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Transmission Spectrum

A 0.9-5.6µm model transmission spectrum of the atmosphere over Cerro Pachon is available (as a 4.9MB text file) here. The spectrum is for an airmass of 1.5 and for 7.6 mm of water (thus somewhat non-optimal conditions at wavelengths where H2O is important). The resolution is 0.00004µm, roughly comparable to the resolution of Phoenix (somewhat lower near 1µm and somewhat higher near 5µm. The wavelength scale is in vacuo.


All Observers

The overhead for slew and set-up is usually 20 minutes. Acquisition of the target consists of images, offsets and instrument configuration changes, all of which are done manually by the observer on the dedicated Phoenix computer.

The following overheads must also be included in the time requested for each scientific observation.

Phoenix ITC

NOAO's exposure time calculator for Phoenix can be used to roughly estimate the Phoenix sensitivity, but it is particularly inaccurate in the 3-5 micron region. For actual measurements see the Sensitivity Table or the Sensitivity Plots.

Sensitivity Table

Slit width

Observing Strategies

Nod size: Like all infrared spectrographs, observations are taken in pairs (ab) or quads (abba) in order to remove sky emission. For small sources (angular dimensions are much less than the slit length of 14 arcsec), the telescope is nodded back and forth along the slit. For large sources the telescope is nodded between the source and blank sky. For pointlike sources nods are thus very small.

Exposure Times

Due to its very high spectral resolution exposure times with Phoenix can be very long. In the JHK windows spectroscopic exposure times of 10,000 seconds on a tenth magnitude star would be needed to saturate the array. Since we are currently unable to abort an exposure in progress, we typically limit the exposure time to 900s.

In the thermal infrared (LL'M) saturation times on the sky and telescope background are 300 seconds near 3µm and 30 seconds near 5µm and limit the individual exposure times.


Slit name Slit width
Slit length

Blocking Filters

The table below lists all filters, including the wavenumbers/wavelengths of half the maximum transmission, that are available for use with Phoenix. Note that the CVF filters described in the NOAO Instrument Manual are no longer available. The second filter wheel is called CVF for historical reasons only.


Near-IR calibrations are discussed in detail on the general near-IR web pages, as they are generally similar for all Gemini near-IR imagers and spectrographs. A baseline calibration set (not charged to the PI) is taken for each observation, generally the minimum calibrations necessary to ensure the utility of the observations in the archive.


In addition to the general acknowledgment to the Gemini Observatory, the following specific acknowledgment should be included in any paper containing Phoenix data:

This paper is based on observations obtained with the Phoenix infrared
spectrograph, developed and operated by the National Optical Astronomy