Difference: Meeting1302 (1 vs. 2)

Revision 213 Feb 2019 - AriannaSaba

Line: 1 to 1
 
META TOPICPARENT name="StewartBoogertPhotometry2018"
JC: I have been working on calculating the centroid coordinates for the detected stars in a given frame.
Line: 19 to 19
  Screen_Shot_2019-02-13_at_11.29.13.png
Added:
>
>
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

 
META FILEATTACHMENT attachment="Screen_Shot_2019-02-13_at_11.44.50.png" attr="" comment="" date="1550059732" name="Screen_Shot_2019-02-13_at_11.44.50.png" path="Screen Shot 2019-02-13 at 11.44.50.png" size="23627" user="zbvd104" version="1"
META FILEATTACHMENT attachment="Screen_Shot_2019-02-13_at_11.29.13.png" attr="" comment="" date="1550059740" name="Screen_Shot_2019-02-13_at_11.29.13.png" path="Screen Shot 2019-02-13 at 11.29.13.png" size="51178" user="zbvd104" version="1"
META FILEATTACHMENT attachment="red_200s_view.png" attr="" comment="" date="1550059746" name="red_200s_view.png" path="red_200s_view.png" size="58224" user="zbvd104" version="1"
META FILEATTACHMENT attachment="Screen_Shot_2019-02-13_at_12.13.23.png" attr="" comment="" date="1550060042" name="Screen_Shot_2019-02-13_at_12.13.23.png" path="Screen Shot 2019-02-13 at 12.13.23.png" size="10754" user="zbvd104" version="1"
META FILEATTACHMENT attachment="Screen_Shot_2019-02-13_at_12.16.09.png" attr="" comment="" date="1550060205" name="Screen_Shot_2019-02-13_at_12.16.09.png" path="Screen Shot 2019-02-13 at 12.16.09.png" size="18496" user="zbvd104" version="1"
Added:
>
>
META FILEATTACHMENT attachment="background.png" attr="" comment="" date="1550061216" name="background.png" path="background.png" size="40248" user="zbvd241" version="1"
META FILEATTACHMENT attachment="fluxes_dim_small_radius.png" attr="" comment="" date="1550061223" name="fluxes_dim_small_radius.png" path="fluxes_dim_small_radius.png" size="29339" user="zbvd241" version="1"
META FILEATTACHMENT attachment="fluxes_dim.png" attr="" comment="" date="1550061231" name="fluxes_dim.png" path="fluxes_dim.png" size="38719" user="zbvd241" version="1"
META FILEATTACHMENT attachment="fluxes.png" attr="" comment="" date="1550061237" name="fluxes.png" path="fluxes.png" size="29940" user="zbvd241" version="1"
META FILEATTACHMENT attachment="m_vs_flux.png" attr="" comment="" date="1550061243" name="m_vs_flux.png" path="m_vs_flux.png" size="21617" user="zbvd241" version="1"
META FILEATTACHMENT attachment="red_fits_grey_scale.png" attr="" comment="" date="1550061251" name="red_fits_grey_scale.png" path="red_fits_grey_scale.png" size="101863" user="zbvd241" version="1"
META FILEATTACHMENT attachment="stars_in_circle.png" attr="" comment="" date="1550061258" name="stars_in_circle.png" path="stars_in_circle.png" size="131607" user="zbvd241" version="1"
META FILEATTACHMENT attachment="stars_of_interest.png" attr="" comment="" date="1550061264" name="stars_of_interest.png" path="stars_of_interest.png" size="103972" user="zbvd241" version="1"
META FILEATTACHMENT attachment="Schermata_2019-02-13_alle_12.34.48.png" attr="" comment="" date="1550061393" name="Schermata_2019-02-13_alle_12.34.48.png" path="Schermata 2019-02-13 alle 12.34.48.png" size="73658" user="zbvd241" version="1"
META FILEATTACHMENT attachment="Schermata_2019-02-13_alle_12.35.12.png" attr="" comment="" date="1550061399" name="Schermata_2019-02-13_alle_12.35.12.png" path="Schermata 2019-02-13 alle 12.35.12.png" size="101616" user="zbvd241" version="1"
META FILEATTACHMENT attachment="Schermata_2019-02-13_alle_12.35.20.png" attr="" comment="" date="1550061405" name="Schermata_2019-02-13_alle_12.35.20.png" path="Schermata 2019-02-13 alle 12.35.20.png" size="74586" user="zbvd241" version="1"

Revision 113 Feb 2019 - JacobChambers

Line: 1 to 1
Added:
>
>
META TOPICPARENT name="StewartBoogertPhotometry2018"
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

META FILEATTACHMENT attachment="Screen_Shot_2019-02-13_at_11.44.50.png" attr="" comment="" date="1550059732" name="Screen_Shot_2019-02-13_at_11.44.50.png" path="Screen Shot 2019-02-13 at 11.44.50.png" size="23627" user="zbvd104" version="1"
META FILEATTACHMENT attachment="Screen_Shot_2019-02-13_at_11.29.13.png" attr="" comment="" date="1550059740" name="Screen_Shot_2019-02-13_at_11.29.13.png" path="Screen Shot 2019-02-13 at 11.29.13.png" size="51178" user="zbvd104" version="1"
META FILEATTACHMENT attachment="red_200s_view.png" attr="" comment="" date="1550059746" name="red_200s_view.png" path="red_200s_view.png" size="58224" user="zbvd104" version="1"
META FILEATTACHMENT attachment="Screen_Shot_2019-02-13_at_12.13.23.png" attr="" comment="" date="1550060042" name="Screen_Shot_2019-02-13_at_12.13.23.png" path="Screen Shot 2019-02-13 at 12.13.23.png" size="10754" user="zbvd104" version="1"
META FILEATTACHMENT attachment="Screen_Shot_2019-02-13_at_12.16.09.png" attr="" comment="" date="1550060205" name="Screen_Shot_2019-02-13_at_12.16.09.png" path="Screen Shot 2019-02-13 at 12.16.09.png" size="18496" user="zbvd104" version="1"
 
This site is powered by the TWiki collaboration platform Powered by PerlCopyright © 2008-2021 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding RHUL Physics Department TWiki? Send feedback