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The Disk Revealed: Part 2

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Posted by bkloppenborg on May 5, 2011 - 12:14am

Back in February I posted an image showing the outline of the disk:

but after talking with Aaron about his recent visit to Tufts, I realized that I didn't actually explain what was in the image.  So I thought I would take a moment and put up a different graphic:

This one is from my 2010 Seattle AAS poster (biblographic reference is here, a copy of the poster can be downloaded from here).  Basically I took the position implied by the orbit and put the center of the reconstructed images at that position.  Then I tweaked the figure slightly (because the orbit isn't exactly right) and, through the magic of GIMP, flattened the image.  Essentially I've let the F-star slide behind the disk, revealing it's silhouette.  Since I made this graphic we obtained two additional epochs.  One in Jan 2011 and the last in Apr. 2011, about 10 days after egress started.

Now I'm going to say that the bottom figure is incorrect.  There's an obvious geometrical problem (where is mid-eclipse?  See Dr. Bob's blog posts) that tells us that the disk is actually highly asymmetric, with as much as a 2/3 reduction in length on the trailing edge from what we would expect.  Also, looking at the light curve we can also tell something about the trailing edge of the disk compared to the leading edge (what might that be?).  I'll leave it up to you all to discuss what I've seen in the data.

 

Hi Brian,We have been

Hi Brian, We have been talking about that relationship between the light curve and the disk shape in February. At that time I was curious about the 0.12 mag jump about JD 5370. Now we got a steep egress for a month, much steepperthan the ingress ! And lastwe gotanother "accident" with that knee, or evenpause, of the last days, about at mid-height. After our February exchange I had some morethinking aboutthe question and even made a tentative of simulation. My feeling was a warped disk could be the solution. Such possibly warpped disk has been described by S.Kumar. If seen edge-on the warp being seen on left and right sides it would fit well the first half of the totality. But the second half shows no symmetry at all! The knee has been accentuated by the phase of the OOE, this could explain the fact it's stronger than on 1984. But is it possible such disk would behighly assymmetrical ? Could orbitals, accretion process (viscosity), be compatible ? Inmost caseswe see in the literaturedisks are of good rotational symmetry. Next the disk chunks rotate on orbits, but what in case of warpping and/or assymmetry ?Woulda warpped "envelope" rotates ? we would not seethe same things on bothhalf of the totality and ingress/egress. But that would be depending of the interactions between the chunks of material, without interaction the warpped envelope should not change, but there are... (viscosity / Kumar ) What do you think about that ? Yours truly, Roger

I had a dream

Hi Roger, I've been doing some thinking about this topic. So much thinking in fact that I've also been dreaming about it and, amazingly, think I figured it out when I was sleeping. I don't think the disk is warped. The interferometric images thus far are in very good agreement that the thickness of the disk (at least in H-band) is very consistent with a possible increase in thickness in Feb. 2010 when there was a minimum in light. The knee is quite interesting. It happened last eclipse and, maybe, in the prior eclipse too. Also notice that the eclipse suddenly started in the shorter wavelengths (see Jeff's plot herehttp://www.hposoft.com/Plots09/UBband.JPG) and this knee is also much stronger than it is in longer wavelengths (see herehttp://www.hposoft.com/Plots09/VBand.JPG). As for the possibility of the disk being highly assymetrical I would say in this instance, yes. Consider what's happening. There's this disk out in space that wants to be in it's most stable configuration, that is with everything as close to the orbital plane as possible. Then as a particle is rotating around it is exposed to the radiation from the (very near) F-star. The radiation pressure and ionizing photons would be enough to erode the disk on the side facing the F-star. This essentially blows some of the material back towards the center of the disk AND pushes it upwards, above the plane of the disk. This essentially foreshortens the disk when it (eventually) rotates into view. "By how much?" you are probably asking. I'm not sure. All of this depends on the distance between the components which depends on the distance to the system and an accurate orbital solution. I'm working on this aspect right now... we'll see what turns up. Ok, so let's see if this idea holds up to observations. Ingress began and progressed fairly smoothly. My initial light curve of an elliptical leading edge agreed fairly well (not exactly though) to the observed data (I need to add in a wavelength dependence factor). The interferometric observations show the disk is almost perfectly uniform in height across the epochs (with the exception in Feb. 2010 when it was thicker). So far, so good. Now, what about egress? If the trailing edge were sharp we would expect a sudden rise and a sharp 4th contact edge which we see as well. So, at least to first order a disk with a smooth, ellipical leading edge, uniform thickness body, and then sharp trailing edge would work. What my model doesn't explain is the knee during egress. I think we can come up with something here that will make sense. Notice that the longer wavelength data shows essentially no egress rate change where as U, B, and V show it (with decreasing intensity). So whatever this is absorbs/scatters shorter wavelength light more efficiently. If there were some residual gas hanging out, but the bigger scatters (i.e. 10-100 um particles) had moved out of view this could support this interpretation. If this were the case though there should be some spectroscopic signatures, but I'm not aware of anything supporting this yet. Lastly the increase in light around mid-eclipse. I would like to think this some light is making it though the disk because there is slightly less material in the way although I haven't been able to convince Dr. Bob of this yet. I'll have to calculate the required change in opacity for this to be possible. For whatever it's worth, the data from SMEI appears to show a mid-eclipse brightening. The CHARA data exclude the possibility that we are seeing through a hole in the center of the disk so it's either "less stuff in the way" or "more scattering above/below the disk which results in an increase in light." I'm not sure which, if either case is right. More than likely it's both. Have a good night! Brian

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