Engineering topics

Wynne, D.

Publications and source records attributed to Wynne, D..

3 records

NASA NTRS1992

A low-cost, CCD solid state star tracker

Applied Research Corporation (ARC) has developed an engineering model of a multi-star CCD-based tracker for space applications requiring radiation hardness, high reliability and low power consumption. The engineering unit compared favorably in functional performance tests to the standard NASA single-star tracker. Characteristics of the ARC star tracker are: field of view = 10 deg x 7.5 deg, sensitivity range of -1 to +5 star magnitude, NEA = 3 in x 3 in, linearity = 5 in x 5 in, and power consumption of 1-3 W (operating mode dependent). The software is upgradable through a remote link. The hardware-limited acquisition rate is 1-5 Hz for stars of +2 to +5 magnitude and 10-30 Hz for -1 to +2 magnitude stars. Mechanical and electrical interfaces are identical to the standard NASA star tracker.

Chmielowski, M.↗

NASA NTRS1992

Photospheric velocity gradients in B1 supergiants

We present IUE spectra for a set of B1 supergiants. These data clearly demonstrate that the Si III 1300A multiplet (lower level 6.6 ev above ground) becomes progressively more asymmetric with increasing luminosity or, equivalently, mass loss. In the most luminous supergiants, the cores of the 1300A multiplets become displaced by up to -150 km/s relative to nearby, weaker lines. In addition, systematic velocity shifts and asymmetries are also present in the strong Si III singlets 1312A and 1417A in the more luminous stars. The obvious implication of these observations is that the outer photospheres of B supergiants are affected by radial expansion, and this may account for why even non-LTE line analyses of these stars require large micro-turbulent velocity fields, and why line blanketed LTE models underestimate their overall UV line blanketing.

Massa, D.↗

NASA NTRS1991

Carbon and nitrogen abundances in the BN supergiant HD 93840, and their implications for normal Galactic supergiants

It is demonstrated how carbon and nitrogen abundances of luminous B stars can be determined by a combined analysis of their UV photospheric and wind lines. It is shown that HD 93840 has nearly the same temperature and surface gravity as the normal B1 Ib star Zeta Per. These two stars are compared on the basis of their UV photospheric silicon spectra and the differences in their photospheric CNO and metallic lines are discussed. A quantitative comparison between the wind profiles of the two stars is made. A simple model for the compositions of both atmospheres is used to derive the fraction of material in each atmosphere which has undergone CNO processing. It is argued that the enriched material must have resided in a nuclear burning core for only a very short time. Best estimates of 0.09 + or - 0.07 and 0.90 + or - 0.1 are made for the carbon abundances relative to cosmic ones for HD 93840 and Zeta Per, respectively.

Massa, D.↗