Permalinks

I upgraded Wordpress and it screwed up the permalinks. I didn’t like the format anyway so I have changed the permalink structure. This might create some problems for bookmarks and links from other sites. I’m going to fix that up when I get back home later this week. Thanks for your patience and please email me if you notice any specific problems.

If you have no idea what I’m talking about just ignore me!

Tip Jar

The right-hand column of the web site now includes a Donate button. We also recently added Google ads to the site. 100% of all income from these activities will be used to provide travel and technology opportunities for Slacker Astronomy so we can provide fun stuff for you to watch, read and listen to.

The PayPal account I’m using I had set up previously and is called Tribe of Angels. It should be clear that you are donating to Slacker Astronomy but don’t get confused if you see references to Tribe of Angels.

Doug and I, with occasional contributions from Aaron, Beth, Travis and, perhaps, YOU, will continue to provide you with the road-less-traveled of astronomy news, interviews and commentary. Stay tuned and thank you for your support!

Milky Way Galaxy Seeks New Dwarf Companion

It is interesting times for hunters of low-luminosity galaxies in the Local Group - our local concentration of galaxies. The low-hanging fruit has all been picked. Anything you could discover by visually examining a Schmidt plate or CCD mosaic image has been found. Is it the end of times for explorers of the Local Group?

Dr. Vasily Belokurov of Cambridge University and his collaborators reveal the answer to be no in their recent submission entitled “Leo V: A Companion of a Companion of the Milky Way Galaxy” found
here. Interestingly, the head-shot of this newly discovered dwarf galaxy shows … nothing! The foreground field stars greatly outnumber the few much more distant evolved stars in the cluster and there is no visible concentration on the image.

Seems like a hard sell, but it isn’t. Belokurov’s team has mined a vast and very influential database of object brightnesses, colors, and spectra known as the Sloan Digital Sky Survey and then obtained follow-up observations to confirm their discovery. The database provides the ability to select out stars from the only-slightly-fuzzy, much-more-distant background galaxies and also precise color information. This latter capability was key to the success of locating the new dwarf galaxy - its stars were sufficiently metal-poor that many of the evolved ones were so-called “blue horizontal branch” stars. The concentration of BHB stars on the sky does make this patch of sky stand out - it indicates a grouping of stars of similar age and metal abundance.

The final clincher was getting radial velocities for the handful of brightest, coolest stars in the galaxy - the so-called “red giant branch” (RGB) stars. Objects within the dwarf galaxy are only moving a few km/sec relative to each other. On the other hand, foreground field stars from the Milky Way have radial velocity differences of tens to hundreds of km/sec since they are orbiting the Milky Way’s much more massive center at various distances and on a variety of orbits. Belokurov’s team obtained 247 spectra on the 6.5m MMT telescope on Mount Hopkins in Arizona and found five RGB stars close to the dwarf galaxy center with near-identical velocities. Score!

The new pup - not to be confused with pope - christened “Leo V” is 180 kpc (about 600,000 light years) distant and is moving away from us at a speed of 132 km/sec. But that radial velocity includes a component of the Sun’s motion around the center of the Milky Way galaxy. When solar orbital component is removed, Leo V ends up moving only about 60 km/sec relative to the center of mass of Local Group galaxies.

Intriguingly, Leo V is found projected on the sky only three degrees away from a very similar beast with the very distinctive name Leo IV - also discovered by Dr. Belokurov and his collaborators! The researchers point out that the proximity of these objects in Local Group space may foreshadow additional discoveries along a stream of such apparently faint and intrinsically low-luminosity objects which could then inform our ideas of the formation of the Milky Way galaxy.

I must point out another very cool use of Local Group galaxy data. You may recall from high school or college physics that if you know velocities and positions of objects and the forces acting on them, you can predict where they were in the past and where they will be in the future. For galaxies, the force is gravity and you can get good estimates of their masses from their brightnesses (corrected by a dark matter fraction). You can also assume that at some time around 10 billion years ago, all of the present-day galaxies were essentially at rest with respect to each other. Given 1) their three-dimensional positions now, 2) their radial velocities now, and the assumption of zero initial velocities way back when, you have enough “boundary conditions” to solve each of their paths in the interim. But - and this is a big but - there is no simple way to do it! One has to try out many, many configurations of starting locations, run the system forward and see if the radial velocities and positions you end up with are similar to those we see now. If not, throw the galaxies back in the box, shake and try again! If you are interested in such games, check out the references and citations in this paper. Leo V can now be added to the list of objects used, so we now have an excuse to re-run these models!

Official Trailer for IYA 2009

The official trailer for the International Year of Astronomy (IYA) in 2009 is out! Check it out on YouTube by clicking here. Let’s just say that “The Dark Night” is opening in skies all over the planet!

Superhumping

You’ve maybe heard of cataclysmic variable stars. They are binary systems where one of the stars is stealing material from the other star due to their close proximity. This material forms a pancake around the star called an accretion disk. We’ve never imaged one of these systems but we have a very, very good theoretical model of how they work.

Every once in a while that accretion disk gets unstable and essentially blows up in what we call an outburst. Sometimes these outbursts are extra bright and carry a signature in their light curve called “superhumps”. These are large oscillations in the light curve at a period very near, but not exactly equal to, the orbital period of the system.

On 6/30/08 one of these systems, VY Aqr, went into a superoutburst. This is a fairly infrequent event for this star. The outbursts themselves happen every few years and the superoutbursts less often than that.

I was heading out to my observatory when the word came in so I slewed my fancy 0.212m telescope (doesn’t that sound more impressive than 8.3″?) and got some data. So did a few other people and I downloaded all of their data from the AAVSO. If you click the image above a light curve will open in a new window. Let me explain it to you.

This is a phase plot using the superhump period of this star (P_sh = 92.7 minutes). So anything that happens 92.7 minutes after something else is plotted at the same phase. So the X axis is the phase of the superhump period and the Y axis is the brightness of the star. Because the star is getting dimmer, each day’s data is lower on the graph than the previous day. So each night is folded upon itself but each subsequent night is below the previous night.

You can see there are some interesting things going on! The superhump amplitude and phase change over time as the systems fades.

The latest papers on this object included Doppler tomography, new parallax measurements and spectroscopy from the Hubble Space Telescope. There is a lot of interesting physics in these systems and they are the subject of on-going study by astronomers. Including me!

Interview: Ben Wiehe on Science Cafes

We have a new podcast on the feed featuring an interview with Ben Wiehe of WGBH on how he conducts science cafes. Subscribe to the feed or click below to listen. You can also watch the video of just the interview portion.

Interview: Science Cafes (MP3, 14.5MB, 15:27, Show Notes)

A white dwarf in the making

The AAVSO has posted their Variable Star of the Season and this time around it’s FG Sagittae, a star that has given us an opportunity to watch it evolve over human timescales, something very rare in stellar evolution.

…many papers have detailed the remarkable evolution of FG Sge from a faint, hot, blue post-asymptotic giant branch star and planetary nebula in the making to a much cooler and brighter yellow supergiant. Even more exciting for variable star observers, following FG Sge’s four-magnitude brightening and several decades of relative constancy, the star now appears to exhibit the dramatic and seemingly random fluctuations and fadings of the R Coronae Borealis class of variable stars. FG Sge is clearly a star undergoing extreme changes, and we’re fortunate to be treated to its amazing show.

If you have access to a telescope you can go take a look for yourself!

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Next up, a tip jar, coming soon.

++Carnival of Space

Here’s your weekly astronomy and space science fix at Carnival of Space #61. I could not get my sh*t together this week but I’m hoping to contribute to future carnivals. Weekly is a daunting thing for slackers.

Go read up and tell us what you think!

Slacker wins award

Slacker Astronomy founder and Tufts grad student Aaron Price has won a Chambliss Astronomy Achievement Student Award for his poster on BZ UMa.

I stopped by Aaron’s poster at AAS in St. Louis and he explained the work he presented while I grabbed it on video.

Here you go — enjoy!

Aaron Price on BZ UMa [FF] (MP4 video, 30.3MB, 04:10)