HD 93795: a late-B supergiant star with a square circumstellar nebula

Gvaramadze, V. V.; Kniazev, A. Y.; Castro, N.; Katkov, Ivan

doi:10.1093/mnras/stz3612

Cited by 4 publications

(1 citation statement)

References 75 publications

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“…In Wheeler et al (2017), we noted that a merger event might have some relation with the interstellar shells of higher density in the vicinity of Betelgeuse. The strangely linear feature about 9' away might be related to the square axisymmetric circumstellar nebula recently discovered around the B9 Ia star HD93795 by Gvaramadze et al (2020). The prominent bow shock at ∼ 7 in the same direction indicates a peculiar velocity with respect to the local standard of rest of v ≈ 25 km s −1 (Harper et al 2008) or perhaps as much as 35 km s −1 (van Loon 2013).…”

Section: Discussionmentioning

confidence: 80%

The Betelgeuse Project III: Merger Characteristics

Sullivan,

Nance,

Wheeler

2020

Preprint

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We previously proposed that Betelgeuse might have been spun up by accreting a companion of about 1 M . Here we explore in more detail the possible systematics of such a merger and a larger range of accreted masses. We use the stellar evolutionary code mesa to add angular momentum to a primary star in core helium burning, core carbon burning, or shell carbon burning. Our models provide a reasonable "natural" explanation for why Betelgeuse has a large, but sub-Keplerian equatorial velocity. They eject sufficient mass and angular momentum in rotationally-induced mass loss to reproduce the observed ratio of the equatorial velocity to escape velocity of Betelgeuse, ≈ 0.23, within a factor of three nearly independent of the primary mass, the secondary mass, and the epoch at which merger occurs. Our models suggest that merger of a primary of somewhat less than 15 M with secondaries of from 1 to 10 M during core helium burning or core carbon burning could yield the equatorial rotational velocity of ∼ 15 km s −1 attributed to Betelgeuse. For accreting models, a wave of angular momentum is halted at the composition boundary at the edge of the helium core. The inner core is thus not affected by the accretion of the companion in these simulations. Accretion has relatively little effect on the production of magnetic fields in the inner core. Our results do not prove, but do not negate that Betelgeuse might have ingested a companion of several M .1. INTRODUCTION Betelguese (α Orionis) is a nearby, massive red supergiant (RSG) that provides clues to a broad range of issues of the evolution and explosion of massive stars. It has been difficult to obtain tight constraints on the evolutionary state of Betelgeuse and hence when it might explode and information about the internal rotational state and associated mixing. It is thus important to understand Betelgeuse in greater depth. The recent extreme dimming episode has only added impetus to this quest (Guinan et al. 2020;Levesque & Massey 2020;Harper et al. 2020;Dharmawardena et al. 2020).The distance to Betelgeuse has been known to only 20% (D ≈ 197 ± 45 pc;Harper et al. 2008Harper et al. , 2017 a situation that is not improved by Gaia that saturates on such a bright star. Key properties such as radius and luminosity are thus somewhat uncertain. Within this uncertainty, models of Betelgeuse might be brought into agreement with observations of L, R, and T ef f at either the minimum-luminosity base of the giant branch or at the tip of the red supergiant branch (RSB). By

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Section: Discussionmentioning

confidence: 80%

The Betelgeuse Project III: Merger Characteristics

Sullivan,

Nance,

Wheeler

2020

Preprint

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The blue supergiant Sher 25 revisited in the Gaia era

Weßmayer,

Przybilla,

Ebenbichler

et al. 2023

A&A

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Aims. The evolutionary status of the blue supergiant Sher 25 and its membership to the massive cluster NGC 3603 are investigated. Methods. A hybrid non-local thermodynamic equilibrium (non-LTE) spectrum synthesis approach is employed to analyse a high-resolution optical spectrum of Sher 25 and five similar early B-type comparison stars in order to derive atmospheric parameters and elemental abundances. Fundamental stellar parameters are determined by considering stellar evolution tracks, Gaia Data Release 3 (DR3) data, and complementary distance information. Interstellar reddening and the reddening law along the sight line towards Sher 25 are constrained employing UV photometry for the first time in addition to optical and infrared data. The distance to NGC 3603 is reevaluated based on Gaia DR3 data of the innermost cluster O-stars. Results. The spectroscopic distance derived from the quantitative analysis implies that Sher 25 lies in the foreground of NGC 3603, which is found to have a distance of dNGC3603 = 6250 ± 150 pc. A cluster membership is also excluded as the hourglass nebula is unaffected by the vigorous stellar winds of the cluster stars and from the different excitation signatures of the hourglass nebula and the nebula around NGC 3603. Sher 25 turns out to have a luminosity of log L/L⊙ = 5.48 ± 0.14, equivalent to that of a ~27 M⊙ supergiant in a single-star scenario, which is about half of the mass assumed so far, bringing it much closer in its characteristics to Sk−69º202, the progenitor of SN 1987A. Sher 25 is significantly older than NGC 3603. Further arguments for a binary (merger) evolutionary scenario of Sher 25 are discussed.

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