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Bohm, K. H.

Publications and source records attributed to Bohm, K. H..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The gas-phase iron abundance in Herbig-Haro objects

The gas-phase abundance ratios Fe/S and Fe/O have been determined for the Herbig-Haro objects HH 1, HH 7, HH 11, HH 43A, and 'Burnham's Nebula' (HH 255). It is the purpose of this study to decide whether a sizeable fraction of the Fe in these HH objects is still bound in dust grains or whether the observed matter has gone through sufficiently fast shock waves so that the dust grains have been essentially destroyed and most of the iron has gone back into the gas phase. We have determined the abundance ratios using statistical equilibrium calculations for the ions Fe(+), S(+), and O(+). (These are the most abundant ions of the elements in question.) Abundance determinations have been made using homogeneous models of the HH objects for which electron temperatures and densities have been determined observationally from forbidden line ratios. The results show that the Fe/S ratio in the objects HH 1, HH 7, HH 11, and HH 43A agrees very well with the Population I abundance ratio. Only Burnham's Nebula (HH255) shows an Fe/S ratio which is about three times lower indicating a shock-wave history which is quite different from that of the other HH objects.

Beck-Winchatz, B.↗
NASA NTRS1991

Ultraviolet and optical extinction for the Herbig-Haro objects HH1 and HH2

Based on a comparison of reddening-corrected line ratios with predictions from bow-shock models, an attempt is made to determine which type of reddening curve is the most appropriate for HH1 and HH2. Specifically, the extinction curves for R = 3.1 and R = 5.4 are considered. In order to discriminate between these two curves, the flux ratios I(C IV 1550)/I(semiforbidden C III 1909) and I(C IV 1550)/I(H-beta) are used together with information on E(B-V). The suprising result is that the R = 3.1 curve leads to a better agreement between predicted and observed line flux ratios than the R = 5.4 curve.

Bohm, K. H.↗
NASA NTRS1985

The unexpected ultraviolet variability of Herbig-Haro object 1

The line fluxes of the C IV 1550 A and semiforbidden C III 1909 A emission lines in HH 1 are noted to have monotonically decreased by factors of 4-6 between 1979 and 1983, despite a lack of indications of optical range changes. The thickness of the shocked layers and preshock density can be estimated on the basis of these rapid changes, with results suggesting a clumpy medium that leads to truncated shock waves with column densities insufficient for the development of complete recombination zones.

Brugel, E. W.↗
NASA NTRS1984

The reflection nebula NGC 1999

The properties of dust particles in regions of recent star formation often seem to be different from the 'average galactic' dust properties. The present investigation is concerned with a determination of the ratio of nebular intensity to the stellar flux for the system NGC 1999/V380 Ori in the ultraviolet. It is found that the stellar flux curve in the ultraviolet agrees surprisingly well with the corresponding curve for the system NGC 7023/HD 200775. This is at least compatible with the assumption that the dust properties in NGC 1999, as well as the basic geometric structure of the reflection nebula, are very similar to those in NGC 7023.

Cardelli, J. A.↗
NASA NTRS1984

The ultraviolet spectrum of a strongly reddened, high-excitation Herbig-Haro object

Short- and long-wavelength IUE spectra of the rather strongly reddened, high radial velocity Herbig-Haro object HH 32A have been obtained. The object is well known for its large positive radial velocity and for its unusually large velocity dispersion. In consequence of the large ultraviolet extinction, the spectra are faint. The semiforbidden C III 1909 and Mg II 2800 emission lines are, however, clearly detected, and their fluxes can be measured with reasonable accuracy. C IV 1550 and Si III 1892 are very probably present. The continuum can be detected convincingly in the wavelength range 1500-1900 A. In other regions it is just barely detectable. The continuum has an energy distribution which is probably very similar to that of HH 1 and HH 2H. If an average galactic extinction curve is used, the line fluxes for semiforbidden C III 1909 and C IV 1550 indicate a shock velocity of at least 140 km/s which is higher than for HH 1 or HH 2. If a Theta Ori-type extinction curve is used instead, ultraviolet line ratios are obtained which are rather similar to those in HH 1 and HH 2.

Bohm, K. H.↗