Based on the ISO spectral catalogue of compact H ii regions by Peeters et al. (2002), we present a rst analysis of the hydrogen recombination and atomic ne-structure lines originated in the ionized gas. The sample consists of 34 H ii regions located at galactocentric distances between RGal = 0 and 15 kpc. The SWS H i recombination lines between 2 and 8 m are used to estimate the extinction law at these wavelengths for 14 H ii regions. An extinction in the K band between 0 and 3 mag has been derived. The ne-structure lines of N, O, Ne, S and Ar are detected in most of the sources. Most of these elements are observed in two dierent ionization stages probing a range in ionization potential up to 41 eV. The ISO data, by itself or combined with radio data taken from the literature, is used to derive the elemental abundances relative to hydrogen. The present data thus allow us to describe for each source its elemental abundance, its state of ionization and to constrain the properties of the ionizing star(s). The main results of this study are as follows. The ionization ratios Ar ++ /Ar + ,N ++ /N + ,S +3 /S ++ and Ne ++ /Ne + , which measure the degree of ionization and to rst order, the hardness of the stellar radiation, seem to increase with RGal. These ionization ratios correlate well with each other, implying that the spectral hardening aects equally the full range of ionizing energies. A Galactocentric gradient of N/O (log N= O= 0:056 0:009 dex kpc 1 ) is observed in the sense of a decreasing abundance ratio with RGal in agreement with previous studies. Abundance gradients for neon and argon are derived of the form log Ne= H= 0:039 0:007 dex kpc 1 and log Ar= H= 0:045 0:011 dex kpc 1 . These elemental gradients could be enlarged by the existing Galactic Te gradient. Adopting a Te gradient of approximately 330 K kpc 1 , the slopes in the Ne/H and Ar/H gradients become 0:06 and 0:07 dex kpc 1 , respectively. Lower limits for

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ISO spectroscopy of compact HII regions in the Galaxy - II. Ionization and elemental abundances

We present a deep JHKs-band imaging survey of the W3 Main star-forming region, using the near-infrared camera SIRIUS mounted on the University of Hawaii 2.2 m telescope. The near-infrared survey covers an area of ~24 arcmin2 with 10 σ limiting magnitudes of ~19.0, 18.1, and 17.3 in the J, H, and Ks bands, respectively. We construct JHK color-color and J versus J-H and K versus H-K color-magnitude diagrams to identify young stellar objects and estimate their masses. Based on these color-color and color-magnitude diagrams, a rich population of young stellar objects is identified that is associated with the W3 Main region. A large number of previously unreported red sources (H-K > 2) have also been detected around W3 Main. We argue that these red stars are most probably pre-main-sequence stars with intrinsic color excesses. We find that the slope of the Ks-band luminosity function (KLF) of W3 Main is lower than the typical values reported for young embedded clusters. The derived slope of the KLF is the same as that found in 1996 by Megeath and coworkers, from which analysis indicated that the W3 Main region has an age in the range of 0.3-1 Myr. Based on the comparison between models of pre-main-sequence stars and the observed color-magnitude diagram, we find that the stellar population in W3 Main is primarily composed of low-mass pre-main-sequence stars. We also report the detection of isolated young stars with large infrared excesses that are most probably in their earliest evolutionary phases.

https://iopscience.iop.org/article/10.1086/420876/pdf

Deep Near-Infrared Observations of the W3 Main Star-forming Region

The Dominion Radio Astrophysical Observatory, in collaboration with other sites, recently began a Galactic plane survey. The data from the pilot project for this survey are presented here. They cover the W3/W4/W5/HB 3 Galactic complex in the Perseus arm. Ten fields were observed to produce mosaic images of this region at two continuum frequencies, 408 and 1420 MHz, as well as in the 21 cm spectral line of atomic hydrogen at 127 velocities covering +55.5 to -153.9 km s-1. At 1420 MHz (continuum and spectral line), an area of approximately 8° × 6° (l × b) is imaged with a resolution of 100 × 114 (east-west by north-south) whereas, at 408 MHz, the coverage was 14° × 10° (l × b) with a resolution of 35 × 40 (east-west by north-south). The spectral-line data cube constitutes the highest resolution atomic hydrogen study of the entire complex to date. A wealth of large-scale filaments, arcs, bubbles, and shells is revealed.

The Dominion Radio Astrophysical Observatory Galactic Plane Survey Pilot Project: The W3/W4/W5/HB 3 Region

Aims. We investigate the structure and velocity of cold molecular pillars, "elephant trunks", in expanding HII regions. Methods. The trunks are seen in silhouette against the bright background in our Ha images. All trunks are filamentary, and show signs of being twisted. Four such trunks in NGC 7822, IC 1805, the Rosette Nebula, and DWB 44 were selected, and then mapped mainly in (CO)-C-12 and (CO)-C-13. We determine the mass and density of the trunks. Most of the mass is concentrated in a head facing the central cluster, and in sub-filaments forming the body of the trunk that is connected to V-shaped filaments to the outer expanding shell. Results. We discovered that all four trunks rotate as rigid bodies ( to a first approximation) about their major axes, and that at least two trunks are stretching along their major axes, meaning that the massive heads are lagging behind in the general expansion of the HII regions. The rotational periods are of the order of a few million years-similar to the age of the clusters. Rotation, then, is responsible for the twisted appearance of many elephant trunks, since they are rooted in the outer shells. The trunks carry surprisingly large amounts of angular momentum, 3 x 10(48)-2 x 10(50) kg m(2) s(-1), with corresponding rotational energies of up to similar to 10(37) J. However, we estimate the total magnetic energies to be even larger. The trunks continuously reshape, and the formation of twined, and in many cases helical, sub-filaments can be understood as a consequence of electromagnetic and inertia forces inside the trunks. A theory based on the concept of magnetically twisted trunks is developed further, where the initial angular momentum is a consequence of the twisting of parent filaments containing mass condensations. Our results also suggest a new process of removing angular momentum from parent molecular clouds.

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Rotating elephant trunks

We have carried out observations toward the W3 complex and G34.3+0.15 using the TRAO 14 m radio telescope to examine in detail the chemical variations occurring while molecular clouds evolve from the prestellar to the H II region phase. Observations include spectral surveys of these objects between 84.7 and 115.6 GHz; mapping observations toward W3(OH) with the emissions of CS (2-1), HCN (1-0), HNC (1-0), and HCO+ (1-0); and mapping of CS (2-1) emission toward W3 IRS 5. Chemical model calculations are used to estimate the age of W3(OH) by comparing with the fractional abundances of detected molecules. We found that G34.3+0.15 and W3(OH) are at a similar evolutionary stage, although large differences in the fractional abundances are found in CH3CN and HC3N. Overall, the properties of the detected species and abundances in three regions support the view that chemistry varies as molecular clouds evolve from a cold, collapsing phase to a high-temperature phase, such as the hot core and H II phase. Chemical model calculations for W3(OH) indicate that the evolutionary age of the cloud is 104-105 yr with temperature in the range 10-60 K.

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A Molecular Line Survey of W3(OH) and W3 IRS 5 from 84.7 to 115.6 GHz: Observational Data and Analyses

The distributions of the emission from /sup 12/CO, /sup 13/CO, CS, and HCN have been mapped in the W3 molecular cloud. The emission is divided into three components according to the spatial distribution of the intensity and the associated velocity. Although the overall cloud is investigated, the emphasis is on the brightest condensation referred to as the W3 core. This dense and dynamically active region contains several embedded compact H II regions, IR sources, and masers. Strong /sup 12/CO self-absorption occurs toward the compact infrared source IRS 5 where emission from dust at 1 mm and in the far-infrared and the emission from /sup 13/CO and HCN are strongest, but the emission from CS, by contrast, is rather weak. Collapse of the W3 core is inferred from the line profiles. A velocity gradient is observed across the W3 core. The observations and derived physical parameters which are presented in this paper will be used in a subsequent paper to develop a model of the W3 region.

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M.W. Werner

Papers

The H II region-molecular cloud complex W3: observations of CO, CS, and HCN.