Slitmask Incentive Protocol





Starting with semester 2005B, August 2005, Keck will implement an incentive plan for LRIS and DEIMOS observers. The deadlines for submitting your slitmask designs are the same: four weeks for both LRIS and DEIMOS slitmasks, and eight weeks for DEIMOS “megamasks,” which are defined as masks with more than 200 slits. In the past there was little or no incentive to meet the deadlines. Keck has always met each slitmask request in time for their observing runs, albeit at times with significant extra cost to the Observatory. A number of times, however, we have come dangerously close to not being able to mill all of the masks in time. Given that observing time is our most precious commodity, we do not want to run the risk of compromising science.

Because of the lack of incentive to meet the deadlines, only 9% of LRIS observers and 16% of DEIMOS observers manage to meet their deadlines (see plot). We have received permission from the SSC and CARA Board to proceed with a plan to charge observers for late slitmasks. Exceptions will be granted for observing programs that simply do not allow an observer to meet the deadline. Such exceptions will be granted by the LRIS and DEIMOS support astronomers and will consist of a whole number of extra weeks which will be allowed before the incentive rates begin. Examples are given below.

We hope to make exactly zero dollars from this proposal. That would mean that everyone who can meet their deadlines will have done so. This will also give observers the best opportunity to have all of their requested slitmasks milled on time and with high quality.

Rate Table

The recharge rate table is given below. Note that the “zeropoint” in time is 9 a.m. HST of the very first day of your observing run. It is based on the nominal cost of a slitmask x 1.3 for each week, or portion thereof, that the mask design is late. On-time mask designs are never charged.

Table 1. Incentive rate table (per mask) for late slitmasks

≥ 8 weeks
no charge
7–8 weeks
no charge
6–7 weeks
no charge
5–6 weeks
no charge
4–5 weeks
no charge
3–4 weeks
2–3 weeks
1–2 weeks
< 1 week


Most questions about the charges can be answered using the following examples.

  1. A LRIS observer submits three mask designs at 9:10 a.m. (HST) on Jan. 1, for a three-night observing run starting January 29.
    The deadline is four weeks before 9 a.m. (HST) of the first night of the run. This would be January 1, 9 a.m. HST. The masks are only 10 minutes late, yet late they are, and the observer will be charged 3 x $40 = $120.
  2. The same LRIS observer submits their three mask designs at 8:55 a.m. HST on January 8.
    This is 5 minutes less than a week late. The observer would incur the same charge, $120.
  3. A DEIMOS observer has been granted a 1 week extension, and submits ten masks eight days late.
    The one week extension effectively shifts the leftmost row in the rate table by one row. But because the observer was one day later than their extension allowed, they still incur a charge of 10 x $80 = $800 for their late mask designs.
  4. A DEIMOS user of “megamasks” submits six “megamask” designs and two normal designs 23 days before their observing run.
    The designs are between three and four weeks before the run, so both types of masks are late. The megamasks incur a $450/mask charge, while the normal masks incur an $80/mask charge. The total late charge is 8 x $450 + 2 x $80 = $3760.


The coversheet for observing proposals will be modified to allow observers to check a box requesting an exemption to the nominal deadlines. Scientific justification for an exemption should be given within the body of the proposal. We will also allow observers to contact their DEIMOS and LRIS support astronomers directly to request an exemption. This allows for exceptions that were not foreseen at the time of proposal submission.

The decision on whether enough scientific justification has been supplied for an exemption, and the amount of the exemption, lies with Keck's support staff. If the observer disagrees with the support astronomer's decision, they may request that the support astronomer confer with the Observatory Director to arrive at a consensus decision.

An example of valid scientific justification would be a program in which the imaging data required to design the mask is taken less than five weeks before the observing run in which the mask is to be used. At least one week should be allowed to design a full suite of masks, so such a program would likely be granted a one week exemption. In another example, a high-redshift supernova project that bases the mask designs on discovery images taken ten days before the observing run would be completely exempted from any charges. Of course there is significant risk that the masks could not be milled in time for the run, but being able to plan for last-minute masks four weeks ahead of time will help us plan accordingly.


An automated system is being put into place to make it easier for LRIS and DEIMOS observers to submit and modify their observing configurations, and reliably transmit these requests to the summit crews that perform instrument reconfigurations. Part of this system is to remind observers about the deadlines and whether any designs for requested slitmasks have been received by the slitmask database. Such reminders will be sent when the semester's schedule is released, then two weeks before a run’s deadline. If the observer has not submitted a configuration form before the deadline, or has submitted a configuration that requests masks that are not in the slitmask database by the deadline, daily reminders will be sent until the situation is resolved. Note that simple errors, such as submitting a configuration form requesting a mask with the name “Mask_1” and then submitting the mask design under the name “Mask_A” can be easily resolved by resubmitting the configuration form with the name “Mask_A”. No extra charges will be incurred if the “Mask_A” design was submitted on time.


The method for recovering the charges from observers is still to be determined.

Justification for the incentives

Some justification has already been given above, but a PowerPoint presentation, presented to the SSC during their January 2005 meeting, provides more details. Some of the highlights: