Engineering topics

Boehm, K. H.

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

10 records

NASA NTRS1992

The ultraviolet spectrum of HH 24A and its relation to optical spectra

The spectrum of the brightest part (HH 24A) of the complex Herbig-Haro object HH 24 is investigated in the short-wavelength (1300-1930 A) UV range. The UV spectrum is detected in three observations with exposure times of 560-680 min. The spectrum shows only a continuum or a quasi-continuum and is neither comparable to that of a typical high-excitation object like HH 1 or HH 2, nor to that of a low-excitation object like HH 43 or HH 47. Two of the three spectra show a surprisingly similar detailed wavelength structure. A study of the spatial distribution of the UV continuum emission shows that this distribution is considerably wider than that of the optical forbidden-line emission, e.g., the forbidden S II 6716/6731 lines.

Boehm, K. H.↗

NASA NTRS1991

The ultraviolet continuum and the fluorescent H2 lines in low-excitation Herbig-Haro objects

Long-exposure IUE observations are used here to determine the spatial distribution of the fluorescent H2 line emission in the low-excitation objects HH 43 and HH 47. In HH 43, the spatial distribution of the fluorescent H2 line emission has a width equal to or smaller than the width of the point-spread function of IUE, while both the short-wavelength UV continuum and the optical forbidden S II lines show distributions which are wider by more than a factor of two. In HH 47, the results are qualitatively analogous, but the differences between the fluorescent HH 23 emission distribution on the one hand, and the UV continuum and optical forbidden S II distribution on the other, are smaller. These distributions indicate that the appropriate conditions for the formation of fluorscent H2 lines are fulfilled only in rather narrow regions for these low-excitation objects. A continuous energy distribution in HH 43 and HH 47 is found which differs only slightly from that in the high-excitation objects HH 1 and HH 2.

Boehm, K. H.↗

NASA NTRS1991

The ultraviolet spectrum of HH 24A and its relation to optical spectra

The spectrum of the brightest part (HH 24A) of the complex Herbig-Haro object HH 24 in the short wavelength UV range was studied. The object is of special interest since it is known that in the optical range the continuum is due to dust scattered light originating in a young stellar object while the shock excited emission lines are formed in HH 24A itself. The spectrum shows only a continuum or a quasi-continuum and is not comparable to that of the typical high excitation object like HH1 or HH2 nor to that of a low excitation object like HH3 or HH47.

Boehm, K. H.↗

NASA NTRS1990

Herbig-Haro objects

The IUE (International Ultraviolet Explorer) spectra of Herbig-Haro (HH) objects and their relation to the very detailed optical spectra available for these objects are studied. Useful information about the physics of HH objects in general and especially about their hydrodynamic models which are contained in these IUE observations is outlined. The merged spectra of high excitation, low excitation HH objects (like HH43 and HH47), and peculiar HH objects are discussed. Results of the spatial variation of lines and continua in HH objects are discussed. Their compatibility with predictions for aerodynamic and especially bow shock models is discussed. The problems arising in the interpretation of the continuous energy distribution in the short wavelength range are discussed. They require the presence of other emission mechanisms in addition to the collisionally enhanced two photon continuum. In HH43 the fluorescent H2 line emission comes from a surprisingly small spatial region. Implications of these results are discussed.

Boehm, K. H.↗

NASA NTRS1988

The spatial distribution of ultraviolet line and continuum emission in Herbig-Haro objects

Archival IUE data and monochromatic CCD images in the optical range are used to compare the spatial distribution of UV and optical emission in HH 1, HH 2, HH 24, HH 32, HH 43, and HH 47. For all six objects, the observed UV radiation is shown to originate in the objects themselves. The results indicate that the C IV and semiforbidden emission-line regions are small. Although the continuum in the IUE short-wavelength range displays a distribution that is broader than that of any measured line emission in the UV or optical range, the continuum distribution in the IUE long-wavelength range is quite narrow.

Lee, M. G.↗

NASA NTRS1987

Ultraviolet spectra of HH 1 and HH 2 - Spatial variations and the continuum problem

High-SNR 12-hr and 14-hr ultraviolet spectra of HH 1 and HH2 in the IUE short-wavelength range are reported. HH 1 data show a (spatial) half-width of the image size in the C IV 1548-A, 1551-A line which is smaller than the spatial half-width for the semiforbidden C II 1907-A, 1909-A line. A qualitatively similar situation is shown for HH 2, although differences in the image sizes are smaller than for HH 1. The continua of HH 1 and HH2 are found to have a relatively similar wavelength dependence, even in rather small features, and to both have their maxima between 1570 and 1580 A. It is noted that the observed wavelength of the continuum maximum agrees with the position of the maximum of the H2 fluorescence spectrum.

Boehm, K. H.↗

NASA NTRS1982

The ultraviolet continuous and emission-line spectra of the Herbig-Haro objects HH 2 and HH 1

Recent studies of the continuous spectrum of Herbig-Haro (HH) objects at optical and near-infrared wavelengths and the observation of continuous radiation in the ultraviolet have shown an unexpectedly steep increase of the flux toward shorter wavelengths. The present investigation provides the results of ultraviolet observations of HH 2. The obtained data are compared with the HH 1 data. It is found that HH 2 has an ultraviolet continuous and emission-line spectrum which is similar to that of HH 1. The UV line spectrum of HH 2H indicates an even somewhat larger ionization than does the HH 1 spectrum. As in HH1, the UV emission-line spectrum shows a much higher degree of ionization than that derived from the optical spectrum. Consequently, the same difficulty arises as in the case of HH 1. The complete UV plus optical spectrum cannot be explained by a single plane-parallel shock-wave model.

Boehm-Vitense, E.↗

NASA NTRS1982

Ultraviolet spectra of Herbig-Haro objects and of the environment of the Cohen-Schwartz star

Observations in both spectral regions were used in order to determine the continuous energy distribution and the emission line fluxes for H-H 2. The continuous spectrum is similar to that in H-H 1 and F lambda increases rapidly towards shorter wavelengths. This statement is found to be qualitatively correct for all obvious choices of the ultraviolet extinction curve if we use the E(B-V) value determined by the use of the S II method. The origin of the continuum remains enigmatic. The emission line spectrum of H-H 2 shows an even somewhat higher degree of ionization than the spectrum of H-H 1, indicating an even larger discrepancy between ionization information from optical data and that contained in the UV spectra. The immediate environment of the Cohen-Schwartz star emits a continuous spectrum similar to that of a H-H-object but increasing even more steeply towards shorter wavelengths.

Boehm, K. H.↗

NASA NTRS1982

IUE observations of Herbig-Haro and related objects

The I.U.E. spectra of the Herbig-Haro objectives H-H 1, H-H 2H, H-H 2G and H-H 32 A are considered. In order to obtain a better understanding of the physics of these intriguing objects and of the formation of the ultraviolet continua and emission lines in H-H objects, the UV spectra of the Cohen-Schwartz star, the T Tauri star AS 353A, and of the reflection nebula NGC 1999 (which is illuminated by the young object V 380 Orionis), are also examined.

Boehm, K. H.↗

NASA NTRS1981

The ultraviolet spectrum of Herbig-Haro Object 1

Continuum and emission line fluxes for HH 1 in the range of 1200-1300 A have been determined using IUE spectra, and it is found that the luminosity of HH 1 in this wavelength interval is slightly larger than 1 solar luminosity, or 20 times greater than for the wavelength range 3200-11,000 A. If averaged over intervals of 100 A, it is shown that the UV continuum rises almost monotonically toward shorter wavelengths over the entire interval 1300-3000 A. The UV continuum energy distribution cannot be explained by a T Tauri stellar continuum that is scattered by dust. Emission line identifications and flux measurements strongly confirm the statement that the high-ionization emission lines are too strong to be explained by shock-wave models derived from the emission line spectrum in the interval 3700-11,000 A. A possible explanation for this fact is discussed.

Boehm, K. H.↗