This page was last updated on August 30, 2019. See Program Updates for the most recent announcements.

Planning to Observe with IGRINS at GEMINI

IGRINS will be back at Gemini South for 2020A semester. The NOAO proposal deadline is September 30, 2019.


Availability

Proposals for IGRINS at Gemini should be submitted through the 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

IGRINS will be installed and available for science roughly from February 1 - July 31, 2020. Proposers should expect IGRINS blocks to occur within the two weeks of bright time each month during this period. 

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 request says 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 parallactic angle.
2) The target will be located in the slit-view-camera.
3) The target will be placed on the slit in the A position (1.25 arcseconds above slit center) and observed.
4) The telescope will be moved so the target is at the B position (1.25 arcseconds below slit center) and observed.
5) We will typically obtain a single ABBA quad on every target with an on-slit separation of 2.5". 
When the seeing is worse than ~2.0" then we will switch to ON-OFF observing. Note - this doubles the time needed.
6) We will observe telluric standards with ABBA quads and obtain SNR~250.

Sensitivity and Exposure Time Estimates - Point Sources

For Band1 and Band2 requests, the bright limit is K=4mag. 
The faint limit (SNR>40 in 8 hours) is K=15mag.
However, those are extreme limits. We suggest limiting to K=6-14.

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 (8 hours).

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. 

The table below shows the total exposure time per target for SNR~100 in typical 0.6" seeing in the H/K band.

K mag itime (sec) itime (hours) itime+overhead (hours)
4 3.00 0.00 0.20
5 7.00 0.00 0.20
6 17.00 0.01 0.21
7 42.00 0.01 0.21
8 110.00 0.03 0.23
9 260.00 0.08 0.28
10 660.00 0.20 0.40
11 1700.00 0.50 0.70
12 4200.00 1.17 1.37
13 10400.00 2.78 2.98
14 26000.00 7.22 7.42
15 - - -


The SNR for your target can be estimated with this equation:
SNR = (273*sqrt(itime)*10^(-0.2*(Kmag-2))) /(1.75)
where itime is the total exposure time and Kmag is your 2MASS magnitude. This assumes a seeing of 6".

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
A simple applet for these equations is available here: IGRINS Simple ETC for Gemini

Our experience with IGRINS shows that SNR=30 is the minimum for producing science (and to be able to use our reduction pipeline), SNR=100 is typical for most applications, and SNR=750 is the maximum photon noise limit on the brightest sources. An ABBA quad on a target would be composed of 4 exposures, each one a quarter of the total exposure time.

Available Exposure Times:
Minimum exposure: The IGRINS detectors read out every 1.63s and this is the minimum exposure time. Every other actual IGRINS exposure time is an integer multiple of 1.63s, rounded down. For example, a 4s request would actually be 3.26s. This feature is inherent to H2RG arrays.

Maximum exposure: The maximum exposure is limited in two important ways. 1) For extremely bright or high SNR observations, the maximum exposure time is to obtain 4000 peak counts. This corresponds to roughly SNR~300 for an ABBA quad, and can thus be found with the equations above or ETC. 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, 1500s may be permissible.

IGRINS proposals need to specify their exposure time estimates using the equations above and then provide SNR requirements in the text and 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.

Bright Targets:
Objects with K-band magnitudes between 4 and 10 can be proposed for and will easily have SNR>100. These brighter objects also make good Band 3 targets. For targets brighter than K=4mag, please contact us to discuss the program and technical concerns. 

Sensitivity and Exposure Time Estimates - Extended Sources

The flux sensitivity of IGRINS on Gemini is the same as any other facility. The IGRINS slit will be 5"x0.34" at Gemini, and so large mapping programs will not be efficient when compared to smaller facilities with larger on-sky slit dimensions. Single pointings and small mapping programs at Gemini South has the benefit of better pointing and tracking, as well as southern targets.

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

The IGRINS Slit View Camera is a K-band imager used for target acquisition and guiding. The figure below shows the SVC dimensions for Gemini. The slit will be 5'' long and 0.34'' wide.

The default slit PA at Gemini is 90 degrees, unless specified otherwise in the proposal. Any PA is allowed and extended sources may request multiple PAs within a program.

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! If the target has several nearby stars or the region is crowded, finder charts are required.

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 SVC is  available for guiding, but is not as effective as the facility guiding. Therefore if SVC guiding is used, exposure times need to be increased to account for less time in the very small slit.

Overheads

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 total 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 5-10 minutes per target for acquisition.

3) Telluric correction (A0V) stars are generally bright (K=6-8mag) and require 15 minutes to acquire and observe with SNR~300. 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." 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. 

Overheads should be included in your proposal. The minimum overhead for each target is a minimum of 12 minutes (Note: add an additional 2 minutes of readout time per additional quad). Add an additional 15 minutes for each telluric star observation (roughly once for every 1.5 hours on target).


Special Notes to Proposers 

Gemini Phase I Tool (PIT) recommendations and warnings:
1) Be sure to include overheads in your time request. These are not automatic for IGRINS as a visitor instrument.
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 easy review your estimates.
3) We assume that any water vapor and sky background is acceptable for IGRINS observations. The ETC on this webpage assumes seeing ~0.6" and clear skies. 
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.

The PI can choose to include telluric and flux calibration targets if special standards 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.

Special Notes to Successful PIs
Gemini Phase II Tool (PIT) recommendations and warnings:
All targets from Phase I need to be assigned an observation in the OT. It is best to setup the template, then copy and paste this template for each target (adjusting time, conditions, etc. as necessary). For each target:
1) Add a yellow note with the specific observing details: observing patterns (ABBA), number of repetitions, individual exposure times, etc. For example "One sequence of ABBA with 90s exposures."
2) Visitor Instrument section. a) Include the readout overhead in your time request. b) The default PA should be 90 degrees, input the desired PA and ALSO add a yellow note to the target. c) Change the wavelength to 2.1um.
3) 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).
4) It is recommended to set the priorities (high, medium, low) for all targets.
5) Upload finder charts if applicable.

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.