- Basic plan of the Milky Way
- Surveying the Galaxy
- Mapping hydrogen
- Face-on map overview
- Introduction to the Milky Way Explorer
- The Cloud Hunters
- The Star Sweepers
- Things Unseen: The Westerhout radio sources
- The Avedisova catalog: A real Hitchhiker's Guide to the Galaxy?
- Avedisova glossary
- Strange new worlds
- Commentary on the Galactic Plane
- Hydrogen-alpha commentary
Submitted by Kevin Jardine on 25 September, 2009 - 10:15
As promised in my last blog entry, I've created overlay maps for the Gum, RCW and Sharpless nebulae. You can find the links and a preliminary analysis, including a description of a surprising error in the Sharpless catalog, here.
Submitted by Kevin Jardine on 13 September, 2009 - 12:14
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.
Submitted by Kevin Jardine on 24 July, 2009 - 17:12
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.
Submitted by Kevin Jardine on 30 May, 2009 - 14:53
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).
Submitted by Kevin Jardine on 30 May, 2009 - 10:37
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.
Submitted by Kevin Jardine on 24 May, 2009 - 09:46
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.
Submitted by Kevin Jardine on 16 May, 2009 - 15:15
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.
Submitted by Kevin Jardine on 15 May, 2009 - 07:07
Just as a follow-on to my last post, the preliminary science program for Herschel is here:
and the only large mapping project I can see is this one:
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:
But perhaps that depends on how long the coolant holds out.
Submitted by Kevin Jardine on 14 May, 2009 - 15:21
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.
Submitted by Kevin Jardine on 21 April, 2009 - 07:28
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.