Science

discussion

RINGS & MOONS

Started by ggccg
Default_user
over 3 years ago

Re: 10616571, I think the best explanation is that this is a detached EB, a largish G subgiant with a smaller ~0.3x M dwarf secondary. Those bumps are most likely due to starspot occultation. It seems curious, possibly not a coincidence, that the rotation period of the primary appears to be ~12 days, or half the period of the secondary's orbit, which could cause the secondary to occult the same spot system, creating the illusion of the bumps being in the same phase. Of course, over time, once we average out enough transits, this illusion dissipates.

See last few comments at:

http://talk.planethunters.org/objects/APH22714177/discussions/DPH100i93f

Default_user
over 3 years ago

Thanks very much Kianjin :-) It looked (probably coincidentally) as thought if a reduction of 30% in the secondary would probably put it very close to the Roche limit. Thanks for the EB confirmation.

Default_user
over 3 years ago

http://arxiv.org/abs/1403.5839

Detecting extrasolar moons akin to Solar System satellites with an Orbital Sampling Effect

René Heller

(Submitted on 24 Mar 2014)

Despite years of high accuracy observations, none of the available theoretical techniques has yet allowed the confirmation of a moon beyond the Solar System. Methods are currently limited to masses about an order of magnitude higher than the mass of any moon in the Solar System. I here present a new method sensitive to exomoons similar to the known moons. Due to the projection of transiting exomoon orbits onto the celestial plane, satellites appear more often at larger separations from their planet. After about a dozen randomly sampled observations, a photometric orbital sampling effect (OSE) starts to appear in the phase-folded transit light curve, indicative of the moons' radii and planetary distances. Two additional outcomes of the OSE emerge in the planet's transit timing variations (TTV-OSE) and transit duration variations (TDV-OSE), both of which permit measurements of a moon's mass. The OSE is the first effect that permits characterization of multi-satellite systems. I derive and apply analytical OSE descriptions to simulated transit observations of the Kepler space telescope assuming white noise only. Moons as small as Ganymede may be detectable in the available data, with M stars being their most promising hosts. Exomoons with the 10-fold mass of Ganymede and a similar composition (about 0.86 Earth radii in radius) can most likely be found in the available Kepler data of K stars, including moons in the stellar habitable zone. A future survey with Kepler-class photometry, such as Plato 2.0, and a permanent monitoring of a single field of view over 5 years or more will very likely discover extrasolar moons via their OSEs

Default_user
over 3 years ago

Is it possible that some of our transit are caused by an undetected asteroid blocking our view of the star?

http://www.slate.com/blogs/bad_astronomy/2014/03/27/asteroid_ring_chariklo_is_the_first_non_planet_found_to_have_a_ring.html

I know it is most unlikelly but still...

Default_user
over 3 years ago

firejuggler:

Is it possible that some of our transit are caused by an undetected asteroid blocking our view of the star?

http://www.slate.com/blogs/bad_astronomy/2014/03/27/asteroid_ring_chariklo_is_the_first_non_planet_found_to_have_a_ring.html

I know it is most unlikelly but still...

That's a great question. Basically its the event duration. So for asteroid occultations, you're blocking out a distant background star. The angular size is small and so events are on the order of seconds (it doesn't take the asteroid very long to traverse that). Asteroid occultations, with the geometry and the angular sizes on the sky, the asteroid is blocking out the entire star typically where as for planet transits that's not the case only a tiny fraction of the star's light is diminished. Transits on the other hand take hours to tens of hours because where the planet is, the angular size of the star is large where the planet and so it takes longer to traverse across the star.

Cheers,

~Meg

Default_user
over 3 years ago

There was an eclipse of Regulus by the asteroid 163 Erigon just a few days ago.

Video here: https://www.youtube.com/watch?feature=player_embedded&v=kluHsjIMs9s

Manually fast forward to about 1:30.

Default_user
over 3 years ago

Here is an intriguing way to try and infer the presence of exomoons:

Transit of Exomoon Plasma Tori: New Diagnosis

Lotfi Ben-Jaffel, Gilda Ballester

(Submitted on 3 Apr 2014)

In the solar system, moons largely exceed planets in number. The Kepler database has been shown to be sensitive to exomoon detection down to the mass of Mars, but the first search has been unsuccessful. Here, we use a particles-in-cell code to predict the transit of the plasma torus produced by a satellite. Despite the small size of a moon, the spatial extent of its plasma torus can be large enough to produce substantial transit absorptions. The model is used for the interpretation of Hubble Space Telescope early ingress absorptions apparently observed during WASP-12b and HD 189733b UV transits for which no consistent explanation exists. For HD 189733b an exomoon transiting ∼16 Rp ahead of the planet and loading ∼1029 C II ions/s into space is required to explain the tentative early ingress absorption observed for C II. For WASP-12b, a moon transiting ∼6 Rp ahead from the planet and ejecting ∼1028 Mg II ions per second is required to explain the NUV early ingress absorption feature. Interestingly, both HD 189733b and WASP-12b predicted satellites are outside the Hill sphere of their planets, an indication that the moons, if present, were not formed in situ but probably captured later. Finally, our simulations show a strong electromagnetic coupling between the polar regions of planets and the orbital position of the moons, an expected outcome of the unipolar induction DC circuit model. Future observations should test our predictions with a potential opportunity to unambiguously detect the first exomoon plasma torus.

http://arxiv.org/abs/1404.1084

Default_user
over 3 years ago

http://m.space.com/25438-exomoon-around-alien-planet-discovery.html?cmpid=514630_20140410_21706734 I'm thinking that hopefully K2 (in conjunction with an earth based telescope or two) will offer a possible solution to any similar events?

Default_user
over 3 years ago
nighthawk_black in response to mjtbarrett

@mjtbarrett I think I read somewhere that Kepler is definitely far enough from Earth it could help with a parallax measurement; if an ML occurs within a Campaign FOV I guess it depends on how quickly they can get a heads up and instruct the detector to pick up the target. There are fewer stars being monitored in each campaign, so chances are slim that the background point source for any emergent microlensing event will already be on the target list.

Default_user
over 3 years ago

Hello NHB :) The FOV should be large enough for near continuous monitoring (for up to 14 days of data at a time) to detect a good number of lensing events. Gould and Horne make a great case for collaborative work between Kepler and earth-based observatories making simultaneous observations: http://keplerscience.arc.nasa.gov/docs/WhitePapers/ulens_kepler.pdf

The trailing heliocentric orbit is extending the baseline by a huge amount (up to 0.4 AU !) which will certainly help in parallax (and presumably xallarap?) measurements and allow both distance and mass to be determined.

From the paper: "The key feature of Kepler for microlensing remains intact: capability to simultaneously observe essentially all ongoing microlensing events. This enables good integrated signal-to-noise ratio (S/N) despite large pixel size (and therefore relatively high background in crowded Bulge fields). Its unique perspective also permits Kepler to independently discover planets in these events, since Kepler’s lightcurves probe regions on the lens plane displaced from those probed by lightcurves from Earth."

Gould and Horne also point out that some lensing events may be seen by Kepler that cannot be seen from earth (and vice versa) because of the distance between the viewpoints.

It would be great if Spitzer could start collaborating this week (c/f Gould and Horne para.7) :-) http://en.wikipedia.org/wiki/Spitzer_Space_Telescope

Please Log In to make comments.