The 20-inch photometric telescope (PT) observes calibration fields for the 2.5 m telescope. When it's dark and photometric SDSS "secondary patches," stars in a 2.5 m stripe, are transferred to the SDSS photometric system. If it is photometric but moonlit, primary stars or other calibrators (metallicity, spectral type, reddening, etc.) are observed to improve the system quality and monitor for variables.
The 20-inch photometric telescope (PT) will operate every night within two nights of full moon. The downtime near full moon may be reserved for maintenance (e.g., cleaning, aluminizing) and will not usually be scheduled for observing.
ObservingPT observing is routine and can almost be done by following the step-by-step instructions. Observers need about 90 minutes before sunset to set up and another hour in the morning to close down.
The evening tasks are checking telescope operation and taking calibration data while the morning work includes taping data and writing reports. Routine telescope pointing and data acquisition is automatic but occasional checks on weather, data quality, and equipment require human attention. For example, focusing is a manual operation required once or twice per night.
Acquiring data that calibrates the PT is automatic: MOP software selects and automatically observes the stars. Choosing secondary patches for the 2.5 m requires observer input but automating this decision is a reasonable goal.
Telescope, Instrumentation, & DomeWe made modest modifcations to the telescope optical train (adding coma correctors), improved the baffling, and added counterweights. The telescope performs at or better than the manufacturer's specifications and has no outstanding problems.
The filter/shutter box works well enough, although upgraded controls are desired to handle more information from the instruments. These include things like local temperature and humidity, ambient light, flat field lamp status, and telescope inclinometer.
The CCD system behaves well except for occasional warmups of the CryoTiger cooling system. These are not serious enough to prevent observations but we don't understand their cause or resolution yet. The control and readout electronics usually perform flawlessly during an entire observing run. We hope to install an ion pump on the dewar in summer 2000.
This past observing season we noticed that the daytime temperature inside the PT dome can exceed 100F in the summer, much warmer than the early evening temperature. Consequently, images are poor for the first half of the night unless the telescope is opened a long time before sunset. In summer this is often impossible because of afternoon thunderstorms. The solution, insulating the dome, is simple and should be done before the next warm season.
StaffingThe personnel requirement is heavily loaded at the beginning and end of the night with some attention needed during the night to watch for problems and bad weather. With 90 minutes startup time, 60 minutes to shut down, and an hour or more during the night to attend to report entries and data checks, we need at least 3.5 hours per night of observing.
Until December 2000 two JHU postdocs, Bing Chen and Eric Neilsen, are each committed to seven nights a month at APO to cover the two weeks centered on new moon. In addition to their observing duties, Chen is responsible for occasional validation of the pipeline software using alternate methods of data reduction (usually IRAF and IDL) while Neilsen maintains and updates MOP, the observer's software.
For bright time we have the assistance of Bryan Laubscher from Los Alamos to cover a few nights per month. In the summer we hope a few JHU undergraduates will take some of bright time duty as well.
During this period (before December 2000):
- Stephanie Snedden, an APO/SDSS observer, will be trained as a PT observer and prepare to take the lead in PT operations.
- Alan Uomoto (JHU) will spend about 25% time validating and improving the observing procedures and guiding the installation of hardware and software modifications.
- About 0.25 fte effort from the JHU Instrument Development Group will be used to install hardware to improve observing efficiency, which will be more important when the JHU observing staff is no longer available.
- John Briggs (Yerkes Observatory) will be Telescope Engineer and spend about 25% of his time maintaining, repairing, and improving the telescope hardware (see the maintenance paragraph below).
- Jon Brinkmann will be Instrument Scientist and spend about 25% of his time maintaining, repairing, and improving the instrument package.
Enhancements 2000In no particular order:
- Software selection of secondary patches. This requires connections to a database system that tracks observed fields (Kent) and additions to MOP for selecting the best fields (Neilsen).
- Automatic generation of photometric quality indicators in near real time
- Automatic focusing
- Inclinometer to eliminate the need for beginning-of-night pointing adjustment
- Dome insulation & aluminum tape
- UPS for CryoTiger
- Temperature control environment for CryoTiger
- Ion pump on CCD dewar to reduce pumping requirements and to readout pressure
- Pickoff mirror on filterbox to enable easy pointing models
- Ambient and skylight meters to estimate sky flat exposure times, to confirm that the flat field lamp is working, and to check for room lights.
- New cables & hoses. The current set has some items that are too short, there is some potential for telescope interference.
- Sanity software suite to extract essential information about the instrumentation with a small number of easily obtained data sets
- The JHU postdocs (Chen & Neilsen) will spend the first quarter of 2001 doing final reports and possibly one last independent analysis of data quality. They are not be expected to observe with the PT.
- Dark time observing will be handled by APO/SDSS observers. We anticipate bright time observing will be covered by a combination of Bryan Laubscher, Alan Uomoto, and JHU students.
- Engineering and instrument maintenance will be handled by the Telescope Engineer (Briggs) and Instrument Scientist (Brinkmann). The level of effort should be about 20% each.
- While most maintenance can be handled at APO, 25% of a JHU research scientist will be retained to cover situations outside the ability of APO staff.
The PT requires routine maintenance, most of which can be performed on-site by the Telescope Engineer or Instrument Scientist. None of the work is time or schedule urgent if proper attention is paid to the checkup and inspection schedule. The total effort should be less than 1/2 fte during the course of a year, divided between the Telescope Engineer and Instrument Scientist.
Expendable supply costs are small and include materials for aluminizing and testing the coatings, air filtration and drying materials, and flat field lamps. Replacement of the computer systems in the dome and observing room every three years or so will also be required.
Specific requirements for the extent to which PT observing must be automated have not been written. In the current system, automation was chosen when it improved scientific productivity but deferred for otherwise. Opening the dome and telescope, which are done when the sky is too bright to observe, are manual operations while pointing the telescope and taking exposures is automated to minimize human errors.
Further Automating Operations
There are very few single things that can enhance automatic operation significantly. The next level of useful automation comes when the telescope can be opened and closed automatically, take calibration frames (flats) without humans, do the usual nighttime observing, and close in the morning. Doing this would be expensive, although perhaps reduced labor might justify the expense. I suspect that humans would be less expensive and more reliable in the end, though.