From astrobites: “Gaia and the Red Clump”

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astrobites

Nov 30, 2017
Philipp Plewa

Title: Red clump stars and Gaia: Calibration of the standard candle using a hierarchical probabilistic model
Authors: K. Hawkins, B. Leistedt, J. Bovy, D. W. Hogg
First Author’s Institution: Department of Astronomy, Columbia University, New York
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Status: Published in MNRAS, open access

Red clump (RC) stars are common stars, once similar to the sun, that have evolved into red giants now supported by helium fusion in their cores. Independent of their exact age or composition, all RC stars end up having about the same absolute luminosity. This is why they tend to “clump” in a particular spot in a color-magnitude or Hertzsprung–Russell diagram, and what makes them standard candles: The apparent brightness of RC stars is directly related to their distance.

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Red clump stars and Gaia, MNRAS
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Hertzsprung-Russell diagram. A plot of luminosity (absolute magnitude) against the colour of the stars ranging from the high-temperature blue-white stars on the left side of the diagram to the low temperature red stars on the right side. “This diagram below is a plot of 22000 stars from the Hipparcos Catalogue together with 1000 low-luminosity stars (red and white dwarfs) from the Gliese Catalogue of Nearby Stars. The ordinary hydrogen-burning dwarf stars like the Sun are found in a band running from top-left to bottom-right called the Main Sequence. Giant stars form their own clump on the upper-right side of the diagram. Above them lie the much rarer bright giants and supergiants. At the lower-left is the band of white dwarfs – these are the dead cores of old stars which have no internal energy source and over billions of years slowly cool down towards the bottom-right of the diagram.”

Next year’s second Gaia data release is expected to provide a significantly larger sample of RC reference stars.

ESA/GAIA satellite

In particular, this will allow a closer study of the impact of such effects as stellar age and metallicity, helium abundance, or binarity on the RC distance calibration, and thus make RC stars even better standard candles.

See the full article here .

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