36 research outputs found
Transiting exocomets detected in broadband light by TESS in the Pictoris system
We search for signs of falling evaporating bodies (FEBs, also known as
exocomets) in photometric time series obtained for Pictoris after
fitting and removing its Scuti type pulsation frequencies. Using
photometric data obtained by the TESS satellite we determine the pulsational
properties of the exoplanet host star Pictoris through frequency
analysis. We then prewhiten the 54 identified Scuti p-modes and
investigate the residual photometric time series for the presence of FEBs. We
identify three distinct dipping events in the light curve of Pictoris
over a 105-day period. These dips have depths from 0.5 to 2 millimagnitudes and
durations of up to 2 days for the largest dip. These dips are asymmetric in
nature and are consistent with a model of an evaporating comet with an extended
tail crossing the disk of the star. We present the first broadband detections
of exocomets crossing the disk of Pictoris, consistent with the
predictions made 20 years earlier by Lecavelier Des Etangs et al. (1999). No
periodic transits are seen in this time series. These observations confirm the
spectroscopic detection of exocomets in Calcium H and K lines that have been
seen in high resolution spectroscopy.Comment: Accepted version updated with correct references to Rappaport et al.
(2018) and various typo
CHEOPS's hunt for exocomets: photometric observations of 5 Vul
The presence of minor bodies in exoplanetary systems is in most cases
inferred through infra-red excesses, with the exception of exocomets. Even if
over 35 years have passed since the first detection of exocomets around beta
Pic, only ~ 25 systems are known to show evidence of evaporating bodies, and
most of them have only been observed in spectroscopy. With the appearance of
new high-precision photometric missions designed to search for exoplanets, such
as CHEOPS, a new opportunity to detect exocomets is available. Combining data
from CHEOPS and TESS we investigate the lightcurve of 5 Vul, an A-type star
with detected variability in spectroscopy, to search for non periodic transits
that could indicate the presence of dusty cometary tails in the system. While
we did not find any evidence of minor bodies, the high precision of the data,
along with the combination with previous spectroscopic results and models,
allows for an estimation of the sizes and spatial distribution of the
exocomets.Comment: Accepted for publication in MNRA
Screen-printed nanoparticles as anti-counterfeiting tags
Metallic nanoparticles with different physical properties have been screen printed as authentication tags on different types of paper. Gold and silver nanoparticles show unique optical signatures, including sharp emission bandwidths and long lifetimes of the printed label, even under accelerated weathering conditions. Magnetic nanoparticles show distinct physical signals that depend on the size of the nanoparticle itself. They were also screen printed on different substrates and their magnetic signals read out using a magnetic pattern recognition sensor and a vibrating sample magnetometer. The novelty of our work lies in the demonstration that the combination of nanomaterials with optical and magnetic properties on the same printed support is possible, and the resulting combined signals can be used to obtain a user-configurable label, providing a high degree of security in anti-counterfeiting applications using simple commercially-available sensors
An unusually large gaseous transit in a debris disc
We present the detection of an unusually large transient gas absorption in several ionized species in the debris disc star HD 37306 using high-resolution optical spectra. We have been analysing a large sample of debris discs searching for circumstellar gas absorptions aiming to determine the frequency of gas in debris discs. HD 37306 stood out showing remarkably broad absorptions superimposed on to several photospheric Ca II, Fe II, and Ti II lines. The observed absorptions, unlike typical exocometary transits, lasted for at least eight days. Here, we analyse simultaneous spectroscopic and photometric data of the event and evaluate different scenarios that might explain the observed features. We conclude that the most likely scenario might be an exocometary break-up releasing a significant amount of gas close to the star, producing an occulting `ring'/`torus' shape
Characterization of K2-167 b and CALM, a new stellar activity mitigation method
We report precise radial velocity (RV) observations of HD 212657 (= K2-167), a star shown by K2 to host a transiting sub-Neptune-sized planet in a 10 day orbit. Using Transiting Exoplanet Survey Satellite (TESS) photometry, we refined the planet parameters, especially the orbital period. We collected 74 precise RVs with the HARPS-N spectrograph between August 2015 and October 2016. Although this planet was first found to transit in 2015 and validated in 2018, excess RV scatter originally limited mass measurements. Here, we measure a mass by taking advantage of reductions in scatter from updates to the HARPS-N Data Reduction System (2.3.5) and our new activity mitigation method called CCF Activity Linear Model (CALM), which uses activity-induced line shape changes in the spectra without requiring timing information. Using the CALM framework, we performed a joint fit with RVs and transits using EXOFASTv2 and find and , which places K2-167 b at the upper edge of the radius valley. We also find hints of a secondary companion at a 22 day period, but confirmation requires additional RVs. Although characterizing lower-mass planets like K2-167 b is often impeded by stellar variability, these systems especially help probe the formation physics (i.e. photoevaporation, core-powered mass loss) of the radius valley. In the future, CALM or similar techniques could be widely applied to FGK-type stars, help characterize a population of exoplanets surrounding the radius valley, and further our understanding of their formation
No thick carbon dioxide atmosphere on the rocky exoplanet TRAPPIST-1 c
Seven rocky planets orbit the nearby dwarf star TRAPPIST-1, providing a
unique opportunity to search for atmospheres on small planets outside the Solar
System (Gillon et al., 2017). Thanks to the recent launch of JWST, possible
atmospheric constituents such as carbon dioxide (CO2) are now detectable
(Morley et al., 2017, Lincowski et al., 2018}. Recent JWST observations of the
innermost planet TRAPPIST-1 b showed that it is most probably a bare rock
without any CO2 in its atmosphere (Greene et al., 2023). Here we report the
detection of thermal emission from the dayside of TRAPPIST-1 c with the
Mid-Infrared Instrument (MIRI) on JWST at 15 micron. We measure a
planet-to-star flux ratio of fp/fs = 421 +/- 94 parts per million (ppm) which
corresponds to an inferred dayside brightness temperature of 380 +/- 31 K. This
high dayside temperature disfavours a thick, CO2-rich atmosphere on the planet.
The data rule out cloud-free O2/CO2 mixtures with surface pressures ranging
from 10 bar (with 10 ppm CO2) to 0.1 bar (pure CO2). A Venus-analogue
atmosphere with sulfuric acid clouds is also disfavoured at 2.6 sigma
confidence. Thinner atmospheres or bare-rock surfaces are consistent with our
measured planet-to-star flux ratio. The absence of a thick, CO2-rich atmosphere
on TRAPPIST-1 c suggests a relatively volatile-poor formation history, with
less than 9.5 +7.5 -2.3 Earth oceans of water. If all planets in the system
formed in the same way, this would indicate a limited reservoir of volatiles
for the potentially habitable planets in the system.Comment: Published in Nature on June 19th. 2023, 10 figures, 4 table
A transmission spectrum of the sub-Earth planet L98-59~b in 1.1-1.7 m
With the increasing number of planets discovered by TESS, the atmospheric
characterization of small exoplanets is accelerating. L98-59 is a M-dwarf
hosting a multi-planet system, and so far, four small planets have been
confirmed. The innermost planet b is smaller and lighter
than Earth, and should thus have a predominantly rocky composition. The Hubble
Space Telescope observed five primary transits of L98-59b in m,
and here we report the data analysis and the resulting transmission spectrum of
the planet. We measure the transit depths for each of the five transits and, by
combination, we obtain a transmission spectrum with an overall precision of
ppm in for each of the 18 spectrophotometric channels. With this level
of precision, the transmission spectrum does not show significant modulation,
and is thus consistent with a planet without any atmosphere or a planet having
an atmosphere and high-altitude clouds or haze. The scenarios involving an
aerosol-free, H-dominated atmosphere with HO or CH are inconsistent
with the data. The transmission spectrum also disfavors, but does not rules
out, an HO-dominated atmosphere without clouds. A spectral retrieval
process suggests that an H-dominated atmosphere with HCN and clouds or haze
may be the preferred solution, but this indication is non-conclusive. Future
James Webb Space Telescope observations may find out the nature of the planet
among the remaining viable scenarios.Comment: 17 pages, 5 figures, 7 tables, accepted for publication in A
Exocomets from a Solar System Perspective
Exocomets are small bodies releasing gas and dust which orbit stars other
than the Sun. Their existence was first inferred from the detection of variable
absorption features in stellar spectra in the late 1980s using spectroscopy.
More recently, they have been detected through photometric transits from space,
and through far-IR/mm gas emission within debris disks. As (exo)comets are
considered to contain the most pristine material accessible in stellar systems,
they hold the potential to give us information about early stage formation and
evolution conditions of extra Solar Systems. In the Solar System, comets carry
the physical and chemical memory of the protoplanetary disk environment where
they formed, providing relevant information on processes in the primordial
solar nebula. The aim of this paper is to compare essential compositional
properties between Solar System comets and exocomets. The paper aims to
highlight commonalities and to discuss differences which may aid the
communication between the involved research communities and perhaps also avoid
misconceptions. Exocomets likely vary in their composition depending on their
formation environment like Solar System comets do, and since exocomets are not
resolved spatially, they pose a challenge when comparing them to high fidelity
observations of Solar System comets. Observations of gas around main sequence
stars, spectroscopic observations of "polluted" white dwarf atmospheres and
spectroscopic observations of transiting exocomets suggest that exocomets may
show compositional similarities with Solar System comets. The recent
interstellar visitor 2I/Borisov showed gas, dust and nuclear properties similar
to that of Solar System comets. This raises the tantalising prospect that
observations of interstellar comets may help bridge the fields of exocomet and
Solar System comets.Comment: 25 pages, 3 figures. To be published in PASP. This paper is the
product of a workshop at the Lorentz Centre in Leiden, the Netherland
The First Habitable Zone Earth-Sized Planet From TESS II: Spitzer Confirms TOI-700 d
We present Spitzer 4.5 μm observations of the transit of TOI-700 d, a habitable-zone Earth-sized planet in a multiplanet system transiting a nearby M-dwarf star (TIC 150428135, 2MASS J06282325–6534456). TOI-700 d has a radius of 1.144^(+0.062)_(-0.061) R⊕ and orbits within its host star's conservative habitable zone with a period of 37.42 days (T_(eq) ~ 269 K). TOI-700 also hosts two small inner planets (R_b = 1.037^(+0.0065)_(-0.064) R⊕ and R_c = 2.65^(+0.16)_(-0.15) R⊕) with periods of 9.98 and 16.05 days, respectively. Our Spitzer observations confirm the Transiting Exoplanet Survey Satellite (TESS) detection of TOI-700 d and remove any remaining doubt that it is a genuine planet. We analyze the Spitzer light curve combined with the 11 sectors of TESS observations and a transit of TOI-700 c from the LCOGT network to determine the full system parameters. Although studying the atmosphere of TOI-700 d is not likely feasible with upcoming facilities, it may be possible to measure the mass of TOI-700 d using state-of-the-art radial velocity (RV) instruments (expected RV semiamplitude of ~70 cm s⁻¹)