# The Brown Dwarf Converter App for iOS

by on August 20, 2012

This is a guest post by Jonathan Gagné at Université de Montréal. Jonathan is a graduate student under direction of René Doyon and David Lafrenière. His research topics include the search for young brown dwarfs in the solar neighborhood and the development of methods for direct exoplanet imaging.

When working with low-mass stars and brown dwarfs, because they cool with time, it isn’t easy to get a mass estimate based just on a spectral type. Brown dwarfs of a given spectral type have a range of masses and ages, which are predicted by stellar evolution models. For instance, masses for a brown dwarf with a spectral type L2 are predicted to have masses from 13 MJup at 10 Myr to 69 MJup at 1 Gyr. Listening to talks and reading papers on a bus or in coffee shops without direct access to a computer inspired me to build an iOS application that would help make it easier to figure out brown dwarf parameters.

I have written a free iPhone and iPad application called the Brown Dwarf Converter, for converting the age and any parameter including mass, spectral type or temperature, into everything you might want to know about a brown dwarf. Or at least every quantity that the Lyon group included in their model atmospheres. The basic idea behind this simple application is that you give it two “measurements” (e.g., age and mass) and then it linearly interpolates the BT-SETTL model isochrone grids. As I’m far from being an expert in iOS app development, and the model grids are not regularly meshed, I took the easy path which is to interpolate a regular grid over them in IDL, and then I gave those to the iOS app.

The second version (v1.1) is currently available on the Appstore. In this version, you must enter the spectral type as a number (K5 is 5, M6 is 16, L0 is 20 and T9 is 39), but the name of the spectral type will be output on the side when you press “convert”. When you encounter NaN quantities, this means you went outside the bounds covered by the model grids. If you find any bug, please leave a comment below or contact me directly.

I wrote this app to fill a personal need. Other scientists have done the same, such as the creators of iObserve and Exoplanet. You should also consider writing your own app to fill a niche need! In a future post, I’ll outline the steps I took in order to develop and publish the app.

1 Cédric August 20, 2012 at 11:17 am

Hi. Yet another nice example of someone writing the software he needs because it doesn’t exist yet! Thanks also for mentionning my app iObserve. As for your own app, if you need a bit of help on iOS, do not hesitate to contact me. I’m sure we can design something a bit more “easy-to-use”. Cheers.

2 John August 20, 2012 at 11:19 am

I’ve found this app very handy to have since I installed it last month. Thanks a lot, Jonathon.

3 Aleks August 20, 2012 at 12:53 pm

While this is certainly convenient, the one issue I have is that it mixes empirical and model parameters and nicely hides the inherent unknowns in the evolutionary models and atmospheric models as well as the problems with the observed parameters (e.g., spectral types). Ideally of course a user is aware of that. Similar to drugs, the app should come with a clear red warning about risks and side-effects.

4 Jonathan Gagné August 20, 2012 at 1:01 pm

Hi Aleks,

as can be read in the info part of the program : “Please note the values given by this application are approximative and in no way a reference value for scientific publications.”

The only intention behind this app is to get an “idea” of the mass of a 100 Myr M8 brown dwarf for example, either when you’re listening to a talk, or reading a paper without your computer close-by, and you want to get the big picture.

5 Aleks August 20, 2012 at 1:43 pm

Ah, good, thanks!