Wild Stars Day One Part 2

Okay, so we still don't find many stars in the CV 'period gap' with orbital periods of 2-3 hours, so in ten years since the last Wild Stars conference, and with all the new CVs discovered and measured in that time, this is a real phenomena.

We find a lot of stars piling up around three hours period and many of these are accreting at very high rates. The secondaries are losing prodigious amounts of mass to their cannibalistic white dwarf companions.

The leading theory explains this gap as the point where magnetic braking ceases and these binaries abruptly stop accreting matter from the secondary to the white dwarf. As these binaries continue to lose orbital energy through gravitational wave propagation they evolve through the period gap from 3 hours to two hours. At this point they've spiraled in close enough for the secondary to fill its Roche lobe and accretion starts up again.

From orbital period (Porb) 2 hours and less the only way the system loses orbital energy is through gravity waves. Typically these stars have low accretion rates and it takes a long time for them to build up enough material in the disk to go into outburst. So the secondaries are not losing mass very quickly, and we'd expect to see another spike in the population of CVs at shorter orbital periods.

One problem is the fact that these systems tend to be quite faint in quiescence, so they are harder to find than their bright actively outbursting friends at the longer Porbs. With the recent results of the Sloan Digital Sky Survey (SDSS) we've uncovered more ad more of these short period low accretion rate CVs, but there is still some debate about whether we have actually begun to pin down the actual spacial density of these objects. There aren't that many faint, short period CVs close to us, so they must indeed be rare objects.

CV theories also predict a minimum Porb of about 65 minutes. There may be something wrong with our models though, because observationally, the minimum seems to be closer to 80 minutes. Either we have a whole bunch of highly evolved, low accreting faint stars out there at 23rd magnitude (beyond the limit of SDSS) or there is something lacking in our understanding of the physics at this minimum threshold for CV period evolution.

To be honest, not much of this is new, or cutting edge astrophysics anymore. A lot of these same issues were being discussed ten years ago. We may have more observations and phenomenology, but we don't seem to have made any significant progress in our understanding of these Wild Stars.

That is a topic I want to interrogate Steve Howell, one of the local organizers, about tomorrow. I'll let you know what he thinks.

Wild Stars -Day One

Much of variable stars research is related to stellar evolution. We have a pretty good handle on how single stars evolve over billions of years. They are born in clouds of dust and gas, contract due to gravity until they reach a critical limit at which nuclear processes begin converting hydrogen to helium and heavier elements. At this point a star is born.

The most important factor in the evolutionary track of a star is its initial mass. Giant stars burn up their fuel quickly and die spectacularly. Dwarf stars live for tens of billions of years, miserly using up their fuel while putting out a conservative amount of energy.

A majority of stars follow an evolutionary path that eventually causes them to swell to hundreds of times their original radius, throwing off layers of their outer atmosphere via stellar winds and from their losing their gravitational grip on the outer layers of their swollen stellar atmosphere. These stars eventually become planetary nebula with white dwarfs at their centers.

These degenerate white dwarf stars are fascinating objects. They do not produce new energy, like stars. They are the remaining ash of the core of evolved stars, slowly cooling through time from their original very high temperatures. They are small and extremely dense, planet sized objects with approximately the mass of our sun squeezed into their small frames.

Things get a lot more complicated when two or more stars in orbit around each other are involved. If the stars' orbits are wide enough, each star may be able to follow its normal evolutionary path for billions of years. However, cataclysmic variables are stellar pairs, typically containing a white dwarf and a swollen M dwarf, in orbit around each other so close that the orbital period can be measured in hours. Mass is exchanged from the secondary to the white dwarf via an accretion disk. This interaction has a profound effect on the evolution of the stars involved.

Some of these white dwarfs have extremely strong magnetic fields. The accretion process is interrupted in part in intermediate polars, or completely in polars (AM Her stars). No real accretion disk is formed. Instead the mass transferred in polars slams down onto a small area at the magnetic pole of the white dwarf, or goes into strange orbits following the magnetic field lines in an intermediate polar.


Fine. We can and do observe all these properties of these binary systems now, along with the outbursts and high and low states of activity CVs are well known for. But, the burning question of the day today was "How do they get this way?"

Where do these pairs come from? Are they born as normal stars in unremarkable circumstances that somehow evolve into wild pairs of objects orbiting each other so closely they are exchanging material? How long does this take? How do they lose their orbital energy, and what is that energy converted into? Even more perplexing is, where do the magnetic fields in CVs come from?

Above: The common envelope explanation for the evolution of CVs from a pair of main sequence stars, to a pair with a Giant Branch star and main sequence dwarf to eventually becoming a white dwarf and main sequence dwarf pair (CV).

The generally accepted explanation is called the Common Envelope evolution scheme. As a pair of stars evolves, changes in the mass of one or both stars affects the orbital characteristics of the pair, and they lose energy and begin to spiral in towards each other. At a critical point in this process one star evolves to the point that it fills its Roche lobe and the pair becomes involved in a cloud of dust and gas shared by both called a 'common envelope'. We believe CVs evolve out of this phase into the semi-detached systems we see as dwarf novae and magnetic CVs.

Just how this happens is still not well understood, and how either star acquires a mega-Gauss magnetic field in the process is an even less understood process. The mystery was framed and discussed in a couple very interesting papers given in the afternoon session. James Liebert pointed out the fact that the Sloan Digital Sky Survey has found over 1200 close pairs containing a white dwarf and an M dwarf, precisely the kinds of pairs we believe are the progenitors of CVs, yet none of them have been found to contain a white dwarf with a strong magnetic field.

Nearly 25% of CVs are magnetic systems so where do they come from if not these pre-CV pairs? In fact, all highly magnetic white dwarfs appears as either single stars or components of CV binaries.

Christopher Tout proposed in the following paper that highly magnetic white dwarfs must be formed as a result of the common envelope phase of binary evolution. He went further to suggest that the single white dwarfs with the highest magnetic fields are the result of a pair of stars merging into one highly magnetic white dwarf from the common envelope phase. And the magnetic CVs we observe, polars and intermediate polars, are the result of systems that almost merge before eveolving into magnetic CVs.

There are also fundamental questions about the evolution of CV pairs. Do these stars continue to spiral in towards each other, reaching shorter and shorter periods? How does accretion and mass loss affect this evolution? How do we explain the well known 'period gap' where there are almost no actively accreting systems with orbital periods between 2 and 3 hours?

A graphical demonstration of the period gap. The vertical axis is the number of known CVs. The horizontal axis is the period in hours (top) or fractions of a day (bottom).

What is so special about this orbital period? What shuts off the accretion process at 3 hours yet lets it re-engage at less than 2 hours. What is the actual period minimum for CVs? Is it 65 minutes, as theory predicts, or is 80 minutes, as observations seem to imply?

There are lots of questions. I hope to get at least some of the answers this week. Stay tuned, and we'll find out together.

The images used in this article are from space artist Mark A. Garlick. Visit him on the web at www.space-art.co.uk and www.markgarlick.com

Wild Stars- Prelude

Travel yesterday was not without problems. After boarding my plane in Detroit, we were informed that the fuel pump that starts the engines was leaking and not working. 45 minutes later, after a 'repair' done on the spot, the plane was pushed out to the tarmac, and nothing...
No engines, no noise, no air conditioning.

Back to the gate, more repairs attempted. Finally the pilot says they're going to 'jump start' !! the engines and then we'll be on our way.

Long story short, we eventually took off two hours late.

My boss, Arne Henden, connected in Detroit from Boston to go to Phoenix, so we ended up touching down in Arizona around the same time and shared the shuttle ride from Phoenix to the University of Arizona in Tucson.

Where the shuttle dropped us off was much further from my hotel than I had anticipated. I did not enjoy walking all the way across campus dragging my luggage in the dry, high altitude desert air of Tucson. After the half way point, I was taking frequent breaks in every shady spot we came across.

The hotel is very nice, and the sympathetic staff assured me I could catch a cab to the welcome reception later that evening, which I did, in spite of the fact that just about everyone else walked.

My world was made right again after settling into my room and having a bite to eat.

The welcome reception was held in the open air second story patio of one of the micro-brewery beer houses on campus. Complimentary drinks and food lubricated the discussions as everyone got to connect or re-connect in the mild night air. I got to meet several of the 'big names' and some enthusiastic grad students.







Above: David Buckley (SAAO) and Steve Howell (NOAO)
Right: front center- Joe Patterson (Columbia University), front right- John Thorstensen (Dartmouth College)

Wild Stars Day Two

You better show up wide awake for these conferences. Tuesday morning we jumped in feet first into the crazy world of AM CVn type stars. This is a rare class of stars that has been garnering more attention lately due to their extremely short orbital periods, (we're talking 10-60 minutes here), and the fact they are sources for low frequency gravitational waves.

AM CVn spectra are totally devoid of Hydrogen lines. They show a rich Helium spectrum along with processed heavy element lines. This makes them exciting to astronomers because supernovae spectra don't show hydrogen, so these stars may be supernovae progenitors. If you want to get grant support or telescope time these days, it helps if you're proposal has something to do with the sexy topics of exoplanets, supernovae or dark matter.

There are several proposed channels for the evolution of these stars. By the third paper of the morning we had heard about all the possible ways these stars can be born and how they may die as helium Ia supernovae. AM CVn's are thought to form via 2-3 different "channels".

1-A detached white dwarf (DWD) system, formed through a series of Common Envelope evolutions, shrinks as a result of angular momentum losses due to Gravitational wave Radiation (GWR). Eventually, the less massive star fills its Roche radius and mass transfer commences. The system then evolves to higher periods due to redistribution of angular momentum.

...or, 2- a low mass helium donor transfers mass to a white dwarf accretor. The system passes through a minimum in period of ~ 10 minutes. The period increases after this minimum and mass transfer keeps falling. During this process the helium donor goes from being a non-degenerate to a degenerate star.

...or , 3- they may evolve from cataclysmic variables with evolved donors. After significant mass loss, the exposed Helium core of the donor in a CV evolves similar to #2 Helium star track.

What's truly amazing, and mind bending if you haven't had enough coffee, is the fact that we just can't find helium core white dwarfs right now. Since these may be members of binary progenitors for both supernovae and classical novae, astronomers are forced to model how these stars contribute to colossal cosmic explosions using math, physics and imagination. Then they have to figure out a way to explain it to other astronomers and survive the question and answer session after they present their talk.

Kudos to graduate student Ken Shen for his paper on Unstable Helium Shell Burning on Accreting White Dwarfs. This young man knows his stuff and can give a presentation. I predict good things for his future.

After lunch we started hearing talks closer to my areas of interest. I already mentioned the awesome 3D Gas Dynamic Modeling movies shown in the talk given by D.V. Bisikalo. Then Don Hoard talked about Dusty Toads, a topic we have seen here before a few times.

SW Sex stars is another class of stars I wanted to learn more about. It seems that all eclipsing nova-like stars in the 3-4 hour period range are SW Sex stars. But eclipses are simply a line of sight effect, so they can't be considered a pre-requisite for inclusion in the SW Sex club. So Linda Schmidtobreick and her colleagues looked at a large sample of non-eclipsing stars in the 3-4 hour period range to see if they had the rest of the required characteristics for inclusion in the SW Sex category. What they found was that most of these stars are indeed SW Sex stars. Remember, the CV period gap is from 2-3 hours, so these stars may represent an important group of stars, with periods just above the gap, in a high mass transfer state which may cause the binaries to lose contact and stop accreting as they evolve through the period gap.

Boris Gaensicke has become a rock star in the CV community. It is almost unfair to have him start the final afternoon session and then expect three more people to deliver talks on essentially the same topic- 'recent results of CV population studies and the space density of classes of CVs'. I'm just glad it wasn't me, because that is exactly what happened.

Boris hit it out of the park with his presentation. He presented results from the new CVs discovered by SDSS. The main points of his talk are that we've now determined where the missing 80 minute period spike stars predicted by CV theory are. Paula Szkody and SDSS have found them down to around 19th magnitude. They do exist, and they are significantly different from the rest of the CV population.

The spectra of the majority of these stars reveal slowly accreting, white dwarf dominated, WZ Sge-like stars. But, we have still not found the "period bouncers"; those stars with periods less than 80 minutes that are near the predicted 65 minute limit where these CVs will begin to evolve back to longer orbital periods. Boris says they will be found if we just dig another couple magnitudes deeper, and I believe him.

Wild Stars Pictorial Review

Steve Howell, head cowboy, and coiner of the famous acronym TOADs (tremendous outburst amplitude dwarf novae) welcomes everyone to the conference and explains where the bathrooms are.

His other main task for this conference seems to be getting everyone who wants one, a receipt for their expense reports. Poor Steve.

His poster on magnetic CVs has an awesome visualization. I'll try to get permission to reproduce it here. It is way cool....err, I mean hot.




Chritsian Knigge opens the paper session by reviewing what we know about the secondaries in CVs and their role in the evolution of these systems.

Check out the visualization of that bloated, star spotted, crazy looking secondary. Wild stars indeed!

More interesting is the fact that CV donor stars are larger and cooler than individual main sequence stars of equal mass. Observing these secondary properties may tell us a lot about the evolutionary track of these systems. Fascinating stuff presented very well. Two Simothumbs up for this one.

What's that? You say you don't understand magnetic braking? Don't worry, I'm in a room full of PhDs who will talk about it all day, but they don't understand it either!


Hands down winner of the animated visualizations for the conference thus far definitely goes to D.V. Bisikalo from the Russian Academy of Sciences, Moscow. His illustrations of accretion and the outflow of material into the envelope around the binary were fascinating to watch and quite detailed. The parameters and science used to achieve these results may be unrealistic, but the animations were glorious! Not only that, but watching the accretion overflow, I had an 'aha moment' for something I've been working on regarding Z Cam outbursts.




For those of you who remember my blog on 'Dusty Toads', here is one of the authors, Don Hoard, talking about surprising dusty environments around cataclysmic variables. They went hunting for information about the red secondary star of WZ Sge with the Spitzer Space Telescope and found so much dust they couldn't observe the secondary! A surprising result that may lead to, well, who knows?

I'll be interviewing Steve and Don about their dusty toads and where this new result may lead CV research.

On a personal note: it has been a lot of fun meeting the people and associating the names with the faces. I met several Japanese observers and important contributors to CVnet-Akira Arai, Hiroshima University, Izumi Hachisu, University of Tokyo, Akira Imada, Kagoshima University, Daisaku Nogami, Kwasan Observatory, Kyoto University. I also got to meet and talk with astronomers using AAVSO data for their papers here at this conference or elsewhere: Brad Schaefer, Louisiana State University, Christian Knigge, University of Southampton.

AAVSO was well represented with Arne Henden giving a poster presentation with hundreds of AAVSO light curves and Paula Szkody talking about pulsating white dwarfs in SDSS CVs.

Boris Gaensicke, who I met for the first time in Cambridge, UK last spring, seems to have his fingers in so many pies here it is quite remarkable. He is listed as a co-author or principle investigator on at least 40% (UNSCIENTIFIC SIMO-ESTIMATE) of the papers being presented.

And on a personal basis, I had the pleasure of meeting Kurtis Williams, of Professor Astronomy's Astronomy Blog .
He has been kind enough to support the AAVSO Writers Bureau with his blogs and is an all around nice guy who it is my pleasure to have met finally.

It's been a good time so far. More later.

Wild Stars- Day Three

For those of you who came in late on this one, I am in Tucson, Arizona, attending a conference on cataclysmic variables called Wild Stars in the Old West. It has been ten years since the last American CV conference, and five years since the last international CV conference. I wouldn't have missed this for the world. CVs are my thing.


Not only that, but this conference's attendees list is a literal who's who of the CV research world. I am having a ball. Writing all about it has been a pleasure too, even if I have to stay up well past midnight local time to get it done.

Day three featured talks on Magnetic CVs, Accretion Disks and Symbiotic Variables.

The morning session began with Kent Honeycutt showing results of time-resolved spectroscopy of He I and H-alpha lines in BZ Cam. He showed some slick animations that illustrate wind events in the system. Axel Schwope's paper investigated the physics of hard x-ray emitting shocks in Polars using the XMM-Newton satellite. I also learned some new acronyms in common use in Polar research. LARPs, HARPs and PREPs. Low accretion rate polars, high accretion rate polars, and pre-polars respectively. You really have to keep up with the acronyms around here or you won't have a clue what they are talking about!

David Buckley gave an animated, and at times humorous talk on the Southern African Large Telescope (SALT) and its fantastic suite of instruments, capable of doing high signal to noise time resolved photometry, spectroscopy and polarimetry. He also gave some honest insight into the pressures and demands of launching a sophisticated instrument program like this and its affects on the stressed out astronomers.

Polars were the prevailing topic in the morning sessions. Fred Walter showed results of nearly continuous coverage of EF Eri with the SMARTS telescopes since 2003, and an overview of the long term behavior of the system since the 1970's and 80's. Paul Mason explained how highly magnetic polars like AT UMa emit at radio wavelengths. It turns out that accretion disks may actually squash radio emission, so the lack of an accretion disk in polars allows radio waves to be detected from these CVs outside of an outburst. Domitilla de Martino summarized results form XMM-Newton observations of Intermediate Polars (IPs). She also pointed out some of the similarities between IPs and Polars.

After lunch we delved into the hearts of magnetic CVs and accretion disks. The first talk described an exceptionally long Chandra observation of EX Hydra and all the science they were able to glean from such a high signal to noise X-ray spectrum. They were able to explore the emission lines formed in the accretion column as well as first time ever views of a broad component that represents photo-ionization of the accreting column.

I think its amazing how these guys can glean so much science out of 140 hours of time on a space telescope. They were also able to tell the size of the accretion spot and the height of the shock area. All this from an x-ray spectrum!

Chris Mauche reported on a multi-wavelength campaign on the amazing star AE Aquarii. The combined radio, optical, UV, x-ray and gamma-ray results were presented eloquently. Chris is an excellent speaker and a brilliant astronomer. Knox Long described in detail his observations of the structure and source of winds in cataclysmic variables. The end result being, our current understanding is just about right.


The talk that generated the most interest and discussion day three was Graham Wynn's talk on RS Ophiuchi and CVs with massive white dwarfs, giant secondaries and massive accretion disks. He had six movies running at once, a conference record, demonstrating the fact that no matter what the rate of accretion, a disk was formed from the secondary wind. He then suggested some unique solutions to dramatic outbursts RS Oph and objects like it.

Big red secondaries and binaries with long periods remained the objects of interest for the last two talks on symbiotic variables. These interacting binaries present their own challenges to astronomers trying to understand binary evolution.


After the sessions were over we all piled into four buses and rode to dinner at a western steak house in Tucson. It was a fitting scene for a conference about wild stars in the old west. 13 hours after heading to the observatory I found myself walking back to the hotel in the crisp dry evening desert air. I woke up the next day with vague recollections of a dream about Willie Nelson (or was that Steve Howell?) and supernovae.

Wild Stars Pictorial Review Continued

This is Koji Mukai and Domitilla de Martino. Koji is one of the leading experts on intermediate polars in the whole world. Domitilla is also involved in IP research and presented a paper on results from the space X-ray observatory XMM Newton. For those of you who thought astronomers were geeks with no looks or personality, these two will shatter your ill-conceived notions in a matter of seconds.

Axel Schwope is another brilliant and entertaining astronomer using XMM Newton and other telescopes to examine some of the brightest polars in x-ray, optical spectroscopy and optical cyclotron spectroscopy.

I wonder what he tells people at parties when they ask him what he does?


You think astronomers don't have a sense of humor? You might be wrong. David Buckley shared this political cartoon from South Africa starring the SALT telescope. He was also brave enough to share this photo of himself in 'trying to get to first light' mode.

He really looks like Saddaam Hussein out of the foxhole.





Below, a rare sighting of Boris Gaensicke (left with pony-tail) actually sitting still!
He was chair of the session on this day. Here he is seen enjoying the talk from David Buckley (right), who looks much better with a shave and a bath.


Nerd Herd- here is a typical coffee break at the conference. The weather has been absolutely fabulous. Everyone enjoyed the outdoor courtyard gatherings in between papers.

Christpher Tout sharing ideas and sunshine during the break. Later, I pulled him aside to do an interview for a podcast. He was great.


Paula Szkody and friend discussing the merits of the poster in front of them. Paula also graced us with an interview for the podcast.

We talked about SDSS results and what is in her future. In a word- LSST. For those of you who are acronym challenged, that is the Large Synoptic Survey Telescope.





More polar humor. EF Eri is known mostly for the fact that it doesn't do anything most of the time. It's not accreting and we can examine the secondary star because there is no accretion light contribution in the way.

A little Star Trek humor lightens the mood.

Astronomy nerds can be fun...

Wild Stars- Looking Back

One of the best things about going to these meetings is you learn what astronomers are really looking at, researching, observing with space telescopes and how much the AAVSO is actually appreciated by the professional community.

There were AAVSO light curves in at least one out of three papers given here every day this week. Astronomers using sophisticated space telescopes and 8 meter telescopes on the ground are using AAVSO light curves of novae, recurrent novae, dwarf novae, symbiotic variables and all manner of CVs in their research.

The paper Brad Schaefer gave on recurrent novae was a virtual smorgasboard of historical AAVSO data. His research would be impossible without us, and he says so enthusiastically in the interview I did with him for the podcast. He has a list of five RN that he predicts will blow up in the next five to ten years, and T Pyx is NOT one of them. He is quite sure it will be the monitoring of these stars by amateurs that will result in the timely notification needed to alert astronomers to the rare opportunities these events present.

The professional CV community has given me a lot of one on one ideas to bring to amateurs about what it is they need and want, and how we can contribute in a meaningful way to their research. Steve Howell, Boris Gaensicke and Paula Szkody, talked with me one on one about what amateurs can do to help and what they have already contributed to the cause.

Personally, I learned a lot at this meeting. I was pretty fuzzy on the current hypothesis on pre-CV evolution, and the difference between symbiotic variables and common envelope binaries. I have a much clearer picture of why population studies are so important to CV
research. I was talking with Arne after the last session and telling him how by Thursday I was even beginning to understand x-ray light curves and recognizing emission, absorption, H alpha and beta lines in optical spectrum. I'm beginning to wonder how many spousal permission units it will cost me to buy a spectrograph!

I have a pretty current understanding now of what the core issues are that CV astronomers are trying to untangle, and what its gonna take to get them there. The exciting thing is WE CAN HELP. There is still a lot for amateurs to do with dwarf novae, symbiotics, recurrent novae (we practically own this field!), novae (lots of interest in novae!), and magnetic variables.

Even better, this was perfect timing, because we will probably launch the new CV Section this year after the spring meeting (if not sooner). I was able to rub elbows with all the top researchers in the field and let them know what we have planned and they are enthusiastic about the role we can play.

I got to spend some time with some of the key players from Japan who contribute to CVnet; and as usual, I was impressed with the way professional astronomers like Joe Patterson, John Thorstensen and Boris Gaensicke are willing to share the love of VSO and advise amateurs on how they can contribute to science.

It was awesome. And now my batteries and enthusiasm are fully charged. I'm glad to be home so I can get back to observing some of these wild stars myself!

Wild Stars- Day Four

Now that it is done, I am feeling a mix of relief and sadness. Relief- because four days of intensive research results presented session after session is like cramming a semester's worth of astronomy into your brain in four days. Sadness- because I could take maybe one more day, just to finish meeting and talking with some of the people I really wanted to talk to one on one. There just wasn't enough time. I think this was the most worthwhile, well-organized and relevant conference I have ever attended.

I'm not knocking any of the organizers of variable star meetings I've been to in the past, but this was all about CVs, all the rock stars of CV research were here, and I had back stage passes. It was frakkin' cool. The last day of the conference was all about things I am interested in- TOADs, Recurrent Novae and Classical Novae.

The talks of the day were also book-ended by two impressive astronomers from Japan's VSNET, Daisaku Nogami and Izumi Hachisu.

First thing in the morning session Daisaku Nogami presented impressive results of the superoutburst evolution of three very interesting CVs- WZ Sge, GW Lib and V455 And. These are three of the most significant outbursts of dwarf novae in the last couple years and Nogami had it all nailed down. The following talks on GW Lib and V455 And were almost redundant after the impressive amount of optical photometric and spectroscopic information Daisaku presented first thing in the morning.

The last talk of the morning session was about the source of negative superhumps, by Michele Montgomery. I had the pleasure of meeting her and talking for an hour or so Tuesday night, at the NOAO reception. She is an excellent presenter and had a great talk, chock full of teasers about her upcoming publication.

You just have to be intrigued by a woman who can teach you all about the minimum accretion disk tilt needed to generate negative superhumps in light curves, the parameters that affect negative superhump signal strength, and the location in the disk that contributes to this phenomena. That is sexy stuff!

Not to dismiss the other presenters who talked about classical novae and recurrent novae after lunch, but Brad Schaefer stole the show with his talk. Brad does not need a microphone to be heard in a room of 200 people. He is enthusiastic and knowledgeable about his topic, recurrent novae, and he knows how to work a room.

Some of the most exciting news from Brad were previously undiscovered eruptions of RN in past years. He and his graduate assistant relentlessly scoured all the archival data in the world to find plates and observations of recurrent novae outbursts. They found three eruptions of U Sco (1917, 1945, 1969) RS Oph in 1907, V2487 Oph in 1900 and CI Aql in 1941.

From these intensive searches, and modeling the results, Brad is able to make some bold predictions about the timing of future eruptions. In the next decade he predicts no less than five recurrent novae eruptions- V2487 Oph, V394 CrA, V745 Sco V3890 Sgr and the one he is most excited about U Sco. U Sco is predicted to erupt in 2009.3, which is RIGHT NOW!
After lunch we were shown amazing results of x-ray observations of recurrent novae and novae. There is a lot of interest in novae eruptions by professionals, more than I realized. What's more, they are making x-ray observations of these objects months and years after the initial outburst in an attempt to observe just when the accretion disk reforms and accretion begins again and what happens at this phase of the outburst.

From this I realized, amateurs need to follow many of these objects for much longer than we typically do as best we can. The AAVSO light curves sort of peter out after six months or so, and rarely is there much follow-up when a star reappears from solar conjunction. It's like we've all forgotten about them and moved on to the next big thing. Unfortunately, this is about the time they become really interesting to professionals, and from what I was seeing there may be some very interesting observational phenomena we are totally missing, like sudden rebrightenings of the systems or flickering. Amateur CV sleuths take note!One of the final talks of the conference was from Izumi Hachisu. He presented the methodology and results of his search for a relationship between the t3 time of decay (the 3 magnitude decay time from optical maximum) and the turn-on and turn-off times of supersoft x-ray emission. He presented detailed light curve analysis of classical novae detected in x-rays, and proposed best fit models that reproduce the optical and supersoft x-ray observations. If all that sounds impressive, you're right, it was. The fact that most of the data was collected with relatively small telescopes makes it that much more impressive.

That's about all I can dig out of my CV overloaded memory and notes at this point. I'm going to let this all digest for a day or two and write a summary review. I know I am looking forward to the next CV conference, which is planned for 2010 in Kyoto, Japan!

Simo Slacker!

As promised, the interviews I did with five astronomers at the Wild Stars in the Old West II conference are now coming online, thanks to my friends at Slacker Astronomy, Michael Koppelman and Doug Welch. The first part of the series is now available.

The first interview in this episode is with Brad Schaefer from LSU. Brad is very excited about the results of his research on recurrent novae. These cataclysmic variables grab our attention and spark our imaginations because of the incredible amplitude of their outbursts, typically 8-12 magnitudes, and the rarity of these spectacular events. Many of these outbursts are once-in-a-lifetime events. Like an apparition of Halley's comet, witnessing an outburst of T CrB twice in a lifetime would be a matter of uncommon luck, longevity or both.

Artist's depiction of the recurrent nova, RS Ophiuchi, in outburst.
(Illustration Credit & Copyright: David A. Hardy & PPARC; Astronomy Picture of the Day 2006 July 26).

I've written about recurrent novae before. The cause of a nova eruption is a thermonuclear reaction on the surface of the white dwarf. After years of mass exchange between the binary pair, temperature and pressure at the surface of the white dwarf build sufficiently to cause the layer of accreted material to explode like a hydrogen bomb. This bomb, however, can have the mass of 30 Earths! Once the temperature becomes high enough, this layer begins to expand. Minutes into the process the shell can be radiating at 100,000 solar luminosities and expanding outwards at 3000 km/s. Eventually the shell envelopes the entire binary and the orbital motion of the pair acts like a propeller to whip things up. After 1000 days or so the envelope expands to the point it can be seen as nebulosity surrounding the pair. Over hundreds of years the shell dissipates into the interstellar medium.

Most novae probably erupt more than once in their lifetime, with the mass of the white dwarf determining the amount of accreted material that needs to accumulate before triggering on outburst. Systems with a white dwarf of 0.6 solar masses might take as long as 5 million years between eruptions. A system with a 1.3 solar mass white dwarf might only take 30,000 years between eruptions. Systems with recurrence times of 100 years or less probably have very massive white dwarf primaries.

With so few known examples and the rarity of these events it is no wonder that recurrent novae eruptions are extremely interesting to astronomers. Monitoring these stars for outbursts over decades of relative inactivity is still one of the extremely valuable contributions visual observers can provide to science.

The second interview is with Steve Howell, of NOAO. Steve and I talked about the advances that have been made in CV research since the last Wild Stars meeting ten years ago. I also asked him where he thinks new research is heading.

But, I have to admit, I really wanted to talk to him about his awesome image of magnetic accretion. I saw this in his poster presentation at the meeting and was blown away by the whole concept of the complicated, beautiful way mass is accreted in polars.

Image credit: S. Howell / P. Marenfeld/NOAO

I hope you enjoy the podcast. My sincere thanks to Michael, Doug, Brad and Steve for making these Simo-interviews possible.

Simostronomy on Slacker Astronomy pt. 2

It took us a while, but the second part of my discussion with Michael and Doug on Slacker Astronomy is now online.

You can download the podcast here.

In this episode, we talk about where research in cataclysmic variables is going, what astronomers are expecting to find and some of the surprises we've found along the way. I was fortunate to get three astronomers from the Wild Stars in the Old West II conference, Christopher Tout, Paula Szkody and Boris Gaensicke, to give up their coffee break time to let me interview them for this show.

My thanks to Michael and Doug for having me on the show, and to Paula, Christopher and Boris for giving me something interesting to contribute.

Boris Gaensicke / Christopher Tout /Paula Szkody

So check it out:

Podcast: Simo-Slacker Interviews Pt. II