PeteUplink's Universe

30 April 2011 by Meg, Planet Hunters Blog

I was talking to last week’s seminar speaker, and we were talking about Planet Hunters and some of the things that might be lurking in the Kepler data.  One cool thought is there might be inverse transits so instead of dimming events, instead the star actually appears brighter.

There are lots of eclipsing binaries that you’ve probably seen as you’ve been classified, but another interesting type of eclipsing binary might be a transiting white dwarf orbiting a main sequence star. White dwarfs are about the same size or a little bit bigger than the Earth about half as massive as the Sun. Depending on where the white dwarf orbits, there could be magnification causing a brightening as the white dwarf crosses in front it’s companion star. This magnification is caused by gravitational microlensing, where a massive object bends  light of a background source resulting in images of the source that are magnified and distorted. Transiting exoplanets are not massive enough to bend and distort the light of their companion stars significantly. For eclipsing binaries it looks white dwarfs are in the sweet spot, if they are orbiting extremely close to their partner main sequence star. Papers in 2003  by Sahu and Gilliland (2003) and Farmer and Agol predicted that Kepler might be able to detect such events. In these cases during the transiting event, the ligthcurve gets brighter rather than fainter. These events last as long as the transit does so only a few hours (if the white dwarf is orbiting at 1 AU the event is ~10 hours in duration).

Here’s some examples from a paper by Sahu and Gilliland (2003) .

A transiting 0.6 solar mass white dwarf orbiting at 1 AU

0.6 solar mass white dwarf at different orbital radii from a solar-type star

There are some estimates of how many might be there ranging from a few to a about a hundred or so events in the Kepler monitored stars, but we really don’t know.  No one has detected them, and there could be 1 or none but with so many eyeballs staring at the data, we might uncover them if they’re there. Anyone seen anything like this in the light curves you’ve classified? It would be very exciting if we found one, it would be the first such discovery – if you see an inverse transit like the examples above, please share on Talk and let us know about your discovery!

Cheers,

~Meg

28 April 2011 by Ben, Galaxy Zoo Blog

Dear all,

After a lot of hard work by all involved, we are very pleased to say that the Galaxy Zoo2 Bar-Drawing paper has finally been accepted in Monthly Notices of the Royal Society. It will appear on the arXiv tomorrow, and there are links to access the data in the paper, and on my website here and the zooniverse repository.

The paper uses the results of an off-shoot Zooniverse project. This project present users with SDSS GalaxyZoo2 galaxies using the Google Maps interface, and asked the users to preform certain tasks. Many of the galaxies had been classified by GZoo2 as containing a bar (an elongated structure extending across the center of the galaxy) and the users were asked to measure the bar length and thickness, and determine how the bar and spiral arms were connected, see the image below.

We had over 200 users on this off-shoot project, and ~14,000 unique bar classifications were made! Without your help, this project would have never have taken place. In fact, at the time we started writing the paper, this work contained almost 100 *times* more galaxies than any previous bar-galaxy research paper! Our statistics were overwhelming.

We found many interesting features, some were already known, but were placed on a far more rigorous footing, and others were new. For example, longer bars inhabit redder disk galaxies and the bars themselves are redder, and that the bluest galaxies host the smallest galactic bars; and we found that galaxies whose bars are directly connected to the spiral arms are preferentially bluer and that these galaxies host typically shorter bars. We also compared our results with previous observational works, and with simulations. E.g. a figure showing the bar length measurement against the galaxy color (as measured by the SDSS) can be seen below.

For those of you desperate for a sneak-peak before tomorrow, you can find our paper here.
here

We thank all of the volunteers again, for making this project such a success.

Best,

Ben [on behalf of the bar team]

28 April 2011 by Robert Simpson, Old Weather Blog

As we said in our recent blog post, Old Weather has been churning through Royal Navy logbooks from World War 1 for long enough now that we can start to extract some interesting stats from the words transcribed by the community.

Social networks are all the rage now, but here at Zooniverse HQ we’ve been wondering what the 90-year-old social graph of Old Weather would look like. We’ll have more to say in the near future about the interactions of people on board the Royal Navy ships from our logs, but what about the ships themselves? When ships pass each other at sea, or meet to exchange supplies, officers and information, they make a note of this in their logs.

This enormous chart shows all of the Old Weather ships in a big grid, highlighting in purple where ships connect to each other. You can look down the chart, or across it, to find the interactions for a given ship. You can see that theHMS Arlanza and the Alsation seem to meet up with quite a few of the other ships of the chart. Both are Armed Merchant Cruisers that cross the busy stretch between the UK and the USA. So is the HMS Motugua, and it too has a fair few interactions with other vessels.

Taking those ships that are often mentioned, we can delve further into their interactions and create arc plots for those vessels. The arc plot below, for the HMS Alsatian, shows that it has encountered 26 ships in the transcriptions made to date. The thickness of the lines connecting vessels indicates the relative number of times that the two ships reference each other. The HMS Moldavia and HMS Patia are fairly well-connected with the Alsatian.

What isn’t shown on the large network plot is that the most mentioned vessel in the Old Weather fleet is the HMS Bee, a river gunboat and a ship that is only 36% complete so far on Old Weather (maybe you could jump aboardand help to complete it?). This ship is not mentioned a great deal by every ship but rather features regularly in the logs of a few vessel in the fleet. The arc plot for the HMS Bee is shown below. The HMS Bee interacts a great deal with the HMS Scarab and the HMS Cricket. all three are gunboats, as is the HMS Gnat. The next step here is to examine the logs and find out when these vessels interacted so much, and why. A blog post of these at a later time.

Finally, for this post, let’s look at the arc plot for the top twenty most-connected vessels in Old Weather so far. These are the ships from the large network plot that connect with the most other ships. These plots can be made for the whole fleet – but they become very large and complex and thus difficult to take value from. This slimmed-down version showing just the top twenty gives you an idea of the ships that are linked to other ships.

This is the kind of simplistic data that can be extracted from your transcriptions of events. So far, only the development team have been looking at this, but the tools are being made available to the historians of Old Weather for further analysis. I’m excited by what they can uncover.

Many of the ships listed in these charts are available on our Old Weather Voyages page, so you can see for yourselves how they interact with each other. You can use that page to read the log entries and see where ships were when they encountered one another. We’re always trying to find new ways for everyone to explore the Old Weather data and if you have any suggestions we’d love to hear them, either here on the blog or via twitter@oldweather.