Observing with SAM

Planning your Observations

The list of targets for SAM (name and J2000 coordinates) must be sent to soarnight@ctio.noao.edu no later than 2 weeks before the scheduled night, so we can submit the laser propagation target file to the Space Command Laser Clearing House. Last-minute additions are not possible (better include extra "maybe" targets in the list, just in case). However, SAM can observe in open loop (without laser, at seeing-limited resolution) any target, e.g. photometric standards. It is a good idea to get in touch with the SAM support scientists Andrei Tokovinin (atokovinin@ctio.noao.edu) and Cesar Briceno (cbriceno@ctio.noao.edu) for planning your observations with SAM.

The instrument setup form must be filled to define the filters, one week before the run. SAM+SAMI have a filter wheel with 7 slots for the 3-inch square filters (normally loaded with Bessell B,V.R,I filters) and can also use the SOI filter wheel that has 5 positions for 4-inch square filters (e.g. Sloan g',r', i', z' or narrow-band). Any filters used at SOI can be also used with SAM. However, SAM has only one filter wheel, filters can be changed only during the day.

Think about the strategy. Do you need dithers? There are pros, cons, and restrictions (contact the support scientists to learn more). What is the worst acceptable image quality needed to reach your science goals? Do you need photometric standards? They can be observed rapidly in open loop. What binning to use in SAMI (usually 2x2, pixel 0.091 arcsec)? Think about a backup program (using SAM or other SOAR instrument) for the case of poor seeing or technical problems. Fill the instrument setup forms for your backup program, too.

Initial preparations

Like other SOAR instruments, SAM+SAMI can be used classically or remotely. During observations, the Adaptive Optics (AO) system is operated by the Support Scientist, while the observer is in charge of operating the imager SAMI (selection of the binning, filters, exposure time, dithering, and object name). The observer is also reponsible for taking the bias and flat-field calibrations before the observations. Sky flats are strongly preferred over dome flats, because the latter do not correct well the shadows of the dust particles. See SAMI User Manual and SAMI Software manual

The observer should connect to the SAMI GUI (via the appropriate VNC connection through the SOAR or CTIO VPN; credentials should have been supplied by the Support Scientist). Once connected, create a folder for the night, with the format YYYY-MM-DD: e.g., in a terminal type "mkdir 2019-06-20". If not already running, open an IRAF window by clicking on the IRAF icon in the SAMI computer desktop (see image at right). Also launch a DS9 image viewer window (by clicking on the corresponding launcher button in the right edge of the desktop), as shown in the figure at right. Go into the SAMI GUI and setup the image directory and reset the counter to 1 or whatever number suits you, as shown below.

Afternoon Calibrations

Calibrations for SAM include flats and bias frames. Flatfielding is best done using sky flats, but in case these cannot be obtained, as a backup one should obtain dome flats on the first night of the run. This also allows the observer to detect any light leaks or problems with the mounting of the filters.

During your Observing Night

As mentioned above, you will be in charge of data acquisition, operating the SAM Imager (SAMI) user interface running on soaric9, and accessed through a VNC window after being connected to the SOAR VPN. The observer is responsible for setting file names, file types, selecting filters, exposure times, and number of exposures. The Support Scientist will operate the AO GUI (ICSoft), taking care of selecting guide stars and setting up the laser and closing the AO loop. Only science target observations are done in closed loop. Observations of photometric standards are done in open loop.

Data Reduction

Standard reduction of SAMI data (bias subtraction, division by the flat field, and combination of the multi-extension FITS file into a single image) can be done at CTIO using the pyraf pipeline developed by L.Fraga, provided that bias and flat-field calibrations are taken. In this page you will find a step-by-step guide on how use the SAM PyRAF software to reduce your SAM data.

Updated on July 26, 2024, 7:22 am