The origin of HE0107-5240 and the production of O and Na in extremely metal-poor stars

We elaborate the binary scenario for the origin of HE0107-5240, the most metal-poor star yet observed ([Fe/H] = -5.3), using current knowledge of the evolution of extremely metal-poor stars. From the observed C/N value, we estimate the binary separation and period. Nucleosynthesis in a helium convective zone into which hydrogen has been injected allows us to discuss the origin of surface O and Na as well as the abundance distribution of s-process elements. We can explain the observed abundances of 12C, 13C, N, O, and Na and predict future observations to validate the Pop III nature of HE0107-5240.Comment: 4 pages, 3 figures, proceedings of the conference, "Nuclei in the Cosmos VIII", Nuclear Physics A in pres

Effects of accretion flow on the chemical structure in the inner regions of protoplanetary disks

We have studied the dependence of the profiles of molecular abundances and line emission on the accretion flow in the hot (\ga 100K) inner region of protoplanetary disks. The gas-phase reactions initiated by evaporation of the ice mantle on dust grains are calculated along the accretion flow. We focus on methanol, a molecule that is formed predominantly through the evaporation of warm ice mantles, to show how the abundance profile and line emission depend on the accretion flow. Our results show that some evaporated molecules keep high abundances only when the accretion velocity is large enough, and that methanol could be useful as a diagnostic of the accretion flow by means of ALMA observations at the disk radius of \la 10AU.Comment: 6 pages, 5 figures, Accepted for publication in A&

From Prestellar to Protostellar Cores II. Time Dependence and Deuterium Fractionation

We investigate the molecular evolution and D/H abundance ratios that develop as star formation proceeds from a dense-cloud core to a protostellar core, by solving a gas-grain reaction network applied to a 1-D radiative hydrodynamic model with infalling fluid parcels. Spatial distributions of gas and ice-mantle species are calculated at the first-core stage, and at times after the birth of a protostar. Gas-phase methanol and methane are more abundant than CO at radii $r\lesssim 100$ AU in the first-core stage, but gradually decrease with time, while abundances of larger organic species increase. The warm-up phase, when complex organic molecules are efficiently formed, is longer-lived for those fluid parcels in-falling at later stages. The formation of unsaturated carbon chains (warm carbon-chain chemistry) is also more effective in later stages; C$^+$, which reacts with CH$_4$ to form carbon chains, increases in abundance as the envelope density decreases. The large organic molecules and carbon chains are strongly deuterated, mainly due to high D/H ratios in the parent molecules, determined in the cold phase. We also extend our model to simulate simply the chemistry in circumstellar disks, by suspending the 1-D infall of a fluid parcel at constant disk radii. The species CH$_3$OCH$_3$ and HCOOCH$_3$ increase in abundance in $10^4-10^5$ yr at the fixed warm temperature; both also have high D/H ratios.Comment: accepted to ApJ. 55 pages, 7 figures, 3 table

Temperature-Grid Coordinates For Treating Pulsations In The Hydrogen Ionization Zone

A temperature grid is used for the description of motion in the hydrogen ionization region (HIR). This means zones are labeled by temperature rather than mass. Outside the HIR, the conventional Lagrangian grid is used, with transitional coordinates at the boundaries. Although our final object is to apply this scheme to the nonlinear periodic integration problem, we have first constructed a linear version as a test. It is found that periods and growth rates agree very well with those calculated using pure Lagrangian coordinates, but the temperature grid scheme proves less sensitive to a reduction of zones in the HIR. This property is desirable for the nonlinear problem where zoning must necessarily be coarse. As a further test of the temperature grid, we formulate the linear work integral in the new coordinates and confirm the consistency of the growth rates. Finally, it is shown that the scheme is insensitive to a change in the manner in which the transition zones are treated

Direct evaporative cooling of 41K into a Bose-Einstein condensate

We have investigated the collisional properties of 41K atoms at ultracold temperature. To show the possibility to use 41K as a coolant, a Bose-Einstein condensate of 41K atoms in the stretched state (F=2, m_F=2) was created for the first time by direct evaporation in a magnetic trap. An upper bound of three body loss coefficient for atoms in the condensate was determined to be 4(2) 10^{-29} cm -6 s-1. A Feshbach resonance in the F=1, m_F=-1 state was observed at 51.42(5) G, which is in good agreement with theoretical prediction.Comment: 4 pages, 4 figure

Cold CO Gas in Protoplanetary Disks

In a disk around DM Tau, previous observation of 13CO (J=2-1 and 1-0 transitions) derived the 13CO gas temperature of \sim 13-20K, which is lower than the sublimation temperature of CO (20 K). We argue that the existence of such cold CO can be explained by a vertical mixing of disk material. As the gas is transported from a warm layer to a cold layer, CO is depleted onto dust grains with a timescale of \sim 10^3 yr. Because of the steep temperature gradient in the vertical direction, an observable amount of CO is still in the gas phase when the fluid parcel reaches the layer of \sim 13 K. Apparent temperature of CO decreases as the maximum grain size increases from micron-size to mm-size.Comment: 11 pages, 2 figures, accepted to ApJ