المؤلفون: Chertow, GM, Chang, AM, Felker, GM, Heise, M, Velkoska, E, Fellstrom, B, Charytan, DM, Clementi, R, Gibson, CM, Goodman, SG, Jardine, M, Levin, A, Lokhnygina, Y, Mears, J, Mehran, R, Stenvinkel, P, Wang, A, Wheeler, DC, Zoccali, C, Ridker, PM, Mahaffey, KW, Tricoci, P, Wolf, M

المصدر: Nature medicine.

مصطلحات موضوعية: Medicin och hälsovetenskap

الوصول الحر: http://kipublications.ki.se/Default.aspx?queryparsed=id:158363150Test

المؤلفون: Brasseur, C. E., Jardine, M. M., Hussain, G. A. J.

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics

الوصف: We present a multiwavelength study of AB Doradus, combining modelling that incorporates a spectropolarimetric magnetic field map with 8.4 GHz radio interferometry to measure the coronal extent and density of this young star. We use the surface magnetic field map to produce a 3D extrapolation of AB Dor's coronal magnetic field. From this model we create synthetic radio images throughout the stellar rotation period which we can compare with the interferometric radio observations. Our models reproduce the two-lobe structure seen in the radio observations. We successfully fit the observed flux magnitude and lobe separation with our model. We conclude that that the features seen in the radio images are a result of centrifugal containment of hot gas at the peak of closed magnetic loops, and that the corona of AB Dor extends to about 8-10 stellar radii, making it much more extended than the present-day solar corona.
Comment: 10 pages, 13 figures. Accepted for publication in the Monthly Notices of the Royal Astronomical Society (MNRAS)

الوصول الحر: http://arxiv.org/abs/2404.06304Test

المؤلفون: Brown, E. L., Jeffers, S. V., Marsden, S. C., Morin, J., Saikia, S. Boro, Petit, P., Jardine, M. M., See, V., Vidotto, A. A., Mengel, M. W., Dahlkemper, M. N., Collaboration, the BCool

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics

الوصف: Spectropolarimetric data allow for simultaneous monitoring of stellar chromospheric $\log{R^{\prime}_{\rm{HK}}}$ activity and the surface-averaged longitudinal magnetic field, $B_l$, giving the opportunity to probe the relationship between large-scale stellar magnetic fields and chromospheric manifestations of magnetism. We present $\log{R^{\prime}_{\rm{HK}}}$ and/or $B_l$ measurements for 954 mid-F to mid-M stars derived from spectropolarimetric observations contained within the PolarBase database. Our magnetically active sample complements previous stellar activity surveys that focus on inactive planet-search targets. We find a positive correlation between mean $\log{R^{\prime}_{\rm{HK}}}$ and mean $\log|B_l|$, but for G stars the relationship may undergo a change between $\log{R'_{\rm{HK}}}\sim-4.4$ and $-4.8$. The mean $\log{R^{\prime}_{\rm{HK}}}$ shows a similar change with respect to the $\log{R^{\prime}_{\rm{HK}}}$ variability amplitude for intermediately-active G stars. We also combine our results with archival chromospheric activity data and published observations of large-scale magnetic field geometries derived using Zeeman Doppler Imaging. The chromospheric activity data indicate a slight under-density of late-F to early-K stars with $-4.75\leq\log{R'_{\rm HK}}\leq-4.5$. This is not as prominent as the original Vaughan-Preston gap, and we do not detect similar under-populated regions in the distributions of the mean $|B_l|$, or the $B_l$ and $\log{R'_{\rm HK}}$ variability amplitudes. Chromospheric activity, activity variability and toroidal field strength decrease on the main sequence as rotation slows. For G stars, the disappearance of dominant toroidal fields occurs at a similar chromospheric activity level as the change in the relationships between chromospheric activity, activity variability and mean field strength.
Comment: 20 pages, 15 figures, 3 tables

الوصول الحر: http://arxiv.org/abs/2205.03108Test

المؤلفون: Strugarek, A., Fares, R., Bourrier, V., Brun, A. S., Réville, V., Amari, T., Helling, Ch., Jardine, M., Llama, J., Moutou, C., Vidotto, A. A., Wheatley, P. J., Zarka, P.

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics, Astrophysics - Earth and Planetary Astrophysics

الوصف: Magnetic interactions between stars and close-in planets may lead to a detectable signal on the stellar disk. HD 189733 is one of the key exosystems thought to harbor magnetic interactions, which may have been detected in August 2013. We present a set of twelve wind models at that period, covering the possible coronal states and coronal topologies of HD 189733 at that time. We assess the power available for the magnetic interaction and predict its temporal modulation. By comparing the predicted signal with the observed signal, we find that some models could be compatible with an interpretation based on star-planet magnetic interactions. We also find that the observed signal can be explained only with a stretch-and-break interaction mechanism, while that the Alfv\'en wings scenario cannot deliver enough power. We finally demonstrate that the past observational cadence of HD 189733 leads to a detection rate of only between 12 to 23%, which could explain why star-planet interactions have been hard to detect in past campaigns. We conclude that the firm confirmation of their detection will require dedicated spectroscopic observations covering densely the orbital and rotation period, combined with scarcer spectropolarimetric observations to assess the concomitant large-scale magnetic topology of the star.
Comment: 16 pages, 8 figures, 4 tables, accepted for publication in MNRAS

الوصول الحر: http://arxiv.org/abs/2203.10956Test

المؤلفون: Jeffers, S. V., Cameron, R. H., Marsden, S. C., Saikia, S. Boro, Folsom, C. P., Jardine, M. M., Morin, J., Petit, P., See, V., Vidotto, A. A., Wolter, U., Mittag, M.

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics

الوصف: Cool main-sequence stars, such as the Sun, have magnetic fields which are generated by an internal dynamo mechanism. In the Sun, the dynamo mechanism produces a balance between the amounts of magnetic flux generated and lost over the Sun's 11-year activity cycle and it is visible in the Sun's different atmospheric layers using multi-wavelength observations. We used the same observational diagnostics, spanning several decades, to probe the emergence of magnetic flux on the two close by, active- and low-mass K dwarfs: 61 Cygni A and Epsilon Eridani. Our results show that 61 Cygni A follows the Solar dynamo with a regular cycle at all wavelengths, while Epsilon Eridani represents a more extreme level of the Solar dynamo, while also showing strong Solar-like characteristics. For the first time we show magnetic butterfly diagrams for stars other than the Sun. For the two K stars and the Sun, the rate at which the toroidal field is generated from surface poloidal field is similar to the rate at which toroidal flux is lost through flux emergence. This suggests that the surface field plays a crucial role in the dynamos of all three stars. Finally, for Epsilon Eridani, we show that the two chromospheric cycle periods, of ~3 and ~13 years, correspond to two superimposed magnetic cycles.
Comment: 8 pages, 5 figures: Accepted by A&A

الوصول الحر: http://arxiv.org/abs/2201.07530Test

المؤلفون: Koshino, A, Neuen, BL, Oshima, M, Toyama, T, Hara, A, Arnott, C, Neal, B, Jardine, M, Badve, SV, Mahaffey, KW, Pollock, C, Hansen, MK, Wada, T, Heerspink, HJL

المصدر: urn:ISSN:2468-0249 ; Kidney International Reports, 9, 2, 347-355

مصطلحات موضوعية: Clinical Research, Clinical Trials and Supportive Activities, Hematology, Kidney Disease, Prevention, Diabetes, 2 Aetiology, 2.1 Biological and endogenous factors, Metabolic and endocrine, Renal and urogenital, 3 Good Health and Well Being, SGLT2 inhibitor, anemia, biomarker, cardiovascular, kidney, mortality

الوصف: Introduction: Autoantibodies to erythropoietin receptor (anti-EPOR antibodies) have been identified in patients with various kidney diseases. However, data in patients with type 2 diabetes (T2D) and chronic kidney disease (CKD) is limited. We assessed the prevalence of anti-EPOR antibodies and their association with clinical outcomes in this population. Methods: The CREDENCE randomized patients with T2D and CKD to canagliflozin or placebo. Serum anti-EPOR antibodies, the exposure of interest, were measured using enzyme-linked immunosorbent assay. The primary outcome was doubling of serum creatinine, end-stage kidney disease, or death from kidney or cardiovascular (CV) causes. Secondary outcomes included CV and all-cause mortality. Multivariable Cox-regression models estimated associations between anti-EPOR antibodies and outcomes. The effects of canagliflozin on hemoglobin and hematocrit, stratified by the presence of anti-EPOR antibodies were assessed with a repeated measures mixed effects model. Results: Of 2600 participants with available biosamples, 191 (7.3%) were positive for anti-EPOR antibodies. Higher baseline anti-EPOR antibodies were associated with increased risk of primary outcome (hazard ratio [HR] per 1-SD increase = 1.12, 95% confidence interval [CI] = 1.01–1.24, P = 0.04), with CV death (HR = 1.27, 95% CI = 1.08–1.48, P < 0.01) and all-cause mortality (HR = 1.26, 95% CI = 1.11–1.43, P < 0.01). During follow-up, canagliflozin, compared to placebo, increased hemoglobin and hematocrit by 7.0 g/l (95% CI = 6.2–7.9) and 2.4% (2.2–2.7), respectively. These effects were consistent across patients with and without anti-EPOR antibodies (P-interaction = 0.24 and 0.36, respectively). Conclusion: In patients with T2D and CKD, anti-EPOR antibodies were associated with the composite kidney and CV outcome, as well as CV and all-cause mortality. Canagliflozin increased hemoglobin and hematocrit regardless of anti-EPOR antibodies.

وصف الملف: application/pdf

العلاقة: http://hdl.handle.net/1959.4/unsworks_85167Test; https://unsworks.unsw.edu.au/bitstreams/fd397001-8203-4fc5-9aaf-f2b8206f7c44/downloadTest; https://doi.org/10.1016/j.ekir.2023.11.024Test

الإتاحة: https://doi.org/10.1016/j.ekir.2023.11.024Test
http://hdl.handle.net/1959.4/unsworks_85167Test
https://unsworks.unsw.edu.au/bitstreams/fd397001-8203-4fc5-9aaf-f2b8206f7c44/downloadTest

المؤلفون: Brasseur, C E, Jardine, M M, Hussain, G A J

المساهمون: NASA

المصدر: Monthly Notices of the Royal Astronomical Society ; volume 530, issue 2, page 2442-2451 ; ISSN 0035-8711 1365-2966

الوصف: We present a multiwavelength study of AB Doradus, combining modelling that incorporates a spectropolarimetric magnetic field map with 8.4 GHz radio interferometry to measure the coronal extent and density of this young star. We use the surface magnetic field map to produce a 3D extrapolation of AB Dor’s coronal magnetic field. From this model we create synthetic radio images throughout the stellar rotation period which we can compare with the interferometric radio observations. Our models reproduce the two-lobe structure seen in the radio observations. We successfully fit the observed flux magnitude and lobe separation with our model. We conclude that that the features seen in the radio images are a result of centrifugal containment of hot gas at the peak of closed magnetic loops, and that the corona of AB Dor extends to about 8–10 stellar radii, making it much more extended than the present-day solar corona.

الإتاحة: https://doi.org/10.1093/mnras/stae996Test
https://academic.oup.com/mnras/article-pdf/530/2/2442/57319035/stae996.pdfTest

المؤلفون: Lund, K., Jardine, M., Russell, A. J. B., Donati, J. -F., Fares, R., Folsom, C. P.

المصدر: 2021MNRAS.tmp..352L

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics

الوصف: The helicity of a magnetic field is a fundamental property that is conserved in ideal MHD. It can be explored in the stellar context by mapping large-scale magnetic fields across stellar surfaces using Zeeman-Doppler imaging. A recent study of 51 stars in the mass range 0.1-1.34 M$_\odot$ showed that the photospheric magnetic helicity density follows a single power law when plotted against the toroidal field energy, but splits into two branches when plotted against the poloidal field energy. These two branches divide stars above and below $\sim$ 0.5 M$_\odot$. We present here a novel method of visualising the helicity density in terms of the linkage of the toroidal and poloidal fields that are mapped across the stellar surface. This approach allows us to classify the field linkages that provide the helicity density for stars of different masses and rotation rates. We find that stars on the lower-mass branch tend to have toroidal fields that are non-axisymmetric and so link through regions of positive and negative poloidal field. A lower-mass star may have the same helicity density as a higher-mass star, despite having a stronger poloidal field. Lower-mass stars are therefore less efficient at generating large-scale helicity.
Comment: 8 pages, 7 figures, 1 table

الوصول الحر: http://arxiv.org/abs/2102.11238Test

المؤلفون: Brown, E. L., Marsden, S. C., Mengel, M. W., Jeffers, S. V., Millburn, I., Mittag, M., Petit, P., Vidotto, A. A., Morin, J., See, V., Jardine, M., González-Pérez, J. N., Collaboration, the BCool

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics

الوصف: Studying cool star magnetic activity gives an important insight into the stellar dynamo and its relationship with stellar properties, as well as allowing us to place the Sun's magnetism in the context of other stars. Only 61 Cyg A (K5V) and $\tau$ Boo (F8V) are currently known to have magnetic cycles like the Sun's, where the large-scale magnetic field polarity reverses in phase with the star's chromospheric activity cycles. ${\tau}$ Boo has a rapid $\sim$240 d magnetic cycle, and it is not yet clear whether this is related to the star's thin convection zone or if the dynamo is accelerated by interactions between ${\tau}$ Boo and its hot Jupiter. To shed light on this, we studied the magnetic activity of HD75332 (F7V) which has similar physical properties to ${\tau}$ Boo and does not appear to host a hot Jupiter. We characterized its long term chromospheric activity variability over 53 yrs and used Zeeman Doppler Imaging to reconstruct the large-scale surface magnetic field for 12 epochs between 2007 and 2019. Although we observe only one reversal of the large-scale magnetic dipole, our results suggest that HD75332 has a rapid $\sim$1.06 yr solar-like magnetic cycle where the magnetic field evolves in phase with its chromospheric activity. If a solar-like cycle is present, reversals of the large-scale radial field polarity are expected to occur at around activity cycle maxima. This would be similar to the rapid magnetic cycle observed for ${\tau}$ Boo, suggesting that rapid magnetic cycles may be intrinsic to late-F stars and related to their shallow convection zones.
Comment: 23 pages, 14 figures, accepted for publication in MNRAS

الوصول الحر: http://arxiv.org/abs/2012.05407Test

المؤلفون: Stauffer, J. R., Rebull, L. M., Jardine, M., Cameron, A. Collier, Cody, A. M., Hillenbrand, L. A., Barrado, D., Kruse, E., Powell, B. P.

مصطلحات موضوعية: Astrophysics - Solar and Stellar Astrophysics

الوصف: Using K2, we recently discovered a new type of periodic photometric variability while analysing the light curves of members of Upper Sco (Stauffer \etal\ 2017). The 23 exemplars of this new variability type are all mid-M dwarfs, with short rotation periods. Their phased light curves have one or more broad flux dips or multiple arcuate structures which are not explicable by photospheric spots or eclipses by solid bodies. Now, using TESS data, we have searched for this type of variability in the other major sections of Sco-Cen, Upper Centaurus-Lupus (UCL) and Lower Centaurus-Crux (LCC). We identify 28 stars with the same light curve morphologies. We find no obvious difference between the Upper Sco and the UCL/LCC representatives of this class in terms of their light curve morphologies, periods or variability amplitudes. The physical mechanism behind this variability is unknown, but as a possible clue we show that the rapidly rotating mid-M dwarfs in UCL/LCC have slightly different colors from the slowly rotating M dwarfs - they either have a blue excess (hot spots?) or a red excess (warm dust?). One of the newly identified stars (TIC242407571) has a very striking light curve morphology. At about every 0.05 in phase are features that resemble icicles, The "icicles" arise because there is a second periodic system whose main feature is a broad flux dip. Using a toy model, we show that the observed light curve morphology results only if the ratio of the two periods and the flux dip width are carefully arranged.
Comment: Accepted by AJ

الوصول الحر: http://arxiv.org/abs/2011.01839Test