UNSW Canberra

Publication Search Results

Now showing 1 - 10 of 28
  • (2006) Lees, Brian; Van Niel, Kimberley; Laffan, Shawn
    Conference Paper

  • (2000) Bandyopadhyay, Srikanta; Gowripalan, Nadarajah; Drayton, Noel; Heslehurst, Rikard
    Conference Paper

  • (2007) Wright, Christopher; Burton, Michael; Van Dishoeck, Ewine; van Langevelde, Huib-Jan; Wilner, David; Hughes, Annie; Lommen, Dave; Maddison, Sarah; Jorgensen, Jes; Bourke, Tyler
    Journal Article
    Context. Low-mass stars form with disks in which the coagulation of grains may eventually lead to the formation of planets. It is not known when and where grain growth occurs, as models that explain the observations are often degenerate. A way to break this degeneracy is to resolve the sources under study. Aims. Our aim is to find evidence for the existence of grains of millimetre sizes in disks around T Tauri stars, implying grain growth. Methods. The Australia Telescope Compact Array (ATCA) was used to observe 15 southern T Tauri stars, five in the constellation Lupus and ten in Chamaeleon, at 3.3 mm. The five Lupus sources were also observed with the SubMillimeter Array (SMA) at 1.4 mm. Our new data are complemented with data from the literature to determine the slopes of the spectral energy distributions in the millimetre regime. Results. Ten sources were detected at better than 3 sigma with the ATCA, with sigma approximate to 1-2 mJy, and all sources that were observed with the SMA were detected at better than 15 sigma, with sigma approximate to 4 mJy. Six of the sources in our sample are resolved to physical radii of similar to 100 AU. Assuming that the emission from such large disks is predominantly optically thin, the millimetre slope can be related directly to the opacity index. For the other sources, the opacity indices are lower limits. Four out of six resolved sources have opacity indices <= 1, indicating grain growth to millimetre sizes and larger. The masses of the disks range from < 0.01 to 0.08 M-circle dot, which is comparable to the minimum mass solar nebula. A tentative correlation is found between the millimetre slope and the strength and shape of the 10-mu m silicate feature, indicating that grain growth occurs on similar (short) timescales in both the inner and outer disk.

  • (2006) Maercker, M; Burton, Michael; Wright, Christopher
    Journal Article
    Context. We present a JHK(s)L survey of the massive star forming region RCW 57 (NGC 3576) based on L-band data at 3.5 mu m taken with SPIREX ( South Pole Infrared Explorer), and 2MASS JHK(s) data at 1.25-2.2 mu m. This is the second of two papers, the first one concerning a similar JHK(s)L survey of 30 Doradus. Aims. Colour-colour and colour-magnitude diagrams are used to detect sources with infrared excess. This excess emission is interpreted as coming from circumstellar disks, and hence gives the cluster disk fraction (CDF). Based on the CDF and the age of RCW 57, it is possible to draw conclusions on the formation and early evolution of massive stars. Methods. The infrared excess is detected by comparing the locations of sources in JHKsL colour-colour and L vs. (K-s - L) colour - magnitude diagrams to the reddening band due to interstellar extinction. Results. A total of 251 sources were detected. More than 50% of the 209 sources included in the diagrams have an infrared excess. Conclusions. Comparison with other JHKsL surveys, including the results on 30 Doradus from the first paper, support a very high initial disk fraction (> 80%) even for massive stars, although there is an indication of a possible faster evolution of circumstellar disks around high mass stars. 33 sources only found in the L-band indicate the presence of heavily embedded, massive Class I protostars. We also report the detection of diffuse PAHs emission throughout the RCW 57 region.

  • (1999) Walsh, Andrew; Burton, Michael; Hyland, A; Robinson, Garry
    Journal Article

  • (1998) Walsh, Andrew; Burton, Michael; Robinson, Garry; Nyland, A
    Journal Article

  • (1999) Walsh, Andrew; Burton, Michael; Hyland, A; Robinson, Garry
    Journal Article
    A survey towards a selection of 35 methanol maser and/or ultracompact (UC) H ii regions, reported in Papers I and II and by Norris et al., has been conducted in the near-infrared (NIR). Out of 25 methanol maser sites surveyed, 12 are associated with a NIR counterpart. Out of 18 UC H ii regions (8 of which overlap with maser emission), 12 are associated with a NIR counterpart. Counterparts can be confidently identified not only by the positional agreements, but also by their unusually red colours. Spectral types for the embedded stars can be unambiguously determined for six sources, all of which imply massive, ionizing stars. One of these infrared sources has methanol maser emission, but no UC H ii region. It is possible that the maser emission associated with this source arises from a pre-UC H ii phase of massive stellar evolution or it could be that nearly all the ultraviolet photons are absorbed by dust within the UC H ii region. We have modelled the spectral energy distributions (SEDs) for some sources and find that a single blackbody can be used to estimate the stellar luminosity, but cannot represent the whole infrared SED. A two-component blackbody model and a radiative transfer model were also used to derive essential parameters of the infrared sources. The radiative transfer model also indicates which infrared sources are relatively young and which are older. Both models show that silicate absorption at 9.7 μm must be a dominant feature of these SEDs.

  • (1998) Walsh, Andrew; Burton, Michael; Hyland, A; Robinson, Garry
    Journal Article
    High spatial resolution radio continuum and 6.67-GHz methanol spectral line data are presented for methanol masers previously detected by Walsh et al. (1997). Methanol maser and/or radio continuum emission is found in 364 cases towards IRAS-selected regions. For those sources with methanol maser emission, relative positions have been obtained to an accuracy of typically 0.05 arcsec, with absolute positions accurate to around 1 arcsec. Maps of selected sources are provided. The intensity of the maser emission does not seem to depend on the presence of a continuum source. The coincidence of water and methanol maser positions in some regions suggests there is overlap in the requirements for methanol and water maser emission to be observable. However, there is a striking difference between the general proximity of methanol and water masers to both cometary and irregularly shaped ultracompact (UC) H ii regions, indicating that, in other cases, there must be differing environments conducive to stimulating their emission. We show that the methanol maser is most likely present before an observable UC H ii region is formed around a massive star and is quickly destroyed as the UC H ii region evolves. There are 36 out of 97 maser sites that are linearly extended. The hypothesis that the maser emission is found in a circumstellar disc is not inconsistent with these 36 maser sites, but is unlikely. It cannot, however, account for all other maser sites. An alternative model which uses shocks to create the masing spots can more readily reproduce the maser spot distributions.

  • (1998) Stolovy, S; Burton, Michael; Erickson, E; Kaufman, Michael; Chrysostomou, A; Young, E; Colgan, Sean; Axon, D; Thompson, Roger; Rieke, M; Schneider, G
    Journal Article
    The core of OMC-1 has been imaged with the Near-Infrared Camera and Multiobject Spectrometer (NICMOS) on board the Hubble Space Telescope at 0 2 resolution in 1% filters at 2.12 and 2.15 μm, revealing intricate structures in both continuum and shocked molecular hydrogen line emission. Numerous H -emitting clumps surrounding the BN/KL region have been resolved for the first time, several of which exhibit prototypical bow-shock morphologies with -shaped tips. We interpret these to be lower excitation analogs of similar structures 2 northwest of the core observed with ground-based telescopes. Many of the elongated H structures and bow-shock features appear to radiate outward from a region within a few arcseconds of radio source I, which suggests that the H energetics are dominated by one or more outflow sources in this region. However, the orientations of some features are unrelated to this apparent outflow pattern. The deeply embedded, suspected outflow source I remains undetected at 2 μm, although two faint new continuum sources have been detected within 1 of it. The newly resolved H features with bow-shock morphologies are located in regions previously identified as bow shocks by highly blueshifted components in their line profiles. In contrast, regions of H emission that are diffuse in the NICMOS image have broad, smooth line profiles. Several continuum features have an arclike appearance, which suggests interactions of winds with the ambient medium. At least 40 stellar or protostellar continuum sources have been detected, including at least one proplyd and four pairs of binary stars.

  • (1998) Stolovy, S; Young, E; Thompson, Roger; Rieke, M; Schneider, G; Burton, Michael; Erickson, E; Kaufman, Michael; Colgan, Sean; Chrysostomou, A; Axon, D
    Conference Paper
    The core of OMC--1 has been imaged with NICMOS on the Hubble Space Telescope at 0.2'' resolution in 1% filters at 2.12 and 2.15mu m, revealing intricate structures in both continuum and shocked molecular hydrogen line emission. Numerous H_2-emitting clumps surrounding the BN/KL region have been resolved for the first time, several of which exhibit prototypical bow-shock morphologies with V-shaped tips. We interpret these to be lower-excitation analogs of similar structures ~ 2' NW of the core observed with ground based telescopes. Many of the elongated H_2 structures and bow-shock features appear to radiate outward from a region within a few arcseconds of radio source 'I', suggesting that the H_2 energetics are dominated by one or more outflow sources in this region. However, the orientations of some features are unrelated to this apparent outflow pattern. The deeply embedded, suspected outflow source `I' remain s undetected at 2 mu m, although two faint new continuum sources have be en detected within ~ 1'' of it. The newly resolved H_2 features with bow-shock morphologies are located in regions previously identified as bow-shocks by highly blueshifted components in their line profiles. Several continuum features have an arc-like appearance, suggesting interactions of winds with the ambient medium. At least 40 stellar or protostellar continuum sources have been detected, including at least one proplyd and four pairs of binary stars.