Current Status of the MOIRCS Upgrade Project
As was annouced already, we have executed the first engineering works since summer 2015. MOIRCS now has two Teledyne Hawaii2 RG detector arrays and new array control electronics (ASIC and SAM from Teledyne). After the laboratory testing, the first engineering observation was successfully done in Dec 26 and 27, 2015.
We have confirmed that the new detectors and electronics provide a significant reduction in electronic noise in the data. The new detectors have 14 and 15 electrons respectively of read noise in a CDS frame, which is about a factor of 2 improvement compared with the old system.
The new detector also has a better sensitivity than the old one. Especially in Y and J bands, roughly ~40% rise of the sensitivity is measured from the observing data. For more detail, please refer the report of the first engineering observation.
The new system offers the 32-channel readout (cf. old system was 4 channel), which offers faster readout speed than the old system. The measured overhead time during a data acquisition, however, is about 15 sec. This is somewhat longer than expected, and we are still working on this.
The instrument control system (ICS) software is also replaced to the new in-house system, i.e., the system that was made entirely by the staff at the Subaru Telescope.
The major issue we have had during the engineering work is the unexpected observation of the large-number of the radiation hit events by the new detector (example image is here: 20-sec dark image). After some investication, we conclude that the radiation source is the AR coating of the last lens which contains the radio-active Thorium which emits the alpha-particle radiation(*). The expected energy range of the decay particle explains the heavily saturated nature of the appearance.
In order to block the incoming raditation, we have decided to install a thin glass window in front of the detector. The high IR-throughput low-reflectivity window is now being manufactured by Asahi Bunkou Co., and we are going to install the window in this spring, before S16A observation starts.
The effect of the alpha-particle blocking window on the measured sensitivity should be minimal. After the installation of the window, we will measure the system throughput again, and will update the numbers in the homepage.
The remaining task need to be done is the confirmation of the MOS system function under new control software. We will execute the functional verification of the system soon before April.
We are also planning to introduce the IFU spectroscopy function to MOIRCS, as well as the upgrade of the current MOS system. The date of the downtime is still TBD, though currently starting from early 2017, when MOIRCS might "hibernate" more than a year for possible SWIMS operation, is expected.
We will update the information via this website.