We report the X-ray detection of the low-mass K7V star WASP-43, which is orbited by a hot Jupiter in one of the closest exoplanet orbits known to date. The high mean density of the planet implies a ...massive core with ≈130 M⊕, yielding a heavy-element mass-fraction of 20%. From an 18 ks long XMM-Newton observation, we derive an X-ray luminosity of 6.7+3.5-3.3 × 1027 ergss-1, which puts WASP-43 among the active K-stars, which is compatible with its relatively young age derived in previous studies. The X-ray luminosity translates into a soft X-ray flux of (10.2 ± 5.4) × 103 erg cm-2 s-1 at the substellar point. According to our modeling, the combined X-ray and extreme ultraviolet flux may trigger mass-loss at a rate of up to ≈1012 gs-1 via energy-limited atmospheric escape. We infer that it is unlikely that the planet has lost more than 2.5% of its current mass through that channel and that activity-induced mass-loss has not substantially altered its evolution.
Context. Recently, the He I triplet at 10 830 Å was rediscovered as an excellent probe of the extended and possibly evaporating atmospheres of close-in transiting planets. This has already resulted ...in detections of this triplet in the atmospheres of a handful of planets, both from space and from the ground. However, while a strong signal is expected for the hot Jupiter HD 209458 b, only upper limits have been obtained so far. Aims. Our goal is to measure the helium excess absorption from HD 209458 b and assess the extended atmosphere of the planet and possible evaporation. Methods. We obtained new high-resolution spectral transit time-series of HD 209458 b using CARMENES at the 3.5 m Calar Alto telescope, targeting the He I triplet at 10 830 Å at a spectral resolving power of 80 400. The observed spectra were corrected for stellar absorption lines using out-of-transit data, for telluric absorption using the MOLECFIT software, and for the sky emission lines using simultaneous sky measurements through a second fibre. Results. We detect He I absorption at a level of 0.91 ± 0.10% (9 σ) at mid-transit. The absorption follows the radial velocity change of the planet during transit, unambiguously identifying the planet as the source of the absorption. The core of the absorption exhibits a net blueshift of 1.8 ± 1.3 km s−1. Possible low-level excess absorption is seen further blueward from the main absorption near the centre of the transit, which could be caused by an extended tail. However, this needs to be confirmed. Conclusions. Our results further support a close relation between the strength of planetary absorption in the helium triplet lines and the level of ionising, stellar X-ray, and extreme-UV irradiation.
Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the ...discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought.
Energy-limited escape revised Salz, M.; Schneider, P. C.; Czesla, S. ...
Astronomy and astrophysics (Berlin),
01/2016, Letnik:
585
Journal Article
Recenzirano
Odprti dostop
Gas planets in close proximity to their host stars experience photoevaporative mass loss. The energy-limited escape concept is generally used to derive estimates for the planetary mass-loss rates. ...Our photoionization hydrodynamics simulations of the thermospheres of hot gas planets show that the energy-limited escape concept is valid only for planets with a gravitational potential lower than log 10(−ΦG)< 13.11 erg g-1 because in these planets the radiative energy input is efficiently used to drive the planetary wind. Massive and compact planets with log 10(−ΦG) ≳ 13.6 erg g-1 exhibit more tightly bound atmospheres in which the complete radiative energy input is re-emitted through hydrogen Lyα and free-free emission. These planets therefore host hydrodynamically stable thermospheres. Between these two extremes the strength of the planetary winds rapidly declines as a result of a decreasing heating efficiency. Small planets undergo enhanced evaporation because they host expanded atmospheres that expose a larger surface to the stellar irradiation. We present scaling laws for the heating efficiency and the expansion radius that depend on the gravitational potential and irradiation level of the planet. The resulting revised energy-limited escape concept can be used to derive estimates for the mass-loss rates of super-Earth-sized planets as well as massive hot Jupiters with hydrogen-dominated atmospheres.
TPCI: the PLUTO-CLOUDY Interface Salz, M.; Banerjee, R.; Mignone, A. ...
Astronomy and astrophysics (Berlin),
04/2015, Letnik:
576
Journal Article
Recenzirano
Odprti dostop
We present an interface between the (magneto-) hydrodynamics code PLUTO and the plasma simulation and spectral synthesis code CLOUDY. By combining these codes, we constructed a new photoionization ...hydrodynamics solver: the PLUTO-CLOUDY Interface (TPCI), which is well suited to simulate photoevaporative flows under strong irradiation. The code includes the electromagnetic spectrum from X-rays to the radio range and solves the photoionization and chemical network of the 30 lightest elements. TPCI follows an iterative numerical scheme: first, the equilibrium state of the medium is solved for a given radiation field by CLOUDY, resulting in a net radiative heating or cooling. In the second step, the latter influences the (magneto-) hydrodynamic evolution calculated by PLUTO. Here, we validated the one-dimensional version of the code on the basis of four test problems: photoevaporation of a cool hydrogen cloud, cooling of coronal plasma, formation of a Strömgren sphere, and the evaporating atmosphere of a hot Jupiter. This combination of an equilibrium photoionization solver with a general MHD code provides an advanced simulation tool applicable to a variety of astrophysical problems.
There is a large body of evidence that the hippocampus is involved in temporal aspects of memory. It remains unclear what neural processes within the hippocampus contribute to this ability. The ...following experiments aim to quantify and qualify these neural processes while rats perform temporal memory tasks. First we examined the firing of neurons in the hippocampus while rats compared a current series of odors to a learned sequence of odors. We found evidence of neural correlates which might represent whether a stimulus odor was in the correct ordinal sequence or not. Next we examined the delay intervals in between learned sequences of events with the goal of identifying the origin of “time cells” in the hippocampus. We used a delayed alternating T-maze task that our lab has used before to record time cells in area CA1 of the hippocampus. We found time cells in CA3, one of the major inputs to CA1 and demonstrated that they behave in many ways like place cells previously observed in these two regions. Time cells had previously been reported to occur only when an animal is engaged in a task with memory load. We demonstrated that memory load isn't necessary to observe time cells. Our observations of the similarities between place and time cells led us to conjecture that the hippocampus might process space and time similarly. In a final study I examined time cell firing properties with an aim at constraining models of time cells. We defined time cells in several ways including a new methodology that is promising as a future unbiased selection criteria. All of our findings help further elucidate several different ways that neural coding in the hippocampus contributes to temporal processing.
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