390 research outputs found
Young planets under extreme UV irradiation. I. Upper atmosphere modelling of the young exoplanet K2-33b
The K2-33 planetary system hosts one transiting ~5 R_E planet orbiting the
young M-type host star. The planet's mass is still unknown, with an estimated
upper limit of 5.4 M_J. The extreme youth of the system (<20 Myr) gives the
unprecedented opportunity to study the earliest phases of planetary evolution,
at a stage when the planet is exposed to an extremely high level of high-energy
radiation emitted by the host star. We perform a series of 1D hydrodynamic
simulations of the planet's upper atmosphere considering a range of possible
planetary masses, from 2 to 40 M_E, and equilibrium temperatures, from 850 to
1300 K, to account for internal heating as a result of contraction. We obtain
temperature profiles mostly controlled by the planet's mass, while the
equilibrium temperature has a secondary effect. For planetary masses below 7-10
M_E, the atmosphere is subject to extremely high escape rates, driven by the
planet's weak gravity and high thermal energy, which increase with decreasing
mass and/or increasing temperature. For higher masses, the escape is instead
driven by the absorption of the high-energy stellar radiation. A rough
comparison of the timescales for complete atmospheric escape and age of the
system indicates that the planet is more massive than 10 M_E.Comment: 11 pages, 7 figure
A grid of upper atmosphere models for 1--40 MEARTH planets: application to CoRoT-7 b and HD219134 b,c
There is growing observational and theoretical evidence suggesting that
atmospheric escape is a key driver of planetary evolution. Commonly, planetary
evolution models employ simple analytic formulae (e.g., energy limited escape)
that are often inaccurate, and more detailed physical models of atmospheric
loss usually only give snapshots of an atmosphere's structure and are difficult
to use for evolutionary studies. To overcome this problem, we upgrade and
employ an already existing upper atmosphere hydrodynamic code to produce a
large grid of about 7000 models covering planets with masses 1 - 39 Earth mass
with hydrogen-dominated atmospheres and orbiting late-type stars. The modeled
planets have equilibrium temperatures ranging between 300 and 2000 K. For each
considered stellar mass, we account for three different values of the
high-energy stellar flux (i.e., low, moderate, and high activity). For each
computed model, we derive the atmospheric temperature, number density, bulk
velocity, X-ray and EUV (XUV) volume heating rates, and abundance of the
considered species as a function of distance from the planetary center. From
these quantities, we estimate the positions of the maximum dissociation and
ionisation, the mass-loss rate, and the effective radius of the XUV absorption.
We show that our results are in good agreement with previously published
studies employing similar codes. We further present an interpolation routine
capable to extract the modelling output parameters for any planet lying within
the grid boundaries. We use the grid to identify the connection between the
system parameters and the resulting atmospheric properties. We finally apply
the grid and the interpolation routine to estimate atmospheric evolutionary
tracks for the close-in, high-density planets CoRoT-7 b and HD219134 b,c...Comment: 21 pages, 4 Tables, 15 Figure
Skin lesions in alpacas and llamas with low zinc and copper status - a preliminary report
WASP-157b, a Transiting Hot Jupiter Observed with K2
We announce the discovery of the transiting hot Jupiter WASP-157b in a 3.95-d
orbit around a V = 12.9 G2 main-sequence star. This moderately inflated planet
has a Saturn-like density with a mass of M and a
radius of R. We do not detect any rotational or
phase-curve modulations, nor the secondary eclipse, with conservative
semi-amplitude upper limits of 250 and 20 ppm, respectively.Comment: 6 pages, 5 figures and 4 tables. Accepted for publication in PAS
WASP-120b, WASP-122b and WASP-123b: Three newly discovered planets from the WASP-South survey
We present the discovery by the WASP-South survey of three planets transiting
moderately bright stars (V ~ 11). WASP-120b is a massive (5.0MJup) planet in a
3.6-day orbit that we find likely to be eccentric (e = 0.059+0.025-0.018)
around an F5 star. WASP-122b is a hot-Jupiter (1.37MJup, 1.79RJup) in a 1.7-day
orbit about a G4 star. Our predicted transit depth variation cause by the
atmosphere of WASP-122b suggests it is well suited to characterisation.
WASP-123b is a hot-Jupiter (0.92MJup, 1.33RJup) in a 3.0-day orbit around an
old (~ 7 Gyr) G5 star.Comment: 15 pages, 10 figures, 5 table
WASP-117b: a 10-day-period Saturn in an eccentric and misaligned orbit
We report the discovery of WASP-117b, the first planet with a period beyond
10 days found by the WASP survey. The planet has a mass of , a radius of and is in
an eccentric (), ~d orbit around
a main-sequence F9 star. The host star's brightness (V=10.15 mag) makes
WASP-117 a good target for follow-up observations, and with a periastron
planetary equilibrium temperature of K and a low
planetary mean density () it is
one of the best targets for transmission spectroscopy among planets with
periods around 10 days. From a measurement of the Rossiter-McLaughlin effect,
we infer a projected angle between the planetary orbit and stellar spin axes of
deg, and we further derive an orbital obliquity of deg. Owing to the large orbital separation, tidal forces
causing orbital circularization and realignment of the planetary orbit with the
stellar plane are weak, having had little impact on the planetary orbit over
the system lifetime. WASP-117b joins a small sample of transiting giant planets
with well characterized orbits at periods above ~8 days.Comment: To appear in A&
The Kepler-11 system: evolution of the stellar high-energy emission and {initial planetary} atmospheric mass fractions
The atmospheres of close-in planets are strongly influenced by mass loss
driven by the high-energy (X-ray and extreme ultraviolet, EUV) irradiation of
the host star, particularly during the early stages of evolution. We recently
developed a framework to exploit this connection and enable us to recover the
past evolution of the stellar high-energy emission from the present-day
properties of its planets, if the latter retains some remnants of their
primordial hydrogen-dominated atmospheres. Furthermore, the framework can also
provide constraints on planetary initial atmospheric mass fractions. The
constraints on the output parameters improve when more planets can be
simultaneously analysed. This makes the Kepler-11 system, which hosts six
planets with bulk densities between 0.66 and 2.45g cm^{-3}, an ideal target.
Our results indicate that the star has likely evolved as a slow rotator (slower
than 85\% of the stars with similar masses), corresponding to a high-energy
emission at 150 Myr of between 1-10 times that of the current Sun. We also
constrain the initial atmospheric mass fractions for the planets, obtaining a
lower limit of 4.1% for planet c, a range of 3.7-5.3% for planet d, a range of
11.1-14% for planet e, a range of 1-15.6% for planet f, and a range of 4.7-8.7%
for planet g assuming a disc dispersal time of 1 Myr. For planet b, the range
remains poorly constrained. Our framework also suggests slightly higher masses
for planets b, c, and f than have been suggested based on transit timing
variation measurements. We coupled our results with published planet atmosphere
accretion models to obtain a temperature (at 0.25 AU, the location of planet f)
and dispersal time of the protoplanetary disc of 550 K and 1 Myr, although
these results may be affected by inconsistencies in the adopted system
parameters.Comment: 8 pages, 3 figure
A low-density hot Jupiter in a near-aligned, 4.5-day orbit around a = 10.8, F5V star
We report the independent discovery and characterisation of a hot Jupiter in
a 4.5-d, transiting orbit around the star TYC 7282-1298-1 ( = 10.8, F5V).
The planet has been pursued by the NGTS team as NGTS-2b and by ourselves as
WASP-179b. We characterised the system using a combination of photometry from
WASP-South and TRAPPIST-South, and spectra from CORALIE (around the orbit) and
HARPS (through the transit). We find the planet's orbit to be nearly aligned
with its star's spin. From a detection of the Rossiter-McLaughlin effect, we
measure a projected stellar obliquity of . From
line-profile tomography of the same spectra, we measure . We find the planet to have a low density ( = 0.67
0.09 , = 1.54 0.06 ), which, along
with its moderately bright host star, makes it a good target for transmission
spectroscopy. We find a lower stellar mass ( = )
than reported by the NGTS team ( = ), though the
difference is only .Comment: Submitted to AJ. 9 pages, 6 figures, 5 table
WASP-86b and WASP-102b: super-dense versus bloated planets
We report the discovery of two transiting planetary systems: a super dense, sub-Jupiter mass planet WASP-86b (Mpl = 0.82 ± 0.06 MJ; Rpl = 0.63 ± 0.01 RJ), and a bloated, Saturn-like planet WASP-102b (Mpl = 0.62 ± 0.04 MJ; Rpl = 1.27 ± 0.03 RJ). They orbit their
host star every ∼5.03, and ∼2.71 days, respectively. The planet hosting WASP-86 is a F7 star (Teff = 6330±110 K, [Fe/H] = +0.23 ± 0.14 dex, and age ∼0.8–1 Gyr); WASP-102 is a G0 star (Teff = 5940±140 K, [Fe/H] = −0.09± 0.19 dex, and age ∼1 Gyr). These two systems highlight the diversity of planetary radii over similar masses for giant planets with masses between Saturn and Jupiter. WASP-102b shows a larger than model-predicted radius, indicating that the planet is receiving a strong incident flux which contributes to the inflation of its radius. On the other hand, with a density of ρpl = 3.24± 0.3 ρJ, WASP-86b is the densest gas giant planet among
planets with masses in the range 0.05 Mpl J. With a stellar mass of 1.34 M⊙ and [Fe/H]= +0.23 dex, WASP-86 could host additional massive and dense planets given that its protoplanetary disc is expected to also have been enriched with heavy elements. In order to match WASP-86b’s density, an extrapolation of theoretical models predicts a planet composition of more than 80% in heavy elements (whether confined in a core or mixed in the envelope). This fraction corresponds to a core mass of approximately 210M⊕ for WASP-86b’s mass of Mpl∼260 M⊕. Only planets with masses larger than about 2 MJ have larger densities than that of WASP-86b, making it exceptional in its mass range
- …