Beijing-Arizona Sky Survey (BASS)

Table of Contents


The Bok telescope is an equatorial mounting one with an aperture in diameter of 2.3 meters, which belongs to the Steward Observatory. The corrected primary focal ratio is f/2.66 and the telescope pointing error is about 3″. The site is Kitt Peak (111°36′01″.6W, +30°57′46″.5), 56 miles southwest away from the Tucson city. The elevation is about 2071 m and the typical seeing is about 1.5″ (Zou et al. 2015).

Bok telescope Bok dome and Kitt Peak


The BASS uses the prime-focus imager, 90Prime, with corrected focal ratio of f/2.98. The optical design includes a four-element corrector and six position filter wheel. The focal plane array is a mosaic of four 4k x 4k CCDs which have been processed for back illumination by the University of Arizona Imaging Technology Laboratory. These CCDs were optimized for the ultraviolet response and built with the funding support from the South Galactic Cap u-band Sky Survey (SCUSS). The quantum efficiencies at both g and r are larger than 80% (see the following figure). The edge-to-edge field of view (FoV) is about 1.08°x1.03° and the pixel scale is 0.454″. There are gaps between CCDs along both right ascension and declination, which are 2.8′ and 0.9′ in width, respectively. The average gain is about 1.5 e/ADU and average readout noise is about 8 e. The CCD layout is shown in the following figure.


The filters are required to be similar to those used in the DES, because the photometric data for the DESI target selection should come from consistent photometric systems. The BASS g band is the existing SDSS g filter deployed on the Bok telescope. The filter is close to the DES g band. The BASS r filter was newly purchased. It is almost the same as used in DES, but fairly different from the SDSS one. The cut-on and cut-off wavelengths are 5680 and 7110 Å. The absolute transmission in passband is larger than 95%. Figure 2 shows the response curves of both BASS g and r filters. The response curves include the filter transmission, CCD quantum efficiency (QE), and the atmospheric extinction at airmass of 1.0. The atmospheric extinction coefficients come from the Kitt Peak National Observatory and the molecular absorptions are not considered. The effective wavelength, and bandwidth for g band is about 4776 and 848 Å, respectively. Those for r band are about 6412 and 833 Å. The BASS r filter is over 200 Å redder and has a broader passband than the SDSS one. The right figure gives a comparison of filter curves for the BASS, DES, and SDSS. The table gives the filter parameters.

Filter parameters for different surveys:

Filter g r
Effective wavelength (Å) 4776 4842 4719 6412 6439 6185
Bandwidth (Å) 848 966 777 833 895 687

The filter response curves are provided below:

The Galactic extinction coefficients we adopt are $A_g = 3.303$ and $A_r = 2.285$.

datarelease/telescope_and_instrument/home.txt · Last modified: 2017/01/18 14:40 by Zou Hu
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