117 research outputs found
Young Stars with SALT
We present a spectroscopic and kinematic analysis of 79 nearby M dwarfs in 77
systems. All are low-proper-motion southern hemisphere objects and were
identified in a nearby star survey with a demonstrated sensitivity to young
stars. Using low-resolution optical spectroscopy from the Red Side Spectrograph
(RSS) on the South African Large Telescope (SALT), we have determined radial
velocities, H-alpha, Lithium 6708\AA, and Potassium 7699\AA~equivalent widths
linked to age and activity, and spectral types for all our targets. Combined
with astrometric information from literature sources, we identify 44 young
stars. Eighteen are previously known members of moving groups within 100
parsecs of the Sun. Twelve are new members, including one member of the TW
Hydra moving group, one member of the 32 Orionis moving group, nine members of
Tucana-Horologium, one member of Argus, and two new members of AB Doradus. We
also find fourteen young star systems that are not members of any known groups.
The remaining 33 star systems do not appear to be young. This appears to be
evidence of a new population of nearby young stars not related to the known
nearby young moving groups.Comment: 23 pages, 11 figures, 6 tables. Accepted to Ap
Observing atmospheric escape in sub-Jovian worlds with JWST
Hydrodynamic atmospheric escape is considered an important process that
shapes the evolution of sub-Jovian exoplanets, particularly those with short
orbital periods. The metastable He line in the near-infrared at m
is a reliable tracer of atmospheric escape in hot exoplanets, with the
advantage of being observable from the ground. However, observing escaping He
in sub-Jovian planets has remained challenging due to the systematic effects
and telluric contamination present in ground-based data. With the successful
launch and operations of JWST, we now have access to extremely stable
high-precision near-infrared spectrographs in space. Here we predict the
observability of metastable He with JWST in two representative and previously
well-studied warm Neptunes, GJ 436 b (, ) and GJ 1214 b (, ). Our simulated JWST observations for GJ 436 b demonstrate that
a single transit with NIRSpec/G140H is sensitive to mass loss rates that are
two orders of magnitude lower than what is detectable from the ground. Our
exercise for GJ 1214 b show that the best configuration to observe the
relatively weak outflows of warm Neptunes with JWST is with NIRSpec/G140H, and
that NIRSpec/G140M and NIRISS/SOSS are less optimal. Since none of these
instrument configurations can spectrally resolve the planetary absorption, we
conclude that the 1D isothermal Parker-wind approximation may not be sufficient
for interpreting such observations. More sophisticated models are critical for
breaking the degeneracy between outflow temperature and mass-loss rate for JWST
measurements of metastable He.Comment: 14 pages, 7 figures, under review at AAS Journals; this version
follows the first round of revision. Feedback from the community is welcom
Importance of Sample Selection in Exoplanet Atmosphere Population Studies
Understanding planet formation requires robust population studies, which are
designed to reveal trends in planet properties. In this work, we aim to
determine if different methods for selecting populations of exoplanets for
atmospheric characterization with JWST could influence population-level
inferences. We generate three hypothetical surveys of
super-Earths/sub-Neptunes, each spanning a similar radius-insolation flux
space. The survey samples are constructed based on three different selection
criteria (evenly-spaced-by-eye, binned, and a quantitative selection function).
Using an injection-recovery technique, we test how robustly individual-planet
atmospheric parameters and population-level parameters can be retrieved. We
find that all three survey designs result in equally suitable targets for
individual atmospheric characterization, but not equally suitable targets for
constraining population parameters. Only samples constructed with a
quantitative method or that are sufficiently evenly-spaced-by-eye result in
robust population parameter constraints. Furthermore, we find that the sample
with the best targets for individual atmospheric study does not necessarily
result in the best constrained population parameters. The method of sample
selection must be considered. We also find that there may be large variability
in population-level results with a sample that is small enough to fit in a
single JWST cycle (12 planets), suggesting that the most successful
population-level analyses will be multi-cycle. Lastly, we infer that our
exploration of sample selection is limited by the small number of transiting
planets with measured masses around bright stars. Our results can guide future
development of programs that aim to determine underlying trends in exoplanet
atmospheric properties and, by extension, formation and evolution processes.Comment: 16 pages, 7 figures, accepted Ap
Starspot occultations in infrared transit spectroscopy: the case of WASP-52b
Stellar activity is one of the main obstacles to high-precision exoplanet
observations and has motivated extensive studies in detection and
characterization problems. Most efforts focused on unocculted starspots in
optical transit spectrophotometry, while the impact of starspot crossings is
assumed to be negligible in the near-infrared. Here, we present
\textit{HST}/WFC3 transit observations of the active star WASP-52, hosting an
inflated hot Jupiter, which present a possible starspot occultation signal. By
using this data set as a benchmark, we investigated whether the masking of the
transit profile distortion or modeling it with both a starspot model and a
Gaussian process affects the shape of the transmission spectrum. Different
methods produced spectra with the same shape and a robust detection of water
vapor, and with different reference radii for the planet.
The solutions of all methods are in agreement and reached a similar level of
precision. Our WFC3 light curve of WASP-52b hints that starspot crossings might
become more problematic with \textit{JWST}'s higher sensitivity and complete
coverage of the transit profile.Comment: 15 pages, 15 figures, 5 tables, data available onlin
Prevalence and risk factors for hepatitis C virus infection in an informal settlement in Karachi, Pakistan
The burden of hepatitis C virus (HCV) infection in Pakistan is amongst the highest in the world. People living in slums are likely to be at high risk of infection. Here, we describe the results of a cross-sectional survey conducted in March 2022 that aimed to quantify the prevalence of HCV infection in Machar Colony, one of the largest and oldest slum settlements in Karachi. Risk factors for HCV seropositivity were identified using multi-level logistic regression. We recruited 1,303 individuals in a random selection of 441 households from Machar Colony. The survey-adjusted HCV-seroprevalence was 13.5% (95% Confidence Interval (CI) 11.1–15.8) and survey-adjusted viraemic prevalence was 4.1% (95% CI 3.1–5.4) with a viraemic ratio of 32% (95% CI 24.3–40.5). Of 162 seropositive people, 71 (44%) reported receiving previous treatment for chronic hepatitis C. The odds of HCV seropositivity were found to increase with each additional reported therapeutic injection in the past 12 months (OR = 1.07 (95% Credible Interval (CrI) 1.00–1.13)). We found weaker evidence for a positive association between HCV seropositivity and a reported history of receiving a blood transfusion (OR = 1.72 (95% CrI 0.90–3.21)). The seroprevalence was more than double the previously reported seroprevalence in Sindh Province. The overall proportion of seropositive people that were viraemic was lower than expected. This may reflect the long-term impacts of a non-governmental clinic providing free of cost and easily accessible hepatitis C diagnosis and treatment to the population since 2015. Reuse of needles and syringes is likely to be an important driver of HCV transmission in this setting. Future public health interventions should address the expected risks associated with iatrogenic HCV transmission in this community
The Hubble PanCET Program:Emission Spectrum of Hot Jupiter HAT-P-41b
We present the most complete emission spectrum for inflated hot Jupiter
HAT-P-41b combining new HST WFC/G141 spectrum from the Hubble Panchromatic
Comparative Exoplanet Treasury (PanCET) program with archival Spitzer eclipse
observations. We found a near blackbody-like emission spectrum which is best
fitted with an isothermal temperature-pressure (TP) profile that agrees well
with the dayside heat redistribution scenario assuming zero Bond albedo. The
non-inverted TP profile is consistent with the non-detection of NUV/optical
absorbers in the transit spectra. We do not find any evidence for significant
H opacity nor a metal-rich atmosphere. HAT-P-41b is an ideal target that
sits in the transitioning parameter space between hot and ultra-hot Jupiters,
and future JWST observations will help us to better constrain the thermal
structure and chemical composition.Comment: Accepted for publication in A
Keck/NIRSPEC Studies of He I in the Atmospheres of Two Inflated Hot Gas Giants Orbiting K Dwarfs: WASP-52b and WASP-177b
We present the detection of neutral helium at 10833 Å in the atmosphere of WASP-52b and tentative evidence of helium in the atmosphere of the grazing WASP-177b, using high-resolution observations acquired with the NIRSPEC instrument on the Keck II telescope. We detect excess absorption by helium in WASP-52b's atmosphere of 3.44% ± 0.31% (11σ), or equivalently 66 ± 5 atmospheric scale heights. This absorption is centered on the planet's rest frame (Δv = 0.00 ± 1.19 km s-1). We model the planet's escape using a 1D Parker wind model and calculate its mass-loss rate to be ∼1.4 × 1011 g s-1, or equivalently 0.5% of its mass per gigayear. For WASP-177b, we see evidence for redshifted (Δv = 6.02 ± 1.88 km s-1) helium-like absorption of 1.28% ± 0.29% (equal to 23 ± 5 atmospheric scale heights). However, due to residual systematics in the transmission spectrum of similar amplitude, we do not interpret this as significant evidence for He absorption in the planet's atmosphere. Using a 1D Parker wind model, we set a 3σ upper limit on WASP-177b's escape rate of 7.9 × 1010 g s-1. Our results, taken together with recent literature detections, suggest the tentative relation between XUV irradiation and He i absorption amplitude may be shallower than previously suggested. Our results highlight how metastable helium can advance our understanding of atmospheric loss and its role in shaping the exoplanet population
ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of , but no evidence of Na or K
We present a new ground-based visual transmission spectrum of the hot Jupiter
WASP-43b, obtained as part of the ACCESS Survey. The spectrum was derived from
four transits observed between 2015 and 2018, with combined wavelength coverage
between 5,300 \r{A}-9,000 \r{A} and an average photometric precision of 708 ppm
in 230 \r{A} bins. We perform an atmospheric retrieval of our transmission
spectrum combined with literature HST/WFC3 observations to search for the
presence of clouds/hazes as well as Na, K, H, and planetary
absorption and stellar spot contamination over a combined spectral range of
5,318 \r{A}-16,420 \r{A}. We do not detect a statistically significant presence
of Na I or K I alkali lines, or H in the atmosphere of WASP-43b. We
find that the observed transmission spectrum can be best explained by a
combination of heterogeneities on the photosphere of the host star and a clear
planetary atmosphere with . This model yields a log-evidence of
higher than a flat (featureless) spectrum. In particular, the
observations marginally favor the presence of large, low-contrast spots over
the four ACCESS transit epochs with an average covering fraction and temperature contrast . Within the planet's atmosphere, we recover a log
volume mixing ratio of , which is consistent with
previous abundance determinations for this planet.Comment: 27 pages, 18 figures, 7 tables. Accepted for publication in AJ.
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