The Night Sky at the Calar Alto Observatory II: The Sky at the Near-infrared
Sánchez, S. F.; Thiele, U.; Aceituno, J.;Cristobal, D.; Perea, J.; Alves, J.. The Night Sky at the Calar Alto Observatory II: The Sky at the Near-infrared. The Publications of the Astronomical Society of the Pacific. 2008, Vol. Volume 120, Issue 873, pp. 1244-1254., p. -2008.
We present the characterization of additional properties of the night
sky at the Calar Alto observatory, following the study started by
Sánchez et al. in 2007. We focus here on the night-sky brightness
at the near-infrared, the telescope seeing, and the fraction of useful
time at the observatory. For this study we have collected a large data
set comprising 7311 near-infrared images taken regularly along the last
four years for the ALHAMBRA survey (, , and bands), together with a
more reduced data set of additional near-infrared images taken for the
current study. In addition, we collected the information derived by the
meteorological station at the observatory during the last 10 yar,
together with the results from the cloud sensor for the last . We
analyze the dependency of the near-infrared night-sky brightness with
the air mass and the seasons, studying its origins and proposing a
zenithal correction. A strong correlation is found between the night-sky
brightness in the band and the air temperature, with a gradient of per
1°C. The typical (darkest) night-sky brightness in the , , and -band
are 15.95 mag (16.95 mag), 13.99 mag (14.98 mag), and 12.39 mag (13.55
mag), respectively. These values have been derived for the first time
for this observatory, showing that Calar Alto is as dark in the
near-infrared as most of the other astronomical sites in the world with
which we could compare it. Only Mauna Kea is clearly darker in the
band, but not only compared to Calar Alto but to any other observatory
in the world. The typical telescope seeing and its distribution were
derived on the basis of the FWHM of the stars detected in the considered
near-infrared images. This value, when converted to the band, is only
slightly larger than the atmospheric seeing measured at the same time by
the seeing monitor, . Therefore, the effects different from the
atmosphere produce a reduced degradation on the telescope seeing, of the
order of . Finally we estimate the fraction of useful time based on the
relative humidity, gust wind speed, and presence of clouds. This
fraction, , is very similar to the one derived in 2007, based on the
fraction of time when the extinction monitor is working.
We present the characterization of additional properties of the night
sky at the Calar Alto observatory, following the study started by
Sánchez et al. in 2007. We focus here on the night-sky brightness
at the near-infrared, the telescope seeing, and the fraction of useful
time at the observatory. For this study we have collected a large data
set comprising 7311 near-infrared images taken regularly along the last
four years for the ALHAMBRA survey (, , and bands), together with a
more reduced data set of additional near-infrared images taken for the
current study. In addition, we collected the information derived by the
meteorological station at the observatory during the last 10 yar,
together with the results from the cloud sensor for the last . We
analyze the dependency of the near-infrared night-sky brightness with
the air mass and the seasons, studying its origins and proposing a
zenithal correction. A strong correlation is found between the night-sky
brightness in the band and the air temperature, with a gradient of per
1°C. The typical (darkest) night-sky brightness in the , , and -band
are 15.95 mag (16.95 mag), 13.99 mag (14.98 mag), and 12.39 mag (13.55
mag), respectively. These values have been derived for the first time
for this observatory, showing that Calar Alto is as dark in the
near-infrared as most of the other astronomical sites in the world with
which we could compare it. Only Mauna Kea is clearly darker in the
band, but not only compared to Calar Alto but to any other observatory
in the world. The typical telescope seeing and its distribution were
derived on the basis of the FWHM of the stars detected in the considered
near-infrared images. This value, when converted to the band, is only
slightly larger than the atmospheric seeing measured at the same time by
the seeing monitor, . Therefore, the effects different from the
atmosphere produce a reduced degradation on the telescope seeing, of the
order of . Finally we estimate the fraction of useful time based on the
relative humidity, gust wind speed, and presence of clouds. This
fraction, , is very similar to the one derived in 2007, based on the
fraction of time when the extinction monitor is working.
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