JC: I have been working on calculating the centroid coordinates for the detected stars in a given frame.

-Process:

  • Algorithm takes list of 'Star coordinates' (max pixel value within array of pixels that constitute a star) and constructs a nxn box of same dimensions as that used for the aperture photometry about the coordinate pixel.
  • I decided that, in order to keep my algorithm well compartmentalised, I would input the x_jth and y_ith pixel into the centroid calculation using numpy.meshgrid: (eg)
Screen_Shot_2019-02-13_at_11.44.50.png
  • For my algorithm, I created a meshgrid the same dimensions as the inset of the total frame being used (algorithm deals in square arrays) starting and ending at the coordinates of the inset. Ie:
Screen_Shot_2019-02-13_at_12.13.23.png
  • This was done in order to return centroid coordinates relative to the original frame.
-Calculation:

Screen_Shot_2019-02-13_at_12.16.09.png

  • Here, boxlstarraybacksub is a list containing background-subtracted pixel values for all pixels inside the box (background is the median background value specific to each star). This is our (n_(i,j) - b)
  • Here, subindexlstx/subindexlsty are lists of the np.meshgrid array as discussed above.
red_200s_view.png

Screen_Shot_2019-02-13_at_11.29.13.png

AS:

This is how the background looks like when the background value for each pixel is calculated; it makes sense that there is a higher ADU value where the hottest stars are.

background.pngred_fits_grey_scale.png

Stars found by my algorithm are 79. Frame taken with an exposure time of 90 seconds.

stars_in_circle.png

Selected some stars to investigate the flux as a function of radius for a circular aperture: (in this image the radius is set to 50 pixels)

stars_of_interest.png

fluxes.pngfluxes_dim.png

fluxes_dim_small_radius.png

Found that an optimal aperture would be with a radius of 12 pixels.

Schermata_2019-02-13_alle_12.34.48.png

The error on the flux was calculated as error_flux = sqrt(flux).

The magnitude: m_i = -2.5 * np.log10(f)

The error in the magnitude: abs(-2.5/np.log(10)) * (error_flux/flux)

Schermata_2019-02-13_alle_12.35.20.pngSchermata_2019-02-13_alle_12.35.12.png

m_vs_flux.png

Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng Schermata_2019-02-13_alle_12.34.48.png r1 manage 71.9 K 13 Feb 2019 - 12:36 AriannaSaba  
PNGpng Schermata_2019-02-13_alle_12.35.12.png r1 manage 99.2 K 13 Feb 2019 - 12:36 AriannaSaba  
PNGpng Schermata_2019-02-13_alle_12.35.20.png r1 manage 72.8 K 13 Feb 2019 - 12:36 AriannaSaba  
PNGpng Screen_Shot_2019-02-13_at_11.29.13.png r1 manage 50.0 K 13 Feb 2019 - 12:09 JacobChambers  
PNGpng Screen_Shot_2019-02-13_at_11.44.50.png r1 manage 23.1 K 13 Feb 2019 - 12:08 JacobChambers  
PNGpng Screen_Shot_2019-02-13_at_12.13.23.png r1 manage 10.5 K 13 Feb 2019 - 12:14 JacobChambers  
PNGpng Screen_Shot_2019-02-13_at_12.16.09.png r1 manage 18.1 K 13 Feb 2019 - 12:16 JacobChambers  
PNGpng background.png r1 manage 39.3 K 13 Feb 2019 - 12:33 AriannaSaba  
PNGpng fluxes.png r1 manage 29.2 K 13 Feb 2019 - 12:33 AriannaSaba  
PNGpng fluxes_dim.png r1 manage 37.8 K 13 Feb 2019 - 12:33 AriannaSaba  
PNGpng fluxes_dim_small_radius.png r1 manage 28.7 K 13 Feb 2019 - 12:33 AriannaSaba  
PNGpng m_vs_flux.png r1 manage 21.1 K 13 Feb 2019 - 12:34 AriannaSaba  
PNGpng red_200s_view.png r1 manage 56.9 K 13 Feb 2019 - 12:09 JacobChambers  
PNGpng red_fits_grey_scale.png r1 manage 99.5 K 13 Feb 2019 - 12:34 AriannaSaba  
PNGpng stars_in_circle.png r1 manage 128.5 K 13 Feb 2019 - 12:34 AriannaSaba  
PNGpng stars_of_interest.png r1 manage 101.5 K 13 Feb 2019 - 12:34 AriannaSaba  
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Topic revision: r2 - 13 Feb 2019 - AriannaSaba

 
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