17 research outputs found

    Spatially-Resolved Recent Star Formation History in NGC 6946

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    The nearby face-on star forming spiral galaxy NGC 6946 is known as the Fireworks Galaxy due to its hosting an unusually large number of supernova. We analyze its resolved near-ultraviolet (NUV) stellar photometry measured from images taken with the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) with F275W and F336W filters. We model the color-magnitude diagrams (CMD) of the UV photometry to derive the spatially-resolved star formation history (SFH) of NGC 6946 over the last 25 Myr. From this analysis, we produce maps of the spatial distribution of young stellar populations and measure the total recent star formation rate (SFR) of nearly the entire young stellar disk. We find the global SFR(age\leq25 Myr)=13.17+0.910.79M/yr13.17 \substack{+0.91 \\-0.79} M_\odot/\rm yr. Over this period, the SFR is initially very high (23.39+2.432.11M/yr23.39\substack{+2.43\\-2.11} M_\odot/\rm yr between 16-25 Myr ago), then monotonically decreases to a recent SFR of 5.31+0.190.17M/yr5.31\substack{+0.19\\-0.17} M_\odot/\rm yr in the last 10 Myr. This decrease in global star formation rate over the last 25 Myr is consistent with measurements made with other SFR indicators. We discuss in detail two of the most active regions of the galaxy, which we find are responsible for 3% and 5% of the total star formation over the past 6.3 Myr.Comment: 19 pages, 11 figures, accepted for publication in Ap

    Considering the Single and Binary Origins of the Type IIP SN 2017eaw

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    Current population synthesis modeling suggests that 30%–50% of Type II supernovae originate from binary progenitors; however, the identification of a binary progenitor is challenging. One indicator of a binary progenitor is that the surrounding stellar population is too old to contain a massive single star. Measurements of the progenitor mass of SN 2017eaw are starkly divided between observations made temporally close to core collapse, which show a progenitor mass of 13–15 M _⊙ (final helium-core mass {M}_{\mathrm{He},\mathrm{core}}=4.4\mbox{--}6.0\,{M}_{\odot } —which is a more informative property than initial mass) and those from the stellar population surrounding the SN, which find M ≤ 10.8 M _⊙ ( MHe,core3.4M{M}_{\mathrm{He},\mathrm{core}}\leqslant 3.4\,{M}_{\odot } ). In this paper, we reanalyze the surrounding stellar population with improved astrometry and photometry, finding a median age of 16.81.0+3.2{16.8}_{-1.0}^{+3.2} Myr for all stars younger than 50 Myr ( MHe,core=4.7M{M}_{\mathrm{He},\mathrm{core}}=4.7{M}_{\odot } ) and 85.96.5+3.2{85.9}_{-6.5}^{+3.2} Myr for stars younger than 150 Myr. 16.8 Myr is now consistent with the helium-core mass range derived from the temporally near-explosion observations for single stars. Applying the combined constraints to population synthesis models, we determine that the probability of the progenitor of SN 2017eaw being an initially single star is 65% compared to 35% for prior binary interaction. 85.9 Myr is inconsistent with any formation scenarios. We demonstrate that combining progenitor age constraints with helium-core mass estimates from red supergiant SED modeling, late-time spectra, and indirectly from light-curve modeling can help to differentiate single and binary progenitor scenarios and provide a framework for the application of this technique to future observations

    Astrometric Confirmation and Preliminary Orbital Parameters of the Young Exoplanet 51 Eridani b with the Gemini Planet Imager

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    We present new Gemini Planet Imager observations of the young exoplanet 51 Eridani b that provide further evidence that the companion is physically associated with 51 Eridani. Combining this new astrometric measurement with those reported in the literature, we significantly reduce the posterior probability that 51 Eridani b is an unbound foreground or background T-dwarf in a chance alignment with 51 Eridani to 2 7 10-7, an order of magnitude lower than previously reported. If 51 Eridani b is indeed a bound object, then we have detected orbital motion of the planet between the discovery epoch and the latest epoch. By implementing a computationally efficient Monte Carlo technique, preliminary constraints are placed on the orbital parameters of the system. The current set of astrometric measurements suggest an orbital semimajor axis of AU, corresponding to a period of years (assuming a mass of 1.75 Mo for the central star), and an inclination of deg. The remaining orbital elements are only marginally constrained by the current measurements. These preliminary values suggest an orbit that does not share the same inclination as the orbit of the distant M-dwarf binary, GJ 3305, which is a wide physically bound companion to 51 Eridani.Peer reviewed: YesNRC publication: Ye

    The Association of Coloproctology of Great Britain and Ireland consensus guidelines in surgery for inflammatory bowel disease.

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    AIM There is a requirement of an expansive and up to date review of surgical management of inflammatory bowel disease (IBD) that can dovetail with the medical guidelines produced by the British Society of Gastroenterology. METHODS Surgeons who are members of the ACPGBI with a recognised interest in IBD were invited to contribute various sections of the guidelines. They were directed to produce a procedure based document using literature searches that were systematic, comprehensible, transparent and reproducible. Levels of evidence were graded. An editorial board was convened to ensure consistency of style, presentation and quality. Each author was asked to provide a set of recommendations which were evidence based and unambiguous. These recommendations were submitted to the whole guideline group and scored. They were then refined and submitted to a second vote. Only those that achieved >80% consensus at level 5 (strongly agree) or level 4 (agree) after 2 votes were included in the guidelines. RESULTS All aspects of surgical care for IBD have been included along with 157 recommendations for management. CONCLUSION These guidelines provide an up to date and evidence based summary of the current surgical knowledge in the management of IBD and will serve as a useful practical text for clinicians performing this type of surgery
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