Abstract Details

Title: Infrared Photometry for Automated Telescopes: Passband Selection

Authors: Eugene F. Milone (rao, Ucalgary) & Andrew T. Young (sdsu)

Institute/Affiliation: University Of Calgary

Abstract Type: talk

Abstract Information:

The high precision that photometry in the near and intermediate infrared region can provide has not been achieved, partly because of technical challenges (including cryogenics, which most IR detectors require), and partly because the filters in common use are not optimized to avoid water-vapor absorptions, which are the principal impediment to precise ground-based IR photometry.

We review the IRWG filters that achieve this goal, and the trials that were undertaken to demonstrate their superiority. We focus especially on the near IR set and, for high elevation sites, the passbands in the N window.

We also discuss the price to be paid for the improved precision, in the form of lower throughput, and why it should be paid: to achieve not only higher precision (i.e., improved signal-to-noise ratio), but also lower extinction, thus producing higher accuracy in extra-atmospheric magnitudes. The edges of the IRWG passbands are not defined by the edges of the atmospheric windows: therefore, they admit no flux from these (constantly varying) edges. The throughput cost and the lack of a large body of data already obtained in these passbands are principal reasons why the IRWG filters are not in wide use at observatories around the world that currently do IR work. Yet a measure of the signal-to-noise ratio varies inversely with both extinction and with a measure of the Forbes effect. So, the small loss of raw throughput is recouped in signal-to-noise gain. We illustrate these points with passbands of both near and intermediate IR passbands. There is also the matter of cost for small production runs of these filters; reduced costs can be realized through bulk orders with uniform filter specifications.

As a consequence, the near-IR IRWG passbands offer the prospect of being able to do photometry in those passbands at both high and low elevation sites that are capable of supporting precise photometry, thereby freeing infrared photometry from the need to access exclusively high and dry elevation sites, although photometry done at those sites can also benefit from improved accuracy and transformability.

We suggest that if the IRWG passbands are made available, they will be used!

New automated systems making use of these passbands have the advantage of establishing the system more widely, creating a larger body of data to which future observations will be fully transformable, and will be cheaper to purchase.

This work has been supported in part by grants to EFM by the Canadian Natural Sciences and Engineering Research Council.