23,089 research outputs found

    Line Emission in the Brightest Cluster Galaxies of the NOAO Fundamental Plane and Sloan Digital Sky Surveys

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    We examine the optical emission line properties of Brightest Cluster Galaxies (BCGs) selected from two large, homogeneous datasets. The first is the X-ray selected National Optical Astronomy Observatory Fundamental Plane Survey (NFPS), and the second is the C4 catalogue of optically selected clusters built from the Sloan Digital Sky Survey Data Release ~3 (SDSS DR3). Our goal is to better understand the optical line emission in BCGs with respect to properties of the galaxy and the host cluster. Throughout the analysis we compare the line emission of the BCGs to that of a control sample made of the other bright galaxies near the cluster centre. Overall, both the NFPS and SDSS show a modest fraction of BCGs with emission lines (~15%). No trend in the fraction of emitting BCGs as a function of galaxy mass or cluster velocity dispersion is found. However we find that, for those BCGs found in cooling flow clusters, 71^{+9}_{-14}% have optical emission. Furthermore, if we consider only BCGs within 50kpc of the X-ray centre of a cooling flow cluster, the emission-line fraction rises further to 100^{+0}_{-15}%. Excluding the cooling flow clusters, only ~10% of BCGs are line emitting, comparable to the control sample of galaxies. We show that the physical origin of the emission line activity varies: in some cases it has LINER-like line ratios, whereas in others it is a composite of star-formation and LINER-like activity. We conclude that the presence of emission lines in BCGs is directly related to the cooling of X-ray gas at the cluster centre.Comment: Accepted for publication in MNRAS. 13 pages mn2e style with 7 figures and 2 table

    The Impact of Nuclear Reaction Rate Uncertainties on Evolutionary Studies of the Nova Outburst

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    The observable consequences of a nova outburst depend sensitively on the details of the thermonuclear runaway which initiates the outburst. One of the more important sources of uncertainty is the nuclear reaction data used as input for the evolutionary calculations. A recent paper by Starrfield, Truran, Wiescher, & Sparks (1998) has demonstrated that changes in the reaction rate library used within a nova simulation have significant effects, not just on the production of individual isotopes (which can change by an order of magnitude), but on global observables such as the peak luminosity and the amount of mass ejected. We present preliminary results of systematic analyses of the impact of reaction rate uncertainties on nova nucleosynthesis.Comment: 4 pages, 3 figures. to appear in "Cosmic Explosions", proceeding of the 10th Annual October Astrophysics Conference in Maryland (ed. S.S. Holt and W. W. Zhang
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