| 1. |
- Begy, Sean B., et al.
(författare)
-
Evolving Pulsation of the Slowly Rotating Magnetic beta Cep Star xi(1) CMa
- 2018
-
Ingår i: 3rd BRITE science conference. - : POLISH ASTRONOMICAL SOC. ; , s. 154-158
-
Konferensbidrag (refereegranskat)abstract
- We report BRITE-Constellation photometry of the beta Cep pulsator xi(1) CMa. Analysis of these data reveals a single pulsation period of 0.2095781(3) d, along with its first and second harmonics. We find no evidence for any other frequencies, limiting the value of this star as a target for magneto-asteroseismology. We employ the 17-year database of RV measurements of xi(1) CMa to evaluate evidence for the reported change in pulsation period, and interpret this period change in terms of stellar evolution. We measure a rate-of-change of the period equal to 0.009(1) s yr(-1), consistent with that reported in the literature.
|
|
| 2. |
- Fletcher, C. L., et al.
(författare)
-
Investigating the Magnetospheres of Rapidly Rotating B-type Stars
- 2017
-
Ingår i: Lives And Death-Throes Of Massive Stars. - 9781107170063 ; , s. 369-372
-
Konferensbidrag (refereegranskat)abstract
- Recent spectropolarimetric surveys of bright, hot stars have found that similar to 10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (similar to kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA's XMM-Newton space telescope, we observed 5 rapidly rotating B-types stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.
|
|
| 3. |
- Kochukhov, Oleg, et al.
(författare)
-
Magnetic field topologies of the bright, weak-field Ap stars θ Aurigae and ε Ursae Majoris
- 2019
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 621, s. 1-18
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The brightest magnetic chemically peculiar stars theta Aur and epsilon UMa were targeted by numerous studies of their photometric and spectroscopic variability. Detailed maps of chemical abundance spots were repeatedly derived for both stars. However, owing to the weakness of their surface magnetic fields, very little information on the magnetic field geometries of these stars is available.Aims. In this study we aim to determine detailed magnetic field topologies of theta Aur and epsilon UMa based on modern, high-resolution spectropolarimetric observations.Methods. Both targets were observed in all four Stokes parameters using the Narval and ESPaDOnS spectropolarimeters. A multi-line technique of least-squares deconvolution was employed to detect polarisation signatures in spectral lines. These signatures were modelled with a Zeeman-Doppler imaging code.Results. We succeed in detecting variable circular and linear polarisation signatures for theta Aur. Only circular polarisation was detected for epsilon UMa. We obtain new sets of high-precision longitudinal magnetic field measurements using mean circular polarisation metal line profiles as well as hydrogen line cores, which are consistent with historical data. Magnetic inversions revealed distorted dipolar geometries in both stars. The Fe and Cr abundance distributions, reconstructed simultaneously with magnetic mapping, do not show a clear correlation with the local magnetic field properties, with the exception of a relative element underabundance in the horizontal field regions along the magnetic equators.Conclusions. Our study provides the first ever detailed surface magnetic field maps for broad-line, weak-field chemically peculiar stars, showing that their field topologies are qualitatively similar to those found in stronger field stars. The Fe and Cr chemical abundance maps reconstructed for theta Aur and epsilon UMa are at odds with the predictions of current theoretical atomic diffusion calculations.
|
|
| 4. |
- Mikulasek, Z., et al.
(författare)
-
Differential rotation in magnetic chemically peculiar stars
- 2018
-
Ingår i: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO. - : SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST. - 1335-1842 .- 1336-0337. ; 48:1, s. 203-207
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic chemically peculiar (mCP) stars constitute about 10% of upper-main-sequence stars and are characterized by strong magnetic fields and abnormal photospheric abundances of some chemical elements. Most of them exhibit strictly periodic light, magnetic, radio, and spectral variations that can be fully explained by a rigidly rotating main-sequence star with persistent surface structures and a stable global magnetic field. Long-term observations of the phase curves of these variations enable us to investigate possible surface differential rotation with unprecedented accuracy and reliability. The analysis of the phase curves in the best-observed mCP stars indicates that the location and the contrast of photometric and spectroscopic spots as well as the geometry of the magnetic field remain constant for at least many decades. The strict periodicity of mCP variables supports the concept that the outer layers of upper-main-sequence stars do not rotate differentially. However, there is a small, inhomogeneous group consisting of a few mCP stars whose rotation periods vary on timescales of decades. The period oscillations may reflect real changes in the angular velocity of outer layers of the stars which are anchored by their global magnetic fields. In CU Vir, V901 On, and perhaps BS Cir, the rotational period variation indicates the presence of vertical differential rotation; however, its exact nature has remained elusive until now. The incidence of mCP stars with variable rotational periods is currently investigated using a sample of fifty newly identified Kepler mCP stars.
|
|
| 5. |
- Mikulasek, Z., et al.
(författare)
-
On the Nature of Rotation Period Variability of Magnetic Stars
- 2017
-
Ingår i: Stars. - 9781583819043 ; , s. 220-223
-
Konferensbidrag (refereegranskat)abstract
- The magnetic chemically peculiar (mCP) stars of the upper main sequence exhibit periodic light, magnetic, radio, and spectroscopic variations that can be adequately explained by a model of a rigidly rotating magnetized star with persistent surface structures. The majority of mCP stars rotate at strictly constant periods. However, there are a few mCP stars whose rotation periods vary on timescales of decades while the shape of their phase curves remains unchanged. In the case of CU Vir and V901 Ori, we have detected cyclic period variations. We demonstrate that the period oscillations of CU Vir may be a consequence of the interaction of the internal magnetic field and differential rotation.
|
|
| 6. |
- O'Brien, William T., et al.
(författare)
-
Biomarkers of Neurobiologic Recovery in Adults With Sport-Related Concussion
- 2024
-
Ingår i: JAMA NETWORK OPEN. - 2574-3805. ; 7:6
-
Tidskriftsartikel (refereegranskat)abstract
- ImportanceSport-related concussion (SRC), a form of mild traumatic brain injury, is a prevalent occurrence in collision sports. There are no well-established approaches for tracking neurobiologic recovery after SRC. ObjectiveTo examine the levels of serum glial fibrillary acidic protein (GFAP) and neurofilament light (NfL) in Australian football athletes who experience SRC. Design, Setting, and Participants A cohort study recruiting from April 10, 2021, to September 17, 2022, was conducted through the Victorian Amateur Football Association, Melbourne, Australia. Participants included adult Australian football players with or without SRC. Data analysis was performed from May 26, 2023, to March 27, 2024. Exposure Sport-related concussion, defined as at least 1 observable sign and/or 2 or more symptoms. Main Outcomes and Measures Primary outcomes were serum GFAP and NfL levels at 24 hours, and 1, 2, 4, 6, 8, 12, and 26 weeks. Secondary outcomes were symptoms, cognitive performance, and return to training times. Results Eighty-one individuals with SRC (median age, 22.8 [IQR, 21.3-26.0] years; 89% male) and 56 control individuals (median age, 24.6 [IQR, 22.4-27.3] years; 96% male) completed a total of 945 of 1057 eligible testing sessions. Compared with control participants, those with SRC exhibited higher GFAP levels at 24 hours (mean difference [MD] in natural log, pg/mL, 0.66 [95% CI, 0.50-0.82]) and 4 weeks (MD, 0.17 [95% CI, 0.02-0.32]), and NfL from 1 to 12 weeks (1-week MD, 0.31 [95% CI, 0.12-0.51]; 2-week MD, 0.38 [95% CI, 0.19-0.58]; 4-week MD, 0.31 [95% CI, 0.12-0.51]; 6-week MD, 0.27 [95% CI, 0.07-0.47]; 8-week MD, 0.36 [95% CI, 0.15-0.56]; and 12-week MD, 0.25 [95% CI, 0.04-0.46]). Growth mixture modeling identified 2 GFAP subgroups: extreme prolonged (16%) and moderate transient (84%). For NfL, 3 subgroups were identified: extreme prolonged (7%), moderate prolonged (15%), and minimal or no change (78%). Individuals with SRC who reported loss of consciousness (LOC) (33% of SRC cases) had higher GFAP at 24 hours (MD, 1.01 [95% CI, 0.77-1.24]), 1 week (MD, 0.27 [95% CI, 0.06-0.49]), 2 weeks (MD, 0.21 [95% CI, 0.004-0.42]) and 4 weeks (MD, 0.34 [95% CI, 0.13-0.55]), and higher NfL from 1 week to 12 weeks (1-week MD, 0.73 [95% CI, 0.42-1.03]; 2-week MD, 0.91 [95% CI, 0.61-1.21]; 4-week MD, 0.90 [95% CI, 0.59-1.20]; 6-week MD, 0.81 [95% CI, 0.50-1.13]; 8-week MD, 0.73 [95% CI, 0.42-1.04]; and 12-week MD, 0.54 [95% CI, 0.22-0.85]) compared with SRC participants without LOC. Return to training times were longer in the GFAP extreme compared with moderate subgroup (incident rate ratio [IRR], 1.99 [95% CI, 1.69-2.34]; NfL extreme (IRR, 3.24 [95% CI, 2.63-3.97]) and moderate (IRR, 1.43 [95% CI, 1.18-1.72]) subgroups compared with the minimal subgroup, and for individuals with LOC compared with those without LOC (IRR, 1.65 [95% CI, 1.41-1.93]). Conclusions and RelevanceIn this cohort study, a subset of SRC cases, particularly those with LOC, showed heightened and prolonged increases in GFAP and NfL levels, that persisted for at least 4 weeks. These findings suggest that serial biomarker measurement could identify such cases, guiding return to play decisions based on neurobiologic recovery. While further investigation is warranted, the association between prolonged biomarker elevations and LOC may support the use of more conservative return to play timelines for athletes with this clinical feature.
|
|
| 7. |
- Pablo, H., et al.
(författare)
-
epsilon Lupi : measuring the heartbeat of a doubly magnetic massive binary with BRITE Constellation
- 2019
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 488:1, s. 64-77
-
Tidskriftsartikel (refereegranskat)abstract
- epsilon Lupi A is a binary system consisting of two main-sequence early B-type stars Aa and Ab in a short period, moderately eccentric orbit. The close binary pair is the only doubly magnetic massive binary currently known. Using photometric data from the BRITE Constellation we identify a modest heartbeat variation. Combining the photometry with radial velocities of both components we determine a full orbital solution including empirical masses and radii. These results are compared with stellar evolution models as well as interferometry and the differences discussed. We also find additional photometric variability at several frequencies, finding it unlikely these frequencies can be caused by tidally excited oscillations. We do, however, determine that these signals are consistent with gravity mode pulsations typical for slowly pulsating B stars. Finally we discuss how the evolution of this system will be affected by magnetism, determining that tidal interactions will still be dominant.
|
|
| 8. |
- Shultz, Matthew, et al.
(författare)
-
Confirming the oblique rotator model for the extremely slowly rotating O8f?p star HD 108
- 2017
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 468:4, s. 3985-3992
-
Tidskriftsartikel (refereegranskat)abstract
- The O8f?p star HD 108 is implied to have experienced the most extreme rotational braking of any magnetic, massive star, with a rotational period P-rot of at least 55 yr, but the upper limit on its spin-down time-scale is over twice the age estimated from the Hertzsprung-Russell diagram. HD 108's observed X-ray luminosity is also much higher than predicted by the X-ray Analytical Dynamical Magnetosphere (XADM) model, a unique discrepancy amongst magnetic O-type stars. Previously reported magnetic data cover only a small fraction (similar to 3.5 per cent) of P-rot, and were furthermore acquired when the star was in a photometric and spectroscopic 'low state' at which the longitudinal magnetic field < B-z > was likely at a minimum. We have obtained a new ESPaDOnS magnetic measurement of HD 108, 6 yr after the last reported measurement. The star is returning to a spectroscopic high state, although its emission lines are still below their maximum observed strength, consistent with the proposed 55-yr period. We measured < B-z > = -325 +/- 45 G, twice the strength of the 2007-2009 observations, raising the lower limit of the dipole surface magnetic field strength to B-d >= 1 kG. The simultaneous increase in < B-z > and emission strength is consistent with the oblique rotator model. Extrapolation of the < B-z > maximum via comparison of HD 108's spectroscopic and magnetic data with the similar Of?p star HD 191612 suggests that B-d > 2 kG, yielding t(S,max) < 3 Myr, compatible with the stellar age. These results also yield a better agreement between the observed X-ray luminosity and that predicted by the XADM model.
|
|
| 9. |
- Shultz, Matthew E., et al.
(författare)
-
The magnetic early B-type stars I : magnetometry and rotation
- 2018
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 475:4, s. 5144-5178
-
Tidskriftsartikel (refereegranskat)abstract
- The rotational and magnetic properties of many magnetic hot stars are poorly characterized, therefore the Magnetism in Massive Stars and Binarity and Magnetic Interactions in various classes of Stars collaborations have collected extensive high-dispersion spectropo-larimetric data sets of these targets. We present longitudinal magnetic field measurements < B-z > for 52 early B-type stars (B5-B0), with which we attempt to determine their rotational periods P-rot. Supplemented with high-resolution spectroscopy, low-resolution Dominion As-trophysical Observatory circular spectropolarimetry, and archival Hipparcos photometry, we determined P-rot for 10 stars, leaving only five stars for which P-rot could not be determined. Rotational ephemerides for 14 stars were refined via comparison of new to historical magnetic measurements. The distribution of P-rot is very similar to that observed for the cooler Ap/Bp stars. We also measured v sin i and v(mac) for all stars. Comparison to non-magnetic stars shows that v sin i is much lower for magnetic stars, an expected consequence of magnetic braking. We also find evidence that v(mac) is lower for magnetic stars. Least-squares deconvolution profiles extracted using single-element masks revealed widespread, systematic discrepancies in < B-z > between different elements: this effect is apparent only for chemically peculiar stars, suggesting it is a consequence of chemical spots. Sinusoidal fits to H line < B-z > measurements (which should be minimally affected by chemical spots), yielded evidence of surface magnetic fields more complex than simple dipoles in six stars for which this has not previously been reported; however, in all six cases, the second- and third-order amplitudes are small relative to the first-order (dipolar) amplitudes.
|
|
| 10. |
- Shultz, Matthew, et al.
(författare)
-
HD 156324 : a tidally locked magnetic triple spectroscopic binary with a disrupted magnetosphere
- 2018
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 475:1, s. 839-852
-
Tidskriftsartikel (refereegranskat)abstract
- HD 156324 is an SB3 (B2VIB5VIB5V) system in the Sco OB4 association. The He-strong primary possesses both a strong magnetic field and Ha emission believed to originate in its centrifugal magnetosphere. We analyse a large spectroscopic and high-resolution spectropolarimetric data set. The radial velocities (RVs) indicate that the system is composed of two subsystems, which we designate A and B. Period analysis of the RVs of the three components yields orbital periods P-orb = 1.5806(1) d for the Aa and Ab components, and P-orb = 6.67(2) d for the B component, a PGa star. Period analysis of the longitudinal magnetic field (B,) and H alpha equivalent widths, which should both be sensitive to the rotational period Prot of the magnetic Aa component, both yield 1.58 d. Since P-orb = P-rot Aa and Ab must be tidally locked. Consistent with this, the orbit is circularized, and the rotational and orbital inclinations are identical within uncertainty, as are the semimajor axis and the Kepler corotation radius. The star's Ha emission morphology differs markedly from both theoretical and observational expectations in that there is only one, rather than two, emission peaks. We propose that this unusual morphology may be a consequence of modification of the gravitocentrifugal potential by the presence of the close stellar companion. We also obtain upper limits on the magnetic dipole strength B-d for the Ab and B components, respectively, finding B-d < 2.6 and <0.7 kG.
|
|
