55 Cancri e -- Transits detected!!

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Re: 55 Cancri e -- Transits detected!!

Post by Sirius_Alpha on 3rd May 2011, 5:47 am

Stalker wrote:If i understand, we have a rocky planet with an extended atmosphere of H2O who block infrared radiations?
As I understand it, they suggest a CO / CO2 exosphere could be absorbing the 4.5 Ám wavelength they're observing in. Meaning what they're detecting as the planet's radius may actually be it's extended atmosphere.

But if the 4.5 Ám radius for the planet corresponds to a real radius, then probably a supercritical water ocean over an Earth-like "nucleus."

They don't think a hydrogen envelope is terribly likely, as the rate at which it would have been escaped is short, compared to the age of the 55 Cancri system.

Tangent: Step back a bit and place yourself back in 2005 or 2006. We're talking about characterising the structure and composition of a super-Earth transiting a naked-eye star, and comparing it to other such super-Earths that we've found so far. This is the kind of happenings we dreamed of only half a decade ago. The pace of extrasolar planet science has been an exciting adventure, and the recent characterisation efforts for 55 Cnc e reinforce this.


Last edited by Sirius_Alpha on 3rd May 2011, 5:56 am; edited 1 time in total (Reason for editing : Wording.)

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Re: 55 Cancri e -- Transits detected!!

Post by Edasich on 3rd May 2011, 6:16 am

Also consider the extremely cold nightside where ice caps of water and solid carbon dioxide may well be located

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Re: 55 Cancri e -- Transits detected!!

Post by Sirius_Alpha on 3rd May 2011, 6:23 am

With 55 Cnc b exciting 55 Cnc e's eccentricity, I wouldn't be surprised if 55 Cnc e is reminiscent of a "super-Io." If this is the case, I would not expect frozen volatiles on the night side.

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Re: 55 Cancri e -- Transits detected!!

Post by tommi59 on 3rd May 2011, 10:41 am

Radius of planet is radius of planet without atmosphere or planet with ?? because it confused me and why they have assumed smaller radius for host star? difference between 1.63 and 2.13 is significant.So every 2 days we wil have update of the planet. e in EPE

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Re: 55 Cancri e -- Transits detected!!

Post by Lazarus on 3rd May 2011, 2:27 pm

tommi59 wrote:because it confused me and why they have assumed smaller radius for host star?
55 Cancri A has a rather interesting history of radius determination, there are some significant discrepancies between various studies. For starters it doesn't help that the metallicity is so high, it is harder to constrain the models at these abundances. It doesn't help that the interferometric studies have come up with radii that are substantially inconsistent with those from determinations via observations of the luminosity and spectrum. See van Belle and von Braun (2009) for some discussion of this: 55 Cancri A appears to sit well outside the typical relationship between effective temperature and colour index. No doubt the discovery that the star hosts a transiting super-Earth will result in follow-up studies.

Would be very interesting to know how Spitzer observations compare to the optically-determined radii for the other short-period super-Earths CoRoT-7b and Kepler-10b...

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Re: 55 Cancri e -- Transits detected!!

Post by atomic7732 on 3rd May 2011, 8:24 pm

Interesting, saw this on the EPE... I didn't expect 55 Cancri to have a near-line of sight planetary system.

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Re: 55 Cancri e -- Transits detected!!

Post by Sirius_Alpha on 4th May 2011, 2:43 am

tommi59 wrote:Radius of planet is radius of planet without atmosphere or planet with ?? because it confused me

When you detect a transit, you get a percentage of starlight blocked, corresponding to a transit depth. What this physically translates to for the planet depends on the planet. It could be an actual radius of the planet, or in the case of a gas giant or mini-Neptune, the radius of it's opaque envelope. For working purposes, we can consider this the planet's "transit radius."

Planets with atmospheres may have wavelength-dependent transit radii. Consider Titan transiting the sun. In visible light, it would appear to block a larger fraction of visible light than radio light, since Titan's atmosphere is more transparent to radio. So, if you were observing a Titan-clone transiting a star, you would derive a larger radius in the visible light than you would in the radio. The reason for this discrepancy would be Titan's atmosphere.

For 55 Cnc e, we aren't sure if the reason for the discrepancy between Spitzer's infrared measurements and MOST's optical measurements is a result of an atmosphere that blocks more infrared light than visible light, or if there's something like an instrumental effect overlooked for the optical transit radius measurement. Hence the desire for follow-up measurements.

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Re: 55 Cancri e -- Transits detected!!

Post by tommi59 on 4th May 2011, 4:57 am

I know all what you wrote sirius only wondered why is such difference in radius of the planet between MOST and SPITZER(it looks like data different planet). Even considering that reason is large atmosphere(so close to the star??) blocking more infrared light.There must be like you guess instrumental efect overlooked itc..Hmm interesting what will be follow up checks.

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Re: 55 Cancri e -- Transits detected!!

Post by Edasich on 4th May 2011, 10:07 am

The reason of no transit for Rho1 Cnc b or c (even f) could be low inclination

From EPE 55 Cnc page:

The star is surrounded by a dust disk extending at least a 40 AU, with an inclination of ~ 25░. If the planets are in the same plane than the disc, this gives to the first planet a mass of 1.9+1.1 -0.4 MJ (Trilling & Brown 1998, Trilling et al 2000).

And for planet c and f planet, masses (doing a rough math, assuming at same inclination) would be around 0.37-0.44 Jupiter masses. Low inclination but not as dismaying as for Rho CrB b Laughing

Although...

But disc not confirmed by Schneider et al (2000b)

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Re: 55 Cancri e -- Transits detected!!

Post by Lazarus on 4th May 2011, 2:41 pm

Both Schneider et al. (2001) and Jayawardhana et al. (2002) fail to detect the disc. In the latter paper there are detections of several background sources unrelated to the 55 Cancri system which may explain the previous detections. Detection of a dust disc at 55 Cancri was likely spurious.

Incidentally, the Spitzer inclination for planet e is 83.4+1.5-1.7 degrees. With an orbital radius of 0.115 AU, planet b will transit if the inclination is greater than 87.8 degrees (for a stellar radius of 0.95 times solar) or 87.5 degrees (for a stellar radius of 1.1 times solar). So if the system is coplanar then we wouldn't expect the outer planets to transit anyway...

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Re: 55 Cancri e -- Transits detected!!

Post by tommi59 on 4th May 2011, 3:39 pm

What if the inclination of b is 94 degrees??Anyway we have hundreds planets (kepler) in need of confirmation by RV

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Re: 55 Cancri e -- Transits detected!!

Post by Lazarus on 4th May 2011, 3:45 pm

From the point of view of these observations, 94 degrees is equivalent to 86 degrees, they both give the same light curve. Unless more information is available about the full 3D orientation of the system, inclination is treated as being between 0 and 90 degrees.

(Once you have full 3D information you can extend it to between 0 and 180 degrees)

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discrepancy in the planetary radius

Post by exoplanet on 4th May 2011, 4:16 pm

Sirius_Alpha wrote:
tommi59 wrote:Radius of planet is radius of planet without atmosphere or planet with ?? because it confused me

For 55 Cnc e, we aren't sure if the reason for the discrepancy between Spitzer's infrared measurements and MOST's optical measurements is a result of an atmosphere that blocks more infrared light than visible light, or if there's something like an instrumental effect overlooked for the optical transit radius measurement. Hence the desire for follow-up measurements.

I would bet on some problem with the MOST measurements also. There have been numerous transit observations done with Spitzer and by now the behavior of the IRAC (Infrared Array Camera) must be very well known.

Let us wait and see...

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Re: 55 Cancri e -- Transits detected!!

Post by Lazarus on 4th May 2011, 4:21 pm

Of course this is now warm Spitzer, rather than an actively-cooled system. That changes the characteristics of the detector. They seem to have done a good job of modelling it though.

Hopefully someone can get the Hubble Space Telescope on the case.

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Re: 55 Cancri e -- Transits detected!!

Post by Sirius_Alpha on 9th May 2011, 9:02 pm

Planetary Phase Variations of the 55 Cancri System
http://arxiv.org/abs/1105.1716

Characterization of the composition, surface properties, and atmospheric conditions of exoplanets is a rapidly progressing field as the data to study such aspects become more accessible. Bright targets, such as the multi-planet 55 Cancri system, allow an opportunity to achieve high signal-to-noise for the detection of photometric phase variations to constrain the planetary albedos. The recent discovery that that inner-most planet, 55 Cancri e, transits the host star introduces new prospects for studying this system. Here we calculate photometric phase curves at optical wavelengths for the system with varying assumptions for the surface and atmospheric properties of 55 Cancri e. We discuss detection limits and how these models may be used with future instrumentation to further characterize these planets and distinguish between various assumptions regarding surface conditions.

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Re: 55 Cancri e -- Transits detected!!

Post by Sirius_Alpha on 6th June 2011, 9:05 pm

A reanalysis of the MOST data suggests it had some errors, and the MOST data actually suggests a larger planet, consistent with the Spitzer results.
More in-depth explanation here.

Updated paper:

A Super-Earth Transiting a Naked-Eye Star
http://arxiv.org/abs/1104.5230v2

We have detected transits of the innermost planet "e" orbiting 55 Cnc (V=6.0), based on two weeks of nearly continuous photometric monitoring with the MOST space telescope. The transits occur with the period (0.74 d) and phase that had been predicted by Dawson & Fabrycky, and with the expected duration and depth for the crossing of a Sun-like star by a hot super-Earth. Assuming the star's mass and radius to be 0.963_{-0.029}^{+0.051} M_sun and 0.943 +/- 0.010 R_sun, the planet's mass, radius, and mean density are 8.63 +/- 0.35 Mearth, 2.00 +/- 0.14 Rearth, and 5.9_{-1.1}^{+1.5} g/cm^3. The mean density is comparable to that of Earth, despite the greater mass and consequently greater compression of the interior of 55 Cnc e. This suggests a rock-iron composition supplemented by a significant mass of water, gas, or other light elements. Outside of transits, we detected a sinusoidal signal resembling the expected signal due to the changing illuminated phase of the planet, but with a full range (168 +/- 70 ppm) too large to be reflected light or thermal emission. This signal has no straightforward interpretation and should be checked with further observations. The host star of 55 Cnc e is brighter than that of any other known transiting planet, which will facilitate future investigations.

Also,
55 Cancri: Stellar Astrophysical Parameters, a Planet in the Habitable Zone, and Implications for the Radius of a Transiting Super-Earth
http://arxiv.org/abs/1106.1152

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Re: 55 Cancri e -- Transits detected!!

Post by Lazarus on 7th June 2011, 12:42 am

Good to see it resolved, though somewhat weird to have a low-mass, volatile-rich planet in such a strongly-irradiated region. Stops it from grouping nicely with CoRoT-7b and Kepler-10b as well, pity.

Doesn't help that the star's age seems to be pretty old as well: wonder what the implications of a star with twice the Sun's iron-to-hydrogen ratio forming over 10 Gyr ago are.

I doubt we've heard the last from this system!

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Re: 55 Cancri e -- Transits detected!!

Post by exoplanet on 7th June 2011, 4:56 am

Very interesting ! With all those metals it is not also a good match for a Neptune with most of its atmosphere gone.

Good that they managed to match both results and that they found the bug in the MOST pipeline before more damage was made !

Kudos to Joshua Winn's team.

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Re: 55 Cancri e -- Transits detected!!

Post by exoplanet on 7th June 2011, 5:10 am

BTW Sirius,

where did you get that link with the reply to the referee ?
Is it ok to use it ?



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Re: 55 Cancri e -- Transits detected!!

Post by Sirius_Alpha on 7th June 2011, 5:14 am

exoplanet wrote:where did you get that link with the reply to the referee ?
On arXiv's page for the 2nd version of the paper, here.
Comments: Submitted to ApJ Letters. (v2) Revised after fixing an error in the data reduction pipeline; for details see this http URL

exoplanet wrote:Is it ok to use it ?
I'd assume so. It's definitely publically accessible.

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Re: 55 Cancri e -- Transits detected!!

Post by exoplanet on 7th June 2011, 6:10 am

I missed that link. Thanks !

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Re: 55 Cancri e -- Transits detected!!

Post by Lazarus on 8th June 2011, 1:26 am

One thing I have to wonder is if 55 Cnc e is actually volatile-rich. Certainly it would appear to be an unfavourable environment due to stellar irradiation.

Maybe it is a carbon planet.

This paper suggests that 55 Cancri should have produced planets more enriched in carbon than our own, particularly in the inner regions:

The location of the C zone also implies that the four inner known giant planets of the 55Cnc system (located at 0.038 AU, 0.115 AU, 0.24 AU, and 0.781 AU) should contain significant amounts of C, both in their solid cores and in their atmospheres if they formed at or in close proximity to their current orbital locations and also depending on the exact time of their formation.
Furthermore carbon planets seem to have the right kind of radii, e.g. from this paper:

While the zero-pressure density of graphite (2.25 g/cm3) is almost twice that of water ice VII (1.46 g/cm3), a graphite planet with an Fe core has a similar average density to a water planet with an iron core and silicate mantle.
So I really have to wonder if we might be looking at a carbon-rich planet. Would certainly provide an interesting validation of the modelled dependence between stellar abundances and terrestrial planet composition.

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Re: 55 Cancri e -- Transits detected!!

Post by Sirius_Alpha on 8th June 2011, 3:47 am

Very interesting! I really like that hypothesis. Perhaps this could be tested by checking for an exosphere around the planet like at Mercury.

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Re: 55 Cancri e -- Transits detected!!

Post by tommi59 on 8th June 2011, 4:38 am

Really likely I doubted this planet could have any light elements and explanation of lazarus with carbon planets seems to be great I am curious how many carbon planet exist really?Hmm?

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Re: 55 Cancri e -- Transits detected!!

Post by Sirius_Alpha on 26th September 2011, 4:42 pm

Spitzer Press Release.

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