Proposal #30

Proposal for Extending APASS Sloan Magnitudes

Tony Mallama

This proposal is to extend the Sloan magnitudes of the AAVSO APASS catalog to brighter stars. Since Sloan magnitudes are becoming more widely used, bright secondary standard stars on that system will be needed as comparisons for nearby novae, supernovae (rare) and other bright variable stars. Just as importantly, they will be required in order to establish the Sloan magnitudes for the planets of our solar system and these, in turn, have applications in exo-planet research.

An entire new APASS-like survey involving all 300,000 stars brighter than magnitude 10 would obviously require a great deal of telescope time as well as a large effort to reduce the data. Therefore, I suggest sampling a smaller number of selected stars. If those stars were located near the ecliptic, then the planetary photometry (with exo-planet applications) described below in the addendum would be feasible.

The two main technical challenges of this project would be recording very bright stars without saturation and linearly extrapolating the magnitudes from +10 to 0. There are solutions to those difficulties though. Bright stars could be imaged with the APASS instruments by putting them out-of-focus. The linearity of the extrapolation could be verified by observing Vega for which Fukugita (reference 1) provides Sloan magnitudes.

Addendum:

This section is not part of the proposal but provides more scientific justification and describes follow-up research. The determination of Sloan magnitudes and phase functions for solar system planets is important in its own right and for exo-planet research as well. The magnitudes of exo-planets will dictate whether these bodies are detectable in direct imaging programs, and their phase functions will allow them to be characterized. For example, planets with cloud producing atmospheres can be differentiated from airless planets based upon the average slope of the phase function (reference 2). Thus, broad-band photometry will enable characterization of exo-planets that are too faint for spectroscopic analysis.

If Sloan magnitudes for bright stars become available as a result of this proposal, I would be interested in establishing the magnitudes of solar system planets on the Sloan system. I have recently established accurate Johnson magnitudes and phase curves of Mercury, Venus, Mars, Jupiter and Saturn (references 3-7). Studies of Uranus and Neptune, which are currently underway, will complete this work. The Sloan planetary magnitudes could be determined with the APASS telescopes or with other facilities.

References:

1) Fukugita et al., Ast. J., 411/4, April 1996, p. 1748-1756
2) http://dx.doi.org/10.1016/j.icarus.2009.07.010
3) http://dx.doi.org/10.1006/icar.2001.6723
4) http://dx.doi.org/10.1016/j.icarus.2005.12.014
5) http://dx.doi.org/10.1016/j.icarus.2007.07.011
6) http://dx.doi.org/10.1016/j.icarus.2012.04.031
7) http://dx.doi.org/10.1016/j.icarus.2011.11.035