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Results for “Herbig-Haro objects”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
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NASA NTRS1981

Spectropolarimetry of Herbig-Haro objects and the exciting star of HH 30

Spectrophotometric and spectropolarimetric observations are presented of three HH objects: HH 11, 30, and 43. Although null polarization results are obtained for HH 11 and 43, the unusually strong continuum of HH 30 is linearly polarized by 3%. The emission lines in this nebula are unpolarized. The electric vector position angle appropriate to the continuum polarization, and the presence of Fe II emission lines apparently from the photosphere of a T Tauri-like star, indicate HL Tau as the exciting/illuminating star for HH 30. Evidence is adduced for a highly anisotropic distribution of circumstellar obscuration around this star.

Cohen, M.↗
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 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 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 NTRS1982

Infrared observations of low-mass star formation in Orion - HH objects

The results of a preliminary analysis of IR data on Herbig-Haro objects in the Orion nebula are reported. The observations were made with the high angular resolution IR photometry equipment on the NASA Kuiper Airborne Observatory and the NASA facility on Mauna Kea, HI. Data were taken in the 1-200 microns region with 40, 6, and 8 arcsec resolution. Attention was focused on NGC 1999 (HH1-3) and M78 (HH24-25) and the determination of absolute luminosities of the exciting stars. Measurements were also made of the IR energy distribution in the thermally emitting dust clouds and the point sources. Herbig-Haro objects featured compact and far IR sizes and large visual extinction, in addition to a steeply rising energy distribution up to 50-100 microns, where the luminosity emitted was concentrated.

Harvey, P. M.↗
NASA NTRS1984

VLA observations of T Tauri stars. II - A luminosity-limited survey of Taurus-Auriga

The results of a 4.885-GHz VLA survey of 46 T Tau stars and Herbig-Haro objects with log L 0.2 or greater in the Taurus-Auriga dark clouds, performed in February 1982, with 40-60-min observation times, are presented in tables and contour maps and discussed. Upper limits are given for objects not detected at 4.885 GHz; additional observations at 1.465, 14.965, and 22.485 GHz are included for the objects detected; and spectral indices are derived for 10 objects. The individual objects are characterized in detail, and it is concluded that detectable radio emission is more likely for T Tau stars with associated Herbig-Haro objects than for those without. The implications of the nonthermal spectra identified in several objects for theories of theoretical models of radio emission are indicated.

Bieging, J. 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 NTRS1985

Radio continuum emission from premain sequence stars and associated structures

VLA 6 cm (4860 MHz with 100 MHz total bandwidth) C-array observations of regions of recent star formation containing premain sequence (PMS) stars, Herbig-Haro objects, and stellar jets, are presented. Three PMS stars, HL Tau, XZ Tau and FS Tau, were definitely (6-sigma) detected and FS Tau B is possibly (5-sigma) detected. The mass loss rates implied for spherically-symmetric stellar winds with outflow velocities of 200 km/s are in the range 1-2 x 10 to the -8th solar masses/yr. HL Tau shows extended structure including a 3-sigma detection of emission possibly associated with the jet from this star. No Herbig-Haro objects were detected at a typical 3-sigma rms level of 0.12 mJy/beam.

Brown, A.↗
NASA NTRS1984

The distribution of shocked gas in the bipolar nebulae CRL 2688 and CRL 618

Maps of the H2 emission from the bipolar nebulae CRL 2688 and CRL 618 are presented, along with a map of the 2.1-micron continuum emission from CRL 2688. The H2 emission is seen in the direction of the lobes of each nebula and not in between the lobes. From the distribution of the H2 and continuum emission, it is argued that the H2 is excited in shock waves produced in the lobes of the visible nebulae by fast winds from the central stars which overtake slower moving material lost in a slow wind during the red-giant phase of each object. These shocks may be similar to those seen in Herbig-Haro objects. The mass-loss rates for the fast winds in each object are estimated from the H2 data, and a brief discussion is given of the origin of these winds.

Gatley, I.↗
NASA NTRS1980

Red and nebulous objects in dark clouds - A survey

A search on the NGS-PO Sky Survey photographs has revealed 150 interesting nebulous and/or red objects, mostly lying in dark clouds and not previously catalogued. Spectral classifications are presented for 55 objects. These indicate a small number of new members of the class of Herbig-Haro objects, a significant number of new T Tauri stars, and a few emission-line hot stars. It is argued that hot, high-mass stars form preferentially in the dense cores of dark clouds. The possible symbiosis of high and low mass stars is considered. A new morphology class is defined for cometary nebulae, in which a star lies on the periphery of a nebulous ring.

Cohen, M.↗
NASA NTRS1978

A study of the Taurus dark cloud complex

A near-infrared survey has been conducted of nearly 20 square degrees of the Taurus dark cloud complex. Additional observations have been made of selected objects detected in this survey. These observations show that recently formed stars are spread throughout the cloud and that these stars are primarily T Tauri stars or T Tauri-like stars. Two luminous objects are identified embedded in the reflection nebulae IC 359 and IC 2087. A new Herbig-Haro object is also described. The reddening law of the dark cloud material is discussed; it does not appear to be unusual in the infrared. Comparison of the young stellar population in Taurus with that in Ophiuchus suggests that the star formation mechanisms in the two regions are qualitatively different

Elias, J. H.↗
NASA NTRS1984

IRAS observations near young objects with bipolar outflows L1551 and HH 46-47

A 6-solar luminosity dust-embedded precursor of a low-mass (about 1 solar mass) pre-main-sequence star has been discovered with IRAS near the northeast lobe of the bipolar outflow region in the dust cloud L1551 and designated L1551 NE. Star formation is proceeding in at least two locations in L1551, reminiscent of the situation in regions of more massive star formation. If the position of NE in the flow from IRS 5 is indicative of the flow having initiated star formation in NE, then the object can be only about 24,000 years old. Alternatively, NE could appear by chance to lie in the flow from IRS 5. In the globule ES 0210-6A, a 12 solar luminosity dust-embedded precursor of a low-mass (about 1 solar mass) pre-main-sequence star is found which drives the bipolar flow responsible for the string of Herbig-Haro objects HH 46-47 A-D. In this globule, there is only one region of active star formation.

Emerson, J. P.↗
NASA NTRS1976

CO observations of NGC 1579 /S222/ and S239

The 2.6-mm lines of (C-12)O and (C-13)O have been observed toward the small galactic diffuse nebulae NGC 1579 (S222) and S239. The H92-alpha recombination line has also been detected from NGC 1579. Toward NGC 1579, evidence was observed for self-absorption in the (C-12)O line. For both regions, high-velocity wings and line broadening are observable in the (C-12)O line; the features observed toward S239 suggest ordered free-fall collapse of a localized region of the cloud onto a newborn stellar cluster. Examination of the available data suggests that NGC 1579 is both a reflection nebula (illuminated by LKH-alpha 101) and an obscured H II region excited by a star of spectral type near B1, while S239 is a reflection nebula or a Herbig-Haro object. The present studies of these regions show that line widening in CO is at least as important an indicator of star-formation activity as enhanced line emission.

Knapp, G. R.↗
NASA NTRS1979

Shock waves in the interstellar medium

Calculations of the optical and UV emission-line intensities and column densities of ions observable in the optical and UV are presented for plane-parallel steady-state shock waves in the interstellar medium. The range of shock velocities considered is from 50 to 200 km/s, and preshock densities are between 1 and 300 per cu cm. The ionization state of the preshock gas is found to be an important parameter, and several sets of elemental abundances corresponding to various amounts of depletion onto grains are used. The results are compared with observations of the Cygnus Loop, the Vela supernova remnant, and Herbig-Haro objects.

Raymond, J. C.↗
NASA NTRS1982

The case for anisotropic mass loss from T Tauri stars

Observational evidence and theoretical arguments are assembled in favor of directed, rather than isotropic, mass flows from T Tauri stars. These arguments include the structure of T Tauri nebulosities, radio continuum maps of the stars, the motions of Herbig-Haro objects away from their exciting T Tauri stars, bipolar CO flows, and particularly the spatial coincidence of an optical jet and radio emission associated with an embedded, probably T Tauri star in the dark cloud L1551.

Cohen, M.↗
NASA NTRS1984

Far-infrared observations of a star-forming region in the Corona Australis dark cloud

A high-resolution far-IR (40-250-micron) survey of a 0.9-sq-deg section of the core region of the Corona Australis dark cloud (containing very young stellar objects such as T Tauri stars, Herbig Ae and Be stars, Herbig-Haro objects, and compact H II regions) is presented. Two extended far-IR sources were found, one associated with the Herbig emission-line star R CrA and the other with the irregular emission-line variable star TY CrA. The two sources have substantially more far-IR radiation than could be expected from a blackbody extrapolation of their near-IR fluxes. The total luminosities of these sources are 145 and 58 solar luminosity, respectively, implying that the embedded objects are of intermediate or low mass. The infrared observations of the sources associated with R CrA and TY CrA are consistent with models of the evolution of protostellar envelopes of intermediate mass. However, the TY CrA source appears to have passed the evolutionary stage of expelling most of the hot dust near the central source, yielding an age of about 1 Myr.

Cruz-Gonzalez, I.↗