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Pearls in an IPHAS oyster

Submitted by Kevin Jardine on 22 May, 2008 - 18:00

The hot stars of the cluster [BDS2003] 66 appear embedded as pearls in a celestial oyster, the HII region Sh 2-211, in this unusually three-dimensional image created using the IPHAS data set, using the process described here. Sh 2-211 is believed to be ionised by at least three hot stars with the classes O9 Ib, O9 V and B0 V, and may share the same molecular cloud as Sh 2-212. Both nebulae are believed to lie well beyond the Perseus arm in what may be an Outer arm of the Milky Way.

This image is so interesting that I've included both a black and white hydrogen-alpha version and a false colour version that adds in the IPHAS Sloan r and Sloan i data as well. The hydrogen-alpha-only version reveals faint details obscured in the colour image.

Sharpless Sh 2-211

Sharpless Sh 2-211

Onto Sh 2-173

Submitted by Kevin Jardine on 21 May, 2008 - 18:10

Continuing our tour of the striking IPHAS images, here are two of Sh 2-173. This HII region appears to be part of a supershell surrounding the Perseus arm OB association Cas OB5. It is believed to be ionised by the O9V star BD +60 39 and may be associated with the star cluster NGC 103, according to Avedisova. The bright star near the emission ridge is the M2II giant HD 1613. These images only show a part of Sh 2-173, which in turn is embedded in a region with a huge amount of diffuse nebulosity, as this large scale image of this part of the sky reveals.

There are several artifacts in these images, partly caused by my awkward construction of a mosaic from IPHAS images with different luminosity levels, but also by banding that exists in the original IPHAS images. A good astroimager would probably be able to remove these artifacts.

Nevertheless, these images reveals a wealth of new details about what has been an obscure nebula up to this point.

These hydrogen-alpha images are so interesting that in the long term I think I'll need to create a separate gallery on this site to showcase them.

Sharpless Sh 2-173

Sharpless Sh 2-173 - detail

IPHAS reveals Sh 2-163

Submitted by Kevin Jardine on 21 May, 2008 - 09:19

Very little is available from the scientific literature on Sh 2-163 beyond a large range of distance estimates (from 2500 to 4000 parsecs) and the fact that it contains the embedded infrared cluster [BDS2003] 45. (These distance estimates place it within or behind the dusty OB association Cas OB2 in the Perseus arm.) So I was very surprised to discover that IPHAS reveals that Sh 2-163 is a large and complex object.

Here's an overview image:

Sharpless Sh 2-163

and a detail:

Sharpless Sh 2-163 - detail

Obviously a lot is going on in this region and it is worth further study!

A new face for the Dragon

Submitted by Kevin Jardine on 19 May, 2008 - 10:28

The great HII region Sh 2-132 is located in the Cep OB1 association within the Perseus arm, at a distance of about 3180 parsecs. It is ionised by two Wolf-Rayet stars (WR 152 and WR 153) and about 11 OB stars. Sh 2-132 has no common name. However, it has always looked like an arched celestial dragon to me, so I think of it as the Dragon nebula.

Last year I mentioned the arrival of the northern hemisphere hydrogen-alpha imaging project IPHAS. IPHAS has released incredibly detailed hydrogen-alpha images of most of the northern galactic plane, radically enhancing our views of many of the Sharpless nebulae. In this blog entry I look at IPHAS's view of Sh 2-132.

Before I get into the details of accessing the IPHAS data, here are some results. Here's an overview of the whole Sh 2-232 region:

Sharpless Sh 2-232

a detail of the Dragon's head:

Sharpless Sh 2-232 - Dragon's head

a closeup of the globule to the right of the Dragon's head at full IPHAS resolution:

Sharpless Sh 2-232 - globule

and a detail of the complex region at the northeast:

Sharpless Sh 2-232 - IRAS 22187+5559 region

The bright region in this last image towards the upper left is the infrared source and star formation region IRAS 22187+5559. It is unclear whether this is part of Sh 2-132. Wouterloot and Brand give a kinematic distance of 5090 parsecs for IRAS 22187+5559, suggesting that it lies well beyond Sh 2-132, but because of known streaming motions in the Perseus arm, this estimate may very well be too large.

Because IPHAS provides Sloan r and i plates in addition to hydrogen-alpha, it is also possible to create false colour images like this one:

Sharpless Sh 2-232 - Dragon's head (colour)

However, I find that this tends to obscure the detail in the hydrogen-alpha data and prefer the black and white images.

Creating your own IPHAS images

For some reason astroimaging sites have been slow to take advantage of the new detailed data available from IPHAS. This is a shame because real astroimagers would be able to create much better images than my limited efforts above!

The recommended option for accessing IPHAS data is Astrogrid, a complex Java application. This application is fantastic for professional astronomers working with many different databases. It's perhaps overkill for simply downloading images, however.

Fortunately, there is now a simpler two step alternative. The first step is the IPHAS postage stamp server here:

http://casu.ast.cam.ac.uk/ag/portal/

(Visit the site and then click on the "Postage Stamps" link at the top.)

Enter the name or coordinates of an object and the postage server will show you small images along with the number of the plate.

IPHAS plates are split into four 2048x4096 pixel images (CCD segments). There are three frequencies available - hydrogen-alpha, Sloan i and Sloan r. The postage stamp server will display the name of the image file in the format:

rXXXXXX.fit[Y]

eg.

r367783.fit[4]

where XXXXXX is the plate number and Y is the CCD segment. It will also tell you the frequency.

You can then retrieve the FITS file for that image using a URL with the format:

http://astrogrid.ast.cam.ac.uk/iphas/siap-atlas/getImage?run=XXXXXX&ccd=Y

I have the desktop version of the Aladin FITS viewer installed, and my browser automatically runs Aladin and displays any downloaded FITS files. I always do a log transform of the data in Aladin, convert it to RGB format and save it as a bmp file for further processing.

I hope that you've found this blog entry interesting and that it encourages you to create your own IPHAS images!

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