Summary
Leptospira are unique among bacteria based on their helical cell morphology with hook‐shaped ends and the presence of periplasmic flagella (PF) with pronounced spontaneous supercoiling. The ...factors that provoke such supercoiling, as well as the role that PF coiling plays in generating the characteristic hook‐end cell morphology and motility, have not been elucidated. We have now identified an abundant protein from the pathogen L. interrogans, exposed on the PF surface, and named it Flagellar‐coiling protein A (FcpA). The gene encoding FcpA is highly conserved among Leptospira and was not found in other bacteria. fcpA‐ mutants, obtained from clinical isolates or by allelic exchange, had relatively straight, smaller‐diameter PF, and were not able to produce translational motility. These mutants lost their ability to cause disease in the standard hamster model of leptospirosis. Complementation of fcpA restored the wild‐type morphology, motility and virulence phenotypes. In summary, we identified a novel Leptospira 36‐kDa protein, the main component of the spirochete's PF sheath, and a key determinant of the flagella's coiled structure. FcpA is essential for bacterial translational motility and to enable the spirochete to penetrate the host, traverse tissue barriers, disseminate to cause systemic infection and reach target organs.
Spirochete is a unique group of bacteria with a distinguish morphology and the presence of periplasmic flagella. Both features are essential for their ability to produce thrust even when in contact with high viscous media. In the present report, we describe a novel protein, FcpA, which is expressed exclusively in Leptospira species, confers the unique structural feature of coiled purified flagella, and is essential for the hooked‐end morphology of the bacteria. FcpA is an abundant surface expressed protein in the flagella structure, and is fundamental for the pathogen's ability to produce translational motility and virulence.
Stellar activity can induce signals in the radial velocities of stars, complicating the detection of orbiting low-mass planets. We present a method to determine the number of planetary signals ...present in radial-velocity datasets of active stars, using only radial-velocity observations. Instead of considering separate fits with different number of planets, we use a birth-death Markov chain Monte Carlo algorithm to infer the posterior distribution for the number of planets in a single run. In a natural way, the marginal distributions for the orbital parameters of all planets are also inferred. This method is applied to HARPS data of CoRoT-7. We confidently recover the orbits of both CoRoT-7b and CoRoT-7c although the data show evidence for the presence of additional signals.
The statistical validation of transiting exoplanets proved to be an efficient technique to secure the nature of small exoplanet signals which cannot be established by purely spectroscopic means. ...However, the spectroscopic diagnoses are providing us with useful constraints on the presence of blended stellar contaminants. In this paper, we present how a contaminating star affects the measurements of the various spectroscopic diagnoses as a function of the parameters of the target and contaminating stars using the model implemented into the pastis planet-validation software. We find particular cases for which a blend might produce a large radial velocity signal but no bisector variation. It might also produce a bisector variation anticorrelated with the radial velocity one, as in the case of stellar spots. In those cases, the full width at half-maximum variation provides complementary constraints. These results can be used to constrain blend scenarios for transiting planet candidates or radial velocity planets. We review all the spectroscopic diagnoses reported in the literature so far, especially the ones to monitor the line asymmetry. We estimate their uncertainty and compare their sensitivity to blends. Based on that, we recommend the use of BiGauss which is the most sensitive diagnosis to monitor line-profile asymmetry. In this paper, we also investigate the sensitivity of the radial velocities to constrain blend scenarios and develop a formalism to estimate the level of dilution of a blended signal. Finally, we apply our blend model to re-analyse the spectroscopic diagnoses of HD 16702, an unresolved face-on binary which exhibits bisector variations.
ABSTRACT Observations of the Rossiter-McLaughlin (RM) effect provide information on star-planet alignments, which can inform planetary migration and evolution theories. Here, we go beyond the ...classical RM modeling and explore the impact of a convective blueshift that varies across the stellar disk and non-Gaussian stellar photospheric profiles. We simulated an aligned hot Jupiter with a four-day orbit about a Sun-like star and injected center-to-limb velocity (and profile shape) variations based on radiative 3D magnetohydrodynamic simulations of solar surface convection. The residuals between our modeling and classical RM modeling were dependent on the intrinsic profile width and v sin i; the amplitude of the residuals increased with increasing v sin i and with decreasing intrinsic profile width. For slowly rotating stars the center-to-limb convective variation dominated the residuals (with amplitudes of 10 s of cm s−1 to ∼1 m s−1); however, for faster rotating stars the dominant residual signature was due a non-Gaussian intrinsic profile (with amplitudes from 0.5 to 9 m s−1). When the impact factor was 0, neglecting to account for the convective center-to-limb variation led to an uncertainty in the obliquity of ∼10°-20°, even though the true v sin i was known. Additionally, neglecting to properly model an asymmetric intrinsic profile had a greater impact for more rapidly rotating stars (e.g., v sin i = 6 km s−1) and caused systematic errors on the order of ∼20° in the measured obliquities. Hence, neglecting the impact of stellar surface convection may bias star-planet alignment measurements and consequently theories on planetary migration and evolution.
Aims. One of the main scientific drivers for ESPRESSO, Échelle SPectrograph, is the detection and characterization of Earth-class exoplanets. With this goal in mind, the ESPRESSO guaranteed time ...observations (GTO) Catalog identifies the best target stars for a blind search for the radial velocity (RV) signals caused by Earth-class exoplanets. Methods. Using the most complete stellar catalogs available, we screened for the most suitable G, K, and M dwarf stars for the detection of Earth-class exoplanets with ESPRESSO. For most of the stars, we then gathered high-resolution spectra from new observations or from archival data. We used these spectra to spectroscopically investigate the existence of any stellar binaries, both bound or background stars. We derived the activity level using chromospheric activity indexes using log (R′HK) $(R' _{\textrm{HK}})$ (RHK′) , as well as the projected rotational velocity v sin i. For the cases where planet companions are already known, we also looked at the possibility that additional planets may exist in the host’s habitable zone using dynamical arguments. Results. We estimated the spectroscopic contamination level, v sin i, activity, stellar parameters and chemical abundances for 249 of the most promising targets. Using these data, we selected 45 stars that match our criteria for detectability of a planet like Earth. The stars presented and discussed in this paper constitute the ESPRESSO GTO catalog for the RV blind search for Earth-class planets. They can also be used for any other work requiring a detailed spectroscopic characterization of stars in the solar neighborhood.
Context.
LHS 1140 is an M dwarf known to host two transiting planets at orbital periods of 3.77 and 24.7 days. They were detected with HARPS and
Spitzer
. The external planet (LHS 1140 b) is a rocky ...super-Earth that is located in the middle of the habitable zone of this low-mass star. All these properties place this system at the forefront of the habitable exoplanet exploration, and it therefore constitutes a relevant case for further astrobiological studies, including atmospheric observations.
Aims.
We further characterize this system by improving the physical and orbital properties of the known planets, search for additional planetary-mass components in the system, and explore the possibility of co-orbitals.
Methods.
We collected 113 new high-precision radial velocity observations with ESPRESSO over a 1.5-yr time span with an average photon-noise precision of 1.07 m s
−1
. We performed an extensive analysis of the HARPS and ESPRESSO datasets and also analyzed them together with the new TESS photometry. We analyzed the Bayesian evidence of several models with different numbers of planets and orbital configurations.
Results.
We significantly improve our knowledge of the properties of the known planets LHS 1140 b (
P
b
~ 24.7 days) and LHS 1140 c (
P
c
~ 3.77 days). We determine new masses with a precision of 6% for LHS 1140 b (6.48 ± 0.46
M
⊕
) and 9% for LHS 1140 c (
m
c
= 1.78 ± 0.17
M
⊕
). This reduces the uncertainties relative to previously published values by half. Although both planets have Earth-like bulk compositions, the internal structure analysis suggests that LHS 1140 b might be iron-enriched and LHS 1140 c might be a true Earth twin. In both cases, the water content is compatible to a maximum fraction of 10–12% in mass, which is equivalent to a deep ocean layer of 779 ± 650 km for the habitable-zone planet LHS 1140 b. Our results also provide evidence for a new planet candidate in the system (
m
d
= 4.8 ± 1.1
M
⊕
) on a 78.9-day orbital period, which is detected through three independent methods. The analysis also allows us to discard other planets above 0.5
M
⊕
for periods shorter than 10 days and above 2
M
⊕
for periods up to one year. Finally, our co-orbital analysis discards co-orbital planets in the tadpole and horseshoe configurations of LHS 1140 b down to 1
M
⊕
with a 95% confidence level (twice better than with the previous HARPS dataset). Indications for a possible co-orbital signal in LHS 1140 c are detected in both radial velocity (alternatively explained by a high eccentricity) and photometric data (alternatively explained by systematics), however.
Conclusions.
The new precise measurements of the planet properties of the two transiting planets in LHS 1140 as well as the detection of the planet candidate LHS 1140 d make this system a key target for atmospheric studies of rocky worlds at different stellar irradiations.
Aims. We explore the possibility that the stellar relative abundances of different species can be used to constrain the bulk abundances of known transiting rocky planets. Methods. We use high ...resolution spectra to derive stellar parameters and chemical abundances for Fe, Si, Mg, O, and C in three stars hosting low mass, rocky planets: CoRoT-7, Kepler-10, and Kepler-93. These planets follow the same line along the mass-radius diagram, pointing toward a similar composition. The derived abundance ratios are compared with the solar values. With a simple stoichiometric model, we estimate the iron mass fraction in each planet, assuming stellar composition. Results. We show that in all cases, the iron mass fraction inferred from the mass-radius relationship seems to be in good agreement with the iron abundance derived from the host star’s photospheric composition. Conclusions. The results suggest that stellar abundances can be used to add constraints on the composition of orbiting rocky planets.
Context. Mass and radius are two fundamental properties for characterising exoplanets, but only for a relatively small fraction of exoplanets are they both available. Mass is often derived from ...radial velocity measurements, while the radius is almost always measured using the transit method. For a large number of exoplanets, either the radius or the mass is unknown, while the host star has been characterised. Several mass-radius relations that are dependent on the planet’s type have been published that often allow us to predict the radius. The same is true for a bayesian code, which forecasts the radius of an exoplanet given the mass or vice versa. Aims. Our goal is to derive the radius of exoplanets using only observables extracted from spectra used primarily to determine radial velocities and spectral parameters. Our objective is to obtain a mass-radius relation independent of the planet’s type. Methods. We worked with a database of confirmed exoplanets with known radii and masses, as well as the planets from our Solar System. Using random forests, a machine learning algorithm, we computed the radius of exoplanets and compared the results to the published radii. In addition, we explored how the radius estimates compare to previously published mass-radius relations. Results. The estimated radii reproduces the spread in radius found for high mass planets better than previous mass-radius relations. The average radius error is 1.8 R⊕ across the whole range of radii from 1–22 R⊕. We find that a random forest algorithm is able to derive reliable radii, especially for planets between 4 R⊕ and 20 R⊕ for which the error is under 25%. The algorithm has a low bias yet a high variance, which could be reduced by limiting the growth of the forest, or adding more data. Conclusions. The random forest algorithm is a promising method for deriving exoplanet properties. We show that the exoplanet’s mass and equilibrium temperature are the relevant properties that constrain the radius, and do so with higher accuracy than the previous methods.
Context. The atmospheric absorption of the Earth is an important limiting factor for ground-based spectroscopic observations and the near-infrared and infrared regions are the most affected. Several ...software packages that produce a synthetic atmospheric transmission spectrum have been developed to correct for the telluric absorption; these are Molecfit, TelFit, and Transmissions Atmosphériques Personnalisées pour l’AStronomie (TAPAS). Aims. Our goal is to compare the correction achieved using these three telluric correction packages and the division by a telluric standard star. We want to evaluate the best method to correct near-infrared high-resolution spectra as well as the limitations of each software package and methodology. Methods. We applied the telluric correction methods to CRIRES archival data taken in the J and K bands. We explored how the achieved correction level varies depending on the atmospheric T-P profile used in the modelling, the depth of the atmospheric lines, and the molecules creating the absorption. Results. We found that the Molecfit and TelFit corrections lead to smaller residuals for the water lines. The standard star method corrects best the oxygen lines. The Molecfit package and the standard star method corrections result in global offsets always below 0.5% for all lines; the offset is similar with TelFit and TAPAS for the H2O lines and around 1% for the O2 lines. All methods and software packages result in a scatter between 3% and 7% inside the telluric lines. The use of a tailored atmospheric profile for the observatory leads to a scatter two times smaller, and the correction level improves with lower values of precipitable water vapour. Conclusions. The synthetic transmission methods lead to an improved correction compared to the standard star method for the water lines in the J band with no loss of telescope time, but the oxygen lines were better corrected by the standard star method.
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