Measles virus undergoes error-prone replication like other RNA viruses, but over time, it has remained antigenically monotypic. The constraints on the virus that prevent the emergence of antigenic ...variants are unclear. As a first step in understanding this question, we subjected the measles virus genome to unbiased insertional mutagenesis, and viruses that could tolerate insertions were rescued. Only insertions in the nucleoprotein, phosphoprotein, matrix protein, as well as intergenic regions were easily recoverable. Insertions in the glycoproteins of measles virus were severely under-represented in our screen. Host immunity depends on developing neutralizing antibodies to the hemagglutinin and fusion glycoproteins; our analysis suggests that these proteins occupy very little evolutionary space and therefore have difficulty changing in the face of selective pressures. We propose that the inelasticity of these proteins prevents the sequence variation required to escape antibody neutralization in the host, allowing for long-lived immunity after infection with the virus.
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•An insertional mutagenesis screen of the measles virus genome is performed•Some genomic regions are tolerant of insertions, but the F or H glycoproteins are not•In comparison to other viruses, the glycoproteins of measles are highly inflexible•The inflexibility of measles F and H may contribute to measles antigenic stability
It is unclear why measles virus is antigenically monotypic. Fulton et al. perform a viral mutagenesis screen and find that the glycoproteins (the major immune response targets) are exceptionally inflexible. These data suggest that the intrinsic rigidity of the glycoproteins is an important constraint on the development of antigenic diversity.
Abstract
One possible formation mechanism for Hot Jupiters is that high-eccentricity gas giants experience tidal interactions with their host star that cause them to lose orbital energy and migrate ...inwards. We study these types of tidal interactions in an eccentric Hot Jupiter called HAT-P-2 b, which is a system where a long-period companion has been suggested and hints of orbital evolution were detected. Using 5 additional years of radial velocity (RV) measurements, we further investigate these phenomena. We investigated the long-period companion by jointly fitting RVs and Hipparcos-Gaia astrometry and confirmed this long-period companion, significantly narrowed down the range of possible periods (
P
2
=
8500
−
1500
+
2600
days), and determined that it must be a substellar object (
10.7
−
2.2
+
5.2
M
j
). We also developed a modular pipeline to simultaneously model rapid orbital evolution and the long-period companion. We find that the rate and significance of evolution are highly dependent on the long-period companion modeling choices. In some cases the orbital rates of change reached
de
/
dt
=
3.28
−
1.72
+
1.75
×
10
−
3
yr
−1
,
d
ω
/
dt
= 1.12° ± 0.22° yr
−1
, which corresponds to a ∼321 yr apsidal precession period. In other cases, the data is consistent with
de
/
dt
= 7.67 ± 18.6 × 10
−4
yr
−1
,
d
ω
/
dt
= 0.76° ± 0.24° yr
−1
. The most rapid changes found are significantly larger than the expected relativistic precession rate and could be caused by transient tidal planet–star interactions. To definitively determine the magnitude and significance of potential orbital evolution in HAT-P-2 b, we recommend further monitoring with RVs and precise transit and eclipse timings.
ABSTRACT We present a catalog of 11 multiplanet systems from Campaigns 1 and 2 of the K2 mission. We report the sizes and orbits of 26 planets split between seven two-planet systems and four ...three-planet systems. These planets stem from a systematic search of the K2 photometry for all dwarf stars observed by K2 in these fields. We precisely characterized the host stars with adaptive optics imaging and analysis of high-resolution optical spectra from Keck/HIRES and medium-resolution spectra from IRTF/SpeX. We confirm two planet candidates by mass detection and validate the remaining 24 candidates to >99% confidence. Thirteen planets were previously validated or confirmed by other studies, and 24 were previously identified as planet candidates. The planets are mostly smaller than Neptune (21/26 planets), as in the Kepler mission, and all have short periods (P < 50 days) due to the duration of the K2 photometry. The host stars are relatively bright (most have Kp < 12.5 mag) and are amenable to follow-up characterization. For K2-38, we measured precise radial velocities using Keck/HIRES and provide initial estimates of the planet masses. K2-38b is a short-period super-Earth with a radius of 1.55 0.16 R⊕, a mass of 12.0 2.9 M⊕, and a high density consistent with an iron-rich composition. The outer planet K2-38c is a lower-density sub-Neptune-size planet with a radius of 2.42 0.29 R⊕ and a mass of 9.9 4.6 M⊕ that likely has a substantial envelope. This new planet sample demonstrates the capability of K2 to discover numerous planetary systems around bright stars.
Abstract
We explore the impact of outer stellar companions on the occurrence rate of giant planets detected with radial velocities. We searched for stellar and planetary companions to a ...volume-limited sample of solar-type stars within 25 pc. Using adaptive optics imaging observations from the Lick 3 m and Palomar 200″ Telescopes, we characterized the multiplicity of our sample stars, down to the bottom of the main sequence. With these data, we confirm field star multiplicity statistics from previous surveys. We additionally combined three decades of radial velocity (RV) data from the California Planet Search with newly collected RV data from Keck/HIRES and the Automated Planet Finder/Levy Spectrometer to search for planetary companions in these same systems. Using an updated catalog of both stellar and planetary companions, as well as detailed injection/recovery tests to determine our sensitivity and completeness, we measured the occurrence rate of planets among the single- and multiple-star systems. We found that planets with masses in the range of 0.1–10
M
J
and with semimajor axes of 0.1–10 au have an occurrence rate of
planets per star when they orbit single stars and an occurrence rate of 0.12 ± 0.04 planets per star when they orbit a star in a binary system. Breaking the sample down by the binary separation, we found that only one planet-hosting binary system had a binary separation <100 au, and none had a separation <50 au. These numbers yielded planet occurrence rates of
planets per star for binaries with separation
a
B
> 100 au and
planets per star for binaries with separation
a
B
< 100 au. The similarity in the planet occurrence rate around single stars and wide primaries implies that wide binary systems should actually host more planets than single-star systems, since they have more potential host stars. We estimated a system-wide planet occurrence rate of 0.3 planets per wide binary system for binaries with separations
a
B
> 100 au. Finally, we found evidence that giant planets in binary systems have a different semimajor-axis distribution than their counterparts in single-star systems. The planets in the single-star sample had a significantly higher occurrence rate outside of 1 au than inside 1 au by nearly 4
σ
, in line with expectations that giant planets are most common near the snow line. However, the planets in the wide binary systems did not follow this distribution, but rather had equivalent occurrence rates interior and exterior to 1 au. This may point to binary-mediated planet migration acting on our sample, even in binaries wider than 100 au.
The molecular constraints affecting Zika virus (ZIKV) evolution are not well understood. To investigate ZIKV genetic flexibility, we used transposon mutagenesis to add 15-nucleotide insertions ...throughout the ZIKV MR766 genome and subsequently deep sequenced the viable mutants. Few ZIKV insertion mutants replicated, which likely reflects a high degree of functional constraints on the genome. The NS1 gene exhibited distinct mutational tolerances at different stages of the screen. This result may define regions of the NS1 protein that are required for the different stages of the viral life cycle. The ZIKV structural genes showed the highest degree of insertional tolerance. Although the envelope (E) protein exhibited particular flexibility, the highly conserved envelope domain II (EDII) fusion loop of the E protein was intolerant of transposon insertions. The fusion loop is also a target of pan-flavivirus antibodies that are generated against other flaviviruses and neutralize a broad range of dengue virus and ZIKV isolates. The genetic restrictions identified within the epitopes in the EDII fusion loop likely explain the sequence and antigenic conservation of these regions in ZIKV and among multiple flaviviruses. Thus, our results provide insights into the genetic restrictions on ZIKV that may affect the evolution of this virus.
Zika virus recently emerged as a significant human pathogen. Determining the genetic constraints on Zika virus is important for understanding the factors affecting viral evolution. We used a genome-wide transposon mutagenesis screen to identify where mutations were tolerated in replicating viruses. We found that the genetic regions involved in RNA replication were mostly intolerant of mutations. The genes coding for structural proteins were more permissive to mutations. Despite the flexibility observed in these regions, we found that epitopes bound by broadly reactive antibodies were genetically constrained. This finding may explain the genetic conservation of these epitopes among flaviviruses.
We identify a sub-Neptune exoplanet (Rp = 2.5 0.2 ) transiting a solar twin in the Ruprecht 147 star cluster (3 Gyr, 300 pc, Fe/H = +0.1 dex). The ∼81 day light curve for EPIC 219800881 (V = 12.71) ...from K2 Campaign 7 shows six transits with a period of 13.84 days, a depth of ∼0.06%, and a duration of ∼4 hr. Based on our analysis of high-resolution MIKE spectra, broadband optical and NIR photometry, the cluster parallax and interstellar reddening, and isochrone models from PARSEC, Dartmouth, and MIST, we estimate the following properties for the host star: M = 1.01 0.03 , R = 0.95 0.03 , and = 5695 50 K. This star appears to be single based on our modeling of the photometry, the low radial velocity (RV) variability measured over nearly 10 yr, and Keck/NIRC2 adaptive optics imaging and aperture-masking interferometry. Applying a probabilistic mass-radius relation, we estimate that the mass of this planet is Mp = 7 + 5 - 3 , which would cause an RV semi-amplitude of K = 2 1 that may be measurable with existing precise RV facilities. After statistically validating this planet with BLENDER, we now designate it K2-231b, making it the second substellar object to be discovered in Ruprecht 147 and the first planet; it joins the small but growing ranks of 22 other planets and three candidates found in open clusters.
Abstract
The California-Kepler Survey (CKS) catalog contains precise stellar and planetary properties for the
Kepler
planet candidates, including systems with multiple detected transiting planets ...(“multis”) and systems with just one detected transiting planet (“singles”, although additional planets could exist). We compared the stellar and planetary properties of the multis and singles in a homogeneous subset of the full CKS-
Gaia
catalog. We found that sub-Neptune-sized singles and multis do not differ in their stellar properties or planet radii. In particular: (1.) The distributions of stellar properties
, Fe/H, and
for the
Kepler
sub-Neptune-sized singles and multis are statistically indistinguishable. (2.) The radius distributions of the sub-Neptune-sized singles and multis with
P
> 3 days are indistinguishable, and both have a valley at ∼1.8
. However, there are significantly more detected short-period (
P
< 3 days), sub-Neptune-sized singles than multis. The similarity of the host-star properties, planet radii, and radius valley for singles and multis suggests a common origin. The similar radius valley, which is likely sculpted by photo-evaporation from the host star within the first 100 Myr, suggests that planets in both singles and multis spend much of the first 100 Myr near their present, close-in locations. One explanation that is consistent with the similar fundamental properties of singles and multis is that many of the singles are members of multi-planet systems that underwent planet–planet scattering.
Understanding the relationship between long-period giant planets and multiple smaller short-period planets is critical for formulating a complete picture of planet formation. This work characterizes ...three such systems. We present Kepler-65, a system with an eccentric (e = 0.28 0.07) giant planet companion discovered via radial velocities (RVs) exterior to a compact, multiply transiting system of sub-Neptune planets. We also use precision RVs to improve mass and radius constraints on two other systems with similar architectures, Kepler-25 and Kepler-68. In Kepler-68 we propose a second exterior giant planet candidate. Finally, we consider the implications of these systems for planet formation models, particularly that the moderate eccentricity in Kepler-65's exterior giant planet did not disrupt its inner system.
Recent years have seen increasing interest in the characterization of sub-Neptune-sized planets because of their prevalence in the Galaxy, contrasted with their absence in our solar system. HD 97658 ...is one of the brightest stars hosting a planet of this kind, and we present the transmission spectrum of this planet by combining four Hubble Space Telescope transits, 12 Spitzer/IRAC transits, and eight MOST transits of this system. Our transmission spectrum has a higher signal-to-noise ratio than those from previous works, and the result suggests that the slight increase in transit depth from wavelength 1.1-1.7 m reported in previous works on the transmission spectrum of this planet is likely systematic. Nonetheless, our atmospheric modeling results are inconclusive, as no model provides an excellent match to our data. Nonetheless, we find that atmospheres with high C/O ratios (C/O 0.8) and metallicities of 100× solar metallicity are favored. We combine the mid-transit times from all of the new Spitzer and MOST observations and obtain an updated orbital period of P = 9.489295 0.000005, with a best-fit transit time center at T0 = 2456361.80690 0.00038 (BJD). No transit timing variations are found in this system. We also present new measurements of the stellar rotation period (34 2 days) and stellar activity cycle (9.6 yr) of the host star HD 97658. Finally, we calculate and rank the Transmission Spectroscopy Metric of all confirmed planets cooler than 1000 K and with sizes between 1 R⊕ and 4 R⊕. We find that at least a third of small planets cooler than 1000 K can be well characterized using James Webb Space Telescope, and of those, HD 97658b is ranked fifth, meaning that it remains a high-priority target for atmospheric characterization.
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