Past ultraviolet and optical observations of stars hosting close-in Jupiter-mass planets have shown that some of these stars present an anomalously low chromospheric activity, significantly below the ...basal level. For the hot Jupiter planet host WASP-13, observations have shown that the apparent lack of activity is possibly caused by absorption from the intervening interstellar medium (ISM). Inspired by this result, we study the effect of ISM absorption on activity measurements (S and log R 'HK indices) for main-sequence late-type stars. To this end, we employ synthetic stellar photospheric spectra combined with varying amounts of chromospheric emission and ISM absorption. We present the effect of ISM absorption on activity measurements by varying several instrumental (spectral resolution), stellar (projected rotational velocity, effective temperature, and chromospheric emission flux), and ISM parameters (relative velocity between stellar and ISM Ca ii lines, broadening b-parameter, and Ca ii column density). We find that for relative velocities between the stellar and ISM lines smaller than 30–40 km s-1 and for ISM Ca ii column densities log NCaII ⪆ 12, the ISM absorption has a significant influence on activity measurements. Direct measurements and three dimensional maps of the Galactic ISM absorption indicate that an ISM Ca ii column density of log NCaII = 12 is typically reached by a distance of about 100 pc along most sight lines. In particular, for a Sun-like star lying at a distance greater than 100 pc, we expect a depression (bias) in the log R 'HK value larger than 0.05–0.1 dex, about the same size as the typical measurement and calibration uncertainties on this parameter. This work shows that the bias introduced by ISM absorption must always be considered when measuring activity for stars lying beyond 100 pc. We also consider the effect of multiple ISM absorption components. We discuss the relevance of this result for exoplanet studies and revise the latest results on stellar activity versus planet surface gravity correlation. We finally describe methods with which it would be possible to account for ISM absorption in activity measurements and provide a code to roughly estimate the magnitude of the bias. Correcting for the ISM absorption bias may allow one to identify the origin of the anomaly in the activity measured for some planet-hosting stars.
For the hot exoplanets CoRoT-24b and CoRoT-24c, observations have provided transit radii R
T of 3.7 ± 0.4R
⊕ and 4.9 ± 0.5R
⊕, and masses of ≤5.7M
⊕ and 28 ± 11M
⊕, respectively. We study their upper ...atmosphere structure and escape applying an hydrodynamic model. Assuming R
T ≈ R
PL, where R
PL is the planetary radius at the pressure of 100 mbar, we obtained for CoRoT-24b unrealistically high thermally driven hydrodynamic escape rates. This is due to the planet's high temperature and low gravity, independent of the stellar EUV flux. Such high escape rates could last only for <100 Myr, while R
PL shrinks till the escape rate becomes less than or equal to the maximum possible EUV-driven escape rate. For CoRoT-24b, R
PL must be therefore located at ≈1.9–2.2R
⊕ and high altitude hazes/clouds possibly extinct the light at R
T. Our analysis constraints also the planet's mass to be 5–5.7M
⊕. For CoRoT-24c, R
PL and R
T lie too close together to be distinguished in the same way. Similar differences between R
PL and R
T may be present also for other hot, low-density sub-Neptunes.
ABSTRACT
Ultraviolet (UV) transmission spectroscopy probes atmospheric escape, which has a significant impact on planetary atmospheric evolution. If unaccounted for, interstellar medium absorption ...(ISM) at the position of specific UV lines might bias transit depth measurements, and thus potentially affect the (non-)detection of features in transmission spectra. Ultimately, this is connected to the so called ‘resolution-linked bias’ effect. We present a parametric study quantifying the impact of unresolved or unconsidered ISM absorption in transit depth measurements at the position of the Mg ii h&k resonance lines (i.e. 2802.705 Å and 2795.528 Å, respectively) in the near-ultraviolet spectral range. We consider main-sequence stars of different spectral types and vary the shape and amount of chromospheric emission, ISM absorption, and planetary absorption, as well as their relative velocities. We also evaluate the role played by integration bin and spectral resolution. We present an open-source tool enabling one to quantify the impact of unresolved or unconsidered Mg ii ISM absorption in transit depth measurements. We further apply this tool to a few already or soon to be observed systems. On average, we find that ignoring ISM absorption leads to biases in the Mg ii transit depth measurements comparable to the uncertainties obtained from the observations published to date. However, considering the bias induced by ISM absorption might become necessary when analysing observations obtained with the next generation space telescopes with UV coverage (e.g. LUVOIR, HABEX), which will provide transmission spectra with significantly smaller uncertainties compared to what obtained with current facilities (e.g. HST).
The necrotic streak of the fique (Furcraea spp.) or “Macana” disease is considered the most limiting disease for this crop in Colombia, whose causal agent is the Furcraea Necrotic Streak Virus - FNSV ...(RNA+). Currently, there are no strategies to control the disease, being necessary to develop methods for detection of this pathogen in the planting material before being taken to the field. In this study, polyclonal antibodies produced in egg yolk (IgY) were produced and assesses for detection FNSV. Two immunoenzymatic methodologies were standardized: dot blot immunobinding assay (DBIA) and enzyme-linked immunosorbent assay (ELISA), determining their specificity and sensitivity. The detection limit by DBIA corresponded to 8 μg/mL of purified virus suspension using 10 μg/mL of primary antibody. In the ELISA test, the primary antibody concentration of 3 μg/mL (1:800 dilution) detected the antigen at concentrations between 10 and 70 μg/mL. The polyclonal antibody anti-FNSV IgY allowed the detection of FNSV in samples of purified virus and extracts of roots and leaves of fique plants with symptoms of “Macana” disease and did not produce any signal with the control samples. Results showed the potential of using egg yolk IgY in immunological tests for the detection of FNSV in fique plants.
•Fique plants are source of natural fiber help to reduce the use of synthetic fibers.•FNSV causes the most detrimental disease named Macana, affecting fiber production.•Anti-FNSV produced in egg yolk was developed to detect the infection.•Detection of infected material could prevent the spread of macana disease.
Context.
Exoplanetary upper atmospheres are low density environments where radiative processes can compete with collisional ones and introduce non-local thermodynamic equilibrium (NLTE) effects into ...transmission spectra.
Aims.
We develop a NLTE radiative transfer framework capable of modelling exoplanetary transmission spectra over a wide range of planetary properties.
Methods.
We adapted the NLTE spectral synthesis code Cloudy to produce an atmospheric structure and atomic transmission spectrum in both NLTE and local thermodynamic equilibrium (LTE) for the hot Jupiter HD 209458b, given a published
T
–
P
profile and assuming solar metallicity. Selected spectral features, including H
α
, Na
I
D, He
I
λ
10 830, Fe
I
and
II
ultra-violet (UV) bands, and C, O, and Si UV lines, are compared with literature observations and models where available. The strength of NLTE effects are measured for individual spectral lines to identify which features are most strongly affected.
Results.
The developed modelling framework that computes NLTE synthetic spectra reproduces literature results for the He
I
λ
10 830 triplet, the Na
I
D lines, and the forest of Fe
I
lines in the optical. Individual spectral lines in the NLTE spectrum exhibit up to 40% stronger absorption relative to the LTE spectrum.
Abstract
WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age (<1 Gyr), the star presents an anomalously low stellar activity level: the measured
activity parameter lies ...slightly below the basal level; there is no significant time-variability in the
value; there is no detection of the star in the X-rays. We present results of far-UV observations of WASP-18 obtained with COS on board of
Hubble Space Telescope
aimed at explaining this anomaly. From the star’s spectral energy distribution, we infer the extinction (
≈ 0.01 mag) and then the interstellar medium (ISM) column density for a number of ions, concluding that ISM absorption is not the origin of the anomaly. We measure the flux of the four stellar emission features detected in the COS spectrum (C
ii
, C
iii
, C
iv
, Si
iv
). Comparing the C
ii
/C
iv
flux ratio measured for WASP-18 with that derived from spectra of nearby stars with known age, we see that the far-UV spectrum of WASP-18 resembles that of old (>5 Gyr), inactive stars, in stark contrast with its young age. We conclude that WASP-18 has an intrinsically low activity level, possibly caused by star–planet tidal interaction, as suggested by previous studies. Re-scaling the solar irradiance reference spectrum to match the flux of the Si
iv
line, yields an XUV integrated flux at the planet orbit of 10.2 erg s
−1
cm
−2
. We employ the rescaled XUV solar fluxes to models of the planetary upper atmosphere, deriving an extremely low thermal mass-loss rate of 10
−20
M
J
Gyr
−1
. For such high-mass planets, thermal escape is not energy limited, but driven by Jeans escape.
Several studies have shown that stellar activity features, such as occulted and non-occulted starspots, can affect the measurement of transit parameters biasing studies of transit timing variations ...and transmission spectra. We present PyTranSpot, which we designed to model multiband transit light curves showing starspot anomalies, inferring both transit and spot parameters. The code follows a pixellation approach to model the star with its corresponding limb darkening, spots, and transiting planet on a two dimensional Cartesian coordinate grid. We combine PyTranSpot with a Markov chain Monte Carlo framework to study and derive exoplanet transmission spectra, which provides statistically robust values for the physical properties and uncertainties of a transiting star-planet system. We validate PyTranSpot’s performance by analyzing eleven synthetic light curves of four different star-planet systems and 20 transit light curves of the well-studied WASP-41b system. We also investigate the impact of starspots on transit parameters and derive wavelength dependent transit depth values for WASP-41b covering a range of 6200−9200 Å, indicating a flat transmission spectrum.
We present here the signal-to-noise (S/N) calculator developed for the Colorado Ultraviolet Transit Experiment (CUTE) mission. CUTE is a 6U CubeSat operating in the near-ultraviolet (NUV) observing ...exoplanetary transits to study their upper atmospheres. CUTE was launched into a low-Earth orbit in September 2021 and it is currently gathering scientific data. As part of the S/N calculator, we also present the error propagation for computing transit depth uncertainties starting from the S/N of the original spectroscopic observations. The CUTE S/N calculator is currently extensively used for target selection and scheduling. The modular construction of the CUTE S/N calculator enables its adaptation and can be used also for other missions and instruments.
The K2-33 planetary system hosts one transiting ~5 R⊕ planet orbiting the young M-type host star. The planet’s mass is still unknown, with an estimated upper limit of 5.4 MJ. The extreme youth of the ...system (<20 Myr) gives the unprecedented opportunity to study the earliest phases of planetary evolution, at a stage when the planet is exposed to an extremely high level of high-energy radiation emitted by the host star. We perform a series of 1D hydrodynamic simulations of the planet’s upper atmosphere considering a range of possible planetary masses, from 2 to 40 M⊕, and equilibrium temperatures, from 850 to 1300 K, to account for internal heating as a result of contraction. We obtain temperature profiles mostly controlled by the planet’s mass, while the equilibrium temperature has a secondary effect. For planetary masses below 7–10 M⊕, the atmosphere is subject to extremely high escape rates, driven by the planet’s weak gravity and high thermal energy, which increase with decreasing mass and/or increasing temperature. For higher masses, the escape is instead driven by the absorption of the high-energy stellar radiation. A rough comparison of the timescales for complete atmospheric escape and age of the system indicates that the planet is more massive than 10 M⊕.
Context. 55 Cnc e is a transiting super-Earth orbiting a solar-like star with an orbital period of ~17.7 h. In 2011, using the Microvariability and Oscillations in Stars (MOST) space telescope, a ...quasi-sinusoidal modulation in flux was detected with the same period as the planetary orbit. The amplitude of this modulation was too large to be explained as the change in light reflected or emitted by the planet. Aims. The MOST telescope continued to observe 55 Cnc e for a few weeks per year over five years (from 2011 to 2015), covering 143 individual transits. This paper presents the analysis of the observed phase modulation throughout these observations and a search for the secondary eclipse of the planet. Methods. The most important source of systematic noise in MOST data is due to stray-light reflected from the Earth, which is modulated with both the orbital period of the satellite (101.4 min) and the Earth’s rotation period. We present a new technique to deal with this source of noise, which we combined with standard detrending procedures for MOST data. We then performed Markov chain Monte Carlo analyses of the detrended light curves, modeling the planetary transit and phase modulation. Results. We find phase modulations similar to those seen in 2011 in most of the subsequent years; however, the amplitude and phase of maximum light are seen to vary, from year to year, from 113 to 28 ppm and from 0.1 to 3.8 rad. The secondary eclipse is not detected, but we constrain the geometric albedo of the planet to less than 0.47 (2σ). Conclusions. While we cannot identify a single origin of the observed optical modulation, we propose a few possible scenarios. Those include star-planet interaction, such as coronal rains and spots rotating with the motion of the planet along its orbit, or the presence of a transiting circumstellar torus of dust. However, a detailed interpretation of these observations is limited by their photometric precision. Additional observations at optical wavelengths could measure the variations at higher precision, contribute to uncovering the underlying physical processes, and measure or improve the upper limit on the albedo of the planet.
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