Sinistro

Technical Data for Sinistro cameras

Note: The gain and saturation limit are reflected in the FITS header keywords GAIN and and SATURATE, respectively, and those are set for each individual camera in the network. The units of the saturation limit will be ADU for raw images, and electrons for BANZAI-processed images.

Description of Standard filters

The CCDs attach below a Filter/Shutter unit with carbon fiber disk shutter and 3 wheels, each 8 positions, providing

• Johnson/Cousins UBVRI
• Sloan primed ugri, PanStarrs zs (short), Y, w

An exposure time calculator can be used to estimate typical exposure times for our different aperture classes.

There are 4 off-axis ports which can all see light simultaneously with the main science camera.

One port to the North of the main science field always has an FLI autoguider with 0.34" pixels and 5.7' Field of View.

Fast cadence readout mode: central_2k_2x2

LCO has introduced a new readout mode for the Sinistro cameras on the 1-meter telescopes. The mode reads the central 2048 x 2048 pixels, with 2x2 pixel binning, and with a readout overhead of 9 seconds.

Science motivation:

Time-sequence observations of bright objects become less efficient with longer CCD readout times and other overheads. An example of a science program that benefits from reduced readout overheads is the observation of planet transits. Also, phenomena that change on time scales on the order of minutes cannot be observed efficiently if the readout overhead is too large. A short readout time will open a window into new science.

LCO has deployed a new CCD readout mode at the 1-meter telescopes where only the central 2k x 2k pixels of Sinistro images are read out, and the pixels are binned 2 x 2, resulting in a 1k x 1k pixel image. To shorten the per-image overhead further, the number of CCD wipes before each exposure are reduced compared to full-frame readouts. The "central 2x2k binned" mode reduces the total overhead from ~28 s per image to ~ 9 s.

The shortened overhead can increase the shutter open time over the duration of an observation, and hence benefits the achievable signal-to-noise. This mode is recommended for the acquisition of time series where:

• Exposure times are < 60 - 120 s,
• There are enough comparison stars in the reduced field of view.

Shared Risk Release:

The new central_2k_2x2 mode is released in shared risk mode. Observers should validate if this new mode is appropriate for their science before committing all allocated time.

• Flat fields are acquired only in the up, gp, rp, ip, zp, and w filters with this readout mode mode at this time.
• Other filters will have no flat fields observed in this mode, and data will not properly process.
• As always, please report any problems to science-support@lco.global .

Characteristics of the new mode:

• Identifier: central_2k_2x2
• Effective Field of View: 13’ x 13’ (down from 26’ x 26’)
• Image size: 1024 pixels x 1024 pixels
• Effective (binned) pixel size: 0.778”
• Effective full well per binned pixel: ~ 340ke-
• Typical gain: 6.6e- / ADU
• Typical read noise: 8e-.
• Readout time ~ 9 s (down from 28 s)

Notes:

1. The single, unbinned pixel full well is of order of 100-120ke-. The binned full well of ~340ke- is less than four times the single pixel full well, as we would expect 4x 100ke = 400ke-, this is limited by the dynamic range of the CCD controller’s 16 bit A/D converter.
   
   For targets near the saturation limit in the full frame mode, exposure times should be multiplied by 0.75 for the binned readout mode.
   
   
2. BIAS, DARK, and SKYFLAT calibration frames will be acquired by LCO as part of the calibration plan. The BANZAI imaging pipeline will correctly process the binned images. Due to limited twilight time, binned flats will be acquired at high priority only in the up, gp, rp, ip, and zp filters. Other filters will be nominally supported, but flat fields might be less current.
   
   
3. Crosstalk between the four amplifiers can be expected at a similar level as for full frame readouts. However, as the analog / digital conversion (ADC) saturates before the dynamical range of the detector does, crosstalk of objects exceeding the ADC saturation limit will be incompletely compensated.
   

Invocation of the central_2k_2x2 mode

In the portal's request composition page, the readout mode is selected from a drop down menu in the Instrument Configuration section.

In the API, include the following statement in the new API language to explicitly select a readout mode:

"instrument_configs": [{

"mode": "full_frame" || “central_2k_2x2”}]

If no readout mode is defined, the full_frame mode will be used per default.

Sinistro Instrument Designations

• Siding Spring (COJ), Dome A: fa12
• Siding Spring (COJ), Dome B: fa19
• Sutherland (CPT), Dome A: fa14
• Sutherland (CPT), Dome B: fa01
• Sutherland (CPT), Dome C: fa06
• Cerro Tololo (LSC), Dome A: fa15
• Cerro Tololo (LSC), Dome B: fa04
• Cerro Tololo (LSC), Dome C: fa03
• McDonald (ELP), Dome A: fa16
• McDonald (ELP), Dome B: fa08
• Tenerife (TFN), Dome A: fa20
• Tenerife (TFN), Dome B: fa11