ABSTRACT
Current stellar model predictions of adiabatic oscillation frequencies differ significantly from the corresponding observed frequencies due to the non-adiabatic and poorly understood ...near-surface layers of stars. However, certain combinations of frequencies – known as frequency ratios – are largely unaffected by the uncertain physical processes as they are mostly sensitive to the stellar core. Furthermore, the seismic signature of helium ionization provides envelope properties while being almost independent of the outermost layers. We have developed an advanced stellar modelling approach in which we complement frequency ratios with parameters of the helium ionization zone while taking into account all possible correlations to put the most stringent constraints on the stellar internal structure. We have tested the method using the Keplerbenchmark star 16 Cyg A and have investigated the potential of the helium glitch parameters to constrain the basic stellar properties in detail. It has been explicitly shown that the initial helium abundance and mixing-length parameters are well constrained within our framework, reducing systematic uncertainties on stellar mass and age arising for instance from the well-known anticorrelation between the mass and initial helium abundance. The modelling of six additional Kepler stars including 16 Cyg B reinforces the above findings and also confirms that our approach is mostly independent of model uncertainties associated with the near-surface layers. Our method is relatively computationally expensive, however, it provides stellar masses, radii and ages precisely in an automated manner, paving the way for analysing numerous stars observed in the future during the ESA PLATO mission.
Abstract
GJ 367 is a bright (
V
≈ 10.2) M1 V star that has been recently found to host a transiting ultra-short period sub-Earth on a 7.7 hr orbit. With the aim of improving the planetary mass and ...radius and unveiling the inner architecture of the system, we performed an intensive radial velocity follow-up campaign with the HARPS spectrograph—collecting 371 high-precision measurements over a baseline of nearly 3 yr—and combined our Doppler measurements with new TESS observations from sectors 35 and 36. We found that GJ 367 b has a mass of
M
b
= 0.633 ± 0.050
M
⊕
and a radius of
R
b
= 0.699 ± 0.024
R
⊕
, corresponding to precisions of 8% and 3.4%, respectively. This implies a planetary bulk density of
ρ
b
= 10.2 ± 1.3 g cm
−3
, i.e., 85% higher than Earth’s density. We revealed the presence of two additional non-transiting low-mass companions with orbital periods of ∼11.5 and 34 days and minimum masses of
M
c
sin
i
c
= 4.13 ± 0.36
M
⊕
and
M
d
sin
i
d
= 6.03 ± 0.49
M
⊕
, respectively, which lie close to the 3:1 mean motion commensurability. GJ 367 b joins the small class of high-density planets, namely the class of super-Mercuries, being the densest ultra-short period small planet known to date. Thanks to our precise mass and radius estimates, we explored the potential internal composition and structure of GJ 367 b, and found that it is expected to have an iron core with a mass fraction of
0.91
−
0.23
+
0.07
. How this iron core is formed and how such a high density is reached is still not clear, and we discuss the possible pathways of formation of such a small ultra-dense planet.
Abstract
The bright star
λ
Ser hosts a hot Neptune with a minimum mass of 13.6
M
⊕
and a 15.5 day orbit. It also appears to be a solar analog, with a mean rotation period of 25.8 days and surface ...differential rotation very similar to the Sun. We aim to characterize the fundamental properties of this system and constrain the evolutionary pathway that led to its present configuration. We detect solar-like oscillations in time series photometry from the Transiting Exoplanet Survey Satellite, and we derive precise asteroseismic properties from detailed modeling. We obtain new spectropolarimetric data, and we use them to reconstruct the large-scale magnetic field morphology. We reanalyze the complete time series of chromospheric activity measurements from the Mount Wilson Observatory, and we present new X-ray and ultraviolet observations from the Chandra and Hubble space telescopes. Finally, we use the updated observational constraints to assess the rotational history of the star and estimate the wind braking torque. We conclude that the remaining uncertainty on the stellar age currently prevents an unambiguous interpretation of the properties of
λ
Ser, and that the rate of angular momentum loss appears to be higher than for other stars with a similar Rossby number. Future asteroseismic observations may help to improve the precision of the stellar age.
ABSTRACT
The Milky Way was shaped by the mergers with several galaxies in the past. We search for remnant stars that were born in these foreign galaxies and assess their ages in an effort to put ...upper limits on the merger times and thereby better understand the evolutionary history of our Galaxy. Using 5D-phase space information from Gaia eDR3, radial velocities from Gaia DR2 and chemical information from apogee DR16, we kinematically and chemically select 21 red giant stars belonging to former dwarf galaxies that merged with the Milky Way. With added asteroseismology from Kepler and K2 , we determine the ages of the 21 ex situ stars and 49 in situ stars with an average σage/age of ∼31 per cent. We find that all the ex situ stars are consistent with being older than 8 Gyr. While it is not possible to associate all the stars with a specific dwarf galaxy, we classify eight of them as Gaia-Enceladus/Sausage stars, which is one of the most massive mergers in our Galaxy’s history. We determine their mean age to be 9.5 ± 1.3 Gyr consistent with a merger time of 8–10 Gyr ago. The rest of the stars are possibly associated with Kraken, Thamnos, Sequoia, or another extragalactic progenitor. The age determination of ex situ stars paves the way to more accurately pinning down when the merger events occurred and hence provide tight constraints useful for simulating how these events unfolded.
Since the onset of the "space revolution" of high-precision high-cadence photometry, asteroseismology has been demonstrated as a powerful tool for informing Galactic archeology investigations. The ...launch of the NASA Transiting Exoplanet Survey Satellite (TESS) mission has enabled seismic-based inferences to go full sky-providing a clear advantage for large ensemble studies of the different Milky Way components. Here we demonstrate its potential for investigating the Galaxy by carrying out the first asteroseismic ensemble study of red giant stars observed by TESS. We use a sample of 25 stars for which we measure their global asteroseimic observables and estimate their fundamental stellar properties, such as radius, mass, and age. Significant improvements are seen in the uncertainties of our estimates when combining seismic observables from TESS with astrometric measurements from the Gaia mission compared to when the seismology and astrometry are applied separately. Specifically, when combined we show that stellar radii can be determined to a precision of a few percent, masses to 5%-10%, and ages to the 20% level. This is comparable to the precision typically obtained using end-of-mission Kepler data.
Abstract Objectives We sought to determine if resident productivity changed based on emergency department (ED) volume, shift time of day, or over time during a shift. Methods This is a retrospective ...review of patients evaluated in the ED by emergency medicine residents. Data were collected using the computerized tracker that provides time of physician assignment and daily volume. Regression analysis was used to determine relationship between productivity and volume as well as relationship between productivity and accumulated time in the ED. Analysis of variance was used to assess for productivity differences by shift time of day. Results One hundred sixty-one postgraduate year-1 (PGY-1), 264 PGY-2, and 193 PGY-3 shifts were included. PGY-1, PGY-2, and PGY-3 residents saw 0.85, 1.13, and 1.25 patients per hour, respectively. PGY-3 and PGY-2 productivity had a weak relationship to ED volume ( R = 0.28, P = .03; and R = 0.36, P = .03), whereas PGY-1 productivity had a moderate relationship to ED volume ( R = 0.44, P = .0001). There were no differences in productivity based on shift time of day. Accumulated time in the ED had a strongly negative relationship to productivity, with R values from −0.79 to −0.93 ( P < .002 for all comparisons). Conclusions Resident productivity is not strongly linked to volume or time of day. If specific times have statistically higher volume, they should be staffed with larger numbers of residents. In addition, emergency medicine resident productivity declines reliably over shift time. Therefore, scheduling should be adjusted to create larger shift overlaps to aid in smoother patient flow.
Did Kepler-444 have a long-lived convective core? Winther, Mark Lykke; Aguirre Børsen-Koch, Víctor; Rørsted, Jakob Lysgaard ...
Monthly notices of the Royal Astronomical Society,
08/2023, Letnik:
525, Številka:
1
Journal Article
Recenzirano
Odprti dostop
ABSTRACT
With the greater power to infer the state of stellar interiors provided by asteroseismology, it has become possible to study the survival of initially convective cores within stars during ...their main-sequence evolution. Standard theories of stellar evolution predict that convective cores in subsolar mass stars have lifetimes below $1\, {\rm Gyr}$. However, a recent asteroseismic study of the star Kepler-444 concluded that the initial convective core had survived for nearly $8\, {\rm Gyr}$. The goal of this paper is to study the convective-core evolution of Kepler-444 and to investigate its proposed longevity. We modify the input physics of stellar models to induce longer convective-core lifetimes and vary the associated parameter across a dense grid of evolutionary tracks. The observations of metallicity, effective temperature, mean density, and asteroseismic frequency ratios are fitted to the models using the basta pipeline. We explore different choices of constraints, from which a long convective-core lifetime is only recovered for a few specific combinations: mainly from the inclusion of potentially unreliable frequencies and/or excluding the covariances between the frequency ratios, whereas for the classical parameters, the derived luminosity has the largest influence. For all choices of observables, our analysis reliably constrains the convective-core lifetime of Kepler-444 to be short, with a median around $0.6\, {\rm Gyr}$ and a 1σ upper bound around $3.5\, {\rm Gyr}$.
Abstract
INTRODUCTION
Telemedicine has been available for more than 20 years and is playing an increasing role in clinical care. However, few studies have evaluated the value of telemedicine in ...neurosurgical consultations and in guiding neurosurgical care.
METHODS
In this prospective observational study, we examined our experience with emergency video telemedicine consultations for neurosurgical patients at a rural hospital system. Our system uses secure and HIPAA-compliant video conferencing to connect providers and patients to a remote neurosurgery consultant, and operates one out of two days.
RESULTS
During a ten-month period, 229 neurosurgical telemedicine consultations were performed. Two-thirds of the patients had intracranial pathology, 28% had spinal pathology and 3% of the consults were for patients who returned after care at our institution or required clearance for another procedure. Five patients required transfer within the hospital system and 12 out of the hospital system for a higher level of care (total 7.4%). Patients that required transfer most frequently had intracranial pathology (70%). The number of patients transferred out was less than in the year before telemedicine was available.
CONCLUSION
Telemedicine consultation for neurosurgery is feasible for a variety of neurosurgical pathologies, improves patient access to neurosurgery expertise, and facilitates appropriate transfers to a higher level of care when required. Our findings are especially relevant in light of the COVID-19 pandemic, which has highlighted the importance of delivering quality medical care when physical patient contact is not possible.
Abstract
Asteroseismology of bright stars has become increasingly important as a method to determine the fundamental properties (in particular ages) of stars. The Kepler Space Telescope initiated a ...revolution by detecting oscillations in more than 500 main-sequence and subgiant stars. However, most Kepler stars are faint and therefore have limited constraints from independent methods such as long-baseline interferometry. Here we present the discovery of solar-like oscillations in
α
Men A, a naked-eye (
V
= 5.1) G7 dwarf in TESS’s southern continuous viewing zone. Using a combination of astrometry, spectroscopy, and asteroseismology, we precisely characterize the solar analog
α
Men A (
T
eff
= 5569 ± 62 K,
R
⋆
= 0.960 ± 0.016
R
⊙
,
M
⋆
= 0.964 ± 0.045
M
⊙
). To characterize the fully convective M dwarf companion, we derive empirical relations to estimate mass, radius, and temperature given the absolute Gaia magnitude and metallicity, yielding
M
⋆
= 0.169 ± 0.006
M
⊙
,
R
⋆
= 0.19 ± 0.01
R
⊙
, and
T
eff
= 3054 ± 44 K. Our asteroseismic age of 6.2 ± 1.4 (stat) ± 0.6 (sys) Gyr for the primary places
α
Men B within a small population of M dwarfs with precisely measured ages. We combined multiple ground-based spectroscopy surveys to reveal an activity cycle of
P
= 13.1 ± 1.1 yr for
α
Men A, a period similar to that observed in the Sun. We used different gyrochronology models with the asteroseismic age to estimate a rotation period of ∼30 days for the primary. Alpha Men A is now the closest (
d
= 10 pc) solar analog with a precise asteroseismic age from space-based photometry, making it a prime target for next-generation direct-imaging missions searching for true Earth analogs.
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