CoRoT Results

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Re: CoRoT Results

Post by Sirius_Alpha on 13th July 2013, 1:06 pm

I think HR 8799 also has some Gamma Doradus pulsations.

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Re: CoRoT Results

Post by Edasich on 14th August 2013, 2:08 pm

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Re: CoRoT Results

Post by Edasich on 23rd November 2013, 5:08 am

I hope to see it in preprint as soon as possible:
 
Source EPE Bibliography:
 
Transiting exoplanets from the CoRoT space mission: XXVII CoRoT-27b: a massive and dense planet on a short-period orbit
PARVIANEN H., GANDOLFI D., DELEUIL M., MOUTOU C., DEEG H. & 32 additional authors
Nov. 18, 2013   |   Astron. & Astrophys., submitted,
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Re: CoRoT Results

Post by Led_Zep on 6th January 2014, 10:10 pm

http://arxiv.org/abs/1401.1122

CoRoT-27b: a massive and dense planet on a short-period orbit
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Re: CoRoT Results

Post by Shellface on 11th May 2014, 10:15 am

You people are slackin'.

Filtering out activity-related variations from radial velocities in a search for low-mass planets

Variations related to stellar activity and correlated noise can prevent the detections of low-amplitude signals in radial velocity data if not accounted for. This can be seen as the greatest obstacle in detecting Earth-like planets orbiting nearby stars with Doppler spectroscopy regardless of developments in instrumentation and rapidly accumulating amounts of data. We use a statistical model that is not sensitive to aperiodic and/or quasiperiodic variability of stellar origin. We demonstrate the performance of our model by re-analysing the radial velocities of the moderately active star CoRoT-7 (log RHK=−4.61) with a transiting planet whose Doppler signal has proven rather difficult to detect. We find that the signal of the transiting planet can be robustly detected together with signals of two other planet candidates. Our results suggest that rotation periods of moderately active stars can be filtered out of the radial velocity noise, which enables the detections of low-mass planets orbiting such stars.
Taking the HARPS data from the public archive and running it through TERRA, Tuomi et al. perform a bayesian analysis and detect all three planets.

With an estimated mass of 4.8+2.3-2.4 M and adopting a radius of 1.69 ± 0.09 R (Léger et al. (2009), the average density of this transiting planet is 5.6+4.2-3.1 gcm-3 that does not constrain the planetary composition very accurately.
I've noticed the planetary parameters found by bayesian methods have considerably larger errors than when applying MC methods to the same data, though the "real" uncertainties likely lie between the two. I'd run this data through systemic to see what it outputs, but the data runs off the page for some reason.

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Re: CoRoT Results

Post by Sirius_Alpha on 11th May 2014, 12:18 pm

You can download the source file for the paper and view the LaTeX table that contains the data.

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Re: CoRoT Results

Post by Shellface on 30th May 2014, 1:00 pm

Sirius_Alpha wrote:You can download the source file for the paper and view the LaTeX table that contains the data.
Oh yeah, I forgot that was possible. Ta.

(the reason it took me 3 weeks to get to this is because there was a data release on the HARPS archive at the end of March, which released a lot of data used in Mayor et al. (2011). As of such, I've been spending spare time going through those systems, which I would like to write about somewhere here but I'm not sure where that could go)

Now, to outline my methodology:

In order to suppress the RV signal caused by the star's magnetic cycle (~15 m/s), I split the dataset into the first and second observing runs, excluding the 3 isolated points from early 2008. This leaves the data with only signals shorter than ~100 days. Then, I fitted the most significant peaks on the periodogram, using the derived values for the activity signals and the periods from this paper for the planets (except for b, which I use the value from the discovery paper because that is from the transit data). In order of fitting, these are: 23.4 d (rotation), 3.7094 d (c),  8.8999 d (d), 0.853585 d (b; alias appears at 5.89 d on periodogram), 17.0 d (activity), 27.9 d (activity) and 7.18 d (activity). After these, no signal exceeds a FAP of 0.01, though some power at 10.6 d exceeds a FAP of 0.1. Because systemic cannot bootstrap a fit with this many signals, I instead derived the residuals for the fit with every non-planetary signal, then re-introduced the planets into the fit to this data. This induces a bias towards the initially fitted values for the planets, which is unfortunately unavoidable in this method. I then bootstrapped the 3-planet fit, which outputted these parameters:

bcd
period (d)0.853548 ± 0.0000253.7093 ± 0.00078.8993 ± 0.0030
K (m/s)3.77 ± 0.325.27 ± 0.474.23 ± 0.65
eccentricity0.07 ± 0.080.046 ± 0.0170.021 ± 0.036
ω (°)137 ± 699 ± 8199 ± 11
m sin i (MJ)0.0165 ± 0.00140.0377 ± 0.00340.0405 ± 0.062
m sin i (M)5.2 ± 0.412.0 ± 1.112.9 ± 2.0

Again, the uncertainties are probably underestimated, though this should be closer to the truth. You should probably not take c's apparent eccentricity with confidence, and the periapsis angle uncertainties are those for local minima, which is why they are so small (again, likely underestimates). 

Anyway, b's inclination of 80.1 ± 0.3 degrees implies (m)/(m sin i) ≈ 1.015, so (m sin i)*1.015 implies b's true mass is 5.3 ± 0.5 M. Assuming a radius of 1.69 ± 0.09 R, b's density is therefore 5.89 ± 1.41 g/cm3, now with a good deal of the uncertainty coming from the radius rather than the mass! Again, I must stress that the uncertainty on the mass is probably underestimated, but this is an excellent result.

(I do seem to recall a more recent value for b's radius being published, but a quick look through literature didn't turn up anything. Does anybody else know what I'm talking about?)


Last edited by Shellface on 30th May 2014, 8:15 pm; edited 1 time in total (Reason for editing : fixing the numbers. density becomes very sensitive to parameter errors in the super-earth regime!)

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Re: CoRoT Results

Post by Sirius_Alpha on 30th May 2014, 7:49 pm

How recent? There's Bruntt, et al's 2010 paper that I found where the radius is slightly lower, at 1.58±0.10 Re.
http://arxiv.org/abs/1005.3208

Shellface wrote:As of such, I've been spending spare time going through those systems, which I would like to write about somewhere here but I'm not sure where that could go

We talked about opening a sub-forum for modelling and fitting a while (5 yr) ago... something that I would still be very much interested in doing.
http://solar-flux.forumandco.com/t254-systemic

It may be time to revisit the option.

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Re: CoRoT Results

Post by Shellface on 30th May 2014, 8:50 pm

Sirius_Alpha wrote:How recent? There's Bruntt, et al's 2010 paper that I found where the radius is slightly lower, at 1.58±0.10 Re.
Oh yeah, that's what I was thinking of. That revises the density to 6.96 ± 1.94 g/cm3, the larger error being due to the larger percentage error in the radius. I suppose it's going to be difficult to decrease the uncertainty on the radius in the short term, though Gaia (and TESS, if it observes the star) should be capable of ~halving it, perhaps. Still, the planet seems constrained to be rocky.

Sirius_Alpha wrote:We talked about opening a sub-forum for modelling and fitting a while (5 yr) ago... something that I would still be very much interested in doing.
http://solar-flux.forumandco.com/t254-systemic

It may be time to revisit the option.
I would appreciate it; 'not many other places on the internet where I can vomit out things like this and have people actually understand. Though the systemic community has evaporated quite a bit, the console is still usable, and with the advent of public RV archives fresh data is pretty much continuously released. It's definitely viable, though it depends on how much the other folks on here would like to use it.

If this were to happen, I could reveal my very secret slightly dumb way of getting HARPS data from the archive ("slightly dumb" because… okay, it uses a hex editor. I'm sure anyone with basic programming capability would be able to automate the process, but I've been doing it manually for 2 years). Then you folks could get all over that data, huh?

The most recent dataset I've been through is HD 136352 (nu2 lupi) from Mayor et al. (2011), which has 608 public observations. Manually sifting through that took about ~20 hours (which is why I stress automation would be the way forward), but the 3 planets and a trend are detected to extreme significance. And I've been through many systems, too; If a forum like that were to be made, I would sure have a lot to write about! If I could assist you lot into using the archive, there could definitely be a lot to come out of it - I have already helped to discover at least one previously unpublished planetary system which should be published soon (no, I'm not telling), so the scientific value is there.

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Re: CoRoT Results

Post by Sirius_Alpha on 5th June 2014, 8:24 pm

Transiting exoplanets from the CoRoT space mission: XXIV. CoRoT-24: A transiting multi-planet system
http://arxiv.org/abs/1406.1270

We present the discovery of a candidate multiply-transiting system, the first one found in the CoRoT mission. Two transit-like features with periods of 5.11 and 11.76d are detected in the CoRoT light curve, around a main sequence K1V star of r=15.1. If the features are due to transiting planets around the same star, these would correspond to objects of 3.7±0.4 and 5.0±0.5 R_earth respectively. Several radial velocities serve to provide an upper limit of 5.7 M_earth for the 5.11~d signal, and to tentatively measure a mass of 28+11−11 M_earth for the object transiting with a 11.76~d period. These measurements imply low density objects, with a significant gaseous envelope. The detailed analysis of the photometric and spectroscopic data serve to estimate the probability that the observations are caused by transiting Neptune-sized planets as >26× higher than a blend scenario involving only one transiting planet, and >900× higher than a scenario involving two blends and no planets. The radial velocities show a long term modulation that might be attributed to a 1.5 M_jup planet orbiting at 1.8~A.U. from the host, but more data are required to determine the precise orbital parameters of this companion.

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Re: CoRoT Results

Post by Shellface on 5th June 2014, 9:30 pm

All I can say is ouch. Does anyone else get the feeling that photometry has progressed faster than spectroscopy can assist it?

Anyway, seems like a pretty regular system, if a little puffy. Sure took a while for the paper to come out, though - I guess they were waiting on the outer companion?

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Re: CoRoT Results

Post by Sirius_Alpha on 6th June 2014, 4:00 am

Shellface wrote:Sure took a while for the paper to come out, though - I guess they were waiting on the outer companion?
Almost certainly. The only real revisions to my notes on the system from this paper are mass estimates (a mass for the outer planet, and a stricter upper limit for the mass of the inner planet).

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Re: CoRoT Results

Post by Sirius_Alpha on 6th July 2014, 8:49 pm

Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
http://arxiv.org/abs/1407.1044

Looks like the d planet doesn't exist.

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Re: CoRoT Results

Post by Lazarus on 7th July 2014, 5:35 pm

Error on the mass of CoRoT-7b still 20% of the value. So still quite uncertain as to the nature of the planet.
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Re: CoRoT Results

Post by Sirius_Alpha on 30th July 2014, 9:00 pm

Revisiting the transits of CoRoT-7b at a lower activity level
http://arxiv.org/abs/1407.8099

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Re: CoRoT Results

Post by Sirius_Alpha on 12th August 2014, 9:01 pm

CoRoT-22 b: a validated 4.9 RE exoplanet in 10-day orbit
http://arxiv.org/abs/1408.2576

The CoRoT satellite has provided high-precision photometric light curves for more than 163,000 stars and found several hundreds of transiting systems compatible with a planetary scenario. If ground-based velocimetric observations are the best way to identify the actual planets among many possible configurations of eclipsing binary systems, recent transit surveys have shown that it is not always within reach of the radial-velocity detection limits. In this paper, we present a transiting exoplanet candidate discovered by CoRoT whose nature cannot be established from ground-based observations, and where extensive analyses are used to validate the planet scenario. They are based on observing constraints from radial-velocity spectroscopy, adaptive optics imaging and the CoRoT transit shape, as well as from priors on stellar populations, planet and multiple stellar systems frequency. We use the fully Bayesian approach developed in the PASTIS analysis software, and conclude that the planet scenario is at least 1400 times more probable than any other false positive scenario. The primary star is a metallic solar-like dwarf, with Ms = 1.099+-0.049 Msun and Rs = 1.136 (+0.038,-0.090) Rsun . The validated planet has a radius of Rp = 4.88 (+0.17,-0.39) RE and mass less than 49 ME. Its mean density is smaller than 2.56 g/cm^3 and orbital period is 9.7566+-0.0012 days. This object, called CoRoT-22 b, adds to a large number of validated Kepler planets. These planets do not have a proper measurement of the mass but allow statistical characterization of the exoplanet population.

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Re: CoRoT Results

Post by Led_Zep on 1st January 2015, 2:58 pm

https://www.youtube.com/watch?v=PkpTly9E7C4

Corot-35b : discovery of a planet in a polar orbit
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Re: CoRoT Results

Post by Sirius_Alpha on 7th April 2015, 8:28 pm

Here's the paper for CoRoT-28 b and CoRoT-29 b.
http://arxiv.org/abs/1504.01532

Apparentlly CoRoT-29 b has an asymmetric light curve due an oblate star.

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Re: CoRoT Results

Post by Shellface on 8th April 2015, 10:10 am

Well, maybe.
The model can measure the deformation and the orientation of the star, but not its rotation rate. The results of Section 4.2 show that for CoRoT-29, the quadrupole moment has a contribution 2 orders of magnitude larger than rotation. Actually, the quadrupole moment of CoRoT-29 measured from the gravity darkening is far too large, J2 = 0.028 ± 0.019, compared to the Sun, J= (1.7 ± 0.4) · 10−7 (Lang 1999). Other authors have claimed large J2 values for fast-rotating stars, such as WASP-33 (J2 = 3.8 · 10−4, Iorio 2011), but not as large as for CoRoT-29.
The gravity darkening model, despite being the most satisfactory one considered, requires CoRoT-29 have an extremely peculiar nature compared to any normal K0 dwarf. I imagine it would be very difficult to explain the star's implied oblateness.

Obviously, there is a lot more to be learned to properly understand this system.

(this is a relevant video)

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Re: CoRoT Results

Post by Lazarus on 8th April 2015, 2:41 pm

Very strange. You don't often see Achernar being used as the closest point of reference for inferred properties of exoplanetary systems!
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Re: CoRoT Results

Post by Sirius_Alpha on 8th April 2015, 3:11 pm

Could it be that the star is heavily spotted around the equator, or has polar phages? It may not be g-darkening at all. That would sound more like a K dwarf than the rapidly rotating Achernar-type star that the authors consider.

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Re: CoRoT Results

Post by Shellface on 8th April 2015, 6:21 pm

There are multiple sections for different models considered as possible solutions to the irregular transit, y'know…
The spot fit yielded BIC = 133, whereas the gravity darkening fit produces BIC = 120. This BIC difference corresponds to a Bayes factor of around 665 for the gravity darkening model (i.e. if the prior probabilities for each model are the same, then the gravity darkening is 665 times more probable than the spot model). Moreover, to explain the observational evidence we are obliged to put requirements on the size and temporal evolution of the spot, which are completely ad hoc. We consider that there is enough evidence to discard the spotted star as a reasonable interpretation of the data.
Of all hypotheses considered, of which there are many, only stellar oblateness provides an (air quotes) "satisfactory" fit.

I am not inclined to believe it is the correct model, however. It requires an exceptionally unlikely combination of stellar parameters, and then requires a Hot Jupiter to be in orbit and transiting, which is dicing with probability to an excessive degree. Nevertheless, the lack of a more satisfactory model means oblateness ought to be considered the most satisfactory model for the moment, but let's not be too surprised if that changes in future.

Again, there is a lot more that is to be learned from this system in order to properly understand it.

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Re: CoRoT Results

Post by Edasich on 25th August 2015, 4:15 am

Another transiting brown dwarf: Corot-33 B.

Transiting exoplanets from the CoRoT space mission XXVIII. CoRoT-33b, an object in the brown dwarf desert with 2:3 commensurability with its host star

We report the detection of a rare transiting brown dwarf with a mass of 59 M_Jup and radius of 1.1 R_Jup around the metal-rich, [Fe/H] = +0.44, G9V star CoRoT-33. The orbit is eccentric (e = 0.07) with a period of 5.82 d. The companion, CoRoT-33b, is thus a new member in the so-called brown dwarf desert. The orbital period is within 3% to a 3:2 resonance with the rotational period of the star. CoRoT-33b may be an important test case for tidal evolution studies. The true frequency of brown dwarfs close to their host stars (P < 10 d) is estimated to be approximately 0.2% which is about six times smaller than the frequency of hot Jupiters in the same period range. We suspect that the frequency of brown dwarfs declines faster with decreasing period than that of giant planets.

*Update*

It has been listed at EPE as planet but I don't get the reason.

http://exoplanet.eu/catalog/corot-33_b/


Last edited by Edasich on 25th August 2015, 8:35 am; edited 1 time in total (Reason for editing : EPE link)
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Re: CoRoT Results

Post by Edasich on 24th September 2015, 1:51 pm

It seems EPE is going to treat "brown dwarfs" as "exoplanets". What about?

http://exoplanet.eu/catalog/corot-15_b/
http://exoplanet.eu/catalog/hr_3549_b/
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Re: CoRoT Results

Post by Stalker on 24th September 2015, 4:27 pm

It's a good idea.

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Re: CoRoT Results

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