Implications of elemental abundances  in dwarf spheroidal galaxies

Tsujimoto, Takuji

doi:10.1051/0004-6361:20054120

Cited by 7 publications

(7 citation statements)

References 51 publications

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“…iii) HNe may produce even a larger amount of Fe due to a smaller fallback mass or a larger energy than the typical HNe in our yields. iv) Also SNe I.5, which are the SN Ia-like explosions of metal-poor AGB stars, have been suggested by Nomoto et al (2003) (see also Tsujimoto 2006).…”

Section: Oxygenmentioning

confidence: 77%

Galactic Chemical Evolution: Carbon through Zinc

Kobayashi

Umeda

Nomoto

et al. 2006

ApJ

827

1,236

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We calculate the evolution of heavy-element abundances from C to Zn in the solar neighborhood, adopting our new nucleosynthesis yields. Our yields are calculated for wide ranges of metallicity (Z ¼ 0YZ ) and the explosion energy (normal supernovae and hypernovae), based on the light-curve and spectra fitting of individual supernovae. The elemental abundance ratios are in good agreement with observations. Among the -elements, O, Mg, Si, S, and Ca show a plateau at ½Fe/H P À1, while Ti is underabundant overall. The observed abundance of Zn (½Zn/Fe $ 0) can be explained only by the high-energy explosion models, as it requires a large contribution of hypernovae. The observed decrease in the odd-Z elements (Na, Al, and Cu) toward low ½Fe/H is reproduced by the metallicity effect on nucleosynthesis. The iron-peak elements (Cr, Mn, Co, and Ni) are consistent with the observed mean values at À2:5 P ½Fe/H P À1, and the observed trend at the lower metallicity can be explained by the energy effect. We also show the abundance ratios and the metallicity distribution functions of the Galactic bulge, halo, and thick disk. Our results suggest that the formation timescale of the thick disk is $1Y3 Gyr.

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Section: Oxygenmentioning

confidence: 77%

Galactic Chemical Evolution: Carbon through Zinc

Kobayashi

Umeda

Nomoto

et al. 2006

ApJ

827

1,236

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“…[Si/Fe] behaves like [Ca/Fe] and [Ti/Fe] in the Galactic bulge. Tsujimoto (2006) suggested that the low α-element signature in the dSph galaxies is a reflection of the contribution of massive stars with smaller rotation compared to solar neighborhood stars, instead of the conventional interpretation that this is a consequence of a low star formation rate. Current data are significantly better than what was available to him in 2006.…”

Section: Comparison With Other Dsph Galaxiesmentioning

confidence: 99%

The Chemical Evolution of the Draco Dwarf Spheroidal Galaxy

Cohen

Huang

2009

ApJ

189

261

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We present an abundance analysis based on high resolution spectra of 8 stars selected to span the full range in metallicity in the Draco dwarf spheroidal galaxy. We find [Fe/H] for the sample stars ranges from −1.5 to −3.0 dex. Combining our sample with previously published work for a total of 14 luminous Draco giants, we show that the abundance ratios [Na/Fe], [Mg/Fe] and [Si/Fe] for the Draco giants overlap those of Galactic halo giants at the lowest [Fe/H] probed, but are significantly lower for the higher Fe-metallicity Draco stars. For the explosive α-elements Ca and Ti, the abundance ratios for Draco giants with [Fe/H] > −2.4 dex are approximately constant and slightly sub-solar, well below values characteristic of Galactic halo stars. The sprocess contribution to the production of heavy elements begins at significantly lower Fe-metallicity than in the Galactic halo.Using a toy model we compare the behavior of the abundance ratios within the sample of Draco giants with those from the literature of Galactic globular clusters, and the Carina and Sgr dSph galaxies. The differences appear to be related to the timescale for buildup of the heavy elements, with Draco having the slowest rate.We note the presence of a Draco giant with [Fe/H] < −3.0 dex in our sample, and reaffirm that the inner Galactic halo could have been formed by early accretion of Galactic satellite galaxies and dissolution of young globular clusters, while the outer halo could have formed from those satellite galaxies accreted later. Stellar Sample and Stellar ParametersOur sample in the Draco dSph galaxy contains 8 stars; details are given in Table 1. It was selected from Table 2.9 of Winnick (2003) to include stars which are known radial velocity members of this satellite to the Galaxy at or near the RGB tip spanning the full range in color and in metallicity and not previously observed at high spectral resolution. Winnick measured the infrared Ca triplet in moderate resolution spectra of Draco stars obtained using the multi-fiber Hydra spectrograph at the WIYN telescope. Her sample was chosen from the photometric survey of Piatek et al. (2001) and previous radial velocity surveys (see, e.g. Armandroff, Olszewski & Pryor 1995). Only confirmed radial velocity members are listed in her table; carbon stars known to be members of Draco were excluded. She developed her own calibration of the relationship between Ca triplet indices and Fe or Ca metallicity based on data for Galactic globular clusters. Details of the calibration and related issues are discussed in the appendix. We adopt the procedures described in Cohen et al. (2002) and used in all subsequent work by the first author published to date to determine the stellar parameters for our sample of luminous Draco giants. Our T ef f determinations are based on the broad band colors V − J and V − K. The optical photometry (we use V only, the V − I color supports the deduced T ef f in most cases, but is not used) is from the SDSS (York et al. 2000) using the transformation equations of Smith e...

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“…Alternative suggestions based on different IMF (e.g. Shetrone et al 2001) or on less rotation of massive stars (compared to solar neighbourhood) have also been invoked (Tsujimoto 2006), but we do not consider here these speculative hypotheses.A glance at Fig. 9 illustrates that in our simulations a decrement of ∼0.2 dex in the plateau is achieved after t ∼ 2.0 Gyr.…”

Section: Comparison To Other Modelsmentioning

confidence: 99%

Star formation feedback and metal enrichment by Types Ia and II supernovae in dwarf spheroidal galaxies: the case of Draco

Marcolini

D’Ercole

Brighenti

et al. 2006

Monthly Notices of the Royal Astronomical Society

140

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We present 3D hydrodynamic simulations aimed at studying the dynamical and chemical evolution of the interstellar medium in dwarf spheroidal galaxies. This evolution is driven by the explosions of Type II supernovae (SNe II) and Type Ia supernovae (SNe Ia), whose different contribution is explicitly taken into account in our models. We compare our results with detailed observations of the Draco galaxy. We assume star formation histories consisting of a number of instantaneous bursts separated by quiescent periods. Diverse histories differ by the number of bursts, but all have the same total duration and give rise to the same amount of stars. Because of the large effectiveness of the radiative losses and the extended dark matter halo, no galactic wind develops, despite the total energy released by the supernovae is much larger than the binding energy of the gas. This explains why the galaxy is able to form stars for a long period (>3 Gyr), consistently with observations. In this picture, the end of the star formation and gas removal must result from external mechanisms, such as ram pressure and/or tidal interaction with the Galaxy. The stellar [Fe/H] distributions found in our models match very well the observed ones. We find a mean value 〈[Fe/H]〉=−1.65 with a spread of ∼1.5 dex. The chemical properties of the stars derive by the different temporal evolution between SNe Ia and SNe II rate, and by the different mixing of the metals produced by the two types of supernovae. We reproduce successfully the observed [O/Fe]–[Fe/H] diagram. However, our interpretation of this diagram differs from that generally adopted by previous chemical models. In fact, we find that the break observed in the diagram is not connected with the onset of a galactic wind or with a characteristic time‐scale for the sudden switchover of the SNe Ia, as sometimes claimed. Instead, we find that the chemical properties of the stars derive, besides the different temporal evolution of the SNe II and SNe Ia rates, from the spatial inhomogeneous chemical enrichment due to the different dynamical behaviour between the remnants of the two types of supernovae.

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Implications of elemental abundances in dwarf spheroidal galaxies

Cited by 7 publications

References 51 publications

Galactic Chemical Evolution: Carbon through Zinc

Galactic Chemical Evolution: Carbon through Zinc

The Chemical Evolution of the Draco Dwarf Spheroidal Galaxy

Star formation feedback and metal enrichment by Types Ia and II supernovae in dwarf spheroidal galaxies: the case of Draco

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