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Field of View

'Alopeke and Zorro have two sets of optics which allow selecting between "Speckle" mode and "Wide-Field" mode. Both modes slightly underfill the detector resulting in circular fields-of-view.

The diameter of the vignetted 'Alopeke wide-field is ~60", however, the diameter of the unvignetted 'Alopeke wide-field is ~35". See the vignetting maps in the following table with overlaid contours at 90, 80, 70, 60, and 50%.

Speckle Wide-Field
Field of View 6.7" 60"
Camera Blue Red Blue Red
'Alopeke Pixel Size 0.00992" 0.01095" ~0.0725"
Zorro Pixel Size 0.00991" 0.01093" ~0.0725"
'Alopeke Vignetting
Zorro Vignetting
Speckle mode Wide-Field mode


We present several figures to display the sensitivity of `Alopeke and Zorro at Gemini North and South, reproduced with the authors' permission.  Below, we show the 5-sigma contrast curves for observations taken between 2019 and 2020 using `Alopeke (Left panel) and Zorro (Right Panel).  Stellar companions with a separation and delta magnitude that fall below a given curve are detectable with speckle imaging.  Blue lines show the curves for data taken using either 466 or 562 nm filters and the red lines display the curves for data taken using either the 716 or 832 nm filters.  The black lines show the fits to the 562 and 832 nm data.

For more information on these plots, please see Scott et al. 2021.

To further highlight the capabilities of Gemini+Speckle, we show two figures displaying delta magnitudes achieved as a function of target magnitude at set angular separations for both `Alopeke and Zorro from Howell & Furlan (2022). Changing colors in the figures represent changes in the seeing while the size of the dots show the number of sets taken for that observation.

`Alopeke (HF2022, Fig 8):

Zorro (HF2022, Fig 9):

Additionally, the following figure from Matson, Howell and Ciardi (2019), reproduced with permission of the authors, shows the 5-sigma detection limit curves for 'Alopeke. Note how the contrast for 'Alopeke is slightly better than DSSI, mostly given the improvement in the detectors. Zorro curves are expected to be very similar.

'Alopeke/Zorro sensitivity curve

Guiding Options

'Alopeke and Zorro use the Gemini peripheral wavefront sensor PWFS2 for guiding. PWFS2 operates at optical wavelengths and can guide on stars as close as 4' and as far as 7' from the science target. Guide star selection is done automatically by the Observing Tool, although it is recommended that users verify the guide stars, rejecting extended object and spurious catalog entries.