arXiv subjects

Steven N. Shore

Publications and source records attributed to Steven N. Shore.

39 records · Page 3Linked to original sources

arXiv1998

A Dynamical Study of the Non-Star Forming Translucent Molecular Cloud MBM16: Evidence for Shear Driven Turbulence in the Interstellar Medium

We present the results of a velocity correlation study of the high latitude cloud MBM16 using a fully sampled $^{12}$CO map, supplemented by new $^{13}$CO data. We find a correlation length of 0.4 pc. This is similar in size to the formaldehyde clumps described in our previous study. We associate this correlated motion with coherent structures within the turbulent flow. Such structures are generated by free shear flows. Their presence in this non-star forming cloud indicates that kinetic energy is being supplied to the internal turbulence by an external shear flow. Such large scale driving over long times is a possible solution to the dissipation problem for molecular cloud turbulence.

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arXiv1997

Detailed NLTE Model Atmospheres for Novae during Outburst: I. New Theoretical Results

We present new detailed NLTE calculations for model atmospheres of novae during outburst. This fully self-consistent NLTE treatment for a number of model atoms includes 3922 NLTE levels and 47061 NLTE primary transitions. We discuss the implication of departures from LTE for the strengths of the lines in nova spectra. The new results show that our large set of NLTE lines constitute the majority of the total line blanketing opacity in nova atmospheres. Although we include LTE background lines, their effect are small on the model structures and on the synthetic spectra. We demonstrate that the assumption of LTE leads to incorrect synthetic spectra and that NLTE calculations are required for reliably modeling nova spectra. In addition, we show that detailed NLTE treatment for a number of ionization stages of iron changes the results of previous calculations and improve the fit to observed nova spectra.

astro-ph↗

arXiv1997

Abundance analysis of the slow nova PW Vulpeculae 1984

We determine the elemental abundances for the ejecta of the slow nova PW Vul 1984. Our technique uses a minimization of the emission line fits of a photoionization model to available ultraviolet, optical and infrared spectra. We find the following abundances (by number) with respect to solar: He/H = 1.0 $\pm$ 0.4, C/H = 7.0 $^{+7}_{-4}$, N/H = 85 $^{+59}_{-41}$ and O/H = 6 $^{+7}_{-2}$. In addition, there is weak evidence for solar Ne and Mg and twice solar Fe. Previous studies (Saizar et al. 1991 and Andreä et al. 1991, 1994) of PW Vul have yielded considerable differences in their derived elemental abundances for the ejecta. Our abundances fall in between the previous studies. To explain the discrepant abundances, we analyze in detail the data and methods used to obtain the previous results. The abundances of Saizar et al. (1991) are significantly smaller then our values because of the lower electron temperature used by Saizar et al. in deriving elemental abundances from ion abundances. Andreä et al. (1991) used an ionization correction method to obtain their abundances and verified their results with a photoionization model (Andreä et al. 1994). Our analysis of their data shows that the absolute fluxes of the optical emission lines used by Andreä are underestimated by 15% leading to a factor of 2 increase in their derived abundances. We also find the photoionization model used by Andreä et al. (1994) predicts 2 times more carbon than the photoionization code we used even when fitting the same data with similar model parameters.

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