We explore the possibility that the star alpha Orionis (Betelgeuse) is the outcome of a merger that occurred in a low mass ratio (q = M2/M1 = 0.07 - 0.25) binary system some time in the past hundreds of thousands of years. To that goal, we present a simple analytical model to approximate the perturbed internal structure of a post-merger object following the coalescence of a secondary in the mass range 1-4 Msun into the envelope of a 15-17 Msun primary. We then compute the long-term evolution of post-merger objects for a grid of initial conditions and make predictions about their surface properties for evolutionary stages that are consistent with the observed location of Betelgeuse in the Hertzsprung-Russell diagram. We find that if a merger occurred after the end of the primary's main-sequence phase, while it was expanding toward becoming a red supergiant star and typically with radius ~200 - 300 Rsun, then it's envelope is spun-up to values which remain in a range consistent with the Betelgeuse observations for thousands of years of evolution. We argue that the best scenario that can explain both the fast rotation of Betelgeuse and its observed large space velocity is one where a binary was dynamically ejected by its parent cluster a few million years ago and then subsequently merged. An alternative scenario in which the progenitor of Betelgeuse was spun up by accretion in a binary and released by the supernova explosion of the companion requires a finely tuned set of conditions but cannot be ruled out.
The past and future evolution of a star like Betelgeuse
我们讨论了一个典型的大质量恒星的物理和演化通过一个类似的参宿四的演化阶段。在简要介绍参宿四的各种观测参数后，我们讨论了前主序星相（PMS）、主序星相（MS）、HR图第一次穿越时间的物理机制、红超巨星相（RSG）、后红超巨星相以及质量在9 ~ 25 M $_\odot$之间的太阳金属丰度恒星的最终命运。我们研究的影响，不同的初始旋转和各种处方的质量损失率在红超巨星阶段。我们证明，无论初始旋转速率如何（在0和0.7 $\times\upsilon_{\rm crit}$之间选择，$\upsilon_{\rm crit}$是表面赤道速度，产生正好平衡重力的离心加速度）和RSG阶段的质量损失率（在标准值和25倍该值之间变化），15 M $_\odot$恒星总是以RSG结束其生命，并以II-P或II-L型超新星爆炸。
We study stellar models for Betelgeuse using the HR diagram and surface abundances as observational constraints. Previous studies on Betelgeuse have not systematically investigated the surface abundances, but we believe they can be impacted by, and thus be used as an observational constraint for various parameters such as initial mass, rotation, and overshoot scheme. We investigate stellar models with varying initial mass as they evolve past the main sequence, and we examine the red supergiant (RSG) properties in detail. For each mass, we vary the initial rotation up to $\sim$ 300 $km\:s^{-1}$…
After core hydrogen burning, massive stars evolve from blue-white dwarfs to red supergiants by expanding, brightening, and cooling within few millennia. We discuss a previously neglected constraint on mass, age, and evolutionary state of Betelgeuse and Antares, namely their observed colour evolution over historical times: We place all 236 stars bright enough for their colour to be discerned by the unaided eye (V$\le$3.3 mag) on the colour-magnitude-diagram (CMD), and focus on those in the Hertzsprung gap. We study pre-telescopic records on star colour with historically-critical methods to find…
According to the standard cosmological scenario, the large galaxies that we observe today have reached their current mass via mergers with smaller galaxy satellites (Moore et al.1999). This hierarchical process is expected to take place on smaller scales for the satellites themselves, that should build-up from the accretion of smaller building blocks (D'Onghia & Lake 2008). The best chance we have to test this prediction is by looking at the most massive satellite of the Milky Way (MW): the Large Magellanic Cloud (LMC). Smaller galaxies have been revealed to orbit around the LMC (Erkal & Belok…
Imaging and spectroscopy of the knots, clumps, and extended arcs in the complex ejecta of VY CMa confirm a record of high mass loss events over the past few hundred years. HST/STIS spectroscopy of numerous small knots close to the star allow us to measure their radial velocities from the strong K I emission and determine their separate motions, spatial orientations, and time since ejecta. Their ages concentrate around 70, 120, 200 and 250 years ago. A K I emission knot only 50 mas from the star ejected as recently as 1985 -- 1995 may coincide with an H2O maser. Comparison with VY CMa's histori…
We perform an asteroseismic investigation of giant stars in the field of NGC 6791 with previous indications of atypical evolution. The analysis makes use of observations from Kepler and Gaia in combination with ground-based photometry, a literature radial-velocity study, and measurements of eclipsing binaries in the cluster. We derive mass, radius, effective temperature, evolutionary stage and apparent distance modulus of each target. Among the investigated cluster giants we find clear evidence of overmassive and undermassive members, and non-members with strong hints of potential past members…
It has been suggested that SNe Ia could be produced in the condition of the violent merger scenario of the double-degenerate model, in which a thermonuclear explosion could be produced when the merging of double carbon-oxygen white dwarfs (CO WDs) is still ongoing. It has been recently found that the nucleus of the bipolar planetary nebula Henize 2-428 consists of double CO WDs that have a total mass of ~1.76Msun, a mass ratio of ~1 and an orbital period of ~4.2 hours, which is the first and only discovered progenitor candidate of SNe Ia predicted by the violent merger scenario. In this work, …
The process of unstable mass transfer in a stellar binary can result in either a complete merger of the stars or successful removal of the donor envelope leaving a surviving more compact binary. "Luminous red nova" (LRN) are the class of optical transients believed to accompany such merger/common envelope events. Past works typically model LRNe using analytic formulae for supernova light curves which make assumptions (e.g., radiation dominated ejecta, neglect of hydrogen recombination energy) not justified in stellar mergers due to the lower velocities and specific thermal energy of the ejecta…
The Milky Way was shaped by the mergers with several galaxies in the past. We search for remnant stars that were born in these foreign galaxies and assess their ages in an effort to put upper limits on the merger times and thereby better understand the evolutionary history of our Galaxy. Using 6D-phase space information from Gaia eDR3 and chemical information from APOGEE DR16, we kinematically and chemically select $23$ red giant stars belonging to former dwarf galaxies that merged with the Milky Way. With added asteroseismology from Kepler and K2, we determine the ages of the $23$ ex-situ sta…
Chemical fingerprints of binary mass transfer in massive stars
Max Planck Institute for Astrophysics（马克斯·普朗克天体物理研究所）；Argelander-Institut für Astronomie, Universität Bonn（波恩大学阿根兰德天文学研究所）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）
A clear link between a dwarf-dwarf merger event and enhanced star formation (SF) in the recent past was recently identified in the gas-dominated merger remnant VCC 848, offering by far the clearest view of a gas-rich late-stage dwarf-dwarf merger. We present a joint analysis of JVLA HI emission-line mapping, optical imaging and numerical simulations of VCC 848, in order to examine the impact of the merger on the stellar and gaseous distributions. VCC 848 has less than 30% of its HI gas concentrated within the central high-surface-brightness star-forming region, while the remaining HI is entrai…
