C/2002 V1 (NEAT)

C/2002 V1 (NEAT) was discovered on 2002 November 6th by the NEAT telescope at Haleakala (Hawaii) as a magnitude 17.4 object and confirmed a few hours later by Salvador Sánchez & Manuel Blasco at the Observatorio Astronómico de Mallorca. The initial orbit showed that it was a sungrazer that would reach perihelion in mid-February 2003. This has been confirmed by further observations.

The orbit is closed with a period of around 40 000 years, showing it to be a Oort Cloud object. The comet has reached perihelion at 0.1AU on February 18th 2003. The images from the SOHO satellite are spectacular. The comet is showing a faint straight gas tail and a broad dust tail several degrees long. An interesting feature of the tail are the straias that are strongly reminiscent of Comet West of 1976. At perihelion the comet has been at a very small elongation, but is evidently at negative magnitude as it saturates on the images. Even visual observers have seen it low in twilight at close to magnitude 0 just before perihelion.

This comet though is rather small and is not of the size of great sungrazers of the past, so it initially seemed likely that it would disappear before perihelion.

 

The light curve

GWith an absolute magnitude of 9.5 this comet bears similarities to C/1987 W1 (Ichimura), a comet that faded out long before perihelion. The comet is brightening rapidly, but it would be surprising if it did not fade out in a similar manner.

Update December 3rd: The latest light curve data show a significant downturn in the brightness in a 10 arcsecond aperture. It seems very early to be the switch-off of activity, but is worth monitoring all the same. At this time the comet should have been brightening at around 0.1 magnitude per day, although this rate should slow with time. The data though shows that the nuclear condensation is of constant brightness or fading slightly.

Update December 13th: As remarked above, the fade in the light curve has bottomed out and it is now rising again, although from a considerably lower level and much more slowly than previously. This makes it appear that the comet was probably discovered on the rise to an outburst and has now returned to its original level. Additional monitoring is required to confirm this.

Update December 28th: The light curve confirms that the magnitude in a 10 arcsecond aperture (which reflects the gas production in the nucleus) shows a significant outburst after discovery. If the comet were to continue to show the same relation as is suggested by Seichii Yoshida below (m1 = 4.0 + 5 log Delta + 30 log r) it would reach m1=-26(!) at perihelion. It is obviously going to show a more conservative rise in brightness when closer to the Sun and the activity in the 10 arcsecond aperture gives a warning of how it may evolve in the future.

 

G

Here we see the magnitude in a 10 arcsecond aperture corrected for the geocentric distance, against time. Although the geocentric distance has been decreasingly steadily (and thus we see a smaller amount of comet in the aperture), we see that the corrected magnitude brightened very rapidly with time until the end of November, when it suddenly started to fade very rapidly. After maximum the corrected magnitude was fading by approximately 0.3 magnitudes per day. This trend was reversed after December 6th and replaced with a very slow brightening.

 

 

 

 

 

 

G

Here we see the magnitude in a 10 arcsecond aperture corrected for the geocentric distance, against the logarithm of the heliocentric distance. In this plot the extent of the nucleus switch-off is obvious.

Up to December 1.0, the equation of the light curve in the 10 arcsecond aperture is:

m(10) = 10.4 + 5 log Delta + 14.1 log r

From November 30.0 to December 7th it is:

m(10) = 19.4 + 5 log Delta - 16.6 log r

From December 6th it is:

m(10) = 14.1 + 5 log Delta + 3.1 log r

Note that the current rate of brightening is very slow indeed, reflecting a very low gas production rate. In fact, it reflects decreasing gas production as, just from the inverse square law of reflected light, the comet should brighten as 5 log r.

This suggests that the comet is tiring significantly and that it may be very optimistic to expect it to be a naked eye object at any time.

 

G

Here we combine visual total magnitude estimates with CCD measures in V made with a large aperture that are close to m1. These are corrected for the geocentric distance and plotted against the logarithm of the heliocentric distance. Unlike the plot of m(10) we see a single trend of steep slope indicating a very fast rate of brightening of the total magenitude with approach to the Sun.

The best fit to the light curve is:

m1 = 6.9 + 5 log Delta + 20.9 log r

This is an extremely rapid rate of brightening. However, it should be noted that the indicated absolute magnitude of 6.5 is greatly exagerated by this rapid rate of brightening and that it is equivalent to a much fainter absolute magnitude in a comet that brightens at an average rate. The fit to the light curve is now very consistent and hardly changes as new points are added with an error of about +/-0.1 magnitudes in the absolute magnitude and about +/-0.3 in the exponent of log r.

At the same time the Degree of Condensation of the coma has dropped sharply from DC=8 initially (a very condensed coma) to DC=4 and then DC=2-3 in late December. Faustino García estimates DC=0-1 in early January. This would indicate that the comet, although still bright in total magnitude, is progressively "fading out" as would be expected from its characteristics and from the CCD data in a small aperture shown above. The next stage of its evolution would be for the total brightness to continue increasing, but for the coma to get increasingly large and difuse until it cannot be detected against the brightness of the night sky.

 

CCD observations in R in a 10 arcsecond aperture by:

CCD observations in a apertures of 0'.6, 1'.2 and 2'.4 and VRI filters by:

Visual estimates by: