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Topic: HII regions

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 [No title]   (Site not responding. Last check: 2007-09-18)
LFs for HII regions in the arms, in the interarm regions, in the inner part, and in the outer part of the galaxy all have the same slopes.
There is no evidence for a different population of HII regions in the spiral arms, nor is there evidence for the existence of a significant population of density-bounded HII regions.
An outer HII region is defined as lying outside the area of the strong spiral arms, d>43 arcsec or 0.4 R25.
www.journals.uchicago.edu /AAS/cdrom/volume4/volume1/aj/v106/p0056/table.doc   (382 words)

 HII region
A volume of space where the hydrogen in the interstellar medium is in an ionized rather than a neutral state.
Generally, these are regions where hot, blue OB stars are pouring large amounts of ultraviolet radiation into the surrounding cloud from which they were recently formed.
HII regions have typical kinetic temperatures of 10,000 to 20,000 K, and a density of about 10 atoms/cm³.
www.daviddarling.info /encyclopedia/H/HII.html   (227 words)

 [No title]
My research centers around the birth and death of massive stars: HII regions (large clouds of ionized hydrogen), which are stellar nurseries, and supernovae, which occur when massive stars exhaust their nuclear fuel, inducing core-collapse events that lead to the destruction of the stars.
HII regions are the birthplace of stars and supernovae are the deaths of stars, so this study leads to a better understanding of the life cycle of stars and how the evolution of stars affects the interstellar medium and ultimately, the evolution of galaxies.
HII regions can be used to gauge the amount of extinction (how much internal gas and dust exists in th line of sight).
boson.physics.sc.edu /~lacey   (769 words)

 Introduction to HII regions model   (Site not responding. Last check: 2007-09-18)
When the filling factor is different from 1, the gas in the HII region is supposed to be divided in small clumps, and e is defined as the ratio between the volume occupied by the clumps and the total volume of the HII region.
HII regions are assumed to be spherical and ionization bounded, with the density constant along the radius, and with a covering factor of 1.
The differences between HII region models excited by SSP spectra and analytical one with the same Q values are not larger than in the case of the Salpeter IMF, despite the very different slope of the IMF.
www.sissa.it /~panuzzo/hii/node3.html   (1955 words)

 [No title]   (Site not responding. Last check: 2007-09-18)
The nebular properties (electronic density, extinction, age, O/H abundances) of \hii\ regions found along the bars of the sample of barred spiral galaxies studied by Martin \& Friedli (1997) are examined.
From line ratio diagnostic diagrams, it is showed that regions located along the major axis of the bars have a normal photoionization spectrum, that is, line ratios reproductible from nebular conditions and ionizing star radiation field normally encountered in extragalactic \hii\ regions.
Although the average \Ha\ equivalent width of bar \hii\ regions ($\sim$250\,{\AA}) is half that of disc regions, this disparity could be due to uncertainties in the galactic continuum and does not translate into a significant age difference.
obswww.unige.ch /~fri/laval/AB0010.html   (241 words)

 Discovery of Intergalactic HII regions in SINGG   (Site not responding. Last check: 2007-09-18)
The SINGG images have been used to deduce that the isolated HII regions are due to newly formed stellar clusters where no stars existed previously, and that an estimated 4-7 young massive stars are responsible for each of the isolated HII regions.
Although HII regions in between galaxies are rare in the Universe today, they may have been more common in the past, which has some interesting implications.
Massive stars born in isolated HII regions will explode as supernovae and pollute the space in between galaxies with heavy elements, the debris from the explosion.
astro.ph.unimelb.edu.au /~eryan/ELdots   (418 words)

 U of Toronto Astronomy Department Thesis Abstract   (Site not responding. Last check: 2007-09-18)
An accurate study of dust associated with HII regions requires a careful study of all of the components of an HII region and the surrounding ISM.
Understanding of this morphology is critical for the calculation of infrared fluxes and for the accurate association of infrared emission with a given HII region.
The HII region KR 140 is the subject of a multiwavelength study.
www.astro.utoronto.ca /theses/thesis99.kerton.html   (350 words)

 JMPA. Disseration. Ch.1, Introduction and Overview
UC HII regions are among the brightest objects in the Galaxy at wavelengths near 100 microns.
If it does not reside in the UC HII region and it is massive, the driver of the flows is probably a massive protostar (at an earlier evolutionary stage than the star that powers the UC HII region) that has not been able to form a detectable HII region yet because of rapid mass accretion.
UC HII regions are among the youngest objects in the Galaxy and are still deeply embedded in the molecular clouds where they formed.
imagiware.com /~acord/astro/dissertation/ch1.php   (3019 words)

 Research Interests   (Site not responding. Last check: 2007-09-18)
UC HII regions are very small (D<0.1 pc) and dense (n_e>10^4 cm^-3) photoionized gas regions, which are excited by O or early B stars (Wood and Churchwell 1989a; Kurtz et al.
So it has been considered that UC HII regions are not as young as they appear and that the expansion of HII regions are constrained by some mechanisms in the ultracompact phase for a long (>10^5 yr) time (Churchwell 1999 and references therein).
The extended emission surrounding UC HII regions could be direct observational evidence supporting that they are not likely to be "bona-fide" UC HII regions but the ultracompact cores of more extended HII regions, and thus provide an important clue to understand the age problem (Kim and Koo 2001).
www.astro.uiuc.edu /~ktkim/research.html   (825 words)

 [No title]
Ionised regions involve the interaction between the exciting star(s) and the surrounding material with the emission depending both on the nature of the exciting star(s), and on the type and conditions of the local interstellar material, including dust.
A major objective is to study the important question of dust in and around the HII regions, to determine the dust size distribution and composition, and understand the way that it modifies the energy balance within the region itself.
OBSERVATION SUMMARY The HII regions for observation have been selected mainly from the catalogue by Sharpless (59), with emphasis on regions which are greater than 5 degrees from the Galactic plane, to avoid source confusion.
www.ipac.caltech.edu /iso/gtotext/REMERY.ISM_IB.txt   (1307 words)

 [No title]
region population in a sample of nearby galaxies with nuclear activity.
region pair separation follows a lognormal distribution, whose mean value is correlated with the size of the galaxy.
region nearest neighbour is such that the median value of the distribution in each galaxy is larger for larger galaxies; thus, larger galaxies are somewhat more roomy.
www.iaa.es /~rosa/research/catalogue/catalogue.html   (332 words)

 Dust scattering of emission lines in HII regions. I.   (Site not responding. Last check: 2007-09-18)
region on the surface of a molecular cloud.
region, and in a layer of overlying neutral material are all included.
Foreground scattering in the neutral lid that overlies the nebula is shown to have little effect on the line profile, although it could account for some of the unexplained broadening seen in all optical lines.
www.astrosmo.unam.mx /~w.henney/papers/orion.html   (256 words)

 Statistics and properties of HII regions in NGC 6814   (Site not responding. Last check: 2007-09-18)
We present a new Halpha image of high quality of the grand-design galaxy NGC 6814, and describe statistical properties of the HII region population.
This table lists the 735 HII regions catalogued in the disk of the grand-design spiral galaxy NGC 6814, using a new H alpha image.
C: center (not an HII region, but included for comparison) A: Arm HII region I: interarm O: outer HII region An outer HII region is defined as lying outside the area of the strong spiral arms, d>43 arcsec or 0.4 R25.
www.cs.wisc.edu /niagara/data/nasa/AJ_106_56.xml   (159 words)

 SCYON: Paper abstracts
To analyze the variations of HII region properties vis-a-vis the galactic structure, the spiral arm areas were defined independently from mm-CO and optical continuum imaging.
The luminosity function is somewhat flatter in spiral arm regions than in the interarm areas (-0.72 -> -0.95); however, this is very likely the result of increased blending of individual HII regions in the arms, which have higher surface density.
We suggest that OB star formation in a cloud core region is terminated at the point that radiation pressure on the surrounding dust exceeds the self-gravity of the core star cluster and that this is what limits the maximum mass of standard OB star clusters.
obswww.unige.ch /webda/scyon/Scoville.html   (853 words)

 HII regions   (Site not responding. Last check: 2007-09-18)
The appearances of the H II regions at 2.2 µm correspond closely to their appearances at radio wavelengths.
A submillimeter-wave study of the HII region W3 My colleagues and I used the James Clerk Maxwell telescope to map the 450-800 µm emission from the W3(Main) star forming region.
We estimate that the three submillimeter sources together contribute 35-50% of the total bolometric luminosity of the region and speculate that the contribution of luminous radio-quiet sources to the total luminosity of HII region/molecular cloud complexes may be larger than is often assumed.
www.ifa.hawaii.edu /~wynnwill/research_star_formation.htm   (477 words)

 [No title]
Photo dissociation region (PDR) models for the LMC HII regions, indicate that the line may be stronger than in Galactic HII regions because of the lower dust content and hence the greater penetration of the UV radiation field into the molecular clouds.
The regions in the Magellanic Clouds fall in three categories: diffuse, extended HII regions such as 30 Doradus, compact and high excitation regions such as N88 and N81 and a couple of hot and cool molecular clouds (LIRS 36, LIRS 49 and SMC-B1#1).
The seven HII regions in M33 have been chosen to ensure a wide range in galactocentric radius and hence metallicity and physical conditions.
www.ipac.caltech.edu /iso/gtotext/JVDHULST.ISM_LGR2.txt   (1002 words)

 Sharpless 212   (Site not responding. Last check: 2007-09-18)
This region of ionized hydrogen (or HII region) is number 212 in the catalog of optical HII regions by Sharpless (1959, ApJS 4, 257).
This HII region is almost spherical around the exciting star, with a radius of 5.9 pc (19 light years).
First, this bright (thus easy to observe) HII region lies far from the Galactic center, and as such, it is a choice region to study the abundance of elements and see how it decreases from the center to the edge of our Galaxy.
www.obs-hp.fr /www/gallery/sh212.html   (469 words)

 Nebula - Wikipedia, the free encyclopedia
The Triangulum Emission Nebula NGC 604 lies in a spiral arm of Galaxy M33, 2.7 million light-years from Earth.
This nebula is a region in which stars are forming.
Emission nebulae are internally illuminated clouds of ionized gas.
en.wikipedia.org /wiki/Nebula   (335 words)

 Catalogue: J/ApJS/91/659/table3
The correlation of UC HII region positions with proposed spiral arms is examined and found to be well correlated only for the local spiral arm or "spur".
No obvious enhancement of UC HII regions is apparent along the proposed Sagittarius and Scutum arms, probably because of inaccuracies in the kinematic distances.
We find that many of the UC HII regions in our sample must be excited by a cluster of stars, and most probably contain significant amounts of dust.
vizier.u-strasbg.fr /cgi-bin/Cat?J/ApJS/91/659/table3   (1459 words)

 [No title]   (Site not responding. Last check: 2007-09-18)
Distance in parsecs from the center of the galaxy to the brightest HII regions plotted as a function of the distance in parsecs to the rotation curve turnover.
Distance in parsecs to the furthest HII regions plotted as a function of the distance in parsecs to the rotation curve turnover.
Distances in parsecs to all the HII complexes in the galaxies plotted as a function of the distances in parsecs to the rotation curve turnover.
www.lowell.edu /users/dah/spatial.html   (410 words)

 [No title]   (Site not responding. Last check: 2007-09-18)
Introduction The early study of HII regions was dominated by investigations of nearby, optically visible regions.
HII regions that are small and bright have been called UC HII regions, and these regions are one of the ways in which we can probe the near environments of the youngest massive stars.
Massive star forming regions are high density regions: In the studies carried out a decade ago related to the evolution of UC HII regions in dense environments, the molecular cloud densities used were of the order 105 cm-3.
ecademy.agnesscott.edu /~cdepree/Project.doc   (5528 words)

 ISOCAM observations of compact HII regions in the LMC   (Site not responding. Last check: 2007-09-18)
The selection of fields was based on the existence of sources unresolved by IRAS with far-infrared colors typical of galactic ultracompact HII regions.
This large ratio suggests that the two point sources in question are true ultracompact HII regions.
The angular resolution of the radio and infrared observations separately is insufficient to reliably pinpoint bona-fide ultracompact HII regions at the distance of the LMC.
isowww.estec.esa.nl /meetings/paris/Paris_abstracts/node224.html   (421 words)

 Jahrbuch-CD der MPG 2003 - The effect of HII regions on ro
The effect of HII regions on rotation measure of pulsars
We find that two pulsars towards l similar to 149degrees (Region 1) and four pulsars towards l similar to 113degrees (Region 2) lie behind HII regions which seriously affect the pulsar rotation measures.
For Region 1, we are able to constrain the random component of the magnetic field to 5.7 muG.
www.mpg.de /forschungsergebnisse/wissVeroeffentlichungen/archivListenJahrbuch/2003/21/publZIM134.html   (195 words)

 Introduction and latest results from the Laval wide field survey of old and peculiar HII Regions
As this work goes forth, we will be observing HII regions where the ionizing star, or star association, has almost completely dissociated and ionized the gas from the parental molecular cloud.
Regions where neutral gas observed by the CGPS is peculiar, either morphologically or by unusual association with ionized nebulae, will also be studied.
regions retains an imprint of it former kinematical behavior.
www.cfht.hawaii.edu /Reference/Proceedings/godbout_color   (937 words)

 [No title]   (Site not responding. Last check: 2007-09-18)
Optical Spectroscopy Of Metal-Rich Extragalactic Hii Regions Fabio Bresolin IfA I discuss the properties of the stellar ionizing clusters of metal-rich (supersolar) extragalactic HII regions, as derived from ground-based spectroscopy in the optical.
The sample studied includes a number of circumnuclear HII regions (hot spots), which are found in general to have spectral properties similar to the HII regions located in the disks.
I derive some conclusions on the age of the ionizing clusters and the shape of their upper initial stellar mass function by means of diagnostics of the stellar content (Wolf-Rayet star features, Balmer lines, He I lines), after a comparison with the predictions of current population synthesis evolutionary models.
www.ifa.hawaii.edu /colloquia/abstracts/bresolin.txt   (199 words)

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