Comet 7P/Pons-Winnecke

Comet 7P/Pons-Winnecke is currently approaching the Sun, during its journey to the inner Solar System. On 2008, March 25.9 we imaged it from the Remanzacco Observatory (Italy): after weeks of bad weather, a storm finally cleared up the sky, so we were able to perform some follow-up of this faint comet, while it was slowing moving in Ursa Major.

In our stacking (average of 20 unfiltered exposures, 120 seconds each, through a 0.45-m f/4.4 reflector + CCD) the comet appears starlike (no coma or tail are visible; same FWHM of the field stars):

We performed a preliminary photometric analysis, that returned a magnitude of R~ 19.5; at this low level of activity, the afrho parameter (proxy of the dust abundance within the coma) is dominated by sunlight scattered by the nucleus, so it doesn't have a straightforward interpretation (just for the record, its current value is close to a few cm).

7P/Pons-Winnecke belongs to the Jupiter family cometary class (q~ 1.2 AU, Q~ 5.6 AU, i~ 22 deg, period~ 6.4 years). During its current approach, it has been recovered at magn.21 on 2007, Dec. 17 by K. Sarneczky (University of Szeged), 0.60-m Schmidt + CCD. It will reach perihelion at the end of September 2008, and it's not supposed to get any brighter than magnitude 12.5 at its best (but at small solar elongation).

C. Snodgrass et Al. [A&A 444, 287-295 (2005)] estimated the nucleus radius at ~2.2 Km, and bracketed its rotation period between 6.8 and 9.5 hours.

This comet has been related to the June Bootids meteor stream, that was pretty active during some of the comet's passages in the first quarter of the past century. However the current activity of this meteor shower is rather modest, probably because the gravitation influence of Jupiter changed significantly the orbital path of the comet and its associated meteoroid debris.

Giovanni Sostero & Ernesto Guido

Comet C/2008 E3 (GARRADD)

IAU circular nr. 8927 published yesterday, announces the discovery of a new comet by Gordon Garradd, named C/2008 E3 (GARRADD). This object has been picked-up on 2008, March 5.8 on images obtained within the Siding Spring 0.5m Uppsala schmidt reflector + CCD.

We peformed some follow-up of this object by means of a remotely controlled scope of the "RAS" network (details on image; click on it for a bigger version):

In our stacking we can appreciate a coma nearly 10 arcsec in diameter, with a strong central condensation. Through strong enhancement of the visualization parameters, a faint and extended outer halo nearly 20arcsec in diameter, possibly elongated toward North-West, seems to be visible (however it must be said that in our frames this detail is very close to the background noise, and thus must be considered as uncertain).

It's also possible to see a faint and broad tail, extending nearly 20 arcsec toward North. We measured the central condensation as m2 almost 18.4, while the 10 arcsec coma has an m1 nearly 17.7 (both are unfiltered CCD magnitudes, approximated to R).

A preliminary afrho (proxy of dust abundance within the coma) measurement provides a value close to 450 +/- 100 cm; this seems to point toward a pretty active comet, considered that it's current distance from the Sun is r~ 5.5 AU.

The Minor Planet Center database points to a (preliminary) retrograde parabolic orbital solution with an inclination on the ecliptic plane of i~ 107 degrees; perihelion will be reached at the end of next October, at 5.2 AU from the Sun.

C/2008 E3 (GARRADD) will remain a southern hemisphere object, and it's not supposed to get significantly brighter than magnitude 17.

Ernesto Guido & Giovanni Sostero

Comet C/2008 E1 (CATALINA)

IAUC 8923, published yesterday, reports the discovery of a new comet: C/2008 E1 (CATALINA). It has been picked-up with the 0.68m Schmidt + CCD of the Catalina Sky Survey on 2008, Mar. 2.14.

According the report of several astrometrist that performed its follow-up, this object is rather faint (nearly magnitude 19) and is currently showing a small coma, 6 to 12 arcsec in diameter, elongated toward North-East.

We imaged it remotely from Mayhill, NM (details on image; click on it for a bigger version):

Preliminary orbital elements published on MPEC 2008-E41 points to a parabolic orbit, with e=1.0 and Incl.=34.3 deg; perihelion will be reached at the end of October 2008 (q=4.8 AU).

This comet is not supposed to get any brighter than V~17, so it shoud remain a rather unconspicuous object, in spite of the fact that it has a significative absolute magnitude, since we are currently observing it at Jupiter's distance.

Ernesto Guido & Giovanni Sostero

Comet C/2008 C1 (CHEN-GAO) Update

Comet C/2008 C1 (Chen-Gao) is currently crossing the rich Milky Way fields within Cassiopeia, not far from the 2.nd magnitude star Gamma Cas. This create some troubles performing its photometry & astrometry follow-up, due to the annoying stellar crowding that usually "pollutes" the cometary coma.

On 2008, Feb. 16.7, we obtained the "cometary first light" on a new scope, a MEADE LX200R 14" OTA, mounted on a 10Micron GM2000 QCI robotic mount (this will be the heart of our remote-controlled set-up, located in the new astronomical observatory atop Mount Matajur, currently under completion):

Selecting a frame series relatively free from background stars, we did some follow-up about this comet. We found that the coma extends nearly 1 arcmin, with a relatively sharp central condensation (m2 almost 15.5). Total (unfiltered) magnitude is equal to 12.5. The Afrho parameter (proxy of the dust abundance within the coma) is ~150 +/- 25 cm, with a typical pattern:

http://tinyurl.com/3xyemj

(for more info's about the Afrho parameter importance, and and the role of amateur astronomers in its determination, please visit the CARA's webpage)

There are signs of a tiny tail extending toward North-East:

http://tinyurl.com/2864y6

This detail moves according the proper motion of the comet:

http://tinyurl.com/2ly9h9

so it's unlikely to be an artefact.

Giovanni Sostero & Ernesto Guido

Is It an Asteroid, a Comet or Both?

There has been a time when asteroids and comets were regarded as quite different objects:

"At most meetings of professional astronomers during the 20th century, asteroids were discussed by one group and comets by a generally different group...it has taken decades to realize that these objects might share similar materials, or to allow the possibility of a smooth transaction from one group to the other, based on ice content" (W.K.Hartmann, 1999, chap.23)

The picture we have today is that of "planetesimals" whose composition difference reflects the temperature of the Solar System area where they formed. Comets, accreted beyond the Snow-Line, are ice-dominated object while asteroids are expected to be relatively ice-deficient.

So, traditionally, an object is defined as a comet when it shows a resolved coma at some point in its orbit:

"Deciding whether an object is an asteroid or a comet thus depends critically on the instrumental resolution and sensitivity to low surface brightness coma" (D.C. Jewitt, 2004)

Moreover as we know, comets pass through inactive phases giving rise to the situation where it's not possible to decide the nature of the object by the means of observations. Another clue of cometary nature of an object can arrive from its dynamical path. The Tisserand “invariant” calculated in respect to Jupiter (Tj) is often used as dynamical discriminator to distinguish the nature of Solar System objects. Comets-like objects have Tj < 3.

For all these reasons is not always easy to decide what classification to assign to some objects.

2005 WY3 is such an object. Discovered by Spacewatch Telescope survey, this asteroid is clearly moving on a typical cometary orbit (a= 6.74 AU, e= 0.74,P= 17.5 year, H= 13.4, Tj 2.116) but it never showed cometary activity.

We shoot 2005_WY3 few hours ago remotely from New Mexico (details on image; click on it for a bigger version):

In our stacking this peculiar object has attained a good S/N (nearly 20) and shows no hints of cometary activity: its FWHM is identical to that of nearby field stars, with no traces of coma and/or tail. Either its cometary activity is currently well below the sensibility of our instrument, or there isn't any at all.

Ernesto Guido & Giovanni Sostero

References

Hartmann, W.K. (1999). Small World: Patterns and Relantionships in "The New Solar System"

Jewitt, D.C. (2004) From Cradle to Grave: The Rise and Demise of the Comets in "Comets II"

Comet C/2008 C1 (CHEN-GAO)

We performed some follow-up of C/2008 C1 (CHEN-GAO) on 2008 Feb 3.10 through one of the R.A.S. telescope (details on image). In our stacking is visible a nice coma, nearly 1.5 arcmin wide. Image processing shows a clear elongation of the coma, and hint of a tail, toward North-East (click on the image below for a bigger version):

Preliminary photometric data reductions returns a total (unfiltered) magnitude close to 13. The central condensation is nearly magn.16. The afrho parameter (proxy of dust abundance within the coma) is almost 80 cm +/- 20cm, with an asymmetric profile (higher values for wider apertures). Considering the current distance from the Sun (r nearly 1.6 AU, inbound) this amount seems to point toward a comet of moderate activity.

Congratulation to our Chinese fellows for this nice find!

Ernesto Guido & Giovanni Sostero (A.F.A.M., C.A.R.A.)

Asteroid 2007 TU24 Close Approach Video

Asteroid 2007 TU24, discovered by the Catalina Sky Survey on October 11, 2007 has closely approached the Earth to within 1.4 lunar distances (334,000 miles) on 2008 Jan. 29 08:33 UT. 

We have observed this object from Remanzacco Observatory with a 45cm f/4.4 reflector and CCD FLI IMG 1001E. Below You can find our video composed of 100 images x 2 seconds showing this asteroid (magnitude 10) from 20h29m to 20h 45m UT.

2007 TU24 will be the closest currently known approach by a potentially hazardous asteroid of this size (between 150 and 600 meters in diameter) or larger until 2027.

Scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif.,  "have obtained the first images of asteroid 2007 TU24 using high-resolution radar data. The data indicate the asteroid is somewhat asymmetrical in shape, with a diameter roughly 250 meters in size." Below you can see the low-resolution radar images of asteroid 2007 TU24 taken over a few hours by the Goldstone Solar System Radar Telescope in California's Mojave Desert. Image resolution is approximately 20-meters per pixel.

Credit: NASA/JPL-Caltech

 

Giovanni Sostero, Luca Donato & Ernesto Guido