Phoenix First Light!

The high resolution 1-5 m infrared spectrograph Phoenix saw first light 19 June on the 2.1-m telescope. The overall performance of the optical, mechanical, and electronic/detector systems was excellent, with the instrument performing as modeled. A science grade Aladdin InSb array with a 512 x 1024 format was the detector. The 1024 pixels in the dispersion direction translates into 1500 km s^-1 of spectral coverage. In the spatial direction 180 pixels are used for a slit length of 1' on the 2.1-m. The illuminated section of the array is cosmetically nearly perfect. Spectra and images, as well as further details on the instrument are available at the Phoenix Web site http://www.noao.edu/kpno/phoenix/phoenix.html or by contacting hinkle@noao.edu.

Due to time limitations, testing concentrated on the K band. Extrapolation from a set of slitless observations of a 2nd magnitude star indicates that S/N = 100 should be possible at K = +8 to +9 for a 1 hour exposure depending on slit width and observing conditions. The R = 100,000 2 pixel slit is only 0.74" wide and slit losses are expected. For limiting performance observations users should consider a 3 pixel (1.1", R = 66,000) or 4 pixel (1.5", R = 50,000) slit. Phoenix is expected to have relatively constant sensitivity through the 1-2.5 m region. However, the sensitivity of the spectrograph decreases very rapidly with wavelength red of 2.5 m as a result of the increasing thermal background. Only a few tests in the thermal infrared were undertaken and no sensitivity numbers are currently available. Modeling indicates a limit of 5th magnitude at 4.6 m for high signal-to-noise. However, a quick integration on a star at M = +1 revealed the telluric spectrum but not the star. At this time we urge an extremely conservative approach to planning observations in the thermal infrared until more test observations are attempted. A second test run is scheduled for late August and, weather permitting, more information on sensitivity will be posted on the Web site in early September.

Availability

Phoenix will be available on the 2.1-m telescope starting in January 1997. Time in January is available on a shared risk basis by submitting a proposal with January specified. Shared risk proposals will be accepted up to the normal spring semester deadline of 30 September. Phoenix will be available as a facility instrument on the 2.1-m telescope starting in February.

The 2.1-m telescope does place some restrictions on guiding, which must be done using the 1' field of view of the instrument; off-axis guide probes are not available with Phoenix on the 2.1-m. Phoenix has an internal dichroic allowing the simultaneous detection of visible and infrared light. In addition, there is a "slit viewing" mode in which an internal mirror inserts into the beam behind the slit wheel and images the field on the array. One may then acquire an object through the 1' diameter open aperture, move to the desired slit, and center up by imaging the object through the slit. Any object in the visible channel field may then be used for telescope guiding. Tests show that flexure between the visual and infrared images is not measurable at the one pixel level.

Ken Hinkle, Dick Joyce