20 research outputs found
Winds of OB stars: impact of metallicity, rotation and binary interaction
Winds of massive stars are an important ingredient in determining their
evolution, final remnant mass, and feedback to the surrounding interstellar
medium. We compare empirical results for OB star winds at low metallicity with
theoretical predictions. Observations suggest very weak winds at SMC
metallicity, but there are exceptions. We identified promising candidates for
rotationally enhanced mass-loss rates with two component wind and partially
stripped stars hiding among OB stars with slow but dense wind in the SMC. A
preliminary analysis of these systems, derived parameters, and their
implications are discussed. Finally, we briefly discuss the interaction of OB
winds near black holes in X-ray binaries.Comment: Accepted for publication in the Proceedings of the International
Astronomical Union for the IAU Symposium 370 "Winds of Stars and Exoplanets"
(eds. A.A. Vidotto, L. Fossati, J.S. Vink
Stellar population of the superbubble N206 in the LMC I. Analysis of the Of-type stars
Massive stars are the key agents of feedback. Consequently, quantitative
analysis of massive stars are required to understand how the feedback of these
objects shapes/ creates the large scale structures of the ISM. The giant HII
region N206 in the Large Magellanic Cloud contains an OB association that
powers a X-ray superbubble, serving as an ideal laboratory in this context. We
obtained optical spectra with the muti-object spectrograph FLAMES at the
ESO-VLT. When possible, the optical spectroscopy was complemented by UV spectra
from the HST, IUE, and FUSE archives. Detailed spectral classifications are
presented for our sample Of-type stars. For the quantitative spectroscopic
analysis we use the Potsdam Wolf-Rayet (PoWR) model atmosphere code. The
physical parameters and nitrogen abundances of our sample stars are determined
by fitting synthetic spectra to the observations. The stellar and wind
parameters of nine Of-type stars are used to construct wind momentum,luminosity
relationship. We find that our sample follows a relation close to the
theoretical prediction, assuming clumped winds. The most massive star in the
N206 association is an Of supergiant which has a very high mass-loss rate. Two
objects in our sample reveal composite spectra, showing that the Of primaries
have companions of late O subtype. All stars in our sample have an evolutionary
age less than 4 million years, with the O2-type star being the youngest. All
these stars show a systematic discrepancy between evolutionary and
spectroscopic masses. All stars in our sample are nitrogen enriched. Nitrogen
enrichment shows a clear correlation with increasing projected rotational
velocities. The mechanical energy input from the Of stars alone is comparable
to the energy stored in the N206 superbubble as measured from the observed
X-ray and H alpha emission.Comment: Accepted for the pubblication in Astronomy & Astrophysic
Testing massive star evolution, star-formation history, and feedback at low metallicity: Photometric analysis of OB stars in the SMC Wing
The supergiant ionized shell SMC-SGS 1 (DEM 167), located in the outer Wing
of the Small Magellanic Cloud (SMC), resembles structures that originate from
an energetic star-formation event and later stimulate star formation as they
expand into the ambient medium. However, stellar populations within and
surrounding SMC-SGS 1 tell a different story. We present a photometric study of
the stellar population encompassed by SMC-SGS 1 in order to trace the history
of this structure and its potential influence on star formation within the
low-density, low-metallicity SMC Wing. For a stellar population that is
physically associated with SMC-SGS 1, we combined near-ultraviolet (NUV)
photometry from the Galaxy Evolution Explorer (GALEX) with archival optical
(V-band) photometry from the ESO Danish 1.54m Telescope. Given their colors and
luminosities, we estimated stellar ages and masses by matching observed
photometry to theoretical stellar isochrone models. We find that the
investigated region supports an active, extended star-formation event spanning
25 - 40 Myr ago, as well as continued star formation into the present.
Using a standard initial mass function (IMF), we infer a lower bound on the
stellar mass from this period of , corresponding
to a star-formation intensity of 6 10 M
kpc yr. The spatial and temporal distributions of young stars
encompassed by SMC-SGS 1 imply a slow, consistent progression of star formation
over millions of years. Ongoing star formation along the edge of and interior
to SMC-SGS 1 suggests a combined stimulated and stochastic mode of star
formation within the SMC Wing. A slow expansion of the shell within this
low-density environment may preserve molecular clouds within the volume of the
shell, leaving them to form stars even after nearby stellar feedback expels
local gas and dust.Comment: 9 pages, 6 figures, 3 table
HYDROGEL FORMULATION FROM CALOTROPIS GIGANTEA PLANT EXTRACT AGAINST FOOT ULCER CAUSING BACTERIA IN DIABETES
Objective: The objective of present study was to develop hydrogel formulations loaded with Calotropis gigantea leaves extract.
Methods: The prepared hydrogel formulations were compliance with their color, odor, homogeneity, pH, and spreadability.
Results: As all the formulations were complies with the all parameters and it can be suggest as a Good antibacterial gel. It is evident that, ethanolic extract of Calotropis gigantea showed a maximum inhibitory zone against bacteria associated with foot ulcer.
Conclusions: The In vitro studies showed a quantity dependent increase in antibacterial activity against foot ulcer causing bacteria, a contraction which is higher than that produced by the control groups. These contractions were statistically significant (p<0.05), during the study with leave extract against foot ulcer causing bacteria in diabetes
The Galactic WC and WO stars: The impact of revised distances from Gaia DR2 and their role as massive black hole progenitors
Wolf-Rayet stars of the carbon sequence (WC stars) are an important
cornerstone in the late evolution of massive stars before their core collapse.
As core-helium burning, hydrogen-free objects with huge mass-loss, they are
likely the last observable stage before collapse and thus promising progenitor
candidates for type Ib/c supernovae. Their strong mass-loss furthermore
provides challenges and constraints to the theory of radiatively driven winds.
Thus, the determination of the WC star parameters is of major importance for
several astrophysical fields. With Gaia DR2, for the first time parallaxes for
a large sample of Galactic WC stars are available, removing major uncertainties
inherent to earlier studies. In this work, we re-examine the sample from Sander
et al. (2012) to derive key properties of the Galactic WC population. All
quantities depending on the distance are updated, while the underlying spectral
analyses remain untouched. Contrasting earlier assumptions, our study yields
that WC stars of the same subtype can significantly vary in absolute magnitude.
With Gaia DR2, the picture of the Galactic WC population becomes more complex:
We obtain luminosities ranging from log L = 4.9 to 6.0 with one outlier having
log L = 4.7. This indicates that the WC stars are likely formed from a broader
initial mass range than previously assumed. We obtain mass-loss rates ranging
between log Mdot = -5.1 and -4.1, with Mdot propto L^0.68 and a linear scaling
of the modified wind momentum with luminosity. We discuss the implications for
stellar evolution, including unsolved issues regarding the need of envelope
inflation to address the WR radius problem, and the open questions in regard to
the connection of WR stars with Gamma-ray bursts. WC and WO stars are
progenitors of massive black holes, collapsing either silently or in a
supernova that most-likely has to be preceded by a WO stage.Comment: 19 pages, 13 figures, 6 tables; A&A, v2: version in pres
Stellar population of the superbubble N206 in the LMC II. Parameters of the OB and WR stars, and the total massive star feedback
Clusters or associations of early-type stars are often associated with a
'superbubble' of hot gas. The formation of such superbubbles is caused by the
feedback from massive stars. The complex N206 in the Large Magellanic Cloud
exhibits a superbubble and a rich massive star population. We observed these
massive stars using the FLAMES multi-object spectrograph at ESO-VLT. Available
UV spectra from HST, IUE, and FUSE are also used. The spectral analysis is
performed with Potsdam Wolf-Rayet (PoWR) model atmospheres. We present the
stellar and wind parameters of the OB stars and the two WR binaries in the N206
complex. Twelve percent of the sample show Oe/Be type emission lines, although
most of them appear to rotate far below critical. We found eight runaway stars
based on their radial velocity. The wind-momentum luminosity relation of our OB
sample is consistent with the expectations. The HRD of the OB stars reveals a
large age spread (1-30 Myr), suggesting different episodes of star formation in
the complex. The youngest stars are concentrated in the inner part of the
complex, while the older OB stars are scattered over outer regions. We derived
the present day mass function for the entire N206 complex as well as for the
cluster NGC2018. Three very massive Of stars are found to dominate the feedback
among 164 OB stars in the sample. The two WR winds alone release about as much
mechanical luminosity as the whole OB star sample. The cumulative mechanical
feedback from all massive stellar winds is comparable to the combined
mechanical energy of the supernova explosions that likely occurred in the
complex. Accounting also for the WR wind and supernovae, the mechanical input
over the last five Myr is ~ erg, which exceeds the current
energy content of the complex by more than a factor of five. The morphology of
the complex suggests a leakage of hot gas from the superbubble.Comment: Accepted for publication in A&
Phase-resolved spectroscopic analysis of the eclipsing black hole X-ray binary M33 X-7: System properties, accretion, and evolution
M33 X-7 is the only known eclipsing black hole high mass X-ray binary. The system is reported to contain a very massive O supergiant donor and a massive black hole in a short orbit. The high X-ray luminosity and its location in the metal-poor galaxy M33 make it a unique laboratory for studying the winds of metal-poor donor stars with black hole companions and it helps us to understand the potential progenitors of black hole mergers. Using phase-resolved simultaneous HST- and XMM-Newton-observations, we traced the interaction of the stellar wind with the black hole. We observed a strong Hatchett-McCray effect in M33 X-7 for the full range of wind velocities. Our comprehensive spectroscopic investigation of the donor star (X-ray+UV+optical) yields new stellar and wind parameters for the system that differ significantly from previous estimates. In particular, the masses of the components are considerably reduced to ≈38 M⊙ for the O-star donor and ≈11.4 M⊙ for the black hole. The O giant is overfilling its Roche lobe and shows surface He enrichment. The donor shows a densely clumped wind with a mass-loss rate that matches theoretical predictions. An extended ionization zone is even present during the eclipse due to scattered X-ray photons. The X-ray ionization zone extends close to the photosphere of the donor during inferior conjunction. We investigated the wind-driving contributions from different ions and the changes in the ionization structure due to X-ray illumination. Toward the black hole, the wind is strongly quenched due to strong X-ray illumination. For this system, the standard wind-fed accretion scenario alone cannot explain the observed X-ray luminosity, pointing toward an additional mass overflow, which is in line with our acceleration calculations. The X-ray photoionization creates an He II emission region around the system emitting ∼1047 ph s−1. We computed binary evolutionary tracks for the system using MESA. Currently, the system is transitioning toward an unstable mass transfer phase, possibly resulting in a common envelope of the black hole and the O-star donor. Since the mass ratio is q ≳ 3.3 and the period is short, the system is unlikely to survive the common envelope, but will rather merge.VR acknowledges support by the Deutsches Zentrum fsür Luft- und Raumfahrt (DLR) under grant 50 OR 1912. VR and AACS acknowledge support by the Deutsche Forschungsgemeinschaft (DFG – German Research Foundation) in the form of an Emmy Noether Research Group (grant number SA4064/1-1, PI Sander). DP acknowledges financial support by the Deutsches Zentrum für Luft und Raumfahrt (DLR) grant FKZ 50 OR 2005
Phase-dependent study of near-infrared disk emission lines in LB-1
The mass, origin and evolutionary stage of the binary system LB-1 has been
the subject of intense debate, following the claim that it hosts an
70 black hole, in stark contrast with the expectations for
stellar remnants in the Milky Way. We conducted a high-resolution,
phase-resolved spectroscopic study of the near-infrared Paschen lines in this
system, using the 3.5-m telescope at Calar Alto Observatory. We find that
Pa and Pa (after proper subtraction of the stellar absorption
component) are well fitted with a standard double-peaked model, typical of disk
emission. We measured the velocity shifts of the red and blue peaks at 28
orbital phases: the line center has an orbital motion in perfect antiphase with
the stellar motion, and the radial velocity amplitude ranges from 8 to 13 km/s
for different choices of lines and profile modelling. We interpret this curve
as proof that the disk is tracing the orbital motion of the primary, ruling out
the circumbinary disk and the hierarchical triple scenarios. The phase-averaged
peak-to-peak half-separation (proxy for the projected rotational velocity of
the outer disk) is 70 km s, larger than the stellar orbital
velocity and also inconsistent with a circumbinary disk. From those results, we
infer a primary mass 4--8 times higher than the secondary mass. Moreover, we
show that the ratio of the blue and red peaks (V/R intensity ratio) has a
sinusoidal behaviour in phase with the secondary star, which can be interpreted
as the effect of external irradiation by the secondary star on the outer disk.
Finally, we briefly discuss our findings in the context of alternative
scenarios recently proposed for LB-1. Definitive tests between alternative
solutions will require further astrometric data from .Comment: To be submitted to ApJ. Comments are welcom
Bringing Stellar Evolution & Feedback Together: Summary of proposals from the Lorentz Center Workshop, 2022
Stars strongly impact their environment, and shape structures on all scales
throughout the universe, in a process known as ``feedback''. Due to the
complexity of both stellar evolution and the physics of larger astrophysical
structures, there remain many unanswered questions about how feedback operates,
and what we can learn about stars by studying their imprint on the wider
universe. In this white paper, we summarize discussions from the Lorentz Center
meeting `Bringing Stellar Evolution and Feedback Together' in April 2022, and
identify key areas where further dialogue can bring about radical changes in
how we view the relationship between stars and the universe they live in.Comment: Accepted to the Publications of the Astronomical Society of the
Pacifi
Randomized Clinical Trial of High-Dose Rifampicin With or Without Levofloxacin Versus Standard of Care for Pediatric Tuberculous Meningitis: The TBM-KIDS Trial
Background. Pediatric tuberculous meningitis (TBM) commonly causes death or disability. In adults, high-dose rifampicin may reduce mortality. The role of fluoroquinolones remains unclear. There have been no antimicrobial treatment trials for pediatric TBM.
Methods. TBM-KIDS was a phase 2 open-label randomized trial among children with TBM in India and Malawi. Participants received isoniazid and pyrazinamide plus: (i) high-dose rifampicin (30Â mg/kg) and ethambutol (R30HZE, arm 1); (ii) high-dose rifampicin
and levofloxacin (R30HZL, arm 2); or (iii) standard-dose rifampicin and ethambutol (R15HZE, arm 3) for 8 weeks, followed by 10 months of standard treatment. Functional and neurocognitive outcomes were measured longitudinally using Modified Rankin Scale (MRS) and Mullen Scales of Early Learning (MSEL).
Results. Of 2487 children prescreened, 79 were screened and 37 enrolled. Median age was 72 months; 49%, 43%, and 8% had stage I, II, and III disease, respectively. Grade 3 or higher adverse events occurred in 58%, 55%, and 36% of children in arms 1, 2, and 3, with 1 death (arm 1) and 6 early treatment discontinuations (4 in arm 1, 1 each in arms 2 and 3). By week 8, all children recovered to MRS score of 0 or 1. Average MSEL scores were significantly better in arm 1 than arm 3 in fine motor, receptive language, and expressive language domains (P < .01).
Conclusions. In a pediatric TBM trial, functional outcomes were excellent overall. The trend toward higher frequency of adverse events but better neurocognitive outcomes in children receiving high-dose rifampicin requires confirmation in a larger trial.
Clinical Trials Registration. NCT02958709