Bright-rimmed Clouds Research Articles

Searches for bright-rimmed clouds with IRAS point sources

We have carried out systematic surveys for small bright-rimmed clouds associated with IRAS point sources in/around HII regions. They are candidate sites for star formation due to radiation-driven implosion.

OBSERVATIONS OF PHOTOEVAPORATING INTERSTELLAR CLOUDS

ABSTRACT In the first part of this thesis, we present a tabulation of parameters for 50 globules, most of which are bright-rimmed clouds, observed in transitions of 12CO, 13CO, CS, and HCO+ with a 1 arcminute diameter beam. H-alpha images for many bright-rimmed clouds and long-slit H-alpha spectra of two such clouds are presented. The observations are interpreted in terms of the rocket effect and D-critical ionization fronts. The elongated clouds (the so called elephant trunk globules and cometary clouds) tend to point toward their source of ionization, although a possible counter-example is presented. They often have velocity gradients along their lengths; a few examples are newly presented along with others collected from the literature. Mechanisms for forming elongated clouds are discussed. Also, means of determining the three-dimensional geometry of an H II region are discussed. The hypothesis that bright rims implode clouds and induce star formation is reviewed and found to be controversial. In the second part, we present images of the Orion Trapezium made with a unique adaptive optics system that uses either starlight or Rayleigh-backscattered laser light to correct for atmospheric wavefront distortion. The H-alpha and I band images reveal the region around the bright Trapezium stars, which has been studied extensively at radio wavelengths. Approximately one half of the stars in this region are positionally associated with knots of ionized gas, known as pigs, which are interpreted as photoevaporating envelopes of low mass stars. Disks are not observed directly but are inferred from the relatively low extinction to the stars inside the pigs. The comet-like morphology of the pigs is the result of an equilibrium between photoionization, recombination, and shadowing; interaction with the wind from theta-1C ~Ori is not required. The sizes of the ionized component of the envelopes increase with distance from the source of ionization, theta-1C Ori. The size-distance relationship suggests that the mass loss rates from the pigs are all approximately the same. The actual value of the mass loss rate is model dependent, but is ~1.2 x 10-7 M⊙ yr-1. In the third and last part, we extend the laser beacon concept to a polychromatic beacon in order to infer the wavefront tilt by measuring the differential tilt caused by dispersion. The general concept of a polychromatic beacon is to make the atmosphere produce a second beacon of a different color at altitude. Two mechanisms capable of producing the color conversion are Raman scattering in the troposphere, and resonant florescence in the mesosphere. Because the differential tilt is quite small, high precision is required and thus also high photon return rates. Our analysis indicates that existing lasers may satisfy the theoretical requirements; however, the installation and operation of such lasers may be prohibitively expensive using current technology.

Observations of the bright-rimmed molecular clouds near the Cepheus OB2 association

Massive stars have significant influence on the evolution of the interstellar medium. Bright rims, cometary morphology of clouds, as well as their motion are some examples of the influence of massive stars on nearby molecular clouds. The cometary clouds in the Gum-Vela region are very good examples. In an attempt to understand the kinematics of the clouds in such regions we have carried out CO line observations towards bright-rimmed clouds near the OB Association Cep OB2. The radial velocities of the clouds are consistent with an expansion of the system at ≈ 4kms−1 away from the dominant O6.5V star in the association, HD206267. We find the rocket mechanism to be the most likely cause for expansion as found for both the Gum-Vela and the Rosette globules. We conclude that such expanding motions are quite common in regions near massive stars and make a brief comparison of the Cepheus system with the Gum-Vela system.

A catalog of bright-rimmed clouds with IRAS point sources: Candidates for star formation by radiation-driven implosion. 2: The southern hemisphere

A catalog of bright-rimmed clouds with IRAS point sources: Candidates for star formation by radiation-driven implosion. 2: The southern hemisphere

A catalog of bright-rimmed clouds with IRAS point sources: Candidates for star formation by radiation-driven implosion. I - The Northern Hemisphere

view Abstract Citations (214) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Catalog of Bright-rimmed Clouds with IRAS Point Sources: Candidates for Star Formation by Radiation-driven Implosion. I. The Northern Hemisphere Sugitani, Koji ; Fukui, Yasuo ; Ogura, Katsuo Abstract Forty-four bright-rimmed clouds associated with IRAS sources have been selected from the Palomar Sky Survey prints. They are good candidates for the sites of star formation induced by radiation-driven implosions; three well-established cases of radiation-driven implosions in bright-rimmed globules have been reported by Sugitani et al. (1989). Nine of the bright-rimmed clouds are known to be associated with molecular outflows and two (including one with an outflow) with HH objects. Most of their sizes are not more than 1 pc, similar to those of Bok globules. The luminosities of the associated IRAS sources are relatively large, about 10 to 10,000 solar luminosities, compared to those of the IRAS sources associated with dark globules or dense cores in dark cloud complexes. IRAS luminosity to cloud mass ratios are significantly greater than those in dark globules or in dense cores of dark cloud complexes. Publication: The Astrophysical Journal Supplement Series Pub Date: September 1991 DOI: 10.1086/191597 Bibcode: 1991ApJS...77...59S Keywords: Astronomical Catalogs; Hydrogen Clouds; Infrared Sources (Astronomy); Star Formation; H Ii Regions; Infrared Astronomy Satellite; Nebulae; Northern Hemisphere; Astrophysics; INFRARED: SOURCES; NEBULAE: H II REGIONS; STARS: FORMATION full text sources ADS | data products SIMBAD (84) Related Materials (1) Part 2: 1994ApJS...92..163S

Bright-rimmed clouds with IRAS point sources: candidates for star formation by radiation-driven implosion

We present preliminary results of a survey of bright-rimmed clouds associated with IRAS point sources.Bright-rimmed globules associated with old HII regions have long been suspected as a potential site for star formation. Physical conditions of such clouds seem to well match to models of radiation-driven implosion, which have been studied as an effective process for induced star formation (e.g. Klein et al. 1985, Bertoldi 1989). Bright-rimmed globules associated with IRAS point sources are good candidates for the sites of induced star formation. Three well-established cases of radiation-driven implosions in bright-rimmed globules (Ori I-2, IC1396-n, and L1206) were reported (Sugitani et al. 1989). Similar examples were also reported in HH46/47 (Olberg et al. 1989) and in GN21.38.9 (Duvert et al. 1990). However, the samples are still not numerous enough to establish comprehensive understanding of star formation by such implosion process.

Bright-rimmed clouds with IRAS point sources: candidates for star formation by radiation-driven implosion

We present preliminary results of a survey of bright-rimmed clouds associated with IRAS point sources.Bright-rimmed globules associated with old HII regions have long been suspected as a potential site for star formation. Physical conditions of such clouds seem to well match to models of radiation-driven implosion, which have been studied as an effective process for induced star formation (e.g. Klein et al. 1985, Bertoldi 1989). Bright-rimmed globules associated with IRAS point sources are good candidates for the sites of induced star formation. Three well-established cases of radiation-driven implosions in bright-rimmed globules (Ori I-2, IC1396-n, and L1206) were reported (Sugitani et al. 1989). Similar examples were also reported in HH46/47 (Olberg et al. 1989) and in GN21.38.9 (Duvert et al. 1990). However, the samples are still not numerous enough to establish comprehensive understanding of star formation by such implosion process.

CO observations of L1582

In this paper, the bright-rimmed cloud L1582 is mapped in (C-12)O and (C-13)O, and the embedded NH3 core is mapped in the CS(3 - 2) line. The optical bright rim coincides with the cloud edge seen in CO. Both the kinetic temperature and column density maps show elongated features along the bright rim, and the NH3 core is located right near the edge of the cloud inside a column density plateau region corresponding to an optical extinction patch. The density enhancement in the CS core is about a factor of three over the ambient cloud and the core mass is estimated at eight solar. The dust luminosity can be supplied by radiation from the Gamma Ori OB association. The most plausible heating source for the cloud gas is the photoelectric ejection of energetic electrons from grains induced by the far-UV flux from the Gamma Ori OB association.

The bright-rimmed molecular cloud around S140 IRS. I - CS (J = 1-0) observations

The bright-rimmed molecular cloud around S140 IRS has been mapped in the CS (J = 1-0) emission with an angular resolution of 33''. The relation between the CS emission and the distance from the ionization front is discussed, based on the position of the optical rim determined from an H..cap alpha.. photograph. The CS intensity decreases rapidly like a step function toward the rim. The step lies 40'' away from the optical rim. The distribution of the CS emission in the vicinity of S140 IRS shows a barlike east-west elongation which is prominent at V/sub LSR/ = -6 km s/sup -1/, and an archlike structure clearly seen at V/sub LSR/ = -8 km s/sup -1/.

Far-infrared observations of FU Orionis

The peculiar star FU Orionis is located in the southeast extension of Barnard 35 (B35), a bright-rimmed molecular cloud, and in the more extended, low-density region around Lambda Orionis. In connection with the present investigation, far-infrared observations of the star were undertaken in order to obtain a better estimate of the total luminosity of FU Ori and to better understand its relationship with the B35 cloud. FU Orionis was observed on 1981 January 23 with the 90 cm telescope on board the NASA Kuiper Airborne Observatory. The far-infrared results suggest that much of the radiation from the stellar source does not interact with either the 225 K circumstellar dust or the exterior 15 K material. The total luminosity of FU Ori is now seen to be about the same as the visible luminosity, and at the distance to B35 ridge dilution would make any isotropic effects negligible.

Far-infrared and submillimeter observations of Barnard 35 - Heat sources for bright-rimmed molecular clouds

Far-infrared and submillimeter continuum observations of a region of enhanced gas temperature in Barnard 35 are presented which were obtained in a study of dust and gas energetics in the bright-rimmed molecular cloud. Observations were obtained with the 90-cm telescope on board the NASA Kuiper Airborne Observatory, together with ground-based observations of the CO lines. The spectrum is found to correspond to a dust temperature of 10 + or - 5 K. A total dust luminosity of about 69 solar luminosities is estimated for the cloud, which may easily be supplied by stellar radiation from the background field or the Lambda Ori cluster. Observations of CO emission at 2.7 mm indicate a gas temperature of 23.4 + or - 3.5 K. The difference between the gas and dust temperatures confirms earlier suggestions that the gas and dust are not in thermal equilibrium and that gas-dust collisions are not the heat source for the molecular gas, however the actual source of the molecular gas heating remains uncertain.

CO observations of the bright-rimmed cloud B 35.

Detailed observations of millimeter-wave emission from $sup 12$CO and $sup 13$CO are made throughout the bright-rimmed molecular cloud B35 and compared with optical photographs. A ridge of enhanced $sup 12$CO brightness temperature is observed directly behind and along the bright-rimmed ionization front which forms the western border of the molecular cloud. Measurements of CO column density through the cloud across both the ridge and the ionization front show that the column density peaks near the ridge and, like the CO brightness temperature, steeply decreases across the ionization front. It is shown that modification of the cloud conditions by shock waves can explain observations and account for the observed CO cooling rates in the cloud. Cloud heating by embedded young stars is also possible, and infrared observations are suggested as a means of distinguishing between the two heating models. (AIP)

Dust and Neutral Hydrogen in the Region of IC 1396

A 21-cm survey at Dwingeloo of a 5° square containing IC 1396 shows several neutral hydrogen concentrations that correspond in shape and position with dust clouds, particularly the bright-rimmed clouds involved with the H II region.