Archive for March, 2013

Obtaining and analysing Kepler data with VStar

March 29, 2013

In this post I will step through an example of using Kepler data with VStar‘s Kepler observation source plug-in.

After installing the plug-in as per the instructions on the plug-in library page, go to the Kepler data search page and type V0838 Cyg into the Target Name box:

Kepler data search

Clicking Search takes you to this dataset result page:

Screen shot 2013-03-29 at 11.00.33 AM

Arbitrarily choose the last dataset entry to give this page:

Screen shot 2013-03-29 at 11.03.11 AM

Notice that the vertical axis is in units of flux instead of magnitude.

Near the top is text thats says: “Light curve file is online (“.fits”). If you click the “online” link you’ll get a page with the data in FITS format. What you really want to do is to save the link/file/page as a file locally, usually via a right-click context menu (in Windows; in Macintosh it’s ctrl-click).

The raw plot obtained from loading this file via VStar’s Kepler observation source plug-in looks like this, via:

V0838Cyg

and the phase plot (from a DCDFT standard scan; see VStar Analysis menu) at ~0.48 days is:

V0838CygPP

This looks like an RRAB given the amplitude, period, shape. I came to that conclusion before asking VSX. :) A beautiful light curve. You have to zoom in quite a way to see any error bars, such is the nature of Kepler data.

By the way, you can get directly to the Kepler data page via the “External Links: Location” section of the V0838 Cyg VSX search result page!

One of the things I want to add to the Kepler and some other observation source plug-ins is the ability to specify the URL obtained from copying the link address (again from the context menu from the “online” link), in this case:

http://archive.stsci.edu/pub/kepler/lightcurves/0107/010789273/kplr010789273-2012277125453_llc.fits

The Kepler plug-in would then read the http stream directly rather than you having to download a file.

The Kepler plug-in converts flux values to a magnitude value. The amplitude should be what you’d expect but not necessarily the numerical value itself. For this star, VSX says “13.040 – 14.138″. In this case, adding 10 to each observation would bring it within the right range. It’s possible that the plug-in will be tweaked in future to produce a different magnitude range.

Other observation source plug-ins are available for VStar such as for:

  • Catalina Sky Survey
  • SuperWASP
  • AAVSO upload format (as used by WebObs)

An ASAS plug-in is planned.


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