Matching Stars
  • Have to find the minimum distance between all stars that are input and the candidate stars
  • Set star-finding threshold to 1*Sigma to include as many stars as possible
  • Distances between true (i) and candidate stars (j):
    DistancesBetweenStars.png
  • Hist_dij_InputOutput_2000.png
  • Hist_dij_InputOutput_1Sigma_20.png

  • Chose a 3 pixel separation as the limit for matching stars between the input simulated data and candidate data
Star Finding Threhold


  • Plotted fraction of stars matched in the simulated Double Cluster with varying threshold values
  • Appears 5*Sigma is an appropriate choice
fractionStarsMatched.png

Scaling Correction

  • Goal: correct the scaling error for the real HR diagram (from 20170119 meeting)
  • Get Aladin coordinates of 2 bright stars for the Visual and Blue images used to make HR
  • Double Cluster blue frame in Aladin indicating 2 coordinates:
    DoubleCluster_40s_blue_5_ASTRO_Aladin_Annotated.png

  • Converting RA/DEC to pixel coordinates:
    Transform.png
  • Transformation Equation:
  • CodeCogsEqn_1.png
  • Where (x,y) is the transformed coordinate, m is the transformation matrix, (x,y) is the reference pixel obtained from the header of the new fits file from Astrometry.net, and (delta_x,delta_y) is the reference pixel converted from RA/DEC.
  • Visual Blue
    Cental Coord RA: 02h 22m 05.712s
    Dec: +57° 11' 09.516"
    Degrees (35.524, 57.186)    		 RA: 02h 22m 06.101s
    Dec: +57° 11' 07.288"
    Degrees (35.525, 57.185)
    Reference Coord
    (deg) (delta)    		 (35.5401978009, 57.173493981) (35.5475695422, 57.1718325267)
    Reference Pixel (v) (710.564499521, 582.921770788) (691.959394509, 588.543775601)
    Transformation
    Matrix    		 [[-0.000168531158698, -5.13170131402E-06]
    [4.85829972477E-06, -0.000168690594262]]    		 [[-0.000168632203737, -5.10181679782E-06]
    [4.90637384969E-06, -0.000168703688821]]
    Inverted Matrix [[-5938.8289203, -180.66387345]
    [171.03864644, 5933.21591892]]    		 [[-5924.85229703, 179.17516318]
    [-172.31123147, -5922.34174989]

  • Converted Reference coordinate into pixel coordinates the same way Aaron did for simulation
  • Reference Coord into Pixel coordinates (delta) = (818.31717994, 435.103886)
  • (v)' = (710.42435476, 582.99914435)
  • vstar1: [[ 171.87468786][ 80.055386 ]]
    vstar1_prime: [[ 171.73454309][ 80.13275956]]
    vstar2: [[ 957.24304638][ 93.475386 ]]
    vstar2_prime: [[ 957.10290161][ 93.55275956]]
Error Propagation
  • Calculated flux as sum over pixels, subtracting background:
\begin{equation} F = \sum_{i,j}^{ } \left ( n_{i,j} - b_{i,j} \right ) \end{equation}
  • $ n_{i,j} $ : pixel ADU. Assume Poisson distributed, hence $ V \left [ n_{i,j} \right ] = n_{i,j} $
  • $ b_{i,j} $ : background value. Determined, along with error, via filter method.
  • Therefore variance of flux given by:
\begin{equation} V \left [ F \right ] = \sum_{i,j}^{ } \left ( n_{i,j} + V \left [ b_{i,j} \right ] \right ) \end{equation}
  • Magnitude calculated using equation:
\begin{equation} m = -2.5 \log_{10} \left ( F \right ) +c \end{equation}
  • Therefore magnitude variance given by:
\begin{equation} V \left [ m \right ] = \left ( \frac{2.5}{ \ln 10} \right )^{2} \frac{V \left [ F \right ] }{F^{2}} \end{equation}
  • Errors shown on zoomed section of simulated candidate HR diagram:
HR_Errors2.png

Astrometry files

* http://nova.astrometry.net/user_images/1467041#annotated

* http://nova.astrometry.net/user_images/1467040#annotated

-- AaronAndrews - 30 Jan 2017

Attachments Attachments
Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng CodeCogsEqn_1.png r1 manage 1.8 K 31 Jan 2017 - 21:47 AnishaVadher Transformation Equation
PNGpng DistancesBetweenStars.png r1 manage 28.7 K 01 Feb 2017 - 10:52 AnishaVadher Distances between true (i) and candidate stars (j)
PNGpng DoubleCluster_40s_blue_5_ASTRO_Aladin_Annotated.png r1 manage 1994.6 K 31 Jan 2017 - 14:44 AnishaVadher Double Cluster blue frame in Aladin indicating 2 coordinates
PNGpng HR_Errors1.png r1 manage 28.8 K 30 Jan 2017 - 14:54 AaronAndrews HR with errors, simulated double cluster
PNGpng HR_Errors2.png r1 manage 31.1 K 30 Jan 2017 - 14:54 AaronAndrews HR with errors, simulated double cluster (zoomed)
PNGpng Hist_dij_InputOutput_1Sigma_20.png r1 manage 31.9 K 31 Jan 2017 - 15:21 LauraBevilacqua distances between all input and output stars
PNGpng Hist_dij_InputOutput_2000.png r1 manage 38.0 K 31 Jan 2017 - 15:22 LauraBevilacqua distances between all input and output stars
PNGpng Transform.png r1 manage 51.2 K 31 Jan 2017 - 21:33 AnishaVadher Converting RA/DEC to pixel coordinates
PNGpng fractionStarsMatched.png r1 manage 32.9 K 31 Jan 2017 - 15:18 LauraBevilacqua fraction of stars matched as a function of threshold
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Topic revision: r8 - 01 Feb 2017 - LauraBevilacqua

 
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