We gratefully acknowledge support from
the Simons Foundation and Leiden University.

Astrophysics

New submissions

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New submissions for Fri, 13 Mar 20

[1]  arXiv:2003.05449 [pdf, other]
Title: Tidal deformations of neutron stars with elastic crusts
Comments: 34 pages, 7 figures. Submitted to Phys. Rev. D
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc)

With the first detections of binary neutron star mergers by gravitational-wave detectors, it proves timely to consider how the internal structure of neutron stars affects the way in which they can be asymmetrically deformed. Such deformations may leave measurable imprints on gravitational-wave signals and can be sourced through tidal interactions or the formation of mountains. We detail the formalism that describes fully-relativistic neutron star models with elastic crusts undergoing static perturbations. This formalism primes the problem for studies into a variety of mechanisms that can deform a neutron star. We present results for a barotropic equation of state and a realistic model for the elastic crust, which enables us to compute relevant quantities such as the tidal deformability parameter. We find that the inclusion of an elastic crust provides a very small correction to the tidal deformability. The results allow us to demonstrate when and where the crust starts to fail during a binary inspiral and we find that the majority of the crust will remain intact up until merger.

[2]  arXiv:2003.05452 [pdf, other]
Title: Global 21-cm signal extraction from foreground and instrumental effects III: Utilizing drift-scan time dependence and full Stokes measurements
Comments: 13 pages, 6 figures, submitted to ApJ
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

When using valid foreground and signal models, the uncertainties on extracted signals in global 21-cm signal experiments depend principally on the overlap between signal and foreground models. In this paper, we investigate two strategies for decreasing this overlap:~(i) utilizing time dependence by fitting multiple drift-scan spectra simultaneously and (ii) measuring all four Stokes parameters instead of only the total power, Stokes I. Although measuring polarization requires different instruments than are used in most existing experiments, all existing experiments can utilize drift-scan measurements merely by averaging their data differently. In order to evaluate the increase in constraining power from using these two techniques, we define a method for connecting Root-Mean-Square (RMS) uncertainties to probabilistic confidence levels.~Employing simulations, we find that fitting only one total power spectrum leads to RMS uncertainties at the few K level, while fitting multiple time-binned, drift-scan spectra yields uncertainties at the $\lesssim 10$ mK level. This significant improvement only appears if the spectra are modeled with one set of basis vectors, instead of using multiple sets of basis vectors that independently model each spectrum. Assuming that they are simulated accurately, measuring all four Stokes parameters also leads to lower uncertainties. These two strategies can be employed simultaneously and fitting multiple time bins of all four Stokes parameters yields the best precision measurements of the 21-cm signal, approaching the noise level in the data.

[3]  arXiv:2003.05456 [pdf, other]
Title: Binary deviations from single object astrometry
Comments: 13 pages, 7 figures, 5 appendices. Submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)

Most binaries are undetected. Astrometric reductions of a system using the assumption that the object moves like a single point mass can be biased by unresolved binary stars. The discrepancy between the centre of mass of the system (which moves like a point mass) and the centre of light (which is what we observe) introduces additional motion. We explore the extent to which binary systems affect single object models fit to astrometric data. This tells us how observations are diluted by binaries and which systems cause the largest discrepancies - but also allows us to make inferences about the binarity of populations based on observed astrometric error. By examining a sample of mock observations, we show that binaries with periods close to one year can mimic parallax and thus bias distance measurements, whilst long period binaries can introduce significant apparent proper motion. Whilst these changes can soak up some of the error introduced by the binary, the total deviation from the best fitting model can be translated into a lower limit on the on-sky separation of the pair. Throughout we link these predictions to data from the Gaia satellite, whilst leaving the conclusions generalizable to other surveys.

[4]  arXiv:2003.05457 [pdf, other]
Title: Fluctuations in galactic bar parameters due to bar-spiral interaction
Comments: 25 p., 19 figures, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We study the late-time evolution of the central regions of two Milky Way-like galaxies formed in a cosmological context, one hosting a fast bar and the other a slow one. We find that bar length, R_b, measurements fluctuate on a dynamical timescale by up to 100%, depending on the spiral structure strength and measurement threshold. The bar amplitude oscillates by about 15%, correlating with R_b. The Tremaine-Weinberg-method estimates of the bars' instantaneous pattern speeds show variations around the mean of up to ~20%, typically anti-correlating with the bar length and strength. Through power spectrum analyses, we establish that these bar pulsations, with a period in the range ~60-200 Myr, result from its interaction with multiple spiral modes, which are coupled with the bar. Because of the presence of odd spiral modes, the two bar halves typically do not connect at exactly the same time to a spiral arm, and their individual lengths can be significantly offset. We estimated that in about 50% of bar measurements in Milky Way-mass external galaxies, the bar lengths of SBab type galaxies are overestimated by ~15% and those of SBbc types by ~55%. Consequently, bars longer than their corotation radius reported in the literature, dubbed "ultra-fast bars", may simply correspond to the largest biases. Given that the Scutum-Centaurus arm is likely connected to the near half of the Milky Way bar, recent direct measurements may be overestimating its length by 1-1.5 kpc, while its present pattern speed may be 5-10 km/s/kpc smaller than its time-averaged value.

[5]  arXiv:2003.05458 [pdf, other]
Title: Realistic gravitational focusing of meteoroid streams
Comments: Accepted for publication by Monthly Notices of the Royal Astronomical Society
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The number density and flux of a meteoroid stream is enhanced near a massive body due to the phenomenon known as gravitational focusing. The greatest enhancement occurs directly opposite the massive body from the stream radiant: as an observer approaches this location, the degree of focusing is unbound for a perfectly collimated stream. However, real meteoroid streams exhibit some dispersion in radiant and speed that will act to eliminate this singularity. In this paper, we derive an analytic approximation for this smoothing that can be used in meteoroid environment models and is based on real measurements of meteor shower radiant dispersion.

[6]  arXiv:2003.05459 [pdf, other]
Title: Beyond Gaia: Asteroseismic Distances of M giants using Ground-Based Transient Surveys
Comments: 13 pages, 8 figures, 2 tables, submitted to AAS Journals
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Evolved stars near the tip of the red giant branch (TRGB) show solar-like oscillations with periods spanning hours to months and amplitudes ranging from $\sim$1 mmag to $\sim$100 mmag. The systematic detection of the resulting photometric variations with ground-based telescopes would enable the application of asteroseismology to a much larger and more distant sample of stars than is currently accessible with space-based telescopes such as $Kepler$ or the ongoing Transiting Exoplanet Survey Satellite ($TESS$) mission. We present an asteroseismic analysis of M giants using data from two ground-based surveys: the Asteroid Terrestrial-impact Last Alert System (ATLAS) and the All-Sky Automated Survey for Supernovae (ASAS-SN). By comparing the extracted frequencies with constraints from $Kepler$, the Sloan Digital Sky Survey Apache Point Observatory Galaxy Evolution Experiment (APOGEE), and Gaia we demonstrate that ground-based transient surveys allow accurate distance measurements to oscillating M giants with a precision of $\sim$15$\%$. Using stellar population synthesis models we predict that ATLAS and ASAS-SN can provide asteroseismic distances to $\sim$2$\times$10$^{6}$ galactic M giants out to typical distances of $20-50$ kpc, vastly improving the reach of Gaia and providing critical constraints for Galactic archaeology and galactic dynamics.

[7]  arXiv:2003.05467 [pdf, other]
Title: Unresolved stellar companions with Gaia DR2 astrometry
Comments: submitted to MNRAS, comments welcome
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

For stars with unresolved companions, motions of the centre of light and that of mass decouple, causing a single-source astrometric model to perform poorly. We show that such stars can be easily detected with the reduced chi2 statistic, or RUWE, provided as part of Gaia DR2. We convert RUWE into the amplitude of the image centroid wobble, which, if scaled by the source distance, is proportional to the physical separation between companions (for periods up to several years). We test this idea on a sample of known spectroscopic binaries and demonstrate that the amplitude of the centroid perturbation scales with the binary period and the mass ratio as expected. We apply this technique to the Gaia DR2 data and show how the binary fraction evolves across the Hertzsprung--Russell diagram. The observed incidence of unresolved companions is high for massive young stars and drops steadily with stellar mass, reaching its lowest levels for white dwarfs. We highlight the elevated binary fraction for the nearby Blue Stragglers and Blue Horizontal Branch stars. We also illustrate how unresolved hierarchical triples inflate the relative velocity signal in wide binaries. Finally, we point out a hint of evidence for the existence of additional companions to the hosts of extrasolar hot jupiters.

[8]  arXiv:2003.05469 [pdf, other]
Title: The Tidal Disruption Event AT 2018hyz II: Light Curve Modeling of a Partially Disrupted Star
Comments: 9 pages, 9 figures, submitted to MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

AT 2018hyz (=ASASSN-18zj) is a tidal disruption event (TDE) located in the nucleus of a quiescent E+A galaxy at a redshift of $z = 0.04573$, first detected by the All-Sky Automated Survey for Supernovae (ASAS-SN). We present optical+UV photometry of the transient, as well as an X-ray spectrum and radio upper limits. The bolometric light curve of AT 2018hyz is comparable to other known TDEs and declines at a rate consistent with a $t^{-5/3}$ at early times, emitting a total radiated energy of $E = 9\times10^{50}$ erg. The light curve shows an excess bump in the UV about 50 days after bolometric peak lasting for at least 100 days, which may be related to an outflow. We detect a constant X-ray source present for at least 86 days. The X-ray spectrum shows a total unabsorbed flux of $\sim 4\times10^{-14}$ erg cm$^{-2}$ s$^{-1}$ and is best fit by a blackbody plus power-law model with a photon index of $\Gamma = 0.8$. A thermal X-ray model is unable to account for photons $> 1$ keV, while the radio non-detection favors inverse-Compton scattering rather than a jet for the non-thermal component. We model the optical and UV light curves using the Modular Open-Source Fitter for Transients (MOSFiT) and find a best fit for a black hole of $5.2\times10^6$ M$_\odot$ partially disrupting a $0.1$ M$_\odot$ star (stripping a mass of $\sim 0.01$ M$_\odot$ for the inferred impact parameter, $\beta=0.6$). The low optical depth implied by the small debris mass may explain how we are able to see hydrogen emission with disk-like line profiles in the spectra of AT 2018hyz (see our companion paper, Short et al.~2020).

[9]  arXiv:2003.05470 [pdf, other]
Title: The Tidal Disruption Event AT 2018hyz I: Double-peaked emission lines and a flat Balmer decrement
Comments: Submitted to MNRAS. Accompanied by companion paper Gomez et al. (2020)
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

We present results from spectroscopic observations of AT 2018hyz, a transient discovered by the ASAS-SN survey at an absolute magnitude of $M_V\sim -20.2$ mag, in the nucleus of a quiescent galaxy with strong Balmer absorption lines. AT 2018hyz shows a blue spectral continuum and broad emission lines, consistent with previous TDE candidates. Modelling of the light curve (presented in our companion paper, Gomez et al. 2020), indicates AT 2018hyz originated from the partial disruption of a low mass star. High cadence follow-up spectra show broad Balmer lines and He I in early spectra, with He II making an appearance after $\sim70-100$ days. The Balmer lines evolve from a smooth broad profile, through a boxy, asymmetric double-peaked phase consistent with accretion disk emission, and back to smooth at late times. The Balmer lines are unlike typical AGN in that they show a flat Balmer decrement (H$\alpha$/H$\beta\sim1.5$), suggesting the lines are collisionally excited rather than being produced via photo-ionisation. The flat Balmer decrement together with the complex profiles suggest that the emission lines originate in a disk chromosphere, analogous to those seen in cataclysmic variables. The low optical depth of material from the partial disruption may be what allows us to observe these double-peaked, collisionally excited lines. The late appearance of He II may be due to an expanding photosphere or outflow, or late-time shocks in debris collisions.

[10]  arXiv:2003.05472 [pdf, other]
Title: Concerns about ground based astronomical observations:quantifying satellites' constellations damages
Authors: Stefano Gallozzi (1), Diego Paris (1), Michele Maris (3), Marco Scardia, (4) David Dubois ((1) INAF-Osservatorio Astronomico di Roma, (2) INAF-Osservatorio Astronomico di Trieste, (3) INAF-Osservatorio Astronomici di Brera, (4) NASA-National Aeronautics and Space Administration)
Comments: 18 pages, 24 figures, 4 tables and 1 algorithm
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

This article is a second analysis step from the descriptive arXiv:2001.10952 preprint. Thiswork is aimed to arise awareness to the scientific astronomical community about the negative impact of satellites' mega-constellations and put in place an approximated estimations about loss of scientific contents expected for ground based astronomical observations when all 50,000 satellites will be displaced in LEO orbit. The first analysis regards the impact on professional astronomical images in optical windows. Than the study is expanded to other wavelengths and astronomical ground based facilities (radio and higher energies) to better understand which kind of effects are expected. Authors also try to perform a quantitative economic estimation related to the loss of value for public finances committed to the ground based astronomical facilities armed by satellites' constellations. These evaluations are intended for general purposes, can be improved and better estimated, but in this first phase they could be useful as evidentiary material to quantify the damage in subsequent legal actions against further satellites deployments.

[11]  arXiv:2003.05484 [pdf, other]
Title: An ALMA survey of the brightest sub-millimetre sources in the SCUBA-2 COSMOS field
Comments: Submitted to MNRAS, comments welcome. Figures 1, 4, A1 degraded to comply with size limits
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present an ALMA study of the ~180 brightest sources in the SCUBA-2 map of the COSMOS field from the S2COSMOS survey, as a pilot study for AS2COSMOS - a full survey of the ~1,000 sources in this field. In this pilot we have obtained 870-um continuum maps of an essentially complete sample of the brightest 182 sub-millimetre sources (S_850um=6.2mJy) in COSMOS. Our ALMA maps detect 260 sub-millimetre galaxies (SMGs) spanning a range in flux density of S_870um=0.7-19.2mJy. We detect more than one SMG counterpart in 34+/-2 per cent of sub-millimetre sources, increasing to 53+/-8 per cent for SCUBA-2 sources brighter than S_850um>12mJy. We estimate that approximately one-third of these SMG-SMG pairs are physically associated (with a higher rate for the brighter secondary SMGs, S_870um>3mJy), and illustrate this with the serendipitous detection of bright [CII] 157.74um line emission in two SMGs, AS2COS0001.1 & 0001.2 at z=4.63, associated with the highest significance single-dish source. Using our source catalogue we construct the interferometric 870um number counts at S_870um>6.2mJy. We use the extensive archival data of this field to construct the multiwavelength spectral energy distribution of each AS2COSMOS SMG, and subsequently model this emission with MAGPHYS to estimate their photometric redshifts. We find a median photometric redshift for the S_870um>6.2mJy AS2COSMOS sample of z=2.87+/-0.08, and clear evidence for an increase in the median redshift with 870-um flux density suggesting strong evolution in the bright-end of the 870um luminosity function.

[12]  arXiv:2003.05486 [pdf, other]
Title: Subsolar Al/Si and Mg/Si ratios of non-carbonaceous chondrites reveal planetesimal formation during early condensation in the protoplanetary disk
Comments: Accepted for publication in EPSL
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The Al/Si and Mg/Si ratios in non-carbonaceous chondrites are lower than the solar (i.e., CI-chondritic) values, in sharp contrast to the non-CI carbonaceous meteorites and the Earth, which are enriched in refractory elements and have Mg/Si ratios that are solar or larger. We show that the formation of a first generation of planetesimals during the condensation of refractory elements implies the subsequent formation of residual condensates with strongly sub-solar Al/Si and Mg/Si ratios. The mixing of residual condensates with different amounts of material with solar refractory/Si element ratios explains the Al/Si and Mg/Si values of non-carbonaceous chondrites. To match quantitatively the observed ratios, we find that the first-planetesimals should have accreted when the disk temperature was ~1,330-1,400 K depending on pressure and assuming a solar C/O ratio of the disk. We discuss how this model relates to our current understanding of disk evolution, grain dynamics, and planetesimal formation. We also extend the discussion to moderately volatile elements (e.g., Na), explaining how it may be possible that the depletion of these elements in non-carbonaceous chondrites is correlated with the depletion of refractory elements (e.g., Al). Extending the analysis to Cr, we find evidence for a higher than solar C/O ratio in the protosolar disk's gas when/where condensation from a fractionated gas occurred. Finally, we discuss the possibility that the supra-solar Al/Si and Mg/Si ratios of the Earth are due to the accretion of ~40% of the mass of our planet from the first-generation of refractory-rich planetesimals.

[13]  arXiv:2003.05493 [pdf, other]
Title: The $γ$-ray Emission of Star-Forming Galaxies
Comments: Under review in The Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

A majority of the $\gamma$-ray emission from star-forming galaxies is generated by the interaction of high-energy cosmic rays with the interstellar gas and radiation fields. Star-forming galaxies are expected to contribute to both the extragalactic $\gamma$-ray background and the IceCube astrophysical neutrino flux. Using roughly 10\,years of $\gamma$-ray data taken by the {\it Fermi} Large Area Telescope, in this study we constrain the $\gamma$-ray properties of star-forming galaxies. We report the detection of 11 bona-fide $\gamma$-ray emitting galaxies and 2 candidates. Moreover, we show that the cumulative $\gamma$-ray emission of below-threshold galaxies is also significantly detected at $\sim$5\,$\sigma$ confidence. The $\gamma$-ray luminosity of resolved and unresolved galaxies is found to correlate with the total (8-1000\,$\mu$m) infrared luminosity as previously determined. Above 1\,GeV, the spectral energy distribution of resolved and unresolved galaxies is found to be compatible with a power law with a photon index of $\approx2.2-2.3$.
Finally, we find that star-forming galaxies account for roughly 5\,\% and 3\,\% of the extragalactic $\gamma$-ray background and the IceCube neutrino flux, respectively.

[14]  arXiv:2003.05499 [pdf, other]
Title: Asteroids' Size Distribution and Colors from HiTS
Authors: J. Peña (1,2), C. Fuentes (1,2), F. Förster (3,2), J. Martínez-Palomer (4,1,3), G. Cabrera-Vives (5,2), J.C. Maureira (3), P. Huijse (6, 2), P.A. Estévez (7,2), L. Galbany (8), S. González-Gaitán (9, 3, 2), Th. de Jaeger (4, 1, 2) ((1) Departamento de Astronomía, Universidad de Chile, Las Condes, Santiago, Chile, (2) Millennium Institute of Astrophysics, Chile., (3) Center for Mathematical Modeling, Santiago, Chile, (4) Department of Astronomy, University of California, Berkeley, CA, USA., (5) Department of Computer Science, Universidad de Concepción, Chile, (6) Informatics Institute, Universidad Austral de Chile, Chile, (7) Electrical Engineering Department, University of Chile, Chile, (8) Departamento de Física Teórica y del Cosmos, Universidad de Granada, Granada, Spain, (9) CENTRA, Instituto Superior Técnico, Universidade de Lisboa, Portugal)
Comments: 17 pages, 18 figures
Journal-ref: The Astronomical Journal, Volume 159, Number 4, Page 148, Year 2020
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

We report the observations of solar system objects during the 2015 campaign of the High cadence Transient Survey (HiTS). We found 5740 bodies (mostly Main Belt asteroids), 1203 of which were detected in different nights and in $g'$ and $r'$. Objects were linked in the barycenter system and their orbital parameters were computed assuming Keplerian motion. We identified 6 near Earth objects, 1738 Main Belt asteroids and 4 Trans-Neptunian objects. We did not find a $g'-r'$ color--size correlation for $14<H_{g'}<18$ ($1<D<10$ km) asteroids. We show asteroids' colors are disturbed by HiTS' 1.6 hour cadence and estimate that observations should be separated by at most 14 minutes to avoid confusion in future wide-field surveys like LSST. The size distribution for the Main Belt objects can be characterized as a simple power law with slope $\sim0.9$, steeper than in any other survey, while data from HiTS 2014's campaign is consistent with previous ones (slopes $\sim0.68$ at the bright end and $\sim0.34$ at the faint end). This difference is likely due to the ecliptic distribution of the Main Belt since 2015's campaign surveyed farther from the ecliptic than did 2014's and most previous surveys.

[15]  arXiv:2003.05513 [pdf, ps, other]
Title: Host galaxy properties and environment of obscured and unobscured X-ray selected Active Galactic Nuclei in the COSMOS survey
Comments: 16 pages, 14 figures, accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We analyse different photometric and spectroscopic properties of active galactic nuclei (AGNs) and quasars (QSOs) selected by their mid-IR power-law and X-ray emission from the COSMOS survey. We use a set of star-forming galaxies as a control sample to compare with the results. We have considered samples of obscured (HR > -0.2) and unobscured (HR < -0.2) sources including AGNs with $L_X$ < $10^{44}$ erg s$^{-1}$, as well as QSOs ($L_X$ > $10^{44}$ erg s$^{-1}$) with 1.4 < z < 2.5. We also study the typical environment of these samples, by assessing neighbouring galaxy number density and neighbour properties such as colour, stellar mass and star formation rate. We find that the UV/optical and mid-infrared colour distribution of the different AGN types differ significantly. Also, we obtain most of AGNs and QSOs to be more compact when compared to the sample of SF galaxies. In general we find that the stellar mass distribution of the different AGN sample are similar, obtaining only a difference of $\Delta\overline{\mathrm{log}M}=0.3$ dex ($M_{\odot}$) between unobscured and obscured QSOs. Obscured and unobscured AGNs and QSOs reside in different local environment at small ($r_p$ < 100 kpc) scales. Our results support previous findings where AGN type correlates with environment. These differences and those found in AGN host properties cast out the simplest unified model in which obscuration is purely an orientation effect.

[16]  arXiv:2003.05516 [pdf, other]
Title: DECam-GROWTH Search for the Faint and Distant Binary Neutron Star and Neutron Star-Black Hole Mergers in O3a
Comments: 9 pages, 4 figures, submitted to Rev. Mex. A. A. (AstroRob 2019 conference proceedings)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Synoptic searches for the optical counterpart to a binary neutron star (BNS) or neutron star-black hole (NSBH) merger can pose significant challenges towards the discovery of kilonovae and performing multi-messenger science. In this work, we describe the advantage of a global multi-telescope network towards this end, with a particular focus on the key and complementary role the Dark Energy Camera (DECam) plays in multi-facility follow-up. We describe the Global Relay of Observatories Watching Transients Happen (GROWTH) Target-of-Opportunity (ToO) Marshal, a common web application we built to ingest events, plan observations, search for transient candidates, and retrieve performance summary statistics for all of the telescopes in our network. Our infrastructure enabled us to conduct observations of two events during O3a, S190426c and S190510g. Furthermore, our analysis of deep DECam observations of S190814bv conducted by the DESGW team, and access to a variety of global follow-up facilities allowed us to place meaningful constraints on the parameters of the kilonova and the merging binary. We emphasize the importance of a global telescope network in conjunction with a power telescope like DECam in performing searches for the counterparts to gravitational-wave sources.

[17]  arXiv:2003.05521 [pdf, other]
Title: Predicting the vulnerability of spacecraft components: modelling debris impact effects through vulnerable-zones
Comments: Article accepted for pubblication in Advances in Space Research
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Computational Engineering, Finance, and Science (cs.CE); Space Physics (physics.space-ph)

The space environment around the Earth is populated by more than 130 million objects of 1 mm in size and larger, and future predictions shows that this amount is destined to increase, even if mitigation measures are implemented at a far better rate than today. These objects can hit and damage a spacecraft or its components. It is thus necessary to assess the risk level for a satellite during its mission lifetime. Few software packages perform this analysis, and most of them employ time-consuming ray-tracing methodology, where particles are randomly sampled from relevant distributions. In addition, they tend not to consider the risk associated with the secondary debris clouds. The paper presents the development of a vulnerability assessment model, which relies on a fully statistical procedure: the debris fluxes are directly used combining them with the concept of the vulnerable zone, avoiding the random sampling the debris fluxes. A novel methodology is presented to predict damage to internal components. It models the interaction between the components and the secondary debris cloud through basic geometric operations, considering mutual shielding and shadowing between internal components. The methodologies are tested against state-of-the-art software for relevant test cases, comparing results on external structures and internal components.

[18]  arXiv:2003.05528 [pdf]
Title: Nightside condensation of iron in an ultra-hot giant exoplanet
Comments: Published in Nature (Accepted on 24 January 2020.) 33 pages, 11 figures, 3 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Ultra-hot giant exoplanets receive thousands of times Earth's insolation. Their high-temperature atmospheres (>2,000 K) are ideal laboratories for studying extreme planetary climates and chemistry. Daysides are predicted to be cloud-free, dominated by atomic species and substantially hotter than nightsides. Atoms are expected to recombine into molecules over the nightside, resulting in different day-night chemistry. While metallic elements and a large temperature contrast have been observed, no chemical gradient has been measured across the surface of such an exoplanet. Different atmospheric chemistry between the day-to-night ("evening") and night-to-day ("morning") terminators could, however, be revealed as an asymmetric absorption signature during transit. Here, we report the detection of an asymmetric atmospheric signature in the ultra-hot exoplanet WASP-76b. We spectrally and temporally resolve this signature thanks to the combination of high-dispersion spectroscopy with a large photon-collecting area. The absorption signal, attributed to neutral iron, is blueshifted by -11+/-0.7 km s-1 on the trailing limb, which can be explained by a combination of planetary rotation and wind blowing from the hot dayside. In contrast, no signal arises from the nightside close to the morning terminator, showing that atomic iron is not absorbing starlight there. Iron must thus condense during its journey across the nightside.

[19]  arXiv:2003.05544 [pdf, other]
Title: Factorization of Antenna Efficiency of Aperture-type antenna: Beam Coupling and Two Spillovers
Comments: 9 pages, 5 figures, submitted to IEEE Transactions on Antennas and Propagation
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Antenna efficiency is one of the most important figures-of-merit of a radio telescope, even for a multibeam radio telescope. To analyze a system where each beam illuminates only a part of the aperture, a lossless antenna consisting of two apertures in series is considered in the frame of the scalar wave approximation. We found that its antenna efficiency is factorized into three factors: efficiencies of beam coupling, transmission spillover, and reception spillover. We numerically confirmed our factorization with an optical simulation. The factorization is applicable to general aperture-type antennas and is useful in design of multibeam radio telescopes.

[20]  arXiv:2003.05561 [pdf, other]
Title: Disentangling the formation history of galaxies via population-orbit superposition: method validation
Comments: 20 pages, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present population-orbit superposition models for external galaxies based on Schwarzschild's orbit-superposition method, by tagging the orbits with age and metallicity. The models fit the density distributions, as well as kinematic, age and metallicity maps from Integral Field Unit (IFU) spectroscopy observations. We validate the method and demonstrate its power by applying it to mock data, similar to those obtained by the Multi-Unit Spectroscopic Explorer (MUSE) IFU on the Very Large Telescope (VLT). These mock data are created from Auriga galaxy simulations, viewed at three different inclination angles ($\vartheta=40^o, 60^o, 80^o$). Constrained by MUSE-like mock data, our model can recover the galaxy's stellar orbit distribution projected in orbital circularity $\lambda_z$ vs. radius $r$, the intrinsic stellar population distribution in age $t$ vs. metallicity $Z$, and the correlation between orbits' circularity $\lambda_z$ and stellar age $t$. A physically motivated age-metallicity relation improves recovering the intrinsic stellar population distributions. We decompose galaxies into cold, warm and hot + counter-rotating components based on their orbit circularity distribution, and find that the surface density, mean velocity, velocity dispersion, age and metallicity maps of each component from our models well reproduce those from simulation, especially for projections close to edge-on. These galaxies exhibit strong global age vs. $\sigma_z$ relation, which is well recovered by our model. The method has the power to reveal the detailed build-up of stellar structures in galaxies, and offers a complement to local resolved, and high-redshift studies of galaxy evolution.

[21]  arXiv:2003.05576 [pdf]
Title: The solar nebula origin of (486958) Arrokoth, a primordial contact binary in the Kuiper belt
Comments: Published in Science 28 Feb 2020 (First release 13 Feb 2020)
Journal-ref: Science 367, eaay6620 (2020)
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The New Horizons spacecraft's encounter with the cold classical Kuiper belt object (486958) Arrokoth (formerly 2014 MU69) revealed a contact-binary planetesimal. We investigate how it formed, finding it is the product of a gentle, low-speed merger in the early Solar System. Its two lenticular lobes suggest low-velocity accumulation of numerous smaller planetesimals within a gravitationally collapsing, solid particle cloud. The geometric alignment of the lobes indicates the lobes were a co-orbiting binary that experienced angular momentum loss and subsequent merger, possibly due to dynamical friction and collisions within the cloud or later gas drag. Arrokoth's contact-binary shape was preserved by the benign dynamical and collisional environment of the cold classical Kuiper belt, and so informs the accretion processes that operated in the early Solar System.

[22]  arXiv:2003.05592 [pdf, other]
Title: A new moving group in the Local Arm
Comments: accepted by AJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a new moving group clustered in kinematics, spatial position and elemental abundances. Its spatial position is around the center of the Local Arm of the Milky Way. A convergent point method was taken to select candidate member stars.\textbf{ Among 206 candidate member stars, 74 are pre-main-sequence stars and some of them have stellar disks.} We presume those pre-main sequence stars belong to Orion nebula. We suggest this moving group is caused by density wave of the Local Arm passing by.

[23]  arXiv:2003.05616 [pdf, ps, other]
Title: Discovery of Extended Structures around Two Evolved Planetary Nebulae M 2-55 and Abell 2
Comments: 16 pages, 7 figures, accepted by Research in Astronomy and Astrophysics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We report a multi-wavelength study of two evolved planetary nebulae (PNs) M 2-55 and Abell 2. Deep optical narrow-band images ([O III], H?, and [N II]) of M 2-55 reveal two pairs of bipolar lobes and a new faint arc-like structure. This arc-shaped filament around M 2-55 appears a well-defined boundary from southwest to southeast, strongly suggesting that this nebula is in interaction with its surrounding interstellar medium. From the imaging data of Wide-field Infrared Survey Explorer (WISE) all-sky survey, we discovered extensive mid-infrared halos around these PNs, which are approximately twice larger than their main nebulae seen in the visible. We also present a mid-resolution optical spectrum of M 2-55, which shows that it is a high-excitation evolved PN with a low electron density of 250 cm^-3. Furthermore, we investigate the properties of these nebulae from their spectral energy distributions (SEDs) by means of archival data.

[24]  arXiv:2003.05625 [pdf, other]
Title: Structure and Instability of the Ionization Fronts around Moving Black Holes
Comments: 12 pages, 9 figures, submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

In this paper we focus on understanding the physical processes that lead to stable or unstable ionization fronts (I-fronts) observed in simulations of moving black holes (BHs). The front instability may trigger bursts of gas accretion accelerating the growth of supermassive BH seeds and rendering the BH significantly more luminous than at steady-state. We perform a series of idealized three dimensional radiation hydrodynamics simulations resolving the I-fronts around BHs of mass $M_\mathrm{BH}$ and velocity $v_\infty$ accreting from a medium of density $n_\mathrm{H}$. The I-front, with radius $R_\mathrm{I}$, transitions from D-type to R-type as the BH velocity becomes larger than a critical value $v_\mathrm{R}\sim 30-55\,\mathrm{km/s}$. The D-type front is preceded by a bow-shock of thickness $\Delta R_\mathrm{I}$ that decreases as $v_\infty$ approaches $v_\mathrm{R}$. We find that both D-type and R-type fronts can be unstable given the following two conditions: i) for D-type fronts the shell thickness must be $\Delta R_\mathrm{I}/R_\mathrm{I}<0.05$ (i.e., $v_\infty \geq 20-30\,\mathrm{km/s}$.), while no similar restriction holds for R-type fronts; ii) the temperature jump across the I-front must be $\Delta_T \equiv T_\mathrm{II}/T_\mathrm{I}>3$. This second condition is satisfied if $T_\mathrm{I}<5000\,\mathrm{K}$ or if $n_\mathrm{H}\,M_\mathrm{BH} \gtrsim 10^6\,M_\odot\,\mathrm{cm^{-3}}$. Due to X-ray pre-heating typically $T_\mathrm{I} \sim 10^4\,\mathrm{K}$, unless the D-type shell is optically thick to X-rays, which also happens when $n_\mathrm{H}\,M_\mathrm{BH}$ is greater than a metallicity-dependent critical value. We thus conclude that I-fronts around BHs are unstable only for relatively massive BHs ($>10^2-10^4\,M_\odot$) moving trough very dense molecular clouds.

[25]  arXiv:2003.05659 [pdf, other]
Title: Investigating the connection between gamma-ray activity and relativistic jet in 3C273 during 2015-2019
Comments: 14 pages, 11 figures, 3 tables. To appear in A&A (submitted: 2020 January 10; accepted: 2020 March 5)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Due to its powerful radiation over the entire electromagnetic spectrum and its radio jet activity, the blazar 3C273 offers the opportunity to study the physics of $\gamma$-ray emission from active galactic nuclei. Since a historically strong outburst in 2009, 3C273 showed relatively weak emission in the gamma-ray band over multiple years. However, recent Fermi-Large Area Telescope observations indicate elevated activity during 2015-2019. We aim at constraining the origin of the gamma-ray outbursts towards 3C273 and investigate their connection to the parsec-scale jet. We generate Fermi-LAT gamma-ray light curves with multiple binning intervals and study the spectral properties of the gamma-ray emission. Using a 3-mm ALMA light curve, we study the correlation between radio and gamma-ray emission. Relevant activity in the parsec-scale jet of 3C273 is investigated with 7-mm VLBA observations obtained close in time to notable gamma-ray outbursts. We find two prominent gamma-ray outbursts in 2016 (MJD 57382) and 2017 (MJD 57883) accompanied by mm-wavelength flaring activity. The gamma-ray photon index time series show a weak hump-like feature around the gamma-ray outbursts. The monthly gamma-ray flux-index plot indicates a transition from softer-when-brighter to harder-when-brighter at $1.03\times10^{-7}\rm\,ph\,cm^{-2}\,s^{-1}$. A significant correlation between the gamma-ray and mm-wavelength emission is found, with the radio lagging the gamma-rays by about 105-112 days. The 43-GHz jet images reveal the known stationary features (i.e., the core, S1, and S2) in a region upstream of the jet. We find indication for a propagating disturbance and a polarized knot between the stationary components around the times of both gamma-ray outbursts.

[26]  arXiv:2003.05663 [pdf, other]
Title: Searching for molecular gas in/outflows in the nuclear regions of five Seyfert galaxies
Comments: Accepted for publication in A&A, 23 pages, 17 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

AGN-driven outflows are believed to play an important role in regulating the growth of galaxies mostly via negative feedback. However, their effects on their hosts are far from clear, especially for low and moderate luminosity Seyferts. To investigate this issue, we have obtained cold molecular gas observations, traced by the CO(2-1) transition, using the NOEMA interferometer of five nearby (distances between 19 and 58 Mpc) Seyfert galaxies. The resolution of approx. 0.3-0.8 arcsec (approx. 30-100 pc) and field of view of NOEMA allowed us to study the CO(2-1) morphology and kinematics in the nuclear regions (approx. 100 pc) and up to radial distances of approx. 900 pc. We have detected CO(2-1) emission in all five galaxies with disky or circumnuclear ring like morphologies. We derived cold molecular gas masses on nuclear (approx. 100 pc) and circumnuclear (approx. 650 pc) scales in the range from $10^6$ to $10^7$M$_{\odot}$ and from $10^7$ to $10^8$ $M_{\odot}$, respectively. In all of our galaxies the bulk of this gas is rotating in the plane of the galaxy. However, non-circular motions are also present. In NGC 4253, NGC 4388 and NGC 7465, we can ascribe the streaming motions to the presence of a large-scale bar. In Mrk 1066 and NGC 4388, the non-circular motions in the nuclear regions are explained as outflowing material due to the interaction of the AGN wind with molecular gas in the galaxy disk. We conclude that for an unambiguous and precise interpretation of the kinematics of the cold molecular gas we need a detailed knowledge of the host galaxy (i.e., presence of bars, interactions, etc) as well as of the ionized gas kinematics and the ionization cone geometry.

[27]  arXiv:2003.05665 [pdf, other]
Title: Observed binary populations reflect the Galactic history. Explaining the orbital period-mass ratio relation in wide hot subdwarf binaries
Comments: Submitted to A&A on 26-11-2019, waiting on referee report
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes of stable mass transfer from evolved red giants. The orbits of these binaries show a strong correlation between their orbital periods and mass ratios. The origins of this correlation have, so far, been lacking a conclusive explanation. We aim to find a binary evolution model which can explain the observed correlation. Radii of evolved red giants, and hence the resulting orbital periods, strongly depend on their metallicity. We have performed a small but statistically significant binary population synthesis study with the binary stellar evolution code MESA. We have used a standard model for binary mass loss and a standard metallicity history of the Galaxy. The resulting sdB systems were selected based on the same criteria as used in observations and then compared with the observed population. We have achieved an excellent match to the observed period - mass ratio correlation without using any free parameters. Furthermore, our models produce a very good match to the observed period - metallicity correlation. We predict several new correlations which link the observed sdB binaries to their progenitors, and a correlation between the orbital period, metallicity and core mass for subdwarfs and young low-mass white dwarfs. We also predict a new population of sdB binaries in the galactic bulge. We demonstrate, for the first time, how the metallicity history of the Milky Way is imprinted in the properties of the observed post-mass transfer binaries. We show that Galactic chemical evolution is an important factor in binary population studies of any systems containing at least one evolved low-mass ($M_{\rm init} < 1.6\,M_{\odot}$) component. Finally, we provide an observationally supported model of mass transfer from low-mass red giants onto main-sequence stars.

[28]  arXiv:2003.05671 [pdf, ps, other]
Title: Revisit the fraction of radio-loud narrow line Seyfert 1 galaxies with LoTSS DR1
Authors: Xu-Liang Fan
Comments: 12 pages, 6 figures, accepted by Universe for the Special Issue "Seyfert Galaxies Astrophysics"
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA)

Radio-Loud narrow-line Seyfert 1 galaxies (NLS1s), especially the extremely radio-loud ones, are widely accepted as the jetted versions of NLS1s. We explore the radio-loud fraction for NLS1s with recently released LoTSS DR1 at 150 MHz. The radio detection rate is about 28\% for LoTSS DR1. The radio detected NLS1s have lower redshift than the non-detected ones. Moreover, the 150 MHz radio luminosity of NLS1s detected by LoTSS are about two orders of magnitude weaker than that of the previous samples. By defining the radio loudness with the ratio between 150 MHz radio flux and SDSS \textit{r} band flux, the radio-loud fraction is about 1\% with the critical radio loudness equalling to 100. Radio loudness shows no dependence on central black hole mass, while weak correlations are found between radio loudness and disk luminosity, as well as Eddington ratio.

[29]  arXiv:2003.05673 [pdf, other]
Title: Precursor flares of short gamma-ray bursts from crust yielding due to tidal resonances in coalescing binaries of rotating, magnetized neutron stars
Comments: 16 pages, 8 figures, 1 table. Accepted for publication in Phys. Rev. D
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

As evidenced by the coincident detections of GW170817 and GRB 170817A, short gamma-ray bursts are likely associated with neutron star-neutron star merger events. Although rare, some bursts display episodes of early emission, with precursor flares being observed up to $\sim 10$ seconds prior to the main burst. As the stars inspiral due to gravitational wave emission, the exertion of mutual tidal forces leads to the excitation of stellar oscillation modes, which may come into resonance with the orbital motion. Mode amplitudes increase substantially during a period of resonance as tidal energy is deposited into the star. The neutron star crust experiences shear stress due to the oscillations and, if the resonant amplitudes are large enough, may become over-strained. This over-straining can lead to fractures or quakes which release energy, thereby fueling precursor activity prior to the merger. Using some simple Maclaurin spheroid models, we investigate the influence of magnetic fields and rapid rotation on tidally-forced $f$- and $r$- modes, and connect the associated eigenfrequencies with the orbital frequencies corresponding to precursor events seen in, for example, GRB 090510.

[30]  arXiv:2003.05700 [pdf, other]
Title: Limiting effects in clusters of misaligned toroids orbiting static SMBHs
Comments: 28 pages, 15 multipanels figures, 1 Table, Monthly Notices of the Royal Astronomical Society, staa503, this https URL Published: 19 February 2020 Key words: black hole physics-accretion, accretion discs-hydrodynamics-(magnetohydrodynamics) MHD--galaxies: active--galaxies: jets
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc)

We consider agglomerates of misaligned, pressure supported tori orbiting a Schwarzschild black hole. A leading function is introduced, regulating the toroids distribution around the central static attractor-it enables to model the misaligned tori aggregate as a single orbiting (macro--)configuration. We first analyze the leading function for purely hydrodynamical perfect fluid toroids. Later, the function is modified for presence of a toroidal magnetic field. We study the constraints on the tori collision emergence and the instability of the agglomerates of misaligned tori with general relative inclination angles. We discuss the possibility that the twin peak high-frequency quasi-periodic oscillations (HF-QPOs) could be related to the agglomerate inner ringed structure. The discrete geometry of the system is related to HF-QPOs considering several oscillation geodesic models associated to the toroids inner edges. We also study possible effect of the tori geometrical thickness on the oscillatory phenomena.

[31]  arXiv:2003.05704 [pdf, ps, other]
Title: Venusian Habitable Climate Scenarios: Modeling Venus through time and applications to slowly rotating Venus-Like Exoplanets
Comments: Submitted to Journal of Geophysics Research - Planets. 54 pages, 10 figures, 2 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

One popular view of Venus' climate history describes a world that has spent much of its life with surface liquid water, plate tectonics, and a stable temperate climate. Part of the basis for this optimistic scenario is the high deuterium to hydrogen ratio from the Pioneer Venus mission that was interpreted to imply Venus had a shallow ocean's worth of water throughout much of its history. Another view is that Venus had a long lived (approximately 100 million year) primordial magma ocean with a CO2 and steam atmosphere. Venus' long lived steam atmosphere would sufficient time to dissociate most of the water vapor, allow significant hydrogen escape and oxidize the magma ocean. A third scenario is that Venus had surface water and habitable conditions early in its history for a short period of time (< 1 Gyr), but that a moist/runaway greenhouse took effect because of a gradually warming sun, leaving the planet desiccated ever since. Using a general circulation model we demonstrate the viability of the first scenario using the few observational constraints available. We further speculate that Large Igneous Provinces and the global resurfacing 100s of millions of years ago played key roles in ending the clement period in its history and presenting the Venus we see today. The results have implications for what astronomers term "the habitable zone," and if Venus-like exoplanets exist with clement conditions akin to modern Earth we propose to place them in what we term the "optimistic Venus zone."

[32]  arXiv:2003.05714 [pdf, other]
Title: SPHERE+: Imaging young Jupiters down to the snowline
Comments: White paper submitted to ESO on Feb. 20th, 2020
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

SPHERE (Beuzit et al,. 2019) has now been in operation at the VLT for more than 5 years, demonstrating a high level of performance. SPHERE has produced outstanding results using a variety of operating modes, primarily in the field of direct imaging of exoplanetary systems, focusing on exoplanets as point sources and circumstellar disks as extended objects. The achievements obtained thus far with SPHERE (~200 refereed publications) in different areas (exoplanets, disks, solar system, stellar physics...) have motivated a large consortium to propose an even more ambitious set of science cases, and its corresponding technical implementation in the form of an upgrade. The SPHERE+ project capitalizes on the expertise and lessons learned from SPHERE to push high contrast imaging performance to its limits on the VLT 8m-telescope. The scientific program of SPHERE+ described in this document will open a new and compelling scientific window for the upcoming decade in strong synergy with ground-based facilities (VLT/I, ELT, ALMA, and SKA) and space missions (Gaia, JWST, PLATO and WFIRST). While SPHERE has sampled the outer parts of planetary systems beyond a few tens of AU, SPHERE+ will dig into the inner regions around stars to reveal and characterize by mean of spectroscopy the giant planet population down to the snow line. Building on SPHERE's scientific heritage and resounding success, SPHERE+ will be a dedicated survey instrument which will strengthen the leadership of ESO and the European community in the very competitive field of direct imaging of exoplanetary systems. With enhanced capabilities, it will enable an even broader diversity of science cases including the study of the solar system, the birth and death of stars and the exploration of the inner regions of active galactic nuclei.

[33]  arXiv:2003.05757 [pdf, other]
Title: A Bayesian Approach to the Vertical Structure of the Disk of the Milky Way
Comments: 7 pages, 6 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

This work investigates the vertical profile of the stars in the disk of the Milky Way. The models investigated are of the form $sech^{2/n}(nz/(2H))$ where, setting $\alpha = 2/n$, the three functions of the sequence $\alpha = 0,1,2$ correspond to exponential, $sech$, $sech^2$ functions. We consider symmetric models and asymmetric models, above and below the plane. The study uses the large sample of K and M stars of Ferguson et al. (2017) and applies the methods of Bayesian model comparison to discriminate between the 6 models. Two inconsistencies in Ferguson et al. (2017), concerning the vertical height cut and the model continuity across the plane, are noted and addressed. We find that (1) in the Milky Way the symmetric disc models are decisively ruled out, with northern thin disc scale heights $\sim25\%$ larger than southern, (2) there is moderate evidence for the exponential and $sech$ models over the $sech^2$ model, though a sample extending further into the Galactic mid-plane is needed to strengthen this result, (3) the photometric distances used by Ferguson et al. underestimate the GAIA distances by a factor of roughly 1.16, and (4) the increase of scale height with Galactic latitude observed by Ferguson et al. is due to incorrect cuts to the data.

[34]  arXiv:2003.05759 [pdf]
Title: How Astronomers Perceive the Societal Impact of Research: An Exploratory Study
Comments: 8 pages, accepted for publication: Communicating Astronomy with the Public Journal
Journal-ref: Communicating Astronomy with the Public Journal, 2020
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

We present an exploratory study of the perception of professional astronomers about the societal impact of astronomy. Ten semi-structured interviews with astronomers from a range of career and cultural backgrounds have been conducted to gain in-depth insight into their opinion about societal impact and their approach in realising it. The results show that the interviewees are aware of the diversity of impacts that astronomical research has. However, they are mostly active in outreach and only a few activities are incorporated into their jobs to achieve an impact on development. There is little contact with stakeholders in industry, policy or other fields, like development. Besides, a structured approach in their personal outreach is lacking, and assessment is only done informally. Despite the limited sample size of this study, the results indicate that a further change is necessary to engage professional astronomers with topics of development and societal impact to create action on the level of individual researchers.

[35]  arXiv:2003.05770 [pdf, other]
Title: Coronal Bright Points as possible sources of density variations in the Solar Corona
Comments: 15 pages, 10 figures, accepted for publication in The Astrophysical Journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Recent analysis of high-cadence white-light images taken by the Solar-Terrestrial RElations Observatory (STEREO) near solar maximum has revealed that outflowing density structures are released in an ubiquitous manner in the solar wind. The present study investigates whether these density fluctuations could originate from the transient heating of the low corona observed during Coronal Bright Points (CBPs). We assume that part of the intense heating measured during CBPs occurs at the coronal base of open magnetic fields that channel the forming solar wind. We employ the solar wind model MULTI-VP to quantify the plasma compression induced by transient heating and investigate how the induced perturbation propagates to the upper corona. We show that for heating rates with statistics comparable to those observed during CBPs the compressive wave initially increases the local plasma density by a factor of up to 50$\%$ at 5 R$_\odot$. The wave expands rapidly beyond 30 solar radii and the local enhancement in density decreases beyond. Based on the occurrence rates of CBPs measured in previous studies, we impose transient heating events at the base of thousands of open magnetic field lines to study the response of the entire 3-D corona. The simulated density cubes are then converted into synthetic white-light imagery. We show that the resulting brightness variations occupy all position angles in the images on timescales of hours. We conclude that a significant part of the ubiquitous brightness variability of the solar corona could originate in the strong transient heating of flux tubes induced by CBPs.

[36]  arXiv:2003.05775 [pdf, other]
Title: Arcminute MicroKelvin Imager observations at 15 GHz of the 2020 February outburst of Cygnus X-3
Comments: Research Notes of the AAS, in press
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Here we report observations of a recent giant radio flare from Cygnus X-3 in 2020 February, made with the Arcminute MicroKelvin Imager.

[37]  arXiv:2003.05777 [pdf, other]
Title: Characterization of hot stellar systems with confidence
Comments: 9 pages; 9 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR); Applications (stat.AP); Machine Learning (stat.ML)

Hot stellar systems (HSS) are a collection of stars bound together by gravitational attraction. These systems hold clues to many mysteries of outer space so understanding their origin, evolution and physical properties is important but remains a huge challenge. We used multivariate $t$-mixtures model-based clustering to analyze 13456 hot stellar systems from Misgeld & Hilker (2011) that included 12763 candidate globular clusters and found eight homogeneous groups using the Bayesian Information Criterion (BIC). A nonparametric bootstrap procedure was used to estimate the confidence of each of our clustering assignments. The eight obtained groups can be characterized in terms of the correlation, mass, effective radius and surface density. Using conventional correlation-mass-effective radius-surface density notation, the largest group, Group 1, can be described as having positive-low-low-moderate characteristics. The other groups, numbered in decreasing sizes are similarly characterised, with Group 2 having positive-low-low-high characteristics, Group 3 displaying positive-low-low-moderate characteristics, Group 4 having positive-low-low-high characteristic, Group 5 displaying positive-low-moderate-moderate characteristic and Group 6 showing positive-moderate-low-high characteristic. The smallest group (Group 8) shows negative-low-moderate-moderate characteristic. Group 7 has no candidate clusters and so cannot be similarly labeled but the mass, effective radius correlation for these non-candidates indicates that they zare larger than typical globular clusters. Assertions drawn for each group are ambiguous for a few HSS having low confidence in classification. Our analysis identifies distinct kinds of HSS with varying confidence and provides novel insight into their physical and evolutionary properties.

[38]  arXiv:2003.05794 [pdf, other]
Title: The wind-driven halo in high-contrast images I: analysis from the focal plane images of SPHERE
Comments: Astronomy and Astrophysics - A&A, EDP Sciences, In press
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Context. The wind driven halo is a feature observed within the images delivered by the latest generation of ground-based instruments equipped with an extreme adaptive optics system and a coronagraphic device, such as SPHERE at the VLT. This signature appears when the atmospheric turbulence conditions are varying faster than the adaptive optics loop can correct. The wind driven halo shows as a radial extension of the point spread function along a distinct direction (sometimes referred to as the butterfly pattern). When present, it significantly limits the contrast capabilities of the instrument and prevents the extraction of signals at close separation or extended signals such as circumstellar disks. This limitation is consequential because it contaminates the data a substantial fraction of the time: about 30% of the data produced by the VLT/SPHERE instrument are affected by the wind driven halo.Aims. This paper reviews the causes of the wind driven halo and presents a method to analyze its contribution directly from the scientific images. Its effect on the raw contrast and on the final contrast after post-processing is demonstrated.Methods. We used simulations and on-sky SPHERE data to verify that the parameters extracted with our method are capable of describing the wind driven halo present in the images. We studied the temporal, spatial and spectral variation of these parameters to point out its deleterious effect on the final contrast.Results. The data driven analysis we propose does provide information to accurately describe the wind driven halo contribution in the images. This analysis justifies why this is a fundamental limitation to the final contrast performance reached.Conclusions. With the established procedure, we will analyze a large sample of data delivered by SPHERE in order to propose, in the future, post-processing techniques tailored to remove the wind driven halo.

[39]  arXiv:2003.05795 [pdf, other]
Title: Wind-Driven Transients as A Unified Model for Peculiar Events AT2018cow and iPTF14hls
Comments: 10 pages, 8 figures, submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

We propose a wind-driven model for peculiar transients, and apply the model to AT2018cow and iPTF14hls. In the wind-driven model, we assume that a continuous outflow like a stellar wind is injected from a central system. While these transients have different observational properties, this unified model can explain their photometric properties which are not reproduced by a supernova-like instantaneous explosion. Furthermore, the model predicts characteristic spectral features and evolution, which are well in line with those of AT2018cow and iPTF14hls. Despite the different observational properties, the wind model shows that they have some common features; the large mass-loss rates (up to $\sim 20M_{\odot}{\rm ~yr^{-1}}$ for AT2018cow and $\sim 30M_{\odot}{\rm ~yr^{-1}}$ for iPTF14hls), the characteristic radii of $\sim 10^{13}{\rm ~cm}$ for the launch of the wind, and the kinetic energies of $\sim 10^{51}{\rm ~erg}$. It would indicate that both may be related to events involving a red super giant (RSG), in which the RSG envelope is rapidly ejected by an event at a stellar core scale. On the other hand, the main differences are time scales and the total ejected mass. We then suggests that iPTF14hls may represent a dynamical common-envelope evolution induced by massive binary systems ($\sim 50M_{\odot}$ each). AT2018cow may be either a tidal disruption event of a low-mass RSG by a black hole (BH), or a BH-forming failed supernova.

[40]  arXiv:2003.05796 [pdf, other]
Title: Simulation of Alfven wave propagation in magnetic chromosphere with radiative loss: effects of non-linear mode coupling on chromospheric heating
Comments: Accepted by ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We perform magnetohydrodynamic (MHD) simulations to investigate the propagation of Alfven wave in magnetic chromosphere. We use the 1.5-dimensional expanding flux tube geometry setting and transverse perturbation at the bottom to generate the Alfven wave. Compared with previous studies, our expansion is that we include the radiative loss term introduced by Carlsson & Leenaarts (2012). We find that when an observation based transverse wave generator is applied, the spatial distribution of the time-averaged radiative loss profile in our simulation is consistent with that in the classic atmospheric model. In addition, the energy flux in the corona is larger than the required value for coronal heating in the quiet region. Our study shows that the Alfven wave driven model has the potential to explain chromospheric heating and transport enough energy to the corona simultaneously.

[41]  arXiv:2003.05827 [pdf, other]
Title: Leveraging the Mathematics of Shape for Solar Magnetic Eruption Prediction
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Instrumentation and Methods for Astrophysics (astro-ph.IM)

Current operational forecasts of solar eruptions are made by human experts using a combination of qualitative shape-based classification systems and historical data about flaring frequencies. In the past decade, there has been a great deal of interest in crafting machine-learning (ML) flare-prediction methods to extract underlying patterns from a training set---e.g., a set of solar magnetogram images, each characterized by features derived from the magnetic field and labeled as to whether it was an eruption precursor. These patterns, captured by various methods (neural nets, support vector machines, etc.), can then be used to classify new images. A major challenge with any ML method is the \textit{featurization} of the data: pre-processing the raw images to extract higher-level properties, such as characteristics of the magnetic field, that can streamline the training and use of these methods. It is key to choose features that are informative, from the standpoint of the task at hand. To date, the majority of ML-based solar eruption methods have used physics-based magnetic and electric field features such as the total unsigned magnetic flux, the gradients of the fields, the vertical current density, etc. In this paper, we extend the relevant feature set to include characteristics of the magnetic field that are based purely on the geometry and topology of 2D magnetogram images and show that this improves the prediction accuracy of a neural-net based flare-prediction method.

[42]  arXiv:2003.05844 [pdf, other]
Title: On Stellar Evolution In A Neutrino Hertzsprung-Russell Diagram
Comments: 11 pages, 5 figures, accepted for publication in the astrophysical journal
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

We explore the evolution of a select grid of solar metallicity stellar models from their pre-main sequence phase to near their final fates in a neutrino Hertzsprung-Russell diagram, where the neutrino luminosity replaces the traditional photon luminosity. Using a calibrated \MESA\ solar model for the solar neutrino luminosity ($L_{\nu,\odot}$ = 0.02398 $\cdot$ $L_{\gamma,\odot}$ = 9.1795 $\times$ 10$^{31}$ erg s$^{-1}$) as a normalization, we identify $\simeq$ 0.3 MeV electron neutrino emission from helium burning during the helium flash (peak $L_{\nu} / L_{\nu,\odot} \simeq$ 10$^4$, flux $\Phi_{\nu, {\rm He \ flash}} \simeq$ 170 (10 pc/$d$)$^{2}$ cm$^{-2}$ s$^{-1}$ for a star located at a distance of $d$ parsec, timescale $\simeq$ 3 days) and the thermal pulse (peak $L_{\nu} / L_{\nu,\odot} \simeq$ 10$^9$, flux $\Phi_{\nu, {\rm TP}} \simeq$ 1.7$\times$10$^7$ (10 pc/$d$)$^{2}$ cm$^{-2}$ s$^{-1}$, timescale $\simeq$ 0.1 yr) phases of evolution in low mass stars as potential probes for stellar neutrino astronomy. We also delineate the contribution of neutrinos from nuclear reactions and thermal processes to the total neutrino loss along the stellar tracks in a neutrino Hertzsprung-Russell diagram. We find, broadly but with exceptions, that neutrinos from nuclear reactions dominate whenever hydrogen and helium burn, and that neutrinos from thermal processes dominate otherwise.

[43]  arXiv:2003.05859 [pdf, other]
Title: An ionised bubble powered by a proto-cluster at z = 6.5
Comments: 5 pages, 1 figure; MNRAS Letter, Accepted
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We show herein that a proto-cluster of Ly$\alpha$ emitting galaxies, spectroscopically confirmed at redshift 6.5, produces a remarkable number of ionising continuum photons. We start from the Ly$\alpha$ fluxes measured in the spectra of the sources detected spectroscopically. From these fluxes we derive the ionising emissivity of continuum photons of the proto-cluster, which we compare with the ionising emissivity required to reionise the proto-cluster volume. We find that the sources in the proto-cluster are capable of ionising a large bubble, indeed larger than the volume occupied by the proto-cluster. For various calculations we have used the model AMIGA, in particular to derive the emissivity of the Lyman continuum photons required to maintain the observed volume ionised. Besides, we have assumed the ionising photons escape fraction given by AMIGA at this redshift.

[44]  arXiv:2003.05902 [pdf, other]
Title: Dust evolution across the Horsehead Nebula
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Micro-physical processes on interstellar dust surfaces are tightly connected to dust properties (i.e. dust composition, size and shape) and play a key role in numerous phenomena in the interstellar medium (ISM). The large disparity in physical conditions (i.e. density, gas temperature) in the ISM triggers an evolution of dust properties. The analysis of how dust evolves with the physical conditions is a stepping-stone towards a more thorough understanding of interstellar dust. The aim of this paper is to highlight dust evolution in the Horsehead Nebula PDR region. We use Spitzer/IRAC (3.6, 4.5, 5.8 and 8 {\mu}m), Spitzer/MIPS (24 {\mu}m) together with Herschel/PACS (70 and 160 {\mu}m) and Herschel/SPIRE (250, 350 and 500 {\mu}m) to map the spatial distribution of dust in the Horsehead over the entire emission spectral range. We model dust emission and scattering using the THEMIS interstellar dust model together with the 3D radiative transfer code SOC. We find that the nano-grains dust-to-gas ratio in the irradiated outer part of the Horsehead is 6 to 10 times lower than in the diffuse ISM. Their minimum size is 2 to 2.25 times larger than in the diffuse ISM and the power-law exponent of their size distribution, 1.1 to 1.4 times lower than in the diffuse ISM. Regarding the denser part of the Horsehead, it is necessary to use evolved grains (i.e. aggregates, with or without an ice mantle). It is not possible to explain the observations using grains from the diffuse medium. We therefore propose the following scenario to explain our results. In the outer part of the Horsehead, all the nano-grains have not yet had time to re-form completely through photo-fragmentation of aggregates and the smallest of the nano-grains that are sensitive to the radiation field are photo-destroyed. In the inner part of the Horsehead, grains most likely consist of multi-compositional, mantled aggregates.

[45]  arXiv:2003.05911 [pdf, other]
Title: A hint on the metal-free star formation rate density from 21cm-EDGES data
Comments: Submitted to MNRAS
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

We aim to provide the first data-constrained estimate of the metal-free (Population III; Pop III) star formation rate density $\dot{\rho}_{*}^{III}$ required at high-redshifts ($z \gtrsim 16$) in order to reproduce both the amplitude and the redshift of the EDGES 21-cm global signal. Our model accounts for the Lyman Alpha (Ly$\alpha$), radio and X-ray backgrounds from both Pop III and metal-enriched Population II (Pop II) stars. For the latter, we use the star formation rate density estimates (and the Ly$\alpha$ background) from the {\it Delphi} semi-analytic model that has been shown to reproduce all key observables for galaxies at $z \gtrsim 5$; the radio and X-ray backgrounds are fixed using low-$z$ values. The constraints on the free parameters characterizing the properties of the Pop III stars are obtained using a Markov Chain Monte Carlo analysis. Our results yield a $\dot{\rho}_{*}^{III}$ that whilst increasing from $z \sim 21-16$ thereafter shows a sharp decline which is in excellent agreement with the results found by \citet{valiante2016} to simulate the growth of $z \sim 6 - 7$ quasars and their host galaxies, suggesting that the bulk of Pop III star formation occurs in the rarest and most massive metal-poor halos at $z \lesssim 20$. This allows Pop III stars to produce a rapidly growing Ly$\alpha$ background between $z \sim 21-15$. Further, Pop III stars are required to provide a radio background that is about $3-4$ orders of magnitude higher than that provided by Pop II stars although Pop II stars dominate the X-ray background.

[46]  arXiv:2003.05927 [pdf, other]
Title: $N$-body simulations for parametrised modified gravity
Comments: 11 pages, 3 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

We present $\texttt{MG-evolution}$, an $N$-body code simulating the cosmological structure formation for parametrised modifications of gravity. It is built from the combination of parametrised linear theory with a parametrisation of the deeply nonlinear cosmological regime extrapolated from modified spherical collapse computations that cover the range of known screening mechanisms. We test $\texttt {MG-evolution}$, which runs at the speed of conventional $\Lambda$CDM simulations, against a suit of existing exact model-specific codes, encompassing linearised and chameleon $f(R)$ gravity as well as the normal branch of the Dvali-Gabadadz-Porrati braneworld model, hence covering both large-field value and large-derivative screening effects. We compare the nonlinear power spectra produced by the parametrised and model-specific approaches over the full range of scales set by the box size and resolution of our simulations, $k=(0.05-2.5)$~h/Mpc, and for two redshift slices, $z=0$ and $z=1$. We find sub-percent to one-percent level recovery of all the power spectra generated with the model-specific codes for the full range of scales. $\texttt {MG-evolution}$ can be used for generalised and accurate tests of gravity and dark energy with the increasing wealth of high-precision cosmological survey data becoming available over the next decade.

[47]  arXiv:2003.05932 [pdf, other]
Title: Three Short Period Jupiters from TESS
Comments: Submitted to A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We report the confirmation and mass determination of three hot Jupiters discovered by the Transiting Exoplanet Survey Satellite (TESS) mission: HIP 65Ab (TOI-129, TIC-201248411) is an ultra-short-period Jupiter orbiting a bright (V=11.1 mag) K4-dwarf every 0.98 days. It is a massive 3.213 +/- 0.078 Mjup planet in a grazing transit configuration with impact parameter b = 1.17 +0.10/-0.08. As a result the radius is poorly constrained, 2.03 +0.61/-0.49 Rjup. We perform a full phase-curve analysis of the TESS data and detect both illumination- and ellipsoidal variations as well as Doppler boosting. HIP 65A is part of a binary stellar system, with HIP 65B separated by 269 AU (3.95 arcsec on sky). TOI-157b (TIC 140691463) is a typical hot Jupiter with a mass 1.18 +/- 0.13 Mjup and radius 1.29 +/- 0.02 Rjup. It has a period of 2.08 days, which corresponds to a separation of just 0.03 AU. This makes TOI-157 an interesting system, as the host star is an evolved G9 sub-giant star (V=12.7). TOI-169b (TIC 183120439) is a bloated Jupiter orbiting a V=12.4 G-type star. It has a mass of 0.79 +/- 0.06 Mjup and radius 1.09 +0.08/-0.05 Rjup. Despite having the longest orbital period (P=2.26 days) of the three planets, TOI-169b receives the most irradiation and is situated on the edge of the Neptune desert. All three host stars are metal rich with Fe/H ranging from 0.18 - 0.24.

[48]  arXiv:2003.05934 [pdf, ps, other]
Title: Unified simulations of planetary formation and atmospheric evolution: Effects of pebble accretion, giant impacts, and stellar irradiations on super-Earth formation
Comments: 17 pages, 10 figures, accepted for publication in ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

A substantial number of super-Earths have been discovered, and atmospheres of transiting super-Earths have also been observed by transmission spectroscopy. Several lines of observational evidence indicate that most super-Earths do not possess massive H$_2$/He atmospheres. However, accretion and retention of less massive atmospheres on super-Earths challenge planet formation theory. We consider the following three mechanisms: (i) envelope heating by pebble accretion, (ii) mass loss during giant impacts, and (iii) atmospheric loss by stellar X-ray and EUV photoevaporation. We investigate whether these mechanisms influence the amount of the atmospheres that form around super-Earths. We develop a code combining an N-body simulation of pebble-driven planetary formation and an atmospheric evolution simulation. We demonstrate that the observed orbital properties of super-Earths are well reproduced by the results of our simulations. However, (i) heating by pebble accretion ceases prior to disk dispersal, (ii) the frequency of giant impact events is too low to sculpt massive atmospheres, and (iii) many super-Earths having H$_2$/He atmospheres of $\gtrsim 10$ wt% survive against stellar irradiations for 1 Gyr. Therefore, it is likely that other mechanisms such as suppression of gas accretion are required to explain less massive atmospheres ($\lesssim 10$ wt%) of super-Earths.

Cross-lists for Fri, 13 Mar 20

[49]  arXiv:2003.05318 (cross-list from gr-qc) [pdf, other]
Title: Positivity bounds on reconstructed Horndeski models
Comments: 11 pages, 3 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

Positivity bounds provide conditions that a consistent UV-completion exists for a quantum field theory. We examine their application to Horndeski gravity models reconstructed from the effective field theory (EFT) of dark energy. This enables us to assess whether particular phenomenological parameterizations of the EFT functions reconstruct theories that respect or violate the positivity bounds. We find that commonly adopted EFT parametrizations, cast in terms of the dark energy density or power laws of the scale factor, only satisfy the positivity bounds in non-trivial regions of the parameter space. We then examine parameterizations of the inherently stable EFT basis, constructed to avoid gradient and ghost instabilities by default. In stark contrast, in this basis the positivity bounds either only provide constraints in a-priori unrealistic regions of the parameter space or do not provide any constraints on parameter values at all. The application of positivity bounds to common parametrizations of the standard EFT functions can therefore lead to artificial conclusions that the region of viable Horndeski modifications of gravity is highly constrained. Our results provide a strong motivation, in addition to the default avoidance of theoretical instabilities, for instead adopting parametrizations of the inherently stable EFT basis when testing dark energy and modified gravity models with forthcoming cosmological survey data.

[50]  arXiv:2003.05657 (cross-list from gr-qc) [pdf, other]
Title: Dynamics of Viscous Phantom Universe
Comments: 14 pages, 6 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The phantom dark energy remarkably boosts our prehension of the accerlerating Universe. In the phantom Universe without bulk viscosity, the models are warmly discussed. In order to generalize the model, we should study it further by considering viscous fluid in the Universe. In this paper, we investigate a class of phantom dark energy models with bulk viscosity by the method of dynamical analysis technique. We show that there are different cosmic late-time behavior and the stability also brings some constraints on the models. We also show that the viscous phantom Universe admit the tracking attractor solution. We find that the viscosity play an important role in the evolution of Universe, the viscosity is big enough, the late time transition from matter dominated to phantom dominated would be different from that of the phantom Universe without viscosity.

[51]  arXiv:2003.05784 (cross-list from gr-qc) [pdf, other]
Title: Fractional Gravity and Modified Newtonian Dynamics
Comments: 23 pages, including 4 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); Astrophysics of Galaxies (astro-ph.GA)

This paper introduces a possible alternative model of gravity based on fractional calculus and its applications to Newtonian gravity. In particular, Gauss's law for gravity as well as Laplace's equation and other fundamental classical laws are extended to a $D$-dimensional metric space, where $D$ can be a non-integer dimension. We show a possible connection between this Newtonian Fractional Gravity (NFG) and Modified Newtonian Dynamics (MOND), the leading alternative gravity model, which accounts for the observed properties of galaxies and other astrophysical structures without requiring the dark matter hypothesis. The MOND acceleration constant $a_{0} \simeq 1.2 \times 10^{ -10}\mbox{m}\thinspace \mbox{s}^{ -2}$ can be related to a natural scale length $l_{0}$ in NFG, i.e., $a_{0} \approx GM/l_{0}^{2}$, for astrophysical structures of mass $M$, and the deep-MOND regime is present in regions of space where the dimension is reduced to $D \approx 2$. For several fundamental spherically-symmetric structures, we compare MOND results such as the empirical Radial Acceleration Relation (RAR), circular speed plots, and logarithmic plots of the observed radial acceleration $g_{obs}$ vs. the baryonic radial acceleration $g_{bar}$, showing that NFG is capable of reproducing these results using a variable local dimension $D\left (w\right )$, where $w =r/l_{0}$ is a dimensionless radial coordinate. At the moment, we are unable to derive explicitly this dimension function $D\left (w\right )$ from first principles, but it can be obtained empirically in each case from the general RAR. Additional work on the subject, including studies of axially-symmetric structures, detailed galactic rotation curves fitting, and a possible relativistic extension, will be needed to establish NFG as a viable alternative model of gravity.

[52]  arXiv:2003.05883 (cross-list from hep-th) [pdf, other]
Title: Multipoint correlators in multifield cosmology
Comments: 30 pages, 7 figures
Subjects: High Energy Physics - Theory (hep-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

Connected $N$-point amplitudes in quantum field theory are enhanced by a factor of $N!$ in appropriate regimes of kinematics and couplings, but the non-perturbative analysis of this for collider physics applications is subtle. We resolve this question for $N$-point correlation functions of cosmological perturbations in multifield inflation, and comment on its application to primordial non-Gaussianity. We find that they are calculably $N!$-enhanced using a simple model for the mixing of the field sectors which leads to a convolution of their probability distributions. This effect leads to model-dependent but interesting prospects for enhanced observational sensitivity.

[53]  arXiv:2003.05931 (cross-list from gr-qc) [pdf, other]
Title: Effects of Gravitational Chern-Simons during Axion-SU(2) Inflation
Comments: 15 pages, 4 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

In this paper, we examine the viability of inflation models with a spectator axion field coupled to both gravitational and SU(2) gauge fields via Chern-Simons couplings. Requiring phenomenological success of the axion-SU(2) sector constrains the coupling strength of the gravitational Chern-Simons term. We find that the impact of this term on the production and propagation of gravitational waves can be as large as fifty percent enhancement for the helicity that is not sourced by the gauge field, if the cut-off scale is as low as {\Lambda} = 20H. The effect becomes smaller for a larger value of {\Lambda}, while the impact on the helicity sourced by the gauge field is negligible regardless of {\Lambda}.

Replacements for Fri, 13 Mar 20

[54]  arXiv:1610.07783 (replaced) [pdf, ps, other]
Title: GMRT observations of IC 711 -- The longest head-tail radio galaxy known
Comments: 15 pages. 12 figures, 3 tables, accepted in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)
[55]  arXiv:1806.02505 (replaced) [pdf, ps, other]
Title: Torsion driven Inflationary Magnetogenesis
Comments: 18 pages no figures, major changes
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
[56]  arXiv:1812.02002 (replaced) [pdf, other]
Title: Equation of state effects in core-collapse supernovae
Comments: 6 pages, 4 figures, minor changes, published version
Journal-ref: Phys. Rev. Lett. 124, 092701 (2020)
Subjects: Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Experiment (nucl-ex)
[57]  arXiv:1904.03201 (replaced) [pdf, other]
Title: Halo Spin from Primordial Inner Motions
Authors: Mark C. Neyrinck (Ikerbasque, UPV Bilbao), Miguel A. Aragon-Calvo (UNAM, Ensenada), Bridget Falck, Alexander S. Szalay (JHU), Jie Wang (NAO, Beijing)
Comments: Accepted to OJA (Open Journal of Astrophysics). 3 movies at this https URL
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)
[58]  arXiv:1905.12212 (replaced) [pdf, other]
Title: Solar System Tests of a New Class of $f(z)$ Theory
Comments: 15 pages, 2 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
[59]  arXiv:1907.03790 (replaced) [pdf, other]
Title: Sub-radian-accuracy gravitational waves from coalescing binary neutron stars II: Systematic study on the equation of state, binary mass, and mass ratio
Comments: 26 pages, 23 figures, to be appeared in PRD. See this http URL for waveform data
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc)
[60]  arXiv:1907.07662 (replaced) [pdf, other]
Title: Stellar cooling anomalies and variant axion models
Comments: 38 pages, 7 figures; revised version of the manuscript, accepted for publication in JCAP
Journal-ref: JCAP03(2020)007
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Solar and Stellar Astrophysics (astro-ph.SR)
[61]  arXiv:1909.10288 (replaced) [pdf, other]
Title: Physics of radiation mediated shocks and its applications to GRBs, supernovae, and neutron star mergers
Comments: Invited review, Physics Reports
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[62]  arXiv:1911.08550 (replaced) [pdf, other]
Title: MeV-GeV $γ$-ray telescopes probing gravitino LSP with coexisting axino NLSP as dark matter in the $μν$SSM
Comments: Discussions expanded, references added, 20 pages, 4 figures. The analysis of the opposite case (axino LSP with gravitino NLSP) was carried out in arXiv:1911.03191
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE)
[63]  arXiv:1912.07616 (replaced) [pdf, other]
Title: Environmental effects in GW physics: tidal deformability of black holes immersed in matter
Comments: 13 pages, 1 figure; v2: minor edits. To appear in Physical Review D
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Theory (hep-th)
[64]  arXiv:2001.02708 (replaced) [pdf, other]
Title: Hints of gamma-ray orbital variability from gamma^2 Velorum
Comments: 7 pages, 6 figures. Accepted by A&A
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[65]  arXiv:2001.05962 (replaced) [pdf, other]
Title: Improving geometric and dynamical constraints on cosmology with intrinsic alignments of galaxies
Comments: 6 pages, 4 figures, updated to match version published in ApJL
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[66]  arXiv:2001.08786 (replaced) [pdf, ps, other]
Title: The orbital clusters among the near Earth asteroids
Authors: Tadeusz J. Jopek
Comments: 14 pages, 19 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
[67]  arXiv:2002.08847 (replaced) [pdf]
Title: Potassium Isotopic Compositions of Enstatite Meteorites
Comments: 46 pages, 7 figures, 2 tables, published in Meteoritics & Planetary Science
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
[68]  arXiv:2002.12600 (replaced) [pdf, other]
Title: 2MASS J15460752-6258042: a mid-M dwarf hosting a prolonged accretion disc
Comments: 7 pages, 6 figures, Accepted for publication in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
[69]  arXiv:2003.00148 (replaced) [pdf, other]
Title: Entering the Era of Dark Matter Astronomy? Near to Long-Term Forecasts in X-Ray and Gamma-Ray Bands
Comments: 18 pages, 12 figures, 1 table. Estimate for eXTP S/N revised, typo on Athena exposure corrected, text improved
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)
[70]  arXiv:2003.02690 (replaced) [pdf, other]
Title: Addressing $H_0$ tension with emergent dark radiation in unitary gravity
Comments: 32 pages, 5 figures, 2 tables. In `Introduction': updated journal info in ref. [64], added SH0ES ref. [12] and amended reference to H0LiCOW
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[71]  arXiv:2003.03059 (replaced) [pdf, ps, other]
Title: Magnetic filed structure of the Galactic plane from differential analysis of interstellar polarization
Comments: 32 pages, 17 figures, accepted in PASJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)
[72]  arXiv:2003.04644 (replaced) [pdf, ps, other]
Title: Periodic Fast Radio Bursts as a Probe of Extragalactic Asteroid Belts
Comments: 5 pages in emulateapj format, 3 figures, a few typos corrected
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[73]  arXiv:2003.04872 (replaced) [pdf, ps, other]
Title: Modelling the He I triplet absorption at 10830 Angstroms in the atmosphere of HD 209458 b
Comments: Accepted to A&A. 15 Pages, 15 figures and 3 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
[74]  arXiv:2003.05354 (replaced) [pdf, other]
Title: Atmospheric compositions and observability of nitrogen dominated ultra-short period super-Earths
Comments: Accepted for publication MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
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