Instrument Description
NOTE: The definitive source for specifications, performance, and limits of the ERIS instrument is the user manual!
AO Performance and Limits
The instrument can be operated in four different AO modes:
- Natural Guide Star (NGS) mode: using either the target star or a slightly off-axis (<30" recommended) guide star.
- Laser Guide Star (LGS) mode: using one of the four lasers of the 4LGSF, and a tip-tilt star for truth sensing.
- Seeing Enhancer (SE) mode: LGS without a tip-tilt star. Only higher-order modes are corrected, uses VLT stabilization.
- No AO (noAO) mode: seeing-limited mode, VLT stabilization only.
Note that the minimum allowed distance between the NGS/TT star and the moon is 25 degrees.
| Gaia BP | Gaia RP | Off-axis? | K-band Strehl |
Airmass Limit |
TCAT (DIMM) Limit |
FLI Limit |
|
|---|---|---|---|---|---|---|---|
| NGS | <=19 | NGS: 1 - 11 | 0" - 60" (<30" recommended) |
< 0.85 | <1.9 | <=85% (<=1.4") | N/A |
| LGS | <=19 | TT star: 7 - 17 | 0" - 60" | < 0.6 | <1.9 | <=85% (<=1.4") | <=0.5 for TT mag > 16 |
| LGS-SE* | N/A | N/A | N/A | TBC | <1.9 | <=30% (<=0.8") | N/A |
| noAO | N/A | N/A | N/A | N/A | <2.9 | Any | N/A |
* Not offered in P111
IFS Performance and Limits
Observations with the IFS can be taken in any one of twelve grating configurations and three plate scale configurations. Note that the spaxels are rectangular, and the name of the plate scale configuration corresponds to the long axis, twice the length of the short.
Grating configurations
| Band | λc (um) | λ range (um) | Resolution |
|---|---|---|---|
| J_low | 1.25 | 1.09--1.42 | ~5000 |
| H_low | 1.66 | 1.45--1.87 | ~5200 |
| K_low | 2.21 | 1.93--2.48 | ~5600 |
| J_short | 1.18 | 1.10--1.27 | ~10000 |
| J_middle | 1.26 | 1.18--1.35 | ~10000 |
| J_long | 1.34 | 1.26--1.43 | ~10000 |
| H_short | 1.56 | 1.46--1.67 | ~10400 |
| H_middle | 1.67 | 1.56--1.77 | ~10400 |
| H_long | 1.76 | 1.66--1.87 | ~10400 |
| K_short | 2.07 | 1.93--2.22 | ~11200 |
| K_middle | 2.20 | 2.06--2.34 | ~11200 |
| K_long | 2.33 | 2.19--2.47 | ~11200 |
Plate scale options
| Tag | Spaxel size | Field of view |
|---|---|---|
| 25mas | 12.5 x 25 mas | 0.8" x 0.8" |
| 100mas | 50 x 100 mas | 3.2" x 3.2" |
| 250mas | 125 x 250 mas | 8.0" x 8.0" |
Brightness limits
To avoid the effects of persistence there is a limit to the brightest star that can be observed with the IFS. These limits are described in the User Manual, and the Phase 2 pages.
NIX Performance and Limits
NIX offers a variety of observing modes that can be used in conjunction with the AO modes described above:
- Short-wavelength imaging: Imaging with the 13 or 27mas camera (FoV of approx 27"x27" and 55"x55") with any filter in the J, H, and K bands.
- Long-wavelength imaging: Imaging with the 13mas camera (FoV of approx 27"x27") with any filter in the L and M bands.
- Apodizing phase plate (APP) coronagraphy: Pupil-plane coronagraphy with K, L and M-band narrowband filters.
- Focal plane coronagraphy (FPC): Focal-plane coronagraphy with a vortex coronagraph and the L and M-band broadband filters. Not offered in P111.
- Sparse aperture mask (SAM) imaging: Sparse aperture masking with one of three aperture masks and any narrowband filter. Not offered in P111.
- Long-slit spectroscopy (LSS): Medium-resolution (R~900) L-band slit spectroscopy. Not offered in P111.
Valid instrument configurations and filters for NIX
This table summarises the filters available in NIX.
| Filter | λc (um) | FWHM (um) | Average transmission (%) |
Peak transmission (%) |
|---|---|---|---|---|
| J | 1.28 | 0.20 | 82 | |
| H | 1.66 | 0.31 | 93 | |
| Ks | 2.18 | 0.39 | 87 | |
| Short-Lp | 3.32 | 0.43 | 80 | |
| L-Broad | 3.57 | 1.04 | 83 | |
| Lp | 3.79 | 0.60 | 78 | |
| Mp | 4.78 | 0.58 | 80 | |
| Pa-b | 1.282 | 0.021 | 75 | 83 |
| Fe-II | 1.644 | 0.020 | 86 | 94 |
| H2-cont | 2.068 | 0.064 | 80 | 90 |
| H2-1-0S | 2.120 | 0.020 | 67 | 77 |
| Br-g | 2.172 | 0.020 | 65 | 75 |
| K-peak | 2.198 | 0.099 | 83 | 89 |
| IB-2.42 | 2.420 | 0.049 | 71 | 82 |
| IB-2.48 | 2.479 | 0.051 | 65 | 78 |
| Br-a-cont | 3.965 | 0.108 | 82 | 91 |
| Br-a | 4.051 | 0.023 | 69 | 80 |
A plot of the filter transmission curves is available here, and the data used to create this plot are available in this archive. The total throughput of the instrument as a function of wavelength can be obtained as an output of the ERIS ETC ("Select Plots" > check the various througput efficiencies).
This table summarises the valid combination of the aperture, camera, filter and pupil wheel, as well as the valid tracking modes. A description of the various pupils can be found in the User Manual.
| Aperture | Camera | Filter | Pupil | Tracking | |
|---|---|---|---|---|---|
| Short imaging | Small | 13mas-JHK | Any < 2.5um | JHK-pupil, Blocking*, ND | Field |
| Large | 27mas-JHK | Any < 2.5um | JHK-pupil, Blocking*, ND | Field | |
| Long imaging | Small | 13mas-LM | Any > 2.5um | LM-pupil, ND | Field |
| Small | 13mas-LM | Any > 2.5um | Spider* | Pupil* | |
| APP | Small | 13mas-JHK | H2-cont, H2-1-0S, Br-g, K-peak IB-2.42, IB-2.48 |
APP | Pupil |
| Small | 13mas-LM | Br-a, Br-a-cont | APP | Pupil | |
| FPC* | AGPM-L | 13mas-LM | Short-Lp, Lp | Lyot, Lyot-ND | Pupil |
| AGPM-M | 13mas-LM | Mp | Lyot, Lyot-ND | Pupil | |
| SAM* | Small | 13mas-JHK | < 2.5um narrow | SAM-7/9/23 | Pupil |
| Small | 13mas-LM | Br-a, Br-a-cont | SAM-7/9/23 | Pupil | |
| LSS* | Slit mask | 13mas-LM | L-Broad | Grism | Field |
* Not offered in P111
This table further details the valid pupil wheel and filter wheel combinations.
| Pupil/Filter | J | H | Ks | Short-Lp | Lp | L-Broad | Mp | Pa-b | Fe-II | H2-cont | H2-1-0S | Br-g | K-peak | IB-2.42 | IB-2.48 | Br-a-cont | Br-a |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| JHK-pupil | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ||||
| Blocking* | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ||||
| LM-pupil | ✔ | ✔ | ✔ | ✔ | ✔ | ||||||||||||
| Spider* | ✔ | ✔ | ✔ | ✔ | ✔ | ||||||||||||
| ND | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |
| APP | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |||||||||
| SAM-7/9/23* | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | ✔ | |||||||
| Lyot* | ✔ | ✔ | ✔ | ||||||||||||||
| Lyot-ND* | ✔ | ✔ | ✔ | ||||||||||||||
| Grism* | ✔ |
* Not offered in P111
Brightness limits
To avoid the effects of persistence there is a limit to the brightest star that can be observed with NIX. These limits are described in the User Manual, and the Phase 2 pages. Very bright stars can be observed with the ND filter to attentuate the flux by between 4.5 and 6.0 magnitudes, depending on the wavelength of the observation.
Bad pixels
The NIX detector suffers from several regions of highly clustered bad pixels. The figure below shows the number of neigbouring bad pixels that each pixel has. The regions in red should be avoided when planning dither patterns around the detector. A representative bad pixel map is also available to download here that can be used to help plan observations.
Short/Long-wavelength Imaging
Details regarding limiting magnitude and off-axis performance to be added after commissioning is completed.
Apodizing Phase Plate (APP) Coronagraphy
APP can be used for high-contrast imaging science to detect faint companions or structures at small angular separations. The APP mask is used in conjunction with a quater-wave plate and Wollaston prism to generate a deep null in a D-shaped region on opposite sides of two complementary PSFs generated by the Wollaston. Astrometric and photometric calibration can be achieved with the three calibration spots between the two PSFs.
This mode is currently only offered with the narrow band filters within the K and L-bands.
Focal Plane Coronagraph (FPC)
This mode is not offered in P111.
Sparse Aperture Mask (SAM)
This mode is not offered in P111.
Long Slit Spectroscopy (LSS)
This mode is not offered in P111.