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Proposal Preparation

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GHOST Phase I Checklist

Please read the guidelines for proposing here. The Phase I Tool (PIT) tutorial video is available here. Below, we provide details to help proposers complete the observations section of PIT.

1. Observing Strategy Overview

  • Resolution Mode
    • ​Select the appropriate resolution mode (Standard or High) for your science goals.
    • Note: Precision radial velocity mode (with simultaneous calibration) is not offered.
  • Sky Subtraction Strategy
    • ​In Standard Resolution mode, is the default sky IFU in IFU1 is sufficient for your needs?
    • If not, and additional sky subtraction using IFU2 is required, the program must be limited to single-target observations only.

2. Target & Field Requirements

  • Target Parameters
    • ​Include target coordinates, V-band magnitudes, and proper motions (if available).
    • V magnitude is essential, as it is used to calculate the slit viewer exposure time. Even approximate values are required.
  • Brightness Constraints
    • ​Avoid targets brighter than V ≈ 4 mag.
    • For targets brighter than V < 10 mag, ensure they do not saturate under conditions better than those requested.
  • Dual-Target Configuration
    • If using dual-IFU mode, include only the fainter target in your proposal.
    • The second target must be within the GHOST field of view.
    • Targets must be separated by > 102 arcsec and < 7.34 arcmin, corrected for proper motion.
    • Do not use spatial binning greater than 8x to avoid fiber cross-talk.
  • If the acquisition may be ambiguous due to crowding, consdier enabling mapping to ensure reliable target identification.
  • 2025B Updates
    • Non-sidereal targets are now supported.
    • Blind-offset acquisition is available for faint targets (e.g., V > 19). Be sure to clearly describe the acquisition strategy in your proposal.

3. Acquisition & Guiding

  • Guide Star Requirements
    • ​GHOST requires guiding with P2WFS.
    • Suitable guide stars must be: within 9.85 arcmin (single-IFU mode), within 6.75 arcmin (dual-IFU mode) and reachable without vignetting.
    • Guide star availability is shown in the PIT.
  • For bright targets, microlenses surrounding the science IFUs provide on-target fine guiding.
  • Blind-offset acquisitions are supported for faint targets. Clearly describe the strategy in your proposal.

4. Exposure Setup & ITC Configuration

  • Exposure Time Guidelines
    • ​Use the GHOST ITC to calculate exposure times meeting your S/N goals.
    • Individual exposures are recommended to be ≤ 20 minutes.
    • For total expousures longer than 1 hour, observing time will not be returned if conditions degrade after the first hour of execution.
  • Instrument Configuration
    • GHOST is mounted on the up-looking port at Gemini South.
    • In Standard Resolution, sky microlenses refer to 3 fibers in IFU1, 7 fibers in IFU2 used for sky subtraction, or 10 fibers total when both are used.
    • Spectral binning is not recommended in High Resolution mode due to undersampling.
    • Avoid spatial binning > 8x in dual-target mode due to potential fiber cross-talk.
    • Recommended read modes: SLOW (blue detector), MEDIUM (red detector). These modes balance overheads and readout performance.

5. Observing Conditions

  • Image Quality (IQ)
    • ​Select an IQ bin suitable for your science wavelength and airmass.
    • Seeing degrades approximately as: airmass^0.6 and wavelength^-0.2.
    • Throughput can drop significantly with poor seeing due to the finite width of the input aperture.
  • Sky Brightness (SB)
    • ​The night sky is brighter at wavelength shortward of the R-band during bright moon.
    • If your science requires senstivity in the blue, consider requesting strong SB constraints (SB80 or better) to ensure enough S/N in the blue.
  • Cloud Cover (CC)
    • ​Select CC bin based on target brightness, wavelength, and S/N.
    • Most spectroscopic observations of medium-bright targets can be conducted under thin cirrus (CC70) or worse. 
    • For accurate flux calibration, photometric conditions (CC50) are required.

6. Calibration Plan

  • Confirm if baseline calibrations are sufficient for your scinece.
  • If not, explictily request additional time for custom calibrations.
  • If absolute flux calibration is required, select photometric conditions (CC50) and include a spectrophotometric standard with the same configuration as your science setup.
  • If removal of telluric lines is needed, include a telluric standard in your time request.
  • If radial velocity comparison is required, include an RV standard with matching resolution and setup.

7. Final Checklist Summary

  • Target coordinates, V magnitude, and proper motions are included.
  • Selected resolution mode, sky subtraction, and guiding strategy match science goals.
  • Exposure times, binning, and read modes are valid in GHOST ITC.
  • IQ, SB, and CC selections align with wavelength, airmass, and calibration needs.
  • Blind-offset or other non-standard acquisition modes are justified and described.
  • All required calibration standards are included in the time request.