277 research outputs found

    Plausible home stars of the interstellar object 'Oumuamua found in Gaia DR2

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    The first detected interstellar object 'Oumuamua that passed within 0.25au of the Sun on 2017 September 9 was presumably ejected from a stellar system. We use its newly determined non-Keplerian trajectory together with the reconstructed Galactic orbits of 7 million stars from Gaia DR2 to identify past close encounters. Such an "encounter" could reveal the home system from which 'Oumuamua was ejected. The closest encounter, at 0.60pc (0.53-0.67pc, 90% confidence interval), was with the M2.5 dwarf HIP 3757 at a relative velocity of 24.7km/s, 1Myr ago. A more distant encounter (1.6pc) but with a lower encounter (ejection) velocity of 10.7km/s was with the G5 dwarf HD 292249, 3.8Myr ago. Two more stars have encounter distances and velocities intermediate to these. The encounter parameters are similar across six different non-gravitational trajectories for 'Oumuamua. Ejection of 'Oumuamua by scattering from a giant planet in one of the systems is plausible, but requires a rather unlikely configuration to achieve the high velocities found. A binary star system is more likely to produce the observed velocities. None of the four home candidates have published exoplanets or are known to be binaries. Given that the 7 million stars in Gaia DR2 with 6D phase space information is just a small fraction of all stars for which we can eventually reconstruct orbits, it is a priori unlikely that our current search would find 'Oumuamua's home star system. As 'Oumuamua is expected to pass within 1pc of about 20 stars and brown dwarfs every Myr, the plausibility of a home system depends also on an appropriate (low) encounter velocity.Comment: Accepted to The Astronomical Journa

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    Calibrating the relation of low-frequency radio continuum to star formation rate at 1 kpc scale with LOFAR

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    9 figures, 6 tables and 17 pages. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal. Reproduced with permission from Astronomy & Astrophysics. © 2018 ESO.Radio continuum (RC) emission in galaxies allows us to measure star formation rates (SFRs) unaffected by extinction due to dust, of which the low-frequency part is uncontaminated from thermal (free-free) emission. We calibrate the conversion from the spatially resolved 140 MHz RC emission to the SFR surface density (ΣSFR\Sigma_{\rm SFR}) at 1 kpc scale. We used recent observations of three galaxies (NGC 3184, 4736, and 5055) from the LOFAR Two-metre Sky Survey (LoTSS), and archival LOw-Frequency ARray (LOFAR) data of NGC 5194. Maps were created with the facet calibration technique and converted to radio ΣSFR\Sigma_{\rm SFR} maps using the Condon relation. We compared these maps with hybrid ΣSFR\Sigma_{\rm SFR} maps from a combination of GALEX far-ultraviolet and Spitzer 24 μm\mu\rm m data using plots tracing the relation at 1.2×1.21.2\times 1.2-kpc2^2 resolution. The RC emission is smoothed with respect to the hybrid ΣSFR\Sigma_{\rm SFR} owing to the transport of cosmic-ray electrons (CREs). This results in a sublinear relation (ΣSFR)RC[(ΣSFR)hyb]a(\Sigma_{\rm SFR})_{\rm RC} \propto [(\Sigma_{\rm SFR})_{\rm hyb}]^{a}, where a=0.59±0.13a=0.59\pm 0.13 (140 MHz) and a=0.75±0.10a=0.75\pm 0.10 (1365 MHz). Both relations have a scatter of σ=0.3 dex\sigma = 0.3~\rm dex. If we restrict ourselves to areas of young CREs (α>0.65\alpha > -0.65; IνναI_\nu \propto \nu^\alpha), the relation becomes almost linear at both frequencies with a0.9a\approx 0.9 and a reduced scatter of σ=0.2 dex\sigma = 0.2~\rm dex. We then simulate the effect of CRE transport by convolving the hybrid ΣSFR\Sigma_{\rm SFR} maps with a Gaussian kernel until the RC-SFR relation is linearised; CRE transport lengths are l=1l=1-5 kpc. Solving the CRE diffusion equation, we find diffusion coefficients of D=(0.13D=(0.13-1.5)×1028cm2s11.5) \times 10^{28} \rm cm^2\,s^{-1} at 1 GeV. A RC-SFR relation at 1.41.4 GHz can be exploited to measure SFRs at redshift z10z \approx 10 using 140140 MHz observations.Peer reviewe

    Exercise is medicine in rural health centers and federally qualified health centers

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    The American College of Sports Medicine in collaboration with the American Medical Association developed the the Exercise is Medicine (EIM) initiative to promote physical activity as a vital sign among health care providers. The purpose of the study is to inform initiative advocacy efforts among Rural Health Centers and Federally Qualified Health Centers. An interview guide was developed through literature review and expert feedback. Provider responses will be recorded via field notes which are coded to extract common themes. The qualitative data collected from these interviews will be used to examine healthcare provider knowledge and awareness of the initiative current behaviors related to patient physical activity, assessment, counseling, prescription, referral and follow-up and the likelihood of these providers using existing Exercise is Medicine (EIM)materials and resources in the future. Our findings and recommendations will be communicated back to the American College of Sports Medicine through the Exercise is Medicine (EIM) Community Health Committee
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