So, you have chosen your comparison stars and done photometry on your night's images. Now what? Inspect the data, and then submit it! Here is how:
- If you followed the steps in the photometry section of the wiki, then AstroImageJ should have spit out a huge data file (make sure that one of the comparison stars you used is the same as the one you choose in step 3). Make sure this data file is stored in csv format.
- Download the files from the dropbox, and put them in their own directory on your machine or use the camera computer at the observatory. (I just went to 'Clone or download' > 'download zip' and downloaded all files there as a zip file. Then I unpacked the zip file).
- Move your csv file to the same folder where you've stored these files.O
- Open the jupyter notebook 'MagnitudeCalculation.ipynb ' and answer the questions! This code will make light curve plots, and also output a text file that can be submitted to AAVSO or CBA.
- In answer to 'Number of comparison stars?', your answer is likely to be 3 or 4, depending on how many comparison stars you chose and did photometry of.
- If you are measuring colors of your object, say YES to 'Transforming the data?' If instead, you are just monitoring a source in one particular band, you can say NO.
- The code will ask for magnitudes of your comparison stars. To find these, go back to the AAVSO chart plotter. Instead of choosing to plot a chart, select to show a photometry table of the stars in the field. By default, the photometry will be given in V band, but you can request information in other filters by scrolling to the bottom. Once again, click "plot chart". You should now see a list of all the comparison stars in the chart you plotted along with their magnitudes in the requested filter(s).
- The code will plot light curves of your target source, comparing it with each of your comparison stars. Consider these plots. Do they all look similar? If all the comparison stars are 'well-behaved', the light curves should all look similar. If they look different, try to understand why. You may need to go back and try addtional comparison stars, to see which star is the outlier and which are well behaved.
- Choose the two comparison stars that yield the two best light curves, and give these when the code asks: "Which comparison star are you using to submit the data?" and "Which comparison star are you using as the check star?". Give the stars' respective AAVSO numbers when the code asks for the 'comp star name' and 'check star name'.
- The code should then make an ascii (pure text) file, formatted as in the example below. The first column is time, reported as mid-exposure Julian Dates with 5 decimal digits. The source magnitude is the second column, which is the value calculated in step 10, and reported with 3 decimal digits. The third column is the photometric error on the magnitude. The airmass values should be given in the fourth column. The header of the file should include what filter you observed in, and what star you used as the comparison star.
- Sending the Data
- CBA: The data file should be attached to an e-mail and sent to: cba-data@cbastro.org with a subject like: Subject: MU Cam, 12 Jan 2016 (JD 400.514 to 400.657) that allows them to identify the target, date, and covered interval. If this is your first time submitting data, send your data file to Laura and/or Lilia to check and give you the OK to send to the CBA.
- AAVSO: To submit to the AAVSO head to www.AAVSO.org and go to Data > WebObs (Submit/Search Data). From here you can upload your file that was produced by the python code. Make sure you have your correct Observer ID entered. Follow the prompts to submit.
- Once your data has been submitted to both CBA and AAVSO rename the folder containing that nights observations with *_SUBMITTED
- Example: 2016_08_28 => 2016_08_28_SUBMITTED
Sample Data File[]
# Variable: MU_Cam
# Date: 12-Jan-2016
# Comp star: 135_AAVSO_(V=13.482)
# Check star: 132_AAVSO_(V=13.219)
# Exp time (s): 45
# Filter: V
# Observatory: Michigan State Campus Observatory
# Location East Lansing, MI, USA
# Comments: Clear most of the night.
# JD Var_Mag Var_eMag Airmass
2457400.51433 15.121 0.019 1.255
2457400.51499 15.145 0.020 1.255
2457400.51564 15.147 0.020 1.256
2457400.51629 15.244 0.021 1.256
2457400.51694 15.267 0.022 1.256
2457400.51760 15.252 0.022 1.257
2457400.51825 15.222 0.021 1.257
2457400.51889 15.166 0.020 1.258
.......
The following webpage has more information if needed: http://image-analysis.readthedocs.io/en/latest/06_photometry_intro/instrumental_mags_and_the_beauty_of_photometry.html.