Our contributions to improving astronomical data acquisition are in three main areas:

  1. differential optical photometry;
  2. infrared photometry; and
  3. spectroscopic methods


The principal reason for carrying out differential photometry is light curve acquisition, and a fairly large number has been obtained at the RAO in the past two decades.
The development of the Rapid Alternate Detection System (RADS) has been arguably the most important instrumental development at the RAO since its inception. This system is a gated, chopping, pulse-counting photoelectric photometry system, using only one detector. The secondary mirror is driven by a Ling driver, fed with the output of a function generator, the parameters of which are selected at the telescope. The device makes it possible to obtain differential photometry of a target star relative to any comparison star within a radius of 45 arc-mins because the chop direction is variable. The system is capable of stopping at four positions along the chopping line. The position of each star and each of two sky channels is selected by means of a high precision 10-turn potentiometer on the face of the function generator. The duty cycle for each channel may be set in millisecs. and the delay time -- to accommodate the ringing of the secondary after motion -- is also preset, as necessary by observing the ouput on an oscilloscope face. See Milone et al. 1982; Robb & Milone 1982; and Milone & Robb 1983 for other details about the system.


In keeping with a need for precise data for light curve analysis, I have been interested for years in developing an infrared photometry system capable of producing high quality light curves through the combination of data from different times and different sites. For the reasons why the IR has not always satisfied this promise, see Milone (1989). The deliberations of a Working Group for Infrared Astronomy has, however, provided the means for achieving this end: see Young, Milone & Stagg (1994) for how this was accomplished. That paper and other data and results may be found here: 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'.

For more about these areas, see photometry


Light curve analysis often requires radial velocity data to discriminate among model solutions and may be indispensable in many cases. For the determinations of semi-major axes and masses, and for systems in eccentric orbits, spectroscopic data are essential.

The improvements we envision in our light curve analysis capabilities depend on the best spectroscopic data obtainable. We have been fortunate to be able to obtain radial velocities using intensified reticon and CCD detectors at DAO for over a decade. Our colleagues and friends at DAO have also helped often and unstintingly. We would like to acknowledge the kindness of DAO's directors Ken Wright, Sidney van den Bergh, and Jim Hesser for making DAO's superb spectroscopic instrumentation available to outside investigators, such as me, and to the staff members who have tried, often heroically, to get badly needed data (Frank Younger, Doug Bond, Les Saddlemyer, and their predecessors, esp., Ed Jakeman). As a result, first class RV data have been acquired over the past quarter century from DAO by many observers as well as by my collaborators and myself, thanks to the generosity of the people at this true center of excellence. Finally, staff members who have freely made their expertise in data reduction available both to us and to other visitors are Graham Hill, Wes Fisher, Peter Stetson, Murray Fletcher, David Crampton, Robert McClure, Stephen Morris, and Dennis Crabtree, among others whom I may have forgotten in this list. Thank you, all!

The use of spectral line profiles in light curve analysis is an even more powerful tool as work by Hill (see Hill & Rucinski 1993) and more recently by Mochnacki asn his students have shown.

My main contribution in RV work in light curve analysis has been to demonstrate the value of intensified images for radial velocity work; the earliest work made use of photographic spectra which were measured on the Arcturus measuring engine at DAO with a variable slit orientation to follow the S-shaped distortion of the spectra. (see, e.g., Naftilan & Milone 1979; 1985). Subsequent work with reticon detectors demonstrated the value of the intensified detection system for short-period variables (see, e.g., Milone et al. 1984; 1985).

In addition to this work, there are further very important uses for spectroscopic data which we hope to develop for light curve analysis in the near future:

  1. Well-calibrated time-resolved spectro-photometric data may be used as light curves in the analysis of eclipsing systems;
  2. the spectra provide limited information about the atmospheric levels in the star;
  3. spectral profile information potentially contain Doppler-imaging information which can be used to correlate brightness variation with velocity fields, to locate sources of light anomalies in the stellar atmospheres, and
  4. multi-object spectroscopy to permit spectral studies of cluster stars, esp., variable stars to support the eclipsing and pulsating variable star programs.
Item 3 is especially important in spotted stars, such as the Sun. Many binary systems have such brightness anomalies (the O'Connell effect, coined by Milone and Adriaan Wesselink -- see Davidge & Milone 1984 for details), and the correct modeling of such effects must be carried out to insure the accuracy of the modeled parameters of the system.


Davidge, T., & Milone, E.F. (1984). Ap J.Supp, 55, 571.

Hill, Fisher, and Holmgren. 1989, A&A , 218, 152.

Hill, G., and Rucinski, S. 1993, in Light Curve Modeling of Elipsing Binary Stars, E.F. Milone, ed., (New York: Springer-Verlag), p. 135.

Kallrath, J. (1993). in Light Curve Modeling of Elipsing Binary Stars, E.F. Milone, ed., (New York: Springer-Verlag), p. 39.

Milone, E.F., ed. (1993). Light Curve Modeling of Elipsing Binary Stars, (New York: Springer-Verlag).

Milone, E.F., Hrivnak, B.J., Hill, G., & Fisher, W.A. (1984). AJ, 90, 109.

Milone, E.F., Hrivnak, B.J., & Fisher, W.A. (1985). AJ, 90, 354.

Milone, E.F., and Robb, R.M. (1983). 'Photometry with the Rapid Alternate Detection System'. PASP, 95, 666.

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

Milone, E.F., Stagg, C.R., Sugars, B.A., McVean, J.R., Schiller, S.J., and Kallrath, J. (1995). AJ, 109, 359.

Naftilan, S.A., & Milone, E.F. (1979). AJ, 84, 1218.

Naftilan, S.A., & Milone, E.F. (1985). AJ, 90, 761.

Robb, R.M., & Milone, E.F. (1982). IAU Info. Bull. Var. Stars No. 2187.

Rucinski, S.M. (1994). PASP, 106, 462.

Schiller, S.J. & Milone, E.F. (1987). AJ, 93, 1471.

Schiller, S.J. & Milone, E.F. (1988). AJ, 95, 1466.

Terrell, D.C., and Wilson, R.E. (1993) in Light Curve Modeling of Elipsing Binary Stars, E.F. Milone, ed., (New York: Springer-Verlag), p. 27.

Young, A.T., Milone, E.F., and Stagg, C.R. (1994). A&A, 105, 259.

Links to other EFM sites:

Variable star programs

Optical & IR photometry

Light Curve Modeling

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RAO Picture Gallery

RAO Detailed Information