Previous Article Next Article Table of Contents
IR News (1Mar94) (from CTIO, NOAO Newsletter No. 37, 1 March 1994) This issue of the Newsletter has considerable news to report - both good and bad. We will be making two new instruments available during second semester - the HgCdTe Imager and the upgraded IRS. These will compensate for the departure of OSIRIS at the end of September. In addition, we have reluctantly decided to discontinue support of the single-channel IR Photometer. This latter decision is prompted by the recognition that we need to focus our limited resources if we are to provide competitive IR instruments on the CTIO telescopes. We welcome constructive feedback on this and some of the other issues raised in this article. OSIRIS Departs Our agreement with OSU ends in September 1994, at which time OSIRIS must be returned to the North to be used there. Its capabilities will be replaced by those of the HgCdTe Imager and the IR Spectrometer, as described below. In the meantime, spectroscopic users will be pleased to learn that some modifications were made to the instrument to reduce the scattered light problems (especially in cross-dispersed mode); this has led to obvious improvements in performance. The broadband J filter has been replaced by a standard CTIO/CIT J filter, which gives better performance and color transformations, and the narrowband filters now include filters for 1.644, 2.122, and 2.166 microns, replacing several less useful filters originally present. These modifications were carried out in early January by Darren DePoy and Tom O'Brien (Ohio State U.). OSIRIS will be shipped from Chile at the end of September and will therefore be available only during August and September. Based on past demand, we would expect to schedule it on the 4-m telescope in August and on the 1.5-m in September. Users should, however, try to avoid proposals where only one of these two months is acceptable, since we will not schedule it on more than one telescope during a given month. It will definitely not be available after 1 October. HgCdTe Imager Commissioning of this instrument is expected to take place during the June-July period. To allow for a shake-down period, though, we do not plan to schedule it until after 1 October. Since its capabilities and performance should be very similar to those of OSIRIS, we consider this to be a reasonable schedule. The instrument will made available on the 1.5-m and 4-m telescopes only. For reference, the expected K magnitude performance under normal (0.8 arcsec) seeing on the 4-m is mag. 19.0 to 10% in 10 minutes. Since both seeing and background vary, actual performance may be somewhat better or worse. Performance on the 1.5-m will be roughly 1 mag. less sensitive with small pixels, and proportionally worse at scales which under-sample the seeing. The available pixel scales are summarized below. These are approximate and will be measured more precisely when the instrument is commissioned on the telescope. Arcsec/Pixel Telescope f/8 f/13.5 f/30 4-m 0.4 NA 0.1 1.5-m 1.1 0.6 0.3 The array, as in OSIRIS, is a 256 x 256 NICMOS III HgCdTe detector. The control of the array will be via the KPNO WILDFIRE electronics, using an upgraded version of the old CTIO IR Imager array electronics. Motor control will be done using the new CTIO motor controller, which will be interfaced with the array software. KPNO is producing most of the array control electronics. Note that, unlike OSIRIS, you must specify the f/ratio at which you intend to work in your original proposal. Some switching between f/ratios is possible during the night, but it is time-consuming and should be thought of as appropriate for a change in program, and not for something like imaging all your program objects at two different scales. The switches that are possible are between f/13.5 and f/7.5 on the 1.5-m, and between f/30 and f/8 on the 4-m. The latter switch is possible only if the f/30 secondary has been installed at prime focus; you must therefore request it in your original proposal - and justify it as well. We will have room to install approximately 30 filters simultaneously. These will include the appropriate broadband filters and most narrowband filters of interest. If you have concerns about the latter please contact us before submitting your proposal to see if we have the filter and plan to install it as part of the initial complement. The initial set will definitely include 1% filters for Brackett-gamma and Paschen-beta, He I 1.083, H2 2.122, Fe II 1.257 and 1.644, and H2O, CO, and continuum filters. Although this instrument will in principle work on the smaller telescopes, it is uncertain whether it will eventually be offered for use there. We will probably undertake some engineering tests on the 0.9-m and Schmidt telescopes during second semester, but the real issue is whether CTIO will run these telescopes with a permanently installed detector (large CCD in both cases), or whether we will have the resources to provide additional detector control hardware and to support a certain number of instrument changes. In any case it will definitely not be offered second semester. IRS Upgrade The IRS Upgrade project consists of the installation of a 256 x 256 SBRC InSb detector in the old, familiar IRS. (Think of it as Release 3.0 of the instrument.) The mechanical and optical aspects of the instrument will be largely unchanged, except that we have succeeded in slightly lengthening the spectrograph slit; as a result the pixel scales are 2.5 times smaller than before, and the spectral resolutions 2.5 times higher, assuming a 2-pixel slit. An additional grating has been purchased, a 75 l/mm grating blazed for 2.0 microns, which should be especially useful with the new, larger array, as it provides nearly complete coverage of a spectral window. The array installation will take place in Tucson in April-May, and commissioning on the 4-m and 1.5-m telescopes will take place in late July. This work is being carried out jointly by CTIO and KPNO staff. We would not plan to make the instrument generally available until September at the earliest, and in September would schedule OSIRIS in preference to the IRS if the project could be done equally well with either instrument. WILDFIRE will also control the IRS array, as well as providing motor control. As a result, you will actually be able to run the instrument typing on a single keyboard! We expect performance to be similar to that achieved by the analogous upgrade to CRSP at KPNO. The detector dark current should be less than a few electrons per second and the read noise should be less than 40 electrons. We would expect performance on the 4-m with good seeing (0.8 arcsec) with R = 700 to give S/N = 5 in about 1 hour at K = 16. A summary of available gratings and their resolutions is provided below. Note that at any one time only two gratings can be installed at once and that grating changes require opening up the instrument. In consequence, you must specify the grating desired in the proposal, and once the grating choice is made (we may discuss it with you during the scheduling process), it cannot be readily altered. Resolution Coverage Grating Name at K at K 12 l/mm, blaze 6.5 um 400 0.5 um (underfills array) 75 l/mm, blaze 4.0 um 1600 0.18 um 75 l/mm, blaze 2.0 um 800 0.36 um 210 l/mm, blaze 4.5 um 4800 0.07 um 632 l/mm, blaze 2.5 um 8400 0.03 um The pixel scales for the lower resolution gratings are roughly 0.32 arcsec/pixel on the 4-m and 0.8 arcsec/pixel on the 1.5-m; the maximum usable slit length now appears to be about 50 pixels. Note that the two gratings blazed around 2 microns cannot be used for the L or M bands. We have yet to find out how well the array works at the longer wavelengths, but users should assume that L band work is possible only at resolutions higher than 1000; M band work may or may not be possible at R = 4800. We will probably not have definitive answers until July; watch the September Newsletter for more information. In order to simplify scheduling, we would prefer to establish a default grating configuration; we suggest that for the upcoming semester users consider using the combination of the two gratings blazed around 2 microns. Note that both of these should provide acceptable performance in the J and H bands, and will work down to and below the CCD cut-off. (In fact, they should do better than a CCD at least down to 1.0 micron.) As a future development, we are hoping to test a cross-dispersed grating in the instrument sometime second semester; it would offer a resolution like the OSIRIS cross-dispersed mode (R ~ 500), but would provide somewhat better short-wavelength coverage. As the grating and prism cross-disperser will be mounted in a single grating cell, this set-up would use one of the two grating positions in the instrument. IR Single-Channel Photometry Discontinued We regret to announce that support for single-channel IR photometry is being discontinued, effective July 1994. The present system will by then be the only use of the aging Tolnet computers, which are becoming increasingly difficult to maintain and repair - spares are no longer available, for example. The effort needed to convert to a more modern computer system and properly integrate it with the telescope control systems is difficult to justify compared with competing demands for resources, given the relatively modest demand for the IR Photometer. We will attempt to support the one scheduled run (June 1994) with the instrument, but this is contingent on survival of Tolnet. If any proposals are submitted for IR Photometry, we will try to contact the proposers and suggest alternatives in time for them to amend the proposal. Search for 10-Micron Imager The end of the IR Photometer means an end to mid-infrared capabilities at CTIO. Since this is the only southern site generally accessible to the US astronomical community, we regard this as extremely unfortunate - but we do not have the resources to resolve the problem on our own. We are therefore very much interested in entering into collaboration with an outside group, which would supply a 10-micron imager for use on the 4-m telescope. Additional capabilities are welcome but not essential. The terms of the agreement would be similar to those for the Rutgers Fabry-Perot or OSIRIS. Specifically, CTIO would not be in a position to provide technical resources beyond limited assistance in interfacing to the telescope. We would be able to provide reimbursement of some costs such as shipping or travel in support of NOAO users of the instrument. Some engineering and discretionary time could be made available, where the amount depends strongly on the overall demand for the instrument. The suppliers could, of course, apply for more time through the regular allocation process (past experience suggests they would do rather well). The instrument would be made available to the NOAO community, with technical support to be provided by its supplier. We would block schedule or limit use as needed to keep the support burden reasonable. This article constitutes an invitation to anyone who feels they would be interested in providing such an instrument; they should contact one of the undersigned to indicate interest. The instrument in question must be a working instrument, since the intention is to offer it to our users. While we will attempt to contact people directly, our failure to do so should not be interpreted as lack of interest on our part - please get hold of us if we don't get hold of you. Jay Elias, Richard Elston, Brooke Gregory, Malcolm Smith
Previous Article Next Article Table of Contents