IPB

Welcome Guest ( Log In | Register )

10 Pages V  « < 6 7 8 9 10 >  
Reply to this topicStart new topic
KIC 8462852 Observations
HSchirmer
post Feb 2 2016, 01:04 AM
Post #106


Member
***

Group: Members
Posts: 266
Joined: 24-July 15
Member No.: 7619



QUOTE (JRehling @ Feb 1 2016, 06:35 PM) *
Could one F dwarf star plausibly have so many giant planet systems?
If we are witnessing ten of them transit in a span of four years, then the star would seemingly have a huge number of other ones that we didn't happen to observe. Is this plausible?


Recent papers suggest a family of obscuring objects, perhaps the result of a large disrupted KBO or centaur, would work. Think of Shoemaker Levy 9, beads on a string...



QUOTE
http://www.centauri-dreams.org/?p=34543
a paper from Eva Bodman and Alice Quillen (University of Rochester) titled “KIC 8462852: Transit of a Large Comet Family.” http://arxiv.org/abs/1511.08821

From the paper:
    …if the comet family model is correct, there is likely a planetary companion forming sungrazers. Since the comets are still tightly clustered within each dip, a disruption event likely occurred recently within orbit, like tidal disruption by the star.

From the abstract
    To reach a transit depth of about 0.2, the comets need to be in a close group of about 30 if around 100 km in radius or in a group of about 300 if around 10 km. The total number of comets required to fit all the dips is 73 around 100 km or 731 around 10 km comets. A single comet family from a large completely disrupted progenitor explains the last roughly 60 days of the unusual KIC 8462852 light curve


Another paper
It’s Lisse et al., “IRTF/SPEX Observations of the Unusual Kepler Lightcurve System KIC8462852,” now available
http://arxiv.org/abs/1512.00121
on the arXiv site. From the abstract, this interesting bit:
    Our results are inconsistent with large amounts of static close-in obscuring material or the unusual behavior of a YSO system, but are consistent with the favored episodic models of a Gyr old stellar system favored by Boyajian et al. (2015). We speculate that KIC8462852, like the ~1.4 Gyr old F2V system η Corvi (Wyatt et al. 2005, Chen et al. 2006, Lisse et al. 2012), is undergoing a Late Heavy Bombardment, but is only in its very early stages.
Go to the top of the page
 
+Quote Post
Gerald
post Feb 2 2016, 12:01 PM
Post #107


Senior Member
****

Group: Members
Posts: 1840
Joined: 7-December 12
Member No.: 6780



A LHB-like scenario, in this case caused by a recent disruption of a planet-like body sounds good in my ears, too.
The T4-type peaks might point towards a progressed re-accretion into ringed structures (think of Arp 147), while the T3-type peaks might be more similar to the cross section of an early instable kind of spiral arm of an accreting structure near the respective Roche limit (e.g. Arp 273), or to antennae immediately after the collision of two clouds of debris.
(I've used galaxies as examples, since there is abundant material available, in contrast to interacting clouds of debris.)
A tidally disrupted or collided planet would also explain lack of a distinct IR structure, since the amount of freed gas and dust would be far less than in a Fomalhaut-like protoplanetary disc.
The T2-type might describe a cross-section of a cloud of debris with rapidly increasing density at the center (Galaxy example ESO-325 G004).
Go to the top of the page
 
+Quote Post
JRehling
post Feb 2 2016, 05:54 PM
Post #108


Senior Member
****

Group: Members
Posts: 1963
Joined: 20-April 05
Member No.: 321



QUOTE (HSchirmer @ Feb 1 2016, 06:04 PM) *
Recent papers suggest a family of obscuring objects, perhaps the result of a large disrupted KBO or centaur, would work.


That's a different hypothesis, and worth considering.

I note, however, that they are only trying to account for the last ~60 days, when many of the biggest events took place, and they're numbering the sub-dips of the dips as distinct events. I find it problematic for their model that the T4 types occur three times with the same shape. If separate, independent comets are causing all of those, then it's nine comets in 3 groups of 3 that just happen to have similar timing and relative magnitudes. That seems unlikely.

The similarity between the six, smaller, earlier dips and the last three (they call them seven, counting the sub-dips) needs an explanation, and they just don't discuss the earlier dips.

On a more general level, explanations include, but aren't limited to, these two sub-categories:

1) A little bit of occulting material that is close to the star but is on a long, elliptical orbit.
2) A lot of occulting material that is far from the star.

Both of these are problematic in different ways.
Go to the top of the page
 
+Quote Post
JRehling
post Feb 2 2016, 07:08 PM
Post #109


Senior Member
****

Group: Members
Posts: 1963
Joined: 20-April 05
Member No.: 321



QUOTE (Gerald @ Feb 2 2016, 05:01 AM) *
(I've used galaxies as examples, since there is abundant material available, in contrast to interacting clouds of debris.)


Galaxies are a potentially useful analogue, since we have countless examples of them visible to a high degree of detail. However, they are only potentially useful – they universally have no single body which is an appreciable total of the sum mass or cross section, and that may or may not be true of Tabby's star's occulting objects.
Go to the top of the page
 
+Quote Post
Gerald
post Feb 3 2016, 02:43 PM
Post #110


Senior Member
****

Group: Members
Posts: 1840
Joined: 7-December 12
Member No.: 6780



Just checking, whether a cloud of debris can be made to fit with the observations.

Regarding the local behaviour of clouds of debris, I guess, eventually according simulations will be needed. The galaxies just provide some ideas.

Regarding the long-term dimming: Somewhat remotely, but might a ring of debris around an oblate (due to rotation) star precess, and that way gradually obscure the star? If so, can this happen in timescales of centuries?
Otherwise a rather homogenious cloud of gradually increasing optical density would need to be assumed, or some mechansim not immediately related to the debris.
Go to the top of the page
 
+Quote Post
JRehling
post Feb 3 2016, 10:18 PM
Post #111


Senior Member
****

Group: Members
Posts: 1963
Joined: 20-April 05
Member No.: 321



Per your galaxy metaphor, Gerald, I wonder if something like the dust ring that surrounds the Sombrero Galaxy might be a useful model for Tabby's star explanations.

I would reiterate that we don't know if the century-long dimming was gradual or not. The data looks to me like the brightness may have dropped in two discrete steps. We'd need more data to know how gradual it was.

I think a dust cloud at long distances certainly can explain Tabby's star – but that doesn't mean it's the right explanation. It seems to me like a "super powerful" explanation – it could potentially explain any light curve, because the amount of and homogeneity of dust could provide arbitrarily many unconstrained variables.

The trio of three-peaked dimming events strikes me as a terribly important clue. That could happen by chance, but isn't very likely. So any hypothesis has to explain why those three-peaked events would occur frequently.
Go to the top of the page
 
+Quote Post
Gerald
post Feb 4 2016, 01:07 PM
Post #112


Senior Member
****

Group: Members
Posts: 1840
Joined: 7-December 12
Member No.: 6780



Yes, the Sombrero galaxy comes very close to a global ring system which, applied to Tabby's star, may partially obscure the central star.

The most advanced theoretical work I'm aware of is that of Eriguchi, e.g. this paper (1978), Fig. 7 on p.515, showing the transition between spheroid, concave hamburger to toroid figure of equilibrium for a differetially rotating polytrope, and Hachisu, with contributions of Miyama (1985): Part I, p.355ff, and Part II, p13ff.
The latter paper mentions, that "probably these ring-like structures in the rotation dominant phase are dynamically unstable against fragmentation." Fig. 2 shows density profiles, including those of systems of rings.

Rotating polytropes aren't necessarily perfect approximations of clouds of debris, but they should be close to it.

Fragmentation leads to multiple systems. The fragments should behave somehow. I'd assume, that they should show features similar to the global system.
So we may again get local spheroids and rings, if undisturbed, or complex structures like for the collided galaxies, if two cloud fragments interact.

Ring(ed) systems should show up e.g. as triple (or higher-order) peaks when occulting a star.

Higher-order nesting might cause repeated triple peaks by the same ring system orbiting a larger body, or a multiple system the components orbiting each other, but due to the small Hill sphere of a "ringed moon" such structures are probably rather unstable.
About nested ring fragmentation, see e.g. this paper (1978), p.497ff.

For multiple system formation, see e.g. Figures 4 and 5 of this paper. p.262.

Assuming a moon rotating too rapidly to accrete all of its mass into its central body might work temporarily.
Another option for the repeated peak triples would be several local ringed systems of a similar size orbiting around the star, the similar size justified by symmetric fragmentation of a roughly symmetric (global) ring.

... so an explanations by occultations of some circumstellar disc may be able to find a theoretical basis, but only further observation can eventually decide...
Go to the top of the page
 
+Quote Post
HSchirmer
post Feb 4 2016, 02:14 PM
Post #113


Member
***

Group: Members
Posts: 266
Joined: 24-July 15
Member No.: 7619



QUOTE (Gerald @ Feb 4 2016, 02:07 PM) *
Another option for the repeated peak triples would be several local ringed systems of a similar size orbiting around the star, the similar size justified by symmetric fragmentation of a roughly symmetric (global) ring.


Or, could they be large moons around a gas giant?

Here's a quick thought experiment- what would our solar system look like under a LHB comet barrage?
There is some discussion that Ganymede and Callisto evolved differently because of LHB comet impacts-
http://www.planetary.org/blogs/emily-lakda.../2010/2363.html
Ok, if Jupiter's moons had multiple comet impacts, then wouldn't they have had transient rings? (eh, millions of years)

So, consider Jupiter during LHB, with a Saturn-sized ring 480k km, actually likely stop at Io's orbit (422k km).
But the other three Galilean moons orbit far enough apart, Europa at 6741k km, Ganymede at 1,070k km, and Callisto at 1,883K KM that they each might sport rings as wide as Saturn's main rings (about 300k km diameter)?
Go to the top of the page
 
+Quote Post
Gerald
post Feb 4 2016, 02:44 PM
Post #114


Senior Member
****

Group: Members
Posts: 1840
Joined: 7-December 12
Member No.: 6780



When taking Ganymede with a mass of about m=14.8e22 kg, and Jupiter with about M=1.9e27 kg, Ganymede orbital radius/semimajor axis a of about 1 million km, I get a Hill radius of r = a (m/3M)^{1/3}=30,000 km.
We'd need either much heavier moons, or the 10-fold distance from Jupiter to allow for a 300,000 km ring.
The ring would be well outside the Roche limit of the moon(s), hence probably unstable, unless sufficiently dilute. But stability isn't necessarily a requirement.
Go to the top of the page
 
+Quote Post
HSchirmer
post Feb 4 2016, 03:04 PM
Post #115


Member
***

Group: Members
Posts: 266
Joined: 24-July 15
Member No.: 7619



QUOTE (Gerald @ Feb 4 2016, 03:44 PM) *
When taking Ganymede with a mass of about m=14.8e22 kg, and Jupiter with about M=1.9e27 kg, Ganymede orbital radius/semimajor axis a of about 1 million km, I get a Hill radius of r = a (m/3M)^{1/3}=30,000 km.


Good point, more likely to be a big ring around Jupiter that has local lumps around the Galilean moons.
Then might see Jupiter with a Saturn-like ring, and the outer Galilean moons holding rings that are
eh, roughly the size (diameter) of Uranus or Neptune.

Well, that would create a rather wierd light curve...
Go to the top of the page
 
+Quote Post
JRehling
post Feb 4 2016, 05:24 PM
Post #116


Senior Member
****

Group: Members
Posts: 1963
Joined: 20-April 05
Member No.: 321



The only way a large moon such as Ganymede could block a non-trivial amount of starlight for an F dwarf would be if a torus/ring in its orbit was made into a considerably opaque ring of impressive width. If Saturn, for example, transited Tabby's star, even if it were seen face-on, its ring system would hardly alter the light curve at all, as opposed to one large planet making a transit.

For the light curve to increase between the hypothesized ring and planet, the ring system would have to be very large. Note that the separation between Ganymede and Jupiter is only about half the diameter of Tabby's star. Callisto, Titan, and (especially) Iapetus would provide enough separation for the star to be seen un-obscured between the planet and the star. Meanwhile, Saturn itself is nowhere near big enough to create the maximum dips that we see, so they would have to be caused by a planet + ring combination that was very impressive itself.

I think if the Saturn system were pulverized, and it transited a star, we could get something very similar to Dip 9. But the devil's in the details – how many rings, what size, what optical depth?
Go to the top of the page
 
+Quote Post
alan
post Feb 4 2016, 05:53 PM
Post #117


Senior Member
****

Group: Members
Posts: 1830
Joined: 20-November 04
From: Iowa
Member No.: 110



Some articles that may be relevant

Iapetus's ridge from impact that led to the formation of a ring and a satellite:

http://adsabs.harvard.edu/abs/2011Icar..214..773L
http://adsabs.harvard.edu/abs/2012JGRE..117.3002D
http://adsabs.harvard.edu/abs/2012AGUFM.P21H..03K

Catastrophic impacts on the inner satellites of Saturn

http://adsabs.harvard.edu/abs/2015GeoRL..42..256M

Ring formation during the Late Heavy Bombardment:

http://adsabs.harvard.edu/abs/2009Icar..199..413C
Go to the top of the page
 
+Quote Post
HSchirmer
post Feb 4 2016, 06:55 PM
Post #118


Member
***

Group: Members
Posts: 266
Joined: 24-July 15
Member No.: 7619



QUOTE (JRehling @ Feb 4 2016, 05:24 PM) *
For the light curve to increase between the hypothesized ring and planet, the ring system would have to be very large. Note that the separation between Ganymede and Jupiter is only about half the diameter of Tabby's star. Callisto, Titan, and (especially) Iapetus would provide enough separation for the star to be seen un-obscured between the planet and the star. Meanwhile, Saturn itself is nowhere near big enough to create the maximum dips that we see, so they would have to be caused by a planet + ring combination that was very impressive itself.


Ever wake up just before dawn in early spring and walk around your lawn? The dew condensing on spiderwebs in the pre-dawn twilight reveals a topography of normally invisible spiderweb funnels and cones.


Is Tabby's Star is an example of "morning dew" where the movement of comet ice and dust reveals a spiderweb of gravity funnels and cones spun by planets and large moons? A flux of dust and grit revealing the invisible topography of gravity?

Until somebody gets, and (long pause) publishes spectra to figure out what exactly is blocking / absorbing / scattering the light from Tabby's star, then we're basically working backwards to figure out a mechanism that gets the most occultation out of the least amount material. E.g. circumstellar clouds, but more likely planetary rings, as a mass of material that is organized into rings has a better chance of getting the opacity and sharp-edged curves that are observed.

Let's see, Saturn's rings are the result of roughly one centaur's (250 km) mass of ice, 10^20 Kg. Tabby's star might have five earth masses of ice and dust to work with, that's, eh, 10^25 Kg. Estimates for our solar system are that roughly 5 earth masses of comets we pitched out to the far Oort cloud by our gas giants, Jupiter and Saturn. What if Tabby's star doesn't have a major league bullpen? What if they only have AAA pitching staff (ice giant)? Then, five eath masses worth of small comets fall back into the system. That's more than enough material to create those Kepler dips. With eh, one-hundred thousand times the mass of saturns' rings available to occult the star, it seems that there should be enough stuff to create those impressive dips that Kelper saw.

Consider a stately Copernican solar system of planets waltzing around the sun; then consider that it turns into a pachinko-pinball mosh pit. If a non-negligible portion of the system's mass is bouncing around and slamming into things, we can expect disruption, dust clouds and rings that create big dips in starlight.
Go to the top of the page
 
+Quote Post
dudley
post Feb 8 2016, 07:42 PM
Post #119


Junior Member
**

Group: Members
Posts: 41
Joined: 27-March 15
Member No.: 7426



The scientific paper that first brought discussion of this star to the fore (Boyajian, et al. Where's the Flux?) contains an interesting, though little-remarked-upon observation. In section 2.1, The authors observe that the dips in light output seem to occur on multiples of periods of about 48 & 1/2 days.
In fact, there appear to be two groups of such dips, offset from one another by one half of the above period.
This might be taken to suggest a planet, comet, or compact debris cloud with an orbital period of ~ 24 days, except for the fact that most multiples of 24 days show no dips in brightness at all.
Any astrophysical explanation for the dimming of KIC 8462852 might be a better one, if it could explain how matter became arrayed in multiples of about 48 days, in an orbit around this star.
Go to the top of the page
 
+Quote Post
Mongo
post Feb 9 2016, 03:27 PM
Post #120


Member
***

Group: Members
Posts: 706
Joined: 13-June 04
Member No.: 82



A podcast with Dr. Josh Grindley of DASCH, about the reported long-term dimming of KIC 8462852.

Grindley is working on a paper about DASCH photometry of the star. In the podcast he destroys Hippke's criticism of Schaefer's paper, describing just how the methodology Hippke used was totally inadequate and inevitably produces incorrect results.

But he is also critical of Schaefer's methodology and results too. In fact, he looks at KIC 84628852 himself, using only the highest-quality data points with no warning flags attached, and finds a flat line -- no secular changes over the century of observations at all! So the observed long-term dimming would be an artifact caused by including doubtful observations.

If the erroneous observations at issue indicate a greater brightness than the correct level on average, and are more frequent the further back you go, then you would see a gradual dimming over time if they are included in the binned averages. But in reality the star's long-term brightness could be unchanged.
Go to the top of the page
 
+Quote Post

10 Pages V  « < 6 7 8 9 10 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 21st July 2017 - 12:51 AM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.