Australia Telescope Compact Array 1.2-cm observations of the massive star-forming region G305.2+0.2

Walsh, A. J.; Chapman, J. F.; Burton, M. G.; Wardle, Mark; Millar, T. J.

doi:10.1111/j.1365-2966.2007.12240.x

Cited by 9 publications

(45 citation statements)

References 31 publications

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“…The 25‐GHz maser was found to be 3 arcsec to the east from the position of the 6.7‐GHz maser 305.202+0.208 (G305B region). It is worth noting that Walsh et al (2007) also detected 25‐GHz emission (several transitions of the series) towards two other locations in this source: near G305A and the south‐eastern H ii region. However, the radial velocity and a clear maser appearance of the feature near G305B allows an unambiguous identification of the suspected 9.9‐GHz maser with this position, near the 6.7‐GHz maser 305.202+0.208.…”

Section: Resultsmentioning

confidence: 59%

“…This most likely implies that markedly different physical conditions exist in this particular source. One may speculate that this might be related to another peculiarity found by Walsh et al (2007): the high‐mass star‐forming region associated with G305B is bright in infrared, old according to the chemistry, but has no H ii region sufficiently developed to be detectable. The expansion of an H ii region could be hindered because of the dense environment and/or by continuing infall of the matter.…”

Section: Resultsmentioning

confidence: 99%

“…These masers have been shown to originate at the same spatial location as the 9.9‐GHz maser in at least one source (Voronkov et al 2006). An accurate position for the 25‐GHz maser ( J = 4 transition with the peak velocity of −42.1 km s −1 observed with the velocity resolution of 0.75 km s −1 ) was determined by Walsh et al (2007), but the reported flux density of the maser is much lower, due to insufficient spectral resolution. The 25‐GHz maser was found to be 3 arcsec to the east from the position of the 6.7‐GHz maser 305.202+0.208 (G305B region).…”

Section: Resultsmentioning

confidence: 99%

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New 9.9-GHz methanol masers

Voronkov¹,

Caswell²,

Ellingsen³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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The Australia Telescope Compact Array (ATCA) has been used to make the first extensive search for the class I methanol masers at 9.9 GHz. In total, 48 regions of high-mass star formation were observed. In addition to masers in W33-Met (G12.80-0.19) and G343.12-0.06 (IRAS 16547-4247) which have already been reported in the literature, two new 9.9-GHz masers have been found towards G331.13-0.24 and G19.61-0.23. We have determined absolute positions (accurate to roughly a second of arc) for all the detected masers and suggest that some class I masers may be associated with shocks driven into molecular clouds by expanding HII regions. Our observations also imply that the evolutionary stage of a high-mass star forming region when the class I masers are present can outlast the stage when the class II masers at 6.7 GHz are detectable, and overlaps significantly with the stage when OH masers are active.Comment: accepted for publication in MNRAS, 14 pages, 3 figures, 4 table

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Section: Resultsmentioning

confidence: 59%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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New 9.9-GHz methanol masers

Voronkov¹,

Caswell²,

Ellingsen³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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“…Observations with Mopra in Walsh & Burton (2006) showed that many detected lines peak at the site of G305A, with weaker emission associated with G305B. As discussed in Walsh et al (2007), Steve Longmore (private communication) has detected the NH 3 (4,4) line in G305A which requires a temperature of at least 100 K, strongly suggesting that G305A is a hot core. In Walsh et al (2007), a hot core chemical model based on the physical conditions of G305A was used to compare the observed column densities of a number of species.…”

Section: Introductionmentioning

confidence: 93%

Cyanopolyynes in hot cores: modelling G305.2+0.2

Chapman¹,

Millar²,

Wardle³

et al. 2009

Monthly Notices of the Royal Astronomical Society

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We present results from a time-dependent gas-phase chemical model of a hot core based on the physical conditions of G305.2+0.2. While the cyanopolyyne HC 3 N has been observed in hot cores, the longer chained species, HC 5 N, HC 7 N and HC 9 N, have not been considered as the typical hot-core species. We present results which show that these species can be formed under hot core conditions. We discuss the important chemical reactions in this process and, in particular, show that their abundances are linked to the parent species acetylene which is evaporated from icy grain mantles. The cyanopolyynes show promise as 'chemical clocks' which may aid future observations in determining the age of hot core sources. The abundance of the larger cyanopolyynes increases and decreases over relatively short time-scales, ∼10 2.5 yr. We present results from a non-local thermodynamic equilibrium statistical equilibrium excitation model as a series of density, temperature and column density dependent contour plots which show both the line intensities and several line ratios. These aid in the interpretation of spectral-line data, even when there is limited line information available. In particular, non-detections of HC 5 N and HC 7 N in Walsh et al. are analysed and discussed.

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“…There is an H ii region some 10 to the southwest (Walsh et al 2007), but the infrared source itself is not associated with centimeter free-free emission (Phillips et al 1998;Walsh et al 2007). The extrapolated IRAS luminosity is > ∼ 10 5 L (Walsh et al 2001), which together with the cm non-detection supports our view that this object is a MYSO in a pre-UCH ii-region stage.…”

Section: G30520+021mentioning

confidence: 99%

The VLTI/MIDI survey of massive young stellar objects

Boley

Linz

Boekel

et al. 2013

A&A

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Context. Because of inherent difficulties involved in observations and numerical simulations of the formation of massive stars, an understanding of the early evolutionary phases of these objects remains elusive. In particular, observationally probing circumstellar material at distances < ∼ 100 AU from the central star is exceedingly difficult, as such objects are rare (and thus, on average, far away) and typically deeply embedded. Long-baseline mid-infrared interferometry provides one way of obtaining the necessary spatial resolution at appropriate wavelengths for studying this class of objects; however, interpreting such observations is often difficult due to sparse spatial-frequency coverage. Aims. We aim to characterize the distribution and composition of circumstellar material around young massive stars and to investigate exactly which physical structures in these objects are probed by long-baseline mid-infrared interferometric observations. Methods. We used the two-telescope interferometric instrument MIDI of the Very Large Telescope Interferometer of the European Southern Observatory to observe a sample of 24 intermediate-and high-mass young stellar objects in the N band (8-13 μm). We had successful fringe detections for 20 objects and present spectrally-resolved correlated fluxes and visibility levels for projected baselines of up to 128 m. We fit the visibilities with geometric models to derive the sizes of the emitting regions, as well as the orientation and elongation of the circumstellar material. Fourteen objects in the sample show the 10 μm silicate feature in absorption in the total and correlated flux spectra. For 13 of these objects, we were able to fit the correlated flux spectra with a simple absorption model, allowing us to constrain the composition and absorptive properties of the circumstellar material. Results. Nearly all of the massive young stellar objects observed show significant deviations from spherical symmetry at mid-infrared wavelengths. In general, the mid-infrared emission can trace both disks and outflows, and in many cases it may be difficult to disentangle these components on the basis of interferometric data alone, because of the sparse spatial frequency coverage normally provided by current long-baseline interferometers. For the majority of the objects in this sample, the absorption occurs on spatial scales larger than those probed by MIDI. Finally, the physical extent of the mid-infrared emission around these sources is correlated with the total luminosity, albeit with significant scatter. Conclusions. Circumstellar material is ubiquitous at distances < ∼ 100 AU around young massive stars. Long-baseline mid-infrared interferometry provides the resolving power necessary for observing this material directly. However, in particular for deeply-embedded sources, caution must be used when attempting to attribute mid-infrared emission to specific physical structures, such as a circumstellar disk or an outflow.

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Australia Telescope Compact Array 1.2-cm observations of the massive star-forming region G305.2+0.2

Cited by 9 publications

References 31 publications

New 9.9-GHz methanol masers

New 9.9-GHz methanol masers

Cyanopolyynes in hot cores: modelling G305.2+0.2

The VLTI/MIDI survey of massive young stellar objects

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