Context. The red supergiant (RSG) Betelgeuse is an irregular variable star. Convection may play an important role in understanding this variability. Interferometric observations can be interpreted using sophisticated simulations of stellar convection. Aims. We compare the visibility curves and closure phases obtained from our 3D simulation of RSG convection with CO5BOLD to various interferometric observations of Betelgeuse from the optical to the H band in order to characterize and measure the convection pattern on this star. Methods. We use 3D radiative-hydrodynamics (RHD) simulation to compute intensity maps in different filters and we thus derive interferometric observables using the post-processing radiative transfer code OPTIM3D. The synthetic visibility curves and closure phases are compared to observations. Results. We provide a robust detection of the granulation pattern on the surface of Betelgeuse in the optical and in the H band based on excellent fits to the observed visibility points and closure phases. Moreover, we determine that the Betelgeuse surface in the H band is covered by small to medium scale (5-15 mas) convection-related surface structures and a large (30 mas) convective cell. In this spectral region, H2O molecules are the main absorbers and contribute to the small structures and to the position of the first null of the visibility curve (i.e. the apparent stellar radius).
We present optical spectrophotometry of the red supergiant Betelgeuse from 2020 February 15, during its recent unprecedented dimming episode. By comparing this spectrum to stellar atmosphere models for cool supergiants, as well as spectrophotometry of other Milky Way red supergiants, we conclude that Betelgeuse has a current effective temperature of 3600 +/- 25 K. While this is slightly cooler than previous measurements taken prior to Betelgeuse's recent lightcurve evolution, this drop in effective temperature is insufficient to explain Betelgeuse's recent optical dimming. We propose that epis…
Long-term spectropolarimetric monitoring of the cool supergiant Betelgeuse
我们报告的长期监测冷超巨星参宿四，使用NARVAL和ESPaDOns高分辨率分光偏振计，分别安装在望远镜伯纳德Lyot（Pic du Midi天文台，法国）和加拿大-法国-夏威夷望远镜（莫纳克亚天文台，夏威夷）。数据集由圆偏振（斯托克斯V）和强度（斯托克斯I）光谱组成，收集于2010年至2012年之间。在这里，我们调查的时间演化的磁场，对流和温度在光球水平，使用同时测量的纵向磁场分量，核心发射的Ca II红外三重态，选定的光球线的线深比和径向速度的明星。
Magnetic field and convection in the cool supergiant Betelgeuse
我们提出了一个高灵敏度的搜索结果的磁场的冷超巨星参宿四。在2010年3月至4月期间，使用Télescope Bernard Lyot（Pic du Midi天文台）的NARVAL分光偏振仪获得了六个圆偏振光谱的时间序列。塞曼签名反复检测到互相关配置文件，对应于约1G的纵向分量。时间序列揭示了一个平滑的纵向场从0.5到1.5 G，与径向速度波动。我们观察到一个强烈的不对称性的斯托克斯V签名，也与径向速度的相关性。Stokes V线剖面相对于Stokes I线剖面发生了约9 km/s的红移，表明观测到的磁元素可能集中在对流的下沉分量中。
Betelgeuse is the nearest red supergiant, one of the brightest stars in our sky, and statistically speaking it would be expected to be "typical". Yet it exhibits many features that seem "curious", to say the least. For instance it has a high proper motion. It rotates fast. It has little dust. It dimmed unexpectedly. Is any of these, and other, phenomena atypical, and taken together does it make Betelgeuse atypical? This is important to know, because we need to know whether Betelgeuse might be a prototype of red supergiants in general, or certain subclasses of red supergiants, since we can stud…
Red supergiants are the most common final evolutionary stage of stars that have initial masses between 8 and 35 times that of the Sun. During this stage, which lasts roughly 100,000 years1, red supergiants experience substantial mass loss. However, the mechanism for this mass loss is unknown. Mass loss may affect the evolutionary path, collapse and future supernova light curve of a red supergiant, and its ultimate fate as either a neutron star or a black hole. From November 2019 to March 2020, Betelgeuse - the second-closest red supergiant to Earth (roughly 220 parsecs, or 724 light years, awa…
The red hypergiant VY CMa and the more typical red supergiant Betelgeuse provide clear observational evidence for discrete, directed gaseous outflows in their optical and infrared imaging, spectra, and light curves. In the very luminous VY CMa, mass loss estimates from the infrared bright knots and clumps, not only dominate its measured overall mass loss, but explain it. In the lower luminosity Betelgeuse, similar mass estimates of its circumstellar condensations show that they contribute significantly to its measured mass loss rate. We present new measurements for both stars and discuss addit…
Betelgeuse is a pulsating red supergiant whose brightness is semi periodically variable and in February 2020 reached a historical minimum, the Great Dimming. The aims of this study are to characterize Betelgeuse's variability based on available archival data and to study possible causes of light variability. Many spectra, from ultraviolet and optical regions, were evaluated for spectral analysis. The spectra were used primarily to determine radial velocities from different layers of atmosphere and their long{-}term evolution. Additionally, photometric data were analyzed in different filters as…
Betelgeuse, one of the most studied red supergiant stars, dimmed in the optical by ~1.2 mag between late 2019 and early 2020, reaching an historical minimum called "the Great Dimming." Thanks to enormous observational effort to date, two hypotheses remain that can explain the Dimming: a decrease in the effective temperature and an enhancement of the extinction caused by newly produced circumstellar dust. However, the lack of multi-wavelength monitoring observations, especially in the mid infrared where emission from circumstellar dust can be detected, has prevented us from closely examining th…
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 first present spatially resolved ALMA and VLA continuum observations of the early-M red supergiant Antares to search for the presence of a chromosphere at radio wavelengths. We resolve the free-free emission of the Antares atmosphere at 11 unique wavelengths between 0.7 mm (ALMA band 8) and 10 cm (VLA S band). The projected angular diameter is found to continually increase with increasing wavelength, from a low of 50.7 mas at 0.7 mm up to a diameter of 431 mas at 10 cm, which corresponds to 1.35 and 11.6 times the photospheric angular diameter, respectively. All four ALMA measurements show …
The bright supergiant, Betelgeuse (Alpha Orionis, HD 39801), underwent a historic optical dimming during 2020 January 27 $-$ February 13. Many imaging and spectroscopic observations across the electromagnetic spectrum were obtained prior to, during, and subsequent to this dimming event. These observations of Betelgeuse reveal that a substantial surface mass ejection (SME) occurred and moved out through the extended atmosphere of the supergiant. A photospheric shock occurred in 2019 January - March, progressed through the extended atmosphere of the star during the following 11 months and led to…
Betelgeuse: Detection of the Expanding Wake of the Companion Star
Center for Astrophysics — Harvard & Smithsonian（哈佛-史密森天体物理中心）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理学研究所）
Radiative hydrodynamics simulations of red supergiant stars. III. Spectro-photocentric variability, photometric variability, and consequences on Gaia measurements
We assess the ability to image the photosphere of red supergiants and, in particular Betelgeuse, through the modelling of the observed linear polarization in atomic spectral lines. We also aim to analyse the resulting images over time, to measure the size and dynamics of the convective structures in these stars. Rayleigh scattering polarizes the continuum and spectral lines depolarize it.This depolarization is seen as a linear polarization signal parallel to the radial direction on the stellar disk. Integrated over the disk, it would result in a null signal, except if brightness asymmetries/in…
Comment on the feasibility of carbon burning in Betelgeuse: a response to "The evolutionary stage of Betelgeuse inferred from its pulsation periods," arXiv:2306.00287
Despite being the best studied red supergiant star in our Galaxy, the physics behind the photometric variability and mass loss of Betelgeuse is poorly understood. Moreover, recently the star has experienced an unusual fading with its visual magnitude reaching a historical minimum. We investigate the nature of this event with the help of a recently developed tomographic technique. Tomography allows us to probe different depths in the stellar atmosphere and to recover the corresponding disk-averaged velocity field. We apply the tomographic method to a few-year time-series high-resolution spectro…
During October 2019 and March 2020, the luminous red supergiant Betelgeuse demonstrated an unusually deep minimum of its brightness. It became fainter by more than one magnitude and this is the most significant dimming observed in the recent decades. While the reason for the dimming is debated, pre-phase of supernova explosion, obscuring dust, or changes in the photosphere of the star were suggested scenarios. Here, we present spectroscopic studies of Betelgeuse using high-resolution and high signal-to- noise ratio near-infrared spectra obtained at Weihai Observatory on four epochs in 2020 cov…
Betelgeuse is the nearest Red Supergiant star and it underwent an unusually deep minimum at optical wavelengths during its most recent pulsation cycle. We present submillimetre observations taken by the James Clerk Maxwell Telescope and Atacama Pathfinder Experiment over a time span of 13 years including the optical dimming. We find that Betelgeuse has also dimmed by \sim20\% at these longer wavelengths during this optical minimum. Using radiative-transfer models, we show that this is likely due to changes in the photosphere (luminosity) of the star as opposed to the surrounding dust as was pr…
Theory surrounding the origin of the dust-laden winds from evolved stars remains mired in controversy. Characterizing the formation loci and the dust distribution within approximately the first stellar radius above the surface is crucial for understanding the physics that underlie the mass-loss phenomenon. By exploiting interferometric polarimetry, we derive the fundamental parameters that govern the dust structure at the wind base of a red supergiant. We present near-infrared aperture-masking observations of Betelgeuse in polarimetric mode obtained with the NACO/SAMPol instrument. We used bot…
We conduct a rigorous examination of the nearby red supergiant Betelgeuse by drawing on the synthesis of new observational data and three different modeling techniques. Our observational results include the release of new, processed photometric measurements collected with the space-based SMEI instrument prior to Betelgeuse's recent, unprecedented dimming event. We detect the first radial overtone in the photometric data and report a period of $185\pm13.5$ d. Our theoretical predictions include self-consistent results from multi-timescale evolutionary, oscillatory, and hydrodynamic simulations …
A significative fraction of all massive stars in the Milky Way move supersonically through their local interstellar medium (ISM), producing bow shock nebulae by wind-ISM interaction. The stability of these observed astrospheres around cool massive stars challenges precedent two-dimensional (magneto-)hydrodynamical simulations of their surroundings. We present three-dimensional magneto-hydrodynamical (3D MHD) simulations of the circumstellar medium of runaway M-type red supergiant stars moving with velocity v_star= 50 km/s. We treat the stellar wind with a Parker spiral and assume a 7 microG ma…
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 proper…
Circumstellar dust is formed and evolved within the envelope of evolved stars, including Asymptotic Giant Branch (AGB) and Red Supergiant (RSG). The extinction of stellar light by circumstellar dust is vital for interpreting RSG/AGB observations and determining high-mass RSG progenitors of core-collapse supernovae. Nevertheless, circumstellar dust properties are not well understood. Modern understanding of dust evolution suggests that intense stellar radiation can radically change the dust properties across the circumstellar envelope through the RAdiative Torque Disruption (RAT-D) mechanism. I…
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…
Context. Red supergiant stars are one of the latest stages in the evolution of massive stars. Their photospheric convection may play an important role in the launching mechanism of their mass loss; however, its characteristics and dynamics are still poorly constrained. Aims. By observing red supergiant stars with near infrared interferometry at different epochs, we expect to reveal the evolution of bright convective features on their stellar surface. Methods. We observed the M2Iab-Ib red supergiant star CE Tau with the VLTI/PIONIER instrument in the H band at two different epochs separated by …
