Foreshortening effects on C/2007 N3 (LULIN)

Comet C/2007 N3 (LULIN) was a nice show in late February this year, when it passed relatively close (nearly 0.42 AU, on Feb. 24th). At about its perigee, another phenomena occurred: its phase angle reached a minimum value, then it quickly started to grow-up again. Nearly simultaneosly we witnessed an abrupt change in the appearance of the comet, due to the consequent foreshortening effect: the ion tail, in a matter of hours, switched from North-West to South-East.

Possibly another, less cospicuous, change in comet's LULIN aspect may be under course: according to our follow-up, some effects of the foreshortening change seems to be readily visible also in a series of images we secured from various sites & through with different scopes, in the past few weeks.

As you may notice from the following panels, the prominent feature (kind of "fan" structure) originating from the central condensation toward South-West (i.e. at about PA 220 deg), plus a secondary one, toward North-East (i.e. at about PA40 deg) that was reported by several observers, visible till March 2nd, now seems to be over:

March 11th: http://tinyurl.com/acq7wr

March 2nd: http://tinyurl.com/d8bnfc

Februaty 27th: http://tinyurl.com/cpslxs

February 19th: http://tinyurl.com/bgt6yd

More data need to be secured to definitely clarify the situation, however at a first glance we have the impression that this might be a foreshortening effects as well. Apparently, the changing geometry really plays a strong role, when interpreting the inner coma details sometimes reported on comets (alleged fans, jets, etc.).

by Giovanni Sostero, Ernesto Guido, Paul Camilleri & Virgilio Gonano

Changing geometry of comet C/2007 N3 (LULIN)

During the past few nights, we witnessed a dramatic change of the viewing geometry of comet C/2007 N3 (LULIN): its ion tail switched its position from North-West, and is currently hidden behind the coma. However this phenomena doesn't change that much the visibility of some details within the inner coma of the comet.

Here you can find an image obtained on 2009, Feb. 27 (details in caption):

Comparison with a similar image, obtained on 2009, Feb. 19 (details in caption):

shows the persistence of some asymmetries in the inner coma. In particular, a kind of "fan" toward PA 200 deg, with a second, similar structure (but less evident) in the opposite direction, toward PA 20 deg. It's not clear yet the explanation of this features; what we can say at the moment, is that they doesn't seem to be artefacts (i.e. artificially generated features using image processing softwares) and that they show no significant changes in spite of the significative change of our perspective angle.

by Ernesto Guido, Giovanni Sostero and Paul Camilleri

Comet Lulin at its best

Today, February 24th, comet C/2007 N3 (LULIN) is making its closest approach to Earth (0.41 A.U.) peaking at magnitude 5.0. After that Lulin is moving away from both Earth and the Sun, so it fades fairly quickly. 

Yesterday, Lulin was just 2 degrees south-southwest of Saturn. Below you can see our image showing the rendez-vous between the comet and the planet (click on it for a bigger version):

While here there is an animation showing the motion of the comet in 5 minutes (this week the comet is moving at over 5° per day):

Because of the particular geometry between Earth, comet and Sun we see the comet Lulin showing a nice sunward pointing dust tail (antitail) along with a ion tail. This diagram shows the geometry of Comet Lulin's tail and anti-tail (click on it for a bigger version):

Credit: Paolo Berardi

For more information and images please check also our past posts about this nice comet:

http://remanzacco.blogspot.com/2009/02/comet-lulin-disconnection-event.html

http://remanzacco.blogspot.com/2009/01/comet-c2007-n3-lulin-animation.html

http://remanzacco.blogspot.com/2009/01/c2007-n3-lulin-update.html

http://remanzacco.blogspot.com/2008/07/comet-c2007-n3-lulin.html

By Ernesto Guido & Giovanni Sostero

Coma asymmetry of comet C/2007 N3 (LULIN)

Few hours ago we imaged C/2007 N3 (LULIN) through a narrowband interferential filter, centered in the dust continuum (647nm, FWHM= 10nm). At these wavelengths, what we see is (nearly) only dust. Some image-processing show a curious asymmetry of the coma, as noticed before in some other comets.

Possible features in (about) PA 40 deg and PA 220 deg became visible, as well  (click on the image for a bigger version):

While here you can see an animation of the comet imaged without filter on 18 February 2009 (click on it for a bigger version):

by Giovanni Sostero, Ernesto Guido and Paul Camilleri

Comet Lulin disconnection event

Today we wanted to make some wide-field imaging of comet C/2007 N3 (LULIN), in search for large scale structural features. In our image (see below, details in the caption; click on it for a bigger version):

is clearly visible the characteristic dichotomy of this comet: a dusty anti-tail pointing toward the Sun (i.e. to South-East) and the highly structured ion (plasma) tail toward West,Northwest. This uncommon configuration, is due to the particular geometric circumstances occuring during these nights, with the comet seen nearly head-on as seen from Earth.

Moreover, we were lucky enough to capture an intriguing phenomena: in our images is clearly visible a nice disconnection event (DE) in the plasma tail of the comet (evidenced by a red circle in this rendition):

The DE indicates that the comet has recently passed through a disturbance in the magnetic field carried by the solar wind, that destroyed the original plasma tail, creating a new one. The separation of the two ion tails indentified by the DE, is visible in our image as a kind of elongated and diffuse "knot" along the plasma tail.

A 3x zoomed view of this feature is available here:

The "knot" is dragged tailward by the solar wind, and will dissipate soon. More events like this are expected in the near future, when comet LULIN will approah Earth. Comet aficionados, heads-up!

by Ernesto Guido, Giovanni Sostero and Paul camilleri

Comet C/2007 N3 (LULIN) Animation

Comet C/2007 N3 (LULIN) is moving closer to Earth. At closest approach (0.41 AU) on February 24th, the comet may be as bright as 4th magnitude becoming a naked eye object.

We imaged Comet Lulin on 16 January 2009 and on 17 January 2009 to show its motion on the background stars. Below you can see the animation composed of 2 stacks of 5X120 seconds each, taken remotely from Mayhill (NM) through a 0.10 f/5 reflector + CCD (click on it for a bigger version):

by Ernesto Guido & Giovanni Sostero