Several nervous days passed in early October with Hydra-CTIO stranded in a warehouse at the Miami airport awaiting the passage of hurricane Georges. Fortunately Hydra arrived safe and sound in Chile with only one day lost to the storm, delivered still on time according to the schedule set when the project began more than two years ago. The project remains basically still within budget even though many things have happened in the meantime and a number of significant improvements have been implemented since it was originally conceived. Well-deserved kudos are due to the members of the two Hydra teams in both hemispheres, which unfortunately consist of too many individuals to list by name.
Hydra was installed on the Blanco Telescope for the first time on 7 October,
beginning the process of commissioning. The mounting went smoothly and the
instrument functioned well. It was first pointed at an astrometic test field
on the night of 27/28 October and spectra were taken with the new bench
spectrograph. The very first time Hydra was turned onto the sky, its fibers
found their targets to within an rms accuracy of better than an arcsec! Now
the task remains to refine the astrometry until the positioning accuracy is
as good as or better than the 25m (0.16") precision of Hydra WIYN.
The instrument functions crisply and robustly, significantly faster and more precisely than WIYN Hydra. The user interface is similar to that in use at WIYN, but has been significantly improved with an eye to making the instrument easier too use.
The bench spectrograph and new comparison lamp system have now been shown to work as expected. The new system illuminates the full Hydra field with bright enough comparison lamps to permit good reference spectra to be taken in 1-2 minutes when the telescope is at any position on the sky.
CTIO Hydra is designed for use with a new wide field Atmospheric Dispersion Compensating (ADC) corrector. Like Hydra, the "RCADC" was built and installed as a joint Tucson-Chile effort. The new corrector insures excellent images over the full 40' field and makes the telescope "telecentric," which is optimal for use with fibers. ADC was incorporated for greater efficiency and spectrophotometric precision. Actual implementation of the ADC function will not occur until second semester 1999 when we expect Hydra's astrometry to be sufficiently well understood to introduce this additional complication.
The RCADC was installed in August and produced subarcsecond images the first time an image was taken through it. The high precision of the initial positioning of Hydra is especially encouraging in the light of the fact that it was the first use of the new corrector as well as the first use of Hydra. The mechanical model of Hydra was measured in Tucson while the optical model of the telescope was generated by computer using the mechanical and optical parameters of the system as measured. The fact that they worked well together without modification implies that the opto-mechanical system is well understood.
But don't get too anxious! Hydra-CTIO is not finished yet. It is still a new instrument. Much work remains to fine tune and test it until it functions "tiki-tiki," as we say in Chile. It will be scheduled only for shared risk observing with selected programs during the coming semester.
At the moment, only the large (2") fibers have been installed and are being calibrated. We expect to install the small (1.3") fibers sometime next semester. If all goes well, they should be operational by the end of the semester. No programs that require the small fibers will be scheduled during first semester 1999.
The bench spectrograph will temporarily use the Loral 1K × 3K CCD with the Blue Air Schmidt camera. Long the workhorse camera on the CTIO R-C Spectrograph, the Loral/BAS combination is not entirely satisfactory for Hydra. It has significant vignetting at the edges of the field and the chip can only cover about 120 of the 138 fibers. Additionally, the camera optics are not quite good enough to cleanly separate the fiber images so there is significant overlap of the wings. For this reason, programs which are critically dependent on sky subtraction and/or photometric precision will also not be scheduled for the coming semester.
We are waiting for a new Orbit 2K × 4K CCD to become available. When it arrives, by the end of the semester or soon thereafter, we expect to implement it in a new 400mm camera. The combination should well address the problems of the Air Schmidt and will be worth waiting for.
S. Barden (sbarden@noao.edu)
T. Ingerson (tingerson@noao.edu)