Presentation

 

Stripe 82 is a 2.5 degree wide stripe along the Celestial Equator in the Southern Galactic Cap. It has been imaged by the Sloan Digital Sky Survey (SDSS) multiple times between 1998 and 2004 as part of the Legacy Survey in 82 runs (94 to 5052) under generally photometric conditions with good seeing and low sky background. Additional coverage of Stripe 82 has been obtained as part of the SDSS Supernovae Survey between 2005 and 2007, resulting in observations from additional 222 runs (5566 to 7202). As the observations in the Supernovae Survey were taken irrespective of seeing, transparency or airmass constraints, only a fraction of the data were taken under photometric conditions.

The IAC Stripe 82 Legacy Project produced optimal co-adds of the whole Stripe 82 dataset and makes them publicly available. The data release contains the co-added images and the corresponding exposure time maps among other data products like source catalogues and representations of the PSF for each co-add.

In our reduction we put special emphasis on preserving the characteristics of the background (sky + diffuse light) in the input images using a non-aggressive sky subtraction strategy. Our reduction reaches a limit of ~28.5 mag / arcsec² (3 sigma, 10 x 10 arcsec² ) in the r band. The effective surface brightness limit (50% completeness for exponential light distribution) lies at <µe(r)> ~ 25.5 mag /arcsec². For point sources we reach 50% completeness limits (3 sigma level) of (24.2, 25.2, 24.7, 24.3, 23.0) mag in (u, g, r, i, z). Details on the reduction process and first science cases like the discovery of stellar streams around NGC0426 and NGC0936 are given in 2016MNRAS.456.1359F.pdf

 

Data release

 

The release includes the co-added images, corresponding exposure time maps and sky-rectified versions of the co-adds. Additionally we provide fits representations of the PSF for each co-add. Furthermore the release includes object catalogues for point and extended sources with stars and galaxies confidently separated until g~23 mag. The IAC Stripe 82 data products can be accessed through the data section. For the cone search please select a radius equal or larger than 0.25 deg.

 

Calibration

 

The data are calibrated to a common zeropoint of 24 mag for all bands. AB magnitudes can be derived from the data via

mag = -2.5 x log10(counts/exptime) + 24

where exptime=53.907456 sec refers to the exposure time of a single SDSS image and counts refer to the ADUs measured in the co-add.

Each co-added image has an exposure time map attached to it which yields for each pixel the number of single images n(x,y) entering the stack. The effective exposure time in each part of the image is given by the product of n(x,y) and exptime.

Additionally we provide images representing the average of the g, r and i co-adds which can be regarded as deep r-band co-adds. As the calibration gets destroyed during this process, above equations are invalid for the deep r-band images.