Discovery of an extended Horizontal Branch in the Large Magellanic Cloud globular cluster NGC1835
Astronomy & Astrophysics(2024)
Abstract
We present a high angular resolution multi-wavelength study of the massive
globular cluster NGC 1835 in the Large Magellanic Cloud. Thanks to a
combination of optical and near ultraviolet images acquired with the WFC3 on
board the HST, we performed a detailed inspection of the stellar population in
this stellar system adopting a “UV-guided search” to optimize the detection
of relatively hot stars. This allowed us to discover a remarkably extended
horizontal branch (HB), spanning more than 4.5 magnitudes in both magnitude and
colour from the region redder than the instability strip, up to effective
temperatures of 30,000 K, and including a large population of RR Lyrae (67
confirmed variables, and 52 new candidates). This is the first time that such a
feature has been detected in an extra-Galactic cluster, demonstrating that the
physical conditions responsible for the formation of extended HBs are
ubiquitous. The acquired dataset has been also used to redetermine the cluster
distance modulus, reddening, and absolute age, yielding (m-M)_0=18.58,
E(B-V)=0.08, and t=12.5 Gyr, respectively.
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