The Nature of the [ITAL]IRAS[/ITAL] Ring G159.6−18.5 in Perseus and Its Exciting Star HD 278942

Bright rims at the edge of dark markings associated with diffuse nebulae have been noticed for more than thirty years. An example is shown in Fig. 1, a photographic negative of the diffuse nebula IC 1396. Figure 1(a) shows the entire nebula, which is excited by an O6 star (circled). Figure 1(b) is an enlargement of one of the bright rims in this nebula. A number of general characteristics can be pointed out. The bright rim is always at the edge of what appears to be dark matter and always is bright on that side of the matter closest to the exciting star. If a line of symmetry is drawn through the dark material it is found in general to pass very near to the exciting star. Sometimes isolated matter similar to Bok's globules are present, and when present also show bright rims. These globules are included in the observational study.

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Bipolar H II regions

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833015 ◽

2018 ◽

Vol 617 ◽

pp. A67 ◽

Cited By ~ 7

Author(s):

M. R. Samal ◽

L. Deharveng ◽

A. Zavagno ◽

L. D. Anderson ◽

S. Molinari ◽

...

Keyword(s):

Star Formation ◽

Molecular Cloud ◽

Galactic Plane ◽

Three Dimensional ◽

Young Stellar Objects ◽

Formation Processes ◽

Two Dimensional ◽

Stellar Objects ◽

Flat Structures ◽

Exciting Star

Aims. We aim to identify bipolar Galactic H II regions and to understand their parental cloud structures, morphologies, evolution, and impact on the formation of new generations of stars. Methods. We use the Spitzer-GLIMPSE, Spitzer-MIPSGAL, and Herschel-Hi-GAL surveys to identify bipolar H II regions and to examine their morphologies. We search for their exciting star(s) using NIR data from the 2MASS, UKIDSS, and VISTA surveys. Massive molecular clumps are detected near these bipolar nebulae, and we estimate their temperatures, column densities, masses, and densities. We locate Class 0/I young stellar objects (YSOs) in their vicinities using the Spitzer and Herschel-PACS emission. Results. Numerical simulations suggest bipolar H II regions form and evolve in a two-dimensional flat- or sheet-like molecular cloud. We identified 16 bipolar nebulae in a zone of the Galactic plane between ℓ ± 60° and |b| < 1°. This small number, when compared with the 1377 bubble H II regions in the same area, suggests that most H II regions form and evolve in a three-dimensional medium. We present the catalogue of the 16 bipolar nebulae and a detailed investigation for six of these. Our results suggest that these regions formed in dense and flat structures that contain filaments. We find that bipolar H II regions have massive clumps in their surroundings. The most compact and massive clumps are always located at the waist of the bipolar nebula, adjacent to the ionised gas. These massive clumps are dense, with a mean density in the range of 105 cm−3 to several 106 cm−3 in their centres. Luminous Class 0/I sources of several thousand solar luminosities, many of which have associated maser emission, are embedded inside these clumps. We suggest that most, if not all, massive 0/I YSO formation has probably been triggered by the expansion of the central bipolar nebula, but the processes involved are still unknown. Modelling of such nebula is needed to understand the star formation processes at play.

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Maser Sources in H ii Regions

Symposium - International Astronomical Union ◽

10.1017/s0074180900026553 ◽

1974 ◽

Vol 60 ◽

pp. 267-273 ◽

Cited By ~ 2

Author(s):

B. F. Burke

Keyword(s):

Background Radiation ◽

Formation Rate ◽

Infrared Emission ◽

Radio Continuum ◽

H Ii Regions ◽

Line Radiation ◽

Compact Source ◽

Stellar Formation ◽

Exciting Star ◽

Compact Sources

When OH and H2O sources are found in Hii regions, a compact source of radio continuum and infrared emission is usually, perhaps always, found nearby, < 1017 cm away (approximately the conjectured size of a prestellar condensation). Whether the masers are self-excited, are amplifying the background radiation, or are themselves associated with an exciting star is clearly model-dependent, and observations have not yet given the answer. H2O masers occur less frequently than OH masers. When they occur together they appear as a cluster of compact sources of line radiation, exhibiting the same range of radial velocities, The OH sources nearly always are strongly polarized, while the H2O maser is not. Both classes of maser are probably saturated, and some care is needed in inferring the maser geometry from the observations. The period of stability of neither OH nor H2O can be much more than 103 yr, and this fact can be used as an estimator of stellar formation rate.

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On the infrared emission of the exciting star of the Herbig-Haro objects 1 and 2

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/224.3.587 ◽

1987 ◽

Vol 224 (3) ◽

pp. 587-593 ◽

Cited By ~ 1

Author(s):

M. Tapia ◽

M. Roth ◽

L. Carrasco ◽

M. T. Ruiz

Keyword(s):

Infrared Emission ◽

Exciting Star

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The Dust Cavity Around the Exciting Star of Small H II Regions

Symposium - International Astronomical Union ◽

10.1017/s0074180900095449 ◽

1987 ◽

Vol 115 ◽

pp. 189-190 ◽

Cited By ~ 1

Author(s):

S. Yoshida ◽

S. Mizuno ◽

M. Nakano ◽

T. Kogure ◽

T. Sasaki ◽

...

Keyword(s):

Image Processing ◽

Angular Size ◽

H Ii Regions ◽

Surface Photometry ◽

Continuum Intensity ◽

V Band ◽

Exciting Star

In a series of observations (Mizuno et al. 1981; Mizuno 1982; Nakano et al. 1983), we have carried out the surface photometry of small H II regions which were selected from Sharpless catalogue (1959) by the following properties: (1) small angular size (≦ 10 arcmin), (2) round and simple appearance, and (3) a single BO V star as the exciting star. Properties (1) and (2) are for the convenience of image processing, and property (3) is to avoid the contamination of [O III] emission in the V-band so as to get pure continuum intensity.

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