My dumb ideas for the mystery of epsilon Aurigae,

Nice artwork ! This is fun, so just my 2cent as an amateur: I think (A) is consistent with the currently predominant hypothesis for eps Aur: a giant cold disk orbiting the primary star. (B) would be something like a giant sunspot that is rotated in and out of view as seen from Earth? I think this is not consistent with the long period and the shape of the light curve with relatively steep flanks. And probably you would see radical changes in the spectrum of the star, but that doesn't seem to be the case. (C) would be a single, massive object like a planet, maybe? I think this is not consistent with the fraction of the eclipse length to the period of the eclipses. That object would occupy roughly 7 % of the orbit's circumference! It would be incredibly massive and we would know that from Doppler shift measuremnts, right??? And we should probably be able to see it outside of eclipses because it would be rather hot, wouldn't it? So all we know for sure is that less photons reach us from eps Aur for so and so long every 27.1 years. Either eps Aur emitts less photons then or something happens to the lost photons in between. There are only so many things that can happen to a photon, I guess: absorption, reflection, dispersion, or maybe gravitational lensing. Anything else?

Hi Bryan, Icommend you for giving it a try. This star system is truly mysterious and noone knows for sure exactly what it is. I'll try commenting on your ideas. First, remember the secondary has been determined to have a mass of around 14 times our Sun and a diameter on the order of 1,500 times the diameter of our Sun. Your ideas in reverse order: Case C. An Asteroid Well an asteroid with a diameter of 1500 times our Sun's diameter and 14 times the mass, would not be an asteroid. Anything approaching that size would most likely collapse to a neutron star or black hole. Since it is not a star (and if it were a star it would be blazing brilliantly, but is not seen) it would have to be some unique hitherto unknown object. And yes, people have suggested the eclipsing body may be a black hole or harbor a black hole. Because the characteristics of a black hole are X-ray emissions and there are none, a black hole is unlikely. There are other reasons too. Case B. A Giant Star Spot There is a class of stars known as RS CVn stars that are known to have giant sun spots or star spots and are variable stars. They tend to have periods in days not years. Also it might be hard to maintain the spot that long. There is also the problem of the system's mass. Case A. A Large Nebula The eclipsing object may indeed be some type of nebula, but not the normal kind. It appears to be a large (extremely) rotating cloud of gas and dust. Normal nebula are much larger and much less dense. Whatever this is it is considerably more dense than just a cloud of gas (e.g., a nebula). Some thoughts: Because of the mid-eclipse brightening, the theory goes that there must be a large hole in the middle of the eclipsing body. What makes the hole? Perhaps a pair of giant planets orbiting and sweeping out the area, or a pair of B stars. Because of some brightening bumps just before and just after the mid-eclipse, there is also a theory that there is a ring opening around the central opening. Kind of like abulls-eye. There is also a strange out-of-eclipse variation that defies explanation and study. WIth some luck and hard work we may get a better idea just what this mysterious system is all about. Keep you ideas coming. Jeff

That's pretty cool, Bryan. Maybe we need to make a video of post-it notes instead of Lite Brite diagrams. :)

Hey, I'm not threatened by dumb ideas! So here's one I thought of: Instead of some kind of hole in the center of the secondary being the cause of the brightening, could it be the mass of the secondary creating a gravity lens to focus light from the primary around the secondary and onto us? Probably not enough mass, though, huh? How can a complete lay-person like me who happens to own a small telescope help out with a project like this? Any ideas on getting kids excited?

Hi Jeff > There is also a strange out-of-eclipse variation that defies explanation and study. Are there other theories than the out-of-eclipse variation beingSR-like pulsations of the F giant ? > Because of the mid-eclipse brightening, the theory goes that there must be a large > hole in the middle of the eclipsing body.What makes the hole?Perhaps a pair of > giant planets orbiting and sweeping out the area, or a pair of B stars. > Because of some brightening bumps just before and just after the mid-eclipse, there >is also a theory that there is a ring opening around the central opening. Kind of like >abulls-eye. On the "The 'Star' of Our Project" page: http://www.citizensky.org/content/star-our-projecta plot with the light curves of the up to now observed eclipses is shown: http://www.citizensky.org/sites/default/files/images/changing-eclipses_big.gif WhenI look at the different light curves in the plots, I can imagine to see at least semi- or quasi-periodic waves. Couldn't thein-totality variations alsomainly or totallybedue toSR-like pulsations of the F giant ? What kind of measurements would it need to prove the SR-like pulsations and the more transparent hole/ring in the middle of the disc theories ? CS Wolfgang

As I recall during the last eclipse there was discussion of a gravity lens, but through math beyond me it was determined not to be a very likely case. Jeff

Hi Wolfgang, The out-of-eclipse variations do not seem to be a pulsation of the F star. Perhaps Dr. Bob can explain in detail. The period of these variations has defied explanation and determination. Season periods can be determined using Fourier transforms to produce time domain plots, using Peranso software, but they change unpredictably from season to season. The same with the amplitudes. One cannot predict what the amplitudes will be. We simply do not know the cause of the variations. These variations cause problems for determining the contact points and any interpretation of variations during totality. One exciting point is the mid-eclipse should occur when we can get significant data this time. The mid-eclipse brightening is greater than the out-of-eclipse variations so it is real. It should also be of sufficient amplitude to be seen and measured visually. Exciting times to come. On top of that is the sodium D lines show a presence some 1000 times stronger than the Sun and then there is the mysterious hydrogen alpha line horn dance. A very interesting system. Jeff

Another dumb idea ... Let's assume current theory is correct. Could we then hope to detect "micro-eclipses" or changes in the spectrum from material that is leading and trailing the secondary in its orbit, e.g. near the L4 and L5 Lagrange points? That would be 4.5 years before and after the middle of totality, right? Have there been efforts in this direction? Clear Skies Heinz

Hi Heinz, If you go to Simbad: http://simbad.u-strasbg.fr/ click on either basic search or by identifier in the Queries section, and type in eps Aur, you will get the basic information page on this exciting star. Note near the middle of the page is a line called "References", which indicates that there are some 412 papers that reference epsilon Aurigae. Clicking on "display" will give you links to each paper. Most of those papers just contain a mention of epsilon Aurigae; they really don't discuss the star itself. You can find some very interesting theories there, as well as through a Google search. When Dr. Bob's talk from the Chicago workshop is posted, you'll see a summary of some of the possibilities. Regarding L4/L5: Jeff has been following epsilon Aurigae outside of eclipse (about the only person to do so!) and hasn't seen any evidence of another dimming. With the infrared satellites, it is possible to look for the secondary eclipse of the cool dust cloud, but that might take too much monitoring time from some very expensive systems! However, like many eclipsing systems, I think you can learn a lot by obtaining the entire light curve, not just the primary eclipse section - now, if we can just convince the Citizen Sky participants to continue monitoring epsilon Aurigae for the next 27 years... Arne

HiHeinz, that is an interesting idea. There are spectralfeatureswhich as far as we know are not connected with variability in the primary and are uniquely seen during the eclipse. This means theyare likely to be due to the eclipsing body. I am following some of them during this eclipse (The shell spectrum of narrow metal lines and the neutral Potassium KI 7699 line) you can see my latest results here http://www.threehillsobservatory.co.uk/astro/spectra_40.htm These have not been covered at such frequent intervals in previous eclipses so I am hoping the dataI produce will cast more light on the detail of the eclipsing object structure, particularly at the edges and during the central brightening which Wolfgang was asking about. Data outside eclipse is even sparser though so this could be a long term project! Robin

> EDIT: Oh and one more thing, HAVEYOUGUYSCONSIDERED the fact that an object as tiny as the moon can eclipse our huge sun, so, WHATIFthis object(nebula or whatever you want to call it) is still undetectable but way closer to the earth and causing this sort of eclipse from our point of view? Our eclipses onlylast afew minutes though. (The analogy is not quite correct as the moon orbits the earth not the sun but you get the idea) The object eclipsing Eps Aur does so for 2 years during its 27 year orbit so it's size has to be a large fraction of thediameter of the orbit.Also the larger the orbitthefurther the secondary would have to go in 27 years and so it would have to have amuch higherorbital velocity. This would then need a much more massive primary to keep Newton happy. The velocity of the primaryhas been measured spectroscopically and with this data we can put constraints on the masses and orbits of the components of the system. Any proposed model has to be consistent with these (and all the other) observations Cheers Robin

Here are a couple of papers that may give you some ideas on how the current models have been derived. There are additional references on the Campaign web site. Check:

http://www.hposoft.com/EAur09/EAUR%20pdfs/Interpretations/1990%20Interp.PDF

and

http://www.hposoft.com/EAur09/EAUR%20pdfs/Interpretations/1991%20Interp.PDF Jeff Hopkins Phoenix Observatory

Phoenix, Arizona USA phxjeff@hpsooft.com

Hi Jeff et al, Iwant to briefly respond to the statement that eps Aur has "a strange out-of-eclipse variation that defies explanation and study." This is just not the case. One thing that Iexpect everyone will agree on is that the primary is a low surface gravity object - this is true for both it being a very luminous F supergiant or a lower-mass but bloated "AGB star". When the atmosphere of a star is tied weakly enough to the star and there are perturbing factors, the resulting pulsation/variation is not periodic. Such a star typically does have a timescale associated with it - roughly 100 days, say - but it will not be regular like a Cepheid variable. Stars with this kind of sloppy variation are very, very common - familiar bright supergiants like Antares and Betelgeuse are two (cooler) examples. Such stars are inconvenient in the sense that their brightness variations are not easily predicted into the future, but they are not mysterious in any deep way. Ihave yet to hear any compelling argument that inidcates why the in-eclipse variations can't be due to the F supergiant's variations (as opposed to some feature of the secondary). Cheers, Doug

Hi Doug, Well that is an interesting theory. You might want to check the two papers I referenced below (in another response). While spectroscopy has shown variations, as far as I know there has been no correlation between the spectroscopic variations and magnitude variations. Also, the variations seem to follow closely in all bands. Between Louis Boyd's UBV data and mine we have a complete record of the variations between the last eclipse and now. Several people have offered suggestions, but as far as I know none have proved the answer. Some other points. Antares and Betelgeuse are very different from the star in the epsilon Aurigae system. While the masses are similar the sizes a nowhere close. Epsilon Aurigae is around 150 solar diameters whereas Antares and Betelgeuse are 800 to 1000 times the diameter of the Sun. Those stars are very diferent and I do not think the analogy is a good one.

Jeff

Hopkins Phoenix Observatory

phoenix,Arizona USA

phxjeff@hposoft.com

hi Jeff, Wolfgang, Is the Caroll et al interpretation of the out of eclipse variations in brightness and colour as being due to pulsation no longer considere valid then? http://adsabs.harvard.edu/abs/1991ApJ...367..278C particularly fig 2 Cheers Robin

Hey, Cyberpilot. You don't need a telescope at all to get involved. Download the 10 Star Tutorial and take it outside to make an observation. That will get you started. As for kids, we are planning on creating some Science Olympiad materials in the next couple of months. If you have any ideas for things we can do, please post them to the education and public outreach forum!

Hi all!Please forget about the L4 & L5 Lagrange points leading & trailing the secondary by 60 degrees from my previous message...that's non sense :-). The 60 deg only apply to systems where the mass of the primary is much greater than that of the secondary, so that the barycenter is very close to the primary, AFAIK. This is sooo not true for Eps Aur . If anything, there could be stuff trailing / leading the secondary ca 90 deg in it's orbit, but I think I've read somewhere that there are no stable orbits around the L4/L5 points unless the mass of the primary is considerably greater than that of the secondary...CSHeinz

Robin,Dr. Stencel and I used the Palomar Testbed interferometer in 2007 and 2008 in an attempt to correlate the changes in brightness with pulsation. Our paper (http://adsabs.harvard.edu/abs/2008ApJ...689L.137S) did not find any correlation between the two within the error bars. There are variations, but they appear to be uncorrelated with the light curve.Brian

Cyberpiolt,You are correct that the masses are probably too small for any significant gravitational lensing effects, but there are other similar phenomenon that could explain what we are seeing.At present, mid-eclipse occurs when Eps is above the horizon during the daytime. When it is finally observable, Eps shows up just before sunrise. This means that when it is observed, there is a lot of atmosphere in the way. If the photometric corrections are not applied correctly, it could result in the star appearing brighter than it actually is. It is unlikely that this is the case because the mid-eclipse brightening has been observed by amateurs and professionals alike.The second possibility is a form of atmospheric lensing. This model was once applied to Eps, but given recent evidence (the re-reduction of SPITZER data showing a 600 K source), debunks it. Let's create another star system composed of an F-supergiant and a small, hot companion. If things are properly aligned, when the companion goes behind the F-star, the extended atmosphere of the F-star could, theoretically, shine brighter in the observer's direction due to the higher-energy photons bombarding the atmosphere and re-radiating in our direction. Dr. Bob mentioned this effect during his talk.Good thinking!Brian

Bryan,Keep those ideas coming. There has been a lot of work on the Eps Aur system and the present (disk) model does a good job explaining the observations, but that doesn't mean it is completely correct. We still have unanswered questions about the system. For instance, what is the cause of the out-of-eclipse light variations? It doesn't appear to be traditional radial pulsation (see below and my talk at Adler). It is quite possible that we will find something with the interferometric observations that will discredit the (disk) model which will require us to go back to the chalkboard.Even if your ideas may not have an application to this particular system, they may be applicable elsewhere. Keep up the good work.Brian

I made back of the envelope calculation of GML in Eps Aur system. For distance I took d= 650 pc, for in system distance 27 AU, for secondary object 10 Solar masses and for simplicity I presumed that it is single object. For Einstein radius I got Theta(E)= 5 muas. Which means that gravitational lensing as reason for central brightening is not plausible.Angular distance between components is 40 mas. Diameter of F star is 3 mas (2 AU). Einstein radius in system s than R(E)= 0.003 AU, it is about 1000 times to small.pc= parsecmuas= micro arc secondAU= Astronomical Unitmag= magnitudeFor formulas see:http://en.wikipedia.org/wiki/Gravitational_microlensingI hope, I didn't make any mistake.

Thank you for taking my silly question seriously! I'm not an astronomer, I just like looking at stars.In my day job I write data acquisition software for somewhat technical stuff. If you give me the equation, I can turn it into C code.