Williamina_Paton_Stevens_Fleming wikipedia
A 1901 Astrophysical Journal paper by Pickering provides a list of sixty four new variables, one of which — a star in the constellation Lyra — was found using the method above on a plate from July 13, 1899. Examination of this plate by one of Pickering’s staff, Williamina Fleming, revealed a short-period, high amplitude star (aavso.org).
In nine years, she (Fleming) catalogued more than 10,000 stars. During her work, she discovered 59 gaseous nebulae, over 310 variable stars, and 10 novae. In 1907, she published a list of 222 variable stars she had discovered (wikipedia).
“RR Lyrae variables are periodic variable stars, commonly found in globular clusters, and often used as standard candles to measure galactic distances.” It is roughly estimated that out of the 200 billion stars in our Milky Way galaxy only 85,000 may be RR Lyrae stars. “They are extensively used in globular cluster studies, and also used to study chemical properties of older stars.” (wikipedia) More on RR Lyrae stars at earthsky.org.
The Kepler spacecraft is monitoring a section of our galaxy that consists of approximately 150,000 stars. In a science paper J.M. Benkő et al dated 22 July 2010, the Kepler science team has identified only 29 of them as RR Lyrae stars, and of those only 14 exhibit Blazhko modulations. It now appears that Planet Hunters has found another RR Lyrae star with Blazhko modulation.
Planet Hunters Light Curve APH23036769
Pattern recognition of light curves at Planet Hunters has helped the Kepler science team find an unlisted RR Lyrae star. It was hiding, so to speak, in the star field background presenting itself as light contamination in the light curve above. Pattern recognition is all about acting on your hunches. This light curve seemed unusual and I took the next step of running the star’s light curve data through a periodogram generator and this is what presented itself:
Periodogram of light curve APH23036769- KID 3448787
When you see this type of pattern in a periodogram, it is a strong indication of the star being an RR Lyrae. Kian Jek, known as Kianjin, at Planet Hunters forum is a co-discoverer of this star. Without his taking an interest in educating members about RR Lyrae stars and what to look for, this find would have been passed by. Kian analyzed the light curve I submitted in the “Discussions” section and this is what he came up with:
I was pretty sure the RRL pattern is in the star itself, just masked by errors in photometry and/or post processing. Here’s how the undetrended but Kepler processed light curve looks like, Q1 to Q3:
Graph by Kian Jek
It’s strange that Q1 doesn’t show any pulsations. Q2 is definitely distorted by the fp16 problem, but even Q3 has some funky distortions of its own. So what I did was to take the raw flux from Q3 alone, detrended it myself and here’s what I got – an RRL-like light curve complete with Blazhko modulation!
Graph by Kian Jek
I’m pretty sure this is what the star should look like, and here’s the final phased waveform:
Graph by Kian Jek
Here is what Dr Chris Lintott (Zookeeper) had to say about this discovery:
Good news! I’ve heard back from our friends in the Kepler team, and this star is interesting and indeed new to them, so this is another #discovery for Planet Hunters! Congratulations, Tom128 (Thomas Lee Jacobs) for spotting it, and Kianjin (Kian Jek) for the analysis. They’re going to do a detailed analysis – indeed, they’ve already started – and keep us informed. Obviously if it makes a paper then full credit will go to you two.
Some extra details; the reason that the variation appears and disappears between quarters might be because it’s a background star; this would explain the small amplitude and if the processing used on different quarters included different parts of the image then that would explain why it comes and goes.
They also say “Any new RRLs – especially the modulated ones – are of great value and very much appreciated! Kepler provides excellent light curves and delivers surprising new discoveries on #RRLyrae stars,” so do tag anything you find. As Robert Szabo, one of the scientists says : ‘Congratulations to this precious discovery’.
Both Kian Jek and Dr. Szabo suspected that the RR Lyrae star that was presenting itself in the original light curve was manifesting itself as light contamination. Here is what Chris Lintott had to say:
Robert Szabo sent me the following image, which is a pixel by pixel light curve for the star.
Graph by Dr. Robert Szabo- Kepler Science Team
Note – You can see the light contamination in the original light curve as Blazhko modulation in the four right columns of the chart.
As he says, it indeed confirms that the RRL star is not the originally proposed and observed 3448787. In the other figure, below, he shows a fainter star (Kp~17.6) which I suspect is the variable. Its KIC ID is 3448777. The third brighter star forming a ‘line’ with 3448787 and 3448777 toward the upper right corner is 3448767. Unfortunately neither 3448777 nor 3448767 were observed by Kepler, but we’re going to see what we can do to change that.
Photograph by Dr. Chris Lintott
This brings me back to pattern recognition at Planet Hunters and RR Lyrae star clues in the light curves as light contamination. I will show two examples of Kepler light curves indicating that a RR Lyrae star is somewhere in the star field contaminating the light curve of interest. The first is the one already posted and discussed in this article. The second is from an already known RR Lyrae star.
Planet Hunters Light Curve APH23036769
Planet Hunters Light Curve APH22143475
Notice that both light curves have a thick line running along the lower edge of the curve along with modulated pulsations, though distorted. These are clues that an RR Lyrae may lie in the star field that is contaminating the light curve. In the case of the second example, it is the grandmother of all the RR Lyrae star types discovered by Williamina Fleming on July 13, 1899.
Sky view image by Kian Jek
