65 research outputs found
Abundant Refractory Sulfur in Protoplanetary Disks
Sulfur is one of the most abundant elements in the Universe, with important
roles in astro-, geo-, and biochemistry. Its main reservoirs in planet-forming
disks have previously eluded detection: gaseous molecules only account for
\% of total elemental sulfur, with the rest likely in either ices or
refractory minerals. Mechanisms such as giant planets can filter out dust from
gas accreting onto disk-hosting stars. For stars above 1.4 solar masses, this
leaves a chemical signature on the stellar photosphere that can be used to
determine the fraction of each element that is locked in dust. Here, we present
an application of this method to sulfur, zinc, and sodium. We analyse the
accretion-contaminated photospheres of a sample of young stars and find
\% of elemental sulfur is in refractory form in their disks. The
main carrier is much more refractory than water ice, consistent with sulfide
minerals such as FeS
Ages for exoplanet host stars
Age is an important characteristic of a planetary system, but also one that
is difficult to determine. Assuming that the host star and the planets are
formed at the same time, the challenge is to determine the stellar age.
Asteroseismology provides precise age determination, but in many cases the
required detailed pulsation observations are not available. Here we concentrate
on other techniques, which may have broader applicability but also serious
limitations. Further development of this area requires improvements in our
understanding of the evolution of stars and their age-dependent
characteristics, combined with observations that allow reliable calibration of
the various techniques.Comment: To appear in "Handbook of Exoplanets", eds. Deeg, H.J. & Belmonte,
J.A, Springer (2018
Estimating magnetic filling factors from Zeeman-Doppler magnetograms
This is the author accepted manuscript. The final version is available from American Astronomical Society via the DOI in this record.Low-mass stars are known to have magnetic fields that are believed to be of dynamo origin. Two complementary techniques are principally used to characterise them. Zeeman-Doppler imaging (ZDI) can determine the geometry of the large-scale magnetic field while Zeeman broadening can assess the total unsigned flux including that associated with small-scale structures such as spots. In this work, we study a sample of stars that have been previously mapped with ZDI. We show that the average unsigned magnetic flux follows an activity-rotation relation separating into saturated and unsaturated regimes. We also compare the average photospheric magnetic flux recovered by ZDI, hBV i, with that recovered by Zeeman broadening studies, hBI i. In line with previous studies, hBV i ranges from a few % to âŒ20% of hBI i. We show that a power law relationship between hBV i and hBI i exists and that ZDI recovers a larger fraction of the magnetic flux in more active stars. Using this relation, we improve on previous attempts to estimate filling factors, i.e. the fraction of the stellar surface covered with magnetic field, for stars mapped only with ZDI. Our estimated filling factors follow the well-known activity-rotation relation which is in agreement with filling factors obtained directly from Zeeman broadening studies. We discuss the possible implications of these results for flux tube expansion above the stellar surface and stellar wind models.European CommissionAustrian Space Application Programm
The magnetic field and multiple planets of the young dwarf AU~Mic
In this paper we present an analysis of near-infrared spectropolarimetric and
velocimetric data of the young M dwarf AU Mic, collected with SPIRou at the
Canada-France-Hawaii telescope from 2019 to 2022, mostly within the SPIRou
Legacy Survey. With these data, we study the large- and small-scale magnetic
field of AU Mic, detected through the unpolarized and circularly-polarized
Zeeman signatures of spectral lines. We find that both are modulated with the
stellar rotation period (4.86 d), and evolve on a timescale of months under
differential rotation and intrinsic variability. The small-scale field,
estimated from the broadening of spectral lines, reaches kG. The
large-scale field, inferred with Zeeman-Doppler imaging from Least-Squares
Deconvolved profiles of circularly-polarized and unpolarized spectral lines, is
mostly poloidal and axisymmetric, with an average intensity of G. We
also find that surface differential rotation, as derived from the large-scale
field, is 30% weaker than that of the Sun. We detect the radial
velocity (RV) signatures of transiting planets b and c, although dwarfed by
activity, and put an upper limit on that of candidate planet d, putatively
causing the transit-timing variations of b and c. We also report the detection
of the RV signature of a new candidate planet (e) orbiting further out with a
period of d, i.e., near the 4:1 resonance with b. The RV
signature of e is detected at 6.5 while those of b and c show up at
4, yielding masses of and
Earth masses for b and c, and a minimum mass of
Earth masses for e.Comment: MNRAS, in press (20 pages and 12 figures + 9 pages of supplementary
material
Stellar Coronal and Wind Models: Impact on Exoplanets
Surface magnetism is believed to be the main driver of coronal heating and
stellar wind acceleration. Coronae are believed to be formed by plasma confined
in closed magnetic coronal loops of the stars, with winds mainly originating in
open magnetic field line regions. In this Chapter, we review some basic
properties of stellar coronae and winds and present some existing models. In
the last part of this Chapter, we discuss the effects of coronal winds on
exoplanets.Comment: Chapter published in the "Handbook of Exoplanets", Editors in Chief:
Juan Antonio Belmonte and Hans Deeg, Section Editor: Nuccio Lanza. Springer
Reference Work
Influence of Calendar Period on the Association Between BMI and Coronary Heart Disease: A Meta-Analysis of 31 Cohorts
Objective: The association between obesity and coronary heart disease (CHD) may have changed over
time, for example due to improved pharmacological treatment of CHD risk factors. This meta-analysis of
31 prospective cohort studies explores the influence of calendar period on CHD risk associated with
body mass index (BMI).
Design and Methods: The relative risks (RRs) of CHD for a five-BMI-unit increment and BMI categories
were pooled by means of random effects models. Meta-regression analysis was used to examine the
influence of calendar period (>1985 v 1985) in univariate and multivariate analyses (including mean
population age as a covariate). Results: The age, sex, and smoking adjusted RR (95% confidence intervals) of CHD for a five-BMI-unit
increment was 1.28(1.22:1.34). For underweight, overweight and obesity, the RRs (compared to normal
weight) were 1.11(0.91:1.36), 1.31(1.22:1.41), and 1.78(1.55:2.04), respectively. The univariate analysis
indicated 31% (95%CI: 56:0) lower RR of CHD associated with a five-BMI-unit increment and a 51%
(95%CI: 78: 14)) lower RR associated with obesity in studies starting after 1985 (n Œ 15 and 10,
respectively) compared to studies starting in or before 1985 (n Œ 16 and 10). However, in the multivariate
analysis, only mean population age was independently associated with the RRs for a five-BMI-unit
increment and obesity ( 29(95%CI: 55: 5)) and 31(95%CI: 66:3), respectively) per 10-year
increment in mean age).
Conclusion: This study provides no consistent evidence for a difference in the association between BMI
and CHD by calendar period. The mean population age seems to be the most important factor that
modifies the association between the risk of CHD and BMI, in which the RR decreases with increasing
age
Mammography stages of change in middle-aged women with schizophrenia: An exploratory analysis
BACKGROUND: Health care providers and educators who seek to create health promotion programs and individualized comprehensive care plans for women with schizophrenia are hindered by the lack of data to guide their efforts. PURPOSE: This study tested the hypothesis that women with schizophrenia adhere to mammography screening guidelines at the same rate as other same-age women. The study also investigated the validity of the Health Belief (HB) and Stages of Change (SOC) models for breast cancer screening among women with schizophrenia. METHODS: Socio-demographic and clinical variables, as well as knowledge, attitudes, and barriers were assessed as a function of stage of change related to breast cancer screening in 46 women with schizophrenia. RESULTS: Women with schizophrenia were statistically less likely to be adherent to the screening recommendations than those without schizophrenia. Some support was found for the validity of the HB and SOC models for breast cancer screening in women with schizophrenia. Women in the Precontemplation stage had significantly higher negative attitude scores compared to Contemplation and Action/Maintenance stages (59.7, 45.7, and 43.2, respectively), and there was a trend for more barriers in the Precontemplation group (4.6, 2.6, 2.7 respectively). CONCLUSION: Given the small sample size, further research on the rates of breast cancer screening in women with schizophrenia is warranted. Nonetheless, these data suggest that providers who care for women with schizophrenia may need to make take additional measures to ensure that this population receives appropriate screening so as to not put them at greater risk for a late-stage diagnosis of breast cancer. Furthermore, these pilot data suggest that HB and SOC theory-based interventions may be valid for increasing mammography rates in women with schizophrenia
The Early Evolution of BitingâChewing Performance in Hexapoda
Insects show a plethora of different mandible shapes. It was advocated that these mandible shapes are mainly a function of different feeding habits. This hypothesis was tested on a larger sampling of non-holometabolan bitingâchewing insects with additional tests to understand the interplay of mandible function, feeding guild, and phylogeny. The results show that at the studied systematic level, variation in mandible bitingâchewing effectivity is regulated to a large extent by phylogenetic history and the configuration of the mandible joints rather than the food preference of a given taxon. Additionally, lineages with multiple mandibular joints such as primary wingless hexapods show a wider functional space occupation of mandibular effectivity than dicondylic insects (= silverfish + winged insects) at significantly different evolutionary rates. The evolution and occupation of a comparably narrow functional performance space of dicondylic insects is surprising given the low effectivity values of this food uptake solution. Possible reasons for this relative evolutionary âstasisâ are discussed
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