1) High-dispersion spectroscopy was used to observe the young exoplanet Beta Pictoris b, detecting a blueshifted radial velocity of -15±1.7 km/s and rotational broadening of 25±3 km/s, indicating it spins faster than any planet in the solar system.
2) Beta Pictoris b's high spin velocity is consistent with an extrapolation of the trend of increasing spin velocity with planet mass seen in the solar system.
3) At an estimated age of 11±5 Myr, Beta Pictoris b is expected to cool and shrink over time, which would cause it to spin up further to a rotation velocity of around 40 km/s.
Multi-phase volcanic resurfacing at Loki Patera on IoSérgio Sacani
The Jovian moon Io hosts the most powerful persistently active
volcano in the Solar System, Loki Patera1,2. The interior of this
volcanic, caldera-like feature is composed of a warm, dark floor
covering 21,500 square kilometres3 surrounding a much cooler
central ‘island’4. The temperature gradient seen across areas of
the patera indicates a systematic resurfacing process4–9, which
has been seen to occur typically every one to three years since the
1980s5,10. Analysis of past data has indicated that the resurfacing
progressed around the patera in an anti-clockwise direction at a
rate of one to two kilometres per day, and that it is caused either
by episodic eruptions that emplace voluminous lava flows or by a
cyclically overturning lava lake contained within the patera5,8,9,11.
However, spacecraft and telescope observations have been unable to
map the emission from the entire patera floor at sufficient spatial
resolution to establish the physical processes at play. Here we report
temperature and lava cooling age maps of the entire patera floor at
a spatial sampling of about two kilometres, derived from groundbased
interferometric imaging of thermal emission from Loki Patera
obtained on 8 March 2015 ut as the limb of Europa occulted Io.
Our results indicate that Loki Patera is resurfaced by a multi-phase
process in which two waves propagate and converge around the
central island. The different velocities and start times of the waves
indicate a non-uniformity in the lava gas content and/or crust bulk
density across the patera.
- Astrônomos descobriram que uma pequena estrela, do tamanho de Júpiter, possui uma tempestade muito parecida com a Grande Mancha Vermelha e que está ali, persistente por dois anos.
- Enquanto nos planetas, esse tipo de característica é normal, em estrelas essa é a melhor evidência encontrada até hoje.
- A estrela é chamada de W1906+40 e pertence a uma classe de objetos frios chamados de Anãs-L.
- Elas são consideradas estrelas pois fundem átomos e geram luz, como o Sol faz, enquanto que as anãs marrons são conhecidas como estrelas que falharam, pois elas não possuem o processo de fusão atômica em seu interior.
- Nesse novo estudo os astrônomos foram capazes de verificar as mudanças na atmosfera da estrela por dois anos. A técnica usada foi semelhante à de detecção de exoplanetas, analisando a curva de luz da estrela, que apresentava quedas, mas que não era por questão de planetas.
- Os astrônomos usaram o Spitzer e estudaram a luz infravermelha da estrela, que revelou uma gigantesca mancha escura que não era uma mancha magnética estelar, mas sim uma tempestade com um diâmetro equivalente ao de 3 Terras. O spitzer foi capaz de estudar camadas diferentes da atmosfera da estrela e esses dados junto com os dados do Kepler, revelaram com clareza a tempestade estelar.
- Futuras observações serão realizadas usando os dois equipamentos para tentar identificar esse tipo de tempestade em anãs marrons, por exemplo, e tentar descobrir se esse tipo de fenômeno é muito comum, ou é raro no universo.
Multi-phase volcanic resurfacing at Loki Patera on IoSérgio Sacani
The Jovian moon Io hosts the most powerful persistently active
volcano in the Solar System, Loki Patera1,2. The interior of this
volcanic, caldera-like feature is composed of a warm, dark floor
covering 21,500 square kilometres3 surrounding a much cooler
central ‘island’4. The temperature gradient seen across areas of
the patera indicates a systematic resurfacing process4–9, which
has been seen to occur typically every one to three years since the
1980s5,10. Analysis of past data has indicated that the resurfacing
progressed around the patera in an anti-clockwise direction at a
rate of one to two kilometres per day, and that it is caused either
by episodic eruptions that emplace voluminous lava flows or by a
cyclically overturning lava lake contained within the patera5,8,9,11.
However, spacecraft and telescope observations have been unable to
map the emission from the entire patera floor at sufficient spatial
resolution to establish the physical processes at play. Here we report
temperature and lava cooling age maps of the entire patera floor at
a spatial sampling of about two kilometres, derived from groundbased
interferometric imaging of thermal emission from Loki Patera
obtained on 8 March 2015 ut as the limb of Europa occulted Io.
Our results indicate that Loki Patera is resurfaced by a multi-phase
process in which two waves propagate and converge around the
central island. The different velocities and start times of the waves
indicate a non-uniformity in the lava gas content and/or crust bulk
density across the patera.
- Astrônomos descobriram que uma pequena estrela, do tamanho de Júpiter, possui uma tempestade muito parecida com a Grande Mancha Vermelha e que está ali, persistente por dois anos.
- Enquanto nos planetas, esse tipo de característica é normal, em estrelas essa é a melhor evidência encontrada até hoje.
- A estrela é chamada de W1906+40 e pertence a uma classe de objetos frios chamados de Anãs-L.
- Elas são consideradas estrelas pois fundem átomos e geram luz, como o Sol faz, enquanto que as anãs marrons são conhecidas como estrelas que falharam, pois elas não possuem o processo de fusão atômica em seu interior.
- Nesse novo estudo os astrônomos foram capazes de verificar as mudanças na atmosfera da estrela por dois anos. A técnica usada foi semelhante à de detecção de exoplanetas, analisando a curva de luz da estrela, que apresentava quedas, mas que não era por questão de planetas.
- Os astrônomos usaram o Spitzer e estudaram a luz infravermelha da estrela, que revelou uma gigantesca mancha escura que não era uma mancha magnética estelar, mas sim uma tempestade com um diâmetro equivalente ao de 3 Terras. O spitzer foi capaz de estudar camadas diferentes da atmosfera da estrela e esses dados junto com os dados do Kepler, revelaram com clareza a tempestade estelar.
- Futuras observações serão realizadas usando os dois equipamentos para tentar identificar esse tipo de tempestade em anãs marrons, por exemplo, e tentar descobrir se esse tipo de fenômeno é muito comum, ou é raro no universo.
Dark side of_comet_67_p_churyumov_gerasiemnko_in_august_october_2014Sérgio Sacani
Usando o instrumento Microwave Instrument for Rosetta Orbiter (MIRO), os cientistas estão estudando a região polar sul do cometa no final de sua longa estação de inverno. Os dados sugerem que essas regiões frias e escuras abrigam gelo nas suas primeiras dezenas de centímetros abaixo da superfície em quantidades muito maiores do que as encontradas em outras áreas do cometa.
Desde a sua chegada no Cometa 67P/Churyumov-Gerasimenko, a Rosetta tem pesquisado a superfície e o ambiente desse corpo de forma curiosa. Mas por um longo período de tempo, uma porção do núcleo, as regiões frias e escuras ao redor do polo sul do cometa, permaneceram inacessíveis para quase todos os instrumentos a bordo da sonda.
Devido a uma combinação de sua forma em lobo duplo e a inclinação do seu eixo de rotação, o cometa da Rosetta, tem um padrão sazonal muito peculiar durante a sua órbita de 6.5 anos. As estações estão distribuídas de maneira muito assimétrica entre os dois hemisférios, cada um deles compreende parte tanto dos lobos como do pescoço do cometa.
Na maior parte da órbita do cometa, o hemisfério norte experimenta um verão muito longo, durando cerca de 5.5 anos, e o hemisfério sul passa por um longo, frio e escuro inverno. Contudo, poucos meses antes do cometa passar pelo seu periélio, o ponto na sua órbita, mais próximo do Sol, a situação muda, e o hemisfério sul passa por um breve porém quente verão.
Jupiter’s atmospheric jet streams extend thousands of kilometres deepSérgio Sacani
The depth to which Jupiter’s observed east–west jet streams extend
has been a long-standing question1,2
. Resolving this puzzle has
been a primary goal for the Juno spacecraft3,4
, which has been in
orbit around the gas giant since July 2016. Juno’s gravitational
measurements have revealed that Jupiter’s gravitational field
is north–south asymmetric5
, which is a signature of the planet’s
atmospheric and interior flows6
. Here we report that the measured
odd gravitational harmonics J3, J5, J7 and J9 indicate that the
observed jet streams, as they appear at the cloud level, extend
down to depths of thousands of kilometres beneath the cloud level,
probably to the region of magnetic dissipation at a depth of about
3,000 kilometres7,8
. By inverting the measured gravity values into a
wind field9
, we calculate the most likely vertical profile of the deep
atmospheric and interior flow, and the latitudinal dependence of its
depth. Furthermore, the even gravity harmonics J8 and J10 resulting
from this flow profile also match the measurements, when taking
into account the contribution of the interior structure10. These
results indicate that the mass of the dynamical atmosphere is about
one per cent of Jupiter’s total mass
Clusters of cyclones encircling Jupiter’s polesSérgio Sacani
The familiar axisymmetric zones and belts that characterize
Jupiter’s weather system at lower latitudes give way to pervasive
cyclonic activity at higher latitudes1
. Two-dimensional turbulence
in combination with the Coriolis β-effect (that is, the large
meridionally varying Coriolis force on the giant planets of the Solar
System) produces alternating zonal flows2
. The zonal flows weaken
with rising latitude so that a transition between equatorial jets and
polar turbulence on Jupiter can occur3,4
. Simulations with shallowwater
models of giant planets support this transition by producing
both alternating flows near the equator and circumpolar cyclones
near the poles5–9. Jovian polar regions are not visible from Earth
owing to Jupiter’s low axial tilt, and were poorly characterized by
previous missions because the trajectories of these missions did
not venture far from Jupiter’s equatorial plane. Here we report
that visible and infrared images obtained from above each pole
by the Juno spacecraft during its first five orbits reveal persistent
polygonal patterns of large cyclones. In the north, eight circumpolar
cyclones are observed about a single polar cyclone; in the south, one
polar cyclone is encircled by five circumpolar cyclones. Cyclonic
circulation is established via time-lapse imagery obtained over
intervals ranging from 20 minutes to 4 hours. Although migration of
cyclones towards the pole might be expected as a consequence of the
Coriolis β-effect, by which cyclonic vortices naturally drift towards
the rotational pole, the configuration of the cyclones is without
precedent on other planets (including Saturn’s polar hexagonal
features). The manner in which the cyclones persist without merging
and the process by which they evolve to their current configuration
are unknown.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
A suppression of differential rotation in Jupiter’s deep interiorSérgio Sacani
Jupiter’s atmosphere is rotating differentially, with zones and
belts rotating at speeds that differ by up to 100 metres per
second. Whether this is also true of the gas giant’s interior has
been unknown1,2
, limiting our ability to probe the structure and
composition of the planet3,4
. The discovery by the Juno spacecraft
that Jupiter’s gravity field is north–south asymmetric5
and the
determination of its non-zero odd gravitational harmonics J3, J5, J7
and J9 demonstrates that the observed zonal cloud flow must persist
to a depth of about 3,000 kilometres from the cloud tops6
. Here we
report an analysis of Jupiter’s even gravitational harmonics J4, J6,
J8 and J10 as observed by Juno5
and compared to the predictions
of interior models. We find that the deep interior of the planet
rotates nearly as a rigid body, with differential rotation decreasing
by at least an order of magnitude compared to the atmosphere.
Moreover, we find that the atmospheric zonal flow extends to more
than 2,000 kilometres and to less than 3,500 kilometres, making
it fully consistent with the constraints obtained independently
from the odd gravitational harmonics. This depth corresponds
to the point at which the electric conductivity becomes large and
magnetic drag should suppress differential rotation7
. Given that
electric conductivity is dependent on planetary mass, we expect the
outer, differentially rotating region to be at least three times deeper
in Saturn and to be shallower in massive giant planets and brown
dwarfs.
Measurement of Jupiter’s asymmetric gravity fieldSérgio Sacani
The gravity harmonics of a fluid, rotating planet can be decomposed
into static components arising from solid-body rotation and dynamic
components arising from flows. In the absence of internal dynamics,
the gravity field is axially and hemispherically symmetric and is
dominated by even zonal gravity harmonics J2n that are approximately
proportional to qn, where q is the ratio between centrifugal
acceleration and gravity at the planet’s equator1
. Any asymmetry in the
gravity field is attributed to differential rotation and deep atmospheric
flows. The odd harmonics, J3, J5, J7, J9 and higher, are a measure of the
depth of the winds in the different zones of the atmosphere2,3
. Here
we report measurements of Jupiter’s gravity harmonics (both even
and odd) through precise Doppler tracking of the Juno spacecraft
in its polar orbit around Jupiter. We find a north–south asymmetry,
which is a signature of atmospheric and interior flows. Analysis of
the harmonics, described in two accompanying papers4,5
, provides
the vertical profile of the winds and precise constraints for the depth
of Jupiter’s dynamical atmosphere.
Bright features have been recently discovered by Dawn on Ceres, which extend
previous photometric and Space Telescope observations. These features should produce
distortions of the line profiles of the reflected solar spectrum and therefore an apparent
radial velocity variation modulated by the rotation of the dwarf planet. Here we report
on two sequences of observations of Ceres performed in the nights of 31 July, 26-
27 August 2015 by means of the high-precision HARPS spectrograph at the 3.6-m
La Silla ESO telescope. The observations revealed a quite complex behaviour which
likely combines a radial velocity modulation due to the rotation with an amplitude of
⇡ ±6 m s
A rocky planet_transiting_a_nearby_low_mass_starSérgio Sacani
Um exoplaneta rochoso do tamanho da Terra, orbita uma estrela pequena e próxima, poderia ser o mundo mais importante já encontrado além do Sistema Solar, disseram os astrônomos.
O planeta localiza-se na constelação de Vela, no hemisfério sul do céu e é próximo o suficiente para que os telescópios possam observar qualquer atmosfera que ele possua, um procedimento que poderia ajudar a registrar algum tipo de vida, se ela existisse em outros planetas, no futuro.
Denominado de GJ 1132b, o exoplaneta é cerca de 16% maior que a Terra, e está localizado a cerca de 39 anos-luz de distância, o que faz com que ele seja três vezes mais próximo da Terra do que qualquer outro exoplaneta rochoso já descoberto. Nessa distância, espera-se que os telescópios sejam capazes de fazer uma análise química de sua atmosfera, a velocidade dos seus ventos e as cores do pôr-do-Sol, que acontecem no exoplaneta.
Os astrônomos registraram o planeta à medida que ele passava na frente da sua estrela, uma estrela do tipo anã vermelha, com somente um quinto do tamanho do Sol. Apesar de muito mais fria e muito mais apagada que o Sol, o GJ 1132b, tem uma órbita tão próxima da estrela que as suas temperaturas superficiais atingem cerca de 260 graus Celsius.
Essa temperatura, obviamente, é muito alta para reter a água em estado líquido na superfície do exoplaneta, fazendo com que ele seja inóspito para a vida, mas não tão quente para queimar toda uma atmosfera que pode ter se formado no planeta.
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
Four new planets_around_giant_stars_and_the_mass_metallicity_correlation_of_p...Sérgio Sacani
Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets.
In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and
that their fraction increases with the stellar mass.
Aims. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in
the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of
giant planets.
Methods. We have taken multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we have computed
precision radial velocities and we have derived atmospheric and physical parameters. Additionally, velocities computed from UCLES
spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar
companions.
Results. We present four new planetary systems around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that
giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5
−5.9 % around stars with [Fe/H] ∼
0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆∼ 1.0 - 2.1 M⊙ ,
with a maximum of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ .
Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the stellar mass range of ∼ 1.0 - 2.1 M⊙ . These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.
Solar system expansion and strong equivalence principle as seen by the NASA M...Sérgio Sacani
The NASA MESSENGER mission explored the innermost planet of the solar system and obtained a rich data set of range measurements for the determination of Mercury’s ephemeris. Here we use these precise data collected over 7 years to estimate parameters related to general relativity and the evolution of the Sun. These results confirm the validity of the strong equivalence principle with a significantly refined uncertainty of the Nordtvedt parameter η=(−6.6±7.2)×10−5. By assuming a metric theory of gravitation, we retrieved the post-Newtonian parameter β=1+(−1.6±1.8)×10−5 and the Sun’s gravitational oblateness, J2 =(2.246±0.022)×10−7. Finally, we obtain an estimate of the time variation of the Sun gravitational parameter, _ GM=GM =(−6.13±1.47)×10−14, which is consistent with the expected solar mass loss due to the solar wind and interior processes. This measurement allows us to constrain _
Large turbulent reservoirs of cold molecular gas around high-redshift starbur...Sérgio Sacani
Starburst galaxies at the peak of cosmic star formation1
are among
the most extreme star-forming engines in the Universe, producing
stars over about 100 million years (ref. 2). The star-formation
rates of these galaxies, which exceed 100 solar masses per year,
require large reservoirs of cold molecular gas3
to be delivered to
their cores, despite strong feedback from stars or active galactic
nuclei4,5
. Consequently, starburst galaxies are ideal for studying the
interplay between this feedback and the growth of a galaxy6
. The
methylidyne cation, CH+, is a most useful molecule for such studies
because it cannot form in cold gas without suprathermal energy
input, so its presence indicates dissipation of mechanical energy7–9
or strong ultraviolet irradiation10,11. Here we report the detection of
CH+ (J=1–0) emission and absorption lines in the spectra of six
lensed starburst galaxies12–15 at redshifts near 2.5. This line has
such a high critical density for excitation that it is emitted only in
very dense gas, and is absorbed in low-density gas10. We find that
the CH+ emission lines, which are broader than 1,000 kilometres
per second, originate in dense shock waves powered by hot galactic
winds. The CH+ absorption lines reveal highly turbulent reservoirs
of cool (about 100 kelvin), low-density gas, extending far (more than
10 kiloparsecs) outside the starburst galaxies (which have radii of
less than 1 kiloparsec). We show that the galactic winds sustain
turbulence in the 10-kiloparsec-scale environments of the galaxies,
processing these environments into multiphase, gravitationally
bound reservoirs. However, the mass outflow rates are found to be
insufficient to balance the star-formation rates. Another mass input
is therefore required for these reservoirs, which could be provided by
ongoing mergers16 or cold-stream accretion17,18. Our results suggest
that galactic feedback, coupled jointly to turbulence and gravity,
extends the starburst phase of a galaxy instead of quenching it
•Lunar laser telemetry consists in determining the round-trip travel time of the light between a transmitter on the Earth and a reflector on the Moon, which is an equivalent measurement of the distance between these two points
An unusual white dwarf star may be a surviving remnant of a subluminous Type ...Sérgio Sacani
Subluminous Type Ia supernovae, such as the Type Iax–class prototype SN 2002cx, are
described by a variety of models such as the failed detonation and partial deflagration
of an accreting carbon-oxygen white dwarf star or the explosion of an accreting, hybrid
carbon-oxygen-neon core. These models predict that bound remnants survive such
events with, according to some simulations, a high kick velocity.We report the discovery
of a high proper motion, low-mass white dwarf (LP 40-365) that travels at a velocity
greater than the Galactic escape velocity and whose peculiar atmosphere is dominated
by intermediate-mass elements. Strong evidence indicates that this partially burnt
remnant was ejected following a subluminous Type Ia supernova event. This supports the
viability of single-degenerate supernova progenitors.
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
Dark side of_comet_67_p_churyumov_gerasiemnko_in_august_october_2014Sérgio Sacani
Usando o instrumento Microwave Instrument for Rosetta Orbiter (MIRO), os cientistas estão estudando a região polar sul do cometa no final de sua longa estação de inverno. Os dados sugerem que essas regiões frias e escuras abrigam gelo nas suas primeiras dezenas de centímetros abaixo da superfície em quantidades muito maiores do que as encontradas em outras áreas do cometa.
Desde a sua chegada no Cometa 67P/Churyumov-Gerasimenko, a Rosetta tem pesquisado a superfície e o ambiente desse corpo de forma curiosa. Mas por um longo período de tempo, uma porção do núcleo, as regiões frias e escuras ao redor do polo sul do cometa, permaneceram inacessíveis para quase todos os instrumentos a bordo da sonda.
Devido a uma combinação de sua forma em lobo duplo e a inclinação do seu eixo de rotação, o cometa da Rosetta, tem um padrão sazonal muito peculiar durante a sua órbita de 6.5 anos. As estações estão distribuídas de maneira muito assimétrica entre os dois hemisférios, cada um deles compreende parte tanto dos lobos como do pescoço do cometa.
Na maior parte da órbita do cometa, o hemisfério norte experimenta um verão muito longo, durando cerca de 5.5 anos, e o hemisfério sul passa por um longo, frio e escuro inverno. Contudo, poucos meses antes do cometa passar pelo seu periélio, o ponto na sua órbita, mais próximo do Sol, a situação muda, e o hemisfério sul passa por um breve porém quente verão.
Jupiter’s atmospheric jet streams extend thousands of kilometres deepSérgio Sacani
The depth to which Jupiter’s observed east–west jet streams extend
has been a long-standing question1,2
. Resolving this puzzle has
been a primary goal for the Juno spacecraft3,4
, which has been in
orbit around the gas giant since July 2016. Juno’s gravitational
measurements have revealed that Jupiter’s gravitational field
is north–south asymmetric5
, which is a signature of the planet’s
atmospheric and interior flows6
. Here we report that the measured
odd gravitational harmonics J3, J5, J7 and J9 indicate that the
observed jet streams, as they appear at the cloud level, extend
down to depths of thousands of kilometres beneath the cloud level,
probably to the region of magnetic dissipation at a depth of about
3,000 kilometres7,8
. By inverting the measured gravity values into a
wind field9
, we calculate the most likely vertical profile of the deep
atmospheric and interior flow, and the latitudinal dependence of its
depth. Furthermore, the even gravity harmonics J8 and J10 resulting
from this flow profile also match the measurements, when taking
into account the contribution of the interior structure10. These
results indicate that the mass of the dynamical atmosphere is about
one per cent of Jupiter’s total mass
Clusters of cyclones encircling Jupiter’s polesSérgio Sacani
The familiar axisymmetric zones and belts that characterize
Jupiter’s weather system at lower latitudes give way to pervasive
cyclonic activity at higher latitudes1
. Two-dimensional turbulence
in combination with the Coriolis β-effect (that is, the large
meridionally varying Coriolis force on the giant planets of the Solar
System) produces alternating zonal flows2
. The zonal flows weaken
with rising latitude so that a transition between equatorial jets and
polar turbulence on Jupiter can occur3,4
. Simulations with shallowwater
models of giant planets support this transition by producing
both alternating flows near the equator and circumpolar cyclones
near the poles5–9. Jovian polar regions are not visible from Earth
owing to Jupiter’s low axial tilt, and were poorly characterized by
previous missions because the trajectories of these missions did
not venture far from Jupiter’s equatorial plane. Here we report
that visible and infrared images obtained from above each pole
by the Juno spacecraft during its first five orbits reveal persistent
polygonal patterns of large cyclones. In the north, eight circumpolar
cyclones are observed about a single polar cyclone; in the south, one
polar cyclone is encircled by five circumpolar cyclones. Cyclonic
circulation is established via time-lapse imagery obtained over
intervals ranging from 20 minutes to 4 hours. Although migration of
cyclones towards the pole might be expected as a consequence of the
Coriolis β-effect, by which cyclonic vortices naturally drift towards
the rotational pole, the configuration of the cyclones is without
precedent on other planets (including Saturn’s polar hexagonal
features). The manner in which the cyclones persist without merging
and the process by which they evolve to their current configuration
are unknown.
The nonmagnetic nucleus_of_comet_67_p_churyumov_gerasimenkoSérgio Sacani
Artigo descreve como a sonda Rosetta e o módulo Philae descobriram que o cometa Churyumov-Gerasimenko não é magnetizado, contrariando uma teoria da formação do Sistema Solar.
A suppression of differential rotation in Jupiter’s deep interiorSérgio Sacani
Jupiter’s atmosphere is rotating differentially, with zones and
belts rotating at speeds that differ by up to 100 metres per
second. Whether this is also true of the gas giant’s interior has
been unknown1,2
, limiting our ability to probe the structure and
composition of the planet3,4
. The discovery by the Juno spacecraft
that Jupiter’s gravity field is north–south asymmetric5
and the
determination of its non-zero odd gravitational harmonics J3, J5, J7
and J9 demonstrates that the observed zonal cloud flow must persist
to a depth of about 3,000 kilometres from the cloud tops6
. Here we
report an analysis of Jupiter’s even gravitational harmonics J4, J6,
J8 and J10 as observed by Juno5
and compared to the predictions
of interior models. We find that the deep interior of the planet
rotates nearly as a rigid body, with differential rotation decreasing
by at least an order of magnitude compared to the atmosphere.
Moreover, we find that the atmospheric zonal flow extends to more
than 2,000 kilometres and to less than 3,500 kilometres, making
it fully consistent with the constraints obtained independently
from the odd gravitational harmonics. This depth corresponds
to the point at which the electric conductivity becomes large and
magnetic drag should suppress differential rotation7
. Given that
electric conductivity is dependent on planetary mass, we expect the
outer, differentially rotating region to be at least three times deeper
in Saturn and to be shallower in massive giant planets and brown
dwarfs.
Measurement of Jupiter’s asymmetric gravity fieldSérgio Sacani
The gravity harmonics of a fluid, rotating planet can be decomposed
into static components arising from solid-body rotation and dynamic
components arising from flows. In the absence of internal dynamics,
the gravity field is axially and hemispherically symmetric and is
dominated by even zonal gravity harmonics J2n that are approximately
proportional to qn, where q is the ratio between centrifugal
acceleration and gravity at the planet’s equator1
. Any asymmetry in the
gravity field is attributed to differential rotation and deep atmospheric
flows. The odd harmonics, J3, J5, J7, J9 and higher, are a measure of the
depth of the winds in the different zones of the atmosphere2,3
. Here
we report measurements of Jupiter’s gravity harmonics (both even
and odd) through precise Doppler tracking of the Juno spacecraft
in its polar orbit around Jupiter. We find a north–south asymmetry,
which is a signature of atmospheric and interior flows. Analysis of
the harmonics, described in two accompanying papers4,5
, provides
the vertical profile of the winds and precise constraints for the depth
of Jupiter’s dynamical atmosphere.
Bright features have been recently discovered by Dawn on Ceres, which extend
previous photometric and Space Telescope observations. These features should produce
distortions of the line profiles of the reflected solar spectrum and therefore an apparent
radial velocity variation modulated by the rotation of the dwarf planet. Here we report
on two sequences of observations of Ceres performed in the nights of 31 July, 26-
27 August 2015 by means of the high-precision HARPS spectrograph at the 3.6-m
La Silla ESO telescope. The observations revealed a quite complex behaviour which
likely combines a radial velocity modulation due to the rotation with an amplitude of
⇡ ±6 m s
A rocky planet_transiting_a_nearby_low_mass_starSérgio Sacani
Um exoplaneta rochoso do tamanho da Terra, orbita uma estrela pequena e próxima, poderia ser o mundo mais importante já encontrado além do Sistema Solar, disseram os astrônomos.
O planeta localiza-se na constelação de Vela, no hemisfério sul do céu e é próximo o suficiente para que os telescópios possam observar qualquer atmosfera que ele possua, um procedimento que poderia ajudar a registrar algum tipo de vida, se ela existisse em outros planetas, no futuro.
Denominado de GJ 1132b, o exoplaneta é cerca de 16% maior que a Terra, e está localizado a cerca de 39 anos-luz de distância, o que faz com que ele seja três vezes mais próximo da Terra do que qualquer outro exoplaneta rochoso já descoberto. Nessa distância, espera-se que os telescópios sejam capazes de fazer uma análise química de sua atmosfera, a velocidade dos seus ventos e as cores do pôr-do-Sol, que acontecem no exoplaneta.
Os astrônomos registraram o planeta à medida que ele passava na frente da sua estrela, uma estrela do tipo anã vermelha, com somente um quinto do tamanho do Sol. Apesar de muito mais fria e muito mais apagada que o Sol, o GJ 1132b, tem uma órbita tão próxima da estrela que as suas temperaturas superficiais atingem cerca de 260 graus Celsius.
Essa temperatura, obviamente, é muito alta para reter a água em estado líquido na superfície do exoplaneta, fazendo com que ele seja inóspito para a vida, mas não tão quente para queimar toda uma atmosfera que pode ter se formado no planeta.
The completeness-corrected rate of stellar encounters with the Sun from the f...Sérgio Sacani
I report on close encounters of stars to the Sun found in the first Gaia data release (GDR1). Combining Gaia astrometry with radial
velocities of around 320 000 stars drawn from various catalogues, I integrate orbits in a Galactic potential to identify those stars which
come within a few parsecs. Such encounters could influence the solar system, for example through gravitational perturbations of the
Oort cloud. 16 stars are found to come within 2 pc (although a few of these have dubious data). This is fewer than were found in a
similar study based on Hipparcos data, even though the present study has many more candidates. This is partly because I reject stars
with large radial velocity uncertainties (>10 km s−1
), and partly because of missing stars in GDR1 (especially at the bright end). The
closest encounter found is Gl 710, a K dwarf long-known to come close to the Sun in about 1.3 Myr. The Gaia astrometry predict
a much closer passage than pre-Gaia estimates, however: just 16 000 AU (90% confidence interval: 10 000–21 000 AU), which will
bring this star well within the Oort cloud. Using a simple model for the spatial, velocity, and luminosity distributions of stars, together
with an approximation of the observational selection function, I model the incompleteness of this Gaia-based search as a function
of the time and distance of closest approach. Applying this to a subset of the observed encounters (excluding duplicates and stars
with implausibly large velocities), I estimate the rate of stellar encounters within 5 pc averaged over the past and future 5 Myr to be
545±59 Myr−1
. Assuming a quadratic scaling of the rate within some encounter distance (which my model predicts), this corresponds
to 87 ± 9 Myr−1 within 2 pc. A more accurate analysis and assessment will be possible with future Gaia data releases.
Four new planets_around_giant_stars_and_the_mass_metallicity_correlation_of_p...Sérgio Sacani
Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets.
In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and
that their fraction increases with the stellar mass.
Aims. During the past six years, we have conducted a radial velocity follow-up program of 166 giant stars, to detect substellar
companions, and characterizing their orbital properties. Using this information, we aim to study the role of the stellar evolution in
the orbital parameters of the companions, and to unveil possible correlations between the stellar properties and the occurrence rate of
giant planets.
Methods. We have taken multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we have computed
precision radial velocities and we have derived atmospheric and physical parameters. Additionally, velocities computed from UCLES
spectra are presented here. By studying the periodic radial velocity signals, we have detected the presence of several substellar
companions.
Results. We present four new planetary systems around the giant stars HIP8541, HIP74890, HIP84056 and HIP95124. Additionally,
we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that
giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7+15.5
−5.9 % around stars with [Fe/H] ∼
0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M⋆∼ 1.0 - 2.1 M⊙ ,
with a maximum of f = 13.0+10.1
−4.2 %, at M⋆= 2.1 M⊙ .
Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. Also, we conclude that they are more
efficiently formed around more massive stars, in the stellar mass range of ∼ 1.0 - 2.1 M⊙ . These observational results confirm previous
findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.
Solar system expansion and strong equivalence principle as seen by the NASA M...Sérgio Sacani
The NASA MESSENGER mission explored the innermost planet of the solar system and obtained a rich data set of range measurements for the determination of Mercury’s ephemeris. Here we use these precise data collected over 7 years to estimate parameters related to general relativity and the evolution of the Sun. These results confirm the validity of the strong equivalence principle with a significantly refined uncertainty of the Nordtvedt parameter η=(−6.6±7.2)×10−5. By assuming a metric theory of gravitation, we retrieved the post-Newtonian parameter β=1+(−1.6±1.8)×10−5 and the Sun’s gravitational oblateness, J2 =(2.246±0.022)×10−7. Finally, we obtain an estimate of the time variation of the Sun gravitational parameter, _ GM=GM =(−6.13±1.47)×10−14, which is consistent with the expected solar mass loss due to the solar wind and interior processes. This measurement allows us to constrain _
Large turbulent reservoirs of cold molecular gas around high-redshift starbur...Sérgio Sacani
Starburst galaxies at the peak of cosmic star formation1
are among
the most extreme star-forming engines in the Universe, producing
stars over about 100 million years (ref. 2). The star-formation
rates of these galaxies, which exceed 100 solar masses per year,
require large reservoirs of cold molecular gas3
to be delivered to
their cores, despite strong feedback from stars or active galactic
nuclei4,5
. Consequently, starburst galaxies are ideal for studying the
interplay between this feedback and the growth of a galaxy6
. The
methylidyne cation, CH+, is a most useful molecule for such studies
because it cannot form in cold gas without suprathermal energy
input, so its presence indicates dissipation of mechanical energy7–9
or strong ultraviolet irradiation10,11. Here we report the detection of
CH+ (J=1–0) emission and absorption lines in the spectra of six
lensed starburst galaxies12–15 at redshifts near 2.5. This line has
such a high critical density for excitation that it is emitted only in
very dense gas, and is absorbed in low-density gas10. We find that
the CH+ emission lines, which are broader than 1,000 kilometres
per second, originate in dense shock waves powered by hot galactic
winds. The CH+ absorption lines reveal highly turbulent reservoirs
of cool (about 100 kelvin), low-density gas, extending far (more than
10 kiloparsecs) outside the starburst galaxies (which have radii of
less than 1 kiloparsec). We show that the galactic winds sustain
turbulence in the 10-kiloparsec-scale environments of the galaxies,
processing these environments into multiphase, gravitationally
bound reservoirs. However, the mass outflow rates are found to be
insufficient to balance the star-formation rates. Another mass input
is therefore required for these reservoirs, which could be provided by
ongoing mergers16 or cold-stream accretion17,18. Our results suggest
that galactic feedback, coupled jointly to turbulence and gravity,
extends the starburst phase of a galaxy instead of quenching it
•Lunar laser telemetry consists in determining the round-trip travel time of the light between a transmitter on the Earth and a reflector on the Moon, which is an equivalent measurement of the distance between these two points
An unusual white dwarf star may be a surviving remnant of a subluminous Type ...Sérgio Sacani
Subluminous Type Ia supernovae, such as the Type Iax–class prototype SN 2002cx, are
described by a variety of models such as the failed detonation and partial deflagration
of an accreting carbon-oxygen white dwarf star or the explosion of an accreting, hybrid
carbon-oxygen-neon core. These models predict that bound remnants survive such
events with, according to some simulations, a high kick velocity.We report the discovery
of a high proper motion, low-mass white dwarf (LP 40-365) that travels at a velocity
greater than the Galactic escape velocity and whose peculiar atmosphere is dominated
by intermediate-mass elements. Strong evidence indicates that this partially burnt
remnant was ejected following a subluminous Type Ia supernova event. This supports the
viability of single-degenerate supernova progenitors.
Proper-motion age dating of the progeny of Nova Scorpii ad 1437Sérgio Sacani
‘Cataclysmic variables’ are binary star systems in which one
star of the pair is a white dwarf, and which often generate bright
and energetic stellar outbursts. Classical novae are one type of
outburst: when the white dwarf accretes enough matter from its
companion, the resulting hydrogen-rich atmospheric envelope
can host a runaway thermonuclear reaction that generates a rapid
brightening1–4. Achieving peak luminosities of up to one million
times that of the Sun5
, all classical novae are recurrent, on timescales
of months6
to millennia7
. During the century before and after an
eruption, the ‘novalike’ binary systems that give rise to classical
novae exhibit high rates of mass transfer to their white dwarfs8
.
Another type of outburst is the dwarf nova: these occur in binaries
that have stellar masses and periods indistinguishable from those
of novalikes9
but much lower mass-transfer rates10, when accretiondisk
instabilities11 drop matter onto the white dwarfs. The coexistence
at the same orbital period of novalike binaries and dwarf
novae—which are identical but for their widely varying accretion
rates—has been a longstanding puzzle9
. Here we report the recovery
of the binary star underlying the classical nova eruption of 11 March
ad 1437 (refs 12, 13), and independently confirm its age by propermotion
dating. We show that, almost 500 years after a classical-nova
event, the system exhibited dwarf-nova eruptions. The three other
oldest recovered classical novae14–16 display nova shells, but lack
firm post-eruption ages17,18, and are also dwarf novae at present.
We conclude that many old novae become dwarf novae for part of
the millennia between successive nova eruptions19,
Polarized reflected light from the Spica binary systemSérgio Sacani
Close binary systems often show linear polarization varying
over the binary period, usually attributed to light scattered
from electrons in circumstellar clouds1–3
. One of the brightest
close binary systems is Spica (alpha Virginis) consisting of
two B-type stars orbiting with a period of just over four days.
Past observations of Spica have shown low polarization with
no evidence for variability4–6. Here we report new high-precision polarization observations of Spica that show variation
with an amplitude of about 200 parts per million. By including
polarized radiative transfer in a binary star model, we show
that the phase-dependent polarization is mainly due to light
reflected from the primary component of the binary system
off the secondary component and vice versa. The stars reflect
only a few per cent of the incident light, but the reflected light
is very highly polarized. The polarization results show that the
binary orbit is clockwise and the position angle of the line of
nodes is 130.4° ± 6.8°, in agreement with intensity interferometer results7
. We suggest that reflected light polarization
may be much more important in binary systems than has previously been recognized and may be a way of detecting previously unrecognized close binaries.
An Earth-sized exoplanet with a Mercury-like compositionSérgio Sacani
Earth, Venus, Mars and some extrasolar terrestrial planets1
have a mass and radius that is consistent with a mass fraction
of about 30% metallic core and 70% silicate mantle2
. At the
inner frontier of the Solar System, Mercury has a completely
different composition, with a mass fraction of about 70%
metallic core and 30% silicate mantle3
. Several formation or
evolution scenarios are proposed to explain this metal-rich
composition, such as a giant impact4, mantle evaporation5
or the depletion of silicate at the inner edge of the protoplanetary
disk6. These scenarios are still strongly debated.
Here, we report the discovery of a multiple transiting planetary
system (K2-229) in which the inner planet has a radius
of 1.165 ± 0.066 Earth radii and a mass of 2.59 ± 0.43 Earth
masses. This Earth-sized planet thus has a core-mass fraction
that is compatible with that of Mercury, although it was
expected to be similar to that of Earth based on host-star
chemistry7
. This larger Mercury analogue either formed with
a very peculiar composition or has evolved, for example, by
losing part of its mantle. Further characterization of Mercurylike
exoplanets such as K2-229 b will help to put the detailed
in situ observations of Mercury (with MESSENGER and
BepiColombo8) into the global context of the formation and
evolution of solar and extrasolar terrestrial planets.
Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U...Sérgio Sacani
During the formation and evolution of the Solar System, significant
numbers of cometary and asteroidal bodies were
ejected into interstellar space1,2. It is reasonable to expect that
the same happened for planetary systems other than our own.
Detection of such interstellar objects would allow us to probe
the planetesimal formation processes around other stars, possibly
together with the effects of long-term exposure to the
interstellar medium. 1I/2017 U1 ‘Oumuamua is the first known
interstellar object, discovered by the Pan-STARRS1 telescope
in October 2017 (ref. 3). The discovery epoch photometry
implies a highly elongated body with radii of ~ 200 × 20 m
when a comet-like geometric albedo of 0.04 is assumed. The
observable interstellar object population is expected to be
dominated by comet-like bodies in agreement with our spectra,
yet the reported inactivity of 'Oumuamua implies a lack
of surface ice. Here, we report spectroscopic characterization
of ‘Oumuamua, finding it to be variable with time but similar
to organically rich surfaces found in the outer Solar System.
We show that this is consistent with predictions of an insulating
mantle produced by long-term cosmic ray exposure4.
An internal icy composition cannot therefore be ruled out by
the lack of activity, even though ‘Oumuamua passed within
0.25 au of the Sun.
Micrometeoroid infall onto Saturn’s rings constrains their age to no more tha...Sérgio Sacani
There is ongoing debate as to whether Saturn’s main rings are relatively young or ancient— having been formed
shortly after Saturn or during the Late Heavy Bombardment. The rings are mostly water-ice but are polluted by
non-icy material with a volume fraction ranging from ∼0.1 to 2%. Continuous bombardment by micrometeoroids exogenic to the Saturnian system is a source of this non-icy material. Knowledge of the incoming mass flux
of these pollutants allows estimation of the rings’ exposure time, providing a limit on their age. Here we report
the final measurements by Cassini’s Cosmic Dust Analyzer of the micrometeoroid flux into the Saturnian system.
Several populations are present, but the flux is dominated by low-relative velocity objects such as from the
Kuiper belt. We find a mass flux between 6.9 · 10−17 and 2.7 · 10−16 kg m−2
s
−1 from which we infer a ring exposure time ≲100 to 400 million years in support of recent ring formation scenarios.
The habitability of Proxima Centauri b - I. Irradiation, rotation and volatil...Sérgio Sacani
Proxima b is a planet with a minimum mass of 1.3 M⊕ orbiting within the habitable zone (HZ) of Proxima Centauri, a very low-mass,
active star and the Sun’s closest neighbor. Here we investigate a number of factors related to the potential habitability of Proxima b
and its ability to maintain liquid water on its surface. We set the stage by estimating the current high-energy irradiance of the planet
and show that the planet currently receives 30 times more EUV radiation than Earth and 250 times more X-rays. We compute the time
evolution of the star’s spectrum, which is essential for modeling the flux received over Proxima b’s lifetime. We also show that Proxima
b’s obliquity is likely null and its spin is either synchronous or in a 3:2 spin-orbit resonance, depending on the planet’s eccentricity and
level of triaxiality. Next we consider the evolution of Proxima b’s water inventory. We use our spectral energy distribution to compute
the hydrogen loss from the planet with an improved energy-limited escape formalism. Despite the high level of stellar activity we find
that Proxima b is likely to have lost less than an Earth ocean’s worth of hydrogen (EOH) before it reached the HZ 100–200 Myr after
its formation. The largest uncertainty in our work is the initial water budget, which is not constrained by planet formation models. We
conclude that Proxima b is a viable candidate habitable planet.
The extremely high albedo of LTT 9779 b revealed by CHEOPSSérgio Sacani
Optical secondary eclipse measurements of small planets can provide a wealth of information about the reflective properties
of these worlds, but the measurements are particularly challenging to attain because of their relatively shallow depth. If such signals
can be detected and modeled, however, they can provide planetary albedos, thermal characteristics, and information on absorbers in
the upper atmosphere.
Aims. We aim to detect and characterize the optical secondary eclipse of the planet LTT 9779 b using the CHaracterising ExOPlanet
Satellite (CHEOPS) to measure the planetary albedo and search for the signature of atmospheric condensates.
Methods. We observed ten secondary eclipses of the planet with CHEOPS. We carefully analyzed and detrended the light curves using
three independent methods to perform the final astrophysical detrending and eclipse model fitting of the individual and combined light
curves.
Results. Each of our analysis methods yielded statistically similar results, providing a robust detection of the eclipse of LTT 9779 b
with a depth of 115±24 ppm. This surprisingly large depth provides a geometric albedo for the planet of 0.80+0.10
−0.17, consistent with
estimates of radiative-convective models. This value is similar to that of Venus in our own Solar System. When combining the eclipse
from CHEOPS with the measurements from TESS and Spitzer, our global climate models indicate that LTT 9779 b likely has a super
metal-rich atmosphere, with a lower limit of 400× solar being found, and the presence of silicate clouds. The observations also reveal
hints of optical eclipse depth variability, but these have yet to be confirmed.
Conclusions. The results found here in the optical when combined with those in the near-infrared provide the first steps toward
understanding the atmospheric structure and physical processes of ultrahot Neptune worlds that inhabit the Neptune desert.
Evidence of a plume on Europa from Galileo magnetic and plasma wave signaturesSérgio Sacani
The icy surface of Jupiter’s moon, Europa, is thought to lie
on top of a global ocean1–4. Signatures in some Hubble Space
Telescope images have been associated with putative water
plumes rising above Europa’s surface5,6, providing support for
the ocean theory. However, all telescopic detections reported
were made at the limit of sensitivity of the data5–7
, thereby calling
for a search for plume signatures in in-situ measurements.
Here, we report in-situ evidence of a plume on Europa from
the magnetic field and plasma wave observations acquired on
Galileo’s closest encounter with the moon. During this flyby,
which dropped below 400 km altitude, the magnetometer8
recorded an approximately 1,000-kilometre-scale field rotation
and a decrease of over 200 nT in field magnitude, and
the Plasma Wave Spectrometer9 registered intense localized
wave emissions indicative of a brief but substantial increase
in plasma density. We show that the location, duration and
variations of the magnetic field and plasma wave measurements
are consistent with the interaction of Jupiter’s corotating
plasma with Europa if a plume with characteristics inferred
from Hubble images were erupting from the region of Europa’s
thermal anomalies. These results provide strong independent
evidence of the presence of plumes at Europa.
Artigo descreve a descoberta feita pelo Hubble de que duas luas de Plutão descrevem suas órbitas realizando cambalhotas imprevisíveis. Além disso, o estudo descobriu um link entre as órbitas das luas menores de Plutão.
Mapping spiral structure on the far side of the Milky WaySérgio Sacani
Little is known about the portion of the Milky Way lying beyond the Galactic center at distances
of more than 9 kiloparsec from the Sun. These regions are opaque at optical wavelengths
because of absorption by interstellar dust, and distances are very large and hard to measure.
We report a direct trigonometric parallax distance of 20:4þ2:8
2:2 kiloparsec obtained with the Very
Long Baseline Array to a water maser source in a region of active star formation. These
measurements allow us to shed light on Galactic spiral structure by locating the ScutumCentaurus
spiral arm as it passes through the far side of the Milky Way and to validate a
kinematic method for determining distances in this region on the basis of transverse motions.
"Impact of front-end architecture on development cost", Viktor TurskyiFwdays
I have heard many times that architecture is not important for the front-end. Also, many times I have seen how developers implement features on the front-end just following the standard rules for a framework and think that this is enough to successfully launch the project, and then the project fails. How to prevent this and what approach to choose? I have launched dozens of complex projects and during the talk we will analyze which approaches have worked for me and which have not.
DevOps and Testing slides at DASA ConnectKari Kakkonen
My and Rik Marselis slides at 30.5.2024 DASA Connect conference. We discuss about what is testing, then what is agile testing and finally what is Testing in DevOps. Finally we had lovely workshop with the participants trying to find out different ways to think about quality and testing in different parts of the DevOps infinity loop.
Connector Corner: Automate dynamic content and events by pushing a buttonDianaGray10
Here is something new! In our next Connector Corner webinar, we will demonstrate how you can use a single workflow to:
Create a campaign using Mailchimp with merge tags/fields
Send an interactive Slack channel message (using buttons)
Have the message received by managers and peers along with a test email for review
But there’s more:
In a second workflow supporting the same use case, you’ll see:
Your campaign sent to target colleagues for approval
If the “Approve” button is clicked, a Jira/Zendesk ticket is created for the marketing design team
But—if the “Reject” button is pushed, colleagues will be alerted via Slack message
Join us to learn more about this new, human-in-the-loop capability, brought to you by Integration Service connectors.
And...
Speakers:
Akshay Agnihotri, Product Manager
Charlie Greenberg, Host
Software Delivery At the Speed of AI: Inflectra Invests In AI-Powered QualityInflectra
In this insightful webinar, Inflectra explores how artificial intelligence (AI) is transforming software development and testing. Discover how AI-powered tools are revolutionizing every stage of the software development lifecycle (SDLC), from design and prototyping to testing, deployment, and monitoring.
Learn about:
• The Future of Testing: How AI is shifting testing towards verification, analysis, and higher-level skills, while reducing repetitive tasks.
• Test Automation: How AI-powered test case generation, optimization, and self-healing tests are making testing more efficient and effective.
• Visual Testing: Explore the emerging capabilities of AI in visual testing and how it's set to revolutionize UI verification.
• Inflectra's AI Solutions: See demonstrations of Inflectra's cutting-edge AI tools like the ChatGPT plugin and Azure Open AI platform, designed to streamline your testing process.
Whether you're a developer, tester, or QA professional, this webinar will give you valuable insights into how AI is shaping the future of software delivery.
Neuro-symbolic is not enough, we need neuro-*semantic*Frank van Harmelen
Neuro-symbolic (NeSy) AI is on the rise. However, simply machine learning on just any symbolic structure is not sufficient to really harvest the gains of NeSy. These will only be gained when the symbolic structures have an actual semantics. I give an operational definition of semantics as “predictable inference”.
All of this illustrated with link prediction over knowledge graphs, but the argument is general.
GDG Cloud Southlake #33: Boule & Rebala: Effective AppSec in SDLC using Deplo...James Anderson
Effective Application Security in Software Delivery lifecycle using Deployment Firewall and DBOM
The modern software delivery process (or the CI/CD process) includes many tools, distributed teams, open-source code, and cloud platforms. Constant focus on speed to release software to market, along with the traditional slow and manual security checks has caused gaps in continuous security as an important piece in the software supply chain. Today organizations feel more susceptible to external and internal cyber threats due to the vast attack surface in their applications supply chain and the lack of end-to-end governance and risk management.
The software team must secure its software delivery process to avoid vulnerability and security breaches. This needs to be achieved with existing tool chains and without extensive rework of the delivery processes. This talk will present strategies and techniques for providing visibility into the true risk of the existing vulnerabilities, preventing the introduction of security issues in the software, resolving vulnerabilities in production environments quickly, and capturing the deployment bill of materials (DBOM).
Speakers:
Bob Boule
Robert Boule is a technology enthusiast with PASSION for technology and making things work along with a knack for helping others understand how things work. He comes with around 20 years of solution engineering experience in application security, software continuous delivery, and SaaS platforms. He is known for his dynamic presentations in CI/CD and application security integrated in software delivery lifecycle.
Gopinath Rebala
Gopinath Rebala is the CTO of OpsMx, where he has overall responsibility for the machine learning and data processing architectures for Secure Software Delivery. Gopi also has a strong connection with our customers, leading design and architecture for strategic implementations. Gopi is a frequent speaker and well-known leader in continuous delivery and integrating security into software delivery.
Builder.ai Founder Sachin Dev Duggal's Strategic Approach to Create an Innova...Ramesh Iyer
In today's fast-changing business world, Companies that adapt and embrace new ideas often need help to keep up with the competition. However, fostering a culture of innovation takes much work. It takes vision, leadership and willingness to take risks in the right proportion. Sachin Dev Duggal, co-founder of Builder.ai, has perfected the art of this balance, creating a company culture where creativity and growth are nurtured at each stage.
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Length: 30 minutes
Session Overview
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- What are the benefits of integrating InfluxDB and Grafana into the load testing stack?
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Fast spin of a young extrasolar planet
1. The fast spin-rotation of a young extra-solar planet
Ignas A. G. Snellen1
, Bernhard R. Brandl1
, Remco J. de Kok1,2
, Matteo Brogi1
, Jayne Birkby1
, and
Henriette Schwarz1
1
Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
2
SRON, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
The spin-rotation of a planet arises from the accretion of angular momentum during its
formation1,2,3
, but the details of this process are still unclear. In the solar system, the equatorial
rotation velocities and spin angular momentum of the planets show a clear trend with mass4
,
except for Mercury and Venus which have significantly spun down since their formation due to
tidal interactions5,6
. Here we report on near-infrared spectroscopic observations at λ/Δλ=100,000
of the young extra-solar gas giant β Pictoris b7,8
. The absorption signal from carbon monoxide in
the planet's thermal spectrum is found to be blueshifted with respect to the velocity of the parent
star by (-15±1.7) km sec-1
, consistent with a circular orbit9
. The combined line profile exhibits a
rotational broadening of 25±3 km sec-1
, meaning that β Pictoris b spins significantly faster than
any planet in the solar system, in line with the extrapolation of the known trend in spin velocity
with planet mass.
Near-infrared high-dispersion spectroscopy has been used to characterize the atmospheres of hot
Jupiters in close-in orbits10-11
. Such observations utilize changes in the radial component of the orbital
velocity of the planet (resulting in changes in Doppler shift) to filter out the quasi-stationary telluric
and stellar contributions in the spectra. Here we make use of the spatial separation and the difference
in spectral signature between the planet and star, which allow the starlight to be filtered out. A similar
technique12
has been applied very successfully13
at a medium spectral dispersion to characterize the
exoplanet HR8799c. We observed the β Pictoris system7,8
(K=3.5) using the Cryogenic high-
Resolution InfraRed Echelle Spectrograph CRIRES14
located at the Nasmyth focus of UT1 of the Very
Large Telescope (VLT) of the European Southern Observatory (ESO) at Cerro Paranal in Chile on the
night of 17 December 2013, with the slit oriented in such way that it encompassed the planet and star.
An important step in the data analysis is the optimal removal of the stellar contribution along the slit,
which for this A-star consists mostly of a telluric absorption spectrum. The resulting spectra were
cross-correlated with theoretical spectral templates constructed in a similar way as in our previous
work on hot Jupiters10-11
, varying the planet's atmospheric temperature pressure (T/p) profile, the
carbon monoxide abundance and that of water vapor and methane, which can also show features in the
observed wavelength range. Note that there is a strong degeneracy between the atmospheric T/p
2. profile and the abundance of the molecular species, meaning that different combinations of these
parameters result in nearly identical template spectra.
At the expected planet position a broad and blue-shifted signal is apparent (see Figure 1), which is
strongest when the cross-correlation is performed with a spectral template from an atmospheric model
with deep carbon monoxide lines and a small contribution from water. We estimate the signal to have a
SNR of 6.4 by cross-correlating the residual spectrum with a broadened model template, and compare
the peak of the cross-correlation profile with the standard deviation. If we use the cross-correlation
profile as seen in Figure 1 to estimate the SNR, we need to take into account the width of the signal
and the dependence of adjacent pixels in the profile. This results in an SNR of 7.8, but this latter
method we found to be less accurate, since it does not properly include contributions from correlated
noise structures on scales of the broad signal. Cross-correlation with the optimal spectrum of water
vapor alone provides a marginal signal at SNR~2, which means we cannot claim a firm detection of
water in the planet atmosphere. No signal is retrieved for methane models (see Extended Data Fig. 1).
We fit the planet profile using a grid of artificial cross-correlation functions, produced by cross-
correlating the optimal template spectrum with a broadened and velocity-shifted copy of itself, for a
range of velocities and rotational broadening functions. The best fit (left panel of Figure 2) was
obtained for a blue-shifted radial velocity of -15.4±1.7 km sec-1
(1σ, including the uncertainties in the
system velocity, +20±0.7 km sec-1
, of the star15
) and a rotational broadening of 25±3 km sec-1
(1σ),
with the uncertainties estimated from chi-squared analysis. Cross-correlation with other less optimal
model templates give only small variations in these values at the < 0.3σ level (see Methods section).
Monitoring the position of the planet over the last decade9
has resulted in an estimate of the orbital
radius of 8 - 9 AU and an orbital period of 17-20 years. The planet ephemeris9
, assuming a circular
orbit, provides a planet radial velocity relative to the star of 13.2 - 14.1 km sec-1
(1σ) either towards or
away from us. This means there is no evidence for an eccentric orbit from our one planet radial
velocity measurement. Since the orbital inclination has been constrained9
to >86.8o
, the planet has a
~20% probability to transit its parent star. Marginal evidence was presented for a possible transit
event16,17
in 1981. That the planet is now moving towards us means that it is approaching inferior
conjunction in the period 2017.5-2018.5, and previously during 1998-2001 and 1978-1984. This is
consistent with a transit event in 1981. Note that if this event is spurious, there was an a priori
probability of 50% for the direction (e.g. clockwise or anti-clockwise) of the planet motion to be
consistent with the 1981 event.
The equatorial spin-rotation velocity of Vspin = 25 km sec-1
of β Pictoris b is higher than for any planet
3. in the Solar-System. The Solar System planets show a clear correlation between their equatorial
rotation velocity (or spin angular momentum) and mass4
(see the right panel of Figure 2), the former
ranging from 0.24 km sec-1
for Mars to 13.3 km sec-1
for Jupiter. Both Mercury and Venus have
dropped significantly below this relation since they have spun down from the tidal interactions with
the Sun5,6
. Also the Earth has slowed down due to the gravitational interaction with the Moon18
. The
origin of the Vspin-mass relation is not known, but must be linked to the mass accretion processes
during planet formation. The mass of β Pictoris b is highly uncertain, with estimates depending
strongly on the time since its formation. A commonly used age estimate for the β Pictoris system is
(12+8
-4) Myr, resulting in mass estimates19,20
of (7+4
-3) MJup to (10+3
-2) MJup. However, recently, lithium
depletion in the β Pictoris moving group21
suggests an age of 21±4 Myr, which would increase these
planet mass estimates by ~30%. We therefore adopt a planet age of 11±5 Myr. As can be seen in panel
b of Figure 2, β Pictoris b appears broadly consistent with an extrapolation of the solar system Vspin-
mass relation to higher planet masses. However, the spread in measured projected spin velocities of
L4-L7 brown dwarfs22,23
(open circles) suggest a more complicated relationship for the general
population of substellar objects. Furthermore, despite rotating faster than any planet in the solar
system, β Pictoris b does appear to have a lower Vspin than expected from a direct extrapolation of the
solar system trend, which would point to a spin velocity of 50±12 km sec-1
. This may well be because
the planet is still young and warm (1575-1650 K) and therefore bloated. Although the radius of the
planet cannot be measured directly as in the case of transiting planets, spectral modeling19
of
broadband photometry obtained by direct imaging provides an estimate of 1.65±0.06 RJup. It implies a
rotation period, the length of day on β Pictoris b, of ~8.1±1.0 hours. Over the next hundreds of
millions of years the planet is expected to cool down and shrink to the size of Jupiter24
. If its angular
moment is preserved during this process, the planet should spin up to Vspin ~ 40 km sec-1
, depending
on possible changes in its internal structure, decreasing its length of day to ~3 hours. The reader
should note that in the above we assume that the obliquity, the axial tilt of the planet, is small – which
may not be the case, as we know from Uranus. However, even if we assume that the distribution of
obliquities of extra-solar gas giants is random, the average component in the direction of Earth is 30o
,
resulting in an underestimate of Vspin of only 1 / cos(30o
) = 15%.
Methods Summary
We targeted the 2-0 R-branch of carbon monoxide absorption using the two central detectors of
CRIRES, resulting in a wavelength range of 2.303 to 2.331 μm. The CRIRES slit (width=0.2″) was
oriented at 30o
North through East to encompass the planet, which, according to recent high-contrast
4. imaging observations, was located 0.4″ South-West from the host star19,20
. We utilized the Multi-
Application Curvature Adaptive Optics system (MACAO)25
in 1-1.3″ seeing conditions. This resulted
in a reduction of the starlight at the planet position of a factor 8 to 30 (depending on the seeing).
Therefore, a certain planet/star contrast can be reached 8-30 times faster compared to ‘classical’ high-
dispersion spectroscopy of hot Jupiters, because the noise in the final planet spectrum originates from
the star. After basic calibrations, we optimally extracted a 1D spectrum for each position along the slit,
and subsequently removed the stellar contribution for each position. The resulting spectra were cross-
correlated with planet model spectra (Extended Data Fig.1), which were produced in a similar way as
for our previous work on hot Jupiters10-12
.
The SNR that can be achieved on a planet spectrum for this type of observation is a strong function of
telescope diameter D. This opens the way of obtaining two-dimensional maps of the planet using
Doppler imaging, a technique used to map spot distributions on fast-rotating active stars26-29
. Very
recently, a first Doppler image map was produced for the nearby brown dwarf Luhman 16B (K=9.73)
using CRIRES on the VLT, showing large-scale bright and dark features, indicative of patchy clouds23
.
The planet β Pictoris b is only a factor 13 fainter than Luhman 16B. Our simulations (Extended Data
Fig.2) show that a similar study can be conducted on β Pictoris b using future instrumentation.
References
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on a circular orbit, Icarus 94, 126-159 (1991)
2. Dones, L., Tremaine, S., On the origin of planetary spins, Icarus 103, 67-92 (1993)
3. Johansen, A., Lacerda, P., Prograde rotation of protoplanets by accretion of pebbles in a gaseous
environment, Mon. Not. R. Astron. Soc. 404, 475-485 (2010)
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206, 1240 (1965)
6. Correia, A. C. M., Laskar, J., The four final rotation states of Venus, Nature 411, 767-770. (2001)
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Rouan, D., Allard, F., Gendron, É., Charton, J., Mugnier, L., Rabou, P., Montri, J., Lacombe, F., A
probable giant planet imaged in the β Pictoris disk, Astron. Astrophys. 493, L21–L25 (2009)
8. Lagrange, A.- M., Bonnefoy, M., Chauvin, G., Apai, D., Ehrenreich, D., Boccaletti, A., Gratadour,
D., Rouan, D., Mouillet, D., Lacour, S., Kasper, M., A Giant Planet Imaged in the Disk of the Young
Star Pictoris, Science 329, 57–59 (2010)
5. 9. Chauvin, G., Lagrange, A.-M., Beust, H., Bonnefoy, M., Boccaletti, A., Apai, D., Allard, F.,
Ehrenreich, D., Girard, J. H. V., Mouillet, D., Rouan, D., Orbital characterization of the β Pictoris b
giant planet, Astron. Astrophys. 542, A41 (2012)
10. Brogi, M., Snellen, I., de Kok, R., Albrecht, S., Birkby, J., de Mooij, E., The signature of orbital
motion from the dayside of the planet tau Bootis b, Nature 486, 502-504 (2012)
11. de Kok, R., Brogi, M., Snellen, I., Birkby, J., Albrecht, S., de Mooij, E., Detection of carbon
monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b, Astron. Astrophys.
554, A82 (2013)
12. Sparks, W.B. & Ford, H.C., Imaging Spectroscopy for Extrasolar Planet Detection, Astrophys. J.
578, 543 (2002)
13. Konopacky, Q.M., Barman, T.S., Macintosh, B.A., Marois, C., Detection of Carbon Monoxide and
Water Absorption Lines in an Exoplanet Atmosphere, Science 339, 1398-1401 (2013)
14. Kaeufl, H.-U., et al., CRIRES: a high-resolution infrared spectrograph for ESO's VLT., Ground-
based Instrumentation for Astronomy 5492, 1218-1227 (2004)
15. Gontcharov, G. A., Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a
common system, Astronomy Letters 32, 759-771 (2006)
16. Lecavelier Des Etangs, A., Deleuil, M., Vidal-Madjar, A., Ferlet, R., Nitschelm, C., Nicolet, B.,
Lagrange-Henri, A. M., beta Pictoris: evidence of light variations, Astron. Astrophys. 299, 557 (1995)
17. Lecavelier Des Etangs, A., Vidal-Madjar, A., Burki, G., Lamers, H., Ferlet, R., Nitschelm, C.,
Sevre, Beta Pictoris light variations. I. The planetary hypothesis, Astron. Astrophys. 328, 311-320
(1997)
18. Cuk, M., Stewart, S., Making the Moon from a Fast-Spinning Earth: A Giant
Impact Followed by Resonant Despinning, Science 338, 1047 (2012)
19. Currie, T., Burrows, A., Madhusudhan, N., Fukagawa, M., Girard, J., Dawson, R., Murray-Clay,
R., Kenyon, S., Kuchner, M., Matsumura, S., Jayawardhana, R., Chambers, J., Bromley, B., A
Combined Very Large Telescope and Gemini Study of the Atmosphere of the Directly Imaged Planet,
β Pictoris b, Astrophys. J. 776, 15 (2013)
20. Bonnefoy, M., et al, The near-infrared spectral energy distribution of beta Pictoris b, Astron.
Astrophys. 555, A107 (2013)
21. Binks A.S, Jeffries R.D., A lithium depletion boundary age of 21 Myr for the Beta Pictoris moving
group, Mon. Not. R. Astron. Soc. 438, L11-L15 (2014)
22. Konopacky Q.M., Ghez A.M., Fabrycky D.C., Macintosh B.A., White R.J., et al., Rotational
velocities of individual components in very low mass binaries, Astroph. J. 750, 79-93 (2012)
23. Crossfield, I., et al., A Global Cloud Map of the Nearest Known Brown Dwarf, Nature 505, 654–
6. 656 (2014)
24. Baraffe I., Chabrier G., Barman T.S., Allard F., Hauschildt P.H., Evolutionarymodels for cool
brown dwarfs and extrasolar giant planets, Astron. Astrophys. 402, 701-712 (2003)
25. Arsenault, R., et al., MACAO-VLTI: An Adaptive Optics system for the ESO VLT interferometer,
Adaptive Optical System Technologies II 4839, 174-185. (2003)
26. Vogt, S., Penrod, G., Doppler Imaging of spotted stars - Application to the RS Canum Venaticorum
star HR 1099, Publications of the Astronomical Society of the Pacific 95, 565-576 (1983)
27. Vogt, S., Hatzes, A., Misch, A., Kurster, M., Doppler Imagery of the Spotted RS Canum
Venaticorum Star HR 1099 (V711 Tauri) from 1981 to 1992, Astrophys. J. Suppl. 121, 547-589 (1999)
28. Barnes, J., Collier Cameron, A., James, D., Donati, J.-F., Doppler images from dual-site
observations of southern rapidly rotating stars - I. Differential rotation on PZ Tel, Mon. Not. R. Astron.
Soc. 314, 162-174 (2000)
29. Vogt, S., Penrod, G., Hatzes, A., Doppler images of rotating stars using maximum entropy image
reconstruction. Astrophys. J. 321, 496-515 (1987)
Acknowledgements We thank ESO director Tim de Zeeuw for granting Director's Discretionary Time
on the Very Large Telescope to perform these observations (292.C-5017(A)). I.S. acknowledges
support from an NWO VICI grant. R.d.K acknowledges the NWO PEPSci program.
Author Contributions I.S. conceived the project with help from B.B, R.d.K, M.B, J.B. The analysis
was led by I.S. and he wrote the first version of the manuscript. I.S. and B.B. conceived the connection
with the ELT. R.d.K constructed the planet atmosphere models. B.B, R.d.K, M.B., J.B., and H.S.
discussed the analyses, results, and commented on the manuscript.
Author Information The authors declare no competing financial interests. Correspondence and
request for materials should be addressed to I.S. (e-mail: snellen@strw.leidenuniv.nl).
Figure 1. The broadened cross-correlation signal of β Pictoris b. Panel a) shows the CO+H2O
cross-correlation (CC) signal as function of the position along the slit (rotated by 30o
North to East),
after the stellar contribution was removed. The x-axis shows the radial velocity with respect the
system velocity (+20±0.7 km sec-1
) of the star15
. The y-axis denotes the relative position with respect
7. to the star β Pictoris with the planet located 0.4″ below, both indicated by horizontal dashed lines. A
broad signal, at an SNR of 6.4 is visible, blue-shifted by -15.4±1.4 km sec-1
(1σ) with respect to the
system velocity. Panel b) shows the CC signal at the planet position. The dotted curve shows the
arbitrarily scaled auto-correlation function of the λ/Δλ=100,000 model template, indicating the CC-
signal expected from a non-rotating planet.
Figure 2. The Spin-rotation of β Pictoris b. Panel a) shows the CO+H2O cross correlation signal of
the planet β Pictoris b (solid line). The dashed line indicates the best fit to the cross-correlation profile
of the model template with a copy of itself, rotationally broadened by 25 km sec-1
. The grey area
indicates the 1σ uncertainty in the level of broadening of ±3 km sec-1
. Panel b) shows the equatorial
rotation velocity of the solar system planets as function of planet mass, each planet indicated by its
first letter. Note that Mercury and Venus are not visible on this plot. Tidal interactions with the Sun
made these planets to significantly spin down to Vspin <<0.1 km sec-1
. β Pictoris b is indicated with a
planet mass of 11±
5 MJup, consistent with the solar system mass-Vspin trend extended to higher masses.
The open circles indicate the projected spin velocities of L4-L7 type brown dwarfs from refs 22 and
23.
Methods
Observations and Data Analysis
We targeted the 2-0 R-branch of carbon monoxide absorption using the two central detectors of
CRIRES, resulting in a wavelength range of 2.303 to 2.331 μm. The slit (width=0.2″) was oriented at
30o
North through East to encompass the planet, which, according to recent high-contrast imaging
observations, was located 0.4″ South-West from the host star19,20
. We took 44 exposures of 4x10
seconds utilizing an ABBA dither pattern to enable accurate background subtraction. In addition, each
dither position was given a small but random offset to minimize potential flat-fielding issues. We
utilized the Multi-Application Curvature Adaptive Optics system (MACAO)25
in 1-1.3″ seeing
conditions. This resulted in a reduction of the starlight at the planet position of a factor 8 to 30
(depending on the seeing). Therefore, a certain planet/star contrast can be reached 8-30 times faster
compared to ‘classical’ high-dispersion spectroscopy of hot Jupiters, because the noise in the final
planet spectrum originates from the star.
We performed the basic calibrations on the individual frames using the standard CRIRES reduction
pipeline30
, including dark subtraction, flat fielding, and non-linearity corrections, after which the
8. frames in the AB or BA pairs of two points along the slit were subtracted from each other.
Subsequently, the frames of each pair of two-dimensional spectra were combined. The subsequent
analysis was performed on the resulting 22 intermediate data products from the pipeline using IDL
routines. We determined the spatial profiles of the star as function of wavelength, which we
subsequently used to optimally extract a 1D spectrum for each position along the slit, in steps of one
spatial pixel of 0.086″, with the planet expected to be located about five pixels from the center of the
star9
. The combined spectrum of 30 pixel rows along the slit was taken as a reference of the stellar
spectrum and used to remove the stellar contribution from each spatial pixel position along the slit – a
crucial step in the data analysis. At the central position of the star, its spatial profile is narrow
compared to the slit-width, resulting in a higher spectral resolution compared to elsewhere along the
slit, in addition to a small wavelength offset because the star was not exactly centered in the slit. To
remove the star light properly at each position along the slit, the reference spectrum not only had to be
scaled, but also shifted and convolved with a broadening function. This broadening function was
determined for each individual slit position and frame, using the Singular Value Decomposition
technique31
. The reader should note that the average reference spectrum contains planet light at a level
of 1/8 to 1/30 of that at the planet position, marginally weakening the expected signal by that amount.
The residual spectra as function of position along the slit for the 22 frames were subsequently
combined, weighing the frames according to their varying (seeing induced) stellar profile, and thus
maximizing the expected SNR of the final planet spectrum.
Planet model spectra were produced in a similar way as for our previous work on hot Jupiters10,11,32,33
.
A uniform temperature-Pressure (T/p) profile was assumed to describe the vertical structure of the
planet atmosphere, parameterized by two points, (T1,p1) and (T2,p2). Below and above these levels in
the atmosphere the temperature was assumed to be constant at T1 and T2, respectively. At pressures
p1>p>p2 a constant lapse rate was assumed as δT/δlog10p = (T2-T1)/(log10p2-log10p1). The model
spectra were subsequently produced using line-by-line calculations including H2-H2 collision-induced
absorption34,35
and absorption from three trace gases, i.e. CO, H2O, and CH4, which are the dominant
sources of opacities at these wavelengths36,37
. Line data for the trace gases were taken38,39
from
HITEMP 2010 for H2O and CO, and HITRAN 2008 for CH4. A Voigt line profile was used for the
calculations.
Since large degeneracies exist between different models, we did not explore a full grid of models
varying (T1,p1) , (T2,p2) and the molecular abundances. This can be seen in Extended Data Figure 1,
which shows the results of five different models, with the parameters indicated in the title. The two top
models have a CO volume mixing ratio (VMR) that differ by three orders of magnitude (VMRCO=10-
1.5
versus 10-4.5
), but both show a strong signal. If we mix in other molecules, the significance of the
9. detected signal becomes lower. This can be seen by cross-correlating with the third model, which is for
a low CO and high H2O VMR, showing that the signal is still visible but at a significantly lower SNR
than above. This is in line with the fourth model spectrum consisting of H2O only, which gives only a
marginal detection at SNR~2. We therefore cannot claim a firm detection of water vapour in this
planet atmosphere. The last model is for CH4 only – showing no signal.
Doppler Imaging simulations
High-dispersion spectral observations that aim to characterize exoplanet atmospheres have so far been
restricted to hot Jupiters in very close-in orbits. Such observations utilize changes in the radial
component of the orbital velocity of the planet (resulting in changes in Doppler shift) to filter out the
quasi-static telluric and stellar contributions in the spectra. Here we use high-dispersion spectroscopy
to characterize the young gas giant β Pictoris b, which was previously discovered using high-contrast
imaging techniques. These observations make use of the angular separation and the spectral
differences between the planet and the star. While the planet to star contrast is about 3800 at 2.3 μm,
the starlight is reduced by a factor 8 to 30 (varying with the seeing) at the planet position 0.4″ away,
making the planet-light buried at a level 1/500th
to 1/100th
in the wing of the stellar spatial profile. This
stellar contribution, which is dominated by telluric absorption, can be filtered out very effectively
since this spectrum is well determined along the slit, albeit with small variations in the spectral
dispersion which are taken into account, and it is therefore known at a very high signal to noise. A
similar technique12
has been applied very successfully13
at a medium spectral dispersion to
characterize the exoplanet HR8799c.
The relative ease at which the presented detection was obtained is noteworthy, using only 1 hour of
observing time (including overheads) on an 8m-class telescope in mediocre seeing. If the CO signal
was not smeared out over -25 to +25 km sec-1
due to the planet rotation, but concentrated in an
unresolved signal, it would have been detected at a SNR~15. We also investigated the scientific
potential of the future European Extremely Large Telescopes (E-ELT) for these kinds of observations.
METIS, the Mid-infrared E-ELT Imager and Spectrograph40
, will have a λ/Δλ=100,000 integral field
spectrograph in the 3-5 μm wavelength range. This does not cover the 2.3 μm CO, but H2O at 3.2 or
3.5 μm can also be targeted highly effectively. The absorption features are probably somewhat weaker
than those of CO at 2.3 μm, but both the planet/star contrast and the flux from the planet are more than
a factor two higher. Alternatively, the HIRES spectrograph41
is expected to cover the optical to near-
infrared wavelength regime, and can be used for this type of observation, if it is designed with a slit or
with multiple fibers that can cover both the star and the planet. The other Extremely Large Telescope
projects, the Giant Magellan Telescope42
and the Thirty Meter Telescope43
, also have optical and
10. infrared high-resolution spectrographs in their instrument roadmaps.
In this work we focus on the E-ELT. For simplicity, we will assume a spectrograph concept similar to
CRIRES, using an adaptive optics system that produces similar Strehl ratios under the same
atmospheric conditions. Since the angular resolution of the telescope scales with λ/D, with D the
telescope diameter (D=39m for the E-ELT), the angular distance of the planet from the star in units of
diffraction elements will be a factor 4.8 larger. In our CRIRES frames the starlight is suppressed by a
factor ~500 at that distance. In addition, the apparent size of the planet is decreased by a factor D2
,
gaining another factor 23. This means that for similar observations with the E-ELT the starlight at the
planet position will be reduced by a factor ~104
, meaning it only marginally contributes to the noise in
the planet spectrum. It implies that with the E-ELT we will be able to observe the K=12.5 planet as if
there were no nearby host star. We use the CRIRES exposure time calculator, multiplying the number
of observations by a factor 23 to account for the increase in collecting area, to estimate that an
exposure of 100 seconds will deliver a λ/δλ=100,000 spectrum of the planet β Pictoris b with an SNR
of ~25 per 1.5 km sec-1
resolution element.
We subsequently take this value to simulate what we can learn about the atmosphere of β Pictoris b
with the E-ELT using Doppler imaging techniques. Doppler imaging26-28
can map inhomogeneities on
a rotator’s surface by monitoring the distortions in rotationally broadened absorption lines. By
monitoring features in the velocity broadening function to appear, shift in velocity and disappear, the
planet brightness distribution can be solved for using maximum entropy mapping29
, as done for stars.
The reader should note that very recently, a first Doppler image map was produced for the nearby
brown dwarf Luhman 16B (K=9.73) using CRIRES on the VLT, showing large-scale bright and dark
features, indicative of patchy clouds23
. The planet β Pictoris b is a factor 13 fainter than Luhman 16B,
meaning that such result can be obtained almost two times faster with the E-ELT for the planet, than
with the VLT for the brown dwarf. To simulate this we have constructed a toy model map of the
planet’s atmospheric surface of 360x180 pixels with an uniform surface brightness, except for one spot
twice as bright, at a latitude of +55o
and with a radius of 10o
. Note that we gave the planet an obliquity
of 30o
. A low spin-axial tilt will result in a degeneracy for features on opposite hemispheres, although
this is not relevant for these forward simulations. We subsequently calculated the overall spectrum of
the planet for three viewing angles, which are consecutively observed at one hour intervals. The CO
model that fits our CRIRES data best is assigned to each pixel in the planet surface map.
Subsequently, each surface-pixel visible from the modelled viewing angle attributed to the overall
spectrum, Doppler shifted according to the radial component of its rotation velocity and weighed by
the cosine of the local surface viewing-angle.
11. The three observations were simulated with an exposure time of 15 minutes each, meaning they have a
SNR of 75 per resolution element. Gaussian noise was added to the three spectra accordingly. The
three spectra were subsequently cross-correlated with the model spectrum, of which the result is
shown in the right panel of Extended Data Figure 2. It shows the great potential of obtaining a 2D map
of the planet by using maximum entropy mapping. This can lead to unique exploration tools, such as
the monitoring of multiple spots or other atmospheric features like dark or bright bands at different
planet latitudes, which can solve for effects from the planet obliquity, oblateness, limb darkening,
and/or differential rotation.
30. CRIRES Data reduction pipeline:
http://www.eso.org/observing/dfo/quality/CRIRES/pipeline/pipe_gen.html
31. Rucinski, S., Determination of Broadening Functions Using the Singular-Value
Decomposition (SVD) Technique, IAU Colloq. 170: Precise Stellar Radial
Velocities 185, 82 (1999)
32. Brogi, M., Snellen, I., de Kok, R., Albrecht, S., Birkby, J., de Mooij, E. Detection of Molecular
Absorption in the Dayside of Exoplanet 51 Pegasi b?, Astrophys. J. 767, 27. (2013)
33. Birkby, J.L., de Kok, R.J., Brogi, M., de Mooij, E.J.W., Schwarz, H., Albrecht, S., Snellen, I.A.G.,
Detection of water absorption in the day side atmosphere of HD 189733 b using ground-based high-
resolution spectroscopy at 3.2 um, Mon. Not. R. Astron. Soc. 436, L35-L39 (2013)
34. Borysow, A. , Jorgensen U.G., Fu, Y, High-temperature (1000–7000 K) collision-induced
absorption of H2 pairs computed from the first principles, with application to cool and dense stellar
atmospheres, J. Quant. Spec. Radiat. Transf. 68, 235 (2001)
35. Borysow, A. 2002, Collision-Induced absorption coefficients of H2 pairs at temperatures from 60
K to 1000 K, Astron. Astroph. 390, 779 (2002)
36. Madhusudhan, N. 2012, C/O Ratio as a Dimension for Characterizing Exoplanetary Atmospheres,
Astrophys. J. 758, 36 (2012)
37. Moses, J. I., Madhusudhan, N., Visscher, C., & Freedman, R. S., Chemical Consequences of the
C/O Ratio on Hot Jupiters: Examples from WASP-12b, CoRoT-2b, XO-1b, and HD 189733b,
Astrophys. J. 763, 25 (2013)
38. Rothman, L. S., Gordon, I. E., Barber, R. J., et al., HITEMP, the high-temperature spectroscopic
database, J. Quant. Spec. Radiat. Transf. 111, 2139 (2010)
39. Rothman, L. S., Gordon, I. E., Barbe, A., et al., The HITRAN 2008 molecular spectroscopic
12. database, J. Quant. Spec. Radiat. Transf., 110, 533 (2009)
40. Brandl, B. et al., METIS: the thermal infrared instrument for the E-ELT, Society of Photo-Optical
Instrumentation Engineers (SPIE) Conference Series 8446 (2012)
41. Maiolino R., et al., A Community Science Case for E-ELT HIRES, http://arxiv.org/abs/1310.3163
(2013)
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SPIE 7735, 87
43. http://www.tmt.org/
CAPTION EXTENDED DATA FIGURE 1
Model Spectra and cross-correlation signals. The model spectral templates (left panels) and the
resulting cross-correlation signals (right panels) for (from top to bottom), 1) a high VMR CO model,
2) a low VMR CO model, 3) the same but adding a high VMR of H2O, 4) a H2O only mode, and 5) a
CH4 model. Atmospheric pressures are in units of bar.
CAPTION EXTENDED DATA FIGURE 2
Simulated E-ELT observations. We simulated observations using the future 39 m European
Extremely Large Telescope (E-ELT) of a rotating spot on β Pictoris b. Such observations could be
conducted with the planned METIS40
. The three panels on the left, denoted a, b, and c, show the
position of the spot approximately 1 hour apart, which was given a surface brightness of twice of the
rest of the planet atmosphere. The right panel shows the difference between three cross-correlation
signals with respect to the average cross-correlation profile as indicated by the dashed curve (scaled
down by a factor 25), with the spot signature moving from -15 to +5 km sec-1
.