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 HIP 41378 - Multi-Planet System from K2

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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty28th June 2016, 8:46 pm

Wow!

Five Planets Transiting a Ninth Magnitude Star
http://arxiv.org/abs/1606.08441

Quote :
The Kepler mission has revealed a great diversity of planetary systems and architectures, but most of the planets discovered by Kepler orbit faint stars. Using new data from the K2 mission, we present the discovery of a five planet system transiting a bright (V = 8.9, K = 7.7) star called HIP 41378. HIP 41378 is a slightly metal-poor late F-type star with moderate rotation (v sin(i) = 7 km/s) and lies at a distance of 116 +/- 18 from Earth. We find that HIP 41378 hosts two sub-Neptune sized planets orbiting 3.5% outside a 2:1 period commensurability in 15.6 and 31.7 day orbits. In addition, we detect three planets which each transit once during the 75 days spanned by K2 observations. One planet is Neptune sized in a likely ~160 day orbit, one is sub-Saturn sized likely in a ~130 day orbit, and one is a Jupiter sized planet in a likely ~1 year orbit. We show that these estimates for the orbital periods can be made more precise by taking into account dynamical stability considerations. We also calculate the distribution of stellar reflex velocities expected for this system, and show that it provides a good target for future radial velocity observations. If a precise orbital period can be determined for the outer Jovian planet through future observations, it will be an excellent candidate for follow-up transit observations to study its atmosphere and measure its oblateness.

Admin note: This has been extracted from the Kepler-K2 Results thread since it deserves its own thread.

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Last edited by Sirius_Alpha on 30th September 2018, 8:31 pm; edited 1 time in total
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty29th June 2016, 2:47 am

Interesting discovery, looking forward to follow-up on this one. Looks like they're all too close to the star to be habitable (though the uncertainties on the outer planet are quite large), maybe there's enough space between HIP 41378 f and the HZ for a planet to be stable there.
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty29th June 2016, 3:23 pm

A week ago, I posted an independent study of this system to Planet Hunters. Vanderburg emailed me not long after, commenting that the results I reached were quite similar to those in this paper. I had no idea it was so close to being put to the presses, however! Martti, the third name on the author list, is a prominent member at PH, and I congratulate him on the recognition.

As far as I am aware, this is the second-brightest K2 system in the V-band. It is also the highest multiplicity planetary system identified by K2 to date - if K2 observations had been at a different time, it is quite likely that at least one of the mono-transiters would have been missed, so there is certainly some serendipity in these results

As it is bright and observable from most of the Earth, this is an exemplary system for planet characterisation. Mass measurements for all planets are plausible with modern technology, and atmospheric observations will be possible in the near future. In particular this is currently the brightest star with a transiting AU Jovian, so f is an excellent target for many projects; observing its Rossiter-McLaughlin effect, determining its oblateness, attempting to detect moons, to name a few. Determining the outer orbital periods is a priority, and I understand dedicated RV observations are underway.
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty8th July 2016, 3:06 pm

HIP 41378 becomes K2-93. Apparently ~50 systems are to be confirmed in the near future.
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty30th September 2018, 8:35 pm

A couple of updates to this system (which I just split from the K2 News and Results thread). The system was observed again by K2 in Campaign 18, revealing new transits of the d and f planets. This has allowed for discrete limits on what their orbital periods are. There's also TTV in the orbit of the c planet detected by Spitzer + Kepler-K2, which could be from the d, e or f planet.

A Discrete Set of Possible Transit Ephemerides for Two Long Period Gas Giants Orbiting HIP 41378
https://arxiv.org/abs/1809.10688

Revisiting the HIP41378 system with K2 and Spitzer
https://arxiv.org/abs/1809.11116

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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty18th November 2019, 9:53 pm

New updates on this system! Including RV mass measurements.

Asteroseismology of the Multiplanet System K2-93
https://arxiv.org/abs/1911.07519

Quote :
We revisit the analysis of the bright multiplanet system K2-93, discovered with data taken by the K2 mission. This system contains five identified planets ranging in size from sub-Neptune to Jupiter size. The K2 data available at the discovery of the system only showed single transits for the three outer planets, which allowed weak constraints to be put on their periods. As these planets are interesting candidates for future atmospheric studies, a better characterization of the host star and tighter constraints on their orbital periods are essential. Using new data from the K2 mission taken after the discovery of the system, we perform an asteroseismic characterization of the host star. We are able to place strong constraints on the stellar parameters and obtain a value for the stellar mass of 1.22+0.03−0.02M⊙, a stellar radius of 1.30±0.01R⊙, and an age of 2.07+0.36−0.27 Gyr. Put together with the additional transits identified for two of the three outer planets, we constrain the orbital periods of the outer planets and provide updated estimates for the stellar reflex velocities induced by the planets.


An extremely low-density and temperate giant exoplanet
https://arxiv.org/abs/1911.07355

Quote :
Transiting extrasolar planets are key objects in the study of the formation, migration, and evolution of planetary systems. In particular, the exploration of the atmospheres of giant planets, through transmission spectroscopy or direct imaging, has revealed a large diversity in their chemical composition and physical properties. Studying these giant planets allows one to test the global climate models that are used for the Earth and other solar system planets. However, these studies are mostly limited either to highly-irradiated transiting giant planets or directly-imaged giant planets at large separations. Here we report the physical characterisation of the planets in a bright multi-planetary system (HIP41378) in which the outer planet, HIP41378 f is a Saturn-sized planet (9.2 ± 0.1 R⊕) with an anomalously low density of 0.09 ± 0.02 g cm−3 that is not yet understood. Its equilibrium temperature is about 300 K. Therefore, it represents a planet with a mild temperature, in between the hot Jupiters and the colder giant planets of the Solar System. It opens a new window for atmospheric characterisation of giant exoplanets with a moderate irradiation, with the next-generation space telescopes such as JWST and ARIEL as well as the extremely-large ground-based telescopes. HIP41378 f is thus an important laboratory to understand the effect of the irradiation on the physical properties and chemical composition of the atmosphere of planets.

Additionally, a sixth (non-transiting) planet is detected from TTVs. HIP 41378 g has a 62-day period and is in a 2:1 MMR with the c planet. They suspect it's possible for the extremely low density of HIP 41378 f to be explained by a ring system propping up the transit depth and refer to a paper in-prep to explore this hypothesis. Could also be a "super-puff" planet like Kepler-51d or Kepler-79d.

Amusingly (not really) the paper refers to the system as both HIP 41378 and HIP 41738.

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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty19th November 2019, 3:53 pm

The low density is really weird. A ring system would be a nice result, might lend some plausibility to all those artists' impressions of Earthlike moons with ringed gas giants hanging in the sky. I wonder how this suggestion will hold up, but I won't get my hopes up just yet.
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty20th November 2019, 7:00 pm

Twitter :

HIP 41378 - Multi-Planet System from K2 96148f1325972771
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty24th November 2019, 4:20 pm

Global observing campaign going on late tonight/tomorrow to observe the transit of HIP 41378 f.

HIP 41378 - Multi-Planet System from K2 EKDwmVzXUAAfm9u?format=jpg&name=large

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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty25th November 2019, 9:57 am



Twitter :


Alexandre Santerne
@a_santerne

#HIP41378 f: really bad news from
@ESO and @LowellObs ! No observation with #ESPRESSO because of a mistake from the support astronomers. No observations with the #DiscoveryChannel telescope because of a drive failure.

it will be OK with @CARMENES_exopl, #SOPHIE & #PARAS
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty26th November 2019, 10:53 am

https://twitter.com/a_santerne/status/1199199472191967233

Quote :
End of the night here at #HauteProvence observatory @OsuPytheas 🔭. What I can confirm now regarding #HIP41378 f is that:
- the transit is confirmed (hence its period of 542d) ✅
- the egress occurred exactly as the predicted time so no large TTVs ✅
- the planet is prograde ✅
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty26th February 2020, 10:22 pm

Can planetary rings explain the extremely low density of HIP 41378f?
https://arxiv.org/abs/2002.11422

Quote :
The presence of rings around a transiting planet can cause its radius to be overestimated and lead to an underestimation of its density if the mass is known. We employ a Bayesian framework to show that the anomalously low density (∼0.09 g cm−3) of the transiting long-period planet HIP41378f might be due to the presence of opaque circum-planetary rings. Given our adopted model priors and data from the K2 mission, we find the statistical evidence for the ringed planet scenario to be comparable to that of the planet-only scenario. The ringed planet solution suggests a larger planetary density of ∼1.23gcm−3 similar to Uranus. The associated ring extends from 1.05 to 2.59 times the planetary radius and is inclined away from the sky-plane by ∼25o. Future high-precision transit observations of HIP41378f would be necessary to confirm/dismiss the presence of planetary rings.

HIP 41378 - Multi-Planet System from K2 Hip41310

I am really not that convinced but we'll see. At least this is easily testable.

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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty27th February 2020, 7:18 am

If it would be case like Saturn planet radius will be decreased significantly
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty28th February 2020, 3:34 pm

That looks like quite a substantial axial tilt for the planet... yet another way it would be similar to Uranus.

Sirius_Alpha wrote:
I am really not that convinced but we'll see. At least this is easily testable.
Easily testable might be a bit optimistic... although it's nice to see there are at least some potential methods that might work, it sounds like they might be pushing the limits of what is possible with the available instruments.
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty28th February 2020, 7:34 pm

My thought that it would be "easily" testable comes from the first figure in the above screenshot, showing a predicted far-infrared transit light curve if the ring model is correct. It's quite a bit shallower, without the rings contributing to the ΔF.

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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty11th January 2022, 6:15 pm

Sirius_Alpha wrote:
Can planetary rings explain the extremely low density of HIP 41378f?
https://arxiv.org/abs/2002.11422

Quote :
The presence of rings around a transiting planet can cause its radius to be overestimated and lead to an underestimation of its density if the mass is known. We employ a Bayesian framework to show that the anomalously low density (∼0.09 g cm−3) of the transiting long-period planet HIP41378f might be due to the presence of opaque circum-planetary rings. Given our adopted model priors and data from the K2 mission, we find the statistical evidence for the ringed planet scenario to be comparable to that of the planet-only scenario. The ringed planet solution suggests a larger planetary density of ∼1.23gcm−3 similar to Uranus. The associated ring extends from 1.05 to 2.59 times the planetary radius and is inclined away from the sky-plane by ∼25o. Future high-precision transit observations of HIP41378f would be necessary to confirm/dismiss the presence of planetary rings.

HIP 41378 - Multi-Planet System from K2 Hip41310

I am really not that convinced but we'll see. At least this is easily testable.

It could. cyclops

The First Near-Infrared Transmission Spectrum of HIP 41378 f, a Low-Mass Temperate Jovian World in a Multi-Planet System

Quote :
We present a near-infrared transmission spectrum of the long period (P=542 days), temperate (Teq=294 K) giant planet HIP 41378 f obtained with the Wide-Field Camera 3 (WFC3) instrument aboard the Hubble Space Telescope (HST). With a measured mass of 12 ± 3 M⊕ and a radius of 9.2 ± 0.1 R⊕, HIP 41378 f has an extremely low bulk density (0.09 ± 0.02 g/cm3). We measure the transit depth with a median precision of 84 ppm in 30 spectrophotometric channels with uniformly-sized widths of 0.018 microns. Within this level of precision, the spectrum shows no evidence of absorption from gaseous molecular features between 1.1-1.7 microns. Comparing the observed transmission spectrum to a suite of 1D radiative-convective-thermochemical-equilibrium forward models, we rule out clear, low-metallicity atmospheres and find that the data prefer high-metallicity atmospheres or models with an additional opacity source such as high-altitude hazes and/or circumplanetary rings. We explore the ringed scenario for this planet further by jointly fitting the K2 and HST light curves to constrain the properties of putative rings. We also assess the possibility of distinguishing between hazy, ringed, and high-metallicity scenarios at longer wavelengths with JWST. HIP 41378 f provides a rare opportunity to probe the atmospheric composition of a cool giant planet spanning the gap between the Solar System giants, directly imaged planets, and the highly-irradiated hot Jupiters traditionally studied via transit spectroscopy.

A circumplanetary ring still seems to be a likely explanation to apparent contrast between low mass and large radius of the planet.
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty13th March 2022, 12:29 pm

Does anyone know if HIP 41378 g is considered confirmed or not? The relevant paper doesn't seem to have been published, and the comment on the arXiv paper says "The results have not been peer-reviewed yet". From what I can tell, subsequent studies haven't really mentioned it.
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty1st April 2022, 7:04 am

Decided to brave the waters of April 1st arXiv...

Belkovski et al. "A Multi-Planet System's Sole Super-Puff: Exploring Allowable Physical Parameters for the Cold Super-Puff HIP 41378 f"
https://arxiv.org/abs/2203.17180

Quote :
In this paper, we attempted to find a feasible structure for HIP 41378 f which does not require invoking the existence of planetary rings. Although hydrostatic solutions do exist, these solutions are not consistent with the paradigm of core accretion due to the combination of core mass and envelope fraction. Because of this, there is no easy explanation for how HIP 41378 f could have formed with its measured parameters. Our analysis provides support for the hypothesis of Piro & Vissapragada (2020) and Akinsanmi et al. (2020) that HIP 41378 f’s anomalously low density could be due to the presence of planetary rings.

And on the subject of HIP 41378 g...

Quote :
In this work, we do not consider HIP 41378 g, which is a low signal-to-noise ratio detection and is only detected in the RVs of Santerne et al. (2019). As HIP 41378 g does not have a measured radius or density, we cannot place meaningful constraints on its physical structure.
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HIP 41378 - Multi-Planet System from K2 Empty
PostSubject: Re: HIP 41378 - Multi-Planet System from K2   HIP 41378 - Multi-Planet System from K2 Empty26th October 2022, 1:06 pm

Rossiter-McLaughlin effect measured for HIP 41378 d. Orbit appears to be prograde, with λ=57.1+26.4−17.9°.

Grouffal et al. "Rossiter-McLaughlin detection of the 9-month period transiting exoplanet HIP41378 d"
https://arxiv.org/abs/2210.14125

In addition, they confirm that the orbital period of this planet is 278 days.

Incidentally I hadn't realised how much ambiguity there is in the orbital periods of the outer planets of this system. I'm not entirely sure that planet e has a reliable period either, although it seems recent papers tend to use the estimate of 369±10 days from the unpublished Santerne et al. (arXiv 2019) paper.
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