by B. H. K. Yung

*Workshop on: "Python and astro-statistics",
Institute of Physics NCU, ToruĊ
27-30 June, 2016*

Plot the given fake H$_{2}$O maser VLBI map data (data_VLBI-map.dat). There are four columns in the file. Columns 1 and 2 give the offset positions (R.A. offset and Dec. offset) of the maser features with respect to an arbitrary point in milliarseconds (mas). Columns 3 and 4 give the local-standard-of-rest velocity, $V_{\rm LSR}$, in km s$^{-1}$, and the peak flux in Jy, for each maser feature. The sizes of the markers plotted are to be proportional to the fluxes.

Hints: In addition to the common commands, you may wish to look up for the following functions or keywords.

- scatter(), cmap
- colorbar(), set_label()
- set_xlabel(), set_ylabel()
- tick_params()
- minorticks_on()

Plot the given real baseline-subtracted spectra of OH maser (in 1612 and 1665 MHz) in three different ways. The two columns of the file give the $V_{\rm LSR}$ and flux in Jy for each spectral channel.

(a) Plot the 1612 MHz spectrum only (data_1612-spec.dat). The baseline root-mean-square (rms) noise of this spectrum is 0.01 Jy. Indicate the blue- and red- shifted peaks with the corresponding colours, and the rest of the spectral curve in black. For simplicity, consider the following conditions for this particular scenario.

- Only the line features with fluxes larger than or equal to 3 times the rms (i.e. 3$\sigma$) are real emission features which require shading in blue or red.
- The systemic velocity of the object is found to be 4 km s$^{-1}$, so the line features with $V_{\rm LSR}$ < 4 km s$^{-1}$ are considered as blue-shifted, while those with $V_{\rm LSR}$ > 4 km s$^{-1}$ are red-shifted.

Hints: You may have to use the **if** and **else** statements and the text() function.

Plot the fake data and model curve (data_power2.dat) together with the error bars. Add a residual plot in another panel below. The model curve is assumed to be $y=x^{2}$.

Hints: You may have to use the following functions.

- GridSpec()
- add_subplot()
- errorbar()
- set_xticklabels()
- set_yticks()
- set_title()