![]() For a simple stellar population, this strip would be much narrower. Notice the spread where the black lines curve upward at (B-R)~1. A color-magnitude diagram (CMD) for an example star cluster with an extended main sequence turnoff (eMSTO). 1, which also appears in this astrobite along with a nice explanation!įigure 1. That’s all about main sequence turnoffs, but what about the “extended” bit? An extended MSTO is an observational feature where the MSTO of a cluster is more extended than what you would expect for a simple population of stars. This gives us a way of estimating the age of a stellar cluster by looking for the turnoff point! If we were to see, for example, an HR diagram for a cluster where no O-type stars are present on the main sequence but a lot of B-M type stars are still on it, we would know that it is a very young cluster. If we look at the HR diagram of a stellar cluster, assuming all the stars in the cluster were created during one burst of star formation, heavier stars will evolve away from the main sequence as the cluster ages. In general, the more massive a star is, the faster it leaves the main sequence. The point at which this occurs is called the main sequence turnoff. Stars evolve away from the main sequence when they exhaust the hydrogen fuel at their cores. The main sequence is a distinctive band of stars that appears on the HR diagram. Think of your standard Hertzsprung-Russell (HR) diagram. Let’s first unpack the acronym, eMSTO, before we delve into the new results. To do this, the authors make use of Gaia DR2, the data gift that keeps on giving, along with archival VLT/FLAMES spectroscopy. Today’s paper examines the phenomenon of extended main sequence turn-off (eMSTO) in a galactic open cluster – NGC 2818. Usherįirst Author’s Institution: Astrophysics Research Institute, Liverpool John Moores University, Liverpool, UK NGC 2818 and the Role of Stellar RotationĪuthors: N. In particular, by plotting a HR diagram for either a globular or open cluster of stars, astronomers can estimate the age of the cluster from where stars appear to turnoff the main sequence (see the entry on main sequence for how this works).Title: Extended Main Sequence Turnoffs in Open Clusters as Seen by Gaia: I. The Sun is found on the main sequence with a luminosity of 1 and a temperature of around 5,400 Kelvin.Īstronomers generally use the HR diagram to either summarise the evolution of stars, or to investigate the properties of a collection of stars. These stars are very hot but have low luminosities due to their small size. white dwarf stars (luminosity class D) are the final evolutionary stage of low to intermediate mass stars, and are found in the bottom left of the HR diagram.Stars enter this evolutionary stage once they have exhausted the hydrogen fuel in their cores and have started to burn helium and other heavier elements. They have low surface temperatures and high luminosities which, according to the Stefan-Boltzmann law, means they also have large radii. red giant and supergiant stars (luminosity classes I through III) occupy the region above the main sequence.Main sequence stars have a Morgan-Keenan luminosity class labelled V. It is here that stars spend about 90% of their lives burning hydrogen into helium in their cores. The main sequence stretching from the upper left (hot, luminous stars) to the bottom right (cool, faint stars) dominates the HR diagram.There are 3 main regions (or evolutionary stages) of the HR diagram: Also plotted are the Morgan-Keenan luminosity classes that distinguish between stars of the same temperature but different luminosity. The giant branch is also well populated and there are many white dwarfs. By far the most prominent feature is the main sequence, which runs from the upper left (hot, luminous stars) to the bottom right (cool, faint stars) of the diagram. This Hertzsprung-Russell diagram shows a group of stars in various stages of their evolution. The giant branch and supergiant stars lie above the main sequence, and white dwarfs are found below it. By far the most prominent feature is the main sequence (grey), which runs from the upper left (hot, luminous stars) to the bottom right (cool, faint stars) of the diagram. The Hertzsprung-Russell diagram the various stages of stellar evolution.
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