Search NASA⌕ Search

SEARCH · Search NASA

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Pre-main sequence stars

Observations of premain-sequence (PMS) stars obtained with the IUE satellite since its launch in 1978 are reviewed. The major types of PMS stars are listed and briefly characterized: T Tau stars, Herbig Ae stars, FU Ori objects, weak-emission PMS stars, and Herbig-Haro objects. The IUE data for a catalog of PMS objects are then presented in a table, graphs, and sample spectra and described in detail. Topics addressed include general spectral profiles, the Mg II h and k lines, the FUV emission lines, the UV continuum, and the impact of the IUE on astrophysical models of PMS stars. The need for observations with higher spectral resolution and much greater sensitivity is indicated, and the ability of the Hubble Space Telescope High-Resolution Spectrograph and the proposed NASA/ESA Lyman FUV Spectroscopic Explorer to meet these requirements is considered.

Imhoff, Catherine L.↗
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 NTRS1987

Radio emission from pre-main-sequence stars in Corona Australis

The central region of the Corona Australis molecular cloud surrounding the stars R and TY CrA has been studied using the VLA at 6 cm. Eleven radio sources are detected including five associated with pre-main-sequence objects. The most striking is associated with the near-IR source IRS 7 and shows a complex structure comprising two strong pointlike sources positioned either side of the deeply embedded IR source and two extended lobes of radio emission. The IRS 7 radio source appears to be similar to that associated with Lynds 1551 IRS 5 but has a considerably larger angular size. The other detected sources include the massive pre-main-sequence star TY CrA, the near-IR sources IRS 1 and IRS 5, and the Herbig-Haro object HH 101. The stars R and T CrA were not detected.

Brown, Alexander↗
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 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.↗
NASA NTRS1986

An infrared reflection nebula surrounding SGS 1 in the NGC 1333 dark cloud

Strom et al. (1974) have conducted a search for infrared sources associated with Herbig-Haro objects. They found an infrared source, SGS 1, near HH 12, embedded in at least 20 visual mag of extinction in the NGC 1333 dark cloud. Various factors suggest the presence of an infrared reflection nebula. In the context of the present investigation, high spatial resolution observations in the infrared have provided the basis for the development of a consistent model for SGS which consists of a low-luminosity, cool star with an accretion disk tilted to the line of sight, and one observed reflection lobe caused by the illumination of material above one of the polar regions of the accretion disk. It is pointed out that this model is similar to that of the infrared reflection nebula GSS 30 in the Ophiuchus dark cloud.

Castelaz, M. W.↗
NASA NTRS1986

Infrared spectra of rotating protostars

Earlier calculations of the infrared emission expected from stars in the process of being made are corrected to include the most important observable effects of rotation and generalized. An improved version of the spherical model of a previous paper is developed, and the corresponding emergent spectral energy distributions are calculated for the theoretically expected mass infall rate in the cores of cool and quiescent molecular clouds. The dust grain opacity model and the temperature profile parameterization are improved. It is shown that the infrared spectrum of the IRAS source 04264+2426, which is associated with a Herbig-Haro object, can be adequately represented in terms of a rotating and accreting protostar. This strengthens the suggestion that collimated outflows in young stellar objects originate when a stellar wind tries to emerge and reverse the swirling pattern of infall which gave birth to the central star.

Adams, F. C.↗
NASA NTRS1987

Outflows in the star-formation region near R CrA

Photographs, spectra, and velocities are presented for the Herbig-Haro objects and visible stars associated with the star-formation region near R CrA. The new data are used to discuss the gas outflows in the area. At least two flows are present; one is linked with the bright variable star R CrA, and the second with the IR source near HH 100. Special attention is given to HH 101. The velocity and spatial structures HH 101 are complex, but are consistent with condensations inside an expanding shell of material ejected from HH 100IR.

Hartigan, Patrick↗
NASA NTRS1987

The magnetic field geometry in the vicinity of HH 7-11/HH 12 and HH 33/HH 40

The small-scale structure of the interstellar magnetic field in the vicinity of the Herbig-Haro objects HH 7-11/HH 12 and HH 33/40 is derived from CCD imaging polarimetry of stars nearby to these young stellar object driven outflows. The outflow associated with SVS 13/HH 7-11 lies approximately parallel to the local field direction. The outflow mapped by HH 33/HH 40 is also well aligned with the local magnetic field. However, the orientation of the outflow associated with HH 12 located 2 arcmin to the north of HH 7-11 is offset from the inferred magnetic field direction by 60 deg. These results taken together with those of previous studies suggest: (1) magnetic fields are directly or indirectly responsible for the observed orientation of outflows associated with newborn stars in the majority of cases; and (2) in some cases, the flow properties may depend upon other characteristics of the parent cloud core.

Heyer, Mark H.↗
NASA NTRS1987

A recent change in the brightness and form of the HH46 reflection nebula

A several-fold increase in the surface brightness of the scattered light component of the southern Herbig-Haro object HH46 took place between January 1984 and May 1986. A more subtle change in the shape of the nebula also occurred in that a small region, formerly only prominent in the infrared, is now the brightest part of the reflection nebula in visible red light. The change is due either to a flaring of the adjacent but still invisible young stellar object or to a partial clearing of the dust which still surrounds it. In May 1987, the nebula still appeared bright suggesting that the change may be a long-term one.

Graham, J. A.↗
NASA NTRS1983

Optical study of a possible bipolar flow associated with Herbig-Haro 12

The region near HH 12 in NGC 1333 has been imaged at V, R, I, and H-alpha using the CCD detector at the Kitt Peak National Observatory 0.9 m telescope. The H-alpha frame reveals a narrow, sinuous structure which extends over a projected distance of 0.3 pc and which emanates from a star which appears to be a T Tauri object of type M0-M2. Velocities along this structure were obtained both north and south of the star. The morphology of this structure as well as the measured velocities suggest that it may be an optical manifestation of a highly collimated bipolar outflow which excites the object heretofore identified as HH 12.

Strom, K. M.↗