Proposing and Phase II

This page was last updated on March 9th, 2023. See Program Updates for the most recent announcements.

Planning to Observe with IGRINS at GEMINI

https://www.gemini.edu/observing/phase-i/standard-semester-program/2023b-call-proposals

IGRINS is at Gemini South for the 2023A and 2023B semesters. 

Availability

Proposals for IGRINS at Gemini should be submitted through the Gemini Phase 1 Tool (PIT) and include the appropriate overheads discussed below. Queue observations for awarded time will be prioritized by TAC-assigned science ranking and as permitted by the conditions, as is typical at Gemini. Specific information about Gemini pointing limits, observing condition constraints and proposals can be found on the Gemini webpages. 

Sample IGRINS Spectra

IGRINS reduced spectra from commissioning in 2014 are public and can be viewed at this link: Sample Data

Typical IGRINS Observing 

Unless the PI requests otherwise, IGRINS observations will be executed as follows:

1) The telescope will be slewed to the target and the slit PA will be set to the default E-W orientation (PA=90).

2) The target will be located in the slit-view-camera. These images will be saved in a compressed format.

3) The target will be placed on the slit in the A position (1.2 arcseconds above slit center) and observed.

4) The telescope will be moved so the target is at the B position (1.2 arcseconds below slit center) and observed.

5) We will typically obtain a single ABBA quad on every target with an on-slit separation of 2.4". 

When the seeing is worse than ~2.0" then we will switch to ON-OFF observing of Band 4 programs.

6) We will observe telluric standards with ABBA quads and obtain SNR>200.

The optimal magnitude range for SNR~100 spectra is between 10 and 13.99 in the K-band. 

In this range (K=10-13.99 mag) the typical exposure time is greater than the overhead time (~12 minutes) 

and within the maximum observable time for a target (5 hours in 1 night).

All the SNRs we quote are the average per resolution element. The center of each order is ~20% higher and the ends of the order are ~20% lower than the average. 

Standard Band 1/2 Observing Condition Constraints are:

The majority of IGRINS programs should use Sky Background (ANY) and Water Vapor (ANY) 

A simple applet for exposure time estimates is available here: IGRINS Simple ETC for Gemini

These exposure times are for the total ABBA quad.

Most IGRINS programs can use the conditions assumed by the ETC: IQ-70, CC-70, SB-ANY, WV-ANY

IQ20, CC50-70 should request half the time estimated by the ETC 

IQ85, CC70-80 should request 1.5 times the ETC estimates

IQANY, CCANY needs to request 2 times the ETC estimates

For more guidance on estimating exposure time, see the tables in the Phase II section below.

Standard Band 3 selections for Observing Condition Constraints are:

CC(80), IQ(ANY), Sky(ANY), WV(ANY)           K (mag) < 11

Objects fainter than K=11mag are not feasible (and not permitted) in Band 3 conditions. 

Standard Poor Weather selections for Observing Condition Constraints are:

CC(ANY), IQ(ANY), Sky(ANY), WV(ANY)        K (mag) < 9

Objects as bright as K=2 can be requested in poor weather, but the A0V for the target should also be specified in the request.

IQ(20) should always be selected for objects fainter than K=13 mag

Want to calculate exposure times with a formula? This is the empirical relationship used by the ETC:

IQ-70, CC-70, SB-ANY, WV-ANY

SNR = (273*sqrt(itime)*10^(-0.2*(Kmag-2))) /(1.75)

where itime is the total exposure time for ABBA, Kmag is your 2MASS magnitude, and seeing is in arcseconds.

The total exposure time in seconds for a desired SNR can be estimated with this equation:

itime = ((1.75*SNR)/(273*10^(-0.2*(Kmag-2))))^2

You can then adjust these calculations based on the conditions that you specify for your program

IQ20, CC50-70 should request half the time estimated by the ETC 

IQ85, CC70-80 should request 1.5 times the ETC estimates

IQANY, CCANY needs to request 2 times the ETC estimates

Available Exposure Times:

Minimum: The IGRINS detectors read out every 1.63s and this is the minimum exposure time.

Maximum: The maximum exposure is limited in two important ways. 

1) For bright observations, the maximum exposure time corresponds to roughly SNR~250 for an ABBA quad. This is to limit detector persistence between queue programs. SNR>250 can be achieved through additional ABBA quads.

2) For extremely faint targets needing long exposure times, cosmic rays increase over time and the variation of sky lines between nodding is too great for them to subtract. The recommended upper limit is 1200s exposures; in the most extreme cases, 1800s may be permissible but must be fully justified in the science case.

IGRINS proposals need to specify their exposure time estimates and the desired SNR in a tables of the proposal. 

The individual exposure times during observation will be adjusted to observing conditions in an effort to obtain the required SNR for the science program. 

An object requiring more hours on source than is possible in a single night may be observed on multiple nights and coadded to obtain the proposed SNR.

Band 3 Exposure Times:

In most cases, Band 3 exposure times should be 1.5 times those requested for Band 1 or 2 conditions. 

Sensitivity and Exposure Time Estimates - Extended Sources

The IGRINS slit will be 5"x0.34" at Gemini. 

We refer observers interested in extended sources to the original IGRINS ETC (Download, Manual, Info).

Absolute flux calibration with IGRINS is difficult because there are many error factors (ex. variable seeing, cirrus, water vapor, PSF centering on the slit, guiding errors). With a 600 second on-source exposure on an outflow with a H2 1-0 S(1) line flux ~10^(-14) [erg/cm^2/s], you might expect SNR(peak intensity/rms) ~ 40. This knot has a velocity width (V_FWHM) = 20 km/s.

An additional estimate for extended sources, from Dr. Harriet Dinerstein using past IGRINS observations, is that the Noise Equivalent Line Flux (1 sigma) of about 1 x 10^-16 erg cm^-2 s^-1 can be reached in a 40 minute (ABBA), while for a roughly 2.4 hour exposure time it is more like 6 x 10^-17 erg cm^-2 s^-1. 

ON-OFF observations of extended sources should specify the location of the OFF frame relative to the target and note that the OFF exposures are an additional overhead for these programs.

FOV and the Slit View Camera

An online tool is available to plot 2MASS images centered on input target coordinates with the SVC footprint overlaid. Please be aware of the high angular resolution at Gemini South. Many targets are resolved into binaries! Finder charts will be required in Phase II if the target has several nearby stars or the region is crowded.

Guiding Options/Constraints

Guiding will primarily be performed by the Gemini peripheral wavefront sensors. Proposers need to ensure that their targets have guide stars within the guiding annulus, which can be checked with the Gemini Phase 2 proposal tools. The IGRINS slit-view camera is available for guiding, and errors related to guide stars in the PIT can be ignored. 

Overheads

There have been adjustments in 2022B to better account for time required to observe telluric stars.

The default overheads in the Gemini PIT for telluric star observations is now 15 minutes per hour.

The other overheads are unchanged.

Observers must add additional overheads for science target acquisition and detector readout.

These additional overheads should be added to the exposure times requested. 

The minimum time request (exposure time + science overheads+ basecal)  for any IGRINS observation is 0.25 hours. 

Two cases where standard overheads need to be adjusted:

1) Bright targets: Overhead dominated targets, with observing times less than 12 minutes, will not have their overheads correctly estimated by the PIT. If your targets have short exposure times, then follow the text below to add target acquisition and detector readout overheads. If total exposure times are less than 300 seconds, then use the minimum time request of 0.25 hours. 

2) Continuous Observation (clock timed): If your science is based on clock time on target, like 3 hours of observation to capture an exoplanet transit, then the PIT will overestimate your overheads. Detector readout time doesn't matter in this case, and a flat 0.2 hours of overhead can be applied to this program for target acquisition and A0V observations. If no A0V telluric is required, state this in the technical justification and add just 0.1 hours of overheads. These non-standard overheads can be accommodated by adding the 0.2 or 0.1 hours to your requested program time for each observation by selecting 'Visitor' in the 'resource configuration' of the 'Observation' window in the PIT instead of the 'IGRINS' setup.

There are three main overhead sources for IGRINS observations and each program needs to consider them in their proposal.

1) Detector readout is 28 seconds per frame, with both detectors reading simultaneously, and the typical ABBA quad has a total of 2 minutes of readout overhead. 

2) Target acquisition is 5-10 minutes on average. Switching between adjacent targets can be much shorter, and alternatively, locating faint targets in a crowded field can be longer. We ask proposers to assume 8 minutes per target for acquisition.

3) Telluric correction (A0V) stars are generally bright (K=6-8mag) and are covered by the 20% Night Basecal. IGRINS will be following the NIR baseline calibration scheme for telluric standards which is: "We will observe one telluric standard per science target for every 1.5 hours of clock time on the science target. Continuous observations of the science target may be up to 3 hours in length, bracketed by two telluric standards." A0V stars can be shared between programs and targets in the same part of the sky, reducing the overhead cost for A0V stars. If your science program requires higher SNR telluric stars, these need to be included in the proposal as separate targets with their own exposure times. 

Gemini Phase I Tool (PIT) recommendations and warnings:

1) Be sure to include proper overheads in your time request. In addition to the standard Night Basecal values, adjust your request to include acquisition and detector readout overheads. 

2) The ITC section of the proposal is not required for visitor instruments, but you should include a table of your targets and calculated exposure times so the technical TAC can easily review your estimates.

3) Use Sky Background (ANY) and Water Vapor (ANY).

4) If you make your IGRINS program Band 3 allowable (Consider for Band 3 = Yes), then make sure to adjust your exposure times in the Band 3 Observations tab to account for worse conditions. In most cases, 1.5x the exposure time is appropriate.

The PI can choose to include telluric and flux calibration targets if specific standard observations are required. If these are not included in the request, then the IGRINS Team will select the best available telluric star for the target and will not observe a flux standard.

Gemini Phase II Tool (PIT) recommendations and warnings:

All targets from Phase I need to be assigned an observation in the OT. 

Please watch the first 3 videos here:

http://www.gemini.edu/sciops/observing-gemini/phase-ii-and-s/w-tools/observing-tool/observing-tool-help

Please Review the checklist here:

http://www.gemini.edu/sciops/observing-gemini/phase-ii-and-s/w-tools/observing-tool/ot/phase-ii-checklist

Start by setting up the template before applying it to your program targets! 

The IGRINS Template now includes a placeholder telluric star for each science target. The IGRINS observer will still be choosing the A0V telluric standard for each IGRINS target. This placeholder simplifies the work of the observer and should be left in the Phase II setup for your program observations. 

1) Visitor Instrument section: The default PA should be 90 degrees, input the desired PA if different. Change the wavelength to 2.1um.

2) Define the offset sequence: ABBA nodding should have A (p=0.0,q=+1.25) and B (p=0.0,q= -1.25) defined. 

ON-OFF sequences should be setup with the necessary pointings. +p is north and -p is south. This uncertainty can also be addressed by including a finder chart that shows the target and off frame together.

3) The 'Observe Sequence Component' under the Offset tab should not be changed from '1X'. If you need more exposures, you need to edit the 'Offset Sequence Component' and use 'Repeat'.

Now, Apply the template to your program targets.

If your science requires SNR>100, we recommend that you divide the total exposure time estimated by the ETC into 8 exposures rather than 4. In the window above, you would then duplicate the ABBA sequence a second time. If you make this choice, you should include the appropriate overheads in Phase I.

Timing Windows should be longer than the amount of time required to make the observation. For example, it you have a 2 hour transit to observe, then the timing window needs to be longer than 2 hours. 

Edit each observation to include:

1) A blue note named 'Scheduling Details' (critical for queue planning): 

- review the Gemini South semester schedule and identify the dates that IGRINS is on the telescope

http://www.gemini.edu/sciops/queue-and-schedules

- add to the note the dates that your object can be observed

- If your program has timing window say 'Timing Windows provided in Observing Conditions tab'.

- If you have any special requirements like 'observe target again 1 night, or 3 nights later', this is where to say it.

2) A yellow note named 'Observing Details' (critical for queue observing): 

observing pattern (ABBA), number of repetitions, SNR desired in the K-band, individual exposure time estimates, slit position angle 

For example "One sequence of ABBA with 90s exposures, SNR=100 in the K-band desired. Default PA=90."

You should specify if your SNR needs are in the K band, H band, or both!

3) Visitor Instrument section. Exposure time per exposure. Do NOT include the 28s readout overhead.

4) Check, or find, the guide star. Guiding will be "PWFS2." After the PA is set, select the guide stars to avoid the P2 probe-arm vignetting (both the heavily and lightly shaded region when plotted with the OT image button and the PWFS button is checked). In most cases the auto-selected guide star is good.

5) It is recommended to set the priorities (high, medium, low) for all targets within your program on the 'Observation' tab.

6) Upload finder charts if the field is crowded or there is a known nearby companion.

There is a 10 minute setup by default that includes the telluric star, target acquisition, and detector readout for a standard ABBA sequence. This accounts for the overhead assumptions of the PIT.

The IGRINS pipeline is publicly available, as discussed here, and all observers will be expected to reduce their own observations. If you would rather expand your collaboration to include someone familiar with IGRINS data, then please contact us prior to the proposal deadline so we can put you in contact with an experienced collaborator who knows how to reduce IGRINS data.

Exposure Time Estimation Tables