Blogs

Gum data

As I've been going through my commentary on the RCW catalog, I've come to realise that there are several dubious or erroneous cross identifications in the RCW catalog, especially with regard to objects in the Gum catalog. In several cases, it appears that Colin Gum was actually referring to a different object or only part of the object as later defined by RCW. To deal with this, I'm going to put up a map showing the locations and extents of all the objects in the Sharpless, RCW and Gum catalogs.

My commentary on the Gum catalog currently uses the coordinates for these objects given in SIMBAD. However, these coordinates are often derived by SIMBAD using identifications with other nebulae and do not reflect the actual data given in Gum's original catalog. Unlike the Sharpless and RCW catalogs, Gum's original catalog data is not available through Vizier, so as a first step, I have manually entered Gum's original data for each of the 97 entries in his catalog into an Excel-format spreadsheet.

Gum supplied 1900 epoch RA and Declination data for these objects. I've used the Python ephem library to convert these into current l and b galactic coordinates and added these to the spreadsheet as well. (Note that the galactic coordinates supplied by Gum in his original catalog are based on the old Lund pole system and I have not included these in the spreadsheet.)

You can find the Gum spreadsheet here. I'll post another blog entry when the nebula map is ready.

Milky Way Explorer revised

I've simplified the interface, fixed a few bugs, and most importantly, added several new datasets to the Milky Way Explorer. There is now context-sensitive help, so you can get information on each map you are looking at by clicking the Help button.

I've tested the interface in Internet Explorer 7, Firefox 3.5 and Safari for Windows.

You can go directly to the Milky Way Explorer here but please read the documentation first if you haven't used it before.

Marker bugs

Some recent changes to the Google Maps API broke some of the marker and overlay functionality for the Milky Way Explorer (especially for the MSX and Spitzer maps).

I've linked in an older version of the API javascript and now everything is working again.

Astronomical conservatism

I'm amazed sometimes by the cultural conservatism I see amongst scientists, including many astronomers. A case in point is Bo Reipurth's wonderful recent Handbook of Star Forming Regions (you can see the contents of Volume 1 and Volume 2). Reipurth is a respected Danish astronomer (currently based in Hawaii) and editor of the Star Formation Newsletter.

There has been an explosion of recent results on star-forming regions, driven in part by the amazing images from space telescopes, especially Chandra (X-rays) and Spitzer (infrared). It is definitely time for a survey that brings this all together. Many of the individual chapters of the Handbook are available for free as preprints (you can google for them or use arXiv). From this content I can see that the Handbook is an amazing resource.

It seems obvious, however, that this survey would have been far better implemented as a website rather than a printed Handbook. As a website, it would have been easy to update, easy to link to all the relevant references through the ADS, easy to search via Google, and could have made use of modern interactive map interfaces such as the Milky Way Explorer to display the objects discussed. Although the content is available as PDFs, these have practically all of the same limitations as print publications and none of the advantages of websites.

Granted, the Astronomical Society of the Pacific can charge for the Handbook (an eye-popping 160 US dollars for both volumes), but they also could have charged for website access (at least for a limited period), and in any case, I doubt that the publishers stand to make much money from this publication.

I suspect that the Handbook has been printed because of a quirk in the sociology of academic science. Specifically, websites are not yet considered to be citeable publications, and it would have been impossible for Reipurth to convince the dozens of astronomers who collaborated to produce the Handbook chapters to spend that considerable time on something that they could not add to their scientific bibliographies.

I can only hope that the Astronomical Society of the Pacific will see the light at some point in the future and rework this content (or perhaps an updated and expanded version of it) into what would be a fascinating, beautiful and extremely useful website.

Sharpless commentary completed

It's been almost four years since I created the Sharpless catalog section of this website. I can finally announce that there is a commentary for each entry in the Sharpless catalog.

The Sharpless commentary would not have been possible without the work of Veta Avedisova and her colleagues at the Institute of Astronomy, Russian Academy of Sciences, in Moscow. Avedisova's crucial paper identifying ionising stars for many HII regions and her recent Catalog of Star-Forming Regions in the Galaxy have brought together a huge amount of information on many Milky Way objects. In so far as the world's astronomers have succeeded in creating an Encyclopedia Galactica, Veta Avedisova is its editor-in-chief.

I'm now moving on to finish my commentaries on the RCW and Gum nebulae and, of course, I will add new research results on Sharpless objects as they become available. Even now, 50 years after the publication of the final Sharpless catalog, there are many unresolved mysteries concerning these objects and at some point I'll put up a special article listing some of these.

Strange new worlds

I've added a new section to the site, Strange New Worlds, that showcases some larger images. I've also re-written the front page and site introduction to better reflect all the new content I've added to this site over the last year-and-a-half.

More on Herschel

Just as a follow-on to my last post, the preliminary science program for Herschel is here:

http://herschel.esac.esa.int/Key_Programmes.shtml

and the only large mapping project I can see is this one:

https://hi-gal.ifsi-roma.inaf.it/higal/

which basically redoes the Spitzer inner galaxy survey but in more detail and with a larger range of frequencies.

That will be exciting when finished (probably in a couple of years).

I do hope that more large surveys are added. For example, it would be fantastic to have a larger survey of the Cygnus region beyond the more focused one mentioned here:

http://starformation-herschel.iap.fr/hobys/cygnus.jpg

But perhaps that depends on how long the coolant holds out.

The king is dead - long live the king

This has been an amazing week for those interested in space telescopes.

As I write this, the Hubble telescope has been lowered into a bay of the Shuttle Atlantis and is being re-equipped for another five-year mission. Seconds ago, the Herschel/Planck teams reported successful activation signals from those two observatories. And, more sadly, the Spitzer infrared telescope has finally run out of coolant after almost six years of wildly successful operation, reducing it to two frequencies from one instrument.

Although the two observatories are different in detail, the Herschel infrared telescope is the natural successor to Spitzer and it is an enormous relief to know (fingers crossed) that the Herschel mission is also on track for success. Herschel is by far the largest space telescope ever launched. As the Herschel website points out:

The telescope's primary mirror is 3.5 m in diameter, more than four times larger than any previous infrared space telescope and almost one and a half times larger than that of the Hubble Space Telescope. The telescope will collect almost twenty times more light than any previous infrared space telescope.

The infrared space telescopes (especially IRAS, MSX and Spitzer) have arguably been more important to mapping our Milky Way than any other scientific instrument. These instruments have been wildly successful in piercing through obscuring dust and giving us a view of our home galaxy that no telescope operating at optical frequencies could ever do.

I can only hope that Herschel will contribute much to this great tradition. This is already a bit of doubt unfortunately, ironically because of the power of the instrument. IRAS, MSX and Spitzer all made large surveys (respectively of the whole sky, the galactic plane, and the inner galaxy). Surveys are essential for mapping the Milky Way and discovering new objects. Because of Herschel's size, there may be a temptation to use it only for examining known objects more closely rather than doing larger surveys. Spitzer team member Barbara Whitney hinted at this when she said:

I suspect that Spitzer's view of the galaxy is the best that we'll have for the foreseeable future. There is currently no mission planned that has both a wide field of view and the sensitivity needed to probe the Milky Way at these infrared wavelengths.

Let's hope that Herschel's greater power does indeed allow it to make an even greater contribution to science than the infrared telescopes that have come before.

Sh 2-168 in IPHAS

Over the last year, I've added a number of powerful tools for mapping the Milky Way to this site, including the Avedisova Catalog, the Milky Way Explorer, and the Commentary on the Galactic Plane.

Recently I've been expanding my illustrated guide to the Sharpless Catalog using information from these new tools. Sometimes, however, there just isn't enough information published in the scientific literature about some of these interesting objects and then at least a detailed image can point to some of the mysteries still to be resolved.

This is the case for Sh 2-168, a compact HII region that appears to be embedded in the expanding ring of gas and dust surrounding the Cas OB5 association in the Perseus arm. Below is an image created from the wonderful IPHAS hydrogen-alpha data using the procedure described here. (You can click on it for a larger version).

Avedisova concludes that this nebula is ionised by the O9 V star LS I +60 50. (SIMBAD reports a slightly cooler B0 V class.) Not surprisingly, this is the bright star near the central bright emission (just above the emission and slightly to the left). What I find interesting, however, are the objects visible in or near the disturbed area to the top left (northeast). At the edge of this region (and embedded in Sh 2-168) there seems to be a compact star cluster. I can't find a reference to this cluster in the scientific literature and perhaps it has never been closely examined. Bica and colleagues have reported a loose cluster visible in infrared in this nebula ([BDS2003] 47) and perhaps this compact grouping is part of that, but it doesn't seem to fit their description.

WorldWide Telescope experiment

At the end of January, the WorldWide Telescope (WWT) team at Microsoft Research released tools to convert images into the WWT's native TOAST format.

I've used these tools to move seven of the Milky Way Explorer sky images into WWT, as well as an overlay view that identifies many of the objects visible in these images.

The link for this is at the end of this blog entry, but first some explanation.

In my initial review of the WorldWide Telescope I praised the basic software but criticised the limited survey data available for it. This has improved somewhat since then. In particular, the spectacular Spitzer infrared survey of the inner galaxy is now available through the WWT.

Nevertheless, many important surveys are still not available through the WWT, including the MSX infrared survey of the full galactic plane and many radio surveys.

The public WWT tools currently require the full image to be loaded into memory before it is TOASTed, preventing me from migrating larger surveys such as the full MSX A-band, which is currently available through the Milky Way Explorer. So for now I have created a low resolution version of this survey for the WWT.

I've also created a WWT version of the composite false-colour Effelsberg/Parkes radio survey of the galactic plane (described in the sources section of the description of the Milky Way Explorer) which reveals many interesting objects including supernova remnants not visible at other frequencies.

The WWT includes an IRAS infrared colour composite image. However, this image is very dark, which highlights bright objects in the galactic plane, but obscures infrared cirrus clouds elsewhere. I've created WWT versions of my "dark" and "bright" IRAS images, both of which are much brighter than the standard WWT image.

I've created WWT images of my false colour CO and hydrogen-alpha maps. Both of these data sets are already available through the WWT, but in a more limited colour range.

I've included my favourite image, which is a mountains-in-the-sky heightmap with the height determined by the Effelsberg/Parkes galactic plane radio intensity and the colour determined by the IRAS survey data.

The overlay image completes the set. This includes white ellipses showing the boundaries of OB associations, yellow circles showing the boundaries of ionising clusters, and pink, violet and blue balls showing, respectively, the locations of Wolf-Rayet, O-class and B-class ionising stars. Avedisova star formation regions are identified as yellow splotches, and supernova remnants as blue-green splotches. The sources for all this data are given in the Sources section of the description of the Milky Way Explorer.

By now I expect that you are impatiently waiting for the WTML link, but just a few more points before I give it:

  • Many of these surveys are for the galactic plane only and the WWT starts up elsewhere (Pisces, apparently, at least for me). So you may need to move your view to see anything.
  • I'm currently storing this data on my own server, which, unlike the Microsoft WWT server, is not a superfast system. So you may need to wait several minutes for the images to finish loading. Fortunately, they should be cached on your own hard drive during subsequent visits.
  • The WWT does not appear to have a marker system, or at least none that has been publicly announced that I am aware of. However, there is a hack that is almost as good if you don't mind editing one of the WWT files. In:

    C:\Documents and Settings\Your Username\Local Settings\Application Data\Microsoft\WorldWideTelescope\data\places

    find the file:

    Stars.xml

    Open this in a text editor, and after the line:

    <dataset name="Common Named Stars" Groups="State" type="place">

    add the line:

    <file name="Overlay Objects" url="http://socnet.bz/wtml/toast/overlay.txt" Browseable="False">Overlay Objects</file>

    This will add several thousand annotations for ionising stars, supernova remnants and Avedisova star formation regions to WWT and works well with the overlay view in particular.

  • One of the greatest strengths of the WWT is its ability to overlay foreground and background images. For example, you can set the Overlay to the foreground and use any other image (one of mine or another one) as the background. You can cross fade in between them. I find it especially interesting to cross fade in between the CO view that shows molecular clouds and the radio/IRAS heightmap image.
  • The MSX image is off by a few pixels, which is slightly noticeable if you cross fade it with another image. I'll fix that when I am able to TOAST the full MSX survey.

Without further ado, if you click on this WTML link, you should be able to view the data in WWT.

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