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

Momany, Y.; Zaggia, S.; Montalto, M.; Jones, David; Boffin, H. M. J.; Cassisi, S.; Bidin, C. Moni; Gullieuszik, Marco; Saviane, I.; Monaco, L.; Mason, E.; Girardi, L.; D’Orazi, V.; Piotto, G.; Milone, A. P.; Lala, H.; Stetson, P. B.; Beletsky, Y.

doi:10.1038/s41550-020-1113-4

Cited by 20 publications

(30 citation statements)

References 71 publications

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“…The 12 vEHB stars and the 3 vEHB candidates (vEHB-C) from Momany et al (2020) were crossidentified in our UV catalogue. We note that some of these vEHB stars did not meet the membershipprobability cut-off.…”

Section: Spotted Ehb Starsmentioning

confidence: 99%

“…We note that some of these vEHB stars did not meet the membershipprobability cut-off. Nevertheless, we include them in our study, as they are considered by Momany et al (2020) and this is a follow up study of their objects. Figure 1 shows the spatial locations of these vEHBs (including candidates) marked over the UVIT F154W image.…”

Section: Spotted Ehb Starsmentioning

confidence: 99%

“…A recent study by Momany et al (2020) utilizing near-UV (NUV) and optical data, led to the discovery of variable stars among the EHB population (vEHB), in three Galactic GCs, namely: NGC 2808, NGC 6752 and NGC 5139 (x Cen.). The EHB stars have extremely thin radiative envelopes (.0.02M ) and T eff ranging from $ 20,000 to 30,000 K. Their counterparts in the Galactic field are sub-dwarf B-type (sdB) stars.…”

Section: Introductionmentioning

confidence: 99%

“…Instead, they briefly brighten up as AGB-manqué stars and then evolve directly towards the WD phase. Momany et al (2020) reported two types of EHB variability, periodic (periodicity of $ 2 to 50 days with DU Johnson % 0:04 to 0.22 mag) and aperiodic. This EHB variability was observed to be tightly connected around the photometric jump at T eff $ 22;500 K (the Momany jump, Momany et al 2002), a feature observed in all GCs (Momany et al 2004;Brown et al 2016).…”

Section: Introductionmentioning

confidence: 99%

“…In this study, we present the far-UV and near-UV photometric analysis and spectral energy distributions (SEDs) of 12 vEHB stars and 3 vEHB candidates newly discovered in the GC NGC 2808 by Momany et al (2020). This GC has an age ¼ 10:9 AE 0:7 Gyrs (Massari et al 2016), ½Fe=H ¼ À1:14 dex and is located at a distance of 9.6 kpc (Harris 1996(Harris , 2010.…”

Section: Introductionmentioning

confidence: 99%

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UV photometry of spotted stars in the horizontal branch of the globular cluster NGC 2808 using AstroSat

2021

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A recent study of hot (20,000 to 30,000 K) extreme horizontal branch (EHB) stars in globular clusters (GCs) has led to the discovery of their variability. It is suggested that this variability is driven by the projected rotation of magnetic spots on the stellar surfaces and is expected to have higher amplitudes at shorter wavelengths. Here, we present the analysis of such hot stars in the massive GC NGC 2808 using the UltraViolet Imaging Telescope (UVIT), aboard AstroSat. We use the UVIT data in combination with the Hubble Space Telescope UV globular cluster survey (HUGS) data for the central region (within $ 2:7 0 Â 2:7 0 ) and ground-based optical photometry for the outer parts of the cluster. We generate the Far-UV (FUV)-optical colour-magnitude diagrams (CMDs) and in these we find a population of hot EHB stars fainter than the zero-age horizontal branch (ZAHB) model. A comparison of our FUV magnitudes of the already reported variable EHB stars (vEHBs) shows that the longest period vEHBs are the faintest, along with a tentative correlation between rotation period and UV magnitude of spotted stars. In order to firmly establish any correlation, further study is essential.

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Section: Spotted Ehb Starsmentioning

confidence: 99%

Section: Spotted Ehb Starsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

UV photometry of spotted stars in the horizontal branch of the globular cluster NGC 2808 using AstroSat

2021

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Understanding structure in line-driven stellar winds using ultraviolet spectropolarimetry in the time domain

Gayley

ud‐Doula

David-Uraz

et al. 2022

Astrophys Space Sci

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The most massive stars are thought to lose a significant fraction of their mass in a steady wind during the main-sequence and blue supergiant phases. This in turn sets the stage for their further evolution and eventual supernova, with consequences for ISM energization and chemical enrichment. Understanding these processes requires accurate observational constraints on the mass-loss rates of the most luminous stars, which can also be used to test theories of stellar wind generation. In the past, mass-loss rates have been characterized via collisional emission processes such as Hα and free-free radio emission, but these so-called "density squared" diagnostics require correction in the presence of widespread clumping. Recent observational and theoretical evidence points to the likelihood of a ubiquitously high level of such clumping in hot-star winds, but quantifying its effects requires a deeper understanding of the complex dynamics of radiatively driven winds. Furthermore, largescale structures arising from surface anisotropies and propagating throughout the wind can further complicate the picture by introducing further density enhancements, affecting mass-loss diagnostics. Time series spectroscopy of UV resonance lines with high resolution and high signal-to-noise are required to better understand this complex dynamics, and help correct "density squared" diagnostics of mass-loss rates. The proposed Polstar mission easily provides the necessary resolution at the soundspeed scale of 20 km s −1 , on three dozen bright targets with signal-to noise an order of magnitude above that of the celebrated IUE MEGA campaign, via continuous observations that track structures advecting through the wind in real time.

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Correction to: UV photometry of spotted stars in the horizontal branch of the globular cluster NGC 2808 using AstroSat

2021

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

Cited by 20 publications

References 71 publications

UV photometry of spotted stars in the horizontal branch of the globular cluster NGC 2808 using AstroSat

UV photometry of spotted stars in the horizontal branch of the globular cluster NGC 2808 using AstroSat

Understanding structure in line-driven stellar winds using ultraviolet spectropolarimetry in the time domain

Correction to: UV photometry of spotted stars in the horizontal branch of the globular cluster NGC 2808 using AstroSat

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