-- AnishaVadher - 16 Jan 2017

Prior to determining flux:

  • Ran mode and Sigma filters on simulated blue and visual Double Cluster, with flat background (mean=900, sigma=10)
  • Ran star finder, used threshold = pixel Mode + 1*maximum sigma.
  • For each cluster of pixels found by algorithm, found approximate centre coordinates of star using:
 \begin{equation} \bar{x}=\frac{ \sum_{i,j}^{N,M} x_{ij} (ADU)_{ij} }{\sum_{i,j}^{N,M} (ADU)_{ij}} \end{equation}
('x' = x or y coordinates)

Aperture Photometry:

  • Subract mode filter from image to remove background.
  • Set radius around central coordinates of star.
  • Sum ADU of each pixel within set radius, gain 'raw flux' value (not true total flux).
Setting radius of aperture
  • Flux of the brightest star in double cluster as a function of radius:
  • Radius will be set to 12 from the graph as the flux levels out above 12.
Matching Stars in Different Frames
  • For simulations, frames are aligned
  • For both simulated frames, minimum seperation between stars (in pixels) ~3.
  • Match stars with minimum seperation.
  • For real data, calculate transformation based on position of brightest star.
Calculate Magnitude
  • Used following equation to calculate magnitudes of simulated data (simplified from proper magnitude calculation):
 \begin{equation} m = -2.5 \log_{10}\left ( ADU_{total} \right )+c \end{equation}
  • c is a scaling factor - calculated based on difference of original and calculated magnitude of brightest star.
  • HR diagram (with c=0):
  • HR_DoubleCluster_BV_1.png
  • Total stars matched and plotted: 86
  • Comparing with input magnitude - set scale factors in reconstructed data to match minimum magnitude point in true data:
  • HRcomparison.png
  • Also attempted for real data - not properly scaled, and needed to set threshold to mode+5*sigma:
  • HR_DoubleCluster_real_BV1.png
  • Total stars matched and plotted: 96
Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng FluxVsRadiusDBCL.png r1 manage 40.7 K 18 Jan 2017 - 10:35 AnishaVadher Flux of the brightest star in double cluster as a function of radius
PNGpng HR_DoubleCluster_BV_1.png r1 manage 29.1 K 18 Jan 2017 - 16:58 AaronAndrews Simulated data HR diagram, B and V
PNGpng HR_DoubleCluster_real_BV.png r1 manage 101.0 K 18 Jan 2017 - 16:59 AaronAndrews Real data HR diagram, B and V
PNGpng HR_DoubleCluster_real_BV1.png r1 manage 117.9 K 19 Jan 2017 - 14:15 AaronAndrews HR comparison for real data taken during observation 2
PNGpng HRcomparison.png r1 manage 103.3 K 18 Jan 2017 - 17:01 AaronAndrews Comaprison HR
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Topic revision: r11 - 04 Feb 2022 - JoolsElliott

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