Francois Cazzolato, Université Laval
OB associations are known to be sites of recent star formation and will likely disrupt their environment and create new stars of their own. We propose to study one such OB association (at least) and dissect all stages of past and ongoing star formation in order to estimate its importance.
The OB association Cas OB7 (l=123 b=1) has been chosen as our first target. It seems to be surrounded by an IR shell seen at all IRAS wavelengths. Furthermore, CGPS H I observations have shown something that looks like a shell surrounding the association (only half of it since the MC1 and MC2 mosaics are not yet available and Cas OB7 lies in the center of the MB1, MB2, MC1 and MC2 mosaics). The velocity of this shell (-36 km/s) is in relative agreement with the distance to Cas OB7 quoted by Humphreys (1978; 2.5 kpc) but disagrees with that quoted by Garmany & Stencel (1992; 1.8 kpc). CO data on the other hand show more than one feature that could be related to the association, each at different velocities.
A look for young stellar objects and T Tauri stars using IR colors extracted from the IRAS point source catalogue around the association has shown some promising candidates.
Cas OB7 is adjacent to a new superbubble located in the Perseus arm (Wallace, Dewdney & Landecker [WDL], CGPS Newsletter Vol. 8 March 1999) where there is also evidence of triggered star formation. Some aspects of this new structure will also be studied (in consultation with WDL) as part of this Ph.D. project.
Additional work was carried out on stellar wind candidates in the summer of 2001 with Serge Pineault and undergraduate student Vanessa Juneau. For details, please read the Newsletter article.
Garmany, C.D. & Stencel, R.E. 1992 A&ASS, 94, 211
Humphreys, R.M. 1978 ApJSS, 38, 309
Anik Daigle, Université Laval
Unsupervised neural networks will be developed to detect H I shells in the Perseus arm. Both morphology and kinematical behavior will be used as input parameters. The results will be used to estimate the porosity of the ISM in that spiral arm.
Kevin Douglas, University of Calgary
Observations of the gas and dust content of high-latitude gas clouds have shown interesting relationships between the emission by the different constituents of these structures. Several studies comparing IRAS, H I and CO emission in these cirrus clouds have yielded evidence of a molecular component which is not traced by the emission of CO molecules (Reach et al 1994, Meyerdierks & Heithausen 1996, Boulanger et al 1998). Infrared excess emission from IRAS data points to the possibilty of molecular gas component that is warmer and more diffuse than the component of molecular gas that is traceable by CO. In these studies, the "diffuse" component of molecular hydrogen is found to be comparable in mass to the H I content. This diffuse gas may be widely abundant in the plane of the Galaxy. If present, on the same scales as in these high latitude clouds, it has important implications for many areas of astrophysical interest.
The Canadian Galactic Plane Survey (CGPS) offers an excellent opportunity to study the phenomenon of diffuse molecular gas in the plane of the Galaxy by combined analysis of pc-scale resolution images of CO, H I and dust emission over a large area of the Galactic disk. I will make use of the datasets available to the CGPS consortium to probe interstellar Galactic clouds for molecular gas not traceable by CO emission. The detection of diffuse molecular gas, an analysis of the environmental condition required for its existence, and the correlation with molecular gas traced by CO emission will provide information on the importance of this ISM component and its relationship to the other states of the ISM. The presence of hot stars in the Galactic plane, while complicating the study in some regions, also yields a warmer and more varied interstellar medium which may give rise to an increase in the amount of molecular gas not seen in CO.
Vanessa Juneau, Université Laval
The CGPS data are used to study the environment of sources known to possess or suspected of possessing strong stellar winds. The first target is a new Wolf-Rayet star (WR142a at galactic longitude and latitude of 79.31 and 2.25 degrees) recently discovered by Pasquali et al. (A&A, in press). Other candidate sources will be taken from a sample identified on the basis of their IR colors (e.g., Pineault, Cazzolato and Juneau, in Seeing through the Dust, p. 332).
Andre Khalil, Université Laval
Topological tools and multifractals will be used to characterise the distribution of matter in both molecular clouds and H I features. Tools already used by astronomers and new ones will be compared. I will attempt to merge the individual informations to provide a better understanding of the gas features. Relative comparisons between molecular clouds and between H I features will be made. I will also compare both types in order to investigate the transition from H I features to molecular clouds.
Yvan Ladouceur, Universite Laval
G78.2+2.1 is a bright shell SNR which has already been the subject of many studies. However, the new CGPS database, in particular the 1420 MHz continuum image, shows new fainter features which justify a detailed re-analysis of this object. The radio images, together with the HIRES data and the 21 cm datacube, are going to be used to test the hypothesis that some of these faint structures are the result of a breakout of the SNR shock wave (with associated spectral index variations?) and to look for evidence of accelerated H I clouds.
Simon Strasser, University of Minnesota
Hundreds of bright continuum background sources exist in the CGPS, SGPS and VGPS regions at 1420 MHz. They are absorbed by the neutral hydrogen (H I) in the Galactic plane. For my Masters thesis, I analyzed the absorption spectra towards over 400 sources in the CGPS region and derived an average 2-component model for the phases of the interstellar medium (ISM).
I am extending this analysis to all three surveys for my PhD. I have developed several methods to fit absorption and emission features toward background continuum sources to extract physical parameters for the H I clouds. In my analysis, I will place particular emphasis on the evidence for very cold H I (below 30 K) and the transitions between the phases of the ISM. The unprecedented resolution and sky coverage of the Galactic plane surveys will allow me to build a detailed picture of the changes as a function of Galactocentric radius. I hope to be able to supplement the H I data with targeted observations of OH spectra.
Maik Wolleben, Max-Planck Institut für Radioastronomie
I will use continuum polarimetry to investigate the magneto-ionic properties of molecular clouds. For this purpose I will examine the IGPS polarization surveys at 21cm wavelength, e.g. the Effelsberg Survey, the CGPS, and a polarization survey which I have carried out using the 26-m Telescope of the DRAO.
A multi-frequency study of polarization features towards the Taurus molecular cloud complex has already revealed a coincidence between positions of minima in polarized intensity and the surface of the molecular cloud. These observations can be explained by Faraday screens associated with the cloud. The cloud obviously has a Faraday active layer and rotates and possibly depolarizes polarized emission from behind the cloud. Those Faraday screens can be modelled on the basis of simple vector additions. By fitting such a model to observed Faraday screens, one can derive the Faraday properties of the cloud and intensities and position angles of the polarized emission in the foreground and background.
I want to extend this study to all local molecular clouds covered by the IGPS. The results of this study might be twofold. At first it would resolve a piece of the puzzle of interpreting Galactic polarization images, and secondly give interesting insights into the structure of magnetic fields and/or ionized components of molecular clouds.
Jo-Anne Brown, University of Calgary
The DRAO ST has the ability to record the four Stokes parameters, I, Q, U and V which characterize an electromagnetic wave. Stoke's I describes the received intensity and is usually the sole parameter used to create images of the sky. Stoke's Q and U describe the linear polarization of the received signal, while Stoke's V describes its circular polarization. The polarized emission received from the interstellar medium (ISM) is predominantly linear. Circularly polarized signals are rare and usually originate from point sources.
As part of the Canadian Galactic Plane Survey (CGPS), I intend to study the interstellar medium with the aid of the Stoke's I, Q, and U maps. The non-thermal radiation from the Galactic disk produces a diffuse linearly polarized radiation field. This radiation field is acted upon and modified by propagation through the interstellar medium. By studying the properties of the polarized radiation in the CGPS images (Q and U in particular), I hope to develop techniques to deduce information about the ISM, such as the magnetic field structure. Part of this study will involve looking at how the polarization properties correlate with radiation from components of the ISM, such as the ionized gas (as seen in the Stokes I images) and the neutral gas (as seen in H I and CO images). As an example, I am currently investigating the region around the ionized filament CXR 11 in Cygnus-X. In the Q and U maps of this region, a distinct shift in the position angle of the linear polarization of the background field corresponds to the location of the filament in the I map, which suggests Faraday rotation of this background field. By inferring the electron density of the filament from the Stoke's I map, and determining the rotation measure using the Q and U maps, the magnitude of the line of site component of the magnetic field within the filament may be estimated. The measurement and modelling techniques I develop by studying this field and others from the CGPS will provide a new method for extracting information about the magneto-ionic component of the ISM.
Tyler Foster, University of Alberta
The comprehensive nature of the CGPS truly lends itself to answering questions of relationships between objects on a grand scale. Such questions draw together many different wavelengths and methods in astronomy, with the CGPS serving as the foundation. In this project I intend to search for evidence of interaction among, and a common ISM shared by, objects in the northern Cygnus region (l=90 to 95 deg., b=-1 to 4 deg.), in particular by uniting the CGPS continuum and H I line survey with new radio and optical observations undertaken.
Objects in this region are principally thermal emitters (H II regions), but include two SNRs (3C434.1 and CTB104A). Upon inspection of the l=93 deg. region in the CGPS 21cm supermosaic, the possibility of a dynamically shared environment becomes clear. Features are apparent such as haloes enveloping SNR / H II region pairs and filamentary bridges of thermal emission between individual objects and groups. The entire region is seen to be embedded in a very large halo of weak emission, connecting objects found in the region's lower latitudes (e.g. CTB104A, b=-0.5 deg.) to the bright H II region CTB102, seen at b=+3 deg.
Until recently, none of the objects in this region has been reliably identified optically. Further, optical emission line luminosities have been measured for very few galactic SNRs. This is changing slowly, however, e.g. with the recent work being done at the University of Alberta's Devon Astronomical Observatory. With the ability to produce deep images in Halpha, OIII, SII, and other lines, Devon provides routine detection of optical nebulosity invisible in even the Palomar Observatory Sky Survey.
I hope to answer questions on two levels: (a) For individual objects, their composition, density, age, and other astrophysical properties will be derived. Exciting star(s) within H II regions will be identified. (b) Global questions will be posed as well. For example, are these objects related, or are they a chance superposition of objects at different distances? Is there evidence of sequential star formation, or are the objects all the same age? Are these objects destroying the environment they were born into?
Tyler Foster, University of Alberta
From an optical standpoint, detailed imaging of all but a few supernova remnants remains difficult. By contrast, the radio fields from the Canadian Galactic Plane Survey are richly endowed with such objects. Their presence not only memorializes the deaths of massive stars, but reveals secrets about its surroundings. In addition to continuum images, the DRAO ST produces H I line data of the region. This can provide a distance, and in turn can lead to reasonable figures for its size and age, which, in concert with other CGPS data, provides a basis on which to model the SNR and its environs.
My particular interest centers on the field of SNR 3C434.1 (G94.0+1.0) and H II region NRAO 655. With 1' resolution, the DRAO ST allows for the preparation of the most detailed radio image of the region ever obtained. Astrophysical data will be extracted from DRAO 1420MHz and 408MHz fields, and H I line data consulted for possible indication of the distance to the SNR's location in the Perseus arm. Spectral index maps of the area will be constructed, and will aid in construction of a model of the SNR, the thermal source NRAO 655, and the immediate vicinity, that, upon visual inspection of the images, seems to suggest the medium's simultaneous interaction with both sources. Linear polarization data will assist in characterizing both the objects and the ISM. Data at other wavelengths (X-ray, IR, gamma), and optical imagery, (obtained with the 0.5m Wide Field telescope/CCD system at the University of Alberta's Devon Astronomical Observatory) will augment the model of the objects and their locale. Finally, consideration of the region as a whole, single system will be given.
Charles Kerton, CITA / University of Toronto
One of the primary goals of the Canadian Galactic Plane Survey (CGPS) regarding interstellar dust is to understand the evolution of dust as it moves through different phases of the interstellar medium (ISM). H II regions are interesting in this regard as they can have a strong effect on interstellar dust through the action of strong ultraviolet radiation fields and shocks associated with their expansion. A combination of high-resolution radio, millimetre and infrared data is ideal for this sort of study since it provides information on the physical conditions in and around a H II region along with information about the interstellar dust directly.
I will be constructing an atlas of high resolution images of 12 and 25 micron emission covering the CGPS survey region. This will be done using IRAS data processed with the HIRES image construction algorithm. These images will complement the existing far-infrared part of the CGPS data base since much of the mid-infrared emission originates from very small grains (VSGs) at 25 microns and polycyclic aromatic hydrocarbons (PAHs) at 12 microns, whereas the far-infrared emission originates from larger grains. The construction of this atlas is currently underway and should be completed in January 1998.
Once completed the mid-infrared images will be used in a number of projects. Current plans are to investigate the effect of weak shocks on the grain size distribution of grains found around H II regions. Weak shocks can modify this distribution due to shattering in grain-grain collisions and it has be speculated that these shocks could also create PAHs due to the splitting of graphite grains. I will also be investigating the effect of UV fields on PAHs, the connection between UV extinction and IR emission, and the 3-D distribution of dust.
Finally I will be studying selected H II regions in greater detail using the Wide-Field Infrared Explorer (WIRE) satellite. This small infrared telescope will provide very high resolution views of a few H II regions. It is hoped that a comparison of these images with HIRES images will lead to improvements in the analysis of other H II regions not observed by WIRE.
Simon Strasser, University of Calgary
I will study the H I line absorption towards background sources. Together with emission spectra measured "off-source" this will allow me to determine the spin temperature and optical depth towards these sources. There are a large number of sources in the survey region so I will be able to systematically study the temperatures and densities of the atomic hydrogen phase of the ISM in the plane of the Galaxy. Using data from the CGPS and the VGPS will allow these properties to be studied globally as a function of galactocentric position and in relation to the spiral structure of the Galaxy.