http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:10332 The Arches cluster is an extraordinarily compact massive star cluster with a core radius of about 10'' (~0.4 pc) and consisting of more than 150 O star candidates with initial stellar masses greater than 20 M⊙ near G0.12-0.02. X-ray observations of the radio Arc near the Galactic center at l ~ 0.°2, which contains the Arches cluster, have been carried out with the Advanced CCD Imaging Spectrometer (ACIS) on board Chandra X-Ray Observatory. We report the detection of two X-ray sources from the Arches cluster embedded within a bath of diffuse X-ray emission extending beyond the edge of the cluster to at least 90'' x 60'' (3:6 pc x 2:4 pc). The brightest component of the X-ray emission coincides with the core of the cluster and can be fitted with a two-temperature thermal spectrum with a soft and hard component of 0.8 and 6.4 keV, respectively. The core of the cluster coincides with several ionized stellar wind sources that have previously been detected at radio wavelengths, suggesting that the X-ray emission from the core arises from stellar wind sources. The diffuse emission beyond the boundary of the cluster is discussed in the context of combined shocked stellar winds escaping from the cluster. We argue that the expelled gas from young clusters such as the Arches cluster may be responsible for the hot and extended X-ray––emitting gas detected throughout the inner degree of the Galactic center. 2010-10-29T02:42:40.063Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:10335 A supernova explosion, the final death throe of a massive star, creates an expanding bubble of hot gas that overruns up the surrounding medium. When a supernova remnant encounters a dense interstellar cloud, the compression may trigger gravitational collapse and the formation of a new generation of stars. This event can be detected through intense stimulated emission in the 1720-megahertz transition of the hydroxyl radical, OH, which yields unique insights into the physical processes and conditions occurring during the interaction. 2010-10-29T02:42:20.520Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5902 Context: The Isaac Newton Telescope Photometric Hα Survey (IPHAS) is currently mapping the Northern Galactic plane reaching to r′ = 20 mag with typically 1″ resolution. Hundreds of Planetary Nebulae (PNe), both point-like and resolved, are expected to be discovered. We report on the discovery of the first new PN from this survey: it is an unusual object located at a large galactocentric distance and has a very low oxygen abundance. Aims: Detecting and studying new PNe will lead to improved estimates of the population size, binary fraction and lifetimes, and yield new insights into the chemistry of the interstellar medium at large galactocentric distances. Methods: Compact nebulae are searched for in the IPHAS photometric catalogue, selecting those candidates with a strong Hα excess in the r′−Hα vs. r′ − i′ colour–colour diagram. Searches for extended nebulae are by visual inspection of the mosaics of continuum-subtracted Hα images at a spatial sampling of 5 × 5 arcsec². Follow-up spectroscopy enables confirmation of the PNe, and their physico-chemical study. Results: The first planetary nebula discovered via IPHAS imagery shows an intricate morphology: there is an inner ring surrounding the central star, bright inner lobes with an enhanced waist, and very faint lobular extensions reaching up to more than 100″. We classify it as a quadrupolar PN, a rather unusual class of planetary showing two pairs of misaligned lobes. From long-slit spectroscopy we derive Tₑ[Nii] = 12 800 ± 1000 K, Nₑ = 390 ± 40 cm⁻³, and chemical abundances typical of Peimbert’s type I nebulae (He/H = 0.13, N/O = 1.8) with an oxygen abundance of 12 + log(O/H) = 8.17 ± 0.15. A kinematic distance of 7.0⁺⁴.⁵₋₃.₀ kpc is derived, implying an unusually large size of >4 pc for the nebula. The photometry of the central star indicates the presence of a relatively cool companion. This, and the evidence for a dense circumstellar disk and quadrupolar morphology, all of which are rare among PNe, support the hypothesis that this morphology is related to binary interaction. 2010-01-27T22:24:54.124Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5904 The Galactic plane has been observed between l = 330° to l = 336° as part of a velocity resolved Hα survey of the southern Milky Way using a scaning Fabry-Perot on a 36 cm telescope. The detailed analysis of the resultant Hα profiles reveals the presence of several layers of ionized gas with different velocities over the surveyed region.We have studied in detail both the 2-D spatial and velocity structure of the HII regions RCW102, RCW104 and RCW106. Combining these Hα observations with stellar and radio data we provide estimates for the most probable distances of these different layers. The first layer at −5 kms⁻¹ is local emission linked to the Sco-Cen association at 170 pc. The next layer, around −24 km s⁻¹, is at 1.9 kpc and traces the near section of the Sagittarius-Carina arm. Well connected to the Sagittarius-Carina arm portions traced in the adjacent regions (l = 328° and l = 338° area), the arm, in this longitude range, clearly shows and confirms the departure from a logarithmic spiral. The Scutum-Crux arm is also traced in this area by faint and diffuse emission at −40 km s⁻¹ which can be placed at 3.2 kpc. The layer at −52 km s⁻¹ is the major spiral-arm feature of the studied area; its most probable stellar distance is 4.2 kpc. An important emission component is also observed at −65 km s⁻¹ in the southern part of the surveyed area. This mainly patchy and filamentary emission we identify as the possible optical counterpart of a supernovae remnant centered at l = 332.0°, b = −3.2°. Finally, two complexes have been determined around 12.5 kpc which places them in the far section of the Norma arm. 2010-01-27T22:24:52.295Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5905 The Macquarie/AAO/Strasbourg Hα Planetary Nebula Catalogue (MASH) of nearly 1000 new Galactic Planetary Nebulae (PNe) discovered from the AAO/UKST Hα survey of the southern Galactic plane is now essentially complete. The survey's excellent combination of resolution, uniformity, areal coverage and depth has enabled detection of this unprecedented new PN sample. MASH PNe are typically more evolved, obscured, of larger angular extent, and of lower surface brightness than those in most previous surveys. The number of PNe in the Galactic bulge has also been doubled. Though most of these are quite compact, more evolved examples have been found. The MASH catalogue represents a seven year programme of discovery and spectroscopic confirmation and will form the basis for significant studies. A key strength is that the whole sample has been obtained from the same, uniform survey data. The 75% increase in known Galactic PNe represents the largest single increase in such discoveries. MASH PNe will have a significant impact on many aspects of PNe research, especially for studies at the extremes of the luminosity function which were previously poorly represented. 2010-01-27T22:24:50.219Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:5906 IPHAS is an ongoing Hα imaging survey of the North Galactic plane. When completed, it is expected to discover several hundred new Galactic planetary nebulae, in addition to a huge number of Hα emitters. We present here the project, the methods used to search for compact and extended ionized nebulae, and some preliminary results about the ~100 new candidate planetary nebulae identified so far. 2010-01-27T22:24:50.208Z ]]>