results measured from images of 30-sec each.

Results measured from images of 120-sec each. Obviously the residuals in photometry decrease, compared to the above one.

I will keep focusing on the comet. Hopefully it can finally genuinely become a fabulous object!

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

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