586 research outputs found
Simultaneous optical and near-infrared linear spectropolarimetry of the earthshine
Aims: We aim to extend our current observational understanding of the
integrated planet Earth spectropolarimetry from the optical to the
near-infrared wavelengths. Major biomarkers like O and water vapor
are strong flux absorbents in the Earth atmosphere and some linear polarization
of the reflected stellar light is expected to occur at these wavelengths.
Methods: Simultaneous optical ( m) and near-infrared (
m) linear spectropolarimetric data of the earthshine were acquired by
observing the nightside of the waxing Moon. The data have sufficient spectral
resolution (2.51 nm in the optical, and 1.83 and 2.91 nm in the near-infrared)
to resolve major molecular species present in the Earth atmosphere.
Results: We find the highest values of linear polarization () at
the bluest wavelengths, which agrees with the literature. Linear polarization
intensity steadily decreases towards red wavelengths reaching a nearly flat
value beyond 0.8 m. In the near-infrared, we measured a polarization
degree of for the continuum. We report the detection of molecular
features due to O at m and HO at 0.6530.725
m, 0.7800.825 m, 0.93 and 1.12 m in the spectropolarimetric
data; most of them show high linear polarimetry degrees above the continuum. In
particular, the broad HO 1.12 m band displays a polarimetric
intensity as high as that of the blue optical. These features may become a
powerful tool to characterize Earth-like planets in polarized light.Comment: 4 pages, 3 figures. Accepted for publication as Letter in Astronomy
and Astrophysics on 23/01/201
Reconstructing the photometric light curves of Earth as a planet along its history
By utilizing satellite-based estimations of the distribution of clouds, we
have studied the Earth's large-scale cloudiness behavior according to latitude
and surface types (ice, water, vegetation and desert). These empirical
relationships are used here to reconstruct the possible cloud distribution of
historical epochs of the Earth's history such as the Late Cretaceous (90 Ma
ago), the Late Triassic (230 Ma ago), the Mississippian (340 Ma ago), and the
Late Cambrian (500 Ma ago), when the landmass distributions were different from
today's. With this information, we have been able to simulate the
globally-integrated photometric variability of the planet at these epochs. We
find that our simple model reproduces well the observed cloud distribution and
albedo variability of the modern Earth. Moreover, the model suggests that the
photometric variability of the Earth was probably much larger in past epochs.
This enhanced photometric variability could improve the chances for the
difficult determination of the rotational period and the identification of
continental landmasses for a distant planets.Comment: 12 pages, 4 figures. Accepted in ApJ. Latest version for publicatio
The GTC exoplanet transit spectroscopy survey X. Stellar spots versus Rayleigh scattering: the case of HAT-P-11b
Rayleigh scattering in a hydrogen-dominated exoplanet atmosphere can be
detected from ground or space based telescopes, however, stellar activity in
the form of spots can mimic Rayleigh scattering in the observed transmission
spectrum. Quantifying this phenomena is key to our correct interpretation of
exoplanet atmospheric properties. We obtained long-slit optical spectroscopy of
two transits of HAT-P-11b with the Optical System for Imaging and
low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at Gran Telescopio
Canarias (GTC) on August 30 2016 and September 25 2017. We integrated the
spectrum of HAT-P-11 and one reference star in several spectroscopic channels
across the 400-785 nm region, creating numerous light curves of
the transits. We fit analytic transit curves to the data taking into account
the systematic effects and red noise present in the time series in an effort to
measure the change of the planet-to-star radius ratio
() across wavelength. By fitting both transits
together, we find a slope in the transmission spectrum showing an increase of
the planetary radius towards blue wavelengths. A closer inspection to the
transmission spectrum of the individual data sets reveals that the first
transit presents this slope while the transmission spectrum of the second data
set is flat. Additionally we detect hints of Na absorption in the first night,
but not in the second. We conclude that the transmission spectrum slope and Na
absorption excess found in the first transit observation are caused by
unocculted stellar spots. Modeling the contribution of unocculted spots to
reproduce the results of the first night we find a spot filling factor of
and a spot-to-photosphere temperature difference
of K.Comment: Accepted for publication in Astronomy & Astrophysics, 13 page
Planet cartography with neural learned regularization
Finding potential life harboring exo-Earths is one of the aims of
exoplanetary science. Detecting signatures of life in exoplanets will likely
first be accomplished by determining the bulk composition of the planetary
atmosphere via reflected/transmitted spectroscopy. However, a complete
understanding of the habitability conditions will surely require mapping the
presence of liquid water, continents and/or clouds. Spin-orbit tomography is a
technique that allows us to obtain maps of the surface of exoplanets around
other stars using the light scattered by the planetary surface. We leverage the
potential of deep learning and propose a mapping technique for exo-Earths in
which the regularization is learned from mock surfaces. The solution of the
inverse mapping problem is posed as a deep neural network that can be trained
end-to-end with suitable training data. We propose in this work to use methods
based on the procedural generation of planets, inspired by what we found on
Earth. We also consider mapping the recovery of surfaces and the presence of
persistent cloud in cloudy planets. We show that the a reliable mapping can be
carried out with our approach, producing very compact continents, even when
using single passband observations. More importantly, if exoplanets are
partially cloudy like the Earth is, we show that one can potentially map the
distribution of persistent clouds that always occur on the same position on the
surface (associated to orography and sea surface temperatures) together with
non-persistent clouds that move across the surface. This will become the first
test one can perform on an exoplanet for the detection of an active climate
system. For small rocky planets in the habitable zone of their stars, this
weather system will be driven by water, and the detection can be considered as
a strong proxy for truly habitable conditions.Comment: 12 pages, 9 figures, accepted for publication in A&A, code on
https://github.com/aasensio/neural_exocartograph
Rotational modulation of the linear polarimetric variability of the cool dwarf TVLM 51346546
Aims: We aimed to monitor the optical linear polarimetric signal of the
magnetized, rapidly rotating M8.5 dwarf TVLM 51346546.
Methods: - and -band linear polarimetry images were collected with the
ALFOSC instrument of the 2.56-m Nordic Optical Telescope on two consecutive
nights covering about 0.5 and 4 rotation cycles in the and filters,
respectively. We also obtained simultaneous intensity curves by means of
differential photometry. The typical precision of the data is 0.46\%
(), 0.35\% () in the linear polarization degree and 9 mmag
(), 1.6 mmag () in the differential intensity curves.
Results: Strong and variable linear polarization is detected in the and
filters, with values of maximum polarization ( = 1.300.35 \%)
similar for both bands. The intensity and the polarimetric curves present a
sinusoid-like pattern with a periodicity of 1.98 h, which we ascribe to
structures in TVLM 51346's surface synchronized with rotation. We found that
the peaks of the intensity and polarimetric curves occur with a phase
difference of 0.180.01, and that the maximum of the linear polarization
happens nearly half a period (0.590.03) after the radio pulse. We
discussed different scenarios to account for the observed properties of the
light curves.Comment: Accepted for publication in Astronomy and Astrophysic
Earthshine observations of an inhabited planet
Earthshine is sunlight that has been reflected from the dayside Earth onto
the dark side of the Moon and back again to Earth. In recent times, there has
been renewed interest in ground-based visible and near-infrared measurements of
earthshine as a proxy for exoplanet observations. Observations of earthshine
allow us to explore and characterize the globally integrated photometric,
spectral and polarimetric features of the Earth, and to extract precise
information on the distinctive characteristics of our planet, and life in
particular. They also allow us to quantify how this feature changes with time
and orbital configuration. Here we present a brief review of the main
earthshine observations and results.Comment: To appear in the proceedings of the Les Houches Winter School
"Physics and Astrophysics of Planetary Systems",(EDP Sciences: EAS
Publications Series
The impact of the Kasatochi eruption on the Moon's illumination during the August 2008 lunar eclipse
The Moon's changeable aspect during a lunar eclipse is largely attributable
to variations in the refracted unscattered sunlight absorbed by the terrestrial
atmosphere that occur as the satellite crosses the Earth's shadow. The
contribution to the Moon's aspect from sunlight scattered at the Earth's
terminator is generally deemed minor. However, our analysis of a published
spectrum of the 16 August 2008 lunar eclipse shows that diffuse sunlight is a
major component of the measured spectrum at wavelengths shorter than 600 nm.
The conclusion is supported by two distinct features, namely the spectrum's
tail at short wavelengths and the unequal absorption by an oxygen collisional
complex at two nearby bands. Our findings are consistent with the presence of
the volcanic cloud reported at high northern latitudes following the 7-8 August
2008 eruption in Alaska of the Kasatochi volcano. The cloud both attenuates the
unscattered sunlight and enhances moderately the scattered component, thus
modifying the contrast between the two contributions.Comment: Accepted for publication in Geophysical Research Letter
- …