Precursor To An Outburst?

Dwarf novae are compact binaries where one star is a sun-like star and the other member is a white dwarf, orbiting so close that it is literally stripping the outer atmosphere off its partner. The material streams over to the white dwarf but can�t slam down to the surface. Instead, it goes into orbit around the white dwarf, forming what is known as an accretion disk.

Image used with permission. Copyright Mark A. Garlick. Do not use this image without permission.

Eventually, the accretion disk builds up enough material to become unstable. The disk material falls down onto the surface of the white dwarf, causing a thermonuclear explosion that releases all kinds of energy across the electromagnetic spectrum. Optically, we see these as sudden brightenings of several magnitudes in a matter of hours. These outbursts can last from days to weeks. The system eventually simmers down into quiescence and the whole process starts over again.

The majority of these binaries have periods measured in hours. Think about that for a second. Imagine a white dwarf racing around our sun in a few hours, so close it is stripping material from the surface. Everything about these systems is extreme.

Some dwarf novae, like SS Cygni, go into outburst every couple weeks. Some may take years or decades to build up enough steam to explode into outburst. No one knows when the next outburst will occur, making these a favorite target for amateur astronomers to monitor on a nightly basis.

Occasionally, one of these cataclysmic variables will tip its hand to an upcoming outburst, by becoming active a week or more before the big event. Sometimes they will actually have a minor precursor outburst, fade to quiescence and then go into a major outburst.

Over the last couple nights, several UK observers have reported an increase in the quiescent level of V630 Cas. It has been measured peeking its head into the 15th magnitude range, slightly brighter than its normal quiescent magnitude around 16.5V.
V630 Cas is rare example of a dwarf nova with a long orbital period. Its period is measured in days, not hours.

The last recorded outburst of V630 Cas was in 1992, and lasted about three months from beginning to end. That is a long time for an outburst to last! The only other recorded outburst was in 1950. Obviously, outbursts of this system are very rare, so astronomers will be excited to catch every last detail from beginning to end of the next outburst.

This current 'activity' could be the precursor to an upcoming outburst. Observers will be paying close attention to V630 Cas in the coming weeks to make sure that a rare, and possibly long, outburst isn't missed.

I�ll let you know what happens.

Refining the Distance Scale

I scan the new astrophysics papers regularly. I almost always find something I end up downloading and reading, either right then and there, or later when I have time to concentrate. Rarely do I stumble across a paper that I can't take my eyes away from, like a great novel. One of those times when, forsaking all else, you must get to the last page.

Yesterday I found a great paper. What I was most pleased with was the fact it was written in plain English, with good grammar and organization. I understood every bit of it from start to end! That almost never happens. I couldn't stop reading it.

I don't have a PhD in astronomy or physics. I do this because I love it, period. So I often find myself part way into a paper on some astrophysical phenomena that the author is trying to explain, but no lights are going on in my brain. Either the subject is too technical for me to grasp, or the author is writing about things at a level only the top five experts in the world would ever understand. Add the poor English skills of foreign scientists writing in a second language and things can get ugly fast.

At some point I have to decide to either suck it up and plow through, hoping that a light will come on somewhere in the process, or skim through the rest to see if anything interesting develops with the plot.

Rarely do I find myself whooping it up and commenting out loud about the paper in my hands.

Okay, enough teasing. The paper is Absolute Magnitudes of Dwarf Novae: Murmurs of Period Bounce by Joe Patterson. Obviously, the subject appeals to me because dwarf novae are my special area of interest. But let me quote you some examples of why I was so impressed with this paper.

The first paragraph:
"Distance is the sine qua non of astrophysics. A distance estimate is required to convert flux to luminosity, and stellar physics is all about luminosity, not flux. Unfortunately, distances to cataclysmic variables are particularly difficult to estimate, because the dominant light source is not a star, but an accretion disk- preventing straightforward application of physical methods developed for single stars."

That will never be stated more clearly, ever. Yet it has a conversational tone to it that invites you in to take a look around. Remember, this is a scientific paper!

There are some other gems near the beginning that particularly caught my attention.

"In the 1980's available data on dwarf nova eruptions consisted of a blend of photographic and visual magnitudes. But now we have access to searchable variable star records, especially that of the AAVSO. The human eye is the ideal detector for this purpose, since it is immune to changes in technology, and used by thousands of observers. Furthermore, the central wavelengths of the eye and the commonly used Johnson V filter are similar; and both detectors are broad enough to render line emission insignificant."

He gives praise to the observations of amateur observers, the AAVSO and explains why visual observations are scientifically valuable all in one breath! I have a new hero.

I won't spoil it by giving away the end, and if you want to find out what period bouncers are you're going to have to read the paper.

I'm going to print it out on fine paper, have it bound in a nice little cover, and get Joe to autograph it for me when I see him in Tucson later this month at the CV conference, 'Wild Stars in the Old West.'

Still On The Rise

As a quick update to my blog about V630 Cas, the anticipated outburst is still under way. This is pretty unusual for the types of dwarf novae I normally follow. Three weeks ago we suspected it was going to go into outburst, and here it is still slowly rising.


Most of the time, a dwarf novae would have risen to maximum in a day or two, remained there for a few days and then began to trail off in brightness until it reached minimum after a week or so. Obviously, V630 Cas is a horse of a different color.

SimoCowboy Ready to Roll!

Next week is a conference I have been excited about attending for a long time. It's an entire week devoted to my specialty, cataclysmic variables. The list of attendees is a literal who's who of CV research.

The conference is called Wild Stars in the Old West II. This special get together doesn't come around that often. I wouldn't miss it for the world.


From the website:

"It has been ten years since the last North American Workshop on Cataclysmic Variables and nearly five years since the last international meeting on cataclysmic variables and their kin. Of particular interest since these last meetings are new results based on observational platforms such as GALEX, Spitzer, Chandra, XMM INTEGRAL and Swift/BAT, large surveys such as SDSS and planned Pan-STARRS and LSST, smaller but equally important surveys such as All Sky Automated Survey (ASAS), Catalina Sky Survey, �Pi of the Sky�, ROTSE, results from large aperture ground-based telescopes, theoretical advances, and evolutionary relationships of CVs to other binary stars."

I plan to blog about the proceedings and talks, and I'm taking a digital audio recorder to do some one on one interviews with some of the leaders in CV research. These will be turned into podcasts for Slacker Astronomy and Restless Universe.

Sunday is a travel day, and the welcome get together in Tucson. Monday, the real stuff begins. Check back for updates next week.

Yeehaw!

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.