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Davis, Robertson, Treister Image of Comet Hale-Bopp

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Observers: Emilio Davis, Jaime Robertson, Ezequiel Treister
Location: Las Campanas Observatory, Chile
Date: January 29-30, 1999

Optical observation of the comets Hale-Bopp (C/1995 O1)
Emilio Davis, Jaime Robertson and Ezequiel Treister
Under the supervision of Franck Marchis

The goal of the project was the observation of two comets: Hale-Bopp and SW1 which are far from Sun. At the time of observation (29-30/01/99) HB was at 7.56 AU in the South direction from Sun and 7.62 from Earth. 29P/SW1 was at 6.2 AU from Sun and 6.35 AU from Earth (Fig. 1).

Observations were done using the telescope Swope (40 inches) of the Las Campanas observatory and a CCD camera (Site #3) with visible filters (U,B,V,R). Apparent pixel size of the detector used was 0.43''. This telescope did not have differential guiding to follow moving objects as planet or comets, that is why the integration time was limited at 2 min for both comet observations to avoid any effect of smearing on the images due to the motion of the comet during the exposure (in 2 min the motion is expected to be inferior at the pixel size).

Hale-Bopp observations

NB: The field is full of stars because of the comet position (inside the Magellan cloud)

Data processing

classical CCD images processing performed with IRAF.

To increase the Signal to Noise on each single image (estimated at 930 on the nucleus of the Hale-Bopp comet), we applied a shift and -add process on every series images. We got a final SNR of 2400 in the 3 V images, 2900 in the R band image and 600 in the B one.

The Hale-Bopp images is quite surprising by the activity of the comet at the distance from Sun. The coma feature reveals a spiral structure which are also visible after applying a mean filter (eclipse software) to improve the SNR (see figure 3 and figure 4). We assume that it is due to the outburst observed by Garrad et al. the 26/12/98 (IAUC circular No. 7073)

Contact: Franck Marchis (fmarchis@sc.eso.org)


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