Blogs / bkloppenborg's blog / What does it mean? Part 2
What does it mean? Part 2
Dr. Bob and I are taking turns explaining the implications of the recent Nature paper. In the first post, Dr. Bob discussed two very important questions: "How big?" and How massive?" In this post, I'm going to cover another big-picture topic: the orientation of the disk.
I'll start with what we thought happened. Most of the literature drew the disk as something that more-or-less bisected the F-star, following Kemp's 1986 drawing (note, a similar drawing was also published in the 1985 epsilon Aurigae conference proceedings):
We now know that this picture was very, very close to being correct. Considering that the parameters in the paper (see pg. L13 of Kemp's work above) all scale to the radius of the F-star, Kemp et. al. did a good job of estimating the parameters for the disk just from polarimetric data and modelling! The only large change is the point of first contact which was assumed to be in the northern hemisphere. Instead, it is clearly in the southern hemisphere.
A big question, and a good team project, might be to investigate whether or not Kemp's polarization data is consistent with the current findings. If it isn't, this could mean the disk or orbit has precessed significantly in the 27 year since the last eclipse! (if you are interested in doing this, please contact me).
For those of you who do not have access to Nature, I have extracted a few parameters in the table below (these are rounded, the parameters in the paper are more precise):
| Disk Radius* | 3.8 AU |
| Disk Thickness** | 0.76 AU |
| Central Opening (?) | 0.5 AU? |
| Disk Inclination** | 85 +/- 5 or 95 +/- 5 degrees |
| Disk Tilt** | < 20 degrees |
| Orbital Inclination (?) | 88 +/- 2 |
* From "Infrared images of the transiting disk in the ε Aurigae system" by Kloppenborg et. al. 2010 April, Nature
** From "Taming the Invisible Monster: System Parameter Constraints for Epsilon Aurigae from the Far-Ultraviolet to the Mid-Infrared" by Hoard et. al. 2010 ApJ.
(?) Unknown parameter, this is a best-guess.
Try out these values in the new light curve generator and see how close you can get the light curve to match with previously observed values! Do the parameters work? If not, what do you think is wrong? Do we have the entire picture or is there more to discover?
Hi Brian, Thanks for the light curve simulator - certainly an improvement on my simple efforts here. Would it be possible tooverlay the last eclipse light curve on the animation so we have something to compare with. (A facility to zoom in just on the eclipse would be nice too) A couple of questions on the parameters Disc inclination:Should that be >85 deg (ie 85-95 deg) ? Disc thickness: Is that the projected thickness? ie doesit include the effect of any disc inclination? Robin
Disk Inclination: I've changed how Ihave it stated above so it allows for mirror symmetry and increased the range. Disk thickness: That's the maximum projected thickness. Keep in mind that the paper reports only on a model extrapolated from the leading edge of the disk and this doesn't account for any flaring (that is likely to be present) in the middle/second portion of the disk. Thanks for asking! Brian
First of all, Hello... Do the spin axis, and equatorial tilt of the F star have any correlation with the Disk's rotational trajectory? e.i. as the Disk orbits, the F star's poles bob side-to-side (according to pulsations seen from Earth) depending on the Disk's location relative to the F star. Or, do both the Disk and Fstar, have their north poles tilted the same degree constantly? Also, exotic theories about exoplanets and gas giants, have these been ruled out after determining an approximation of the disks density?
Nico! Good to hear from you. At the moment, we still don't know the orientation of the F-star's pole. If this is a typical binary system, we can expect the rotational axis of the F-star is aligned or closely aligned with the orbit of the B5V star (the orbital tilt). Keep in mind that the disk itself is tilted with respect to it's own orbit both in the plane of the sky and out of the plane of the sky. As for the theories about exoplanets, nothing for sure yet. If the disk is a debris disk with particle sizes >10 micrometers, then there is a possibility that there could be even larger objects. No direct observational evidence though, just supposition.
Hi! I wonder if the results rule out the theory that the disk has a "Cassini-divison" like gap. CS Heinz
Heinz, Good question. Either Dr. Bob or I will cover this in our next post.
I think this wil be the solution. In the near futur we will stop diskussing about a disk. But we wil start to speak about rings!! Minimal there must be two of them. An outer ring and an inner ring. The outer ring makes the main eclipse of the F-star and the inner ring hides the B-star. The inner ring must be smaller then the radius of the F-star therefore we can see e brightening in the light-Curve during the mid eclipse, and it reaches very close to the B-star. Otherwise it wouldn't be able to hide the B-star. This is my Guess. _______________ Please excuse my poor English, am not a native speaker. (If you find a spelling error, then you can keep it ;-))
Is it possible to increase the maximum value for the disk opening to 50 %? What about a simulation with 2 Rings?
fruehwf, From previous eclipses we've found the central opening, if it exists, is about 0.5 AU and from those same results, it was assumed the disk was 10 AU in extent, making 30% reasonable. I'm sure both of these could be added in, but that would require modifying the source code. Ihaven't developed in Java before and I think we have exhausted our alloted time with the developer (but I'll check on this and reply again later). We hope that we can get a team to form that can continue developing this tool so we have provided a link to the source code below the simulator. If we have any Java saavy CSmembers, that want to contribute to modifications of the simulator, please contact me via. the contact page on my profile. Cheers, Brian
Note there appears to be an error in the size of the F star in the light curve simulator (It is ~2x too large compared with the disc. It should be ~1.4AU diameter but it is more like 2.8 AU) Robin
the link to the simulator source code reports "page not found"
I'll ask why the source code isn't posted. Thanks for catching the broken link, Robin. Brian