Article - GCNEWS, Vol. 1, May 1996


A Newsletter for Galactic Center Research
This Volume was edited by Angela Cotera & Heino Falcke

Volume 1, May 1996 - ARTICLE

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NICMOS Views the Galactic Center

by Marcia Rieke

The NICMOS (Near-Infrared Camera and Multi-Object Spectrometer) instrument (see coverpage) will be inserted into the Hubble Space Telescope next February. It has three cameras with plate scales of 0.045''/pixel, 0.75''/pixel, and 0.2''/pixel. The cameras may be operated simultaneously, and are equipped with a selection of filters, polarizers, and 3 slitless grisms for low resolution spectroscopy. Especially in the 1.0-2.0 micron region where HST's background is extremely low, NICMOS will have superb sensitivity with 3 sigma detections at H=24.8 in 1000 seconds using the medium plate scale camera.
With these capabilities, the NICMOS instrument team has slated an exciting program of Galactic Center observations. Four programs will be executed: 1) Measurement of proper motions near SgrA*; 2) Search for variability of sources in the central parsec; 3) Search for the tip of the main sequence associated with star formation in the central parsec; and 4) Search for ionized tails from cool giant stars.
The proper motion program will extend over the 5 year lifetime of NICMOS with the first data being acquired as soon as possible after the on-orbit operation of NICMOS is verified. The last data will be taken at a judiciously chosen time shortly before the solid nitrogen cryogen runs out. The variability search will be conducted on times scales of 10's of seconds to several orbits (roughly 90 minutes each). The main sequence search will take multi-color images looking for a blue stellar population indicative of the tip of a young main sequence. The color-magnitude diagram for these stars will indicate the epoch of last star formation at the Galactic Center. The ionized tail project will use NICMOS' Paschen-alpha filter to look for more instances similar to IRS7's tail caused by ionization of its mass-loss wind.
The first call for proposals to use NICMOS will come as part of HST's Cycle 7. This call should be released soon with proposals likely to be due in August.

More informations will be available at the STScI Home-Page in due time.

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