Engineering topics

Hagen, W.

Publications and source records attributed to Hagen, W..

10 records

NASA NTRS1986

Ultraviolet and infrared observations of stars with 'quenched' chromospheres and the nature of mass loss

Previous observational evidence implies that the presence of Ca II emission, a chromospheric indicator, is correlated with the gas/dust ratio in the envelopes of red giant and supergiant stars. An attempt is made to determine whether this correlation can be generalized to all chromospheric activity indicators and the gas/dust ratio. New ultraviolet observations address the strength of UV emission features and the fraction of the total chromospheric flux emitted in various lines. Evidence is found that chromospheres are not completely quenched in the presence of dust, but that significant alteration of relative radiative loss patterns may occur. These observations are interpreted in terms of an instability that converts warm, chromospheric gas into near-surface dust grains and cool gas capable of supporting molecular masing. This supports the dust-driven mass loss scenario for red giant winds.

Stencel, R. E.↗

NASA NTRS1986

IUE and IRAS observations of luminous M stars with varying gas-to dust ratios

Circumstellar gas and dust surrounding M giants and supergiants show luminous M stars to split into two distinct classes. Stars with a high gas to dust ratio all show chromospheric Ca II, H, and K emission. Stars with a high dust to gas ratio do not show chromospheric Ca II emission but are the only ones to show Balmer emission indicative of atmospheric shocks and are also the only ones to show maser emission. In order to determine whether all chromospheric indicators disappear in high dust to gas ratio stars, a survey of stars in both these classes was conducted with the IUE satellite. Long wavelength infrared fluxes for the program stars were obtained from the IRAS point source catalog. There is no obvious difference in the long wavelength observations between the two groups of stars. The long wavelength excess tends to follow the 10 micron excess and not the dust to gas ratio.

Hagen, W.↗

NASA NTRS1985

On the rarity of FK Com stars

Very high-dispersion spectra (2.5 A/mm) were obtained of 31 southern late-type stars, predominantly early G giants, in an effort to find new rapidly rotating, active stars which would be FK Com-like. Measurements of linewidths and the strength of chromospheric Ca II K-line emission are presented, but no new star could be added to the class of 'rapid rotators'. Space densities and evolutionary lifetimes for FK Com stars are discussed.

Hagen, W.↗

NASA NTRS1984

The 1982 eclipse of 31 Cygni

UBV photometry and optical-UV spectroscopy of the primary eclipse of the long period Zeta Aurigae-like system 31 Cygni are reported. The precise timings made possible by the photometry imply that the spectral features could be due to an accretion shock associated with a hot star embedded in an extended chromosphere surrounding the red supergiant. The data also suggest an extended clumpy structure to the atmosphere of the late-type supergiant in the binary.

Hopkins, J. L.↗

NASA NTRS1983

A laboratory study of the infrared spectra of interstellar ices

The 3 micron 'ice' band observed in absorption and polarization and other absorption features in interstellar infrared spectra are studied in the laboratory in low temperature (10-130 K) solid mixtures of H2O and other molecules. General empirical rules are derived which relate the shape and relative intensity of the H2O infrared absorptions to thermal history, degree of H2O dilution and hydrogen bonding capacity of the dilutant. Observations of specific features anticipated in low noise medium resolution spectra will yield potentially valuable information on the degree of H2O dilution, the nature of the dilutant and the thermal history of the absorbing solid mixture. Under well defined conditions the peak of the hitherto unobserved librational '12 micron' H2O absorption is shifted to outside the current infrared observation window beyond 13.5 microns.

Hagen, W.↗

NASA NTRS1983

The three micron 'ice' band in grain mantles

Attention is given to the influence of different mantle constituents on extinction and polarization due to H2O absorption in grain mantles, particularly the 3250/cm band. With respect to BN, the simultaneous reproduction of the extinction and polarization band shapes occurs by normal size particles containing mixtures of H2O with other molecules. As regards the 3-micron absorption in OH 231.8 plus 4.2, the data can be best fitted with pure amorphous H2O grains which have been heated to (or created at) about 80 K. The variation in grain mantle composition between young stellar objects and late-type stars loosing mass is attributed to a fundamental difference in grain formation and evolution.

Hagen, W.↗

NASA NTRS1983

Interstellar ice

The 3250/cm 'ice' band observed in absorption and polarization in interstellar spectra is studied in the laboratory in low-temperature solid mixtures of H2O and other molecules. General empirical rules are derived which relate the shape and relative intensity of the H2O infrared absorptions to the degree of H2O dilution and hydrogen-bonding capacity of the dilutant. The chemical composition of mantles accreting on interstellar grains inside dense (1000-100,000/cu cm) molecular clouds has been calculated numerically. The reaction scheme comprises gas-phase as well as grain surface reactions. The results show that in most circumstances grain mantles consist of the molecules H2O, H2CO, NH3, N2, O2, CO, and CO2. The expected infrared characteristics of the calculated grain mantles are discussed with an emphasis on the observed 3250/cm 'ice' band. Grain mantles accreted at a density of about 10,000/cu cm contain large concentrations of H2O (about 60 percent) and produce a broad 3250/cm 'ice' band.

Tielens, A. G. G. M.↗

NASA NTRS1982

Model calculations of the molecular composition of interstellar grain mantles

A chemical reaction scheme comprising gas phase as well as grain surface reactions is used for the numerical calculation of the chemical composition of mantles accreting on interstellar grains. The composition of the growing grain mantle is determined on the basis of the relative accretion rates of the gas phase molecules and diffusion-controlled surface reactions. Results show that grain mantles generally consist of the molecules H2O, H2CO, N2, O2, CO, CO2, H2O2, and NH3. A detailed examination of the formation of H2 on grain surfaces leads to the conclusion that it proceeds through hydrogen abstraction from such molecules as H2CO, H2S, N2H2, and N2H4. The IR characteristics of the calculated grain mantles are discussed with emphasis on the observed ice band at the 3250/cm wavelength.

Tielens, A. G. G. M.↗

NASA NTRS1981

The circumstellar envelopes of F- and G-type supergiants in the Large Magellanic Cloud

The outer atmospheres of four F- and G-type supergiants in the LMC are compared with those of their Milky Way counterparts by means of 2.5 and 5.1 A/mm high dispersion Echelle spectra. Na I D line doubling indicates extensive circumstellar envelopes, mass loss rates greater than 0.00001 solar masses/year, and outflow velocities of 10-60 km/sec. The Ca II H and K lines yield new data on extragalactic star chromospheres.

Hagen, W.↗

NASA NTRS1981

A comparison of circumstellar gas and dust in M giants and supergiants

This paper presents the results of a study of circumstellar gas and dust in a larger sample of stars than that of Hagen (1978). The gas-to-dust ratio varies considerably from star to star. The observations were obtained at Cerro Tololo Interamerican Observatory and Kitt Peak National Observatory. CS gas was observed with 2.5 and 5.1 A/mm echelle spectra obtained with the 4-meter telescopes. CS dust was observed through infrared photometry done with the CTIO 60 and KPNO 50 telescopes.

Hagen, W.↗