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Schwartz, R. D.

Publications and source records attributed to Schwartz, R. D..

16 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Optical spectroscopy of HH-exciting stars from scattered light continua

Optical spectra of the reflected light continua visible in parts of several Herbig-Haro objects are presented. HH 100 unmistakably scatters the chromospheric spectrum of a strong emission-line T Tau star. HH 48S also reflects a T Tau stellar spectrum, as perhaps do HH 24 and HH 55, but less convincingly. HH 55 reveals photospheric absorption features too, corresponding to an M3.5 T Tau star. The continuum in HH 120 (= CG 30 HH) is unclassifiable while that in HH 46A has dimmed considerably (by a factor of order 20) although, only 7 yr ago, it clearly reflected a strong-line T Tau spectrum. It is concluded that at least some of the stars that excite Herbig-Haro nebulae, even when those stars are not directly visible, pass through a strong-line T Tau phase, and can undergo abrupt and dramatic changes in visual luminosity.

Cohen, M.↗
NASA NTRS1986

The dynamics of Herbig-Haro objects

Radial-velocity and proper-motion information on Herbig-Haro (HH) objects is analyzed for clues to the character of the supersonic flows that produce the objects. The correlations among space velocities, excitation states, internal velocity dispersions, electron densities, and positions relative to the exciting stars for the emission knots of HH 1 and HH 2 is examined. Whereas the interstellar-bullet model may account for most of the phenomena in the HH 1-HH 2 system, HH 43 is found to show characteristics of a stellar wind shock against an obstacle cloudlet. By contrast, the HH 46-HH 47 system exhibits a continuous, well-collimated jet of emission with knots that may be due to instabilities in the confined, supersonic flow.

Schwartz, R. D.↗
NASA NTRS1985

Highly supersonic bipolar mass ejection from a red giant OH/IR source - OH 0739 - 14

From long-slit spectrophotometry of the bipolar nebula associated with the unusual OH source, OH 0739 - 14, the presence of a blue companion to the M9 III central star was shown and a Herbig-Haro-like knot beyond each nebular lobe was discovered. From differential colors of the lobes and from radial velocities of these knots it was demonstrated that the system inclines its northern lobe in the forward direction. It was also shown that the nebulous knots are shocks being driven into an extensive circumstellar envelope, and that this material is very overabundant in nitrogen, suggesting that it is matter lost from a star of mass greater than 3 solar masses. A model of biconical ejection from a central binary is consistent with the OH observations, and a possible relation of OH 0739 - 14 to the symbiotic stars and to bipolar planetary nebulae is suggested.

Cohen, M.↗
NASA NTRS1985

Far-infrared observations of the exciting stars of Herbig-Haro objects. III - Circumstellar disks

Far-infrared observations of the exciting stars of Herbig-Haro objects are presented that (1) show these stars to be of low luminosity; (2) indicate that it is not usual for these objects themselves to be visible at far-infrared wavelengths; and (3) demonstrate the existence of spatially resolved, physically large, potentially disklike structures. These latter structures are resolved perpendicular to the directions of flow from the stars, but not parallel to the flows. In addition to these general properties, two new HH-exciting stars were discovered by searching along the extrapolated proper motion vectors for these HHs; and the jetlike object 'DG Tau B' was also detected.

Cohen, M.↗
NASA NTRS1985

The structure of Herbig-Haro object 43 and Orion dark cloud extinction

New ultraviolet and optical observations of Herbig-Haro object No. 43 are reported. Continuum and emission-line fluxes in the wavelength range 1250 to 7350 A have been measured. The continuum fluxes are best matched by an enhanced H exp 0 two-photon component added to H free-bound emission, assuming a Theta Ori extinction curve with E(B - V) = 0.2, R = 5. The structure and dynamics of three components within the object are discussed. The object has a radiative output of not less than 0.23 solar luminosities in ultraviolet and optical radiation combined. The energy requirements are discussed in terms of the production of shock waves by a collimated, supersonic mass outflow from a nearby infrared source.

Schwartz, R. D.↗
NASA NTRS1985

Low-excitation Herbig-Haro objects and interstellar extinction

Previous work on low-excitation Herbig-Haro (HH) objects has confirmed the existence of a strongly-enhanced hydrogen two-photon continuum which is produced by low-velocity shocks in neutral material. The theoretical two-photon energy distribution was compared with that observed for HH 43. With the addition of optical (3300 lambda 7000A) data to the ultraviolet (1200 lambda 3100A) data obtained with the I.U.E, the wavelength dependence of interstellar extinction toward HH 43 has been determined.

Schwartz, R. D.↗
NASA NTRS1985

Ultraviolet observations of low-excitation Herbig-Haro objects

The Herbig-Haro (HH) objects rank among the faintest objects (v approx. 17) observed with the I.U.E. Expectations that the low-excitation shock-excited HHs should be dominated by H two-photon (2q) UV emission were borne out in the first observation of HH 43 and 47 obtained in 1982. The UV continuous energy distributions in the SWP spectra of these objects were found to peak near 1500 Angstroms as predicted by the 2q hypothesis. In addition, emission lines in the Lyman band of H sub 2, excited by Lyman alpha fluorescence, were detected in HH 43. It is not clear if the molecular gas is coextensive with the atomic gas responsible for the optical emission, or if the molecular gas is immediately adjacent to the region of optical emission. The two-photon energy distribution and H sub 2 fluorescent emission were previously discussed.

Schwartz, R. D.↗
NASA NTRS1985

The nature and origin of Herbig-Haro objects

A brief description of the nature of Herbig-Haro nebulae is given, and the shock-wave origin of the nebulae is discussed. Kinematical evidence suggests that Herbig-Haro objects are ejected in bipolar flows from young stars. Evidence from infrared observations of the stars that excite Herbig-Haro objects is summarized; these stars appear to be T Tauri stars. The origin of these nebulae is discussed emphasizing energy required to power them, and a number of questions are posed pertaining to outflow mechanisms associated with the exciting stars.

Schwartz, R. D.↗
NASA NTRS1984

Far-infrared observations of southern Herbig-Haro objects

Ground-based and airborne infrared observations are presented of the vicinities of several HH objects. New photographs of these HH nebulae have made it possible to locate the exciting stars of HH 46/47 and HH 57 from their infrared peak positions. Bolometric luminosities of the exciting stars lie in the range 4-12, consistent with those for low-mass accreting protostars.

Cohen, M.↗
NASA NTRS1984

Far-infrared studies of Herbig-Haro objects and their exciting stars

Far-infrared (40-160 micron) observations of Herbig-Haro objects and their probable exciting stars are presented. The importance of these far-infrared observations is epitomized by the fact that, on average, 70 percent of the bolometric luminosity of a typical candidate star is radiated beyond the longest detected ground-based wavelength, even for those objects observed out to 20 micron from the ground. Extended far-infrared emission characterizes some of these regions. Some Herbig-Haro nebulae are themselves conspicuous 100 micron peaks (e.g., HH 1 and HH 25). A bipolar structure is found at 100 micron in the vicinity of the Cohen-Schwartz star. All the exciting stars must be low-mass objects (approximately less than 3 solar mass). It is argued that they might be approximately 1 solar mass protostars still in their accretion phase.

Cohen, M.↗
NASA NTRS1984

The structure of Herbig-Haro object 43 and Orion dark cloud extinction

New ultraviolet and optical observations of Herbig-Haro Object No. 43 are reported. Continuum and emission line fluxes in the range 1250 A equal to or less than lambda equal to less than 7350A have been measured. The continuum fluxes are best matched by an enhanced H two photon component added to H free bound emission, assuming theta Ori extinction curve with E(B-V) = 0.2, R = 5. The strucutre and dynamics of three components within the object are discussed. The object has a radiative output of equal to or greater than 0.23 infrared luminosity in ultraviolet and optical radiation combined. The energy requirements are discussed in terms of the production of shock waves by a collimated, supersonic mass outflow from a nearby infrared source.

Schwartz, R. D.↗
NASA NTRS1983

Ultraviolet continuum and H2 fluorescent emission in Herbig-Haro objects 43 and 47

IUE short wavelength spectra are presented for the low excitation Herbig-Haro objects HH 43 and HH 47. In the former, several emission lines in the Lyman band of H2 from an excited state are observed which are due to fluorescence from the H Ly-alpha line pumping a lower state (that is in turn excited by a low-velocity shock wave). No evidence of highly ionized gas emission is found in the UV spectra, and both objects exhibit a UV continuum which peaks in the vicinity of 1500 A and is probably caused by H two-photon emission enhanced by low velocity shock collisional excitation.

Schwartz, R. D.↗
NASA NTRS1983

The exciting stars of Herbig-Haro objects

Accurate astrometry and infrared photometry are presented for 16 objects that are believed to represent the exciting stars for Herbig-Haro (HH) objects in their vicinities. These identifications are made on the bases of steeply rising energy distributions, proper motions of HH objects, alignment of sources with HH objects, or far-infrared emission. Exciting stars for the following HH objects are newly discovered or recognized: HH 17; HH 31; HH 32; HH 33 and 40; HH 34; HH 38 and 43; HH group 14 in NGC 2264; RNO 40; RNO 43; and GGD 33a, 33b, and 35. Geometrical alignments of some sources with HH objects support the view that young stars are capable of channeling kinetic energy into small solid angles, as does the fact that some sources are slightly displaced from the apices of fan nebulae (HH 17, R Mon, Haro 6-10). These exciting stars span a wide range of bolometric luminosity, although all are likely to be very young.

Cohen, M.↗
NASA NTRS1978

Search with Copernicus for ultraviolet emission lines in the planetary nebula NGC 3242

The high-excitation planetary nebula NGC 3242 has been observed with the ultraviolet telescope-spectrometer aboard Copernicus. Wavelength intervals corresponding to the emission lines of O VI at 1032 A, He II at 1085 A, Si III at 1206 A, and N V at 1239 A have been scanned. Upper limits to the observed fluxes are reported and compared with predicted emission-line fluxes from this object.

Schwartz, R. D.↗
NASA NTRS1973

Apollo experience report: The development of design-loads criteria, methods, and operational procedures for prelaunch, lift-off, and midboost conditions

The prelaunch, lift-off, and midboost conditions that are important to the design of spacecraft are described. Original Apollo design concepts that were deficient in realistic and accurate analysis of spacecraft structural loads in a wind environment also are included. Important improvements in design criteria, mathematical models, wind-monitoring procedures, and loads analyses are discussed. Recommendations for future programs are presented.

Mackey, A. C.↗