Eclipsing binary imaged

The ecplising binary system Beta Lyrae has been imaged with interferometry. From the abstract:

We present the first resolved images of the eclipsing binary Beta Lyrae, obtained with the CHARA Array interferometer and the MIRC combiner in the H band. The images clearly show the mass donor and the thick disk surrounding the mass gainer at all six epochs of observation. The donor is brighter and generally appears elongated in the images, the first direct detection of photospheric tidal distortion due to Roche-lobe filling.

This is the beginning of a new era of imaging systems that have hitherto been observed (somewhat) indirectly. We understand systems like Beta Lyrae very, very well. But resolving the components is something new and quite exciting. The image on the right is Figure 2 from the paper and shows the images from both instruments as well as a model of the system.

Interview: Doug Baum on the BIPH

Astronomers spend a lot of time and money getting telescopes with bigger apertures to try to collect more photons. The BIPH (Binocular Photon Machine) is a device which makes better use of the photons you do get, multiplying the signal 50,000 times, effectively tripling your aperture.

Doug Welch and I interview Doug Baum, who along with his partner Russ Lederman, has developed the BIPH. We talk about the device, how it works and the cool ways it can be used.

Interview: Doug Baum on the BIPH (MP3, 24.3MB, 35:21, Show Notes)

Interview: Ethan Vishniac

We have another interview up on the feed! Doug interviews Dr. Ethan Vishniac, a theoretical astrophysicist and editor-in-chief of The Astrophysical Journal, “a prestigious international journal founded in 1890 at the University of Chicago. Vishniac is only the third editor since its inception.”

ApJ, as it is known, is one of the major professional astronomy publications in the world, along with the very similarly named Astronomical Journal (or AJ).

Then Doug and I spend a few minutes at the end begging for money.

More great podcasts and interviews coming up so stay tuned!

Interview: Ethan Vishniac (MP3, 30.4M, 44:05, Show Notes)

Variable Star Blogging

Well, we created a monster in Mike Simonsen, the AAVSO person who runs CVNet and Simostronomy. He has now created a very cool site which aggregates astronomy blogging, especially those blogs and posts which relate to stellar astrophysics and variables stars. It’s called the AAVSO Writer’s Bureau and the intent is to provide content to whomever wants it for their astronomy club newsletter or similar not-for-profit endeavors.

So add this one to Google Reader and you’ll get a firehose of great astronomy blogging.

UPDATE: D’oh, I’m not the sharpest tool in the shed. Right now there is no RSS feed and eventually the site will be password-protected and access granted by request to editors of astro club newsletters and websites. So get it while you can!

Polaris’s Pulsation

(For the grammar nerds, my understanding is, if a proper name ends with an ’s’ you still put an apostrophe ’s’ after it. The only case where you put only the apostrophe after the ’s’ is when the word is plural e.g. “our clients’ best interests”.)

I was going to write up a post about Polaris aka the North Star but Simostronomy beat me to it. In a nutshell, Polaris is a Cepheid variable star with a very low amplitude, so the brightness does not change very much. A new paper points out that the amplitude is increasing and Mike does a very nice job of explaining it.

One thing I like to do when under a dark sky like at a camp fire or floating in a boat is ask people to point at the North Star. Most people look for the brightest star and will point to it without giving any thought to the direction to which they are pointing! The North Star is due north of you everywhere you can see it and it is not the brightest star, by far. Its altitude above the horizon is equal to your latitude so here in Minneapolis it is 45 degrees above the horizon.

Besides it’s important (and temporary) role as the North Star, Polaris is one of the brighter Cephied stars and it appears to be going through changes in human time scales, which is always fun for astronomers.

So, thanks Mike! Now instead of blogging I can go play some Age of Conan.

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!