The Night Sky at the Calar Alto Observatory
- Author(s)
- S. F. Sánchez, J. Aceituno, U. Thiele, D. Pérez-Ramírez, J. Alves
- Abstract
We present characterization of the main properties of the night sky at the Calar Alto observatory for the time period between 2004 and 2007. We use optical spectrophotometric data, photometric-calibrated images takenin moonless observing periods, together with the observing conditionsregularly monitored at the observatory, such as atmospheric extinctionand seeing. We derive, for the first time, the typical moonlessnight-sky optical spectrum for the observatory. The spectrum shows astrong contamination by different pollution lines, in particular frommercury lines, whose contribution to the sky brightness in the differentbands is of the order of ~0.09, ~0.16, and ~0.10 mag in B, V, and R, respectively. Regarding the strength of the sodium pollution line in comparison with the airglow emission, the observatory does not fulfill the IAU recommendations for a dark site. The zenith-corrected values ofthe moonless night-sky surface brightness are 22.39, 22.86, 22.01,21.36, and 19.25 mag arcsec-2 in U, B, V, R and I, which indicates that Calar Alto is a particularly dark site for optical observations up to the I band. The fraction of astronomical usefulnights at the observatory is ~70%, with ~30% of photometric nights. Thetypical extinction at the observatory is κV~0.15 mag in the winter season, with little dispersion. In summer the extinction hasa wider range of values, although it does not reach the extreme peaks observed at other sites. The analysis of the winter and summer extinction curves indicates that the Rayleigh scattering is almostconstant throughout the year. The rise of the extinction in the summer season is due to an enhancement of the aerosol extinction, most probably associated with an increase of dust in the atmosphere. The median seeing for the last two years (2005-2006) was ~0.90", being smaller in the summer (~0.87") than in the winter (~0.96"). We conclude in general thatafter 26 years of operations, Calar Alto is still a good astronomical site. Its main properties are similar in many aspects to those of other major observatories where 10 m-like telescopes are under operation or construction, thus being a natural candidate for future large aperture optical telescopes.
- Organisation(s)
- Department of Astrophysics
- External organisation(s)
- Centro Astronómico Hispano Alemán (CAHA), Universidad de Granada
- Journal
- Publications of the Astronomical Society of the Pacific
- Volume
- 119
- Pages
- 1186-1200
- No. of pages
- 15
- ISSN
- 0004-6280
- DOI
- https://doi.org/10.1086/522378
- Publication date
- 10-2007
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 103003 Astronomy
- Keywords
- Portal url
- https://ucris.univie.ac.at/portal/en/publications/the-night-sky-at-the-calar-alto-observatory(3ef956a3-9776-4970-992a-5f0eb3eff86b).html