An 8000-spectrum Night

2.5m Observing Log, 12/3/2010 Night Observers: Audrey Simmons, Dmitry Bizyaev

A “model” SDSS-III night: seeing ~ 1″, clear sky, ALL plates plugged (8) were finished from scratch.

The key to all of the SDSS spectroscopic surveys has been multiplexing at an unprecedented scale. The original SDSS spectrographs were fed by fiber plugplates with 640 optical fibers. For the Baryon Oscillation Spectroscopic Survey (BOSS) of SDSS-III, this number was upped to 1000 fibers per plate. Under excellent conditions, a complete BOSS observation takes about an hour, including three fifteen minute “science exposures,” calibration observations, and the time required to swap one plugplate cartridge for another on the back of the telescope.

The light of sunset comes through a BOSS cartridge attached to the bottom of the APO 2.5-m telescope (still in its enclosure). Strands visible in silhouette are individual optical fibers that transmit the light of BOSS targets from holes in the fiber plugplate to the spectrographs, which are themselves mounted on the back of the telescope.

When the seeing isn’t needle-sharp or a thin layer of cirrus obscures the sky, it takes more exposures to measure the redshifts and absorption spectra of the faint galaxies and quasars that are the targets of BOSS. Many nights have intervals of clouds or poor seeing, and often there are holdover plates that were observed but not completed the previous night.

But every once in a while, things are perfect, like the night of December 2, 2010. Eleven hours, eight plates, every one done from start to finish. By the morning of December 3, BOSS was richer by 8,000 spectra, the largest one night haul in the history of the SDSS.

Of course, observing eight plates in a night means that our fiber plugging specialists have 8,000 new tasks for the next day. We have placed a rush order for extra liniment. A ninth BOSS cartridge went into service on the night of December 3 (!), so when the next perfect night arrives, we can aim for a clean 9,000.

Congratulations to the SDSS-III observing and telescope team.

Written by David Weinberg

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