CFHT Information Bulletin Number 37, Semester 97II
CFH12k Filters
Dennis Crabtree, CFHT (crabtree@cfht.hawaii.edu)
The large filters required for CFH12k require a lead time of 4-6 months in their acquisition. This means that we cannot always wait until observing time is granted before acquiring necessary filters. CFHT feels that we should have filters which we expect to be requested in house to ensure they will be available for scheduled runs. We have already ordered broadband B, V, R, and I filters. We did an e-mail survey asking the communities which other filters they would like to see available for use with CFH12k.
Given the size of the filters (165 mm x 250 mm) required for CFH12k there are some limitations. We have yet to find a manufacturer who will construct a filter this size with a bandpass < 50 Å. Also, filters of this size are fairly expensive so we will have to be selective about which ones are ordered.
We received more than 10 responses to the e-mail request for suggested filters, in addition to B, V, R, and I which have been ordered, for CFH12K. Filters that were suggested included:
- H
on/off. The H bandpass will allow for studies of nearby galaxies out to a redshift of ~1800 km/sec. The SII filter (see below) also serves as an H filter for the Coma cluster.
- SII (6716+6731) - to be used for Herbig-Haro objects, jets, photo-ionized nebuluae, etc.
- `VR' with 2000Å bandpass - to allow for limiting object detection.
- Sloan z' with a bandpass from 8500Å to the CCD cutoff - to do wide-field `near-IR' imaging with the reddest possible bandpass usable with CCDs.
- Washington filter set (C, M, T_1, T_2) which is useful for studying metallicities of old stellar populations. The problem with this filter set is the C filter which is between U and B and whose bandpass extends down to 3400Å. The CCDs in CFH12k will have very little Q.E. below 3850Å.
- CN and TiO filters - same as the ones which have been used with Focam to identify carbon stars in nearby galaxies. Could be used to survey for dwarf C stars, map M33 and M31 including halo for C stars. Also to identify low-mass stars/brown dwarfs.
- Harris B, V, R filters for supernova light-curve followup. These filters are used at CTIO and KPNO.
- HeII 4686 on/off to look for young, hot massive stars in nearby galaxies.
- [OII] to identify planetary nebulae in nearby galaxies.
- [OIII] to identify star formation regions.
- Stroemgren u,v,b,y filters to study stellar populations. Again, we expect the CFH12k devices to have very poor efficiency in the u bandpass..
- Filters to measure the star formation rate in galaxies at redshifts of ~0.81, 1.28 and 1.39 using redshifted [OII].
CFHT has decided to get quotes for the following filters and then make a final decision depending upon how many of these filters can be accomodated within the budget.
CFHT Information Bulletin Number 37, Semester 97II
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