arXiv subjects

Satoshi Honda

Publications and source records attributed to Satoshi Honda.

102 records · Page 6Linked to original sources

arXiv2008

Enrichment of lead (Pb) in the Galactic halo

We have determined lead (Pb) abundances for twelve red giants having [Fe/H] between -2.1 and -1.3, and its upper-limits for two lower metallicity objects, as well as the abundances of lanthanum (La) and europium (Eu). The averages of [Pb/Fe] and [Pb/Eu] are -0.3 and -0.6, respectively, and no clear increase of these ratios with increasing metallicity is found. The [La/Eu] values are only slightly higher than that of the r-process component in solar-system material. Combining the previous studies for globular clusters, these results suggest little contribution of the s-process to Pb of the field stars studied here, supporting the estimate of Pb production by the r-process from the solar-system abundances.

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arXiv2008

Carbon-Enhanced Metal-Poor Stars. III. Main-Sequence Turn-Off Stars from the SDSS/SEGUE Sample

The chemical compositions of seven Carbon-Enhanced Metal-Poor (CEMP) turn-off stars are determined from high-resolution spectroscopy. Five of them are selected from the SDSS/SEGUE sample of metal-poor stars. The effective temperatures of these objects are all higher than 6000 K, while their metallicities, parametrized by [Fe/H], are all below -2. Six of our program objects exhibit high abundance ratios of barium ([Ba/H]> +1), suggesting large contributions of the products of former AGB companions via mass transfer across binary systems. Combining our results with previous studies provides a total of 20 CEMP main-sequence turn-off stars for which the abundances of carbon and at least some neutron-capture elements are determined. Inspection of the [C/H] ratios for this sample of CEMP turn-off stars show that they are generally higher than those of CEMP giants; their dispersion in this ratio is also smaller. We take these results to indicate that the carbon-enhanced material provided from the companion AGB star is preserved at the surface of turn-off stars with no significant dilution. In contrast, a large dispersion in the observed [Ba/H] is found for the sample of CEMP turn-off stars, suggesting that the efficiency of the s-process in very metal-poor AGB stars may differ greatly from star to star. Four of the six stars from the SDSS/SEGUE sample exhibit kinematics that are associated with membership in the outer-halo population, a remarkably high fraction.

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arXiv2007

Neutron-capture elements in the very metal-poor star HD88609: another st ar with excesses of light neutron-capture elements

We obtained a high resolution, high signal-to-noise UV-blue spectrum of the extremely metal-poor red giant HD88609 to determine the abundances of heavy elements. Nineteen neutron-capture elements are detected in the spectrum. Our analysis revealed that this object has large excesses of light neutron-capture elements while heavy neutron-capture elements are deficient. The abundance pattern shows a continuously decreasing trend, as a function of atomic number, from Sr to Yb, which is quite different from those in stars with excesses of r-process elements. Such an abundance pattern is very similar to that of HD122563 that was studied by our previous work. The results indicate that the abundance pattern found in the two stars could represent the pattern produced by the nucleosynthesis process that provided light neutron-capture elements in the very early Galaxy.

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arXiv2007

The first determination of the actinide Th abundance for a red giant of the Ursa Minor dwarf galaxy

The Thorium abundance for the red giant COS82 in the Ursa Minor dwarf spheroidal galaxy is determined based on a high resolution spectrum. This is the first detection of actinides in an extra Galactic object. A detailed abundance pattern is determined for 12 other neutron-capture elements from the atomic number 39 to 68. These elements are significantly over-abundant with respect to other metals like Fe (> 1 dex) and their abundance pattern agrees well with those of the r-process-enhanced, very metal-poor stars known in the Galactic halo, while the metallicity of this object ([Fe/H] ~ -1.5) is much higher than these field stars ([Fe/H] ~ -3.0). The results indicate that the mechanism and the astrophysical site that are responsible for neutron-capture elements in COS82 is similar to that for field r-process-enhanced stars, while the condition of low mass star formation is quite different. An estimate of the age of this object based on the Th abundance ratio is discussed.

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arXiv2007

Spectroscopic Studies of Extremely Metal-Poor Stars with the Subaru High Dispersion Spectrograph. IV. The alpha-Element-Enhanced Metal-Poor Star BS16934-002

A detailed elemental abundance analysis has been carried out for the very metal-poor ([Fe/H]=-2.7) star BS16934-002, which was identified in our previous work as a star exhibiting large overabundances of Mg and Sc. A comparison of the abundance pattern of this star with that of the well-studied metal-poor star HD122563 indicates excesses of O, Na, Mg, Al, and Sc in BS16934-002. Of particular interest, no excess of C or N is found in this object, in contrast to CS22949-037 and CS29498-043, two previously known carbon-rich, extremely metal-poor stars with excesses of the alpha elements. No established nucleosynthesis model exists that explains the observed abundance pattern of BS16934-002. A supernova model, including mixing and fallback, assuming severe mass loss before explosion, is discussed as a candidate progenitor of BS16934-002.

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arXiv2006

Chemical Abundance Analysis of the Extremely Metal-Poor Star HE 1300+0157

We present a detailed chemical abundance analysis of HE 1300+0157, a subgiant with [Fe/H]=-3.9. From a high-resolution, high-S/N Subaru/HDS spectrum we find the star to be enriched in C ([C/Fe]_1D ~ +1.4) and O ([O/Fe]_1D ~ +1.8). With the exception of these species, HE 1300+0157 exhibits an elemental abundance pattern similar to that found in many other very and extremely metal-poor stars. The Li abundance is lower than the Spite-plateau value, in agreement with expectation for its evolutionary status. Of particular interest, no neutron-capture elements are detected in HE 1300+0157. This type of abundance pattern has been found by recent studies in several other metal-poor giants. We suggest that HE 1300+0157 is an unevolved example of this group of stars, which exhibit high C abundances together with low (or absent) abundances of neutron-capture elements. Several potential enrichment scenarios are presented. The low neutron-capture elements, including Sr, Ba, and Pb, suggests that the carbon excess observed in HE 1300+0157 is not due to mass transfer across a binary system. Such a scenario is applied to carbon-rich objects with excesses of s-process elements. The normal observed Li abundance supports this interpretation. Most likely, the high levels of C and O were produced prior to the birth of this star. It remains unclear whether a single hypernova is responsible for its overall chemical pattern, or whether one requires a superposition of yields from a massive Population III object and a normal Type II SN. These scenarios provide important information on the C production in the early Universe, and on the formation of C-rich stars in the early Galaxy.

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arXiv2006

Constructing the Subaru Advanced Data and Analysis Service on VO

We present our activity on making the Subaru Data Archive accessible through the Japanese Virtual Observatory (JVO) system. There are a lot of demand to use the archived Subaru data from various fields of astronomers. To be used by those who are not familiar with the way to reduce the Subaru data, the data reduction should be made before providing for them, or at least it should be easily done without precise knowledge about instrument's characteristic and environment where data are taken. For those purposes, data quality assessment system NAQATA is developed, which is presented in this meeting by Nakata et al. (2006), and the science-ready image data are provided for some of the SuprimeCam data at SMOKA data service which is presented by Enoki et al (2006). JVO portal will provide the way to access the reduce data, and also provides the way to reduce from raw data with very few efforts through the user-friendly web browser I/F. To provide such a CPU-intensive service, we have developed a GRID computing system. The architecture of this Subaru Data and Analysis system are discussed.

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arXiv2006

Neutron-capture elements in the metal-poor globular cluster M15

We report on observations of six giants in the globular cluster M15 (NGC 7078) using the Subaru Telescope to measure neutron-capture elemental abundances. Our abundance analyses based on high-quality blue spectra confirm the star-to-star scatter in the abundances of heavy neutron-capture elements (e.g., Eu), and no significant s-process contribution to them, as was found in previous studies. We have found, for the first time, that there are anti-correlations between the abundance ratios of light to heavy neutron-capture elements ([Y/Eu] and [Zr/Eu]) and heavy ones (e.g., Eu). This indicates that light neutron-capture elements in these stars cannot be explained by only a single r-process. Another process that has significantly contributed to the light neutron-capture elements is required to have occurred in M15. Our results suggest a complicated enrichment history for M15 and its progenitor.

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arXiv2005

Non-LTE Line-Formation and Abundances of Sulfur and Zinc in F, G, and K Stars

Extensive statistical-equilibrium calculations on neutral sulfur and zinc were carried out, in order to investigate how the non-LTE effect plays a role in the determination of S and Zn abundances in F, G, and K stars. Having checked on the spectra of representative F-type stars (Polaris, Procyon, and alpha Per) and the Sun that our non-LTE corrections yield a reasonable consistency between the abundances derived from different lines, we tried an extensive non-LTE reanalysis of published equivalent-width data of S I and Zn I lines for metal-poor halo/disk stars. According to our calculations, S I 9212/9228/9237 lines suffer significant negative non-LTE corrections amounting to <~ 0.2--0.3 dex, while LTE is practically valid for S I 8683/8694 lines. Embarrassingly, as far as the very metal-poor regime is concerned, a marked discordance is observed between the [S/Fe] values from these two abundance indicators, in the sense that the former attains a nearly flat plateau (or even a slight downward bending) while the latter shows an ever-increasing trend with a further lowering of metallicity. The reason for this discrepancy is yet to be clarified. Regarding Zn, we almost confirmed the characteristic tendencies of [Zn/Fe] reported from recent LTE studies (i.e., an evident/slight increase of [Zn/Fe] with a decrease of [Fe/H] for very metal-poor/disk stars), since the non-LTE corrections for the Zn I 4722/4810 and 6362 lines (tending to be positive and gradually increasing towards lower [Fe/H]) are quantitatively of less significance (<~ 0.1 dex).

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arXiv2005

Spectroscopic Studies of Very Metal-Poor Stars with the Subaru High Dispersion Spectrograph. III. Light Neutron-Capture Elements

Elemental abundance measurements have been obtained for a sample of 18 very metal-poor stars using spectra obtained with the Subaru Telescope High Dispersion Spectrograph. Seventeen stars, among which 16 are newly analyzed in the present work, were selected from candidate metal-poor stars identified in the HK survey of Beers and colleagues. The metallicity range covered by our sample is -3.1 ~< [Fe/H] ~< -2.4. The abundances of carbon, alpha-elements, and iron-peak elements determined for these stars confirm the trends found by previous work. One exception is the large over-abundance of Mg, Al and Sc found in BS16934--002, a giant with [Fe/H] = -2.8. By combining our new results with those of previous studies, we investigate the distribution of neutron-capture elements in very metal-poor stars, focusing on the production of the light neutron-capture elements (e.g., Sr, Y, and Zr).

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arXiv2005

Nucleosynthetic signatures of the first stars

The chemically most primitive stars provide constraints on the nature of the first stellar objects that formed in the Universe; elements other than hydrogen, helium and traces of lithium within these objects were generated by nucleosynthesis in the very first stars. The relative abundances of elements in the surviving primitive stars reflect the masses of the first stars, because the pathways of nucleosynthesis are quite sensitive to stellar masses. Several models have been suggested to explain the origin of the abundance pattern of the giant star HE 0107-5240, which hitherto exhibited the highest deficiency of heavy elements known. Here we report the discovery of HE 1327-2326, a subgiant or main-sequence star with an iron abundance about a factor of two lower than that of HE 0107-5240. Both stars show extreme overabundances of carbon and nitrogen with respect to iron, suggesting a similar origin of the abundance patterns. The unexpectedly low Li and high Sr abundances of HE 1327-2326, however, challenge existing theoretical understanding: none predicts the high Sr abundance or provides a Li depletion mechanism consistent with data available for the most metal-poor stars.

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arXiv2004

Structured Query Language for Virtual Observatory

Currently two query languages are defined as standards for the Virtual Observatory (VO). Astronomical Data Query Language (ADQL) is used for catalog data query and Simple Image Access Protocol (SIAP) is for image data query. As a result, when we query each data service, we need to know in advance which language is supported and then construct a query language accordingly. The construct of SIAP is simple, but they have a limited capability. For example, there is no way to specify multiple regions in one query, and it is difficult to specify complex query conditions. In this paper, we propose a unified query language for any kind of astronomical database on the basis of SQL99. SQL is a query language optimized for a table data, so to apply the SQL to the image and spectrum data set, the data structure need to be mapped to a table like structure. We present specification of this query language and an example of the architecture for the database system.

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