Estimating the magnetic field strength in hot Jupiters

Estimating the magnetic field strength in hot Jupiters

Authors:

Yadav et al

Abstract:
A large fraction of known Jupiter like exoplanets are inflated as compared to Jupiter. These "hot" Jupiters orbit close to their parent star and are bombarded with intense starlight. Many theories have been proposed to explain their radius inflation and several suggest that a small fraction of the incident starlight is injected in to the planetary interior which helps to puff up the planet. How will such energy injection affect the planetary dynamo? In this Letter, we estimate the surface magnetic field strength of hot Jupiters using scaling arguments that relate energy available in planetary interiors to the dynamo generated magnetic fields. We find that if we take into account the energy injected in the planetary interior that is sufficient to inflate hot Jupiters to observed radii, then the resulting dynamo should be able generate magnetic fields that are more than an order of magnitude stronger than the Jovian values. Our analysis highlights the potential fundamental role of the stellar light in setting the field strength in hot Jupiters.

Seeing double with K2: Testing re-inflation with two remarkably similar planets around red giant branch stars

Seeing double with K2: Testing re-inflation with two remarkably similar planets around red giant branch stars

Authors:

Grunblatt et al

Abstract:

Determining the mechanism that causes anomalously large radii of strongly irradiated exoplanets has remained a puzzle since before the radius of an exoplanet was first measured. Here, we report the discovery of a new inflated gas giant planet found with the NASA K2 Mission, EPIC2287.01, and a revised mass for the previously discovered inflated gas giant K2-97b. These planets orbit at moderate (~9 day) orbital distances around host stars which recently evolved into red giants. We constrain the irradiation history of these systems using a model constrained by parameters determined by asteroseismology and Keck/HIRES spectroscopy and radial velocity measurements. We find that both planets resided near the planet inflation irradiation threshold during their main sequence lifetimes. We also find that the current irradiation of these planets is typical for the population of planets with similar radii, but the main sequence irradiation of these planets would have been atypically small for the population of planets inflated to their size. Our precise constraints of the masses and radii of the stars and planets in this system allow us to constrain the planetary heating efficiencies of both systems to 0.03% +0.03%/-0.02%. These results are consistent with a planet re-inflation scenario, but suggest the efficiency of planet re-inflation is significantly lower than previously theorized. Finally, we discuss the similarity of both planetary systems (agreement within 10% of stellar masses and radii, and planet masses, radii, and orbital periods) and speculate that this may be due to selection bias in searching for planets around evolved stars.

EPIC 228735255b: an eccentric 6.57 day transiting hot Jupiter in Virgo

EPIC 228735255b - An eccentric 6.57 day transiting hot Jupiter in Virgo

Authors:

Giles et al

Abstract:

We present the discovery of EPIC 228735255b, a P= 6.57 days Jupiter-mass (MP=1.019±0.070 MJup) planet transiting a V=12.5 (G5-spectral type) star in an eccentric orbit (e=0.120+0.056−0.046) detected using a combination of K2 photometry and ground-based observations. With a radius of 1.095±0.018RJup the planet has a bulk density of 0.726±0.062ρJup. The host star has a [Fe/H] of 0.12±0.045, and from the K2 light curve we find a rotation period for the star of 16.3±0.1 days. This discovery is the 9th hot Jupiter from K2 and highlights K2's ability to detect transiting giant planets at periods slightly longer than traditional, ground-based surveys. This planet is slightly inflated, but much less than others with similar incident fluxes. These are of interest for investigating the inflation mechanism of hot Jupiters.

HAT-P-65b and HAT-P-66b: Two Transiting Inflated Hot Jupiters and Observational Evidence for the Re-Inflation of Close-In Giant Planets

HAT-P-65b and HAT-P-66b: Two Transiting Inflated Hot Jupiters and Observational Evidence for the Re-Inflation of Close-In Giant Planets

Authors:

Hartman et al

Abstract:

We present the discovery of the transiting exoplanets HAT-P-65b and HAT-P-66b, with orbital periods of 2.6055 d and 2.9721 d, masses of 0.527±0.083 MJ and 0.783±0.057 MJ and inflated radii of 1.89±0.13 RJ and 1.59+0.16−0.10 RJ, respectively. They orbit moderately bright (V=13.145±0.029, and V=12.993±0.052) stars of mass 1.212±0.050 M⊙ and 1.255+0.107−0.054 M⊙. The stars are at the main sequence turnoff. While it is well known that the radii of close-in giant planets are correlated with their equilibrium temperatures, whether or not the radii of planets increase in time as their hosts evolve and become more luminous is an open question. Looking at the broader sample of well-characterized close-in transiting giant planets, we find that there is a statistically significant correlation between planetary radii and the fractional ages of their host stars, with a false alarm probability of only 0.0041%. We find that the correlation between the radii of planets and the fractional ages of their hosts is fully explained by the known correlation between planetary radii and their present day equilibrium temperatures, however if the zero-age main sequence equilibrium temperature is used in place of the present day equilibrium temperature then a correlation with age must also be included to explain the planetary radii. This suggests that, after contracting during the pre-main-sequence, close-in giant planets are re-inflated over time due to the increasing level of irradiation received from their host stars. Prior theoretical work indicates that such a dynamic response to irradiation requires a significant fraction of the incident energy to be deposited deep within the planetary interiors.

KELT-12b: A Highly Inflated Hot Jupiter Transiting a Mildly Evolved Hot Star

KELT-12b: A P∼5 Day, Highly Inflated Hot Jupiter Transiting a Mildly Evolved Hot Star

Authors:

Stevens et al

Abstract:

We report the discovery of KELT-12b, a highly inflated Jupiter-mass planet transiting a mildly evolved host star. We identified the initial transit signal in the KELT-North survey data and established the planetary nature of the companion through precise follow-up photometry, high-resolution spectroscopy, precise radial velocity measurements, and high-resolution adaptive optics imaging. Our preferred best-fit model indicates that the V=10.64 host, TYC 2619-1057-1, has Teff=6278±51 K, logg⋆=3.89+0.054−0.051, and [Fe/H] = 0.19+0.083−0.085, with an inferred mass M⋆=1.59+0.071−0.091M⊙ and radius R⋆=2.37±0.18R⊙. The planetary companion has MP=0.95±0.14MJ, RP=1.79+0.18−0.17RJ, loggP=2.87+0.097−0.098, and density ρP=0.21+0.075−0.054 g cm−3, making it one of the most inflated giant planets known. The time of inferior conjunction in BJDTDB is 2457088.692055±0.0009 and the period is P=5.0316144±0.0000306 days. Despite the relatively large separation of ∼0.07 AU implied by its ∼5.03-day orbital period, KELT-12b receives significant flux of 2.93+0.33−0.30×109 erg s−1 cm−2 from its host. We compare the radii and insolations of transiting giant planets around hot (Teff≥6250 K) and cool stars, noting that the observed paucity of known transiting giants around hot stars with low insolation is likely due to selection effects. We underscore the significance of long-term ground-based monitoring of hot stars and space-based targeting of hot stars with the Transiting Exoplanet Survey Satellite (TESS) to search for inflated giants in longer-period orbits.

KELT-11b/HD 93396b: a Highly Inflated hot Saturn Orbiting a subGiant Host Star

KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V=8 Subgiant HD 93396

Authors:

Pepper et al

Abstract:

We report the discovery of a transiting exoplanet, KELT-11b, orbiting the bright (V=8.0) subgiant HD 93396. A global analysis of the system shows that the host star is an evolved subgiant star with Teff=5370±51 K, M∗=1.438+0.061−0.052M⊙, R∗=2.72+0.21−0.17R⊙, log g∗=3.727+0.040−0.046, and [Fe/H]=0.180±0.075. The planet is a low-mass gas giant in a P=4.736529±0.00006 day orbit, with MP=0.195±0.018MJ, RP=1.37+0.15−0.12RJ, ρP=0.093+0.028−0.024 g cm−3, surface gravity log gP=2.407+0.080−0.086, and equilibrium temperature Teq=1712+51−46 K. KELT-11 is the brightest known transiting exoplanet host in the southern hemisphere by more than a magnitude, and is the 6th brightest transit host to date. The planet is one of the most inflated planets known, with an exceptionally large atmospheric scale height (2763 km), and an associated size of the expected atmospheric transmission signal of 5.6%. These attributes make the KELT-11 system a valuable target for follow-up and atmospheric characterization, and it promises to become one of the benchmark systems for the study of inflated exoplanets.

WASP-92b, WASP-93b and WASP-118b: Three new hot Jupiters

WASP-92b, WASP-93b and WASP-118b: Three new transiting close-in giant planets

Authors:

Hay et al

Abstract:

We present the discovery of three new transiting giant planets, first detected with the WASP telescopes, and establish their planetary nature with follow up spectroscopy and ground-based photometric lightcurves. WASP-92 is an F7 star, with a moderately inflated planet orbiting with a period of 2.17 days, which has Rp=1.461±0.077RJ and Mp=0.805±0.068MJ. WASP-93b orbits its F4 host star every 2.73 days and has Rp=1.597±0.077RJ and Mp=1.47±0.029MJ. WASP-118b also has a hot host star (F6) and is moderately inflated, where Rp=1.440±0.036RJ and Mp=0.513±0.041MJ and the planet has an orbital period of 4.05 days. They are bright targets (V = 13.18, 10.97 and 11.07 respectively) ideal for further characterisation work, particularly WASP-118b, which is being observed by K2 as part of campaign 8. WASP-93b is expected to be tidally migrating outwards, which is divergent from the tidal behaviour of the majority of hot Jupiters discovered.

EPIC 211351816.01: A (Re-?)Inflated Planet Orbiting a Red Giant Star

EPIC 211351816.01: A (Re-?)Inflated Planet Orbiting a Red Giant Star

Authors:

Grunblatt et al

Abstract:

Giant planets with high incident fluxes have been observed with radii larger than thermal evolution models would allow. Although these inflated planets have been known for almost two decades, it is unclear whether their inflation is caused by deposition of energy from the host star, or inhibited cooling of the planet. These processes can be distinguished if the planet becomes highly irradiated only when the host star evolves onto the red giant branch. We report the discovery of EPIC 211351816.01, a 1.27 +/- 0.09 RJ, 1.10 +/- 0.11 MJ planet orbiting a 4.20 +/- 0.14 Rsun, 1.16 +/- 0.12 Msun red giant star with an orbital period of 8.4 days. We precisely constrained stellar and planetary parameters by combining asteroseismology, spectroscopy, and granulation noise modeling along with transit and radial velocity measurements. Our calculations suggest the incident flux on this planet was ~200 +/- 100 times the flux on Earth while the star was on the main sequence, comparable to the suggested threshold flux for planet inflation. This suggests the planet was significantly less inflated in the past, and its current measured planet radius is inconsistent with delayed cooling since formation. Thus, this system provides the first clear evidence that planets are inflated directly from a process dependent on the incident stellar radiation rather than by delayed loss of heat from formation. Further studies of planets around red giant branch stars will confirm or contradict this inflation hypothesis, and may reveal a new class of re-inflated planets.

final paper with the exoplanet renamed K2-97b.

HAT-P-47b AND HAT-P-48b: Two Low Density Sub-Saturn-Mass Transiting Planets on the Edge of the Period--Mass Desert

HAT-P-47b AND HAT-P-48b: Two Low Density Sub-Saturn-Mass Transiting Planets on the Edge of the Period--Mass Desert

Authors:

Bakos et al

Abstract:

We report the discovery of two new transiting extrasolar planets orbiting moderately bright (V = 10.7 and 12.2 mag) F stars (masses of 1.39 Msun and 1.10 Msun, respectively). The planets have periods of P = 4.7322 d and 4.4087 d, and masses of 0.21 MJ and 0.17 MJ which are almost half-way between those of Neptune and Saturn. With radii of 1.31 RJ and 1.13 RJ, these very low density planets are the two lowest mass planets with radii in excess that of Jupiter. Comparing with other recent planet discoveries, we find that sub-Saturns (0.18MJ < Mp < 0.3MJ) and super-Neptunes (0.05MJ < Mp < 0.18MJ) exhibit a wide range of radii, and their radii exhibit a weaker correlation with irradiation than higher mass planets. The two planets are both suitable for measuring the Rossiter-McLaughlin effect and for atmospheric characterization. Measuring the former effect would allow an interesting test of the theory that star-planet tidal interactions are responsible for the tendency of close-in giant planets around convective envelope stars to be on low obliquity orbits. Both planets fall on the edge of the short period Neptunian desert in the semi-major axis-mass plane.

WASP-South transiting exoplanets: WASP-130b, WASP-131b, WASP-132b, WASP-139b, WASP-140b, WASP-141b & WASP-142b

WASP-South transiting exoplanets: WASP-130b, WASP-131b, WASP-132b, WASP-139b, WASP-140b, WASP-141b & WASP-142b

Authors:

Hellier et al

Abstract:

We describe seven new exoplanets transiting stars of V = 10.1 to 12.4.
WASP-130b is a "warm Jupiter" having an orbital period of 11.6 d, the longest yet found by WASP. It transits a V = 11.1, G6 star with [Fe/H] = +0.26. Warm Jupiters tend to have smaller radii than hot Jupiters, and WASP-130b is in line with this trend (1.23 Mjup; 0.89 Rjup).
WASP-131b is a bloated Saturn-mass planet (0.27 Mjup; 1.22 Rjup). Its large scale height coupled with the V = 10.1 brightness of its host star make the planet a good target for atmospheric characterisation.
WASP-132b is among the least irradiated and coolest of WASP planets, being in a 7.1-d orbit around a K4 star. It has a low mass and a modest radius (0.41 Mjup; 0.87 Rjup). The V = 12.4, [Fe/H] = +0.22 star shows a possible rotational modulation at 33 d.
WASP-139b is the lowest-mass planet yet found by WASP, at 0.12 Mjup and 0.80 Rjup. It is a "super-Neptune" akin to HATS-7b and HATS-8b. It orbits a V = 12.4, [Fe/H] = +0.20, K0 star. The star appears to be anomalously dense, akin to HAT-P-11.
WASP-140b is a 2.4-Mjup planet in a 2.2-d orbit that is both eccentric (e = 0.047) and with a grazing transit (b = 0.93) The timescale for tidal circularisation is likely to be the lowest of all known eccentric hot Jupiters. The planet's radius is large (1.4 Rjup), but uncertain owing to the grazing transit. The host star is a V = 11.1, [Fe/H] = +0.12, K0 dwarf showing a prominent 10.4-d rotational modulation. The dynamics of this system are worthy of further investigation.
WASP-141b is a typical hot Jupiter, being a 2.7 Mjup, 1.2 Rjup planet in a 3.3-d orbit around a V = 12.4, [Fe/H] = +0.29, F9 star.
WASP-142b is a typical bloated hot Jupiter (0.84 Mjup, 1.53 Rjup) in a 2.1-d orbit around a V = 12.3, [Fe/H] = +0.26, F8 star.

Inflated Hot Jupiter HAT-P-32b has Clouds and/or Haze

Transmission spectroscopy of HAT-P-32b with the LBT: confirmation of clouds/hazes in the planetary atmosphere

Authors:

Mallonn et al

Abstract:

Spectroscopic observations of a transit event of an extrasolar planet offer the opportunity to study the composition of the planetary atmosphere. We observed a transit of the inflated Hot Jupiter HAT-P-32b with MODS at the LBT to characterize its atmosphere from 3300 to 10000 AA. A time series of target and reference star spectra was binned in two broad-band wavelength channels, from which differential transit light curves were constructed. These broad-band light curves were used to confirm previous transit parameter determinations. To derive the planetary transmission spectrum with a resolution of R ~ 60, we created a chromatic set of 62 narrow-band light curves with an average wavelength width of about 100 AA. The spectrum was corrected for the third-light of a near-by M star, whose spectrum was resolved in the individual exposures. Additionally, we undertook a photometric monitoring campaign of the host star to correct for the influence of starspots. The transmission spectrum of HAT-P-32b shows no pressure-broadened absorption features from Na and K, which is interpreted by the presence of clouds or hazes in the planetary atmosphere. This result is in agreement to previous studies on the same planet. The presence of TiO in gas phase could be ruled out. We find a 2.8 sigma indication of increased absorption in the line core of potassium (KI~7699 AA). No narrow absorption features of Na and Halpha were detected. Furthermore, tentative indications were found for a slope of increasing opacity toward blue wavelengths from the near-IR to the near-UV with an amplitude of two scale heights. If confirmed by follow-up observations, it can be explained by aerosols either causing Mie scattering or causing Rayleigh scattering with an aerosol - gas scale height ratio below unity.

EPIC 210957318b & EPIC 212110888b: two inflated hot-Jupiters around Solar-type stars

EPIC210957318b and EPIC212110888b: two inflated hot-Jupiters around Solar-type stars

Authors:

Lillo-Box et al

Abstract:

We report the discovery of the two hot-Jupiters EPIC210957318b and EPIC212110888b (hereafter EPIC-318b and EPIC-888b, respectively). The two planets were detected transiting their main-sequence star with periods ∼ 4.099 and ∼ 2.996 days, in campaigns 4 and 5 of the extension of the Kepler mission, K2. Subsequent ground-based radial velocity follow-up with SOPHIE, HARPS-N and CAFE, established the planetary nature of the transiting objects. We analyzed the transit signal, radial velocity and spectral energy distributions of the two systems to characterize their properties. Both planets (EPIC-318b and EPIC-888b) are bloated hot-Jupiters (1.25 RJup and 1.33 RJup) around relatively bright (V =13.5 and V=11.5), slow rotating main-sequence (G8 and F9) stars. Thus, these systems are good candidates for detecting the Rossiter-MacLaughlin effect to measure their obliquity and for atmospheric studies.

EPIC-203771098b & EPIC-203771098c: Two Transiting hot low Density Sub-Saturns from K2

Two Transiting Low Density Sub-Saturns from K2

Authors:

Petigura et al

Abstract:

We report the discovery and confirmation of two sub-Saturn planets orbiting a bright (V = 11.3), metal-rich ([Fe/H] = 0.42 ± 0.04 dex) G3 dwarf in the K2 Campaign 2 field. The planets are 5.68 ± 0.56 Earth-radii and 7.82 ± 0.72 Earth-radii and have orbital periods of 20.8851 ± 0.0003 d and 42.3633±0.0006 d, near to the 2:1 mean-motion resonance. We obtained 32 radial velocities (RVs) with Keck/HIRES and detected the reflex motion due to EPIC-203771098b and c. These planets have masses of 21.0 ± 5.4 Earth-masses and 27.0 ± 6.9 Earth-masses, respectively. With low densities of 0.63 ± 0.25 g/cc and 0.31 ± 0.12 g/cc, respectively, the planets require thick envelopes of H/He to explain their large sizes and low masses. Interior structure models predict that the planets have fairly massive cores of 17.6 ± 4.3 Earth-masses and 16.1 ± 4.2 Earth-masses, respectively. They may have formed exterior to their present locations, accreted their H/He envelopes at large orbital distances, and migrated in as a resonant pair. The proximity to resonance, large transit depths, and host star brightness offer rich opportunities for TTV follow-up. Finally, the low surface gravities of the EPIC-203771098 planets make them favorable targets for transmission spectroscopy by HST, Spitzer, and JWST.

K2-25b (EPIC 210490365b): an Inflated hot Neptune Around an M Dwarf

Zodiacal Exoplanets In Time (ZEIT) I: A Neptune-sized planet orbiting an M4.5 dwarf in the Hyades Star Cluster

Authors:

Mann et al

Abstract:

Studying the properties of young planetary systems can shed light on how the dynamics and structure of planets evolve during their most formative years. Recent K2 observations of nearby young clusters (10-800 Myr) have enabled the discovery of such planetary systems. Here we report the discovery of a Neptune-sized planet transiting an M4.5 dwarf (EPIC 210490365) in the Hyades cluster (650-800 Myr). The lightcurve shows a strong periodic signal at 1.88 days, which we attribute to spot coverage and rotation. We confirm the planet host is a member of the Hyades by measuring the radial velocity of the system with the high-resolution near-infrared spectrograph IGRINS. This enables us to calculate a distance based on EPIC 210490365's kinematics and membership to the Hyades, which in turn provides a stellar radius and mass to 5-10%, better than what is currently possible for most Kepler M dwarfs (12-20%). We use the derived stellar density as a prior on fitting the K2 transit photometry, which provides weak constraints on eccentricity. Utilizing a combination of adaptive optics imaging and high-resolution spectra we rule out the possibility that the signal is due to a bound or background eclipsing binary, confirming the transits' planetary origin. EPIC 210490365b has a radius (3.43+0.95−0.31RE) much larger than older Kepler planets with similar orbital periods (3.484 days) and host-star masses (0.29M⊙). This suggests that close-in planets lose some of their atmospheres past the first few hundred Myr. Additional transiting planets around the Hyades, Pleiades, and Praesepe clusters from K2 will help confirm if this planet is atypical or representative of other close-in planets of similar age.

WASP-135b: an Inflated hot Jupiter in a 1.4 day Orbit Around a G5 Dwarf Star

WASP-135b: a highly irradiated, inflated hot Jupiter orbiting a G5V star

Authors:

Spake et al

Abstract:

We report the discovery of a new transiting planet from the WASP survey. WASP-135b is a hot Jupiter with a radius of 1.30 pm 0.09 Rjup, a mass of 1.90 pm 0.08 Mjup and an orbital period of 1.401 days. Its host is a Sun-like star, with a G5 spectral type and a mass and radius of 0.98 pm 0.06 Msun and 0.96 pm 0.05 Rsun respectively. The proximity of the planet to its host means that WASP-135b receives high levels of insolation, which may be the cause of its inflated radius. Additionally, we find weak evidence of a transfer of angular momentum from the planet to its star.

Reexamination of the Inflated hot Jupiters

On the Radius Anomaly of Hot Jupiters: Reexamination of the Possibility and Impact of Layered Convection

Authors:

Kurokawa et al

Abstract:

Observations have revealed that a significant number of hot Jupiters have anomalously large radii. Layered convection induced by compositional inhomogeneity has been proposed to account for the radius anomaly of hot Jupiters. To reexamine the impact of the compositional inhomogeneity, we perform an evolutionary calculation by determining convection regime at each evolutionary time step according to the criteria from linear analyses. It is shown that the impact is limited in the case of the monotonic gradient of heavy element abundance. The layered convection is absent for the first 1 Gyr from the formation of hot Jupiters and instead overturning convection develops. The super-adiabaticity of the temperature gradient is limited by the neutrally stable state for the Ledoux stability criterion. The effect of the increased mass of heavy elements essentially compensates the effect of the delayed contraction on the planetary radius caused by compositional inhomogeneity. In addition, even in the case where the layered convection is artificially imposed, this mechanism requires extremely thin layers (~ 10^1-10^3 cm) to account for the observed radius anomaly. The long-term stability of such thin layers remains to be studied. Therefore, if the criteria adopted in this paper are adequate, it might be difficult to explain the inflated radii of hot Jupiters by monotonic gradient of heavy element abundance alone.

Do hot Jupiters Inflate Because of Solar Wind/Magnetic Field Interaction Driven Heating?

Extended Heat Deposition in Hot Jupiters: Application to Ohmic Heating

Authors:

Ginzburg et al

Abstract:

Many giant exoplanets in close orbits have observed radii which exceed theoretical predictions. One suggested explanation for this discrepancy is heat deposited deep inside the atmospheres of these "hot Jupiters". Here, we study extended power sources which distribute heat from the photosphere to the deep interior of the planet. Our analytical treatment is a generalization of a previous analysis of localized "point sources". We model the deposition profile as a power law in the optical depth and find that planetary cooling and contraction halt when the internal luminosity (i.e. cooling rate) of the planet drops below the heat deposited in the planet's convective region. A slowdown in the evolutionary cooling prior to equilibrium is possible only for sources which do not extend to the planet's center. We estimate the Ohmic dissipation resulting from the interaction between the atmospheric winds and the planet's magnetic field, and apply our analytical model to Ohmically heated planets. Our model can account for the observed radii of many inflated planets which have equilibrium temperatures ≈1500 K−2500 K, and are inflated to a radius ≈1.5RJ. However, some extremely inflated planets remain unexplained by our model. We also argue that Ohmically inflated planets have already reached their equilibrium phase, and no longer contract. Following Wu & Lithwick (2013) who argued that Ohmic heating could only suspend and not reverse contraction, we calculate the time it takes Ohmic heating to re-inflate a cold planet to its equilibrium configuration. We find that while it is possible to re-inflate a cold planet, the re-inflation timescales are longer by a factor of ≈30 than the cooling time.

Effects on Inflated Hot Jupiters Like HD 209458b's Magnetic Field

ATMOSPHERE EXPANSION AND MASS LOSS OF CLOSE-ORBIT GIANT EXOPLANETS HEATED BY STELLAR XUV. II. EFFECTS OF PLANETARY MAGNETIC FIELD; STRUCTURING OF INNER MAGNETOSPHERE

Authors:

Khodachenko et al

Abstract:

This is the second paper in a series where we build a self-consistent model to simulate the mass-loss process of a close-orbit magnetized giant exoplanet, so-called hot Jupiter (HJ). In this paper we generalize the hydrodynamic (HD) model of an HJ's expanding hydrogen atmosphere, proposed in the first paper, to include the effects of intrinsic planetary magnetic field. The proposed self-consistent axisymmetric 2D magnetohydrodynamics model incorporates radiative heating and ionization of the atmospheric gas, basic hydrogen chemistry for the appropriate account of major species composing HJ's upper atmosphere and related radiative energy deposition, and ${{\rm{H}}}_{3}^{+}$ and Lyα cooling processes. The model also takes into account a realistic solar-type X-ray/EUV spectrum for calculation of intensity and column density distribution of the radiative energy input, as well as gravitational and rotational forces acting in a tidally locked planet–star system. An interaction between the expanding atmospheric plasma and an intrinsic planetary magnetic dipole field leads to the formation of a current-carrying magnetodisk that plays an important role for topology and scaling of the planetary magnetosphere. A cyclic character of the magnetodisk behavior, composed of consequent phases of the disk formation followed by the magnetic reconnection with the ejection of a ring-type plasmoid, has been discovered and investigated. We found that the mass-loss rate of an HD 209458b analog planet is weakly affected by the equatorial surface field less than 0.3 G, but is suppressed by an order of magnitude at the field of 1 G.

Re-inflated Warm Jupiters Around Red Giants

Re-inflated Warm Jupiters Around Red Giants

Authors:

Lopez et al

Abstract:

Since the discovery of the first transiting hot Jupiters, models have sought to explain the anomalously large radii of highly irradiated gas giants. We now know that the size of hot Jupiter radius anomalies scales strongly with a planet's level of irradiation and numerous models like tidal heating, ohmic dissipation, and thermal tides have since been developed to help explain these inflated radii. In general however, these models can be grouped into two broad categories: 1) models that directly inflate planetary radii by depositing a fraction of the incident irradiation into the interior and 2) models that simply slow a planet's radiative cooling allowing it to retain more heat from formation and thereby delay contraction. Here we present a new test to distinguish between these two classes of models. Gas giants orbiting at moderate orbital periods around post main sequence stars will experience enormous increases their irradiation as their host stars move up the sub-giant and red-giant branches. If hot Jupiter inflation works by depositing irradiation into the planet's deep interiors then planetary radii should increase in response to the increased irradiation. This means that otherwise non-inflated gas giants at moderate orbital periods less than 10 days can re-inflate as their host stars evolve. Here we explore the circumstances that can lead to the creation of these "re-inflated" gas giants and examine how the existence or absence of such planets can be used to place unique constraints of the physics of the hot Jupiter inflation mechanism. Finally, we explore the prospects for detecting this potentially important undiscovered population of planets.

KELT-4Ab: an Inflated hot Jupiter in a Hierarchical Trinary System

KELT-4Ab: An inflated Hot Jupiter transiting the bright (V~10) component of a hierarchical triple

Authors:

Eastman et al

Abstract:

We report the discovery of KELT-4Ab, an inflated, transiting Hot Jupiter orbiting the brightest component of a hierarchical triple stellar system. The host star is an F star with Teff=6206±75 K, logg=4.108±0.014, [Fe/H]=−0.116+0.065−0.069, M∗=1.201+0.067−0.061 M⊙, and R∗=1.610+0.078−0.068 R⊙. The best-fit linear ephemeris is BJDTDB=2456193.29157±0.00021+E(2.9895936±0.0000048). With a magnitude of V∼10, a planetary radius of 1.699+0.046−0.045 RJ, and a mass of 0.902+0.060−0.059 MJ, it is the brightest host among the population of inflated Hot Jupiters (RP>1.5RJ), making it a valuable discovery for probing the nature of inflated planets. In addition, its existence within a hierarchical triple and its proximity to Earth (210 pc) provides a unique opportunity for dynamical studies with continued monitoring with high resolution imaging and precision radial velocities. In particular, the motion of the binary stars around each other and of both stars around the primary star relative to the measured epoch in this work should be detectable when it rises in October 2015.