Transits of HD 97658 b Detected

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Transits of HD 97658 b Detected

Post by Sirius_Alpha on 12th September 2011, 8:15 pm

Detection of a Transiting Low-Density Super-Earth
http://arxiv.org/abs/1109.2549

We present evidence for photometric transits of the low-mass planet HD 97658b across the disk of its host star, an early K dwarf. This planet was previously discovered in radial velocities (RVs) from Keck/HIRES as part of the Eta-Earth Survey. Using photometry from the Automated Photometric Telescopes at Fairborn Observatory, we detected four separate planetary egress events at times predicted from the RV orbit. We measured a transit depth of 1470 +/- 260 ppm, a result that should be confirmed and refined with space-based photometry. We also collected additional Keck-HIRES RV measurements that refined the transit ephemeris and planet mass. With an orbital period of 9.4957 +/- 0.0022 days, HD 97658b is a close-in planet that had been classified as a `super-Earth' based on its mass of 6.4 +/- 0.7 Mearth. However, the planet radius of 2.93 +/- 0.28 Rearth implies a density of 1.40 g/cc and suggests `sub-Neptune' status. The low density can be explained by an extended atmosphere of volatiles such as hydrogen, helium, and water. HD 97658b is similar to GJ 1214b in mass, radius, and density, although HD 97658b has a higher equilibrium temperature of 510 - 720 K. The star HD 97658 (V = 7.8, K = 5.7) is among the brightest known to host a transiting planet, which will facilitate detailed follow-up measurements.


Last edited by Sirius_Alpha on 17th April 2012, 7:21 am; edited 2 times in total

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Re: Transits of HD 97658 b Detected

Post by tommi59 on 13th September 2011, 3:57 am

Next mini neptune but twice denser than kepler 11 f not so bad with 2.93 radius
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Re: Transits of HD 97658 b Detected

Post by Lazarus on 13th September 2011, 1:55 pm

Good news, hopefully this will help pin down the nature of these planets as sub-Neptunes, waterworlds or outgassed super-Earths.
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Re: Transits of HD 97658 b Detected

Post by pochimax on 13th September 2011, 2:23 pm

This planet needs a better photometry and full transits to be sure of its radius
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Re: Transits of HD 97658 b Detected

Post by Sirius_Alpha on 16th April 2012, 8:40 pm

Failure to detect transits of HD 97658b with MOST.
http://arxiv.org/abs/1204.3135

(Where is the thread describing the discovery of transits?)

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Re: Transits of HD 97658 b Detected

Post by Lazarus on 17th April 2012, 2:24 am

Sirius_Alpha wrote:(Where is the thread describing the discovery of transits?)
Here it is

Also notable that the paper claiming the detection of transits has been withdrawn by the authors.
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Re: Transits of HD 97658 b Detected

Post by Sirius_Alpha on 17th April 2012, 7:21 am

Thanks! Moved relevant posts.

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Re: Transits of HD 97658 b Detected

Post by tommi59 on 17th April 2012, 3:17 pm

The planet probably is not transiting or has much smaller
radius but interesting is why claim of existence was not disproven earlier
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Re: Transits of HD 97658 b Detected

Post by Lazarus on 26th April 2012, 4:06 pm

EPE seems to still be listing this one as a transiting planet... hmmmm...
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Re: Transits of HD 97658 b Detected

Post by Sirius_Alpha on 3rd June 2013, 12:00 am

Okay so maybe it does transit.

A warm, likely volatile-rich super-Earth: HD 97658b transits, but not quite when expected
http://arxiv.org/abs/1305.7260

Through photometric monitoring of the extended transit window of HD 97658b with the MOST space telescope, we have found that this exoplanet transits with an ephemeris consistent with that predicted from radial velocity measurements. The mid-transit times are 6$\sigma$ earlier than those of the unverified transit-like signals reported in 2011, and we find no connection between the two sets of events. The transit depth indicates a 2.34$^{+0.18}_{-0.15}$ $R_\earth$ super-Earth. When combined with the radial velocity determined mass of 7.86 $\pm 0.73$ $M_\earth$, our radius measure allows us to derive a planet density of 3.44$^{+0.91}_{-0.82}$ g cm$^{-3}$. Models suggest that a planet with our measured density has a rocky core that is enveloped in an atmosphere composed of lighter elements. The star of the HD 97658 system is the second brightest known to host a transiting super-Earth, facilitating folllow-up studies of this not easily daunted, warm and likely volatile-rich exoplanet.

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Re: Transits of HD 97658 b Detected

Post by tommi59 on 3rd June 2013, 4:20 am

Is back,good news with smaller radius has density 3.44 g/ cm3 quite high for volatile rich exoplanet,especially being not very hot 600-700 K.Planet seems to be however outside significant mass loss zone.
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Re: Transits of HD 97658 b Detected

Post by Lazarus on 3rd June 2013, 1:17 pm

That's an interesting development. Wonder what else we've been missing because we haven't searched sufficiently far away from the RV predicted time.

Though I guess if Trojan planets were common, Kepler would have seen some by now?
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Re: Transits of HD 97658 b Detected

Post by Shellface on 3rd June 2013, 5:17 pm

Eccentricities are going to have a significant effect on times of transit, which is unfortunate because eccentricity detection is difficult for poor s/n, low amplitude planets. The slight difference in observed time of transit as expected suggests a slightly non-zero eccentricity for HD 97658 b, which is reasonable because it has quite a long orbital period. The broad range of plausible eccentricities for Super-Earths will necessitate rather long transit photometry, like here.

Hm. The only other major search for transits of an RV-detected Super-Earth was HD 40307 b a while back. The paper is quite thorough, but it's interesting to note that Tuomi et al. 2012 found a slightly non zero (1 sigma) eccentricity, in contrast to the ~0 found from the original dataset. Maybe that needs a re-take, too?

With a second Super-Earth transiting a bright, solar-type star, it will be interesting to see how HD 97658 b compares to 55 Cancri e. They have rather similar masses but the former has a much lower insolation, yet it is less dense. I suppose loss of atmosphere in 55 Cnc e could explain that? A secondary transit detection of HD 97658 b would be interesting.

Now I gots to update the wikipedia article again.

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Re: Transits of HD 97658 b Detected

Post by Lazarus on 3rd July 2013, 3:22 pm

Now starring in its very own press release.
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Re: Transits of HD 97658 b Detected

Post by Edasich on 25th February 2014, 4:59 am

Transit confirmation for HD 97658 b.

Transit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star

Super-Earths transiting nearby bright stars are key objects that simultaneously allow for accurate measurements of both their mass and radius, providing essential constraints on their internal composition. We present here the confirmation, based on Spitzer transit observations, that the super-Earth HD 97658 b transits its host star. HD 97658 is a low-mass (M*=0.77\pm0.05\,M_{\odot}$) K1 dwarf, as determined from the Hipparcos parallax and stellar evolution modeling. To constrain the planet parameters, we carry out Bayesian global analyses of Keck-HIRES radial velocities, and MOST and Spitzer photometry. HD 97658 b is a massive (MP=7.55+0.83-0.79 M_{\oplus}$) and large ($R_{P} = 2.247+0.098-0.095 R_{\oplus}$ at 4.5 $\mu$m) super-Earth. We investigate the possible internal compositions for HD 97658 b. Our results indicate a large rocky component, by at least 60% by mass, and very little H-He components, at most 2% by mass. We also discuss how future asteroseismic observations can improve the knowledge of the HD 97658 system, in particular by constraining its age. Orbiting a bright host star, HD 97658 b will be a key target for coming space missions TESS, CHEOPS, PLATO, and also JWST, to characterize thoroughly its structure and atmosphere.
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Re: Transits of HD 97658 b Detected

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