Slitmask Incentive Protocol

Deadlines

Starting March 2023, the deadlines for submitting your slitmask designs are as follows:

FIVE WEEKS for both LRIS and DEIMOS slitmasks,
and eight weeks for DEIMOS “megamasks,” which are defined as masks with more than 200 slits.

Slit mask milling requests made later than the deadlines stablished above will be declined unless explicitly approved by the WMKO Chief Scientist. Observers with late mask requests should contact John O‘Meara (jomeara at keck.hawaii.edu) and the LRIS/DEIMOS staff astronomer directly with their requests, and should do so before submitting the slitmask file. Late requests will only be approved if they do not significantly disrupt summit operations and if the scientific need is time critical (such as for transient events like supernovae).

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, DEIMOS and LRIS observers not always manage to meet their deadlines. We 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 staff astronomers and will consist of a whole number of extra weeks which will be allowed before the incentive rates begin. Examples are given below.

Our hope is to make exactly zero dollars from this policy. 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

Timescale	LRIS masks	DEIMOS masks	DEIMOS “megamasks”
≥ 8 weeks	no charge
7–8 weeks	no charge		$160
6–7 weeks	no charge		$200
5–6 weeks	no charge		$260
4–5 weeks	no charge		$340
3–4 weeks	$40	$80	$450
2–3 weeks	$50	$100	$580
1–2 weeks	$70	$130	$750
< 1 week	$90	$170	$980

Examples

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

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.
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.
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.
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.

Exceptions

The box Special Requests and Comments on the coversheet for observing proposals can be used by observers to request 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 staff 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 Chief Scientist and support staff. If the observer disagrees with the staff astronomer's decision, they may request that the staff 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.

Reminders

An automated system is in 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 are 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.

Implementation

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

Justification for the incentives

The current deadline is still ignored by some observing teams, and further incentive is needed if we are to avoid compromising science.
While the Observatory is committed to providing the resources for milling all requested masks, we prefer to do this with normal scheduling of the resources, not using overtime and disrupting other planned Observatory work. The cost of late slitmasks is paid by the Observatory in this disruption and extra cost.
The four-week deadline is reasonable, given the desire to spread the milling work evenly across a lunation, and given the historical load on the milling process.