V154, Hunting Barnard's Variable in the Globular Cluster M3
I read an article in Sky and Telescope online today by Bob King with the above title. I’d recently imaged Messier 3 and wondered if I could use the diagrams in the article to find the star near the globular cluster’s core.
I went back to my linear image and performed a very gentle stretch so as not to obscure the core stars and altered the orientation to match the diagrams. As this is an image of just the core of the cluster, it’s rather small.
The star marked in the image above was the first variable star located in a globular cluster. It’s magnitude varies between 11.8 and 13.2 over a period of 15.3 days. That longer period classifies it as a W Virginis type star or a Type II Cepheid. Most of the variables in M3 are RR Lyrae type with shorter periods.
The star pulsates regularly as an outer layer contracts slightly then heats up and traps energy radiating from the core. The star then dims slightly until rising pressure pushes the layer back out. And repeat... ...every 15.3 days.
It fuses Helium at its core with Hydrogen burning occurring in an outer shell. Variations in the pressure and temperature of the shell cause the pulsations.
The relationship between the luminosity and period of stars like this can be used as a “standard candle” to work out the distance to stars.
The stars light curve was first described by EE Barnard in 1906 and hence it is known as Barnard’s variable.
After this exercise, I can spot V154 in my main image of M3, it is somewhat brighter and whiter than most of the stars in the cluster.
Not certain but I think it is likely to be a F class star so hotter and bluer than most stars in a Globular cluster.
V154, Hunting Barnard's Variable in the Globular Cluster M3
I read an article in Sky and Telescope online today by Bob King with the above title. I’d recently imaged Messier 3 and wondered if I could use the diagrams in the article to find the star near the globular cluster’s core.
I went back to my linear image and performed a very gentle stretch so as not to obscure the core stars and altered the orientation to match the diagrams. As this is an image of just the core of the cluster, it’s rather small.
The star marked in the image above was the first variable star located in a globular cluster. It’s magnitude varies between 11.8 and 13.2 over a period of 15.3 days. That longer period classifies it as a W Virginis type star or a Type II Cepheid. Most of the variables in M3 are RR Lyrae type with shorter periods.
The star pulsates regularly as an outer layer contracts slightly then heats up and traps energy radiating from the core. The star then dims slightly until rising pressure pushes the layer back out. And repeat... ...every 15.3 days.
It fuses Helium at its core with Hydrogen burning occurring in an outer shell. Variations in the pressure and temperature of the shell cause the pulsations.
The relationship between the luminosity and period of stars like this can be used as a “standard candle” to work out the distance to stars.
The stars light curve was first described by EE Barnard in 1906 and hence it is known as Barnard’s variable.
After this exercise, I can spot V154 in my main image of M3, it is somewhat brighter and whiter than most of the stars in the cluster.
Not certain but I think it is likely to be a F class star so hotter and bluer than most stars in a Globular cluster.