後期スペクトルを軸とした超新星の親星進化と爆発機構の解明

京都大学新制・課程博士博士(理学)甲第24419号理博第4918号新制||理||1702(附属図書館)京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 前田 啓一, 講師 LEE Shiu Hang, 教授 太田 耕司学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDFA

Age spreads and the temperature dependence of age estimates in Upper Sco

Past estimates for the age of the Upper Sco Association are typically 11-13 Myr for intermediate-mass stars and 4-5 Myr for low-mass stars. In this study, we simulate populations of young stars to investigate whether this apparent dependence of estimated age on spectral type may be explained by the star formation history of the association. Solar and intermediate mass stars begin their pre-main sequence evolution on the Hayashi track, with fully convective interiors and cool photospheres. Intermediate mass stars quickly heat up and transition onto the radiative Henyey track. As a consequence, for clusters in which star formation occurs on a similar timescale as the transition from a convective to a radiative interior, discrepancies in ages will arise when ages are calculated as a function of temperature instead of mass. Simple simulations of a cluster with constant star formation over several Myr may explain about half of the difference in inferred ages versus photospheric temperature; speculative constructions that consist of a constant star formation followed by a large supernova-driven burst could fully explain the differences, including those between F and G stars where evolutionary tracks may be more accurate. The age spreads of low-mass stars predicted from these prescriptions for star formation are consistent with the observed luminosity spread of Upper Sco. The conclusion that a lengthy star formation history will yield a temperature dependence in ages is expected from the basic physics of pre-main sequence evolution and is qualitatively robust to the large uncertainties in pre-main sequence evolutionary models.Comment: 13 pages, accepted by Ap

Inferring the Progenitor Mass-Kinetic Energy Relation of Stripped-envelope Core-collapse Supernovae from Nebular Spectroscopy

The relation between the progenitor mass and the kinetic energy of the explosion is a key toward revealing the explosion mechanism of stripped-envelope core-collapse supernovae (SESNe). Here, we present a method to derive this relation using the nebular spectra of SESNe, based on the correlation between [O i]/[Ca ii], which is an indicator of progenitor mass, and the width of [O i], which measures the expansion velocity of the oxygen-rich material. To explain the correlation, the kinetic energy (EK) is required to be positively correlated with the progenitor mass as represented by the CO core mass (MCO). We demonstrate that SNe IIb/Ib and SNe Ic/Ic-BL follow the same MCO–EK scaling relation, which suggests that helium-rich and helium-deficient SNe share the same explosion mechanism. The MCO–EK relation derived in this work is compared with the ones derived from early phase observations. The results are largely in good agreement. Combined with early phase observations, the method presented in this work provides a chance to scan through the ejecta from the outermost region to the dense inner core, which is important to reveal the global properties of the ejecta and constrain the explosion mechanism of core-collapse SNe

The low-mass population in the young cluster Stock 8: Stellar properties and Initial Mass Function

The evolution of HII regions/supershells can trigger a new generation of stars/clusters at their peripheries, with environmental conditions that may affect the initial mass function, disk evolution and star formation efficiency. In this paper we study the stellar content and star formation processes in the young cluster Stock 8, which itself is thought to be formed during the expansion of a supershell. We present deep optical photometry along with JHK and 3.6, 4.5 {\mu}m photometry from UKIDSS and Spitzer-IRAC. We use multi-color criteria to identify the candidate young stellar objects in the region. Using evolutionary models, we obtain a median log(age) of ~6.5 (~3.0 Myr) with an observed age spread of ~0.25 dex for the cluster. Monte Carlo simulations of the population of Stock 8, based on estimates for the photometric uncertainty, differential reddening, binarity, and variability, indicate that these uncertainties introduce an age spread of ~0.15 dex. The intrinsic age spread in the cluster is ~0.2 dex. The fraction of young stellar objects surrounded by disk is ~35%. The K-band luminosity function of Stock 8 is similar to that of the Trapezium cluster. The IMF of Stock 8 has a Salpeter- like slope at >0.5 Msun and the IMF flattens and peaks at ~0.4 Msun, below which declines into the substellar regime. Although Stock 8 is surrounded by several massive stars, there seems to be no severe environmental effect in the form of IMF due to the proximity of massive stars around the cluster.Comment: Accepted for publication in Ap

An aspherical distribution for the explosive burning ash of core-collapse supernovae

It is widely believed that asphericity in the explosion is the crucial ingredient leading to successful core-collapse (CC) supernovae. However, direct observational evidence for the explosion geometry and for the connection with the progenitor properties are still missing. Based on the thus-far largest late-phase spectroscopic sample of stripped-envelope CC supernovae, we demonstrate that about half of the explosions exhibit a substantial deviation from sphericity. For these aspherical CC supernovae, the spatial distributions of the oxygen-burning ash and the unburnt oxygen, as traced by the profiles of [Ca II] {\lambda}{\lambda}7291,7323 and [O i] {\lambda}{\lambda}6300,6363 emissions, respectively, appear to be anticorrelated, which can be explained if the explosion is bipolar and the oxygen-rich material burnt into two detached iron-rich bubbles. Our combined analysis of the explosion geometry and the progenitor mass further suggests that the degree of asphericity grows with the mass of the carbon-oxygen core, which may be used to guide state-of-the-art simulations of CC supernova explosions.Comment: Author version of paper published in Nature Astronomy on Oct 26th 2023; DOI:10.1038/s41550-023-02120-

Prolonged post-rift magmatism on highly extended crust of divergent continental margins (Baiyun Sag, South China Sea)

Three-dimensional (3D) seismic, borehole and geochemical data reveal a prolonged phase of post-rift magmatism on highly extended crust of the Baiyun Sag, South China Sea. Two volcanic complexes are identified and described in the context of continental rifting and diachronous continental breakup of the South China Sea. Biostratigraphic data from exploration wells BY7-1 and BY2, complemented by K–Ar datings from core samples, confirm that magmatic activity in the Baiyun Sag occurred in two main stages: (1) a first episode at the base of the Miocene (23.8 Ma); and (2) a second episode occurring at the end of the Early Miocene (17.6 Ma). The relative location of volcanic complexes in the Baiyun Sag, and their stratigraphic position, reveals prolonged magmatism inboard of the ocean–continent transition zone during continental breakup. We suggest that magmatism in the Baiyun Sag reflects progressive continental breakup in the South China Sea, with the last volcanic episode marking the end of a breakup sequence representing the early post-rift tectonic events associated with the continental breakup process. Seismic and borehole data from this breakup sequence records diachronous magma emplacement and complex changes in depositional environments during continental breakup

Statistical Properties of the Nebular Spectra of 103 Stripped-envelope Core-collapse Supernovae

We present an analysis of the nebular spectra of 103 stripped-envelope (SE) supernovae (SNe) collected from the literature and observed with the Subaru Telescope from 2002 to 2012, focusing on [O i] λλ6300, 6363. The line profile and width of [O i] are employed to infer the ejecta geometry and the expansion velocity of the inner core; these two measurements are then compared with the SN subtypes, and further with the [O i]/[Ca ii] ratio, which is used as an indicator of the progenitor CO core mass. Based on the best-fit results of the [O i] profile, the objects are classified into different morphological groups, and we conclude that the deviation from spherical symmetry is a common feature for all types of SESNe. There is a hint (at the ∼1σ level) that the distributions of the line profile fractions are different between canonical SESNe and broad-line SNe Ic. A correlation between [O i] width and [O i]/[Ca ii] is discerned, indicating that the oxygen-rich material tends to expand faster for objects with a more massive CO core. Such a correlation can be utilized to constrain the relation between the progenitor mass and the kinetic energy of the explosion. Further, when [O i]/[Ca ii] increases, the fraction of objects with Gaussian [O i] profile increases, while those with double-peaked profile decreases. This phenomenon connects ejecta geometry and the progenitor CO core mass

Statistical Properties of the Nebular Spectra of 103 Stripped-envelope Core-collapse Supernovae*

We present an analysis of the nebular spectra of 103 stripped-envelope (SE) supernovae (SNe) collected from the literature and observed with the Subaru Telescope from 2002 to 2012, focusing on [O i] lambda lambda 6300, 6363. The line profile and width of [O i] are employed to infer the ejecta geometry and the expansion velocity of the inner core; these two measurements are then compared with the SN subtypes, and further with the [O i]/[Ca ii] ratio, which is used as an indicator of the progenitor CO core mass. Based on the best-fit results of the [O i] profile, the objects are classified into different morphological groups, and we conclude that the deviation from spherical symmetry is a common feature for all types of SESNe. There is a hint (at the similar to 1 sigma level) that the distributions of the line profile fractions are different between canonical SESNe and broad-line SNe Ic. A correlation between [O i] width and [O i]/[Ca ii] is discerned, indicating that the oxygen-rich material tends to expand faster for objects with a more massive CO core. Such a correlation can be utilized to constrain the relation between the progenitor mass and the kinetic energy of the explosion. Further, when [O i]/[Ca ii] increases, the fraction of objects with Gaussian [O i] profile increases, while those with double-peaked profile decreases. This phenomenon connects ejecta geometry and the progenitor CO core mass