A plague of magnetic spots among the hot stars of globular clusters

Journal
Date Issued
2020
Author(s)
•
•
Montalto, M
•
Jones, D
•
Boffin, HMJ
•
•
Bidin, CM
•
•
Saviane, I
•
Monaco, L
•
•
•
•
Piotto, G
•
Milone, AP
•
Lala, H
•
Stetson, PB
•
Beletsky, Y
DOI
Abstract
For more than six decades, the quest to understand the formation of hot (about 20,000−30,000 K) extreme horizontal branch (EHB) stars in Galactic globular clusters has remained one of the most elusive in stellar evolutionary theory. Here we report on two discoveries that challenge the idea of the stable luminosity of EHB stars. The first mode of EHB variability is periodic and cannot be ascribed to either binary evolution or pulsation. Instead, we attribute it here to the presence of magnetic spots: superficial chemical inhomogeneities whose projected rotation induces the variability. The second mode of EHB variability is aperiodic and manifests itself on timescales of years. In two cases, six-year-long light curves display superflare events that are several million times more energetic than solar analogues. We advocate a scenario in which the two EHB variability phenomena are different manifestations of diffuse, dynamo-generated, weak magnetic fields. Magnetism is therefore a key player driving the formation and evolution of EHB clusters stars and, likewise, operating in the Galactic field counterparts. Our conclusions bridge similar variability/magnetism phenomena in all radiative-enveloped hot-stars: young main-sequence stars, old EHBs and defunct white dwarfs.
Volume
4
Issue
11
Start page
1092
Uri
Url
Issn Identifier
2397-3366
Ads BibCode
2020NatAs...4.1092M
Rights
open.access
File(s)
Loading...
Thumbnail Image
Name

2006.02308.pdf

Description
preprint
Size

6.22 MB

Format

Adobe PDF

Checksum (MD5)

0b2374353811fa472f8d7d08f8d8236d

Loading...
Thumbnail Image
Name

s41550-020-1113-4.pdf

Description
[Administrators only]
Size

6.86 MB

Format

Adobe PDF

Checksum (MD5)

22747e5aae036ccb0be87d154ab72196