Ages of Normal and Blue Lurker Stars in Open Cluster M67

About Me

My name is Justyce Watson. I'm a rising senior at Lewis University in Romeoville, IL. I'm majoring in Physics with a minor in math. I spend my time at school helping run our Black Student Union club and participating in SPS events. This summer I worked with Aaron Geller and Anna Childs on developing a method to find ages of individual stars.If you have any questions, you can contact me at justycetwatson [at]


Star cluster M67 is an open cluster with an age of 4 Gyr. Many clusters, such as M67, may contain exotic stars called blue lurkers. Blue lurkers are stars identified based on their rotation speed. They may be rotating quicker than the rest of the population due to binary mergers, mass transfers, or stellar collisions. Since they have a rapid rotation rate, they may be rejuvenated, which could make them appear younger than similar stars. (Leiner+2019), who coined the term blue lurkers, identified eleven of these exotic blue lurker stars in M67.

Using a high-performance computer, called Quest, and a program known as BASE-9, we analyzed the nearly 1500 members of M67. We used photometry files created using Gaia data and ran them through BASE-9 using Quest to createe files for each of these stars. These files included information on each star's age, reddening, parallax, and absorption. With this data, we figured out how the error on the ages of the stars compared to the parallax and reddening errors. We compared the brightness of each star to its age uncertainty and found that brighter stars have a more precise estimate for their ages.


Using the high-performance computer at Northwestern, called Quest, and a program known as BASE-9(Bayesian Analysis of Stellar Evolution with 9 parameters), we analyzed the members of M67. We used photometry files created using Gaia data and ran them on Quest to create files for each of these stars. These files include the logarithmic age, reddening, parallax, and absorption. With the given data, we analyzed the error of each parameter against the error of the age.

These graphs are comparing the precision of ages, which is distance between error bars, for individual stars to parallax error, AV error, and brightness. The first graph shows an increasing parallax error as the error on the ages increases. The middle graph does not show a clear trend with the reddening error and the error on age. The final graph is comparing the uncertainty of the ages to the brightness of the stars. The uncertainty on the ages increases as the brightness of the star decreases. This means brighter stars have a higher precision on their ages. We decided to focus on stars with a Gmag less than 15.5.
This graph features 100 of the brighter stars in the cluster. The red line represents the median age of the cluster at 9.64. Each black dot is an individual star with error bars that represent the uncertainty of its age. Some have larger bars, which means the age calculation isn't as accurate. Some have smaller error bars, which means the age is more accurate. The blue dots represent 7 of the blue lurkers found in the cluster. While some of them are right at the red line, which means they agree with the cluster age, majority of them have big error bars. This means that the ages calculated for the blue lurkers aren't as accurate as we would want them.
This color magnitude diagram confirms what we saw in the graph comparing the uncertainty on age to the brightness of the stars. The stars colored in blue have less uncertainty on their ages. Most of these stars are above the dashed line, which is at Gmag equal to 15.5. The majority of stars below the dashed line are stars with a greater uncertainty on their ages. The stars highlighted in black are the seven blue lurkers mentioned above. Three of the seven are colored in blue, so their age measuremetns are more accurate. These would be the three blue points with smaller error bars in the graph above.

Overall, our results showed that the method could be more accurate on brighter stars. The next steps for this project would be to perfect this method by analyzing the rest of the brightest stars in the cluster. Once this is done, we want to apply this to field stars, which are stars not in clusters. This would be a great way to identify more blue lurkers in M67 and also in other clusters. Finding more blue lurkers could give us an insight into the lifetime of different stars.

Blue Outer Space Stars

This material is based upon work supported by the National Science Foundation under grant No. AST 2149425, a Research Experience s for Undergraduates (REU) grant awarded to CIERA at Northwestern University. Any opinions, findings, and conclusions or recommendations expressed in this material a re those of the author(s) and do not necessarily reflect the views of the National Science Foundation. This research was supported in part through the computational resources and staff contributions provided for the Quest high performance computing facility at Northwestern University which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology.