Engineering topics

Hamilton, Andrew J. S.

Publications and source records attributed to Hamilton, Andrew J. S..

5 records

NASA NTRS1993

Cosmic evolution of extragalactic C 1, C 2, and CO luminosity

Carbon is the fourth most abundant element in the Galaxy with an abundance of approximately 4 x 10(exp -4) relative to hydrogen. Of all abundant metals it is the easiest to observe in the interstellar medium (ISM). Carbon can be found in four dominant forms: dust grains, C 2, C 1, and CO. The latter is the most abundant molecule (next to H2) in molecular clouds. All three gas-phase forms produce strong sub-mm wavelength emission lines and are the principal tracers of the warm and dense neutral phases of the ISM. We calculate the gas-phase abundances of neutral carbon (C 1), ionized carbon (C 2), and carbon monoxide (CO) as a function of cosmic time or redshift z in an idealized scenario of galactic evolution.

Bally, John↗

NASA NTRS1989

Topology of large-scale structure. IV - Topology in two dimensions

In a recent series of papers, an algorithm was developed for quantitatively measuring the topology of the large-scale structure of the universe and this algorithm was applied to numerical models and to three-dimensional observational data sets. In this paper, it is shown that topological information can be derived from a two-dimensional cross section of a density field, and analytic expressions are given for a Gaussian random field. The application of a two-dimensional numerical algorithm for measuring topology to cross sections of three-dimensional models is demonstrated.

Melott, Adrian L.↗

NASA NTRS1988

Ejecta in SN 1006: The knotty issue

The 1988 IUE SWP observations of a faint sdOB star situated behind the remnant of the supernova of AD 1006 are presented. These spectra along with IUE spectra of the star taken between 1982 and 1986 provide a detailed look at the elemental composition and dynamical properties of the SN 1006 remnant. Over the 6 years there were no significant changes in the absorption features associated with the remnant at 1281, 1330, or 1420 A. While the lack of variability in these absorption lines makes it impossible to decide whether the ejecta is distributed smoothly or in knots, it is clear that the 1281 A feature is a blend, requiring either S II absorption redshifted at 6000 km/sec plus Si II 1260 at 5200 km/sec, or else 2 individual Si absorbing regions.

Fesen, Robert A.↗

NASA NTRS1988

High-velocity ultraviolet iron, silicon, oxygen, and sulfur absorption features associated with the remnant of SN 1006

New low-dispersion IUE spectra of a faint sdOb star located in a direction near the center of the SN 1006 remnant are presented. The UV spectrum of the star exhibits several strong absorption features which are uncharacteristic of its optical sdOB star classification. The identification by Wu et al. (1983) of very broad absorption features at 1610, 2370, 2600 A as Fe II gas associated with the SN 1006 remnant is supported. The observed Fe II line profiles indicate a concentration of Fe(+) toward the remnant's center with a radial velocity range on the order of + or - 5000 km/s. Strong absorption lines at 1281, 1331, and 1420 A are interpreted as originating from clumps of O-, Si- and S-rich ejecta with central radial velocities in the range 5000-6500 km/s. The presence in the SN 1006 remnant of an expanding sphere of iron-rich ejecta interior to O-, Si-, and S-rich clumps of ejecta having velocities over the maximum seen for the Fe II absorbing gas is consistent with type Ia Sn observations and carbon deflagration models.

Fesen, Robert A.↗

NASA NTRS1988

The reionization of unshocked ejecta in SN 1006

The validity of carbon-deflagration models white dwarf models for type Ia supernovae is investigated by examining whether most of the iron in the center of SN 1006 exists in forms other than Fe II, such as iron grains or other ionic stages of iron, as the models require. The possible ways in which iron can be hidden in SN 1006 are reviewed, and an argument on observational grounds is made against any appreciable fraction of iron in grains or Fe I. Various mechanisms for ionizing unshocked iron beyond Fe II are discussed; the most probable mechanism for ionizing the iron appears to be photoionization by UV and X-ray emission from reverse-shocked ejecta. A detailed model for this reverse-shcok photoionization mechanism is described.

Hamilton, Andrew J. S.↗