This image, taken at a higher resolution
(1.1"/pixel) than most of the images on this web site shows a
bright 'jet' of material pointing almost due north, about 12"
long and 6" wide as well as a fainter and shorter fan of
material to the west. A very faint tail may be visible to the
southwest (almost in the opposite direction to the Sun as would
normally be expected).
Discovered on 20 April 2006 by Robert McNaught and Gordon Garrard
at Siding Spring Observatory it was originally announced as a minor
planet in MPEC
2006-H40 and given designation 2006 HR30.
The discovery MPEC included pre-discovery Siding Spring positions
from 2005 July and from 2005 October from the NEAT survey from
Palomar Mountain, so the orbit was well determined from the outset.
Perihelion distance was just outside the Earths orbit at 1.22 AU and
the period was just under 22 years. The absolute brightness of the
object (the brightness it would have at a distance of 1 AU from both
Sun and Earth) was 11.9, which in normal minor planet terms would
indicate a diameter in the range 7-24 Km. The object was likely to
be a comet, but no cometary features were indicated in the initial
observations.
Several amateur astronomers followed the object after discovery
to check whether, as it approached perihelion in 2007 January it
would show signs of being a comet. However, two professional teams
were first to announce cometary features had actually been observed,
Lowry and Fitzsimmons using the 3.5-m New Technology Telescope at
the European Southern Observatory (ESO), La Silla on 2006 July 29.3
detected a coma extending to 5.5" in p.a. 31° in a stack of
3x10 second exposures, while Hicks and Lawrence using the Palomar
5-m Hale telescope detected a faint coma extending approximately
10" on 2006 August 3. IAUC
8735 (subscription
required) was issued on 2006 August 3rd announcing the comet
and changing its asteroidal designation to the periodic comet
designation P/2006 HR30.
Subsequently, on 2006 August 4th, Giovanni Sostero and Ernesto Guido noted on the
Comets Mailing List (message
10375) that on 2006 July 20 UT they could not detect any
cometary features on stacks of images taken with a 0.45-m reflector
totalling 42 minutes exposure. Juan Lacruz also noted on the Comets Mailing list
(message
10382) that on 2006 July 29, although it looked
stellar, he had measured the
FWHM
to be nearly 40% larger than nearby stars in images taken with a
0.3-m, with a total exposure of 62.5 minutes.
It appears that the object 'turned on' to show cometary features
at the end of 2006 July and by 2006 Aug 4th (see image
above) significant activity was evident.
The comet may reach 10th magnitude or brighter around perihelion
time in 2007 January. However, it was poorly placed when at perihelion
at its two previous returns:
- 1985 March (but it was well placed in 1984 August and may have
then been mag 14-15). It may have been recorded on a single 2 hour
exposure at the ESO from 1986 March 5, when its distance from
Earth was 3.5 AU and from the Sun 4.2AU
- 1963 June (but it was well placed in 1962 Aug and 1964 March
and may have been mag +17 on both occasions, though at southerly
declinations).
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