Archive | July 2010

WolframAlpha Widgets

Here is a little widget I made to have a play with the wolfram alpha widget builder, it allows you to quickly compare the mass of two celestial objects:

(note: requires javascript)

Interesting Astronomical Papers

Most days I index papers, generally on radio astronomy, that interest me – currently these are posted to the cyberska site and they should go to my [twitter page]…. but I thought it would be nice to index it on here too, so take a look at the astro papers page.

More convolutions

So a friend of mine asked if I could produce the same animation I did the other day of the [convolution of two top hats] but this time of two Gaussians. Pretty straight forward really:
Annimation of Gaussian Convolution
If you want to take a look at the code, see [gauss_convolve.py].

Stampede Parade

I am currently experiencing my first [Calgary Stampede] and I have to say what I’ve seen so far I’ve thoroughly enjoyed. I still need to properly Cowboy up though, I must do this properly at some point this week. Yesterday I went to the Stampede parade which was a 2 hour long show with the downtown full of people and effectively shut down. It was good fun, lots of marching bands, horses and strange looking floats… I think the highlight was either the [Snowbirds] flying over or a tank doing a burnout! [Here] is a video of some of the things that happened as they went passed us and a couple of pics:

Stampede Parade 2010 - Snowbirds fly over
Stampede Parade 2010 - street cleaning
Stampede Parade 2010 - Tank
Stampede Parade 2010 - Flames
After the show we braved a very packed, it was the third train that turned up that we managed to get on, C-train down to the Stampede grounds to explore what was going on. I managed to get a Stampede pack (dunno quite why I wanted one, but I’m quite pleased with the backpack), saw the [world championship blacksmith competition, some sheep shearing, some giants cows, a crazy dog show (“[Superdogs]” with its own theme music) and miniature horse [chuckwagon] racing (probably the most hilarious type of horse racing I’ve ever seen). I’m sure we saw lots more too and I’m hoping to go down some point in the next week to experience more of the festivities. Lots of fun and [here] is a video of some of my highlights…

The chuckwagon races in the Saddledome:
Mini chuckwagon races @ Stampede
How to heard ducks:
hearding ducks @Stampede Park
and a Texas Longhorn:
Longhorn @ Stampede Park

matplotlib convolution animation

I’ve recently been doing quite a few convolutions, quite important in the paper I’m working on (hopefully to finish soon, more on that soon I hope), and I thought I’d demonstrate a nice example of how todo a convolution in python with the aid of scipy, numpy and matplotlib (actually this is as much a posting for myself so I don’t have to go hunting through my python script directory). It’s actually fairly straight forward, but before that I should just recap what a convolution is.
Essentially a convolution is just an integral that expresses the amount of overlap of one function as it is shifted over by another. This is of great importance in radio astronomy. In synthesis imaging (the key to all large interferometer imaging), the measured dirty map is a convolution of the “true” CLEAN map with the dirty beam (this is determined from the Fourier Transform of the uv-data that is taken by the telescope). If you want to know more about this kind of thing, specifically for radio astronomy, take a look at the [NRAO workshop pages] – tons of info. Mathematically the convolution of two functions is (over infinite range):
convolution_inf
Here is an example of the convolution (the green curve) of two rectangular (top hat) functions, there is a slight issue with my plotting that makes them not quite look rectangular (lack of points basically):
Convolution of two tophats
As you can see the final product is a triangle. This is really quite simple to code and I’ve aimed to make this a nice an accessible program by doing things in a simplistic manner – take a look at [convolve.py]. The animation is produced using imagemagick and the convert task at the end of the script, if you don’t have this then just comment it out.

FAS Societies Map

As part of my work as the [FAS] (Federation of Astronomical Societies) webmaster I’ve been updating a few of the functions on the webpages. We now have a [Google map] with accurate society locations (and this now links from the [society diary]) – I think its starting to come together nicely (see below for the map), though I have to say I find that the postcode database not being fully public quite annoying but you can get around it, just got to convert from postcode to Lat/Long.

View FAS Societies in a larger map

Non-Thermal Radio Emission from Late B and Early A-type Magnetically Peculiar Stars

The conference proceedings from High Energy Phenomena in Massive Stars held last year where my colleague, Dr Ian Stevens, presented our results for observations from CU Virgins have now been published. biggrin.gif
“Non-Thermal Radio Emission from Late B and Early A-type Magnetically Peculiar Stars” – Ian R. Stevens, Samuel J George (High Energy Phenomena in Massive Stars)
“The Magnetic Chemically Peculiar star CU Virginis (A0Vp) has shown unusual variations in its rotational period and has also recently been discovered to be radio variable, showing two short period bursts of emission per (0.52 days) rotation period. These bursts have been attributed to electron cyclotron maser emission from the magnetic poles of the star. We present new low-frequency radio observations of CU Virginis taken with the Giant Metrewave Radio Telescope at 610 MHz and 1.2 GHz. We discuss our results and their implications for the the origin of the radio emission from CU Virginis and our general understanding of the magnetosphere and the particle acceleration processes in the stellar magnetosphere. We discuss possible relationships with other high energy phenomena in massive stars. ”