HOYS-LCO – Target IC5146 – A Beginners Experience

By: Andrew Sutkowski, Norwich Astronomical Society

As a new participant in the HOYS-LCO Citizen Science project, I have been following the email and video instructions in order to acquire images of the target IC5146 – the Cocoon Nebula. I have to admit that setting up the request for remote acquisition of the images was quite straightforward. That is apart from adjusting the time window. Perhaps this task is simple and intuitive using a mouse, but from the keyboard, it took me some time to figure out how I could adjust the values. That challenge overcome it was then a simple question of waiting for the images to be taken.

Once the images were captured and stacked, it was then my responsibility to check the images ensuring that the metadata was correct and that both the astrometric and photometric calibrations were correct before the data is sent into the database. It was during the photometric calibrations that I got nervous, worrying that if I failed to get the calibration adjustments correct I could mess up the database. What would be nice here would be an interactive trial dataset that new users could experiment on to see the effects and obtain feedback on how good the fit was. But, I survived and submitted my data.

The next step was to investigate the data, again with a useful video showing how. Having prior experience using the SIMBAD database, it was simple to find a range of stars around the target to have a look at. Occasionally you have to be patient with the Data Server while it finds the data, but then accessing the plot and manipulating is relatively easy with the tools provided. The only thing I missed was an indication on the plot as to what target I was looking at. If you get distracted or called away and come back to the screen some time later, it is easy to forget where you are.

The challenge was to do something useful, so looking through the data for different stars I noticed something odd. There were different stars which showed a brightening all at roughly the same time. The light curve shown in this article is for 2MASS J21532583+4715514 and as you can see there is an apparent peak at around JD=2458500.

Had this been the only instance of this behaviour my suspicions would not have been piqued, but similar peaks, at identical times are also visible in 2MASS J21533310+4716092, 2MASS J21532961+4713542, 2MASS J21534065+4716494, EM* LkHA 245, EM* LkHA 252, EM* LkHA 239, EM* LkHA 238 and EM* LkHA 237. By turning the error bars on in the plots, it was obvious to see that data in the region of the peak have a large uncertainty, so they are suspect. I did try downloading the data sets, but was unable to reconstruct the plot in Excel to examine trends in the data. Thankfully, Dirk is extremely helpful. He investigated and found that these data come from a user with a camera that has a large pixel size. This means that stars, which are close together, are not resolved. When the software measures the brightness in such images, the magnitudes can thus be too bright as they include more than one star. This is a particular problem for this field as it is close to the Galactic Plane.  This also explains why most of the datasets are fine, since the stars in those regions are better resolved.

The results of my first foray into the data may not have revealed new observations of variation in young stellar objects, but it may help tidy up the database making the discovery of such events easier. The process has also taught me a lot about the data and what is involved in the analysis of light curves for HOYS.