Core helium burning primary red clump (RC) stars are evolved red giant stars which are excellent standard candles. As such, these stars are routinely used to map the Milky Way or determine the distance to other galaxies among other things. However distinguishing RC stars from their less evolved precursors, namely red giant branch (RGB) stars, is still a difficult challenge and has been deemed the domain of asteroseismology. In this work, we use a sample of 1,676 RGB and RC stars which have both single epoch infrared spectra from the APOGEE survey and asteroseismic parameters and classification to show that the spectra alone can be used to (1) predict asteroseismic parameters with precision high enough to (2) distinguish core helium burning RC from other giant stars with less than 2% contamination. This will not only allow for a clean selection of a large number of standard candles across our own and other galaxies from spectroscopic surveys, but also will remove one of the primary roadblocks for stellar evolution studies of mixing and mass loss in red giant stars.
We present preliminary results of an experimental study exploring helium at photospheric conditions of white dwarf stars. These data were collected at Sandia National Laboratories' Z-machine, the largest x-ray source on earth. Our helium results could have many applications ranging from validating current DB white dwarf model atmospheres to providing accurate He pressure shifts at varying temperatures and densities. In a much broader context, these helium data can be used to guide theoretical developments in new continuum-lowering models for two-electron atoms. We also discuss future applicati…
Theoretical predictions for the core helium burning phase of stellar evolution are highly sensitive to the uncertain treatment of mixing at convective boundaries. In the last few years, interest in constraining the uncertain structure of their deep interiors has been renewed by insights from asteroseismology. Recently, Spruit (2015) proposed a limit for the rate of growth of helium-burning convective cores based on the higher buoyancy of material ingested from outside the convective core. In this paper we test the implications of such a limit for stellar models with a range of initial mass and…
Stellar cores may be considered as a nuclear reactor that play important role in injecting new synthesized elements in the interstellar medium Helium burning is an important stage that contribute to the synthesis of key elements such as carbon, through the triple- α process, and oxygen. In the present paper, we introduce a computational method for the fractional model of the nuclear helium burning in stellar cores. The system of fractional differential equations is solved simultaneously using series expansion method. The calculations are performed in the sense of modified Riemann-Liouville fra…
Overshooting and semiconvection are among the most uncertainties in the evolution of massive stars. Complete mixing over a certain distance beyond the convective boundary (Stothers \& Chin 1985) and an exponentially decaying diffusion outside the convection zone (Herwig 2000) are commonly adopted for the overshoot mixing. Recently, Li (2012, 2017) developed the $k$-$ω$ model, which can be used in both convection zones and overshooting regions. We incorporated it in calculations of $30M_{\odot}$ stellar models. We find that in the main sequence stage, models with the $k$-$ω$ model are almost id…
Transport of angular momentum has been a challenging topic within the stellar evolution community, even more since the recent asteroseismic surveys. All published studies on rotation using asteroseismic observations show a discrepancy between the observed and calculated rotation rates, indicating there is an undetermined process of angular momentum transport active in these stars. We aim to constrain the efficiency of this process by investigating rotation rates of 2.5 M$_{\odot}$ stars. First, we investigated whether the Tayler-Spruit dynamo could be responsible for the extra transport of ang…
We explore the question of whether the interior state of massive red supergiant supernova progenitors can be effectively probed with asteroseismology. We have computed a suite of ten models with ZAMS masses from 15 to 25 m_sun in intervals of 1 m_sun, including the effects of rotation, with the stellar evolutionary code MESA. We estimate characteristic frequencies and convective luminosities of convective zones at two illustrative stages, core helium burning and off-center convective carbon burning. We also estimate the power that might be delivered to the surface to modulate the luminous outp…
Extra modes in helium-core-burning stars probing an infra core cavity
Université PSL（巴黎文理研究大学）；CNRS（法国国家科学研究中心）；Sorbonne Université（索邦大学）；Université Paris Cité（巴黎西岱大学）；CY Cergy Paris Université（塞吉-巴黎大学）；The University of Tokyo（东京大学）；Université Paris-Saclay（巴黎萨克雷大学）；Universidade do Porto（波尔图大学）；Université Côte d’Azur（蔚蓝海岸大学）；Université de Toulouse（图卢兹大学）；University of Bologna（博洛尼亚大学）
Red Clump stars have been found to be enhanced in lithium relative to stars at the tip of the Red Giant Branch (TRGB), which is unexpected in current stellar models. At the TRGB, stars undergo the helium flash, during which helium burning briefly generates roughly $10^9 \, L_\odot$ of power and drives vigorous convection within the star's core. The helium-burning shell excites large fluxes of internal gravity waves. Here we investigate whether or not these waves can deposit enough heat to destabilize the hydrogen-burning shell, generate a convection zone there, and thereby drive the Cameron-Fo…
Stars between two and three solar masses rotate rapidly on the main sequence, and the detection of slow core and surface rotation in the core-helium burning phase for these stars places strong constraints on their angular momentum transport and loss. From a detailed asteroseismic study of the mixed-dipole mode pattern in a carefully selected, representative sample of stars, we find that slow core rotation rates in the range reported by prior studies are a general phenomenon and not a selection effect. We show that the core rotation rates of these stars decline strongly with decreasing surface …
Blue large-amplitude pulsators (BLAPs) are a newly discovered type of variable star. Their typical pulsation periods are on the order of a few tens of minutes, with relatively large amplitudes of 0.2-0.4 mag in optical bands, and their rates of period changes are on the order of $10^{-7} yr^{-1}$ (both positive and negative). They are extremely rare objects and attempts to explain their origins and internal structures have attracted a great deal of attention. Previous studies have proposed that BLAPs may be pre-white dwarfs, with masses around $0.3M_\odot$, or core-helium-burning stars in the …
A Helium-shell Burning Blue Horizontal Branch Star Produced from Common Envelope Evolution
Yunnan Observatories, Chinese Academy of Sciences（中国科学院云南天文台）；National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Hebei Normal University（河北师范大学）
Asteroseismology of non-radial pulsations in Hot B Subdwarfs (sdB stars) offers a unique view into the interior of core-helium-burning stars. Ground-based and space-borne high precision light curves allow for the analysis of pressure and gravity mode pulsations to probe the structure of sdB stars deep into the convective core. As such asteroseismological analysis provides an excellent opportunity to test our understanding of stellar evolution. In light of the newest constraints from asteroseismology of sdB and red clump stars, standard approaches of convective mixing in 1D stellar evolution mo…
Shaping the horizontal branch: The role of envelope mass in the evolution of stripped core-helium-burning stars
Instituto de Física y Astronomía, Universidad de Valparaíso（瓦尔帕莱索大学物理与天文学研究所）；School of Physics and Astronomy, Monash University（蒙纳士大学物理与天文学院）；Australian Research Council Centre of Excellence for Gravitational Wave Discovery（澳大利亚研究委员会引力波发现卓越中心）
CHARA Interferometry and TESS Asteroseismology of the Core-Helium Burning Red Giant $κ$ Cyg
Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院天体物理研究所）；Institute for Astronomy, University of Hawai‘i（夏威夷大学天文研究所）；Sydney Informatics Hub, Core Research Facilities, University of Sydney（悉尼大学核心研究设施悉尼信息学中心）
Stars between two and three solar masses rotate rapidly on the main sequence, and their rotation rates in the core helium burning (secondary clump) phase can therefore be used to test models of angular momentum loss used for gyrochronology in a new regime. Because both their core and surface rotation rates can be measured, these stars can also be used to set strong constraints on angular momentum transport inside stars. We find that they are rotating slower than angular momentum conservation and rigid rotation would predict. Our results are insensitive to the degree of core-envelope coupling b…
Accretion-induced collapse (AIC) occurs when an O/Ne white dwarf (WD) grows to nearly the Chandrasekhar mass ($M_{\rm Ch}$), reaching central densities that trigger electron captures in the core. Using Modules for Experiments in Stellar Astrophysics ($\texttt{MESA}$), we present the first true binary simulations of He star + O/Ne WD binaries, focusing on a $1.5 M_\odot$ He star in a 3 hour orbital period with $1.1-1.3 M_\odot$ O/Ne WDs. The helium star fills its Roche lobe after core helium burning is completed and donates helium on its thermal timescale to the WD, $\dot{M}\approx3\times10^{-6…
A star expands to become a red giant when it has fused all the hydrogen in its core into helium. If the star is in a binary system, its envelope can overflow onto its companion or be ejected into space, leaving a hot core and potentially forming a subdwarf-B star. However, most red giants that have partially transferred envelopes in this way remain cool on the surface and are almost indistinguishable from those that have not. Among $\sim$7000 helium-burning red giants observed by NASA's Kepler mission, we use asteroseismology to identify two classes of stars that must have undergone dramatic m…
We have used effective reaction rates (ERR) for the helium burning reactions to predict the yield of the gamma-emitting nuclei 26Al, 44Ti, and 60Fe in core col- lapse supernovae. The variations in the predicted yields for values of the reaction rates allowed by the ERR are much smaller than obtained previously, and smaller than other uncertainties. A "filter" for supernova nucleosynthesis yields based on pre-supernova structure was used to estimate the effect of failed supernovae on the initial mass function-averaged yields; this substantially reduced the yields of all these isotopes, but the …
The treatment of convective boundaries during core helium burning is a fundamental problem in stellar evolution calculations. In Paper~I we showed that new asteroseismic observations of these stars imply they have either very large convective cores or semiconvection/partially mixed zones that trap g-modes. We probe this mixing by inferring the relative lifetimes of asymptotic giant branch (AGB) and horizontal branch (HB) from $R_2$, the observed ratio of these stars in recent HST photometry of 48 Galactic globular clusters. Our new determinations of $R_2$ are more self-consistent than those of…
The CEMP-no stars are long-lived small mass stars presenting a very low iron content and overabundances of carbon with no sign or only very weak signs for the presence of s- or r-elements. Although the origin of that abundance pattern is still a matter of debate, it was very likely inherited from a previous massive star, that we shall call here the source star. We rely on a recent classification of CEMP-no stars arguing that some of them are made of a material processed by hydrogen burning that was enriched in products of helium burning during the nuclear life of the source star. We examine th…
The evolution of helium stars with initial masses in the range 1.6 to 120 Msun is studied, including the effects of mass loss by winds. These stars are assumed to form in binary systems when their expanding hydrogenic envelopes are promptly lost just after helium ignition. Significant differences are found with single star evolution, chiefly because the helium core loses mass during helium burning rather than gaining it from hydrogen shell burning. Consequently presupernova stars for a given initial mass function have considerably smaller mass when they die and will be easier to explode. Even …
Stars on the ascending helium giant branch I. From white dwarf merger to helium giant: the evolutionary state of the rapidly rotating hot subdwarf HE 1518-0948
Universität Potsdam（波茨坦大学）；Instituto de Astrofísica de La Plata, Consejo Nacional de Investigaciones Científicas y Técnicas（拉普拉塔天体物理研究所，国家科学研究委员会）；Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata（拉普拉塔国立大学天文与地球科学学院）；Hamburger Sternwarte, University of Hamburg（汉堡大学汉堡天文台）
通过光谱分析研究极端富氦热亚矮星 HE 1518-0948，发现其是双氦白矮星并合产物，目前处于氦壳燃烧并沿氦巨星分支上升阶段，为理解大质量热亚矮星在核心氦燃烧后的演化提供了重要实验室。
Temperature-resolved sensitivities of $^{56}{\rm Ni}$ production to helium-burning reactions in pair-instability supernovae
The University of Tokyo（东京大学）；RIKEN Nishina Center for Accelerator-Based Science, RIKEN（理化学研究所加速器科学研究中心）；Kogakuin University（工学馆大学）；Center for Nuclear Study, The University of Tokyo（东京大学核研究分中心）；Astrophysical Big-Bang Laboratory, Pioneering Research Institute, RIKEN（理化学研究所先驱研究院天体大爆炸实验室）；Yukawa Institute for Theoretical Physics (YITP), Kyoto University（京都大学汤川理论物理研究所）
Abundance Calculations of Neon Isotopes in the Predicted Lifetime of the Sun
University of Sharjah（沙迦大学）；Sharjah Academy for Astronomy, Space Sciences and Technology（沙迦天文学、空间科学与技术学院）；Arab Union for Astronomy and Space Sciences（阿拉伯天文学与空间科学联盟）；The University of Jordan（约旦大学）
Context. Metal-poor massive stars are supposed to be progenitors of certain supernovae, gamma-ray bursts and compact object mergers, potentially contributing to the early epochs of the Universe with their strong ionizing radiation. However, they remain mainly theoretical as individual spectroscopic observations of such objects have rarely been carried out below the metallicity of the SMC. Aims. This work aims at exploring what our state-of-the-art theories of stellar evolution combined with those of stellar atmospheres predict about a certain type of metal-poor (0.02 Z$_{\odot}$) hot massive s…
The evolutionary calculations for population I stars with masses on the main sequence 5 M_\odot <= M_0 <= 6.1 M_\odot and initial fractional abundances of helium Y_0=0.28 and heavier elements Z_0=0.02 were carried out to the stage of central helium exhaustion. Selected core helium--burning models were used as initial conditions for solution of the equations of hydrodynamics and time--dependent convection describing radial pulsations of Cepheids. In the Hertzsprung--Russel diagram the evolutionary tracks are shown to cross the red edge of the instability strip for M_0 > 5.1M_\odot. The grid of …
We evolve stellar models to study the common envelope (CE) interaction of an early asymptotic giant branch star of initial mass $5\,\rm M_{\odot}$ with a companion star of mass ranging from $0.1$ to $2\,\rm M_{\odot}$. We model the CE as a fast stripping phase in which the primary experiences rapid mass loss and loses about 80 per cent of its mass. The post-CE remnant is then allowed to thermally readjust during a Roche-lobe overflow (RLOF) phase and the final binary system and its orbital period are investigated. We find that the post-CE RLOF phase is long enough to allow nuclear burning to p…
White dwarfs accreting from helium stars can stably burn at the accreted rate and avoid the challenge of mass loss associated with unstable Helium burning that is a concern for many Type Ia supernovae scenarios. We study binaries with helium stars of mass $1.25 M_\odot\le M_{\rm{He}} \le 1.8 M_\odot$, which have lost their hydrogen rich envelopes in an earlier common envelope event and now orbit with periods ($P_{\rm orb}$) of several hours with non-rotating $0.84$ and $1.0 M_\odot$ C/O WDs. The helium stars fill their Roche lobes (RLs) after exhaustion of central helium and donate helium on t…
