<center>E. F. Milone: PHOTOMETRIC WORK</center>

This page describes work in two main areas: optical photometry, just below, and infrared photometry.

Differential Optical Photometry

My primary contribution in this area is to have created, with the help of colleagues at the University of Calgary, a digital analogue of the Walraven Photometer. The Rapid Alternate Detection System (RADS) is a gated, pulse- counting, background compensating photoelectric photometry system, capable of rapid, sequential four channel operation. When on the 0.4-m telescope at the RAO, the system employed a Ling Driver on the secondary mirror, restored by a pair of flex pivots. The location of each of the windows, the size of which is determined by the aperture selected at the telescope, along the chopping line is set by a ten-turn potentiometer. The duty cycle of each channel and the delay time for each channel is selected at the telescope to optimize conditions and eliminate light loss through the ringing of the mirror after motion. RADS has the advantage over other 'two-star' photometers, in providing a measure of the sky brightness near each target star as well as the two star channels. It also consists of but a single light path, a single set of electronics, and a single detector, thus avoiding concern about differential drifts and sensistivity. The selection of filters and the order of observations is programmable on the control computer, located in the warm room. The system takes about 15-min to set up on a star, and observations are automatic thereafter except for dome rotation and centering checks. See Milone et al. Robb (1983) and Milone et al. 1982 for further details and examples of the value of this system.

The system has been used in the past to observe short-period variables, esp., contact system and short-period detached or semi-detached systems. It has supplied data for about two dozen student projects, for a score of programs. Work on the systems DS And, H235 in NGC 752, TY Boo, AC Boo, CC Boo, 44i Boo, AO Cam, IR Cas, RW Com, CG Cyg, CH Cyg, V444 Cyg, DY Her, V728 Her, EH Lib, UZ Lyr, DY Peg, HD 27130 resulted in one or more publications per system.

Targets have included the enigmatic 5.07-day eclipsing binary RT Lacertae, and a host of short-period variables, including RW Com, AI CVn, and V369 Sct (the latter two are delta Scuti stars).

Since being moved to the 1.8-m to be able to observe fainter stars, the RADS has not been used as much, and, currently, because of the complexity of the system compared to stare instruments, is not on the telescope.

Hopefully, it will be restored one day, while it is still functional.

It is still arguably the best available photometer for photometry of single stellar targets.

Improving IR Photometric Passbands

This work has been carried out by Andy Young, Russell (formerly Chris) Stagg and myself as part of the agenda of the Working Group on Infrared Astronomy of IAU Comm. 25.

The passbands of the Johnson JHKL broadband photometric system used at a number of major observatories have been compared to the atmospheric window transmissions calculated by MODTRAN and a family of solar-composition model stellar fluxes from Kurucz (1991 private communication) have been used as input to model the atmospheric extinction under different water vapour content, altitude, and airmass conditions. A figure of merit related to the slope of the extinction curve at zero airmass describes the sensitivity of the response function to atmospheric extinction. We have compared passbands used at several observatories, and recommend an improved set of passbands (Young, Milone, & Stagg, 1994).

The improved set of infrared passbands promises to open up a new vista for infrared astronomy by permitting observations at lower altitudes, under less favorable circumstances, than previously possible with traditional and even with some of the newer infrared passbands. The improvements may well lead to fully automated infrared observatories (Milone, Stagg, & Young, 1995).

The advantages in the acquisition of differential infrared lightcurves is obvious. Although, one may well hope that the effects of varying bandpass characteristics will be the same for comparison and variable star observations, especially of the observations are made at the same or nearly the same instants, a better transformable set of data may allow for combinations of observations from different sites, a tricky proposition at present if observations are sought above the 1% precision level.

AN earlier optimization and calculated S/N for a set of models can be found at the following link, created for the IAU IR Working Group: IRWG

Note that the S/N plots are in magnitude measure increasing upwards; therefore the best passbands are those which are the most shallow in the histogram plots. The new passbands are prefixed with 'i' (for 'improved') or 'y' (for 'Young'); the Customs Scientific passbands are prefixed with 'ci' or 'cy'. This work was subsequently upgraded. See Milone & Young (2005, 2006, 2008) for more details.

See techniques for further discussion of some of these topics.

References

Milone, E.F., & Young, A.T. (2005). "An Improved Infrared Passband System for Ground-based Photometry: Realization". PASP, 117, 485-502.

Milone, E.F., & Young, A.T. (2006). "Standardization and the Enhancement of Infrared Precision", in The Future of Photometric, Spectrophotometric, and Polarimetric Standardization, ed. C. Sterken. ASP Conference Series, 364, pp. 387-407.

Milone, E.F., & Young, A.T. (2008). "Infrared Passbands for Precise Photometry of Variable Stars by Amateur and Professional Astronomers". JAAVSO, 36, in press. Milone, E.F., Stagg, C.R., & Young, A.T. (1995). "Towards Robotic IR Observatories: Improved IR Passbands", in Robotic Observatories, ed. M. F. Bode (Chichester: Wiley-Praxis), pp. 117-124.

Milone, E.F., Robb, R.M. Babott, F.M., & Hansen, C.H. (1982). "Rapid Alternate Detection System of the Rothney Astrophysical Observatory". Applied Optics, 21, 2992-2995.

Milone, E.F., & Robb, R.M. (1983). "Photometry with the Rapid Alternate Detection System". PASP, 95, 666-673.

Young, A.T., Milone, E.F., & Stagg, C.R. (1994). "On Improving IR Photometric Passbands", Astronomy & Astrophysics Suppl., 105, 259-279.


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