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1
المؤلفون: Wako Aoki, Timothy C Beers, Satoshi Honda, Hiroyuki T Ishikawa, Tadafumi Matsuno, Vinicius M Placco, Jinmi Yoon, Hiroki Harakawa, Teruyuki Hirano, Klaus Hodapp, Masato Ishizuka, Shane Jacobson, Takayuki Kotani, Tomoyuki Kudo, Takashi Kurokawa, Masayuki Kuzuhara, Jun Nishikawa, Masashi Omiya, Takuma Serizawa, Motohide Tamura, Akitoshi Ueda, Sébastien Vievard
المساهمون: Astronomy
المصدر: Publications of the Astronomical Society of Japan, 74(2), 273-282. Oxford University Press
مصطلحات موضوعية: stars: abundances, abundances, FOS: Physical sciences, nucleosynthesis, stars: Population II, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), nuclear reactions
الوصف: Silicon and Strontium are key elements to explore the nucleosynthesis and chemical evolution of the Galaxy by measurements of very metal-poor stars. There are, however, only a few useful spectral lines of these elements in the optical range that are measurable for such low-metallicity stars. Here we report on abundances of these two elements determined from near-infrared high-resolution spectra obtained with the Subaru Telescope Infrared Doppler instrument (IRD). Si abundances are determined for as many as 26 Si lines for six very and extremely metal-poor stars (-4.0
Comment: 3 figures, 6 tables, PASJ, in pressوصف الملف: application/pdf
URL الوصول: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::05c8596b53ba4967c4923d4c98c55530
https://doi.org/10.1093/pasj/psab123 -
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المؤلفون: Wako Aoki, Tadafumi Matsuno, Mudumba Parthasarathy
المساهمون: Astronomy
المصدر: Publications of the Astronomical Society of Japan, 74, 1368-1377. Oxford University Press
مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), stars: distances, FOS: Physical sciences, Astronomy and Astrophysics, stars: AGB and post-AGB, stars: evolution, Astrophysics - Astrophysics of Galaxies, Solar and Stellar Astrophysics (astro-ph.SR)
الوصف: Using the Gaia DR2 and EDR3 data and list of post-AGB candidates, we investigate the parallax, proper motion and binarity for twenty post-AGB stars and candidates having high radial velocities. From their Gaia distances their luminosities and kinematics are derived. The evolutionary status of these stars is discussed from their location on the post-AGB evolutionary tracks. Nine stars are confirmed to be post-AGB stars that have their initial main-sequence mass around one or two solar masses. From their kinematics information, two objects among them are identified to clearly belong to the halo population, suggesting that low-mass. We discuss on the origin and evolutionary status of other objects in the sample of this work with high radial velocities.
18 pages, 2 figures, 3 tables, to appear in PASJوصف الملف: application/pdf
URL الوصول: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::35ff5640701f8ec7cab01770b2d0c7d1
https://research.rug.nl/en/publications/434f99e0-4207-46db-923d-65d240311cb1 -
3
المؤلفون: Tadafumi Matsuno, Emma Dodd, Helmer H. Koppelman, Amina Helmi, Miho N. Ishigaki, Wako Aoki, Jingkun Zhao, Zhen Yuan, Kohei Hattori
المساهمون: Kapteyn Astronomical Institute, Astronomy
المصدر: Astronomy and astrophysics, 665:A46. EDP Sciences
مصطلحات موضوعية: Galaxy: stellar content, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Stars: abundances, FOS: Physical sciences, Galaxy: abundances, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies, Solar and Stellar Astrophysics (astro-ph.SR), Galaxy: halo
الوصف: Context: The Helmi streams are a kinematic substructure whose progenitor is likely a dwarf galaxy. Although 20 years have passed since their discovery, it is still unclear whether their members are chemically distinguishable from other halo stars in the Milky Way. Aim: We aim to precisely characterize the chemical properties of the Helmi streams. Methods: We analyzed high-resolution, high signal-to-noise ratio spectra for 11 Helmi stream stars through a line-by-line abundance analysis. We compared the derived abundances to homogenized literature abundances of the other halo stars, including those belonging to other kinematic substructures, such as Gaia-Enceladus and Sequoia. Results: Compared to typical halo stars, the Helmi stream members clearly show low values of [X/Fe] in elements produced by massive stars, such as Na and $\alpha$-elements. This tendency is seen down to metallicities of at least [Fe/H]$\sim -2.2$, suggesting type~Ia supernovae already started to contribute to the chemical evolution at this metallicity. We find that the [$\alpha$/Fe] ratio does not evolve significantly with metallicity, making the Helmi stream stars less distinguishable from Gaia-Enceladus stars at [Fe/H]$\gtrsim -1.5$. The almost constant but low value of [$\alpha$/Fe] might be indicative of quiescent star formation with low efficiency at the beginning and bursty star formation at later times. We also find extremely low values of [Y/Fe] at low metallicity, providing further support for the claim that light neutron-capture elements are deficient in Helmi streams. While Zn is deficient at low metallicity, it shows a large spread at high metallicity. The origin of the extremely low Y abundances and Zn variations remains unclear. Conclusion: The Helmi stream stars are distinguishable from the majority of the halo stars if homogeneously derived abundances are compared.
Comment: Accepted versionوصف الملف: application/pdf
URL الوصول: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::21297703dd04680383cfd5dce9272793
https://research.rug.nl/en/publications/529da96b-de17-437b-b16d-74028bf0c0b2 -
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المؤلفون: Haining Li, Wako Aoki, Tadafumi Matsuno, Qianfan Xing, Takuma Suda, Nozomu Tominaga, Yuqin Chen, Satoshi Honda, Miho N. Ishigaki, Jianrong Shi, Jingkun Zhao, Gang Zhao
المساهمون: Astronomy
المصدر: Astrophysical Journal, 931(2):147. IOP PUBLISHING LTD
مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies, Solar and Stellar Astrophysics (astro-ph.SR)
الوصف: We present homogeneous abundance analysis of over 20 elements for 385 very metal-poor (VMP) stars based on the LAMOST survey and follow-up observations with the Subaru Telescope. It is the largest high-resolution VMP sample (including 363 new objects) studied by a single program, and the first attempt to accurately determine evolutionary stages for such a large sample based on Gaia parallaxes. The sample covers a wide metallicity range from [Fe/H]=-1.7 down to [Fe/H]=-4.3, including over 110 objects with [Fe/H] 0.7) is in the range of 20-30% for turn-off stars depending on the treatment of objects for which C abundance is not determined, which is much higher than that in giants (~8%). Twelve Mg-poor stars ([Mg/Fe] < 0.0) have been identified in a wide metallicity range from [Fe/H] =-3.8 through -1.7. Twelve Eu-rich stars ([Eu/Fe]> 1.0) have been discovered in -3.4
66 pages, 28 figure, 8 tables, to appear in ApJوصف الملف: application/pdf
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المؤلفون: Tadafumi Matsuno, Helmer H. Koppelman, Amina Helmi, Wako Aoki, Miho N. Ishigaki, Takuma Suda, Zhen Yuan, Kohei Hattori
المساهمون: Astronomy
المصدر: Astronomy and astrophysics, 661:A103. EDP Sciences
مصطلحات موضوعية: Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Stars: abundances, FOS: Physical sciences, Galaxy: abundances, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies, Galaxy: halo
الوصف: Context: Sequoia is a retrograde kinematic substructure in the nearby Galactic halo, whose properties are a matter of debate. For example, previous studies do not necessarily agree on the chemical abundances of Sequoia stars, which are important for understanding its nature. Aim: We characterize the chemical properties of a sample of stars from Sequoia by determining high-precision abundances. Methods: We measured abundances of Na, Mg, Si, Ca, Ti, Cr, Mn, Ni, Zn, Y, and Ba from a differential abundance analysis on high signal-to-noise ratio, high-resolution spectra from new observations and from archival data. We compared precisely measured chemical abundances of 12 Sequoia candidates with those of typical halo stars from the literature, which also includes stars from Gaia-Enceladus. This allowed us to characterize Sequoia and compare it to another Galactic building block. The comparison was made after putting all the abundances onto the same scale using standard stars. Results: There are significant differences in [Na/Fe], [Mg/Fe], [Ca/Fe], [Ti/Fe], [Zn/Fe], and [Y/Fe] between Sequoia and Gaia-Enceladus stars at $-1.8\lesssim [\mathrm{Fe/H}]\lesssim -1.4$ in the sense that these abundance ratios are lower in Sequoia. These differences are similar to those seen between Gaia-Enceladus and in situ stars at a higher metallicity, suggesting that Sequoia is affected by type~Ia supernovae at a lower metallicity than Gaia-Enceladus. We also confirm that the low [{Mg}/{Fe}] of Sequoia is seen in the literature and in surveys, namely APOGEE DR17 and GALAH DR3, if the stars are kinematically selected in the same way. Conclusion: Sequoia stars have a distinct chemical abundance pattern and can be chemically separated from in situ stars or Gaia-Enceladus stars if abundances are measured with sufficient precision, namely $\sigma([\mathrm{X/Fe}])\lesssim 0.07\,\mathrm{dex}$.
Comment: Accepted versionوصف الملف: application/pdf
URL الوصول: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::4d19482ce21ccfce7bd51cb010e27ea1
https://research.rug.nl/en/publications/f1db4e7e-414a-4070-826b-ea0df4fdd62f -
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المؤلفون: Yutaka Hirai, Timothy C Beers, Masashi Chiba, Wako Aoki, Derek Shank, Takayuki R Saitoh, Takashi Okamoto, Junichiro Makino
مصطلحات موضوعية: High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies, Solar and Stellar Astrophysics (astro-ph.SR)
الوصف: The $r$-process-enhanced (RPE) stars provide fossil records of the assembly history of the Milky Way and the nucleosynthesis of the heaviest elements. Observations by the $R$-Process Alliance (RPA) and others have confirmed that many RPE stars are associated with chemo-dynamically tagged groups, which likely came from accreted dwarf galaxies of the Milky Way (MW). However, we do not know how RPE stars are formed. Here, we present the result of a cosmological zoom-in simulation of an MW-like galaxy with $r$-process enrichment, performed with the highest resolution in both time and mass. Thanks to this advancement, unlike previous simulations, we find that most highly RPE ($r$-II; [Eu/Fe] $> +0.7$) stars are formed in low-mass dwarf galaxies that have been enriched in $r$-process elements for [Fe/H] $\
20 pages, 15 figures, published in MNRASURL الوصول: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::fad1c8fe31fafbced438216aa027bf9e
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المؤلفون: Hiroki Harakawa, Takuya Takarada, Yui Kasagi, Teruyuki Hirano, Takayuki Kotani, Masayuki Kuzuhara, Masashi Omiya, Hajime Kawahara, Akihiko Fukui, Yasunori Hori, Hiroyuki Tako Ishikawa, Masahiro Ogihara, John Livingston, Timothy D Brandt, Thayne Currie, Wako Aoki, Charles A Beichman, Thomas Henning, Klaus Hodapp, Masato Ishizuka, Hideyuki Izumiura, Shane Jacobson, Markus Janson, Eiji Kambe, Takanori Kodama, Eiichiro Kokubo, Mihoko Konishi, Vigneshwaran Krishnamurthy, Tomoyuki Kudo, Takashi Kurokawa, Nobuhiko Kusakabe, Jungmi Kwon, Yuji Matsumoto, Michael W McElwain, Koyu Mitsui, Takao Nakagawa, Norio Narita, Jun Nishikawa, Stevanus K Nugroho, Eugene Serabyn, Takuma Serizawa, Aoi Takahashi, Akitoshi Ueda, Taichi Uyama, Sébastien Vievard, Ji Wang, John Wisniewski, Motohide Tamura, Bun’ei Sato
مصطلحات موضوعية: Earth and Planetary Astrophysics (astro-ph.EP), Space and Planetary Science, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - Earth and Planetary Astrophysics
الوصف: We report the near-infrared radial-velocity (RV) discovery of a super-Earth planet on a 10.77-day orbit around the M4.5 dwarf Ross 508 ($J_\mathrm{mag}=9.1$). Using precision RVs from the Subaru Telescope IRD (InfraRed Doppler) instrument, we derive a semi-amplitude of $3.92^{+0.60}_{-0.58}$ ${\rm m\,s}^{-1}$, corresponding to a planet with a minimum mass $m \sin i = 4.00^{+0.53}_{-0.55}\ M_{\oplus}$. We find no evidence of significant signals at the detected period in spectroscopic stellar activity indicators or MEarth photometry. The planet, Ross 508 b, has a semimajor-axis of $0.05366^{+0.00056}_{-0.00049}$ au. This gives an orbit-averaged insolation of $\approx$1.4 times the Earth's value, placing Ross 508 b near the inner edge of its star's habitable zone. We have explored the possibility that the planet has a high eccentricity and its host is accompanied by an additional unconfirmed companion on a wide orbit. Our discovery demonstrates that the near-infrared RV search can play a crucial role to find a low-mass planet around cool M dwarfs like Ross 508.
Comment: Accepted for publication in PASJ (May 23, 2022)وصف الملف: application/pdf
URL الوصول: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::7ad5d76e7e553e48e1c87d6a72ebdaae
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المؤلفون: Wako Aoki, Haining Li, Tadafumi Matsuno, Qianfan Xing, Yuqin Chen, Norbert Christlieb, Satoshi Honda, Miho N. Ishigaki, Jianrong Shi, Takuma Suda, Nozomu Tominaga, Hong-Liang Yan, Jingkun Zhao, Gang Zhao
المساهمون: Astronomy
المصدر: Astrophysical Journal, 931(2):146. IOP PUBLISHING LTD
مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics::Solar and Stellar Astrophysics, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR)
الوصف: The chemical abundances of very metal-poor stars provide important constraints on the nucleosynthesis of the first generation of stars and early chemical evolution of the Galaxy. We have obtained high-resolution spectra with the Subaru Telescope for candidates of very metal-poor stars selected with a large survey of Galactic stars carried out with LAMOST. In this series of papers, we report on the elemental abundances of about 400 very metal-poor stars and discuss the kinematics of the sample obtained by combining the radial velocities measured in this study and recent astrometry obtained with Gaia. This paper provides an overview of our survey and follow-up program, and reports radial velocities for the whole sample. We identify seven double-lined spectroscopic binaries from our high-resolution spectra, for which radial velocities of the components are reported. We discuss the frequency of such relatively short-period binaries at very low metallicity.
Comment: 24 pages, 9 figures, 5 tables, to appear in ApJوصف الملف: application/pdf
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المؤلفون: Yerra Bharat Kumar, B. E. Reddy, Wako Aoki, Raghubar Singh
المصدر: Monthly Notices of the Royal Astronomical Society. 491:3838-3843
مصطلحات موضوعية: Physics, Field (physics), 010308 nuclear & particles physics, Star (game theory), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, 01 natural sciences, Spectral line, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, 0103 physical sciences, Low Mass, 010303 astronomy & astrophysics, Red clump, Solar and Stellar Astrophysics (astro-ph.SR), Line (formation)
الوصف: Given the implications for the origin of Li enhancement in red giants we have reviewed Li-rich classification of KIC~9821622, the only bonafide RGB giant with He inert-core till date, reported as a Li-rich giant by reanalyzing the high-resolution spectra. We have obtained $A(Li)_{LTE} = 1.42 \pm 0.05$ dex. After correcting for non-LTE it is $A(Li)_{NLTE} = 1.57 \pm 0.05 $ dex which is significantly less than the reported A(Li) = $1.80 \pm 0.2$~dex. We found the sub-ordinate line at 6103 \AA\ is too weak or absent to measure Li abundance. The derived abundance is normal for red giants undergoing dilution during the 1st dredge-up. Since all the known Kepler field Li-rich giants belong to the red clump region, this clarification removes the anomaly and strengthens the evidence that the Li enhancement in low mass giants may be associated only with the He-core burning phase. The Li excess origin, probably, lies during He-flash at the RGB tip, an immediate preceding phase to red clump.
Comment: 6 Pages, 4 Figures, Accepted, MNRASURL الوصول: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::cfeb59fecfd0d150fb1949444d84e159
https://doi.org/10.1093/mnras/stz3222
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المؤلفون: Ke-Jung Chen, Xiaodong Tang, Norhasliza Yusof, Zhi Li, M. Bhuyan, Jianrong Shi, A. Li, Motohiko Kusakabe, Zhuoran Liu, Kuo-Chuan Pan, Shigeru Kubono, Tae-Sun Park, Wei Wang, Tohru Motobayashi, Dong Ha Kim, Meng-Ru Wu, Haining Li, Liangjian Wen, Hasan Abu Kassim, K. I. Hahn, Wako Aoki, Azni Abdul Aziz, W. Liu, Toshitaka Kajino, Gang Guo, Hong-Liang Yan, Su Ahn, Nor Sofiah Ahmad
المصدر: AAPPS Bulletin, Vol 31, Iss 1, Pp 1-31 (2021)
مصطلحات موضوعية: Nuclear reaction, Physics, Nuclear Theory, QC1-999, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astronomy, General Medicine, Southeast asia, Nuclear Theory (nucl-th), Hot topics, Astrophysics - Solar and Stellar Astrophysics, Nucleosynthesis, Nuclear astrophysics, Nuclear Experiment (nucl-ex), Nuclear Experiment, East and southeast Asia, Nuclear theory, Dense matter, Solar and Stellar Astrophysics (astro-ph.SR)
الوصف: Nuclear astrophysics is an interdisciplinary research field of nuclear physics and astrophysics, seeking for the answer to a question, how to understand the evolution of the Universe with the nuclear processes which we learn. We review the research activities of nuclear astrophysics in east and southeast Asia which includes astronomy, experimental and theoretical nuclear physics and astrophysics. Several hot topics such as the Li problems, critical nuclear reactions and properties in stars, properties of dense matter, r-process nucleosynthesis and $\nu$-process nucleosynthesis are chosen and discussed in further details. Some future Asian facilities, together with physics perspectives, are introduced.
Comment: 49 pages, 10 figures, published in AAPPS (Association of Asia Pacific Physical Societies) BulletinURL الوصول: https://explore.openaire.eu/search/publication?articleId=doi_dedup___::bebfb1d69249f18750b48c42d9614fb6
https://doi.org/10.1007/s43673-021-00018-z
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