View Full Version : [help needed] "The IAU Two-Parameter Magnitude System for Asteroids"

2010-Oct-08, 06:20 PM
Could someone here help me find a certain publication?

I'm working on improving the way asteroids and comets are managed in Stellarium (http://stellarium.org/). This will include, among other things, the ability to import asteroid data in various formats. (For the curious, there is a screenshot (http://badlyhonedbytes.wordpress.com/2010/10/02/comets-and-asteroids-gui-for-stellarium-screenshots/) of some work-in-progress on my blog.)

One of the problems is the way magnitude is handled. Stellarium uses radius and albedo, which is OK for the major planets, but most on-line sources of asteroid data, such as the Minor Planets Center's lists (example (http://www.minorplanetcenter.org/iau/Ephemerides/Soft00.html)), use the absolute magnitude/slope parameter (H-G) system.

I need a source that describes how an asteroid's current magnitude can be derived from these parameters. So far, the best match for my needs that I've found is this PDF (http://www.britastro.org/asteroids/dymock4.pdf) (~0.5 MB).

What I'd like to have is an article by E. Bowell, "The IAU Two-Parameter Magnitude System for Asteroids", that have been published in 1989 in "Asteroids II". It either is not available online, or I can't find it. :( (And, before someone suggests a trip to the library, I'd like to point to the "Location" field in the header of this post.)

2010-Oct-08, 08:57 PM
I should add that the problem is not urgent and may not be a problem at all: using the information from the PDF file I've linked to above, I was able to get a magnitude value for Eris that matches the one given by the MPC's website. It's a much closer match than the value calculated by the algorithm currently used in Stellarium. :)

2010-Oct-09, 01:20 PM
Not the paper you ask for, but the formulae for the two-parameter models as used by XEphem (H-G among them) are given in the XEphem documentation. In the version 3.6.4 sources I have at hands they are found in the file xephem-3.6.4/GUI/xephem/help/xephem.html, section Magnitude models. Perhaps this helps with your task.

2010-Oct-09, 07:46 PM
Thanks! I found XEphem's manual online, here's a link to the relevant section:
The formulae and the constants appear to be the same as the ones I've used (the ones from the PDF file). I'm somewhat confused by the remark about phase angle. Isn't it what the manual marks "beta" in H-G explanation?

2010-Oct-10, 03:42 PM
I'm somewhat confused by the remark about phase angle. Isn't it what the manual marks "beta" in H-G explanation?
I remember having been puzzled by this remark some years ago too. Yes, beta is, in my book, the phase angle. In the Dymock paper it is also explicitly named as such (α).