Gemini Observatory tracks completion rates for queue programs, open shutter efficiency, acquisition times and weather losses for both telescopes. In addition, the Observatory has investigated how observing conditions and program length may affect the probability of a program getting data. The results of these investigations may be particularly useful for PIs with programs in band 3. Information on RA distributions as well as the demand for the various GMOS gratings in semesters 2006B-2007B is also available. The following summarizes current status of these Science Operations Statistics. The graphs and this web page will be updated as time allows. Last update August 29, 2007.

• Weather loss and delivered science nights
• Completion rates for queue programs
• Acquisition times
• Open shutter efficiency
• The effect of requested observing conditions and the program length
• GMOS gratings - demand and execution
• RA distributions for 2006B-2007A

Weather loss and delivered science nights

Each semester at the time of the Call for Proposals, the Observatory with input from the Operations Working Group decides on the number of offered science nights. The science queue (and classical nights) are filled using this number of science nights. The actual delivered number of science nights can either be larger (if planned engineering or commissioning tasks did not happen) or smaller (if engineering or commissioning tasks take longer than planned or if unforeseen events happen). In addition, the weather loss for a given semester will affect the completion rates. Figure 1 shows the weekly weather loss during semesters 2005A-2007A, while the table below lists the planned and delivered science nights. In 2006B Gemini North was closed for a month for recovery after the magnitude 6.7 earthquake that occured October 15, 2006.

Figure 1: Weekly weather loss at Gemini North and South during the semesters 2005A, 2005B, and 2006A. Each bar on the histogram represents a week in the semester. The total weather loss for a semester in this period varies between 18.3% and 36% (see the red lines). It is also clear that in some semesters, e.g. GS-2005A and GN-2006A, the weather loss is very unevenly distributed through the semester contributing further to the challenge of completing the scheduled queue programs.

Site/Semester	Planned science nights	Delivered science nights	Delivered/planned	Weather loss
GN-2005A	127	161	127%	18%
GN-2005B	129	147	114%	19%
GN-2006A	157	157	100%	36%
GN-2006B	166	123	74%	23%
GN-2007A	157	157	104%	22%
GS-2005A	141	164	116%	36%
GS-2005B	136	162	119%	23%
GS-2006A	127	171	135%	26%
GS-2006B	138	184	133%	18%
GS-2007A	127	150	118%	25%

Completion rates for queue programs

The completion rates of queue programs is closely tracked and queue planning is carried out to optimize the completion rates. Full multi-instrument queue planning was put in place at Gemini North starting in semester 2005A, with Gemini South following in semester 2005B. This change combined with better reliability of instruments and telescopes has led to a significant improvement in the completion rates across all scientific ranking bands. Further, in semester 2004A the sizes of the ranking bands were changed from equal size to roughly 20%, 30%, and 50% for band 1, 2, and 3, respectively. At the same time the national TACs were given the option of granting band 1 programs rollover status such that it would be active in the queue for a total of three semesters. Starting in 2007A, the ranking bands were adjusted to roughly 30%, 30%, and 40% for band 1, 2, and 3, respectively.

Figure 2 compares the completion rates in the earlier semesters (2003A-2004B) with those of the semesters 2005A-2006A and semesters 2006B-2007A. Both sites are included on Figure 2. More detailed information by site and semester is given in Figure 3. For all the completion statistics, target-of-opportunity programs are excluded as the completion of these depends on the availability of triggers rather than planning from the Observatory's side.

The completion rates in band 1 and 2 in semesters 2005A-2006A were 90% and 73%, respectively. While in 2006B-2007A these decreased to 81% and 54%, respectively. In 2006B the earth quake at Gemini North significantly affected the completion rates. The change in ranking band size in 2007A may have contributed to the decrease in the completion rates for 2007A, though other factors like the RA distribution especially for the queue on Gemini North and the failure of GNIRS on Gemini South, also contributed. It should also be kept in mind that there are still active programs with rollover status from 2006B and 2007A, which may get completed, see Figure 3 for details.

For band 3 programs the queue planning aims at getting a significant amount of data for the programs that are in fact started, rather than getting a little bit of data for many programs. The effect of this planning can especially be seen on Figure 3 for semesters GN-2005A and GN-2005B, where the completion rate for band 3 programs that got started is between 70% and 80%.

Figure 2: Summary of the completion rates by band in the semesters 2003A-2004B, 2005A-2006A, and 2006B-2007A. The figure includes both Gemini North and South. The significant improvement of the completion rates in 2005A-2006A is, in part, due to the full multi-instrument queue planning now in place at both sites. The completion rates for 2006B-2007A were affected by the earth quake at Gemini North (2006B), the GNIRS failure at Gemini South (2007A), and a very overfilled queue at RA=12-14h in good conditions at Gemini North (2007A), see plots of the RA distributions. Also these two semesters still have active programs with rollover status in band 1. Thus, the final completion rate for band 1 is expected to be higher than shown on this figure.

Figure 3: Details of the completion rates by band and semester. Starting in 2004A the national TACs could assign rollover status to band 1 program. With rollover status a program remains active in the queue for a total of three semesters. Thus, semester 2006B and 2007A may still have active programs; the green histograms show the projected completion rates for these semesters under the assumption that all programs with rollover status get completed.

Acquisition times

The acquisition times are tracked from the records in the observing database. From an earlier study of this, it is known that the median time to slew and acquire a guide star for a new target is about 6 minutes. The exact time of course depends strongly on the length of the slew. In the following, this time is excluded from the statistics. Figures 4 and 5, and the tables below summarize the acquisition times for all the spectroscopic modes, and for the only imaging mode (NIRI+Altair) that has significant acquisition time above the slew and guide star acquisition. For the spectroscopic modes, the measured acquisition time is the time it takes to image the target and align it in the spectroscopic aperture (slit, IFU or MOS mask). For NIRI+Altair the measured acquisition time is the time it takes to center the target on the NIRI array.

Figure 4: Summary of all acquisitions for spectroscopic observing modes done in queue time for Gemini North and South during the semesters 2005B and 2006A. The distributions for the two sites are very similar.

Figure 5: The acquisition times for spectroscopic observing modes by instrument. The gray histogram on each panel show the distribution of all acquisition times for spectroscopic observing modes at that site. GMOS-N and GMOS-S are very similar as expected. NIRI and GNIRS are also very similar. The histograms clearly reflect the higher usage of GMOS-N compared to GMOS-S, and GNIRS compared to NIRI. The acquisition times for T-ReCS are significantly longer than for Michelle. The reasons for this is that T-ReCS images through the slit, while Michelle does not, and that Michelle is better integrated into the multi-instrument operations than is the case for T-ReCS at this point.

Open shutter efficiency

The open shutter efficiency for Gemini instruments has been tracked since August 2004. For each night the open shutter time is extracted from the FITS headers of the obtained observations. For the mid-IR instruments (Michelle and T-ReCS) the tracked open-shutter efficiency includes the overhead from nodding+chopping. This means one should expect the listed efficiency for these instruments to be similar to the other instruments while of course the actual exposure time on the target will be lower. Currently with guiding on one side of the beam the exposure time on the target is factor 3.73 lower than what is listed in the table as "open-shutter" efficiency for the mid-IR instruments.

The observing conditions for each night are assessed. Stable (and good) conditions are assigned to nights where the seeing is stable and the night is either photometric or has very thin (stable) cirrus. Less stable conditions are assigned to nights during which either the seeing and/or the cloud cover varied sufficiently to force the observer to change observing programs. Unstable conditions are assigned to nights with several such changes in observing program and/or significant time loss due to the weather. In all cases, the open shutter efficiency is derived as the fraction of the usable time during the night, less any loss due to weather or technical faults.

The table below and Figure 6 summarize the open shutter efficiency in the period August 2004 to February 2006, see also Gemini Focus June 2006. The main conclusions from the data are as follows.

• The open shutter efficiency in stable observing conditions is typically between 60% and 70%, with peak values larger than 80%.
• The open shutter efficiency in less stable observing conditions is typically 5-10% lower than in stable conditions.
• The near-IR instruments on Gemini North and Gemini South have comparable open-shutter efficiencies.
• GMOS-N has about 5% higher open shutter efficiency than GMOS-S. This may be due to the effect of consistent queue planning of all GMOS-N nights since its commissioning.
• The use of multiple instruments has no effect on the open shutter efficiency at Gemini North in stable (good) conditions and less stable conditions, while at Gemini South the open shutter efficiency is about 5% lower than the average of the nights during which only one instrument was used.

The significance of the listed differences have been confirmed using a Kolmogorov-Smirnov test.

Figure 6: Open shutter efficiency for facility instruments at Gemini North and South for the period August 2004 to February 2006. The first bar for each instrument shows the efficiency in stable (good) observing conditions, while the second bar shows the efficiency in less stable observing conditions. "GN 1 inst" and "GS 1 inst" show the average efficiency for all nights at Gemini North and South, respectively, that used only one instrument. "GN multi-inst" and "GS multi-inst" shows the average for all multi-instrument nights.

In order to improve the tracking of open shutter efficiency, it is planned to put in place automatic software to track this efficiency within blocks of nights, such that it will be possible to assess in further detail the effect of using multiple instruments on a given night. Until this software is in place, it is not expected that the open shutter efficiency statistics presented on this web page will be updated.

The effect of requested observing conditions and the program length

Recently a detailed investigation was carried out to better understand how the requested observing conditions and program length affect the probability of a program getting the requested data. Only semesters 2005A-2006A were included in this investigation since these semesters closely reflect the current queue planning principles and methods, while this is not the case for the earlier semesters.

Figure 7: Comparison of the distribution of program lengths for scheduled programs (gray) and programs that got at least 75% of the requested data (orange). For band 1 and 2 the distributions are identical. Thus, the program length for these two ranking bands has no influence on whether the program gets data. For band 3 there is a tendency that more of the shorter programs get executed. This is as expected since the queue planning focuses on selecting programs from band 3 that have a fair chance of getting a significant faction of the requested data. The median program length in band 3 for scheduled programs is 9 hours, while the median program length for those that got at least 75% of the requested data is 6 hours.

In order to simplify the investigation of the effect of the observing conditions, six broad bins of observing conditions were defined as follows based on the percentile bins used by the PIs to specify the required observing conditions. (IQ=Image quality, BG=Sky background, CC=Cloud cover)

IQ<= 70%, BG<= 50% (dark), CC=50% (photometric)

IQ<= 70%, BG> 50% (gray/bright), CC=50% (photometric)

IQ<= 70%, CC>=70% (cirrus, clouds)

IQ= 85%, CC=50% (photometric)

IQ= 85%, CC>=70% (cirrus, clouds)

IQ=Any

All the science observations in the observing database for the semesters 2005A, 2005B and 2006A were mapped onto these six broad observing condition bins. This was done both for the planned science observations and the executed science observations. Figure 8 shows the distribution by band and site.

As expected, the distributions of observing conditions for planned and executed observations in band 1 are very similar (due to the high completion rate), and the emphasis is on using the best conditions, specifically image quality of 70%-ile or better. The observations in band 1 shown at IQ=Any are primarily the Rapid ToO observations.

In band 2 the distributions of planned and executed observations are also very similar to each other. A larger fraction of IQ=85% observations are present in band 2 than in band 1.

For band 3 observations almost none are planned for the very best observing conditions (bin "1") and almost none get executed in these conditions. Further, 58% of the planned observations can be done in IQ=85% or worse. It is important to note that more than 70% of the executed band 3 observations are in fact observations that can tolerate IQ=85% or worse. Thus, the single most important condition for band 3 PIs to consider relaxing (if possible) is the image quality requirement.

Figure 8: Distribution requested observing conditions of planned (top) and executed (bottom) observations in the semesters 2005A, 2005B and 2006B at both sites. The observing condition bins are explained above.

GMOS gratings - demand and execution

Because the two GMOSs can carry only three gratings simultaneously, it is of special interest to PIs with programs in band 3 to know which gratings are in highest demand and therefore will most often be in the instruments. Figure 9 shows this info for semesters 2006B-2007B. The information for semester 2007B does not include ToO programs, though most of the Rapid ToO spectroscopy as well as a large Standard ToO program in band 1 use R400.

Figure 9: GMOS gratings: Total planned time in science observations as well as the executed time are shown for the six gratings for GMOS-N (top) and GMOS-S (bottom).

Last update August 29, 2007; Inger Jørgensen