European Southern Observatory

About: European Southern Observatory is a facility organization based out in Garching bei München, Germany. It is known for research contribution in the topics: Galaxy & Stars. The organization has 3594 authors who have published 16157 publications receiving 823095 citations. The organization is also known as: The European Southern Observatory，ESO & ESO.

First Stars. II. Elemental abundances in the extremely metal-poor star CS 22949--037. A diagnostic of early massive supernovae

Abstract: CS 22949-037 is one of the most metal-poor giants known ((Fe=H) 4:0), and it exhibits large overabundances of carbon and nitrogen (Norris et al.). Using VLT-UVES spectra of unprecedented quality, regarding resolution and S=N ratio, covering a wide wavelength range (from= 350 to 900 nm), we have determined abundances for 21 elements in this star over a wide range of atomic mass. The major new discovery is an exceptionally large oxygen enhancement, (O=Fe)= 1:97 0:1, as measured from the (O I) line at 630.0 nm. We find an enhancement of (N/Fe) of 2:56 0:2, and a milder one of (C=Fe)= 1:17 0:1, similar to those already reported in the literature. This implies Z? = 0:01 Z. We also find carbon isotopic ratios 12 C/ 13 C= 42: 0a nd 13 C/ 14 N= 0:03 +0:035 0:015 , close to the equilibrium value of the CN cycle. Lithium is not detected. Na is strongly enhanced ((Na=Fe)=+2:1 0:2), while S and K are not detected. The silicon-burning elements Cr and Mn are underabundant, while Co and Zn are overabundant ((Zn=Fe)=+0:7). Zn is measured for the first time in such an extremely metal-poor star. The abundances of the neutron-capture elements Sr, Y, and Ba are strongly decreasing with the atomic number of the element: (Sr=Fe) +0:3, (Y=Fe) 0:1, and (Ba=Fe) 0:6. Among possible progenitors of CS 22949-037, we discuss the pair- instability supernovae. Such very massive objects indeed produce large amounts of oxygen, and have been found to be possible sources of primary nitrogen. However, the predicted odd/even eect is too large, and the predicted Zn abundance much too low. Other scenarios are also discussed. In particular, the yields of a recent model (Z35Z) from Heger and Woosley are shown to be in fair agreement with the observations. The only discrepant prediction is the very low abundance of nitrogen, possibly curable by taking into account other eects such as rotationally induced mixing. Alternatively, the absence of lithium in our star, and the values of the isotopic ratios 12 C/ 13 Ca nd 13 C/ 14 N close to the equilibrium value of the CN cycle, suggest that the CNO abundances now observed might have been altered by nuclear processing in the star itself. A 30-40 M supernova, with fallback, seems the most likely progenitor for CS 22949-037.

Deep Impact: Observations from a worldwide Earth-based campaign

Abstract: On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics.

A SECOND CASE OF VARIABLE Na I D LINES IN A HIGHLY REDDENED TYPE Ia SUPERNOVA

Abstract: Recent high-resolution spectra of the Type Ia supernova SN 2006X have revealed the presence of time-variable and blueshifted Na I D features, interpreted by Patat et al. as originating in circumstellar material within the progenitor system. The variation seen in SN 2006X induces relatively large changes in the total Na I D equivalent width (ΔEW ~ 0.5 A in just over two weeks) that would be detectable at lower resolutions. We have used a large data set comprising 2400 low-resolution spectra of 450 Type Ia supernovae (SNe Ia) obtained by the CfA Supernova Program to search for variable Na I D features. Out of the 31 SNe Ia (including SN 2006X) in which we could have detected similar EW variations, only one other (SN 1999cl) shows variable Na I D features, with an even larger change over a similar ~10 day timescale (ΔEW = 1.66 ± 0.21 A). Interestingly, both SN 1999cl and SN 2006X are the two most highly reddened objects in our sample, raising the possibility that the variability is connected to dusty environments.

Predicted UV properties of very metal-poor starburst galaxies

Abstract: Aims. We study the expected properties of starburst galaxies in order to provide the point of reference for interpretation of high-z galaxy surveys and of very metal-poor galaxies. We concentrate mainly on the UV characteristics such as the ionizing spectra, the UV continuum, the Lyα and He ii λ1640 line and two-photon continuum emission. Methods. We use evolutionary synthesis models covering metallicities from Pop III to solar and a wide range of IMFs. We also combine the synthetic SEDs with the CLOUDY photoionization code for more accurate predictions of nebular emission, and to study possible departures from case B assumed in the synthesis models. Results. The ionizing fluxes, UV continuum properties, and predicted Lyα and He ii λ1640 line strengths are presented for synthesis models covering a wider range of parameter space than our earlier calculations. Strong departures from case B predictions are obtained for Lyα and 2γ continuum at low metallicities. At low nebular densities both are shown to be enhanced proportionally to the mean energy carried by the Lyman continuum photons emitted by the ionizing source. Larger Lyα equivalent widths are therefore predicted at low metallicity. The He ii λ1640 line can be weaker than case B predicts (in terms of flux as well as the equivalent width) due to its ionization parameter dependence and to the enhanced underlying 2γ continuum. Conclusions. Our results have implications for the interpretation of star-forming metal-poor and/or high redshift galaxies, for galaxies among the Lyα emitters (LAE) and Lyman Break galaxy (LBG) populations, and for searches of Population III stars in the distant Universe.

Pōniuā‘ena: A Luminous z = 7.5 Quasar Hosting a 1.5 Billion Solar Mass Black Hole

Abstract: We report the discovery of a luminous quasar, J1007+2115 at $z=7.515$ (\"Pōniuā'ena\"), from our wide-field reionization-era quasar survey. J1007+2115 is the second quasar now known at $z>7.5$, deep into the reionization epoch. The quasar is powered by a $(1.5\\pm0.2)\\times10^9$ $M_{\\odot}$ supermassive black hole (SMBH), based on its broad MgII emission-line profile from Gemini and Keck near-IR spectroscopy. The SMBH in J1007+2115 is twice as massive as that in quasar J1342+0928 at $z=7.54$, the current quasar redshift record holder. The existence of such a massive SMBH just 700 million years after the Big Bang significantly challenges models of the earliest SMBH growth. Model assumptions of Eddington-limited accretion and a radiative efficiency of 0.1 require a seed black hole of $\\gtrsim 10^{4}$ $M_{\\odot}$ at $z=30$. This requirement suggests either a massive black hole seed as a result of direct collapse or earlier periods of rapid black hole growth with hyper-Eddington accretion and/or a low radiative efficiency. We measure the damping wing signature imprinted by neutral hydrogen absorption in the intergalactic medium (IGM) on J1007+2115's Ly$\\alpha$ line profile, and find that it is weaker than that of J1342+0928 and two other $z\\gtrsim7$ quasars. We estimate an IGM volume-averaged neutral fraction $\\langle x\\rm_{HI}\\rangle=0.39^{+0.22}_{-0.13}$. This range of values suggests a patchy reionization history toward different IGM sightlines. We detect the 158 $\\mu$m [C II] emission line in J1007+2115 with ALMA; this line centroid yields a systemic redshift of $z=7.5149\\pm0.0004$ and indicates a star formation rate of $\\sim210$ $M_{\\odot}$ yr$^{-1}$ in its host galaxy.