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The AAO/UKST SuperCOSMOS Hα survey
The UK Schmidt Telescope (UKST) of the Anglo-Australian Observatorycompleted a narrow-band Hα plus [NII] 6548, 6584-Åsurvey ofthe Southern Galactic Plane and Magellanic Clouds in late 2003. Thesurvey, which was the last UKST wide-field photographic survey and theonly one undertaken in a narrow-band, is now an online digital dataproduct of the Wide-Field Astronomy Unit of the Royal ObservatoryEdinburgh (ROE). The survey utilized a high specification, monolithicHα interference bandpass filter of exceptional quality. Inconjunction with the fine-grained Tech-Pan film as a detector it hasproduced a survey with a powerful combination of area coverage (4000square degrees), resolution (~1 arcsec) and sensitivity (<=5Rayleighs), reaching a depth for continuum point sources of R~= 20.5.The main survey consists of 233 individual fields on a grid of centresseparated by 4° at declinations below +2° and covers a swatheapproximately 20° wide about the Southern Galactic Plane. Theoriginal survey films were scanned by the SuperCOSMOS measuring machineat the Royal Observatory, Edinburgh, to provide the online digital atlascalled the SuperCOSMOS Hα Survey (SHS). We present the backgroundof the survey, the key survey characteristics, details and examples ofthe data product, calibration process, comparison with other surveys anda brief description of its potential for scientific exploitation.
| Star formation in RCW 108: Triggered or spontaneous?
We present visible, near infrared and mm-wave observations of RCW 108, amolecular cloud complex in the Ara OB1 association that is being erodedby the energetic radiation of two O-type stars in the nearby cluster NGC6193. The western part of the RCW108 molecular cloud, for which wederive a mass of ~8000 Mȯ, contains an embedded compactHII region, IRAS 16362-4845, ionized by an aggregate of early-type starsfor which we estimate a mass of 210 Mȯ. Thespectral type of the earliest star is O9, as confirmed by the visiblespectrum of the compact HII region. We notice a lack of stars later thanA0 in the aggregate, at least having the moderate reddenings that arecommon among its B-type stars, and we speculate that this might be aconsequence of the extreme youth of the aggregate. We also note theexistence of a dense ionized clump (n > 104cm-3) appearing near the main ionizing star of the compactHII region. We examine the distribution of stars displaying infraredexcesses projected across the molecular cloud. While many of them arelocated in the densest (n 104-5 cm-3) areaof the molecular cloud near the position of IRAS 16362-4845, we alsofind a group concentrating towards the edge of the cloud that faces NGC6193, as well as some other stars beyond the edge of the molecularcloud. The intense ionizing radiation field by the O stars in NGC 6193is a clear candidate trigger of star formation in the molecular cloud,and we suggest that the existence and arrangement of stars in thisregion of the molecular cloud supports a scenario in which theirformation may be a consequence of this. However, infrared excess starsare also present in some areas of the opposite side of the cloud, whereno obvious candidate external trigger is identified. The existence ofsuch tracers of recent star formation scattered across the more massivemolecular cloud associated with IRAS 16362-4845, and the low starformation efficiency that we derive, indicate that it is in a state tostill form stars. This is in contrast to the less massive cloud (660 Mȯ) close to NGC 6193, which seems to be moreevolved and mostly already recycled into stars, and whose internalkinematics show hints of having been perturbed by the presence of themassive stars formed out of it.
| A 12CO (J = 1 -> 0) study towards the Ara OB1 region
Intermediate angular resolution (HPBW=8\farcm7 ) carbon monoxide(12CO J=1->0) line observations towards the OB associationAra OB1 are reported. The molecular line observations cover an area of2\fdg75 x 3\fdg00 , and disclose a rich and complex distribution of themolecular line emission. The molecular features likely to be associatedwith the OB-association Ara OB1 span the velocity range from -28 to -20km s-1. The most negative radial velocities are observedalong NGC 6188 (equiv Rim nebula). This nebula marks the interfacebetween the HII region RCW 108 and the highly absorbing molecularmaterial located westwards of the ionised region. The dominant COstructures, labeled E and F, have a radial velocity of about -23.5 and-21.8 km s-1, respectively. The former harbours a brightoptical knot, the infrared cluster RCW-108 and the strong IRAS source16362-4845. IRAS point sources are also seen in projection onto12CO concentrations F and H. This may indicate that the starforming process is a widespread phenomenon in this molecular complex.Extended continuum emission, having a high degree of spatial correlationwith both the infrared and molecular emission, is observed in theregion. We believe that this emission, thermal in nature, arises fromthe ionised surface layers of the molecular complex. The ionising agentsare the high mass stars of NGC 6193, the nucleus of Ara OB1. The totalamount of molecular gas related to Ara OB1 is about ~ 1.4x104 Msun.
| Beauty and astrophysics
Spectacular colour images have been made by combining CCD images inthree different passbands using Adobe Photoshop. These beautiful imageshighlight a variety of astrophysical phenomena and should be a valuableresource for science education and public awareness of science. The widefield images were obtained at the Siding Spring Observatory (SSO) bymounting a Hasselblad or Nikkor telephoto lens in front of a 2K by 2KCCD. Options of more than 30 degrees or 6 degrees square coverage areproduced in a single exposure in this way. Narrow band or broad bandfilters were placed between lens and CCD enabling deep, linear images ina variety of passbands to be obtained. We have mapped the LMC and SMCand are mapping the Galactic Plane for comparison with the MolongloRadio Survey. Higher resolution images have also been made with the 40inch telescope of galaxies and star forming regions in the Milky Way.
| The unstable O6.5f?p star HD 148937 and its interstellar environment.
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| The young Of star HD148937 and its associated interstellar bubble: H 2 region
The star HD148937 and nebulosities surrounding the star are found to beclosely inter-related. IUE spectroscopy of HD148937 shows the star to bea young Of star with low mass loss. Properties Of the surroundinginterstellar bubble and the H II region support the implied youth ofHD148937.
| Cosmic Radio Sources Observed at 600 Mc/s
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| Radio Observations of Ionized Hydrogen Nebulæ and Other Discrete Sources at a Wave-length of 9.4 cm.
IN recent attempts1-3 to account for the general radioemission from the Galaxy as the integrated radiation of discretegalactic radio sources, it was found necessary to introduce the effectof ionized interstellar hydrogen, H II regions, to fit the observedradio isophotes at various frequencies. Scheuer and Ryle4detected, at wave-lengths of 1.4 and 3.7 m., a bright band of emissionconfined within 2° of the galactic equator superimposed on thegeneral radiation. They identified the bright band with thermal emissionfrom a distribution of H II regions. H II regions are stronglyconcentrated in the galactic plane. The large source, Cygnus X, has beententatively described as thermal emission5, perhaps fromseveral bright H II regions surrounding γ Cygni5, orfrom the integrated radiation of all the H II regions in the spiral armin the direction of Cygnus8. However, Baldwin6attempted unsuccessfully to detect, at a wave-length of 1.4 m., a verybright individual H II region, the Orion nebula. Observations ofdiscrete sources have been almost entirely confined to metrewave-lengths, where spectra of more than twenty sources have beenobtained7. Piddington and Minnett5,8 observed fivediscrete sources at a wavelength of 25 cm. and the emission at 25 and 10cm. from a region near the galactic centre. This was an appreciableextension of the short-wave limit of source spectra.
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