CGPS News: Volume 5

CGPS News Volume 5
Nouvelles du RCPG Volume 5
June / juin 1998


Word from the editor

Magdalen Normandeau

As we gear up to do science with the lovely data that the kind folks at DRAO have provided, it has become more important than ever to keep fellow consortium members apprised of what we're doing. To this end, a few web pages have sprung up for various science teams and science projects. Please have a look at the CGPS consortium web page to find links to all of these.

In particular, the web page for all stellar winds related project is meant to keep a running tally of objects being studied. So if you see an object which intrigues you and which could be related to stellar winds in some way,

1. Check that no-one else is working on it
If someone is, contact them, maybe they could use some help!
2. If no one is working on it, have your name and your object listed on the web page.
We're trying to avoid duplication of effort and ruffled feathers.

On a different note, thanks again to Judith and Jayanne for organising the 1998 CGPS science meeting. Best of luck in Baltimore, Jayanne!


From the management committee

Russ Taylor

Heartfelt thanks to Judith and Jayanne for hosting an excellent annual science meeting at Queens'. The meeting was a commendable blend of fantastic data and stimulating science. Best of luck to Judith and Dieter as they move on to their adventure in India. And congratulations and sad goodbye to Jayanne, who will be leaving Kingston at the end of the summer to take up a position at the Space Telescope Science Institute in Baltimore. Anchors away, Jayanne!

The Kingston meeting was the first at which final versions of DRAO mosaic images were available. The tremendous effort put in by the data processing team has paid off. The images are essentially as good as they can be. We are achieving noise-limited images with dynamic range of several thousand, at both wavelengths. This corresponds to approximately 0.25 mJy at 21 cm continuum and 3 mJy at 74 cm. The fields are registered to position accuracy well below 1" and the flux scale is consistent everywhere in the images to better than 1%, on the same scale as the NVSS survey. The short spacing data and the algorithm to incorporate them into the CGPS mosaics result in low spatial frequency data that is accurate to a few % with artifacts level below 1 K. With four mosaics now produced (as of this newsletter) and the reprojected and regridded HIRES and FCRAO data completed we can look forward to real scientific progress in the coming year, and exciting results from the CGPS at the Naramata workshop.

As decided at the Kingston meeting, in the near future we will register and add short spacing data to the preliminary Cygnus and "A" mosaics. This will give the supernova remnant and stellar winds groups something to work on over the summer.

An important issue discussed at the Kingston meeting was the proprietary period for the DRAO images. Following the open discussion on this, the management committee recommends that the proprietary period for the mosaic images be 18 months. The first mosaic MV2 will thus become public domain in June 1999. Public access to the images will be handled by the Canadian Astronomical Data Centre. The calibrated u-v data is public three years after observations and is available upon request to DRAO.

After the annual science meeting, the three non-permanent members of the management committee are open for replacement. Judith Irwin, Lloyd Higgs and Gilles Joncas are rotating off the committee. Thanks for the year of service. Those eligible for the committee are the Canadian co-investigators on the CSP grant. The technique we have adopted to elect replacements is to send around a complete list of names by email and offer everyone the chance to withdraw their name from the list. We then hold an electronic vote. The initial list will be sent around soon after this newsletter appears.

With the beginning of the fourth year of the project, our second CGPS postdoc competition begins. Subject to a successful 3-year review, we will provide funding for half the salary of three new CGPs postocs. The new positions are for two years and can begin anytime between 1 November 1998 and 31 October 1999. Applications are due by September 30. An email announcement with details will appear shortly.

Wishing you all a wonderful summer. See you in Naramata!


IGA HIRES and FCRAO 12CO Regridded Data

Steven Gibson

Data from the High Resolution IRAS Galaxy Atlas and the FCRAO CO Survey of the Outer Galaxy have been available to CGPS consortium members for some time, but not in the form of images and cubes with the same centers, scales, and projections as the CGPS release mosaics, making direct comparison of the multiwavelength data difficult - until now! Yes, at long last, these data have been regridded and quietly await your scientific perusal. There are two methods of distribution:

  1. CD-ROM versions will be shipped with the appropriate DRAO release mosaics as they become available, so that you will have a complete set of data to compare for a given location.

  2. However, for those who cannot wait, the HIRES and FCRAO data are also available immediately by FTP from Calgary (see the ftp site article in this issue of the newsletter).

Details about the regridding process and available data:

The HIRES data have been pieced together from the collection of 1.4° x 1.4° IGA fields to make images covering the M-mosaic areas on a 15" / pixel grid. These were then resampled to the actual M-mosaic 18" / pixel grids using the DRAO program MAPCONVRT with bi-cubic interpolation. Comparison of images before and after regridding shows excellent agreement. The data products available are 60 & 100 µm maps of each M-mosaic, with both 1st and 20th iteration versions of four different types of data:

All of these are FITS-format images. In addition, there are also text table files giving the parameters for each sample beam in the beam sample maps.
COVERAGE NOTE: HIRES data north of b > 4.7° was not included in the IGA dataset, so these areas of the regridded HIRES data are blank. However in the near future they will be filled in using data supplied by the good folks at CITA, who, in the more distant future, will also be releasing maps at 12 & 25 µm.

The FCRAO data path was a little more complex. Preliminary cubes on the 50.22" & 0.812565 km/s / pixel FCRAO grid were assembled from l-v slices. These cubes were then spatially smoothed with the DRAO program CONVOLVE to the Nyquist resolution limit of 1.674' (2 FCRAO pixels) prior to spatial regridding. The user should thus be aware that the angular resolution is not that of the 45" FCRAO beam, but has been limited by the sampling of the FCRAO 2nd Quadrant Survey to 100.44". Spatial regridding to the CGPS 18" / pixel scale was carried out with DRAO MAPCONVRT using bi-cubic interpolation. Following this, the cubes were regridded in velocity to the CGPS 0.82446 km/s / pixel grid using cubic interpolation with DRAO CUBINTERP.

The regridded FCRAO cubes are stored in scaled 16-bit integer FITS format to save space. Even so, they take up as much room as their HI spectral line counterparts: 544 megabytes each. For this reason, while the files can be obtained via FTP from Calgary, it may be easier to wait for CD-ROM copies.

COVERAGE NOTE: The FCRAO survey does not cover the entire CGPS area. It is limited to a Galactic longitude range of 141.5° > l > 102.5°, which touches only 20 CGPS fields: MW1, MW2, MX1, MX2, MY1, MY2, MA1, MA2, MB1, MB2, MC1, MC2, MD1, MD2, ME1, ME2, MF1, MF2, MG1, & MG2 (MH1 & MH2 contain a small FCRAO strip, but it is already covered by MG1 & MG2). The Galactic latitude range of the FCRAO data is -3.0° < b < 5.4°. Areas outside of this are left blank in the regridded data.

For any questions about the regridded data, please send email to gibson@ras.ucalgary.ca.


CGPS Data FTP Site in Calgary

Steven Gibson

To aid in the distribution of CGPS data products such as the regridded HIRES & FCRAO data (discussed elsewhere in this newsletter), a restricted-access FTP site has been set up in Calgary.

Two means of access exist. Both require passwords, and, please note, due to the arcane requirements of Unix, the passwords are NOT the same!

Contents of the FTP site include CGPS release mosaic data, some old preliminary mosaics, one or two images of the entire survey area, and a collection of Karma annotation files which people might find useful when viewing the data (note: you will need Karma version 1.6.25 or higher to use these annotations). A README file in the top directory gives fairly detailed descriptions of all of these.

For any questions about the ftp site, please send email to gibson@ras.ucalgary.ca.


Public talk

Charles Kerton

On April 2nd I gave a talk entitled, "The Canadian Galactic Plane Survey" as part of the public tour program at the St. George Campus Observatory at the University of Toronto. The audience was very interested in hearing about a Canadian-lead project in astronomy. Most of the astronomy that people hear about has to do with the Hubble Space Telescope and NASA, so I think this is a very important point to emphasize in any public talks that people give.

Questions ranged from explaining how Earth-rotation aperture synthesis works (always fun!), through, "What are the black dots in the HI image?", to will the survey include gamma-ray observations (Hey! Why stop at IR?).

As our editor mentioned in a previous newsletter these public talks are fun to give and the A/V material you prepare can be used over and over again at other talks you give. More importantly they can help increase the public profile of astronomy in Canada.


Disk-Halo Interaction Update

Attendees at the group's discussion during the May CGPS meeting in Kingston were Shantanu Basu, Jayanne English, Judith Irwin, Sergey Mashchenko, Magdalen Normandeau, and Russ Taylor. Welcome to the group Sergey! Your other collaborators are Neb Duric and Carl Heiles.

The enthusiasm for understanding outflow phenomena spilled over from the talks by Jayanne, Shantanu, and Doug Johnstone into this discussion. It appears from the simulations by Shantanu and Doug that the W4 chimney is at a phase of shell expansion which precedes the "blowout" evolutionary stage represented by the Anchor. Sergey notes that even thinner primary shells, i.e. "stems", can be obtained by including the vertical pressure gradient of the surrounding ISM in the simulations. Other energy input scenarios of interest include analogies to atomic weapon blasts and flow dynamics (e.g. circulation patterns in the plane causing vortices and turbulent structures in the latitude direction). The fact that Sergey and Shantanu (along with Doug of course) are keen to model various energy input scenarios for the anchor delights the observers. We are also looking forward to Charles Kerton's IGA IRAS images of the anchor.

Evolution of the shock front in the Kompaneets solution, as the bubble expands in an exponential atmosphere and eventually blows out (Basu, Johnstone, and Martin 1998). Ionized hydrogen map (Dennison, Topasna, and Simonetti 1997) showing the extended superbubble associated with the chimney and overlaid with a Kompaneets solution (Basu, Johnstone, and Martin 1998).
Numerical model of a stellar wind blown superbubble blowout. Kompaneets solution is the thick line (Mac Low, McCray, and Norman 1989; multiple supernovae models have more distinct "mushroom" clouds (Tenorio-Tagle, Rozyczka, and Bodenheimer 1990); and Sergey has models with even thinner stems.) An inverted map of the anchor in neutral hydrogen emission integrated over a 9 km/s velocity range (English, Taylor, and Irwin 1998).

Additionally Magdalen outlined potential approaches for examining the currently available fields for vertical worm-like structures. Jayanne's beastiary of objects in the anchor dataset will be placed online for perusal by consortium members. The password protected website is http://www.astro.queensu.ca/~english/gps/secur.html .


HI Self-Absorption Project: First Results

Steven Gibson

A new science project was initiated in early April: the study of the environments and physical properties of HI self-absorption (HISA) features in the CGPS dataset. The science team members are Gibson, Taylor, Dewney, McCutcheon, Wendker, and Higgs.

Inspection by eye of the available HI data shows numerous complex HISA features such as those in the figure below. Many, but not all, of these objects show good agreement with HIRES IRAS and FCRAO CO clouds and filaments.

Our challenge is to find ways of describing these entities algorithmically, so that they may be extracted and converted to optical depth ``cubes'' in space and velocity. We have begun experimenting with methods of estimating the background brightness in the area of interest using values on the periphery (a 3-D analog to ``continuum fitting'' stellar absorption lines), with fair success for simple regions that can be easily enclosed in a 3-D box. Simplistic analysis of data extracted in this way shows encouragingly reasonable values for physical properties (e.g., T = 90 K, nH = 40 cm-3), though as yet these can only be considered order of magnitude estimates. More sophisticated methods of defining the boundaries of HISA features in 3-D are required for us to proceed. We are exploring these now.

For much more information on this project and current results, please see the CGPS HISA feature page.


Commentaires ou suggestions? Comments or suggestions?
Ecrivez à / Write to mnormandeau@astro.berkeley.edu