• The changing mass of glaciers on the Tibetan Plateau, 2002–2016, using time-variable gravity from the GRACE satellite mission

      Beveridge, Alyson K.; Harig, Christopher; Simons, Frederik J.; Univ Arizona, Dept Geosci (DE GRUYTER POLAND SP ZOO, 2018-01)
      The Tibetan Plateau is the largest region of high elevation in the world. The source of water for a number of important rivers, the Himalayan region is vital to the billions of inhabitants of the Asian continent. Over the last fifty years, the climate in the region has warmed more rapidly than anywhere else at the same latitude. Causes and effects, and the geographical details of these alarming warming trends are as yet not fully known. One way of assessing the effects of climate change in this area is to measure the change in glacier volume in the region, but estimates made on the basis of different techniques have not been conclusive to date, and remain difficult to reconcile. We examine the temporal behavior of the mass flux integrated over four distinct groupings of Tibetan glaciers using satellite gravimetry from the Gravity Recovery and Climate Experiment (GRACE). We use a technique known as spatio-spectral localization using spherical Slepian functions to convert global spherical harmonic expansions of the time-dependent geopotential into monthly estimates of mass changes over the Tibetan Plateau. Subsequent reductions are aimed at interpreting this mass change as due to gains or losses in ice mass. We find that (ice) mass has been decreasing on the Tibetan Plateau between 2002 and 2016 but with significant spatial variability throughout the region. Specifically, in the regions of Himalaya, Pamir, Qilian, and Tien Shan, glaciers have been losing ice mass at a rate of -11 +/- 3, -1 +/- 2, +8 +/- 2, and -6 +/- 1 Gt/yr, respectively, over the last decade.
    • New observations and asteroseismic analysis of the subdwarf B pulsator PG 1219+534

      Van Grootel, Valérie; Péters, Marie-Julie; Green, Elizabeth M.; Charpinet, Stéphane; Brassard, Pierre; Fontaine, Gilles; Univ Arizona, Steward Observ (DE GRUYTER POLAND SP ZOO, 2018-02)
      We present a new asteroseismic modeling of the hot B subdwarf (sdB) pulsator PG 1219+534, based on a 3-month campaign with the Mont4K/Kuiper combination at Mt Bigelow (Arizona) and on updated atmospheric parameters from high S/N low and medium resolution spectroscopy. On the basis of the nine independent pulsation periods extracted from the photometric light curve, we carried out an astroseismic analysis by applying the forward modeling approach using our latest (third and fourth generation) sdB models. Atmospheric parameters (T-eff = 34 258 +/- 170 K, log g = 5.838 +/- 0.030) were used as independent constraints, as well as partial mode identification based on observed multiplet structures we ascribed to stellar rotation. The optimal model found is remarkably consistent between various analyses with third and fourth generation of sdB models, and also with previously published analysis with second generation sdB models. It corresponds to a sdB with a canonical mass (0.46 +/- 0.02 M-circle dot), rather thin H-He envelope (log q(envl) = -3.75 +/- 0.12), and close to He-burning exhaustion (X-core(C + O) = 0.86 +/- 0.05). We also investigate the internal rotation of the star. We find that PG 1219+534 rotates very slowly (P-rot = 34.91 +/- 0.84 days) and that solid-body rotation is reached at least down to similar to 60% of the radius.