445 research outputs found
HAZMAT VI: The Evolution of Extreme Ultraviolet Radiation Emitted from Early M Star
Quantifying the evolution of stellar extreme ultraviolet (EUV, 100 -- 1000
) emission is critical for assessing the evolution of
planetary atmospheres and the habitability of M dwarf systems. Previous studies
from the HAbitable Zones and M dwarf Activity across Time (HAZMAT) program
showed the far- and near-UV (FUV, NUV) emission from M stars at various stages
of a stellar lifetime through photometric measurements from the Galaxy
Evolution Explorer (GALEX). The results revealed increased levels of
short-wavelength emission that remain elevated for hundreds of millions of
years. The trend for EUV flux as a function of age could not be determined
empirically because absorption by the interstellar medium prevents access to
the EUV wavelengths for the vast majority of stars. In this paper, we model the
evolution of EUV flux from early M stars to address this observational gap. We
present synthetic spectra spanning EUV to infrared wavelengths of 0.4
0.05 M stars at five distinct ages between 10 and 5000 Myr, computed
with the PHOENIX atmosphere code and guided by the GALEX photometry. We model a
range of EUV fluxes spanning two orders of magnitude, consistent with the
observed spread in X-ray, FUV, and NUV flux at each epoch. Our results show
that the stellar EUV emission from young M stars is 100 times stronger than
field age M stars, and decreases as t after remaining constant for a few
hundred million years. This decline stems from changes in the chromospheric
temperature structure, which steadily shifts outward with time. Our models
reconstruct the full spectrally and temporally resolved history of an M star's
UV radiation, including the unobservable EUV radiation, which drives planetary
atmospheric escape, directly impacting a planet's potential for habitability.Comment: 23 pages, 15 figures, accepted to Ap
Current Population Statistics Do Not Favor Photoevaporation over Core-Powered Mass Loss as the Dominant Cause of the Exoplanet Radius Gap
We search for evidence of the cause of the exoplanet radius gap, i.e. the
dearth of planets with radii near . If the cause was
photoevaporation, the radius gap should trend with proxies for the early-life
high-energy emission of planet-hosting stars. If, alternatively, the cause was
core-powered mass loss, no such trends should exist. Critically, spurious
trends between the radius gap and stellar properties arise from an underlying
correlation with instellation. After accounting for this underlying
correlation, we find no trends remain between the radius gap and stellar mass
or present-day stellar activity as measured by near-UV emission. We dismiss the
nondetection of a radius gap trend with near-UV emission because present-day
near-UV emission is unlikely to trace early-life high-energy emission, but we
provide a catalog of GALEX near-UV and far-UV emission measurements for general
use. We interpret the nondetection of a radius gap trend with stellar mass by
simulating photoevaporation with mass-dependent evolution of stellar
high-energy emission. The simulation produces an undetectable trend between the
radius gap and stellar mass under realistic sources of error. We conclude that
no evidence, from this analysis or others in the literature, currently exists
that clearly favors either photoevaporation or core powered mass loss as the
primary cause of the exoplanet radius gap. However, repeating this analysis
once the body of well-characterized planets has roughly doubled
could confirm or rule out photoevaporation.Comment: 27 pages, 32 figures, accepted to Ap
Flares, Rotation, Activity Cycles and a Magnetic Star-Planet Interaction Hypothesis for the Far Ultraviolet Emission of GJ 436
Variability in the far ultraviolet (FUV) emission produced by stellar
activity affects photochemistry and heating in orbiting planetary atmospheres.
We present a comprehensive analysis of the FUV variability of GJ 436, a
field-age, M2.5V star ( d) orbited by a warm,
Neptune-size planet (, ,
d). Observations at three epochs from 2012 to 2018
span nearly a full activity cycle, sample two rotations of the star and two
orbital periods of the planet, and reveal a multitude of brief flares. Over
2012-2018, the star's yr activity cycle produced the largest
observed variations, % in the summed flux of major FUV emission lines.
In 2018, variability due to rotation was %. An additional %
scatter at 10 min cadence, treated as white noise in fits, likely has both
instrumental and astrophysical origins. Flares increased time-averaged emission
by 15% over the 0.88 d of cumulative exposure, peaking as high as 25
quiescence. We interpret these flare values as lower limits given that flares
too weak or too infrequent to have been observed likely exist. GJ 436's flare
frequency distribution (FFD) at FUV wavelengths is unusual compared to other
field-age M dwarfs, exhibiting a statistically-significant dearth of high
energy ( erg) events that we hypothesize to be the result of
a magnetic star-planet interaction (SPI) triggering premature flares. If an SPI
is present, GJ 436 b's magnetic field strength must be 100 G to
explain the statistically insignificant increase in orbit-phased FUV emission.Comment: 18 pages, 9 figures, accepted to the Astronomical Journa
Identification of a putative quantitative trait nucleotide in guanylate binding protein 5 for host response to PRRS virus infection
Citation: Koltes, J. E., Fritz-Waters, E., Eisley, C. J., Choi, I., Bao, H., Kommadath, A., . . . Reecy, J. M. (2015). Identification of a putative quantitative trait nucleotide in guanylate binding protein 5 for host response to PRRS virus infection. Bmc Genomics, 16, 13. doi:10.1186/s12864-015-1635-9Background: Previously, we identified a major quantitative trait locus (QTL) for host response to Porcine Respiratory and Reproductive Syndrome virus (PRRSV) infection in high linkage disequilibrium (LD) with SNP rs80800372 on Sus scrofa chromosome 4 (SSC4). Results: Within this QTL, guanylate binding protein 5 (GBP5) was differentially expressed (DE) (p < 0.05) in blood from AA versus AB rs80800372 genotyped pigs at 7,11, and 14 days post PRRSV infection. All variants within the GBP5 transcript in LD with rs80800372 exhibited allele specific expression (ASE) in AB individuals (p < 0.0001). A transcript re-assembly revealed three alternatively spliced transcripts for GBP5. An intronic SNP in GBP5, rs340943904, introduces a splice acceptor site that inserts five nucleotides into the transcript. Individuals homozygous for the unfavorable AA genotype predominantly produced this transcript, with a shifted reading frame and early stop codon that truncates the 88 C-terminal amino acids of the protein. RNA-seq analysis confirmed this SNP was associated with differential splicing by QTL genotype (p < 0.0001) and this was validated by quantitative capillary electrophoresis (p < 0.0001). The wild-type transcript was expressed at a higher level in AB versus AA individuals, whereas the five-nucleotide insertion transcript was the dominant form in AA individuals. Splicing and ASE results are consistent with the observed dominant nature of the favorable QTL allele. The rs340943904 SNP was also 100 % concordant with rs80800372 in a validation population that possessed an alternate form of the favorable B QTL haplotype. Conclusions: GBP5 is known to play a role in inflammasome assembly during immune response. However, the role of GBP5 host genetic variation in viral immunity is novel. These findings demonstrate that rs340943904 is a strong candidate causal mutation for the SSC4 QTL that controls variation in host response to PRRSV.Additional Authors: Lunney, J. K.;Liu, P.;Carpenter, S.;Rowland, R. R. R.;Dekkers, J. C. M.;Reecy, J. M
Constraining the Physical Properties of Stellar Coronal Mass Ejections with Coronal Dimming: Application to Far Ultraviolet Data of Eridani
Coronal mass ejections (CMEs) are a prominent contributor to solar system
space weather and might have impacted the Sun's early angular momentum
evolution. A signal diagnostic of CMEs on the Sun is coronal dimming: a drop in
coronal emission, tied to the mass of the CME, that is the direct result of
removing emitting plasma from the corona. We present the results of a coronal
dimming analysis of Fe XII 1349 A and Fe XXI 1354 A emission from
Eridani ( Eri), a young K2 dwarf, with archival far-ultraviolet
observations by the Hubble Space Telescope's Cosmic Origins Spectrograph.
Following a flare in February 2015, Eri's Fe XXI emission declined
by %. Although enticing, a scant 3.8 min of preflare observations
allows for the possibility that the Fe XXI decline was the decay of an earlier,
unseen flare. Dimming nondetections following each of three prominent flares
constrain the possible mass of ejected Fe XII-emitting (1 MK) plasma to less
than a few g. This implies that CMEs ejecting this much or more
1 MK plasma occur less than a few times per day on Eri. On the Sun,
g CMEs occur once every few days. For Eri, the mass loss
rate due to CME-ejected 1 MK plasma could be , well below
the star's estimated 30 mass loss rate (wind + CMEs). The
order-of-magnitude formalism we developed for these mass estimates can be
broadly applied to coronal dimming observations of any star.Comment: 27 pages, 22 figures, accepted to Ap
HAZMAT. VIII. A Spectroscopic Analysis of the Ultraviolet Evolution of K Stars: Additional Evidence for K Dwarf Rotational Stalling in the First Gigayear
Efforts to discover and characterize habitable zone planets have primarily
focused on Sun-like stars and M dwarfs. K stars, however, provide an appealing
compromise between these two alternatives that has been relatively unexplored.
Understanding the ultraviolet (UV) environment around such stars is critical to
our understanding of their planets, as the UV can drastically alter the
photochemistry of a planet's atmosphere. Here we present near-UV and far-UV
\textit{Hubble Space Telescope}'s Cosmic Origins Spectrograph observations of
39 K stars at three distinct ages: 40 Myr, 650 Myr, and 5 Gyr. We find
that the K star (0.6 -- 0.8 M) UV flux remains constant beyond 650
Myr before falling off by an order of magnitude by field age. This is distinct
from early M stars (0.3 -- 0.6 M), which begin to decline after only
a few hundred Myr. However, the rotation-UV activity relation for K stars is
nearly identical to that of early M stars. These results may be a consequence
of the spin-down stalling effect recently reported for K dwarfs, in which the
spin-down of K stars halts for over a Gyr when their rotation periods reach
10 d, rather than the continuous spin down that G stars experience.
These results imply that exoplanets orbiting K dwarfs may experience a stronger
UV environment than thought, weakening the case for K stars as hosts of
potential "super-habitable" planets.Comment: 18 pages, 7 figure
Holomorphic Quantization on the Torus and Finite Quantum Mechanics
We construct explicitly the quantization of classical linear maps of on toroidal phase space, of arbitrary modulus, using the holomorphic
(chiral) version of the metaplectic representation. We show that Finite Quantum
Mechanics (FQM) on tori of arbitrary integer discretization, is a consistent
restriction of the holomorphic quantization of to the subgroup
, being the principal congruent subgroup mod l,
on a finite dimensional Hilbert space. The generators of the ``rotation group''
mod l, , for arbitrary values of l are determined as
well as their quantum mechanical eigenvalues and eigenstates.Comment: 12 pages LaTeX (needs amssymb.sty). Version as will appear in J.
Phys.
HAZMAT. IV. Flares and Superflares on Young M Stars in the Far Ultraviolet
M stars are powerful emitters of far-ultraviolet light. Over long timescales, a significant, possibly dominant, fraction of this emission is produced by stellar flares. Characterizing this emission is critical to understanding the atmospheres of the stars producing it and the atmospheric evolution of the orbiting planets subjected to it. Ultraviolet emission is known to be elevated for several hundred million years after M stars form. Whether or not the same is true of ultraviolet flare activity is a key concern for the evolution of exoplanet atmospheres. Hubble Space Telescope (HST) observations by the HAZMAT program (HAbitable Zones and M dwarf Activity across Time) detected 18 flares on young (40 Myr) early M stars in the Tucana-Horologium association over 10 hr of observations, 10 having energy >1030 erg. These imply that flares on young M stars are 100-1000Ă more energetic than those occurring at the same rate on âinactive,â field age M dwarfs. However, when energies are normalized by quiescent emission, there is no statistical difference between the young and field age samples. The most energetic flare observed, dubbed the âHazflare,â emitted an energy of 1032.1 erg in the FUV, 30Ă more energetic than any stellar flare previously observed in the FUV with HSTâs COS or STIS spectrographs. It was accompanied by 15,500 ± 400 K blackbody emission bright enough to designate it as a superflare (E > 1033 erg), with an estimated bolometric energy of {10}{33.6-0.2+0.1} erg. This blackbody emitted {18}-1+2% of its flux in the FUV (912-1700 Ă
), where molecules are generally most sensitive to photolysis. Such hot superflares in young, early M stars could play an important role in the evolution of nascent planetary atmospheres. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555
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