Engineering topics

Jura, Michael

Publications and source records attributed to Jura, Michael.

3 records

NASA NTRS1991

Carbon stars with oxygen-rich circumstellar material

The IUE satellite was used to search for companions to two carbon-rich stars with oxygen-rich circumstellar envelopes, EU And and V778 Cyg. Depending upon the amount of interstellar extinction and distances (probably between 1 and 2 kpc from the Sun) to these two stars, upper limits were placed between approx. 1.5 and 6 solar mass to the mass of any main sequence companions. For the 'near' distance of 1 kpc, it seems unlikely that there are white dwarf companions because the detection would be expected of ultraviolet emission from accretion of red giant wind material onto the white dwarf. A new model is proposed to explain the oxygen-rich envelopes. If these stars have a high nitrogen abundance, the carbon that is in excess of the oxygen may be carried in the circumstellar envelopes in HCN rather than C2H2 which is a likely key seed molecule for the formation of carbon grains. Consequently, carbon particles may not form; instead, oxygen-rich silicate dust may nucleate from the SiO present in the outflow.

Jura, Michael↗

NASA NTRS1988

Interstellar matter within elliptical galaxies

Multiwavelength observations of elliptical galaxies are reviewed, with an emphasis on their implications for theoretical models proposed to explain the origin and evolution of the interstellar matter. Particular attention is given to interstellar matter at T less than 100 K (atomic and molecular gas and dust), gas at T = about 10,000 K, and gas at T = 10 to the 6th K or greater. The data are shown to confirm the occurrence of mass loss from evolved stars, significant accretion from companion galaxies, and cooling inflows; no evidence is found for large mass outflow from elliptical galaxies.

Jura, Michael↗

NASA NTRS1987

The C-12/C-13 isotope ratio of the interstellar medium in the neighborhood of the sun

Data from observations of Xi Per, P Cyg, 20 Tau, and 23 Tau, obtained at 4232 and 3957 A using a coude spectrograph and a 1872-element reticon on the 3-m Shane telescope at Lick Observatory during 1984-1985, are combined with data on Zeta Oph (Hawkins et al., 1985) and used to estimate the C isotope ratio of the ISM near the sun. The results are presented in extensive tables and graphs and characterized in detail. The (C-12)H(+)/(C-13)H(+) abundance ratios toward the five stars are found to agree to within 12 percent and shown to be representative of the C-12/C-13 ratios in the gas, strongly indicating that the local ISM is homogeneous. The difference between the ISM ratio (43 + or - 4) and the solar-system value (89) is attributed to the chemical evolution of the ISM in the 4.9 Gyr since the formation of the sun.

Hawkins, Isabel↗