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Pulsational Pair-Instability Supernova I: Pre-Collapse Evolution and Pulsation Shing-Chi Leung1, Ken’Ichi Nomoto1, Ming-Chung Chu3, Sergei Blinnikov1,21,2,3

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Pulsational Pair-Instability Supernova I: Pre-Collapse Evolution and Pulsation Shing-Chi Leung1, Ken’Ichi Nomoto1, Ming-Chung Chu3, Sergei Blinnikov1,21,2,3 Draft version June 15, 2018 Typeset using LATEX twocolumn style in AASTeX62 Pulsational Pair-Instability Supernova I: Pre-collapse Evolution and Pulsation Shing-Chi Leung1, Ken’ichi Nomoto1, Ming-Chung Chu3, Sergei Blinnikov1,21,2,3 11Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan 22Institute for Theoretical and Experimental Physics, Moscow, Russia 33Physics Department, the Chinese University of Hong Kong, Hong Kong S. A. R., China (Dated: June 15, 2018) ABSTRACT Pulsational Pair-Instability Supernova (PPISN) is the explosion of main-sequence stars of masses from 80 - 140 M⊙. The electron-positron pair production in the stellar core is believed to make strong contraction of the carbon-oxygen after the depletion of He core, which triggers the explosive O-burning and then enormous mass ejection. The ejected mass then becomes the circumstellar material around the star, which has strong optical effects when the star finally explodes as its core collapses. In this article we reexamine this idea by using the one-dimensional stellar evolution code MESA to model PPISN. Using the recent implicit hydrodynamics formalism we are able to follow the whole evolution from the main-sequence to the onset of collapse in single runs. We study the influence of metallicity on the progenitor. Then we examine in details the dynamical and chemical properties of pulsations as a function of He core mass. At last, we discuss its connection to superluminous supernova and to the massive black hole formation. 1. INTRODUCTION causes ejection of high velocity matter on the surface Stars with a progenitor mass 80 - 160 solar masses and dissipates the energy. After that, the core becomes have very distinctive paths of evolution compared to bounded again. The pulsation restarts after it has lost more massive or less massive stars. For more mas- most of its previously produced energy by radiation and 56 sive stars, they directly explode as pair-instability su- neutrinos. The whole process repeats until the Fe de- 56 pernovae (PISN); for less massive stars, they collapse cayed from Ni exceeds the Chandrasekhar mass that after the iron core of Chandrasekhar mass has been it collapses by its own gravity before the compression 16 formed. This class of stars experiences strong pulsations heating can reach the further outgoing O-rich enve- before their collapse, thus referred to as Pulsation Pair- lope. instability supernova (PPISN) in the literature. The The origin of massive star has been a matter of debate. pulsation phase occurs due to electron-positron pair in- One major uncertainty is the mass loss rate. For PPISN, stability (γ → e−+e+). The core is mostly supported by owing to its high luminosity during its H-burning main- the radiation pressure. With the catastrophe in pair pro- sequence phase, almost the whole hydrogen envelope is duction, the supporting pressure suddenly drops, where shed off before advanced burning takes place. In par- the core softens with corresponding equation of state ticular, for PPISN, the mass loss by stellar wind can adiabatic index γ < 4/3 in the core. However, unlike the contribute to more than half of the initial progenitor mass. Such mass loss can suppress the build up of the stars with 15 - 40 M⊙ which have rich iron cores at the moment of their collapse, in PPISN the core is mostly helium core, leaving a light He core instead. The ex- made of 16O when contraction starts. The softened core act mass of the He core as a function of metallicity allows a very strong contraction and the 16O-rich core and progenitor mass remains less well constrained com- can reach the explosive temperature which releases a pared to the hydrogen counterpart (Vink & de Koter large amount of energy, sufficient to unbind the star. 2002; Smith & Owocki 2006). 28Si and 56Ni can be produced during the contraction, The effects of pair-production induced instability have where the central temperature can reach beyond 109.5 been studied since a few decades ago, starting from the K. As a result, the star stops its contraction and starts treatise for pair-formation in massive stars and super- its expansion. The rapid expansion causes strong com- novae (Fowler & Hoyle 1964). The possibilities of pul- pression to the matter on the surface, which efficiently sation prior to its collapse in massive star is suggested 2 in Barkat et al. (1967). The evolution of unstable mas- their evolution scenario. As indicated in Woosley et al. sive He- and CO cores maintained by rotation can be (2007), the origin of 40 - 60 M⊙ He cores can be from found in Glatzel et al. (1985); Chatzopoulos & Wheeler stars about 95 − 130M⊙, which is the mass range of (2012). The optical aspect of pair-instability induced PPISN. Therefore, in order to study the mass spectrum pulsation and explosion is connected to super-luminous of BH in this mass range, the evolutionary path of this supernovae, such as SN2006gy (Woosley et al. 2007; class of objects becomes necessary. Kasen et al. 2011; Chen et al. 2014). In order to pin For these reasons, we want to re-examine the concept down the mass range of PPISN, a mass survey of main- of PPISN by using the open-source stellar evolution code sequence star models is done in Heger & Woosley (2002) MESA to study PPISN. We use the MESA code for two with focus on the zero metallicity stars. In Woosley reasons. First, its open-source nature allows future val- (2017) the hydrodynamics of PPISN pulsation is studied idation and confirmation from other users in the com- in details with further connection to the well observed munity. Second, the recent update of the MESA code Eta Carinae, which has demonstrated significant mass (Paxton et al. 2015) has included an implicit energy- loss about 30 M⊙ (Smith et al. 2007; Smith 2008). conserving (Grott et al. 2005) hydrodynamics scheme as Compared to pair-instability supernovae (PISN) one of its evolution option. Such dynamical treatment (Heger & Woosley 2002; Scammapieco et al. 2005; in the fluid motion can naturally address the dynami- Chatzopoulos et al. 2013; Chen et al. 2014), which are cal perspective of PPISN in the stellar evolution con- thermonuclear explosion of very massive stars, PPISN text, where conventionally hydrostatic approximation has received much less study in the literature. Woosley with acceleration correction is frequently used. (2017) is the first work extensively devoted to PPISN systematically using the KEPLER code. A series of 1.1. Structure main-sequence star models with masses from 70 - 140 In Section 2 we describe the code we use for prepar- M⊙ is studied. This corresponds to the helium core ing for the initial models and the details of the one- mass from ≈ 35 to 70M⊙. The pulsation history is ex- dimensional implicit hydrodynamics code for the pul- plored with a focus on the possible optical signals from sation phase. Then in Section 3 we present the pre- the pulsation. The connection to different subclasses in bounce stellar evolution and its thermodynamics prop- Type II supernova is also discussed. erties. We first present the pre-pulsation evolution of The pulsation of the PPISN is a dynamical phe- our models which include the He- and C- burning. Then nomenon. During the pulsation, the dynamical we study the dynamics of the pulsation and its effects timescale can be comparable with the nuclear timescale on the shock-induced mass loss. After that, we present that hydrostatic approximation is no longer a good ap- evolution models of He cores with 40 - 64 M⊙. We proximation. Also, when the star drastically expands examine their properties from four aspects, the thermo- after the energetic nuclear burning triggered at the con- dynamics, mass loss, energetic and chemical properties. traction, the subsequent shock breakout near the surface In Section 4 we refer to the connections of our models to is obviously a dynamical phenomenon. This suggests super-luminous progenitors. We then further study the that during this dynamical but short phase, hydrody- effects of some physical input in the numerical modeling, namics instead of hydrostatic is required in order to including the convective mixing and artificial viscosity. follow the evolution consistently. The expected neutrino detection rates by the existing Recent modelling of super-luminous supernovae and proposed neutrino detectors are discussed. At last PTF12dam (Tolstov et al. 2017) has required an ex- we conclude our results. plosion of 40 M⊙ star with 20-40 M⊙ circumstellar 56 medium (CSM) with a sum of 6 M⊙ Ni in the explo- 2. METHODS sion. The shape, rising time and fall rate of the light 2.1. Stellar Evolution curves provides constraints on the composition, density To prepare the pre-collapse model, we use the open and velocity of the ejecta, which provides insights to the source code Modules for Experiments in Stellar Astro- modeling of PPISN. It demonstrates the importance to physics (MESA) version 8118 (Paxton et al. 2015). It track the mass loss history of a star prior to its collapse. is an one-dimensional stellar evolution code with realis- Furthermore, recent detections of the gravitational tic microphysics input including the OPAL opacity ta- waves emitted by the merging of black holes (BH) ble. The modular structure of the code allows attach- (Abbott et al. 2016a,b), such as GW150914 imply ex- ing extra physics components to the main structure of istence of BHs of masses about 30 M⊙. This has led to the code. Recent updates of this code have also in- the interest of the origin of BHs in this mass range and cluded packages for stellar pulsation analysis and im- 3 plicit hydrodynamics extension with artificial viscosity.
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