Abstract New boron abundances or upper limits have been determined for eight early B stars in the young Galactic open cluster NGC 3293, using UV spectra obtained by the Hubble Space Telescope Cosmic ...Origins Spectrograph. With previous observations, there are now 18 early B stars in this cluster with boron measurements. Six of the newly observed stars have projected rotational velocities greater than 200 km s −1 , allowing new constraints on rotationally driven mixing in main-sequence stars. When comparing to synthetic model populations, we find that the majority of our sample stars agree well with the predicted trends of stronger boron depletion for larger rotation and for larger mass or luminosity. Based on those, a smaller than the canonical rotational mixing efficiency ( f c ≈ 0.0165 versus the more standard value of 0.033) appears to be favored. In addition, the five mostly slowly rotating stars, when considered as a group, tend to show more boron depletion than expected from rotational mixing, and we speculate that most or all of these originate from binary mergers.
We present the first quantitative ultraviolet spectroscopic analysis of resolved OB stars in IC 1613. Because of its alleged very low metallicity (lap1/10 Z sub(middot in circle), from H II regions), ...studies in this Local Group dwarf galaxy could become a significant step forward from the Small Magellanic Cloud (SMC) toward the extremely metal-poor massive stars of the early universe. We present HST-COS data covering the ~1150-1800 A wavelength range with resolution R ~ 2500. We find that the targets do exhibit wind features, and these are similar in strength to SMC stars. Wind terminal velocities were derived from the observed P Cygni profiles with the Sobolev plus Exact Integration method. The upsilon sub(infinity)-Z relationship has been revisited. The terminal velocity of IC 1613 O stars is clearly lower than Milky Way counterparts, but there is no clear difference between IC 1613 and SMC or LMC analog stars. We find no clear segregation with host galaxy in the terminal velocities of B-supergiants, nor in the upsilon sub(infinity)/upsilon sub(esc) ratio of the whole OB star sample in any of the studied galaxies. Finally, we present the first evidence that the Fe-abundance of IC 1613 OB stars is similar to the SMC, which is in agreement with previous results on red supergiants.With the confirmed ~1/10 solar oxygen abundances of B-supergiants, our results indicate that IC 1613's alpha/Fe ratio is sub-solar.
ABSTRACT
We present an optical analysis of 55 members of R136, the central cluster in the Tarantula Nebula of the Large Magellanic Cloud. Our sample was observed with STIS aboard the Hubble Space ...Telescope, is complete down to about 40 M⊙, and includes seven very massive stars with masses over 100 M⊙. We performed a spectroscopic analysis to derive their physical properties. Using evolutionary models, we find that the initial mass function of massive stars in R136 is suggestive of being top-heavy with a power-law exponent γ ≈ 2 ± 0.3, but steeper exponents cannot be excluded. The age of R136 lies between 1 and 2 Myr with a median age of around 1.6 Myr. Stars more luminous than log L/L⊙ = 6.3 are helium enriched and their evolution is dominated by mass-loss, but rotational mixing or some other form of mixing could be still required to explain the helium composition at the surface. Stars more massive than 40 M⊙ have larger spectroscopic than evolutionary masses. The slope of the wind–luminosity relation assuming unclumped stellar winds is 2.41 ± 0.13 which is steeper than usually obtained (∼1.8). The ionizing ($\log Q_0\, {\rm ph/s} = 51.4$) and mechanical ($\log L_{\rm SW}\, {\rm erg/s} = 39.1$) output of R136 is dominated by the most massive stars ($\gt 100\, \mathrm{ M}_{\odot }$). R136 contributes around a quarter of the ionizing flux and around a fifth of the mechanical feedback to the overall budget of the Tarantula Nebula. For a census of massive stars of the Tarantula Nebula region, we combined our results with the VLT-FLAMES Tarantula Survey plus other spectroscopic studies. We observe a lack of evolved Wolf–Rayet stars and luminous blue and red supergiants.
Abstract Blue supergiants are the brightest stars in their host galaxies, and yet their evolutionary status has been a long-standing problem in stellar astrophysics. In this pioneering work, we ...present a large sample of 59 early B-type supergiants in the Large Magellanic Cloud with newly derived stellar parameters and identify the signatures of stars born from binary mergers among them. We simulate novel 1D merger models of binaries consisting of post main-sequence giants with helium-rich cores (primaries) and main-sequence companions (secondaries), and consider the effects of interaction of the secondary with the core of the primary along with the mixing induced by the merger in the envelope. Thereafter, the evolution of the newborn 17–43 M ⊙ stars is followed until core-carbon depletion, close to their final pre-explosion stage. Unlike stars born alone with comparable masses, stars born from mergers of evolved binaries are blue throughout their core helium-burning phase and replicate the surface gravities and Hertzsprung–Russell diagram positions of most of our sample, thus indicating that B-type supergiants structurally resemble stars born from such mergers. Moreover, the large nitrogen-to-carbon and nitrogen-to-oxygen number ratios, coupled with helium enhancements exhibited by at least half our data sample, is uniquely reproduced by our merger models. Collectively, these findings provide compelling evidence toward the important role of binary mergers in producing the currently observed population of blue supergiants in our Universe.
ABSTRACT
The presence of massive stars (MSs) in the region close to the Galactic Centre (GC) poses several questions about their origin. The harsh environment of the GC favours specific formation ...scenarios, each of which should imprint characteristic kinematic features on the MSs. We present a 2D kinematic analysis of MSs in a GC region surrounding Sgr A* based on high-precision proper motions obtained with the Hubble Space Telescope. Thanks to a careful data reduction, well-measured bright stars in our proper-motion catalogues have errors better than 0.5 mas yr−1. We discuss the absolute motion of the MSs in the field and their motion relative to Sgr A*, the Arches, and the Quintuplet. For the majority of the MSs, we rule out any distance further than 3–4 kpc from Sgr A* using only kinematic arguments. If their membership to the GC is confirmed, most of the isolated MSs are likely not associated with either the Arches or Quintuplet clusters or Sgr A*. Only a few MSs have proper motions, suggesting that they are likely members of the Arches cluster, in agreement with previous spectroscopic results. Line-of-sight radial velocities and distances are required to shed further light on the origin of most of these massive objects. We also present an analysis of other fast-moving objects in the GC region, finding no clear excess of high-velocity escaping stars. We make our astro-photometric catalogues publicly available.
Spectra from the Hubble Space Telescope Cosmic Origins Spectrograph and the Space Telescope Imaging Spectrograph covering the B iii resonance line have been obtained for 10 early-B stars near the ...turnoff of the young Galactic open cluster NGC 3293. This is the first sample of boron abundance determinations in a single, clearly defined population of early-B stars that also covers a substantial range of projected rotational velocities. In most of these stars we detect partial depletion of boron at a level consistent with that expected for rotational mixing in single stars, but inconsistent with expectations for depletion from close binary evolution. However, our results do suggest that the efficiency of rotational mixing is at or slightly below the low end of the range predicted by the available theoretical calculations. The two most luminous targets observed have a very large boron depletion and may be the products of either binary interactions or post-main-sequence evolution.
To study the incidence of complications when undergoing right heart catheterization (RHC) and right ventricular biopsy (RVB).
Complications following RHC and RVB are not well reported. We studied the ...incidence of death, myocardial infarction, stroke, unplanned bypass, pneumothorax, hemorrhage, hemoptysis, heart valve repair/replacement, pulmonary artery perforation, ventricular arrhythmias, pericardiocentesis, complete heart block, and deep vein thrombosis (primary endpoint) following these procedures. We also adjudicated the severity of tricuspid regurgitation and causes of in-hospital death following RHC. Diagnostic RHC procedures, RVB, multiple right heart procedures alone or combined with left heart catheterization, and complications from January 1, 2002, through December 31, 2013, were identified using the clinical scheduling system and electronic records at Mayo Clinic, Rochester, Minnesota. International Classification of Diseases, Ninth Revision billing codes were used. Registration was queried to identify all-cause mortality. All clinical events and echocardiograms for worsening tricuspid regurgitation were reviewed and adjudicated.
A total of 17,696 procedures were identified. Procedures were categorized into those undergoing RHC (n=5556), RVB (n=3846), multiple right heart catheterization (n=776), and combined right and left heart catheterization procedures (n=7518). Primary endpoint was seen in 21.6 and 20.8 of 10,000 procedures for RHC and RVB, respectively. There were 190 (1.1%) deaths during hospital admission and none was related to the procedure.
Complications following diagnostic RHC and RVB are seen in 21.6 and 20.8 procedures, respectively, of 10,000 procedures and all deaths were secondary to acute illness.
Chronic kidney disease (CKD) is a common complex condition associated with high morbidity and mortality. Polygenic prediction could enhance CKD screening and prevention; however, this approach has ...not been optimized for ancestrally diverse populations. By combining APOL1 risk genotypes with genome-wide association studies (GWAS) of kidney function, we designed, optimized and validated a genome-wide polygenic score (GPS) for CKD. The new GPS was tested in 15 independent cohorts, including 3 cohorts of European ancestry (n = 97,050), 6 cohorts of African ancestry (n = 14,544), 4 cohorts of Asian ancestry (n = 8,625) and 2 admixed Latinx cohorts (n = 3,625). We demonstrated score transferability with reproducible performance across all tested cohorts. The top 2% of the GPS was associated with nearly threefold increased risk of CKD across ancestries. In African ancestry cohorts, the APOL1 risk genotype and polygenic component of the GPS had additive effects on the risk of CKD.
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