DI at ESO Campaign - Update July 3, 2005

The Deep Impact campaign at ESO has entered its final phase. Last night, July 2, 2005, the team of astronomers from Belgium, Bulgaria, Chile, France, Germany and Italy used all four 8.2m Unit Telescopes of the VLT on Paranal and the three main telescopes on La Silla to simultaneously observe Comet 9P/Tempel 1. They will continue to do so for one week.

The purpose of these pre-impact observations is to acquire an unprecedented and complete set of data with in total eleven instruments. The observations cover the wavelength domain between 350 nm (ultraviolet side of the visible light) and 20 micrometer (thermal infrared).

These observations will be used to obtain a detailed understanding of the effects of the impact, as they will serve as reference for post-impact observations.

The final aim of the campaign is the characterization of the cometary gas and dust that was embedded into the cometary nucleus during its formation some 4.6 billion years ago, i.e. before the planets including our own one were born, thus giving us an insight in the formation conditions of the solar system.



Dust Component

Caption: FORS2 image of Comet Tempel 1, taken during the night of July 2 to 3, 2005. The R-band image appears in a logarithmic grey scale on the left. On the right image, it has been processed using a method that enhances the low contrast features in the coma (by subtracting a mean radial profile). This puts in evidence the various "fans" and "jets" that correspond to areas of the nucleus surface that are more active (i.e. releasing more dust and gas in space) than the surrounding. The scale in kilometres indicates the extension of the coma - the nucleus, only 6km long, is completely hidden in the single central pixel of the image.

Images obtained with FORS2 on Antu (VLT) show the comet in red light (R-band), mostly showing the light of the sun as it is reflected by the dust surrounding the nucleus of the comet. The comet appears to be fainter than expected, which costs extra exposure time to achieve the anticipated science goals.

The coma pattern continues to show jets and fans - though modified compared to last week's images - produced by various active regions on the rotating nucleus.


ESO PR Photo 02a/05

Gas Component

Caption: False-colour image of Comet Tempel 1 observed with EMMI on the NTT during the night of July 2-3, 2005. Background stars passing through the field of view due to the motion of the comet, appear like a "string of pearls" at the upper edge of the image. The colour coding in these star trails represents the usage of three filters transmitting light in different wavelength regions in the blue and UV part of the spectrum: red colour represents the transmission filter for light typical for C3 gas, green for the CN gas and blue for dust reflected sunlight in the coma. The field of view is 6 x 6 arcmin, i.e. 133000 x 133000 km at the distance of the comet. North is up and East is to the right. In the image the sun is on the right hand side of the comet.

Another set of images was collected with EMMI on the NTT at La Silla in several wavebands. This shows the gas around the comet.

The cometary coma is well developed due to the gas and dust released by the nucleus as a result of surface heating by the Sun. It extends several arcminutes from the nucleus that is hidden behind gas and dust in the central brightness peak of the coma. The coma appears slightly asymmetric due to enhanced activity of the nucleus towards sun direction.

In addition, spectroscopy was obtained with FORS2 on Antu, UVES on Kueyen and with SINFONI on Yepun. The prominent CN, NH, OH, C3, C2 and NH2 molecules are clearly seen in the spectra and their spatial distribution in the coma was measured. No ion features were detected, implying that 9P/Tempel 1 does not produce a strong ion tail throughout this perihelion passage - something not necessarily surprising, but noteworthy to mention.



[1]: Leading scientists of the ESO DI campaign: H. Boehnhardt (MPI, Lindau, Germany), O. Hainaut (ESO), H.U. Kaufl (ESO), H. Rauer (DLR, Germany).

Members of the ESO DI observing team on site: N. Ageorges (ESO, Chile), S. Bagnulo (ESO, Chile), L. Barrera (UMCE, Chile), H. Boehnhardt (MPS, Germany), T. Bonev (Astr. Inst. Sofia, Bulgaria), O. Hainaut (ESO, Chile), E. Jehin (ESO, Chile), H.U. Kaufl (ESO, Germany), F. Kerber (ESO, Germany), J. Manfroid (U.Liège, Belgium), O. Marco (ESO, Chile), E. Pantin (CEA, France), E. Pompei (ESO, Chile), C. Sterken (Vrije Universiteit Brussel, Belgium), G.P. Tozzi (Obs. Arcetri, Italy), M. Weiler (DLR, Germany)

Members of the ESO DI observing team not on site: C. Arpigny (U.Liège, Belgium), A. Cochran (McDonald, USA), C. Delahodde (Univ. Florida, USA), Y. Fernandez (Univ. Hawaii, USA), D. Hutsemekers (U.Liège, Belgium), H. Kawakita (Gunma, Japan), J. Knollenberg (DLR, Germany), L. Kolokolova (Univ. Maryland, USA), M. Kretlow (MPS, Germany), M. Kueppers (MPS, Germany), E. Kuehrt (DLR, Germany), L. Lara (IAA, Spain), J. Licandro (IAC, Spain), C. Lisse (Univ. Maryland, USA), K. Meech (U.Hawaii, USA), R. Schulz (ESTEC, The Netherlands), G. Schwehm (ESTEC, The Netherlands), M. Sterzik (ESO, Chile), J.A. Stüwe (Leiden, The Netherlands), I. Surdej (Univ. Liège, Belgium and ESO, Garching), D. Wooden (Ames, USA), J.-M. Zucconi (Besancon, France)