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<p class="MsoNormal"><b><span lang="EN-AU" style="font-size:11.0pt">SkyMapper Southern Survey Data Release 4 (SMSS DR4)<o:p></o:p></span></b></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt">We are pleased to announce the immediate availability of Data Release 4 from the SkyMapper Southern Survey at the SkyMapper website -- <a href="https://protect-au.mimecast.com/s/1S1rCZY1Nqi7Nz7RDuz4q5q?domain=skymapper.anu.edu.au">https://skymapper.anu.edu.au</a> -- and via the tools of the
All-Sky Virtual Observatory (ASVO).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt">SMSS DR4 contains optical photometry in the 6 SkyMapper filters (<i>u,v,g,r,i,z</i>) for ~700 million astrophysical sources over 26,000 sq.deg, ranging from the South Celestial Pole to Dec=+16deg
for objects with data in all bands, and some sources as far North as +29deg. The photometry is drawn from over 13 billion measurements made from more than 400,000 images acquired by the 1.3m SkyMapper telescope between March 2014 and September 2021. The typical
10-sigma depths for each field range between 18.5 and 20.5 ABmag, depending on the filter, but certain sky regions include longer exposures that reach as deep as 22 ABmag.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt">Compared to previous SkyMapper data releases, DR4 includes significant enhancements in data processing, most notably a new photometric calibration anchored to synthetic photometry from
<i>Gaia</i> low-resolution spectroscopy, which resolves reddening- and spatial-trends identified in previous releases, especially in the bluest filters,
<i>u</i> and <i>v</i>.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt">A large number of other photometric and spectroscopic surveys have been cross-matched to the
</span><span lang="EN-AU" style="font-size:11.0pt;font-family:"Courier",serif">dr4.master</span><span lang="EN-AU" style="font-size:11.0pt"> table of objects, to facilitate various scientific investigations.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt">Further details about SkyMapper and SMSS DR4 can be found at the SkyMapper website -- <a href="https://protect-au.mimecast.com/s/1S1rCZY1Nqi7Nz7RDuz4q5q?domain=skymapper.anu.edu.au">https://skymapper.anu.edu.au</a> -- and in the associated paper recently submitted to PASA: <a href="https://protect-au.mimecast.com/s/HQOxC1WLPxc6Y86mkIGpWO4?domain=arxiv.org">https://arxiv.org/abs/2402.02015</a>
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt">Please contact the SkyMapper team with any questions or issues: skymapper@anu.edu.au<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-AU" style="font-size:11.0pt">- Christopher A. Onken, Christian Wolf, and the SkyMapper Team<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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