Alistair Walker - DECam Instrument Scientist Tim Abbott – Blanco Telescope Scientist CTIO/NOAO DES Collaboration Meeting Oct The Blanco Telescope & DECam

Status DECam has been on-sky for three years. – ~ exposures – In the the unscheduled down-time averages 2.5% from all causes. In 2013 it was 9.1% has been exciting! – Electrical storms March took out the Tololo commercial power – Snow storm on August 8. This took out the generator power and DECam warmed up – Richter 8.3 earthquake on September 16, and 10 aftershocks > 6.0, Max. horizontal ground acceleration at Tololo = 0.345g. DES Collaboration Meeting Oct 20152

DECam is also a seismograph DES Collaboration Meeting Oct 20153

DECam: Improved Focal Plane Temperature Stability The temperature stability of the focal plane temperature has been improved by a factor 10 by discarding a noisy sensor The CCDs run 1C cooler now, at -101C. A DECal scan afterwards did not show any Y band response difference DES Collaboration Meeting Oct 20154

DECam: F&A CCD Lightbulb DES Collaboration Meeting Oct Hot pixel on FN2 became hotter in April and then superhot during July (image ) Does not affect adjacent CCDs (N28, N31) AOS analysis discards the affected regions Afternoon calibration script now includes 1s and 90s dark exposures

DECam: Replacement of the 1S and 1R LN2 lines DES Collaboration Meeting Oct LN2 pump is being replaced at ~ 8 month intervals – new pump bearings may increase this In July 2015 the 1S and 1R LN2 lines were replaced A month later we fixed a leak in 1S We still have a leak in 1R. And 7S…

DECam: Cryo-compressors DES Collaboration Meeting Oct The LN2 cooling servo has worked as it ought to for 3 months of the last 3 years (100 psi, tank heater watts, no LN2 use) Basic issue is that the head room (cooling power – heat load) is marginal, and there are lots of ways to degrade this – poor vacuums, thermal shorts, cryo issues etc We are running the glycol-cooled compressors too cold. Change from 9C to 13C last week helped, we are about 20 watts from stability Next pump change we will also service or replace the cryo heads All of this (we hope) happens behind the scenes and the observer only notices the steamship noises…

Blanco: Throughput DES Collaboration Meeting Oct What causes this? - degradation of M1 aluminium coating? - dust on the optical corrector? Courtesy Arjun Dey, DECaLS

Blanco: Throughput DES Collaboration Meeting Oct Realuminize in Small chance of 2016? Inspect & remove dust off C1 October 26

Blanco: Image Quality DES Collaboration Meeting Oct Telescope tracking and guiding Telescope optical performance Environmental Effects (dome seeing, mirror seeing)

Blanco: Image Quality DES Collaboration Meeting Oct Telescope tracking and guiding are excellent But pointing into the wind can degrade image quality by vibrating the telescope. (guiding update is 1 Hz, heavily damped) Mitigate by Closing lateral doors Raising wind blind Tools: Anemometer Webcam 

Blanco: Optical Performance DES Collaboration Meeting Oct We use the Active Optics System (AOS = F&A CCDs, hexapod) to keep the telescope in focus and aligned (displacement, tilt) in closed loop, at a per-exposure frequency. The tweaks are on-top of a Look Up Table (LUT).

Blanco: Optical Performance DES Collaboration Meeting Oct The primary mirror also has an active support system - open loop compensation for gravity, and a single-valued correction for astigmatism. We have a test LUT for astigmatism as a function of sky position, but there appears to be hysteresis at a level ~ the size of the entries Maybe we will need to tweak exposure by exposure? If so, how much damping will be needed? Etc TESTS THIS SEMESTER

Blanco: Environment DES Collaboration Meeting Oct DAY TIME We actively cool the dome and telescope with two large air- handling units on the Console-level Floor. A large horizontal fan “the helicopter” on the Main Floor blows air upwards We can cool the primary mirror front surface (part of the day) NIGHT TIME Lateral doors and dome open Air sucked from around the primary ALL TIME Floor Cooling Coude Room (adjacent) has AC Prime focus cage contents are cooled (to ambient) DECam CCD Controllers and Heater crates are cooled by water

Blanco: Environment DES Collaboration Meeting Oct PROTOCOL: Requirement is to keep the primary mirror surface between 0 and 2C cooler than the ambient, at night time. And to have the inside “lower” dome temperature the same as outside Input: present mirror temp Input: outside air temp Input: zero deg isotherm today Input: zero isotherm tomorrow Decision time ~ Noon Decision: Change from cooling to sucking at Noon, 2 pm, 4pm, or at opening time. Who? Alistair -> Telops. Automate eventually, maybe?

Too cool Sucker on 5 pm Sucker On Sucker on 3pm Sucker on 2 pm Sucker on 4 pm

DES Collaboration Meeting Oct Sept DIMM DECam BOTH

The corresponding temperatures DES Collaboration Meeting Oct

DES Y1+Y2 DIMM subtracted DES Collaboration Meeting Oct Thanks to Eric Nielsen Instrument Floor ~ 0.45 arcsec

Auxiliary Equipment DES Collaboration Meeting Oct RASICAM has a new mirror aTmCam is working every night So is the GPS And a new DIMM is coming soon

THE END DES Collaboration Meeting Oct CTIO DECam Scientist Support Team Alistair Walker*, Tim Abbott, David James, Kathy Vivas*, Alfredo Zenteno*, Chris Smith * At this meeting

LSST Construction DES Collaboration Meeting Oct 2015 Thanks to David Walker DECam 

The End DES Collaboration Meeting Oct