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The nature of the first massive stars may be inferred by investigating the origin of the extremely metal-poor (EMP) stars, likely formed from the ejecta of one or a few previous massive stars. We investigate the rotational properties of early massive stars by comparing the abundance patterns of EMP stars with rotating massive stellar models. Low metallicity 20 $M_{\odot}$ stellar models with initial rotation rates between 0 and $70~\%$ of the critical velocity are computed. Explosions with strong fallback are assumed. The ejected material is considered to fit individually the abundance patterns of 272 EMP stars with $-4<$ [Fe/H] $<-3$. With increasing initial rotation, the [C/H], [N/H], [O/H], [Na/H], [Mg/H] and [Al/H] ratios in the massive star ejecta are gradually increased. Among the 272 EMP stars considered, $\sim 40-50~\%$ are consistent with our models. About $60 - 70~\%$ of the CEMP star sample is reproduced against $\sim 20 - 30~\%$ for the C-normal EMP star sample. The CEMP stars are preferentially reproduced with a material coming from mid to fast rotating massive stars. The velocity distribution derived from the best massive star models increases from no rotation to fast rotation. The maximum is reached for massive stars having initial equatorial velocities of $\sim 550 - 640$ km~s$^{-1}$. Although subject to significant uncertainties, these results suggest that the rotational mixing operating in between the H-burning shell and the He-burning core of early massive stars played an important role in the early chemical enrichment of the Universe. The comparison of the velocity distribution derived from the best massive star models with velocity distributions of nearby OB stars suggests a greater amount of massive fast rotators in the early Universe. This may have important consequences for reionization or integrated light from high redshift galaxies., Comment: 25 pages, 15 figures, 6 tables, published in A&A

We present a study of the high-resolution optical spectrum for the hot post-asymptotic giant branch (post-AGB) star, Hen 3-1013, identified as the optical counterpart of the infrared sourceIRAS 14331-6435. For the first time the detailed identifications of the observed absorption and emission features in the wavelength range 3700-9000 \AA\ is carried out. Absorption lines of HI, HeI, CI, NI, OI, NeI, CII, NII, OII, SiII, SII, ArII, FeII, MnII, CrII, TiII, CoII, NiII, SIII, FeIII and SIV were detected. From the absorption lines, we derived heliocentric radial velocities of $V_r=-29.6\pm0.4$ km/s. We have identified emission permitted lines of OI, NI, FeII, MgII, SiII and AlII. The forbidden lines of [NI], [FeII], [CrII] and [NiII] have been identified also. Analysis of [NiII] lines in the gaseous shell gives an estimate for the electron density $N_e\sim10^7$ cm$^{-3}$ and the expansion velocity of the nebula $V_{exp}=12$ km/s. The mean radial velocity as measured from emission features of the envelope is $V_r=-36.0\pm0.4$ km/s. The Balmer lines H$\alpha$, H$\beta$ and H$\gamma$ show P Cyg behaviour which indicate ongoing post-AGB mass-loss. Based on ASAS and ASAS-SN data, we have detected rapid photometric variability in Hen 3-1013 with an amplitude up to 0.2 mag in the V band. The star's low-resolution spectrum underwent no significant changes from 1994 to 2012. Based on archival data, we have traced the photometric history of the star over more than 100 years. No significant changes in the star brightness have been found., Comment: 19 pages, 6 figures, 8 tables, accepted for publication in MNRAS

High-resolution spectroscopy of the core of the Perseus Cluster of galaxies, using the $Hitomi$ satellite above 2 keV and the $XMM$-$Newton$ Reflection Grating Spectrometer at lower energies, provides reliable constraints on the abundances of O, Ne, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, and Ni. Accounting for all known systematic uncertainties, the Ar/Fe, Ca/Fe, and Ni/Fe ratios are determined with a remarkable precision of less than 10%, while the constraints on Si/Fe, S/Fe, and Cr/Fe are at the 15% level, and Mn/Fe is measured with a 20% uncertainty. The average biases in determining the chemical composition using archival CCD spectra from $XMM$-$Newton$ and $Suzaku$ range typically from 15-40%. A simple model in which the enrichment pattern in the Perseus Cluster core and the proto-solar nebula are identical gives a surprisingly good description of the high-resolution X-ray spectroscopy results, with $\chi^2=10.7$ for 10 d.o.f. However, this pattern is challenging to reproduce with linear combinations of existing supernova nucleosynthesis calculations, particularly given the precise measurements of intermediate $\alpha$-elements enabled by $Hitomi$. We discuss in detail the degeneracies between various supernova progenitor models and explosion mechanisms, and the remaining uncertainties in these theoretical models. We suggest that including neutrino physics in the core-collapse supernova yield calculations may improve the agreement with the observed pattern of $\alpha$-elements in the Perseus Cluster core. Our results provide a complementary benchmark for testing future nucleosynthesis calculations required to understand the origin of chemical elements., Comment: MNRAS in press

Gravitational lensing by clusters of galaxies offers a powerful probe of their structure and mass distribution. Deriving a lens magnification map for a galaxy cluster is a classic inversion problem and many methods have been developed over the past two decades to solve it. Several research groups have developed techniques independently to map the predominantly dark matter distribution in cluster lenses. While these methods have all provided remarkably high precision mass maps, particularly with exquisite imaging data from the Hubble Space Telescope (HST), the reconstructions themselves have never been directly compared. In this paper, we report the results of comparing various independent lens modeling techniques employed by individual research groups in the community. Here we present for the first time a detailed and robust comparison of methodologies for fidelity, accuracy and precision. For this collaborative exercise, the lens modeling community was provided simulated cluster images -- of two clusters Ares and Hera -- that mimic the depth and resolution of the ongoing HST Frontier Fields. The results of the submitted reconstructions with the un-blinded true mass profile of these two clusters are presented here. Parametric, free-form and hybrid techniques have been deployed by the participating groups and we detail the strengths and trade-offs in accuracy and systematics that arise for each methodology. We note in conclusion that lensing reconstruction methods produce reliable mass distributions that enable the use of clusters as extremely valuable astrophysical laboratories and cosmological probes., Comment: 38 pages, 25 figures, submitted to MNRAS, version with full resolution images can be found at http://pico.bo.astro.it/~massimo/papers/FFsims.pdf

Na I D absorbing systems toward Type Ia supernovae (SNe Ia) have been intensively studied over the last decade with the aim of finding circumstellar material (CSM), which is an indirect probe of the progenitor system. However, it is difficult to deconvolve CSM components from non-variable, and often dominant, components created by interstellar material (ISM). We present a series of high-resolution spectra of SN Ia 2014J from before maximum brightness to ~250 days after maximum brightness. The late-time spectrum provides unique information for determining the origin of the Na I D absorption systems. The deep late-time observation allows us to probe the environment around the SN at a large scale, extending to ~40 pc. We find that a spectrum of diffuse light in the vicinity, but not directly in the line-of-sight, of the SN has absorbing systems nearly identical to those obtained for the "pure" SN line-of-sight. Therefore, basically all Na I D systems seen toward SN 2014J must originate from foreground material that extends to at least ~40 pc in projection and none at the CSM scale. A fluctuation in the column densities at a scale of ~20 pc is also identified. After subtracting the diffuse, "background" spectrum, the late-time SN Na I D profile along the SN line-of-sight is consistent with the profile in the near-maximum brightness spectra. The lack of variability on a ~1 year timescale is consistent with the ISM interpretation for the gas., Comment: 20 pages, 17 figures, 1 table. Accepted for publication in ApJ

Supernova "Refsdal," multiply imaged by cluster MACSJ1149.5+2223, represents a rare opportunity to make a true blind test of model predictions in extragalactic astronomy, on a time scale that is short compared to a human lifetime. In order to take advantage of this event, we produced seven gravitational lens models with five independent methods, based on Hubble Space Telescope (HST) Hubble Frontier Field images, along with extensive spectroscopic follow-up observations by HST, the Very Large and the Keck Telescopes. We compare the model predictions and show that they agree reasonably well with the measured time delays and magnification ratios between the known images, even though these quantities were not used as input. This agreement is encouraging, considering that the models only provide statistical uncertainties, and do not include additional sources of uncertainties such as structure along the line of sight, cosmology, and the mass sheet degeneracy. We then present the model predictions for the other appearances of SN "Refsdal." A future image will reach its peak in the first half of 2016, while another image appeared between 1994 and 2004. The past image would have been too faint to be detected in existing archival images. The future image should be approximately one third as bright as the brightest known image (i.e., H_AB~25.7 mag at peak and H_AB~26.7 mag six months before peak), and thus detectable in single-orbit HST images. We will find out soon whether our predictions are correct., Comment: 26 pages, 13 figures, ApJ in press; redshifts available at https://archive.stsci.edu/prepds/glass/

We report the late-time evolution of Type IIb Supernova (SN IIb) 2013df. SN 2013df showed a dramatic change in its spectral features at ~1 year after the explosion. Early on it showed typical characteristics shared by SNe IIb/Ib/Ic dominated by metal emission lines, while later on it was dominated by broad and flat-topped Halpha and He I emissions. The late-time spectra are strikingly similar to SN IIb 1993J, which is the only previous example clearly showing the same transition. This late-time evolution is fully explained by a change in the energy input from the $^{56}$Co decay to the interaction between the SN ejecta and dense circumstellar matter (CSM). The mass loss rate is derived to be ~(5.4 +- 3.2) x 10^{-5} Msun/yr (for the wind velocity of ~20 km/s), similar to SN 1993J but larger than SN IIb 2011dh by an order of magnitude. The striking similarity between SNe 2013df and 1993J in the (candidate) progenitors and the CSM environments, and the contrast in these natures to SN 2011dh, infer that there is a link between the natures of the progenitor and the mass loss: SNe IIb with a more extended progenitor have experienced a much stronger mass loss in the final centuries toward the explosion. It might indicate that SNe IIb from a more extended progenitor are the explosions during a strong binary interaction phase, while those from a less extended progenitor have a delay between the strong binary interaction and the explosion., Comment: Accepted for publication in ApJ (May 7, 2015). 14 pages, 6 figures

We present the abundance analysis of 97 nearby metal-poor (-3.3<[Fe/H]<-0.5) stars having kinematics characteristics of the Milky Way (MW) thick disk, inner, and outer stellar halos. The high-resolution, high-signal-to-noise optical spectra for the sample stars have been obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of Fe, Mg, Si, Ca and Ti have been derived using a one-dimensional LTE abundance analysis code with Kurucz NEWODF model atmospheres. By assigning membership of the sample stars to the thick disk, inner or outer halo components based on their orbital parameters, we examine abundance ratios as a function of [Fe/H] and kinematics for the three subsamples in wide metallicity and orbital parameter ranges. We show that, in the metallicity range of -1.5<[Fe/H]<= -0.5, the thick disk stars show constantly high mean [Mg/Fe] and [Si/Fe] ratios with small scatter. In contrast, the inner, and the outer halo stars show lower mean values of these abundance ratios with larger scatter. The [Mg/Fe], [Si/Fe] and [Ca/Fe] for the inner and the outer halo stars also show weak decreasing trends with [Fe/H] in the range [Fe/H]$>-2$. These results favor the scenarios that the MW thick disk formed through rapid chemical enrichment primarily through Type II supernovae of massive stars, while the stellar halo has formed at least in part via accretion of progenitor stellar systems having been chemically enriched with different timescales., Comment: Accepted for publication in ApJ

We present chemical abundances of 57 metal-poor stars that are likely constituents of the outer stellar halo in the Milky Way. Almost all of the sample stars have an orbit reaching a maximum vertical distance (Z_max) of >5 kpc above and below the Galactic plane. High-resolution, high signal-to-noise spectra for the sample stars obtained with Subaru/HDS are used to derive chemical abundances of Na, Mg, Ca, Ti, Cr, Mn, Fe, Ni, Zn, Y and Ba with an LTE abundance analysis code. The resulting abundance data are combined with those presented in literature that mostly targeted at smaller Z_max stars, and both data are used to investigate any systematic trends in detailed abundance patterns depending on their kinematics. It is shown that, in the metallicity range of -2<[Fe/H]<-1, the [Mg/Fe] ratios for the stars with Z_max>5 kpc are systematically lower (~0.1 dex) than those with smaller Z_max. This result of the lower [alpha/Fe] for the assumed outer halo stars is consistent with previous studies that found a signature of lower [alpha/Fe] ratios for stars with extreme kinematics. A distribution of the [Mg/Fe] ratios for the outer halo stars partly overlaps with that for stars belonging to the Milky Way dwarf satellites in the metallicity interval of -2<[Fe/H]<-1 and spans a range intermediate between the distributions for the inner halo stars and the stars belonging to the satellites. Our results confirm inhomogeneous nature of chemical abundances within the Milky Way stellar halo depending on kinematic properties of constituent stars as suggested by earlier studies. Possible implications for the formation of the Milky Way halo and its relevance to the suggested dual nature of the halo are discussed., Comment: 68 pages with 23 figures, Accepted for publication in PASJ

AKARI, the first Japanese satellite dedicated to infrared astronomy, was launched on 2006 February 21, and started observations in May of the same year. AKARI has a 68.5 cm cooled telescope, together with two focal-plane instruments, which survey the sky in six wavelength bands from the mid- to far-infrared. The instruments also have the capability for imaging and spectroscopy in the wavelength range 2 - 180 micron in the pointed observation mode, occasionally inserted into the continuous survey operation. The in-orbit cryogen lifetime is expected to be one and a half years. The All-Sky Survey will cover more than 90 percent of the whole sky with higher spatial resolution and wider wavelength coverage than that of the previous IRAS all-sky survey. Point source catalogues of the All-Sky Survey will be released to the astronomical community. The pointed observations will be used for deep surveys of selected sky areas and systematic observations of important astronomical targets. These will become an additional future heritage of this mission., Comment: 13 pages, 4 figures, and 3 tables. Accepted for publication in the AKARI special issue of the Publications of the Astronomical Society of Japan

The Infrared Camera (IRC) is one of two focal-plane instruments on the AKARI satellite. It is designed for wide-field deep imaging and low-resolution spectroscopy in the near- to mid-infrared (1.8--26.5um) in the pointed observation mode of AKARI. IRC is also operated in the survey mode to make an all-sky survey at 9 and 18um. It comprises three channels. The NIR channel (1.8--5.5um) employs a 512 x 412 InSb array, whereas both the MIR-S (4.6--13.4um) and MIR-L (12.6--26.5um) channels use 256 x 256 Si:As impurity band conduction arrays. Each of the three channels has a field-of-view of about 10' x 10' and are operated simultaneously. The NIR and MIR-S share the same field-of-view by virtue of a beam splitter. The MIR-L observes the sky about $25' away from the NIR/MIR-S field-of-view. IRC gives us deep insights into the formation and evolution of galaxies, the evolution of planetary disks, the process of star-formation, the properties of interstellar matter under various physical conditions, and the nature and evolution of solar system objects. The in-flight performance of IRC has been confirmed to be in agreement with the pre-flight expectation. This paper summarizes the design and the in-flight operation and imaging performance of IRC., Comment: Publications of the Astronomical Society of Japan, in press