RHUL Physics Department TWiki> Public Web>UserList>StewartBoogert>StewartBoogertAstronomy>StewartBoogertMSciProjects>StewartBoogertPhotometry2015>20160201MSciPhotometryAnalysisOb1part8 (04 Feb 2016, ElenaCukanovaite) EditAttach

- p values give a probability, so should be normalised to 1.
- Found p value for each pixel, and summed over all pixels
- Found summed values as:
1*0.999999876234048* - Found previously around 80% signal and 20% background,
- Performed back of the envelope calculations to validate this, found s = 80%, b = 20% as was fitted.

- Since our stars looked skewed, decided to fit skewed Gaussians.
- The new total function fitted, :

- Below are examples of fitted stars from one of our images:

- Well fitted stars seemed to have at around 1.
- Therefore, we could set our threshold for the boundary between 1 star and 2 stars as .
- It appears that the most bright stars have been fitted terribly and their are even bigger than 2. It seems that although the tails fit nicely, the fit cannot reach the required amplitude.
- Below are histograms for the same stars in the same order of

- This should have produced a Gaussian with mean 0 and standard deviation of 1.

- As one would expect, the bigger the , the further away the histogram is from a normalised Gaussian.

- Generated 40 images (100x100 pixels) of the same BRIGHT star.
- As before generated a star according to:

- Therefore, each pixel had a distinct pixel value.
- Added a background of 160 pixel values.
- Then for each pixel, its pixel value was taken as the mean value of the Poisson distribution and a new pixel value was then generated according to that distribution for the given pixel.
- The 40 images were fitted using our maximum likelihood fitting algorithm.

- For each parameter fitted the following was calculated:

- Bellow are the histograms for the above calculation:

- Decided to take the error on the parameter as the difference between the biggest and smalles fractional errors.
- Here is the fractional errors:

- An example with fitted parameters:

- Generated dimmer star to see how errors scaled:

- For a dim star, fractional errors:

- An example with fitted params:

- Took a series of bias, dark and flat frames to check for variabilities and to figure out how long it took the cooling ring to disappear.
- Here is the progression of the cooling ring:

- The ring took 1hr50mins to dissapear.
- Took a selection of master frames for later analysis porpoises.
- We had a major problem, for some reason the average pixel value for the bias frame, the dark frame exposure time 30s and 60s were all around 900.

- We tried some initial removal of bias and flat frames:
- Original:

- Bias master frame removed (substracted bias):

- Master flat removed (divided by master flat):

-- DavidHadden - 01 Feb 2016

Physics Webpages
•
RHUL Webpages
•
Campus Connect
•
Royal Holloway, University of London, Egham, Surrey TW20 0EX; Tel/Fax +44 (0)1784 434455/437520

Topic revision: r6 - 04 Feb 2016 - ElenaCukanovaite

Copyright © 2008-2018 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

Ideas, requests, problems regarding RHUL Physics Department TWiki? Send feedback