DFOSC

The Danish Faint Object Spectrograph and Camera (DFOSC) is an instrument which was installed on the Danish 1.54-metre telescope at La Silla Observatory in 1992. The telescope is a Danish national facility now jointly run by Ondřejov Observatory in Czechia and the Niels Bohr Institute in Denmark, with on demand support from ESO.

DFOSC was built as a spectrograph and camera similar to ESO’s EFOSC1 and EFOSC2. The original purpose of DFOSC was to provide a versatile instrument for the Danish community, to allow Danish astronomers to do much of the same research that was possible with the larger ESO telescopes.

DFOSC initially had the ability to change between imaging and spectroscopy, and could do so within one minute. The imager had an attached focal reducer, which changed the focal length of the telescope and allowed for a wider field of view on the sky. In the spectroscopic mode, DFOSC could separate visible wavelengths into a spectrum to allow astronomers to determine different characteristics, like chemical composition or rotation, of astronomical objects. The spectrograph on DFOSC was decommissioned in 2003.

DFOSC has allowed astronomers to make several first discoveries. In 2000, DFOSC helped to determine the distance to the most distant long gamma-ray burst known at the time. Five years later, the visible light from a short gamma-ray burst was observed for the first time with DFOSC. In 2006, together with other telescopes, DFOSC contributed to the discovery of an exoplanet about five times the mass of the Earth that orbits its star around once every ten years.

DFOSC has received a number of updates since seeing first light. DFOSC now uses an EMCCD, which is a detector that uses the lucky imaging technique. With this technique, the imager takes many images per second and picks only those that are sharper than the average “seeing” at the time, which is a measure of how the atmosphere distorts the incoming light. This instrument discovered the rings around the asteroid Chariklo, which was only possible because the imager took 10 exposures per second (eso1410). The instrument could be used remotely thanks to a complete renovation of the control system in 2012.

Two DFOSC sister instruments were also built. One instrument was for the Instituto de Astrofísica de Andalucía (IAA), Spain, and is in operation at the Nordic Optical Telescope, while the other one was for the INAF–Bologna Astronomical Observatory in Italy, and has been in operation since 1993 at the Loiano Site.

Science highlights with DFOSC

• ESO telescopes see afterglows of elusive short gamma-ray bursts (eso0533)
• First ESO image of new comet 1998 P1 (eso9838)
• New discoveries about comet Hyakutake (eso9616, eso9815, eso9814)