A detailed abundance analysis of the hot post-AGB star ZNG-1 in M10

We present a model-atmosphere analysis for the bright ( V ∼13) star ZNG-1, in the globular cluster M10. From high-resolution ( R ∼40 000) optical spectra we confirm ZNG-1 to be a post-asymptotic giant branch (post-AGB) star. The derived atmospheric parameters are T _eff=26 500±1000 K and log  g =3.6±0.2 dex . A differential abundance analysis reveals a chemical composition typical of hot post-AGB objects, with ZNG-1 being generally metal poor, although helium is approximately solar. The most interesting feature is the large carbon underabundance of more than 1.3 dex. This carbon deficiency, along with an observed nitrogen enhancement relative to other elements, may suggest that ZNG-1 evolved off the AGB before the third dredge-up occurred. Also, iron depletions observed in other similar stars suggest that gas–dust fractionation in the AGB progenitor could be responsible for the observed composition of these objects. However, we need not invoke either scenario since the chemical composition of ZNG-1 is in good agreement with abundances found for a Population II star of the same metallicity.     

Profiles of spectral lines of an accretion ring around a Kerr black hole

Profiles of spectral lines emitted from an accretion ring around an object with strong gravitational field should be affected by Doppler shift, gravitational redshift, and deflection of light. Taking these effects into account, precise line profile of a Keplerian ring around a Kerr black hole for a distant observer is obtained by solving the kinetic equation of photons.     

Observations on the ecological importance of salt marshes in the Cumberland Basin,a macrotidal estuary in the Bay of Fundy

The Cumberland Basin, a 118 km² estuary at the head of the Bay of Fundy which has an average tidal range of about 11m, contains large tracts of salt marsh (15% of the area below highest high water). Low marsh (below about 0·9 m above mean high water) is composed almost exclusively of Spartina alterniflora while the vegetation on high marsh is more diverse but dominated by Spartina patens. Because of its higher elevation, high marsh is flooded infrequently for short periods by only extreme high tides. Low marsh is inundated much more frequently by water as much as 4m deep for periods as long as 4 h per tide. Temporal variability in the occurrence of extreme tides influences the flooding frequency of high marsh for any given month and year. Using a modification of Smalley's method, the mean annual net aerial primary production (NAPP) of low and high marsh is estimated to be 272 and 172 g C m^?2, respectively. Vegetation turnover times average 1·0 and 2·0 y for low and high marsh, respectively. Because of abundant tidal energy, much of the low marsh production appears to be exported and distributed widely about the estuary. Since high levels of turbidity suppress phytoplankton production, salt marshes produce approximately half of the carbon fixed photosynthetically in the Cumberland Basin. It is concluded that salt marshes play a major ecological role in the Cumberland Basin.     

A 2000-YEAR CONTEXT FOR MODERN CLIMATE CHANGE

ABSTRACT. Although considerable attention has been paid to the record of temperature change over the last few centuries, the range and rate of change of atmospheric circulation and hydrology remain elusive. Here, eight latitudinally well-distributed (pole-equator-pole), highly resolved (annual to decadal) climate proxy records are presented that demonstrate major changes in these variables over the last 2000 years. A comparison between atmospheric ¹⁴C and these changes in climate demonstrates a first-order relationship between a variable Sun and climate. The relationship is seen on a global scale.     

On the structure of oscillatory boundary layers

An empirical analysis is performed on the most detailed, recent measurements of turbulent oscillatory boundary layer flow. The measurements show that throughout elevations where the flow can be considered horizontally uniform, one deficit model is sufficient for describing the fundamental mode. Some general properties of the non dimensional velocity deficit D₁(z) appear with striking consistency. First of all the identity $\text{ln}\text{¦D}{}_{\mathrm{<mtext>1</mtext>}}\text{¦ ≡}\text{Arg}\text{D}{}_{\mathrm{<mtext>1</mtext>}}$, which is a theoretical result for smooth laminar flow, seems to hold with great accuracy for a large range of turbulent flow conditions as well. This is of principal theoretical interest because all previous analytical eddy viscosity models as well as numerical mixing length models predict a consistent and fairly large difference between Arg D₁ and $\text{ln}\text{¦D}{}_{\mathrm{<mtext>1</mtext>}}\text{¦}$. If the identity between $\text{ln}\text{¦D}{}_{\mathrm{<mtext>1</mtext>}}\text{¦}$ and Arg D₁ extends all the way to the bed, it means that the bed shear stress leads the free stream velocity by 45 degrees. It is also found that the structure of smooth turbulent oscillatory flows as measured by Kalkanis (1964) corresponds to a sharp maximum in the normalized energy dissipation rate.     

Spatial and temporal variations of solar coronal loops

Skylab EUV observations of an active region near the solar limb were analyzed. Both cool (T < 10⁶ K) and hot (T > 10⁶ K) loops were observed in this region. For the hot loops the observed intensity variations were small, typically a few percent over a period of 30 min. The cool loops exhibited stronger variations, sometimes appearing and disappearing in 5 to 10 min. Most of the cool material observed in the loops appeared to be caused by the downward flow of coronal rain and by the upward ejection of chromospheric material in surges. The frequent EUV brightenings observed near the loop footpoints appear to have been produced by both in situ transient energy releases (e.g. subflares) and the infall/impact of coronal rain. The physical conditions in the loops (temperatures, densities, radiative and conducting cooling rates, cooling times) were determined. The mean energy required to balance the radiative and conductive cooling of the hot loops is approximately 3 × 10^–3 erg cm^–3 s^–1. One coronal heating mechanism that can account for the observed behavior of the EUV emission from McMath region 12634 is heating by the dissipation of fast mode MHD waves.     

Magnetic stratigraphy observed in ferromanganese crust

Summary. A sample of ferromanganese crust deposit (SCHW-1D) was cut into two sets of 1 mm slices for palaeomagnetic study. Alternating field and thermal demagnetization, and isothermal remanent magnetization analyses were performed on each thin slice. The results reveal the presence of a stable magnetism and both normal and reversed polarity intervals in the specimens. The observed polarity intervals cannot be confidently correlated with the geomagnetic polarity time-scale of the last 10 Myr due to the polarity overlap inherent in the sampling technique. But the results confirm the slow accretion rate of ferromanganese deposit determined by ¹⁰Be method and suggest potential use of ferromanganese deposits in palaeomagnetic and tectonic studies.     

Gravitational and magnetic fields of some simple solids of revolution

Summary. Exact spherical harmonic expansions are given for calculating the gravitational and magnetic fields associated with certain uniform solids of revolution. The figures are those made by rotating a conic section about one of its principal axes. The coefficients in the expansions can be computed accurately and efficiently and this approach leads to a very satisfactory method for calculating the fields of geological bodies with approximate circular symmetry about a vertical axis. A complete theory of convergence is given for the expansions. Somewhat unexpectedly, the sphere of convergence is determined by the location of a number of equivalent point or line sources that lie within the body or on its edges.