26 research outputs found
A Temperature Trend for Clouds and Hazes in Exoplanets Atmospheres
The transmission spectra of exoplanet atmospheres observed with the Hubble
Space Telescope (HST) in the near-infrared range (1.1-1.65m) frequently
show evidence for some combination of clouds and hazes. Identification of
systematic trends in exoplanet clouds and hazes is potentially important for
understanding atmospheric composition and temperature structure. Here we report
on the analysis of spectral modulation using a large, uniformly processed
sample of HST/WFC3 transit spectra from 62 exoplanets. The spectral retrieval
includes the capability to detect and represent atmospheres in which the
composition departs from thermochemical equilibrium. By using this unique
catalog and measuring the dampening of spectral modulations compared to
strictly clear atmospheres, we identify two populations. One is completely
cloud/haze free spanning a wide temperature range, while the other population,
identified as ``Partial cloud/hazes'', follows a trend from mostly cloudy/hazy
around 500~K to mostly clear at 1500~K. We also find that a partially
transparent aerosol component is frequently present and that it is typically
vertically distributed throughout the atmospheric column. Our findings also
suggest that while clouds and hazes are common in exoplanet atmospheres, the
majority of planets have some level of detectable spectral modulation.
Additionally, the empirical trend that clouds and hazes are minimized at
1460.86K revealed in our catalog has predictive utility for
modelling the performance of large-scale transiting exoplanets survey, such as
planned with the Ariel mission. This trend can also be used for making a
probability-based forecast of spectral modulation for a given source in the
context of future JWST observations. Future observations including the optical
and/or a broader spectral coverage may be useful to further quantify the trend
reported here.Comment: 12 pages, 4 figures, accepted for publication in Apj
Impact of M-dwarf Stellar Wind and Photoevaporation on the Atmospheric Evolution of Small Planets
The evolution of a planet's atmosphere depends strongly on its host star's
properties. When their host stars are younger, planets can experience stronger
winds and EUV emissions. This is particularly true for planets orbiting
M-dwarfs due to their close proximity to the host star. To determine if these
planets retain an atmosphere, we consider the impacts from stellar wind and EUV
fluxes in driving atmospheric escape throughout the planet's lifetime. For
this, we determined the atmospheric mass loss due to stellar wind and
photoevaporation on 4 planets in close orbit and 34 in their star's habitable
zone (HZ). The M-dwarf host stars' wind velocity, density, and EUV flux were
calculated through rotation period and X-ray flux scaling over time. The mass
loss rate due to stellar wind and photoevaporation was then computed as a
function of time and accumulated throughout the planet's age to determine the
total atmospheric mass loss of the planet's initial H/He envelope. We find that
for HZ planets at orbits 0.1 AU, stellar wind can only remove of
the H/He envelope, while photoevaporation is essential for completely removing
the H/He envelope of most targets. Moreover, due to either mechanism, most
planets orbiting at 0.1 AU do not have their primordial envelope stripped.
Overall, out of the 38 planets studied, 13 were predicted to have lost the
primordial envelope due to photoevaporation, while 2 planets lost the envelope
due to both stellar wind and photoevaporation.Comment: 12 pages, 5 figures, published in MNRA
An integrative, multi-scale, genome-wide model reveals the phenotypic landscape of Escherichia coli.
Given the vast behavioral repertoire and biological complexity of even the simplest organisms, accurately predicting phenotypes in novel environments and unveiling their biological organization is a challenging endeavor. Here, we present an integrative modeling methodology that unifies under a common framework the various biological processes and their interactions across multiple layers. We trained this methodology on an extensive normalized compendium for the gram-negative bacterium Escherichia coli, which incorporates gene expression data for genetic and environmental perturbations, transcriptional regulation, signal transduction, and metabolic pathways, as well as growth measurements. Comparison with measured growth and high-throughput data demonstrates the enhanced ability of the integrative model to predict phenotypic outcomes in various environmental and genetic conditions, even in cases where their underlying functions are under-represented in the training set. This work paves the way toward integrative techniques that extract knowledge from a variety of biological data to achieve more than the sum of their parts in the context of prediction, analysis, and redesign of biological systems
Identificação de ciclos magnéticos em estrelas do tipo solar observadas pelo satélite Kepler
O campo magnético desempenha um papel crucial nos mecanismos internos da estrela,
assim como também nas interações com o seu meio. O estudo das manchas estelares nos dá informações
sobre o campo magnético da estrela, e caracteriza o seu ciclo de atividade. Além disso, a
análise de estrelas do tipo solar é muito importante para se entender a origem do campo magnético
solar. O objetivo deste trabalho é caracterizar o campo magnético dessas estrelas. Inicialmente,
nós estudamos duas estrelas do tipo solar: Kepler-17 e Kepler-63. Dois métodos foram usados para
estimar o perÃodo da atividade magnética. O primeiro deles caracteriza as manchas (raio e intensidade)
ao ajustar pequenas variações nas curvas de luz da estrela causadas pela ocultação de uma
mancha durante um trânsito planetário. Com este método obtemos o número de manchas presentes
na superfÃcie da estrela e o déficit do fluxo da estrela devido a presença das manchas durante o
trânsito. O segundo método nos dá uma estimativa da atividade magnética a partir da análise dos
excessos nos resÃduos das curvas de trânsito. Este excesso é obtido ao subtrair um modelo sem
manchas da curva de luz observada, e em seguida integrando todos os resÃduos durante o trânsito.
A presença de uma periodicidade de longa duração é obtida ao se aplicar o periodograma Lomb
Scargle nas séries temporais. Com o primeiro método, nós obtivemos Pciclo = 1,12 0,16 ano
(Kepler-17) e Pciclo = 1,27 0,16 ano (Kepler-63), enquanto que com o segundo os valores são de
1,35 0,27 ano e 1,27 0,12 ano, respectivamente. Os resultados de ambos os métodos estão em
acordo e confirmam a eficácia dos mesmos. Por ser mais eficiente, aplicamos o segundo método
para mais 4 estrelas observadas pelo Kepler e estimamos perÃodos de ciclos de curta duração. Os
perÃodos obtidos são consistentes com os perÃodos de curta duração encontrados na literatura para
outras estrelas análogas ao Sol.The stellar magnetic field plays a crucial role in the star internal mechanisms, as well as in
the interactions with its environment. The study of starspots gives us information about the magnetic field of the star, and characterizes the cycle. Moreover, the analysis of solar-type stars is also useful to shed light onto the origin of the solar magnetic field. The objective of this work is to characterize the magnetic activity of stars. Initially, we studied two solar-type stars Kepler-17 and Kepler-63. Two methods were used to estimate the magnetic cycle length. The first one characterizes the spots (radius and intensity) by fitting the small variations in the light curve of a star caused by the occultation of a spot during a planetary transit. This approach yields the number of spots present in the stellar surface and the flux deficit subtracted from the star by their presence during each transit. The second method estimates the activity from the excess in the residuals of the transit lightcurves. This excess is obtained by subtracting a spotless model transit from the lightcurve, and then integrating all the residuals during the transit. The presence of long term periodicity is estimated
from the analysis of a Lomb-Scargle periodogram of both time series. With the first method,
we obtained Pcycle = 1.12 0.16 year (Kepler-17) and Pcycle = 1.27 0.16 year (Kepler-63), and for the second approach the values are 1.35 0.27 year and 1.27 0.12 year, respectively. Since the results of both methods agreed with each other, we used the second method to estimate short magnetic cycles of four more active stars with transiting planets observed by Kepler. These periods are consistent with short cycle periods of stars found in the literature.Coordenação de Aperfeiçoamento de Pessoal de NÃvel Superio
Detection of Aerosols at Microbar Pressures in an Exoplanet Atmosphere
Formation of hazes at microbar pressures has been explored by theoretical
models of exoplanet atmospheres to explain Rayleigh scattering and/or
featureless transmission spectra, however observational evidence of aerosols in
the low pressure formation environments has proved elusive. Here, we show
direct evidence of aerosols existing at 1 microbar pressures in the
atmosphere of the warm sub-Saturn WASP-69b using observations taken with Space
Telescope Imaging Spectrograph (STIS) and Wide Field Camera 3 (WFC3)
instruments on the Hubble Space Telescope. The transmission spectrum shows a
wavelength-dependent slope induced by aerosol scattering that covers 11 scale
heights of spectral modulation. Drawing on the extensive studies of haze in our
Solar System, we model the transmission spectrum based on a scaled version of
Jupiter's haze density profile to show that WASP-69b transmission spectrum can
be produced by scattering from an approximately constant density of particles
extending throughout the atmospheric column from 40 millibar to microbar
pressures. These results are consistent with theoretical expectations based on
microphysics of the aerosol particles that have suggested haze can exist at
microbar pressures in exoplanet atmospheres.Comment: 15 pages, 13 figures, accepted for publication in A