Near and mid infrared observations of ultracompact HII regions

Crowther, P. A.

doi:10.1017/s1743921305004795

Cited by 7 publications

(5 citation statements)

References 39 publications

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“…Sources A and B dominate the mid-IR luminosity of the whole system, though the former is the brightest source at λ > 9 μm. At d = 8 kpc, the total luminosity of source A is found to be about 5.0 × 10 4 L (Table 3), which corresponds to a 09.5 -B1 V star (Crowther 2005). As mentioned earlier, this object is associated with a compact HII region (see Fig.…”

Section: Spectral Energy Distributions Of the Young Luminous Sourcessupporting

confidence: 56%

“…The nearby source B, for which we can only determine its infrared (1 to 13 μ) luminosity of 6.6 × 10 3 L (Table 3), has a total luminosity of probably a factor of 1.5 to 2 higher (see SED in Fig. 10), which would correspond to a B2-B3 V star (Crowther 2005); such a star would emit no more than 10 45 UV photons (Panagia 1973), sufficient to ionize the surrounding gas and produce a small HII region. Its free-free emission would be observable at 6 cm, with a flux density of approximately 0.1 mJy, Table 4. well below the sensitivity of Urquhart et al's (2009) radio survey.…”

Section: Spectral Energy Distributions Of the Young Luminous Sourcesmentioning

confidence: 99%

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The distant young embedded stellar cluster CBJC 8 associated with G085.40-0.00

Persi

Tapia

Gómez

2010

A&A

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Context. The infrared cluster CBJC 8 is associated with a 6.7 GHz methanol maser and a compact radio-continuum source, G85.40-0.00. It is located at a distance of about 8 kpc.Aims. The aim is to study the characteristics of this distant and compact embedded cluster and derive the properties of its stellar population. Methods. We present new ground-based near-and mid-infrared imaging observations of this region. The calibrated images were analysed together with archive Spitzer IRAC images. Results. Based on the discovery of a considerable fraction of embedded sources with infrared excess emission that are concentrated within a radius around 16 centred near the position of the compact HII region G85.40-0.00, we were able to confirm the presence of a very young embedded cluster. It was found to contain more than 58 members brighter than M K = 2.6, two-thirds of which showing significant near-or mid-IR excess emission. We present spectral energy distributions and extrapolated total luminosities for nine sources with large mid-infrared excesses that were measured in all four IRAC bands. For the brightest of these, G8540A, which is associated with a methanol maser and a compact HII region, we fitted a model of an infalling envelope plus disc plus central star to its observed 1.6 to 850 μm fluxes to get an idea of its physical properties. We also report a single 2.12 μm molecular hydrogen line emission knot near the centre of the cluster, which support the idea about an outflow activity.

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Section: Spectral Energy Distributions Of the Young Luminous Sourcessupporting

confidence: 56%

Section: Spectral Energy Distributions Of the Young Luminous Sourcesmentioning

confidence: 99%

The distant young embedded stellar cluster CBJC 8 associated with G085.40-0.00

Persi

Tapia

Gómez

2010

A&A

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“…where a s is the sound speed of the molecular cloud, Q 0 is the H I ionizing flux, and n 0 is the density of the molecular cloud. The exciting star of KR 120 is B0 V (Arvidsson and Kerton, 2011) corresponding to Q 0 = 10 47.4 photons s −1 using the Crowther (2005) calibration. For n 0 , we use the value n 0 = 1000 cm −3 from Joncas et al (1992).…”

Section: Formation Scenariosmentioning

confidence: 99%

“…For KR 7, the ionizing photon flux, log N L = 48.2 which corresponds to an exciting star of O9V star (Crowther, 2005) (Kerton, 2006). The estimated flux of ionizing photons from the exciting star, log N L = 47.2 corresponds to a single B0V star (Table 2.2).…”

Section: Chapter 1 Introductionmentioning

confidence: 99%

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A study of four galactic small H II regions: searching for spontaneous and sequential star formation scenarios

Kang

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Kinematics and stability of high-mass protostellar disk candidates at sub-arcsecond resolution

Ahmadi¹,

Beuther²,

Bosco³

et al. 2023

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Context. The fragmentation mode of high-mass molecular clumps and the accretion processes that form the most massive stars (M ≳ 8 M⊙) are still not well understood. A growing number of case studies have found massive young stellar objects (MYSOs) to harbour disk-like structures, painting a picture that the formation of high-mass stars may proceed through disk accretion, similar to that of lower-mass stars. However, the properties of such structures have yet to be uniformly and systematically characterised. Aims. The aim of this work is to uniformly study the kinematic properties of a large sample of MYSOs and characterise the stability of possible circumstellar disks against gravitational fragmentation. Methods. We have undertaken a large observational programme (CORE) making use of interferometric observations from the Northern Extended Millimetre Array (NOEMA) for a sample of 20 luminous (L > 104 L⊙) protostellar objects in the 1.37 mm wavelength regime in both continuum and spectral line emission, reaching 0.4″ resolution (800 au at 2 kpc). Results. We present the gas kinematics of the full sample and detect dense gas emission surrounding 15 regions within the CORE sample. Using the dense gas tracer CH3CN, we find velocity gradients across 13 cores perpendicular to the directions of bipolar molecular outflows, making them excellent disk candidates. The extent of the CH3CN emission tracing the disk candidates varies from 1800 to 8500 au. Analysing the free-fall to rotational timescales, we find that the sources are rotationally supported. The rotation profiles of some disk candidates are well described by differential rotation while for others the profiles are poorly resolved. Fitting the velocity profiles with a Keplerian model, we find protostellar masses in the range of ~ 10–25 M⊙. Modelling the level population of CH3CN (12K–11K) K = 0–6 lines, we present temperature maps and find median temperature in the range 70–210 K with a diversity in distributions. Radial profiles of the specific angular momentum (j) for the best disk candidates span a range of 1–2 orders of magnitude, on average ~10−3 km s−1 pc, and they follow j ∝ r1.7, which is consistent with a poorly resolved rotating and infalling envelope-disk model. Studying the Toomre stability of the disk candidates, we find almost all (11 out of 13) disk candidates to be prone to fragmentation due to gravitational instabilities at the scales probed by our observations, as a result of their high disk to stellar mass ratio. In particular, disks with masses greater than ~ 10–20% of the mass of their host (proto)stars are Toomre unstable, and more luminous YSOs tend to have disks that are more massive compared to their host star and hence more prone to fragmentation. Conclusions. In this work, we show that most disk structures around high-mass YSOs are prone to disk fragmentation early in their formation due to their high disk to stellar mass ratio. This impacts the accretion evolution of high-mass protostars which will have significant implications for the formation of the most massive stars.

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Near and mid infrared observations of ultracompact HII regions

Cited by 7 publications

References 39 publications

The distant young embedded stellar cluster CBJC 8 associated with G085.40-0.00

The distant young embedded stellar cluster CBJC 8 associated with G085.40-0.00

A study of four galactic small H II regions: searching for spontaneous and sequential star formation scenarios

Kinematics and stability of high-mass protostellar disk candidates at sub-arcsecond resolution

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