Entry 11 ======== .. image:: entry11.png :width: 800 `Video `__ Authors ------- - Robert Nikutta **Clustering of astronomical objects in WISE 3D color space** Based on: Nikutta, Hunt-Walker, Ivezic, Nenkova, Elitzur, 'The meaning of WISE colours - I. The Galaxy and its satellites', MNRAS 442, 3361-3379 (2014) http://dx.doi.org/10.1093/mnras/stu1087 http://adsabs.harvard.edu/abs/2014MNRAS.442.3361N NASA's Wide-field Infrared Survey Explorer (WISE) mapped the entire Infrared (IR) sky with unprecedented sensitivity. It produced a staggering catalog with more than half a billion objects, with precise measurements of their magnitudes in four different wavelength filters: http://wise2.ipac.caltech.edu/docs/release/allsky/ We can learn a lot about these IR sources by studying not only their magnitudes (how bright they are), but also their colors (how much their brightness changes between filters). Taking for this plot from the catalog only bright objects which have robust detections (not much noise), we end up with ~15,000 sources for which we have three color measurements, W1-W2, W2-W3, W3-W4, where the 'Wx' are the magnitudes measured by WISE. We then plot the three colors of all 15k objects in a 3D scatter plot - every dot is one star. Because of different physical properties, these stars tend to occupy different regions in this color-color-color (CCC) diagram. Some are so-called Asymptotic Giant Branch stars (AGB), evolving stars that are 1000 times as bright as our Sun and shrouded in layers of dust that blow away from the star like a wind, propelled by the star's light. Depending on the dust chemistry (carbon or oxygen-rich) these shells produce different WISE colors, and so the two sub-types of AGBs separate in the CCC diagram. We plot them red (O-rich) and blue (C-rich) here. Curiously, most C-rich AGBs are found in the Large Magellanic Cloud, a beautiful small satellite galaxy of our Milky Way, which can be seen in the Southern Hemisphere with the naked eye. It is chemically quite different from our Galaxy. Other types of stars, so called Young Stellar Objects (YSO) have different WISE colors still! In green we show YSOs which we know have thin dusty shells with constant density profiles, and are of moderate/cool temperatures (~600 Kelvin). In orange we show also YSOs, but their optical depths are larger, and their temperatures are higher (~1200 Kelvin). Other, unclassified, objects are shown as small black dots. We demonstrated in our paper http://adsabs.harvard.edu/abs/2014MNRAS.442.3361N how same-type objects can be identified using only WISE measurements. With this plot we demonstrate that a 3D view of the color space is necessary, because in classical 2D CC diagrams the clusters can overlap, and it is then impossible to separate them cleanly. I used matplotlib to generate this plot. Two views of the scene are produced, offset by 5 degrees from each other in azimuthal direction. If you cross your eyes (try to see the tip of your nose) you can easily see the clusters in 3D, where everything appears extra-sharp. If you then move your head very slightly up/down or left/right, the illusion of 3D is perfect. A function is included in the code to generate the frames of a movie, with the scene rotating in in front of the camera. You can watch the entire movie in 3D if you "cross your eyes" during the first frames of the movie. Products -------- - `Video `__ - :download:`PDF ` Source ------ .. literalinclude:: plot.py - :download:`IPython notebook ` - :download:`data.npz `