Distance determination from J-band magnitudes of carbon stars on the asymptotic giant branch (JAGB)
We used a new method of distance determination, based on carbon AGB stars, to derive distances to nine galaxies in the Local and Sculptor Group.
The Araucaria Project. Distances to Nine Galaxies Based on a Statistical Analysis of their Carbon Stars (JAGB Method)
B. Zgirski, G. Pietrzyński, W. Gieren, M. Górski, P. Wielgórski, P. Karczmarek, F. Bresolin, P. Kervella, R.-P. Kudritzki, J. Storm, D. Graczyk, G. Hajdu, W. Narloch, B. Pilecki, K. Suchomska, M. Taormina
Although carbon stars have been discovered already in the mid 1800s, their use in distance determinations started only in 1980s, with NGC 300. They are thermally pulsating AGB stars with the convective envelope, which is being enriched in carbon, brought to the surface via thermal pulses from the helium-burning shell. Stars with masses less than 1.3 solar masses don’t have their convective zones developed enough to bring carbon to the surface, while stars with higher masses experience hot bottom burning by converting carbon into nitrogen at the base of their convective envelopes (the exact threshold depends on the metallicity). As a result, carbon stars have their masses in a small range, which translates to their constant luminosity, making them useful standard candles.
In the near-infrared J-band, carbon stars populate an area of approximately constant magnitude, with the distribution which can be fitted by a superposition of a Gaussian and a quadratic function. The mean of the Gaussian function denotes the mean observed J-band magnitude of the carbon stars.
Comparison of distances determined with JAGB stars and Cepheids shows a remarkable agreement of the two methods.
JAGB expected magnitude determinations and diagnostic plots for all analyzed galaxies are available here.