adsabs/WIESP2022-NER huggingface dataset:
Paper: 2016ApJ...825..101B (fulltext)
use for power beaming are in the millimeter band, so are outside the microwave range the Allen Telescope Array observed. Similarly, power beaming using near-IR frequencies would be undetectable by the Boquete observatory. Therefore, the Harp et al. ( 2016 ) and Schuetz et al. ( 2016 ) limited observation times and wavelength coverage are not sufficient to produce firm conclusions on power beaming from KIC 8462852. Most applications would be seen in the radio—if transmissions were oriented in our direction at the proper time and at the frequencies observed—but are not. More extensive observations should be made in more systematic studies of power beaming leakage, including observing at higher radio frequencies and for longer times at visible wavelengths. 5. CONCLUSIONS AND IMPLICATIONS We have listed several classes of power beaming applications/missions, quantifying the principal observable parameters. Applying this reasoning to the recent observations of KIC 8462852, we conclude that if power beaming were in use at the time observed, generally pointed in our direction, and at frequencies between 1 and 10 GHz, that most power beaming applications would have been detectable. The non-detection provides a weak (owing to the caveat of the probabilities listed) rejection of the popular hypothesis that the system is inhabited by an advanced spacefaring extraterrestrial civilization. As discussed above, the beaming power levels are high and transient and easily dwarf any ETI civilization’s diffuse leakage to space (Sullivan et al. 1978 ). Power beaming described here is larger than that necessary for beaming systems for communication: for a 1000 ly range beacon (Benford et al. 2010 ). SETI programs could explore a different part of parameter space by observations suitable to finding leakage from power beams. Such beams would be visible over large interstellar distances. This implies a new approach to the SETI search: instead of focusing on narrowband beacon transmissions generated by another civilization, look for more powerful beams with much wider bandwidth. This requires a new approach for their discovery by telescopes on Earth. Past SETI observations have been in the 1–10 GHz microwave band. For our atmosphere, future observations should look in bands where with lower oxygen and water vapor allow transmission: windows at 35 GHz, 70–115 GHz, 130–170 GHz, and 200–320 GHz. And, of course, such transient sources require longer observing times. A promising avenue is to revisit past observations of transient events, of which there are many, to look for patterns and identify as possible regions of the sky to emphasize. ETIs would know their power beams could be observed. They could put a message on the power beam and broadcast it for our receipt at little additional energy or cost. By observing leakage from power beams, we may well find a message embedded on the beam. That message may use optimized power-efficient designs such as spread spectrum and
Paper: 2016MNRAS.457..993P (acknowledgments)
LS is grateful for the support from SNSF grant SCOPES IZ73Z0 152581, GNSF grant FR/339/6-350/14. This work was supported in part by DOE grant DEFG 03-99EP41093. NASA's Astrophysics Data System Bibliographic Service and the arXiv e-print service were used for this work. Additionally, we wish to acknowledge gnuplot , a free open-source plotting utility which was used to create all of our figures and perform the function fitting central to this work. We wish to acknowledge the many useful conversations with Bharat Ratra while performing this work. Lastly, we would like to thank the referee for their useful comments.
Paper: 2019ApJ...882..182C (fulltext)
determines the age, metallicity, and dust attenuation of the stellar populations. Consequently, the light-weighted ages and metallicities derived above are driven by spectral features that are less degenerate than the spectral shape alone (see Figure 1 and Table 1 ). Table 1 Prominent Stellar Features Note. The first column gives the feature and wavelength. The second and third columns give the age range that the features are found in, in a 0.4 Z ⊙ bpass and starburst 99 model, respectively. The two main types of FUV stellar features are strong, broad stellar wind P-Cygni features and weak stellar photospheric absorption lines. Both types of features can be contaminated by neighboring ISM absorption and require high S/N and moderate spectral resolutions to resolve. In the following two subsections, we discuss both types of spectral features individually, and we illustrate how the individual features relate to the inferred stellar population ages and metallicities. The purpose of these subsections is not to advocate for determining the stellar ages and metallicities using single features, but rather to demonstrate that the stellar properties inferred from the full spectral fits are entirely consistent with the trends of stellar spectral features. 4.1. Stellar Wind Features The most notable stellar features in the FUV are the broad blueshifted absorption and redshifted emission profiles (called P-Cygni profiles; orange labels in Figure 1 ). These P-Cygni profiles arise from strong winds that are radiatively driven off of stellar photospheres (Castor et al. 1975 ; Lamers Cassinelli 1999 ). The terminal velocity, ionization structure, and mass-outflow rates sensitively depend on the stellar luminosity (Castor et al. 1975 ; Lamers Leitherer 1993 ; Lamers et al. 1995 ; Leitherer et al. 1995 ; Puls et al. 1996 ; Kudritzki Puls 2000 ). The terminal velocity describes the maximal velocity extent of the absorption component, while the mass-loss rate determines the depth of the profile. In turn, these establish the shape of the P-Cygni absorption and emission. Whether a given ion is observed as a P-Cygni profile in the wind depends on the ionization structure of the stellar wind. The peak ionization stages for stellar winds typically are the C v , N iv , O iv , and Si v states (Lamers Cassinelli 1999 ), none of which have resonant transitions in the rest-frame FUV. Alternatively, the presence of adjacent ionization stages with P-Cygni profiles (N v , C iv , or Si iv ) provides information on the stellar temperature of the most luminous stars and, by inference, the stellar population age. The age of a stellar population can be inferred from the strength of the observed P-Cygni transitions: O v and N v have the highest ionization states and are strongest in stars with lifetimes of 2–3 Myr, while C iv and Si iv are lower ionization and peak in stars with lifetimes near 5 Myr. Stellar temperature, or age, is not the sole determinant of the stellar wind
Paper: 2021MNRAS.501.2734W (fulltext)
are required to grid the raw data generated by FAST in real-time with the existing methods, which could greatly increase the cost of computation for this survey. In the past decade, various studies on optimization of gridding performance have been carried out. For example, Winkel et al. ( 2016b ) have presented a versatile gridding module ( Cygrid : A fast Cython-powered convolution-based gridding module for python ) for radio astronomical data reduction, featuring a single-level lookup table based on the c ++ standard template library (STL) for gridding parallelization, as well as the Hierarchical Equal Area Latitude Pixelation ( healpix) -based spherical tessellation for fast neighbour searching. And the performance of the Cygrid code can be significantly improved when using multiple CPU cores. However, utilizing the STL vector, which features dynamical arrangements of storage allocations with a relatively small initial storage volume, to construct a lookup table for input raw data is not always practical. For example, if the raw samples are unevenly distributed, with more data points in the central regions and less on all sides, the required storage needs to be expanded in the middle part of each healpix -tessellated ring frequently. In this case, the STL vectors have to make massive data copies of the data frequently, which would consume broad bandwidth, thus resulting in degradation of gridding performance. In addition, the main workload of gridding can be considered as a combination of a large number of single-instruction, multidata stream operations. For such tasks, the high parallelization level, as well as throughput of GPUs brings a possibility for better performance. Thus, Romein ( 2012 ) has developed a work-distribution scheme for radio data gridding with GPUs, which could significantly reduce the memory access time of computing device, and map observed samples on to a grid with high efficiency. Merry ( 2016 ) has further optimized this algorithm with thread coarsening strategy, making one thread handle multiple samples simultaneously. However, the method proposed by Romein ( 2012 ) and Merry ( 2016 ) has been deeply customized for radio telescope arrays, strongly relying on the spatial coherence of the interference matrix, thus cannot be easily adapted for single-dish telescopes. Accordingly, in order to meet the requirements of large data volume from the latest single-dish radio telescopes, and to overcome the shortcomings of GPU-based gridding methods mainly designed for radio telescope array, inspired by Winkel et al. ( 2016b ), and based upon our previous work (Luo et al. 2018 ), here we present a convolutional gridding framework with hybrid computing environments, HCGrid , for radio astronomy, which can greatly improve the performance of the gridding process. Key features of our framework can be summarized as follows: We have designed a gridding module with high performance for large single-dish radio telescopes. We
Paper: 2016A&A...586A..38M (fulltext)
for a triangle of interferometric baselines: For a symmetrical Gaussian intensity distributions on the sky, the visibility phase is expected to be zero and so is the closure phase. Any deviation from a zero closure phase will indicate the source deviation from a Gaussian or point-like structure, and this observable can in principle be used to compare the model and observed emission shape without reconstructing the radio maps. We have calculated the theoretical visibility closure phases. For the model with , which shows the crescent on the N side of the BH (see Fig. 8 ), the closure phases are positive; ,19,11,11, where the four values correspond to different time moments of the observation. The evolution is caused by the rotation of the Earth, and it is probing slightly different values. A typical observation duration is two to three hours. This is about three times shorter than the dynamical time scale of the source (8.5 h) with its BH mass, . For , for which the crescent is on the S side of the BH (Fig. 8 ), the closure phases are negative: , , , . In both cases, the values are consistent with the observed value: (Akiyama, priv. comm.). In summary, for the fiducial model RH100 (for both viewing angles of and ), visibility amplitudes and closure phases are roughly consistent with the preliminary observations of the M 87 core obtained by the EHT (visibility amplitudes and closure phases on a single VLBI triangle). Fig. 9 Theoretical visibility amplitudes along E-W ( left ) and N-S ( right ) baselines, computed for model RH100 with (solid lines) and 160(dashed lines). 4. Discussions Deriving the appearance of a jet in the direct vicinity of a SMBH is not straightforward. The jet formation mechanism, as well as particle acceleration in jets, is generally not understood well. Moreover, one has to take spacetime curvature into account, which affects the plasma dynamics and light propagation. Using GRMHD simulations of a weakly magnetized accretion flow, a jet appears naturally, and we calculate the appearance of the M 87 jet base at radio and millimeter wavelengths. For the electron heating, we assume that the electrons are weakly coupled to protons in the accretion disk and strongly coupled in the jet – a simple, but crucial concept that we have already used successfully to explain the appearance of the SMBH in the center of the Milky Way. Below we discuss our results in a context of observational constraints. We also discuss the model limitations. Fig. 10 Comparisons of the visibility amplitudes from our models and those from the EHT observations. The visibility amplitudes, computed at mm ( GHz), along three baselines (SMT-CARMA, SMT-HAWAII, and CARMA-HAWAII) are shown for model RH100 with (solid lines) and 160 (dashed lines). The distance between the VLBI stations is expressed in units of ( km). The observed visibility amplitudes (points) and the tracks are taken from Doeleman et al. (2012) . 4.1. Mass-accretion rate The accretion rate onto M 87
Paper: 2016A&A...592A.140L (acknowledgments)
The authors are grateful to an anonymous referee for a careful reading of the manuscript and several stimulating comments that helped to improve this work. A.F.L. and S.M. are grateful to Drs. J. Bouvier, A. Frasca, A. Klutsch, A. C. Lanzafame, and E. Moraux for interesting discussions. The authors acknowledge support through the PRIN-INAF 2012 funding scheme of the National Institute for Astrophysics (INAF) of the Italian Ministry of Education, University and Research. This work is based on data obtained by the CoRoT Space Experiment and made available through the CoRoT Archive at the IAS Operation Center whose availability is gratefully acknowledged. CoRoT is a space mission of the French Space Agency CNES in association with French CNRS Laboratories and participation of Austria, Belgium, Brazil, Germany, Spain, and the European Space Agency.
Paper: 2017A&A...597A..15D (fulltext)
between 323 and 608 MHz (black solid-line). Radio flux density at 323 MHz across the source extension (red dashed-line). The data-points correspond to the regions displayed in Fig. 1d . Error-bars on the -axes correspond to the region size. Table 2 Galaxy cluster properties. Notes. (a) Coordinates of the BCG. (b) Rescaled with spectral index from 323 MHz. (c) k-corrected with spectral index 0.7. 4. Discussion A prediction from simple DSA theory is a relation between the Mach number of the shock and the injection spectral index of the accelerated electrons: Therefore, a spectral index implies an unphysical Mach number. In the case of this specific relic the injection spectral index appears extremely flat. If we assume the outer region as representative for the injection index we find: . This value seems to point towards a stronger Mach number shock than what is usually found for radio relics. However, we note that Eq. ( 2 )has been shown not to hold in at least the well-studied case of the “toothbrush” cluster ( van Weeren et al. 2016 ). Also the integrated spectral index (extracted from -harmonised images at 323 and 608 MHz) appears quite flat () with respect to the average spectral index of radio relics (; Feretti et al. 2012 ). As already noted for another radio relic with a flat integrated spectral index (Abell 2256; van Weeren et al. 2012b ; Trasatti et al. 2015 ), if the stationary shock conditions do not hold. As a consequence, a possible way to reconcile the flat spectrum with shock acceleration is that the relic must have been produced very recently (0.1 Gyr ago). This means that the time for energy losses is longer than the age of the shock at some observed energies and that the integrated spectrum of the relic will still evolve, getting steeper. We note that using the total flux density at 148, 323, 608, and 1400 MHz ( mJy; from NVSS), we obtain a steeper integrated spectral index of . However, given the different -coverages, these maps can be sensitive to different spatial scales. The X-ray luminosity extracted from ROSAT data is erg/s. From this luminosity, we derived the associated cluster mass: ( Pratt et al. 2009 ). The cluster is amongst the least massive clusters hosting a radio relic discovered so far (see Fig. 7b in de Gasperin et al. 2014 ). Only two other less-massive systems are known to host radio relics: Abell 3365 (, , from X-ray; van Weeren et al. 2011 ) and Abell 3376 (, , from SZ; Kale et al. 2012 ). Both galaxy clusters host a double radio-relic system. In de Gasperin et al. (2014) , we discussed the presence of a scaling relation between radio-relic power and hosting-cluster mass. Given that relation, Abell 3527-bis is almost an order of magnitude over-luminous for the hosting cluster mass. Nonetheless, Abell 3527-bis provides a rare example of low-mass cluster hosting a radio relic at . Nuza et al. (2012) investigated the predicted abundance of radio relics in current and future radio surveys. They estimated the
Paper: 2018MNRAS.476.2238G (fulltext)
panel: p rich ). For the helium burning problem, discussed in this study, we find global agreement between the two solvers, whereas there are larger differences in the small-scale features. Figure 1. Density colour map of the in initial state for the floating torus. Figure 2. Density colour map of the floating torus at time 0.2 sec (left-hand panel: vulcan ; right-hand panel: rich) . Figure 3. Density colour map of the floating torus at time 0.3 sec (left-hand panel: vulcan ; right-hand panel: rich) . In particular, although the two solvers successfully suppress numerical transition to detonation in very different ways, the final conclusions are the same. Finally, some caution must be taken due to the issue of possible turbulence. We recognize that our simulations cannot follow fully developed turbulence since the spatial resolution is too coarse and also the missing third dimension limits the correct cascading of turbulent scales. It is well known that fully developed turbulence may enhance burning and as a result may trigger detonations. However, since we reach detonations in our 2D simulations, the presence of possible turbulence cannot alter our final conclusions. 2.1 The <sc>vulcan</sc> methodology The code v2d (Vulcan-2D; Livne 1993 ) consists of an ALE method with a second-order advection scheme. In the problems discussed here, the grid moves rather slowly and the simulations are nearly Eulerian. For astrophysical combustion problems, a ‘multi-phase’ method has been added, which allows to handle separately fuel and ashes as different substances. The advection algorithm can use either a ‘slopes method’ (a la Van-Leer scheme) or VOF (Volume of Fluid) method. VOF is actually a family of schemes in which sharp boundaries between phases are constructed for advecting phases with minimal numerical diffusion (Hirt 1981 ; Ubbnik 1999 ; Gopala 2008 ). In v2d , we implement the basic idea during the advection step, by constructing, in each mixed cell, a local planar interface using the known partial volume fractions. For two phases, the partial volumes and the orientation of the surface provide enough information for interface reconstruction. The orientation, or a vector normal to the interface, is calculated from the phases gradients, based on cell centres values. In cases of more than two phases, the algorithm is much more complicated, not uniquely defined and less accurate. Once we have the local linear interface, we use it to cut the boundaries of the cell and to compute exact phase fluxes between cells. The VOF method is rather accurate as long as the boundaries between the phases are smooth. When small-scale fragmentation develops it is harder to define accurate normals and as a result the method becomes less reliable. The VOF method is more appropriate to the issue of this work and was implemented in all our helium burning simulations. The phases are defined according to a ‘critical temperature,’ which is in our case T c = 3 × 10 8 K.
Paper: 2016A&A...587A..58B (fulltext)
for the planets d and e (along with the other wavelengths), despite the lack of non-equilibrium chemistry, non-solar metallicity compositions, and local variation of the cloud thickness in the models, suggest that these ingredients are not critically needed here. Our analysis rather demonstrates that a higher content in dust and reduced CIA of H resulting from a low surface gravity can explain the deviation of the planet’s SED with respect to those of standard field L and T dwarfs. This does however not mean that such additional ingredients do not play a role, especially for HR8799b and c. Barman et al. (2011a) noted that the -band spectrum of the high-amplitude variable brown dwarf T1 dwarf 2MASS J21392676+0220226 fitted well the SED of HR8799 b. The spectrophotometric properties of the two objects representing the best the properties of HR8799 b and c, 2MASS J13243553+6358281 and SDSS J151643.01+305344.4 , can be modeled by blended spectra of L-T dwarfs, e.g. as unresolved L/T transition binary at field dwarf ages ( Burgasser et al. 2010 ; Geißler et al. 2011 ). Beside its possible young age, we can speculate that SDSS J151643.01+305344.4 is a good template because the integrated flux of the possible binaries mimics layered patchy atmospheres. Conversely, Heinze et al. (2015) find that 2MASS J13243553+6358281 experiences high amplitude variability in the red-optical. The planets e and d could also be variable objets. The best fitting template to HR8799d’s SED – PSO J318.5338-22.8603 – was recently found to experience photometric variability in the near-infrared ( Biller et al. 2015 ). In addition, the red late-L dwarf WISE 1738, which reproduces well the properties of HR8799d and e also has a highly variable near-infrared spectrum ( Mace et al. 2013 ). In that sense, the good fit of the planet spectra with field dwarfs templates reddened by sub-micron iron, corundum, or silicate grain opacities in Sect. 3 is in line with the conclusions of Yang et al. (2015) who find that the observed variability of L5 dwarfs can be explained by the presence of spatially varying high-altitude haze layers above the condensate clouds. Such a layer may exist into the planet atmospheres and could be added to the current self-consistent cloud models (e.g. BT-SETTL, DRIFT-PHOENIX) to bring the and radii estimate in agreement with the expectations from evolutionary models. 5.2. Masses and diversity among the HR8799 system Marois et al. (2008) , Marois et al. (2010) , and Currie et al. (2011b) used the bolometric luminosity of the planets to estimate masses of 5, 7, 7, and 7 for HR8799b,c,d and e, respectively if the system is 30 Myr old. We retrieve the same luminosity – and then mass estimate – for HR8799d and e using the bolometric correction estimated for the dusty L7 dwarf WISE 0047 by Gizis et al. (2015) . The radii and log derived from the best atmospheric model fit yield masses marginally consistent with these values. This is most likely due to the
Paper: 2015MNRAS.454.2736C (acknowledgments)
This work has made use of the HPC resources of CINES (Jade and Occigen supercomputer) under the time allocations 2013047012, 2014047012 and 2015047012 made by GENCI. This work is partially supported by the Spin(e) grants ANR-13-BS05-0005 ( http://cosmicorigin.org ) of the French Agence Nationale de la Recherche and by the ILP LABEX (under reference ANR-10-LABX-63 and ANR-11-IDEX-0004-02). Part of the analysis of the simulation was performed on the DiRAC facility jointly funded by STFC, BIS and the University of Oxford. NEC is supported by a Beecroft Postdoctoral Research Fellowship. We thank S. Rouberol for running smoothly the Horizon cluster for us. NEC thanks Rachel Mandelbaum for useful discussion regarding the grid-locking effect.