250 research outputs found
MOST detects corotating bright spots on the mid-O type giant {\xi} Persei
We have used the MOST (Microvariability and Oscillations of STars)
microsatellite to obtain four weeks of contiguous high-precision broadband
visual photometry of the O7.5III(n)((f)) star {\xi} Persei in November 2011.
This star is well known from previous work to show prominent DACs (Discrete
Absorption Components) on time-scales of about 2 d from UV spectroscopy and NRP
(Non Radial Pulsation) with one (l = 3) p-mode oscillation with a period of 3.5
h from optical spectroscopy. Our MOST-orbit (101.4 min) binned photometry fails
to reveal any periodic light variations above the 0.1 mmag 3-sigma noise level
for periods of hours, while several prominent Fourier peaks emerge at the 1
mmag level in the two-day period range. These longer-period variations are
unlikely due to pulsations, including gravity modes. From our simulations based
upon a simple spot model, we deduce that we are seeing the photometric
modulation of several co-rotating bright spots on the stellar surface. In our
model, the starting times (random) and lifetimes (up to several rotations) vary
from one spot to another yet all spots rotate at the same period of 4.18 d, the
best-estimated rotation period of the star. This is the first convincing
reported case of co-rotating bright spots on an O star, with important
implications for drivers of the DACs (resulting from CIRs - Corotating
Interaction Regions) with possible bright-spot generation via a breakout at the
surface of a global magnetic field generated by a subsurface convection zone.Comment: 9 pages, 4 figures, 2 tables, MNRAS in pres
X-Shooting ULLYSES: Massive stars at low metallicity. III. Terminal wind speeds of ULLYSES massive stars
The winds of massive stars have an impact on stellar evolution and on the
surrounding medium. The maximum speed reached by these outflows, the terminal
wind speed, is a global wind parameter and an essential input for models of
stellar atmospheres and feedback. With the arrival of the ULLYSES programme, a
legacy UV spectroscopic survey with HST, we have the opportunity to quantify
the wind speeds of massive stars at sub-solar metallicity (in the Large and
Small Magellanic Clouds, 0.5Z and 0.2Z) at an unprecedented scale. We
empirically quantify the wind speeds of a large sample of OB stars, including
supergiants, giants, and dwarfs at sub-solar metallicity. Using these
measurements, we investigate trends of terminal wind speed with a number of
fundamental stellar parameters, namely effective temperature, metallicity, and
surface escape velocity. We empirically determined the terminal wind speed for
a sample of 149 OB stars in the Magellanic Clouds either by directly measuring
the maximum velocity shift of the absorption component of the Civ 1548-1550
line profile, or by fitting synthetic spectra produced using the Sobolev with
exact integration method. Stellar parameters were either collected from the
literature, obtained using spectral-type calibrations, or predicted from
evolutionary models. We find strong trends of terminal wind speed with
effective temperature and surface escape speed when the wind is strong enough
to cause a saturated P Cygni profile in Civ 1548-1550. We find evidence for a
metallicity dependence on the terminal wind speed proportional to Z^0.22+-0.03
when we compared our results to previous Galactic studies. Our results suggest
that effective temperature rather than surface escape speed should be used as a
straightforward empirical prediction of terminal wind speed and that the
observed metallicity dependence is steeper than suggested by earlier works.Comment: 21 pages, 16 figures, 8 tables. Accepted in A&
Wealthiest is Not Always Healthiest: What Explains Differences in Child Mortality in West Africa?
Elevated levels of numerous cytokines in drainage fluid after primary total hip arthroplasty
As cytokines are involved in wound healing and other inflammatory processes, it could be valuable to measure their levels at the operative site. This study was conducted to investigate whether different cytokines are measurable in drainage fluid and, when measurable, whether we can find a difference in cytokine levels between one and six hours postoperatively. Samples from the drainage system in 30 consecutive patients undergoing primary total hip replacement were collected at one and six hours after closure of the wound. Levels of several cytokines were measured in the drainage fluids. A significant elevation of almost all cytokines was observed between the sample after one hour and six hours postoperatively. We found a strong correlation between the different pro-inflammatory cytokines. The IL-6 to IL-10 ratio were also raised, showing a pro-inflammatory predominance. Levels were much higher than those previously shown in serum
The Evolution of Compact Binary Star Systems
We review the formation and evolution of compact binary stars consisting of
white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and
BHs are thought to be the primary astrophysical sources of gravitational waves
(GWs) within the frequency band of ground-based detectors, while compact
binaries of WDs are important sources of GWs at lower frequencies to be covered
by space interferometers (LISA). Major uncertainties in the current
understanding of properties of NSs and BHs most relevant to the GW studies are
discussed, including the treatment of the natal kicks which compact stellar
remnants acquire during the core collapse of massive stars and the common
envelope phase of binary evolution. We discuss the coalescence rates of binary
NSs and BHs and prospects for their detections, the formation and evolution of
binary WDs and their observational manifestations. Special attention is given
to AM CVn-stars -- compact binaries in which the Roche lobe is filled by
another WD or a low-mass partially degenerate helium-star, as these stars are
thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure
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