### 55 articles on Wednesday, June 26

arXiv:1906.10126v1 [pdf, other]
Evidence for Sub-Chandrasekhar Type Ia Supernovae from Stellar Abundances in Dwarf Galaxies
Comments: Accepted to ApJ on 2019 June 22. 21 pages, 9 figures. This is a companion paper to arXiv:1906:08284. Figure 6 presents the main result

There is no consensus on the progenitors of Type Ia supernovae (SNe Ia) despite their importance for cosmology and chemical evolution. We address this question by using our previously published catalogs of Mg, Si, Ca, Cr, Fe, Co, and Ni abundances in dwarf galaxy satellites of the Milky Way to constrain the mass at which the white dwarf explodes during a typical SN Ia. We fit a simple bi-linear model to the evolution of [X/Fe] with [Fe/H], where X represents each of the elements mentioned above. We use the evolution of [Mg/Fe] coupled with theoretical supernova yields to isolate what fraction of the elements originated in SNe Ia. Then, we infer the [X/Fe] yield of SNe Ia for all of the elements except Mg. We compare these observationally inferred yields to recent theoretical predictions for two classes of Chandrasekhar-mass (M_Ch) SN Ia as well as sub-M_Ch SNe Ia. Most of the inferred SN Ia yields are consistent with all of the theoretical models, but [Ni/Fe] is consistent only with sub-M_Ch models. We conclude that the dominant type of SN Ia in ancient dwarf galaxies is the explosion of a sub-M_Ch white dwarf. The Milky Way and dwarf galaxies with extended star formation histories have higher [Ni/Fe] abundances, which could indicate that the dominant class of SN Ia is different for galaxies where star formation lasted for at least several Gyr.

arXiv:1906.10128v1 [pdf, other]
Discovery of an equal-mass "twin'' binary population reaching 1000+ AU separations
Comments: 24 pages, 16 figures, plus appendices. Submitted to MNRAS. Comments welcome

We use a homogeneous catalog of 42,000 main-sequence wide binaries identified by Gaia to measure the mass ratio distribution, p(q), of binaries with primary masses $0.1 < M_1/M_{\odot} < 2.5$, mass ratios $0.1 < q < 1$, and separations $50 <s/{\rm AU} < 50,000$. A well-understood selection function allows us to constrain p(q) in 35 independent bins of primary mass and separation, with hundreds to thousands of binaries in each bin. Our investigation reveals a sharp excess of equal-mass ''twin'' binaries that is statistically significant out to separations of 1,000 to 10,000 AU, depending on primary mass. The excess is narrow: a steep increase in p(q) at $0.95 \lesssim q < 1$, with no significant excess at $q\lesssim 0.95$. A range of tests confirm that the signal is real, not a data artifact or selection effect. Combining the Gaia wide binary constraints with those from close binaries, we show that the twin excess decreases with increasing separation, but its width ($q\gtrsim 0.95$) is constant over $0.01 < a/{\rm AU} < 10,000$. The wide twin population would be difficult to explain if the components of all wide binaries formed via core fragmentation, which is not expected to produce strongly correlated component masses. We conjecture that twin wide binaries formed at closer separations (a < 100 AU), likely via accretion from circumbinary disks, and were subsequently widened by dynamical interactions in their birth environments. The separation-dependence of the twin excess then constrains the efficiency of dynamical widening and disruption of binaries in young clusters. We also constrain p(q) across $0.1 \lesssim q < 1$. Besides changes in the twin fraction, p(q) is independent of separation at fixed primary mass over 100 < s/AU < 50,000. It is flatter than expected for random pairings from the IMF but more bottom-heavy for wide binaries than for binaries with a < 100 AU.

arXiv:1906.10129v1 [pdf, other]
The geometry of the gas surrounding the Central Molecular Zone: on the origin of localised molecular clouds with extreme velocity dispersions
Comments: 12 pages, 10 figures. Movies of the simulation are available at the link provided in the Supplementary Information section

Observations of molecular gas near the Galactic centre ($| l | < 10^\circ$, $| b | < 1^\circ$) reveal the presence of a distinct population of enigmatic compact clouds which are characterised by extreme velocity dispersions ($\Delta v > 100\, \rm km/s$). These Extended Velocity Features (EVFs) are very prominent in the datacubes and dominate the kinematics of molecular gas just outside the Central Molecular Zone (CMZ). The prototypical example of such a cloud is Bania Clump 2. We show that similar features are naturally produced in simulations of gas flow in a realistic barred potential. We analyse the structure of the features obtained in the simulations and use this to interpret the observations. We find that the features arise from collisions between material that has been infalling rapidly along the dust lanes of the Milky Way bar and material that belongs to one of the following two categories: (i) material that has 'overshot' after falling down the dust lanes on the opposite side; (ii) material which is part of the CMZ. Both types of collisions involve gas with large differences in the line-of-sight velocities, which is what produces the observed extreme velocity dispersions. Examples of both categories can be identified in the observations. If our interpretation is correct, we are directly witnessing (a) collisions of clouds with relative speeds of $\sim 200\, \rm km/s$ and (b) the process of accretion of fresh gas onto the CMZ.

arXiv:1906.10130v1 [pdf, other]
Evidence for Low Radiative Efficiency or Highly Obscured Growth of $z>7$ Quasars
Comments: 11 pages, 5+2 figures, submitted to ApJ Letters

The supermassive black holes (SMBHs) observed at the centers of all massive galaxies are believed to have grown via luminous accretion during quasar phases in the distant past. The fraction of inflowing rest mass energy emitted as light, the radiative efficiency, has been inferred to be 10\%, in agreement with expectations from thin disk accretion models. But the existence of billion solar-mass SMBHs powering quasars at $z > 7$ challenges this picture: provided they respect the Eddington limit, there is not enough time to grow $z>7$ SMBHs from stellar remnant seeds unless the radiative efficiency is below 10\%. Here we show that one can constrain the radiative efficiencies of the most distant quasars known using foreground neutral intergalactic gas as a cosmological-scale ionizing photon counter. From the Ly$\alpha$ absorption profiles of ULAS J1120+0641 ($z=7.09$) and ULAS J1342+0928 ($z=7.54$), we determine posterior median radiative efficiencies of 0.08\% and 0.1\%, respectively, and the combination of the two measurements rule out the canonical 10\% efficiency at 99.8\% credibility after marginalizing over the unknown obscured fraction. This low radiative efficiency implies rapid mass accretion for the earliest SMBHs, greatly easing the tension between the age of the Universe and the SMBH masses. However, our measured efficiency may instead reflect nearly complete obscuration by dusty gas in the quasar host galaxies over the vast majority of their SMBH growth. Assuming 10\% efficiency during unobscured phases, we find that the obscured fraction would be $>82\%$ at 95\% credibility, and imply a $25.7^{+49.6}_{-16.5}$ times larger obscured than unobscured luminous quasar population at $z>7$.

arXiv:1906.10134v1 [pdf, other]
CMB-HD: An Ultra-Deep, High-Resolution Millimeter-Wave Survey Over Half the Sky
Comments: Draft APC White Paper for the Astro2020 Decadal. If you would like to join the proposing team, please email the primary contact by June 30th

A millimeter-wave survey over half the sky, that spans frequencies in the range of 30 to 350 GHz, and that is both an order of magnitude deeper and of higher-resolution than currently funded surveys would yield an enormous gain in understanding of both fundamental physics and astrophysics. By providing such a deep, high-resolution millimeter-wave survey (about 0.5 uK-arcmin noise and 15 arcsecond resolution at 150 GHz), CMB-HD will enable major advances. It will allow 1) the use of gravitational lensing of the primordial microwave background to map the distribution of matter on small scales (k~10/hMpc), which probes dark matter particle properties. It will also allow 2) measurements of the thermal and kinetic Sunyaev-Zel'dovich effects on small scales to map the gas density and gas pressure profiles of halos over a wide field, which probes galaxy evolution and cluster astrophysics. In addition, CMB-HD would allow us to cross critical thresholds in fundamental physics: 3) ruling out or detecting any new, light (< 0.1eV), thermal particles, which could potentially be the dark matter, and 4) testing a wide class of multi-field models that could explain an epoch of inflation in the early Universe. Such a survey would also 5) monitor the transient sky by mapping the full observing region every few days, which opens a new window on gamma-ray bursts, novae, fast radio bursts, and variable active galactic nuclei. Moreover, CMB-HD would 6) provide a census of planets, dwarf planets, and asteroids in the outer Solar System, and 7) enable the detection of exo-Oort clouds around other solar systems, shedding light on planet formation. CMB-HD will deliver this survey in 5 years of observing half the sky, using two new 30-meter-class off-axis cross-Dragone telescopes to be located at Cerro Toco in the Atacama Desert. The telescopes will field about 2.4 million detectors (600,000 pixels) in total.

arXiv:1906.10135v1 [pdf, other]
The $Iκεα$ model of feedback-regulated galaxy formation

We present the $I\kappa\epsilon\alpha$ model of galaxy formation, in which a galaxy's star formation rate is set by the balance between energy injected by feedback from massive stars and energy lost by the deepening of the potential of its host dark matter halo due to cosmological accretion. Such a balance is secularly stable provided that the star formation rate increases with the pressure in the star forming gas. The $I\kappa\epsilon\alpha$ model has four parameters that together control the feedback from star formation and the cosmological accretion rate onto a halo. $I\kappa\epsilon\alpha$ reproduces accurately the star formation rate as a function of halo mass and redshift in the EAGLE hydrodynamical simulation, even when all four parameters are held constant. It predicts the emergence of a star forming main sequence along which the specific star formation rate depends weakly on stellar mass with an amplitude that increases rapidly with redshift. We briefly discuss the emerging mass-metallicity relation, the evolution of the galaxy stellar mass function, and an extension of the model that includes feedback from active galactic nuclei (AGN). These self-regulation results are independent of the star formation law and the galaxy's gas content. Instead, star forming galaxies are shaped by the balance between stellar feedback and cosmological accretion, with accurately accounting for energy losses associated with feedback a crucial ingredient.

arXiv:1906.10136v1 [pdf, other]
Hints of Sterile Neutrinos in Recent Measurements of the Hubble Parameter

Local Universe observations find a value of the Hubble constant $H_0$ that is larger than the value inferred from the Cosmic Microwave Background and other early Universe measurements, assuming known physics and the $\Lambda$CDM cosmological model. We show that additional radiation in active neutrinos produced just before Big Bang Nucleosynthesis by an unstable sterile neutrino with mass $m_s=$ O(10) MeV can alleviate this discrepancy. The necessary masses and couplings of the sterile neutrino, assuming it mixes primarily with $\nu_{\tau}$ and/or $\nu_{\mu}$ neutrinos, are within reach of Super-Kamiokande as well as upcoming laboratory experiments such as NA62.

arXiv:1906.10138v1 [pdf, other]
The Sloan Digital Sky Survey Reverberation Mapping Project: Accretion and Broad Emission Line Physics from a Hypervariable Quasar
Comments: 14 pages, 8 figures, submitted to AAS journals

We analyze extensive spectroscopic and photometric data of the hypervariable quasar SDSS J131424+530527 (RMID 017) at z=0.456, an optical "changing look" quasar from the Sloan Digital Sky Survey Reverberation Mapping project that increased in optical luminosity by a factor of 10 between 2014 and 2017. The observed broad emission lines all respond in luminosity and width to the changing optical continuum, as expected for photoionization in a stratified, virialized broad emission line region. The luminosity changes therefore result from intrinsic changes in accretion power rather than variable obscuration. The variability is continuous and apparently stochastic, disfavoring an origin as a discrete event such as a tidal disruption flare or microlensing event. It is coordinated on day timescales with blue leading red, consistent with reprocessing powering the entire optical SED. We show that this process cannot work in a standard thin disk geometry on energetic grounds, and would instead require a large covering factor reprocessor. Disk instability models could potentially also explain the data, provided that the instability sets in near the inner radius of a geometrically thick accretion disk.

arXiv:1906.10142v1 [pdf, other]
The cosmological distribution of compact object mergers from dynamical interactions with SMBH binaries

We combine sophisticated high precision scattering experiments, together with results from the Millenium-II simulation, to compute the cosmic merger rate of bound compact object (CO) binaries dynamically interacting with supermassive black hole binaries (SMBHBs). We consider binaries composed of white dwarfs (WDs), neutron stars (NSs) and black holes (BHs). The overall merger rates for WD-WD, NS-NS, BH-BH, BH-NS binaries and EBBH (eccentric binaries of black holes) from redshift $\sim 5$ are found to be $4.32\times 10^3\,\yr^{-1}$($5.93\times10^2\,\yr^{-1}$ for Type Ia SNe), $82.7\,\yr^{-1}$, $96.3\,\yr^{-1}$, $13.1\,\yr^{-1}$ and $148\,\yr^{-1}$ , respectively, {for a nominal CO binary fraction in the Galactic centre of 0.1.} We calculate the distance ($R$) distribution of the merger sites with respect to the host galaxies of the binaries. The distribution shows a wide range of distances up to $\sim \mpc$; this tail is produced by escaped hyper-velocity CO binaries. Due to the differences in the matter density of the surrounding environment, merger events with different $R$ are expected to display significantly different signatures in their EM counterparts. In particular, merger events (and especially NS-NS) producing a relativistic jet but occurring in the intergalactic medium will have very weak afterglow radiation relative to their prompt emission. These events, which we call 'off-center', can only be produced from a close encounter between CO binaries and SMBHBs; hence the detection of such merger events would indicate the existence of nearby SMBHBs, and in particular with high mass ratio, produced in the aftermath of a major galaxy merger.

arXiv:1906.10143v1 [pdf, other]
Three-Dimensional Boltzmann-Hydro Code for core-collapse in massive stars III. A New method for momentum feedback from neutrino to matter

We present a new method for neutrino-matter coupling in multi-dimensional radiation-hydrodynamic simulations of core-collapse supernova (CCSN) with the full Boltzmann neutrino transport. The development is motivated by the fact that the accurate conservation of momentum is required for reliable numerical modelings of CCSN dynamics including a recoil of proto-neutron star (PNS). The new method is built on a hybrid approach, in which we use the energy-momentum tensor of neutrinos to compute the momentum feedback from neutrino to matter in the optically thick region while we employ the collision term in the optically thin region. In this method we utilize a general relativistic description of radiation-hydrodynamics with angular moments, which allows us to evaluate the momentum feedback from neutrino to matter without inconsistency with our Boltzmann solver. We demonstrate that the new method substantially improves the accuracy of linear momentum conservation in our CCSN simulations under reasonable angular resolutions in momentum space, alleviating the difficulty in giving the diffusion limit precisely with the discrete ordinate (Sn) method. It is the first-ever demonstration that the PNS kick can be handled directly and properly in multi-dimensional radiation-hydrodynamic simulations with the full Boltzmann neutrino transport.

arXiv:1906.10147v1 [pdf, other]
Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M Dwarf System at 6.9 Parsecs
Comments: Submitted to AJ; 21 pages, 8 tables, 7 figures

We present the discovery from TESS data of LTT 1445Ab. At a distance of 6.9 parsecs, it is the second nearest transiting exoplanet system found to date, and the closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use follow-up observations from MEarth and the centroid offset analysis in the TESS data validation report to determine that the planet transits the primary star in the system. The planet has a radius 1.35 R_Earth, an orbital period of 5.35882 days, and an equilibrium temperature of 428 K. With radial velocities from HARPS, we place a three-sigma upper mass limit of 8.4 M_Earth on the candidate. The planet provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. The presence of stellar companions of similar spectral type may facilitate such ground-based studies by providing a calibration source to remove telluric variations. In addition, we present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicates a moderate amount of variability, in agreement with the observed low-level, short-term variability in the TESS light curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system raises the possibility that the entire system is co-planar, which implies that the system may have formed from the early fragmentation of an individual protostellar core.

arXiv:1906.10151v1 [pdf, other]
Galactic Rotation Based on OB Stars from the Gaia DR2 Catalogue
Comments: 14 pages, 2 tables, 4 figures. arXiv admin note: substantial text overlap with arXiv:1903.09313, arXiv:1904.12686, arXiv:1809.10512, arXiv:1609.08341

We have studied a sample containing about 6000 OB stars with proper motions and trigonometric parallaxes from the Gaia DR2 catalogue. The following parameters of the angular velocity of Galactic rotation have been found: $\Omega_0=29.70\pm0.11$ km s$^{-1}$ kpc$^{-1}$, $\Omega'_0=-4.035\pm0.031$ km s$^{-1}$ kpc$^{-2}$, and $\Omega''_0= 0.620\pm0.014$ km s$^{-1}$ kpc$^{-3}$. The circular rotation velocity of the solar neighborhood around the Galactic center is $V_0=238\pm5$ km s$^{-1}$ for the adopted Galactocentric distance of the Sun $R_0=8.0\pm0.15$ kpc. The amplitudes of the tangential and radial velocity perturbations produced by the spiral density wave are $f_\theta=4.4\pm1.4$ km s$^{-1}$ and $f_R=5.1\pm1.2$ km s$^{-1}$, respectively; the perturbation wavelengths are $\lambda_\theta=1.9\pm0.5$ kpc and $\lambda_R=2.1\pm0.5$ kpc for the adopted four-armed spiral pattern. The Sun's phase in the spiral density wave is $\chi_\odot=-178^\circ\pm12^\circ$.

arXiv:1906.10195v1 [pdf, other]
Secular and Rotational Light Curves of 6478 Gault
Comments: 23 pages, 10 Figures, 6 Tables

We obtained 877 images of active asteroid 6478 Gault on 41 nights from January 10th to June 8th, 2019, using several telescopes. We created the phase, secular and rotational light curves of Gault, from which several physical parameters can be derived. From the phase plot we find that no phase effect was evident. This implies that an optically thick cloud of dust surrounded the nucleus hiding the surface. The secular light curve (SLC) shows several zones of activity the origin of which is speculative. From the SLC plots a robust absolute magnitude can be derived and we find mV(1,1,alpha) = 16.11+-0.05. We also found a rotational period Prot = 3.360+-0.005 h and show evidence that 6478 might be double. The parameters of the pair are derived. Previous works have concluded that 6478 is in a state of rotational disruption and the above rotational period supports this result. Our conclusion is that 6478 Gault is a suffocated comet getting rid of its suffocation by expelling surface dust into space using the centrifugal force. This is an evolutionary stage in the lifetime of some comets. Besides being a MBC the object is classified as a methuselah Lazarus comet.

arXiv:1906.10201v1 [pdf, other]
The 2019 July 2 Total Solar Eclipse: Prediction of the Coronal Magnetic Field Structure and Polarization Characteristics
Comments: 18 Pages, 4 Figures, Submitted

On 2019 July 2 a total solar eclipse -- visible across some parts of the Southern Pacific Ocean, Chile and Argentina -- will enable observations of the Sun's large-scale coronal structure. The structure of the Sun's corona and their emission characteristics are determined by underlying magnetic fields which also govern coronal heating and solar eruptive events. However, coronal magnetic field measurements remain an outstanding challenge. Computational models of coronal magnetic fields serve an important purpose in this context. Earlier work has demonstrated that the large-scale coronal field is governed by slow surface flux evolution and memory build-up which allows for prediction of the coronal structure on solar rotational timescales. Utilizing this idea and based upon a 51 day forward run of a data-driven solar surface flux transport model and a Potential Field Source Surface model, we predict the Sun's coronal structure for the 2019 July 2 solar eclipse. We also forward model the polarization characteristics of the coronal emission from the predicted magnetic fields. We predict two large-scale streamer structures and their locations on the east and west limbs of the Sun and discuss the possibility of development of a pseudo-streamer based on an analysis of field line topology. This study is relevant for coronal magnetometry initiatives from ground-based facilities such as the Daniel K. Inouye Solar Telescope and Coronal Multichannel Polarimeter, and upcoming space-based instruments such as the Solar Ultraviolet Imaging Telescope and the Variable Emission Line Coronagraph onboard ISRO's Aditya-L1 space mission.

arXiv:1906.10212v1 [pdf, other]
Multi-Messenger Astrophysics
Comments: Manuscript version as originally submitted on March 31, 2019, to appear in revised and extended form in Nature Physics Review, 2019; 22 pages, 9 figures

Multi-messenger astrophysics, a long-anticipated extension to traditional and multiwavelength astronomy, has recently emerged as a distinct discipline providing unique and valuable insights into the properties and processes of the physical universe. These insights arise from the inherently complementary information carried by photons, gravitational waves, neutrinos, and cosmic rays about individual cosmic sources and source populations. Realizing the observation of astrophysical sources via non-photonic messengers has presented enormous challenges, as evidenced by the fiscal and physical scales of the multi-messenger observatories. However, the scientific payoff has already been substantial, with even greater rewards promised in the years ahead. In this review we survey the current status of multi-messenger astrophysics, highlighting some exciting recent results, and addressing the major follow-on questions they have raised. Key recent achievements include the measurement of the spectrum of ultra-high energy cosmic rays out to the highest observable energies; discovery of the diffuse high energy neutrino background; the first direct detections of gravitational waves and the use of gravitational waves to characterize merging black holes and neutron stars in strong-field gravity; and the identification of the first joint electromagnetic + gravitational wave and electromagnetic + high-energy neutrino multi-messenger sources. We then review the rationales for the next generation of multi-messenger observatories, and outline a vision of the most likely future directions for this exciting and rapidly advancing field.

arXiv:1906.10216v1 [pdf, other]
First light demonstration of the integrated superconducting spectrometer

Ultra-wideband 3D imaging spectrometry in the millimeter-submillimeter (mm-submm) band is an essential tool for uncovering the dust-enshrouded portion of the cosmic history of star formation and galaxy evolution. However, it is challenging to scale up conventional coherent heterodyne receivers or free-space diffraction techniques to sufficient bandwidths ($\geq$1 octave) and numbers of spatial pixels (>$10^2$). Here we present the design and first astronomical spectra of an intrinsically scalable, integrated superconducting spectrometer, which covers 332-377 GHz with a spectral resolution of $F/\Delta F \sim 380$. It combines the multiplexing advantage of microwave kinetic inductance detectors (MKIDs) with planar superconducting filters for dispersing the signal in a single, small superconducting integrated circuit. We demonstrate the two key applications for an instrument of this type: as an efficient redshift machine, and as a fast multi-line spectral mapper of extended areas. The line detection sensitivity is in excellent agreement with the instrument design and laboratory performance, reaching the atmospheric foreground photon noise limit on sky. The design can be scaled to bandwidths in excess of an octave, spectral resolution up to a few thousand and frequencies up to $\sim$1.1 THz. The miniature chip footprint of a few $\mathrm{cm^2}$ allows for compact multi-pixel spectral imagers, which would enable spectroscopic direct imaging and large volume spectroscopic surveys that are several orders of magnitude faster than what is currently possible.

arXiv:1906.10218v1 [pdf, other]
Cosmological constraints on post-Newtonian parameters in effectively massless scalar-tensor theories of gravity
Comments: 16 pages, 24 figures, 2 tables

We study the cosmological constraints on the variation of the Newton's constant and on post-Newtonian parameters for simple models of scalar-tensor theory of gravity beyond the extended Jordan-Brans-Dicke theory. We restrict ourselves to an effectively massless scalar field with a potential $V \propto F^2$, where $F(\sigma)=N_{pl}^2+\xi\sigma^2$ is the coupling to the Ricci scalar considered. We derive the theoretical predictions for cosmic microwave background (CMB) anisotropies and matter power spectra by requiring that the effective gravitational strength at present is compatible with the one measured in a Cavendish-like experiment and by assuming adiabatic initial condition for scalar fluctuations. When comparing these models with $Planck$ 2015 and a compilation of baryonic acoustic oscilation (BAO) data, all these models accomodate a marginalized value for $H_0$ higher than in $\Lambda$CDM. We find no evidence for a statistically significant deviation from Einstein's general relativity. We find $\xi < 0.064$ ($|\xi| < 0.011$) at 95 % CL for $\xi > 0$ (for $\xi < 0$, $\xi \ne -1/6$). In terms of post-Newtonian parameters, we find $0.995 < \gamma_{\rm PN} < 1$ and $0.99987 < \beta_{\rm PN} < 1$ ($0.997 < \gamma_{\rm PN} < 1$ and $1 < \beta_{\rm PN} < 1.000011$) for $\xi >0$ (for $\xi < 0$). For the particular case of the conformal coupling, i.e. $\xi=-1/6$, we find constraints on the post-Newtonian parameters of similar precision to those within the Solar System.

arXiv:1906.10234v1 [pdf, other]
The full evolution of supernova remnants in low and high density ambient media
Comments: 14 pages, 12 figures, to be published in MNRAS

Supernova explosions and their remnants (SNRs) drive important feedback mechanisms that impact considerably the galaxies that host them. Then, the knowledge of the SNRs evolution is of paramount importance in the understanding of the structure of the interstellar medium (ISM) and the formation and evolution of galaxies. Here we study the evolution of SNRs in homogeneous ambient media from the initial, ejecta-dominated phase, to the final, momentum-dominated stage. The numerical model is based on the Thin-Shell approximation and takes into account the configuration of the ejected gas and radiative cooling. It accurately reproduces well known analytic and numerical results and allows one to study the SNR evolution in ambient media with a wide range of densities $n_{0}$. It is shown that in the high density cases, strong radiative cooling alters noticeably the shock dynamics and inhibits the Sedov-Taylor stage, thus limiting significantly the feedback that SNRs provide to such environments. For $n_{0}>5 \times 10^{5}$ cm$^{-3}$, the reverse shock does not reach the center of the explosion due to the rapid fall of the thermal pressure in the shocked gas caused by strong radiative cooling.

arXiv:1906.10249v1 [pdf, other]
Ionization Mechanisms in Quasar Outflows
Comments: 20 pages, 23 figures, accepted for publication in ApJ

The various ionization mechanisms at play in active galactic nuclei (AGN) and quasars have been well studied, but relatively little has been done to separately investigate the contributions of these ionization mechanisms within the host galaxy and outflowing components. Using Gemini integral field spectroscopy (IFS) data, we study the ionization properties of these two components in four nearby ($z \lesssim$ 0.2) radio-quiet Type 1 quasars. Emission line ratios and widths are employed to identify the dominant ionization mechanisms for the host and outflow components in each object. We find that photoionization by the AGN often dominates the ionization of both gaseous components in these systems. In three cases, the outflowing gas is more highly ionized than the gas in the host, indicating that it is more strongly exposed to the ionizing radiation field of the AGN. In two objects, a positive correlation between the line widths and line ratios in the outflowing gas component indicates that shocks with velocities of order 100 $-$ 500 km s$^{-1}$ may also be contributing to the ionization and heating of the outflowing gas component. The line ratios in the outflowing gas of one of these two objects also suggest a significant contribution from photoionization by hot, young stars in the portion of the outflow that is closest to star-forming regions in the host galaxy component. The data thus favor photoionization by hot stars in the host galaxy rather than stars formed in the outflow itself.

arXiv:1906.10260v1 [pdf, other]
Black Holes: The Next Generation

When two black holes merge in a dense star cluster, they form a new black hole with a well-defined mass and spin. If that "second-generation" black hole remains in the cluster, it will continue to participate in dynamical encounters, form binaries, and potentially merge again. Using a grid of 96 dynamical models of dense star clusters and a cosmological model of cluster formation, we explore the production of binary black hole mergers where at least one component of the binary was forged in a previous merger. We create four hypothetical universes where every black hole born in the collapse of a massive star has a dimensionless Kerr spin parameter, $\chi_{\rm birth}$, of 0.0, 0.1, 0.2, or 0.5. We show that if all stellar-born black holes are non-spinning ($\chi_{\rm birth} = 0.0$), then more than 10% of merging binary black holes from clusters have components formed from previous mergers, accounting for more than 20% of the mergers from globular clusters detectable by LIGO/Virgo. Furthermore, nearly 7% of detectable mergers would have a component with a mass $\gtrsim 55M_{\odot}$, placing them clearly in the mass "gap" region where black holes cannot form from isolated collapsing stars due to the pulsational-pair instability mechanism. On the other hand, if black holes are born spinning, then the contribution from these second-generation mergers decreases, making up as little as 1% of all detections from globular clusters when $\chi_{\rm birth} = 0.5$. We make quantitative predictions for the detected masses, mass ratios, and spin properties of first- and second-generation mergers from dense star clusters, and show how these distributions are highly sensitive to the birth spins of black holes.

arXiv:1906.10285v1 [pdf, other]
Observations of a Pre-Merger Shock in Colliding Clusters of Galaxies

Clusters of galaxies are the largest known gravitationally-bound structures in the Universe. When clusters collide, they create merger shocks on cosmological scales, which transform most of the kinetic energy carried by the cluster gaseous halos into heat. Observations of merger shocks provide key information of the merger dynamics, and enable insights into the formation and thermal history of the large-scale structures. Nearly all of the merger shocks are found in systems where the clusters have already collided, knowledge of shocks in the pre-merger phase is a crucial missing ingredient. Here we report on the discovery of a unique shock in a cluster pair 1E 2216 and 1E 2215. The two clusters are observed at an early phase of major merger. Contrary to all the known merger shocks observed ubiquitously on merger axes, the new shock propagates outward along the equatorial plane of the merger. This discovery uncovers an important epoch in the formation of massive clusters, when the rapid approach of the cluster pair leads to strong compression of gas along the merger axis. Current theoretical models predict that the bulk of the shock energy might be dissipated outside the clusters, and eventually turn into heat of the pristine gas in the circum-cluster space.

arXiv:1906.10294v1 [pdf, other]
Estimating the Fuel Supply Rate on the Galactic Disk from High Velocity Clouds (HVCs) Infall

Previous studies suggest that the estimated maximum accretion rate from approaching high velocity clouds (HVCs) on the Galactic disk can be up to ~ 0.4 solar mass per year. In this study, we point out that the hydrodynamic interaction between the HVCs and the Galactic disk is not considered in the traditional method of estimating the infall rate and therefore the true supply rate of fuel from HVCs can be different from the suggested value depending on the physical configurations of HVCs including density, velocity, and distance. We choose 11 HVC complexes and construct 4 different infall models in our simulations to give an idea of how the fuel supply rate could be different from the traditional infall rate. Our simulation results show that the fuel supply rate from HVC infall is overestimated in the traditional method and can be lowered by a factor of ~ 0.072 when the hydrodynamic interaction of the HVC complexes and the disk is considered.

arXiv:1906.10302v1 [pdf, other]
Rapid Particle Acceleration due to Re-collimation in Injected Jets with Helical Magnetic Fields
Comments: 8 pages, 5 figures, submitted to ApJL, movie will be added if possible (dBtotByz11MF_011.mp4 5.8MB)

One of the key open questions in the study of relativistic jets is how magnetic reconnection occurs and whether it can effectively accelerate the jet's electrons. We investigate the evolution of an electron-proton relativistic jet containing helical magnetic fields, focusing on the interaction with the ambient plasma. We have performed 3D particle-in-cell (PIC) simulations of a jet containing a relatively large radius with embedded helical magnetic fields, in order to examine how the helical magnetic field excites kinetic instabilities such as the Weibel instability (WI), the kinetic Kelvin-Helmholtz instability (kKHI) and the mushroom instability (MI). In our simulations these kinetic instabilities are indeed excited and particles are accelerated. We observe a recollimation-like instability near the center of the jet at the linear stage. As the electron-proton jet evolves, the helical magnetic field becomes untangled due to a reconnection-like phenomena at the end of nonlinear stage, and electrons are further accelerated by multiple magnetic reconnection events/sites within the turbulent magnetic field.

arXiv:1906.10316v1 [pdf, other]
Constraining light fermionic dark matter with binary pulsars
Comments: 11 pages, 3 figures. Accepted for publication in Physics of the Dark Universe

A binary system embedded in a Dark Matter (DM) background may experience a change in its orbital period due to dynamical friction as the binary moves through a wind of DM particles. We compute such a perturbative effect on the binary evolution considering that DM is constituted of degenerate gas of free fermions. The analysis point out that the secular change of the orbital period is more sensitive, and likely measurable, to degenerate fermions with masses $\gtrsim50$ eV, depending slightly, but still being distinguishable, on the binary star configuration (e.g. NS-NS, NS-WD and WD-WD). Interestingly, we find that NS-NS binary systems with large orbital periods, $P_{b}\gtrsim100$ days, experience larger orbital period decays. We also show that this effect is clearly increased, under the former conditions, in binaries orbiting small DM halos, which correspond to extragalactic pulsars. This situation represents the best astrophysical scenario to test such effects of light fermionic DM. We use some available measurements of the orbital period time-derivative for long-period binaries in the Milky-Way to quantify more realistically this effect. For instance, measurements of the J1713+0747 pulsar set an upper bound on the fermion mass of $m_{f}\lesssim 1$ keV. This bound can be considerably improved by using pulsar timing observations of extragalactic pulsars. Under this perspective, high precision of timing pulsar observations will reveal whether DM dynamical friction effect may be tested with the upcoming generation of surveys leading to the possibility of constraining more strongly the properties of light fermionic DM.

arXiv:1906.10330v1 [pdf, other]
Thermal Tides in Rotating Hot Jupiters

We calculate tidal torque due to semi-diurnal thermal tides in rotating hot Jupiters, taking account of the effects of radiative cooling in the envelope and of the planets rotation on the tidal responses. We use a simple Jovian model composed of a nearly isentropic convective core and a thin radiative envelope. To represent the tidal responses of rotating planets, we employ series expansions in terms of spherical harmonic functions $Y_l^m$ with different $l$s for a given $m$. For low forcing frequency, there occurs frequency resonance between the forcing and the $g$- and $r$-modes in the envelope and inertial modes in the core. We find that the resonance enhances the tidal torque, and that the resonance with the $g$- and $r$-modes produces broad peaks and that with the inertial modes very sharp peaks, depending on the magnitude of the non-adiabatic effects associated with the oscillation modes. We also find that the behavior of the tidal torque as a function of the forcing frequency (or period) is different between prograde and retrograde forcing, particularly for long forcing periods because the $r$-modes, which have long periods, exist only on the retrograde side.

arXiv:1906.10353v1 [pdf, other]
On the relation between transition region network jets and coronal plumes
Comments: The preprint of an article accepted for publication in Solar Physics

Both coronal plumes and network jets are rooted in network lanes. The relationship between the two, however, has yet to be addressed. For this purpose, we perform an observational analysis using images acquired with the Atmospheric Imaging Assembly (AIA) 171{\AA} passband to follow the evolution of coronal plumes, the observations taken by the Interface Region Imaging Spectrograph (IRIS) slit-jaw 1330{\AA} to study the network jets, and the line-of-sight magnetograms taken by the Helioseismic and Magnetic Imager (HMI) to overview the the photospheric magnetic features in the regions. Four regions in the network lanes are identified, and labeled ''R1--R4''. We find that coronal plumes are clearly seen only in ''R1''&''R2'' but not in ''R3''&''R4'', even though network jets abound in all these regions. Furthermore, while magnetic features in all these regions are dominated by positive polarity, they are more compact (suggesting stronger convergence) in ''R1''&''R2'' than that in ''R3''&''R4''. We develop an automated method to identify and track the network jets in the regions. We find that the network jets rooted in ''R1''&''R2'' are higher and faster than that in ''R3''&''R4'',indicating that network regions producing stronger coronal plumes also tend to produce more dynamic network jets. We suggest that the stronger convergence in ''R1''&''R2'' might provide a condition for faster shocks and/or more small-scale magnetic reconnection events that power more dynamic network jets and coronal plumes.

arXiv:1906.10359v1 [pdf, other]
Including massive neutrinos in thermal Sunyaev Zeldovich power spectrum and cluster counts analyses

We consistently include the effect of massive neutrinos in the thermal Sunyaev Zeldovich (SZ) power spectrum and cluster counts analyses, highlighting subtle dependencies on the parameterisation and data combination. In $\Lambda$CDM, with an X-ray mass bias corresponding the expected hydrostatic mass bias, i.e., $b\simeq0.2$, our constraints from Planck SZ data are consistent with the latest results from SPT, DES-Y1 and KiDS+VIKING-450. In $\nu\Lambda$CDM, without prior information on $b$, our joint analyses of Planck SZ with Planck 2015 primary CMB yield a small improvement on the total neutrino mass bound compared to the Planck 2015 primary CMB constraint, as well as $(1-b)=0.64\pm0.04$~(68\%~CL). For forecasts, we find that a combination of a mock cosmic variance limited SZ power spectrum with primary CMB and BAO can improve the uncertainty on the total neutrino mass by 14\% with respect to CMB combined with BAO. This requires masking the heaviest clusters and probing the small-scale SZ power spectrum up to multipoles of $\ell_\mathrm{max}=10^4$. For a future competitive measurement of the total neutrino mass using CMB and the SZ power spectrum, but excluding BAO and lensing power spectrum, we find that a 1\% precision on the mass calibration is needed. Although SZ power spectrum-based measurements of the neutrino masses are challenging, we find that the SZ power spectrum can be used to tightly constrain intra-cluster medium properties.

arXiv:1906.10361v1 [pdf, other]
On Fabry Pérot Etalon based Instruments. II. The Anisotropic (Birefringent) Case

Crystalline etalons present several advantages with respect to other types of filtergraphs when employed in magnetographs. Specially that they can be tuned by only applying electric fields. However, anisotropic crystalline etalons can also introduce undesired birefringent effects that corrupt the polarization of the incoming light. In particular, uniaxial Fabry-P\'erots, such as LiNbO3 etalons, are birefringent when illuminated with an oblique beam. The farther the incidence from the normal, the larger the induced retardance between the two orthogonal polarization states. The application of high-voltages, as well as fabrication defects, can also change the direction of the optical axis of the crystal, introducing birefringence even at normal illumination. Here we obtain analytical expressions for the induced retardance and for the Mueller matrix of uniaxial etalons located in both collimated and telecentric configurations. We also evaluate the polarimetric behavior of Z-cut crystalline etalons with the incident angle, with the orientation of the optical axis, and with the f-number of the incident beam for the telecentric case. We study artificial signals produced in the output Stokes vector in the two configurations. Last, we discuss the polarimetric dependence of the imaging response of the etalon for both collimated and telecentric setups.

arXiv:1906.10381v1 [pdf, other]
General solutions of the leakage in integral transforms and applications to the EB-leakage and detection of the cosmological gravitational waves
Comments: 17 pages, 6 figures, 2 appendices

For an orthogonal integral transform with complete dataset, any two components are linearly independent; however, when some data points are missing, there is going to be leakage from one component to another, which is referred to as the ''leakage in integral transforms'' in this work. A special case of this kind of leakage is the EB-leakage in detection of the cosmological gravitational waves (CGW). We first give the general solutions for all integral transforms, prove that they are the best solutions, and then apply them to the case of EB-leakage and detection of the CGW. In the upcoming decade, all cosmic microwave background (CMB) experiments are ground based, so they provide only partial sky coverage. Within this context, the EB-leakage becomes inevitable. We show how to use the general solutions to achieve the minimal error bars of the EB-leakage, and use it to find out the maximal ability to detect the CGW through CMB. The results show that $1\%$ sky coverage ($f_{sky}=1\%$) is enough for a $5\sigma$-detection of $r\ge 10^{-2}$, but is barely enough for $r=10^{-3}$. If the target is to detect $r\sim 10^{-4}$ or $10^{-5}$, then $f_{sky}\ge 10\%$ or higher is strongly recommended to enable a $5\sigma$-detection and to reserve some room for other errors.

arXiv:1906.10421v1 [pdf, other]
An inspirational Toy Model for the Missing Mass Problem on Galactic Scales

In this study a simple toy model solution to the missing mass problem on galactic scales is reverse engineered from galactic data via imposing broad assumptions. It is shown that the toy model solution can be written in terms of baryonic quantities, that it is highly similar to pseudo-isothermal dark matter on galactic scales and can accommodate the same observations (on galactic scales). In this way the toy model solution is similar to MOND modified gravity in the Bekenstein-Milgrom formulation. However, where it differs is in the similarity to pseudo-isothermal dark matter and in the functional form. In loose terms it is shown that pseudo-isothermal dark matter can be written in terms of baryonic quantities and on a form that suggest it may be worth looking into a mechanism that can increase the magnitude of the post-Newtonian correction from general relativity for low accelerations.

arXiv:1906.10425v1 [pdf, other]
Towards the Tunka-Rex Virtual Observatory
Comments: Proceedings of the 3rd International Workshop on Data Life Cycle in Physics, Irkutsk, Russia, April 2-7, 2019

The Tunka Radio Extension (Tunka-Rex) is a cosmic-ray detector operating since 2012. The detection principle of Tunka-Rex is based on the radio technique, which impacts data acquisition and storage. In this paper we give a first detailed overview of the concept of the Tunka-Rex Virtual Observatory (TRVO), a framework for open access to the Tunka-Rex data, which currently is under active development and testing. We describe the structure of the data, main features of the interface and possible applications of the TRVO.

arXiv:1906.10426v1 [pdf, other]
Searches for TeV gamma-ray counterparts to Gravitational Wave events with H.E.S.S
Comments: Proceedings of the 12th INTEGRAL conference and 1st AHEAD Gamma-ray Workshop, Geneva (Switzerland), 11-15 February 2019, Ed. C. Ferrigno, E. Bozzo, P. von Balmoos

The search for electromagnetic counterparts for gravitational waves events is one of the main topics of multi-messenger Astrophysics. Among these searches is the one for high energy gamma-ray emission with the H.E.S.S. Imaging Atmospheric Cherenkov Telescopes in Namibia. During their second Observation Run O2, the Advanced Virgo detector in Italy and the two advanced LIGO detectors in Washington and Louisiana while conducting joint observations, detected for the first time, on August $14^{th}$, 2017 a transient GW signal due to the coalescence of two stellar masses black holes, an event labeled GW170814. The alert announcing the event was issued two hours later and H.E.S.S. observations could be scheduled for the nights of $16^{th}$, $17^{th}$ and $18^{th}$ August 2017. Three days after the binary BH merger, on August $17^{th}$, the coalescence of two neutron star was detected for the first time, followed by a GRB detection by Fermi's GBM starting a new era in multi-messenger Astronomy. Observations started 5.3 h after the merge and contained the counterpart SSS17a that was identified several hours later. It stands as the first data obtained by a ground-based pointing instrument on this object. In this contribution, we will present the results of the search of high-energy gamma ray emission as electromagnetic counterpart of these two GW events. No significant gamma ray emission was detected for either event. Nevertheless upper limit maps were derived constraining, for the first time, the non-thermal, high-energy emission on the remnant of a three detector binary black hole coalescence (GW170814), and a binary neutron star coalescence (GW170817).

arXiv:1906.10435v1 [pdf, other]
Probing the ionosphere by the pulsar B0950+08 with help of RadioAstron ground-space baselines

The ionospheric scattering of pulses emitted by PSR B0950+08 is studied with help of the 10-m {\it Space Radio Telescope} in conjunction with the 300-m Arecibo Radio Telescope and 14x25-m Westerbork Synthesis Radio Telescope at the frequency band from 316 to 332 MHz. We analyse this phenomenon based on a simulation model of the phase difference obtained between the widely-separated antennas of nearly 25 Earth's diameters. We represent the technique for processing and analysing ionospheric total electron content (TEC) at the ground station of the ground-space interferometer. This method allowed us to derive almost synchronous half-hour time structures of TEC in the ionosphere at the intercontinental distance between Arecibo and Westerbork. We find that amplitude values of the detected structures are approximately two times larger than the values of TEC from the International Reference Ionosphere (IRI) project. Furthermore, derived TEC outside these structures are almost the same as TEC from IRI. According to a preliminary analysis, the detected structures could be due to the influence of interplanetary and magnetospheric phenomena on ionospheric disturbances. We show that the space Very Long Baseline Interferometry provides us a new opportunities to study TEC, and we demonstrate the capabilities of this instrument to research the ionosphere.

arXiv:1906.10438v1 [pdf, other]
Thermal X-ray emission identified from the millisecond pulsar PSR J1909-3744
Comments: 5 pages, 4 figures, accepted for publication in A&A

Pulsating thermal X-ray emission from millisecond pulsars can be used to obtain constraints on the neutron star equation of state, but to date only five such sources have been identified. Of these five millisecond pulsars, only two have well constrained neutron star masses, which improve the determination of the radius via modelling of the X-ray waveform. We aim to find other millisecond pulsars that already have well constrained mass and distance measurements that show pulsed thermal X-ray emission in order to obtain tight constraints on the neutron star equation of state. The millisecond pulsar PSR~J1909--3744 has an accurately determined mass, M = 1.54$\pm$0.03 M$_\odot$ (1 $\sigma$ error) and distance, D = 1.07$\pm$0.04 kpc. We analysed {\em XMM-Newton} data of this 2.95 ms pulsar to identify the nature of the X-ray emission. We show that the X-ray emission from PSR~J1909--3744 appears to be dominated by thermal emission from the polar cap. Only a single component model is required to fit the data. The black-body temperature of this emission is kT=0.26\ud{0.03}{0.02} keV and we find a 0.2--10 keV un-absorbed flux of 1.1 $\times$ 10$^{-14}$ erg cm$^{-2}$ s$^{-1}$ or an un-absorbed luminosity of 1.5 $\times$ 10$^{30}$ erg s$^{-1}$. Thanks to the previously determined mass and distance constraints of the neutron star PSR~J1909--3744, and its predominantly thermal emission, deep observations of this object with future X-ray facilities should provide useful constraints on the neutron star equation of state.

arXiv:1906.10455v1 [pdf, other]
The XXL Survey: XLII. Scatters and correlations of X-ray proxies in the bright XXL cluster sample
Comments: 19 pages, in press on Astronomy and Astrophysics

Context. Scaling relations between cluster properties embody the formation and evolution of cosmic structure. Intrinsic scatters and correlations between X-ray properties are determined from merger history, baryonic processes, and dynamical state. Aims. We look for an unbiased measurement of the scatter covariance matrix between the three main X-ray observable quantities attainable in large X-ray surveys -- temperature, luminosity, and gas mass. This also gives us the cluster property with the lowest conditional intrinsic scatter at fixed mass. Methods. Intrinsic scatters and correlations can be measured under the assumption that the observable properties of the intra-cluster medium hosted in clusters are log-normally distributed around power-law scaling relations. The proposed method is self-consistent, based on minimal assumptions, and requires neither the external calibration by weak lensing, dynamical, or hydrostatic masses nor the knowledge of the mass completeness. Results. We analyzed the 100 brightest clusters detected in the XXL Survey and their X-ray properties measured within a fixed radius of 300 kpc. The gas mass is the less scattered proxy (~8%). The temperature (~20%) is intrinsically less scattered than the luminosity (~30%) but it is measured with a larger observational uncertainty. We found some evidence that gas mass, temperature and luminosity are positively correlated. Time-evolutions are in agreement with the self-similar scenario, but the luminosity-temperature and the gas mass-temperature relations are steeper. Conclusions. Positive correlations between X-ray properties can be determined by the dynamical state and the merger history of the halos. The slopes of the scaling relations are affected by radiative processes.

arXiv:1906.10463v1 [pdf, other]
Constraining primordial black holes in dark matter with kinematics of dwarf galaxies
Comments: 6 pages, 4 figures, and 1 table. Accepted by PRD. Comments are welcome

We propose that the kinematical observations of dwarf galaxies can be used to constrain the primordial black hole's (PBH) abundance in dark matter since the presence of primordial black holes in star clusters will lead to the radial velocity dispersion of the system. For instance, using the velocity dispersion observations from Leo I we show that the primordial black hole fraction $f_{\rm PBH}\gtrsim 2.0\times(1~M_{\odot}/m_{\rm PBH})^2$ is ruled out at a 99.99\% confidence level. This method yields the most stringent limits on the PBH abundance at the mass scales $\sim (1-10^3)~M_{\odot}$ and tightly constrains the primordial origin of gravitational wave events observed by the LIGO experiments.

arXiv:1906.10479v1 [pdf, other]
Conversion of Tycho-2 to Johnson-Cousins Magnitudes in the Gaia Era

We take advantage of the availability of precision parallax data from Gaia Data Release 2 together with machine learning to develop a set of equations for transforming Tycho-2 (VT, BT) magnitudes into the Johnson-Cousins (J-C) system. Starting with data for 558 standard stars with apparent magnitudes brighter than 11.0, we employed one step supervised learning with weight decay regularization and 10-fold cross validation to produce a set of transformation equations from Tycho-2 into J-C, which in turn were used to derive transformations of the Tycho-2 standard deviations into the J-C system. Both the aggregated cross validation data sets and the in-sample results from the final training were essentially unbiased (average errors << 1 mmag in both B and V) and had error standard deviations comparable to those of the input data. Comparison of errors in- and out-of-sample indicate modest generalization error growth. Moreover, testing of the distributions of the normalized errors indicated that the predicted standard deviations are accurate, enabling them to be reliably employed in the suitability ranking of comparison star candidates. These results thus enable utilization of a substantial portion of the 2.5 million star Tycho-2 data set as comparison stars for two-color bright star ensemble photometry.

arXiv:1906.10492v1 [pdf, other]
The spectroscopic binaries RV Tauri and DF Cygni

Aim: The focus of this paper is on two famous but still poorly understood RV Tauri stars: RV Tau and DF Cyg. We aim at confirming their suspected binary nature and deriving their orbital elements to investigate the impact of their orbits on the evolution of these systems. This research is embedded into a wider endeavour to study binary evolution of low- and intermediate-mass stars. Method: The high amplitude pulsations were cleaned from the radial-velocity data to better constrain the orbital motion. We used Gaia DR2 parallaxes in combination with the SEDs to compute their luminosities which were complemented with the ones computed using a period-luminosity-colour relation. The ratio of the circumstellar infrared flux to the photospheric flux obtained from the SEDs was used to estimate the orbital inclination of each system. Results: DF Cyg and RV Tau are binaries with spectroscopic orbital periods of 784$\pm$16 days and 1198$\pm$17 days, respectively. These orbital periods are found to be similar to the long-term periodic variability in the photometric time series, indicating that binarity indeed explains the long-term photometric variability. Both systems are surrounded by a circumbinary disc which is grazed by our line-of-sight. As a result, the stellar photometric flux is extinct periodically with the orbital period. Our derived orbital inclinations enabled us to obtain accurate companion masses for DF Cyg and RV Tau. Analysis of the Kepler photometry of DF Cyg revealed a power spectrum with side lobes around the fundamental pulsation frequency. This modulation corresponds to the spectroscopic orbital period and hence to the long-term photometric period. Finally we report on the evidence of high velocity absorption features related to the H$_{\alpha}$ profile in both objects, indicating outflows launched from around the companion.

arXiv:1906.10501v1 [pdf, other]
Supernovae and their host galaxies -- VI. Normal Type Ia and 91bg-like supernovae in ellipticals
Comments: 15 pages, 8 figures, 5 tables, submitted to MNRAS

With the aim to find links between the properties of supernova (SN) Ia progenitors and elliptical host stellar populations, we present an analysis of the galactocentric distributions of the "normal" and peculiar "91bg-like" subclasses of SNe Ia, and study the global parameters (absolute magnitude, colour, size, stellar mass, metallicity and age) of their host galaxies. We use a well-defined sample of morphologically non-disturbed 109 SNe Ia host ellipticals from the Sloan Digital Sky Survey. The galactocentric distributions of normal and 91bg-like SNe are consistent with each other, and with the radial light distribution of host stellar populations, when excluding bias against central SNe. Among the global parameters, only the distributions of u-r colours and ages are inconsistent significantly between the ellipticals of different SN Ia subclasses: the hosts of normal SNe are on average bluer and younger than those of 91bg-like SNe. In the colour-mass diagram, the tail of colour distribution of normal SN hosts stretches into the Green Valley - transitional state of galaxy evolution, while the same tail of 91bg-like SN hosts barely reaches that region. Therefore, the bluer and younger ellipticals might have more residual star formation that gives rise to younger "prompt" progenitors, resulting in normal SNe Ia with shorter delay times. These ellipticals can also produce "delayed" 91bg-like events with lower rate, because of long delay times of these SNe. The redder and older ellipticals that already exhausted their gas for star formation may produce significantly less normal SNe Ia with shorter delay times, outnumbered by 91bg-like SNe with long delay times. Our results favor SN Ia progenitor models such as He-ignited violent mergers as a unified model for normal and 91bg-like SNe that have the potential to explain their observed properties.

arXiv:1906.10506v1 [pdf, other]
GaussPy+: A fully automated Gaussian decomposition package for emission line spectra
Comments: Accepted for publication in A&A. 36 pages, 33 figures (main text: 23 pages, 18 figures; Appendix: 13 pages, 15 figures). The GaussPy+ package is written in Python 3 and is freely available at GitHub under https://github.com/mriener/gausspyplus

Our understanding of the dynamics of the interstellar medium is informed by the study of the detailed velocity structure of emission line observations. One approach to study the velocity structure is to decompose the spectra into individual velocity components; this leads to a description of the dataset that is significantly reduced in complexity. However, this decomposition requires full automation lest it becomes prohibitive for large datasets, such as Galactic plane surveys. We developed GaussPy+, a fully automated Gaussian decomposition package that can be applied to emission line datasets, especially large surveys of HI and isotopologues of CO. We built our package upon the existing GaussPy algorithm and significantly improved its performance for noisy data. New functionalities of GaussPy+ include: i) automated preparatory steps, such as an accurate noise estimation, which can also be used as standalone applications; ii) an improved fitting routine; iii) an automated spatial refitting routine that can add spatial coherence to the decomposition results by refitting spectra based on neighbouring fit solutions. We thoroughly tested the performance of GaussPy+ on synthetic spectra and a test field from the Galactic Ring Survey. We found that GaussPy+ can deal with cases of complex emission and even low to moderate signal-to-noise values.

arXiv:1906.10556v1 [pdf, other]
A high-mass Planetary Nebula in a Galactic Open Cluster
Comments: 22 pages, 4 figures, 3 tables. Nature Astronomy

Planetary Nebulae are the ionised ejected envelopes surrounding the remnant cores of dying stars. Theory predicts that main-sequence stars with one to about eight times the mass of our sun may eventually form planetary nebulae. Until now no example has been confirmed at the higher mass range. Here we report that planetary nebula BMP J1613-5406 is associated with Galactic star cluster NGC 6067. Stars evolving off the main sequence of this cluster have a mass around five solar masses. Confidence in the planetary nebula-cluster association comes from their tightly consistent radial velocities in a sightline with a steep velocity-distance gradient, common distances, reddening and location of the planetary nebula within the cluster boundary. This is an unprecedented example of a planetary nebular whose progenitor star mass is getting close to the theoretical lower limit of core-collapse supernova formation. It provides evidence supporting theoretical predictions that 5+ solar mass stars can form planetary nebulae. Further study should provide fresh insights into stellar and Galactic chemical evolution.

arXiv:1906.10561v1 [pdf, other]
Atmospheric Evolution on Low-Gravity Waterworlds
Comments: accepted for publication in ApJ

Low-gravity waterworlds ($M\lesssim 0.1 M_{\oplus}$) are of interest for their potential habitability. The weakly bound atmospheres of such worlds have proportionally larger radiative surfaces and are more susceptible to escape. We conduct a unified investigation into these phenomena, combining analytical energy balance and hydrodynamic escape with line-by-line radiative transfer calculations. Because outgoing radiation is forced to increase with surface temperature by the expansion of the radiative surface, we find that these worlds do not experience a runaway greenhouse. Further we show that a long-lived liquid water habitable zone is possible for low-gravity waterworlds of sufficient mass. Its inner edge is set by the rate of atmospheric escape, because a short-lived atmosphere limits the time available for life to evolve. In describing the physics of the parameter space transition from "planet-like" to "comet-like", our model produces a lower bound for habitability in terms of gravity. These results provide valuable insights in the ongoing hunt for habitable exoplanets and exomoons.

arXiv:1906.10569v1 [pdf, other]
Influence of magnetic activity on the determination of stellar parameters through asteroseismology
Comments: Paper accepted for publication in Frontiers Astronomy and Space Sciences. 24 pages and 9 figures

Magnetic activity changes the gravito-acoustic modes of solar-like stars and in particular their frequencies. There is an angular-degree dependence that is believed to be caused by the non-spherical nature of the magnetic activity in the stellar convective envelope. These changes in the mode frequencies could modify the small separation of low-degree modes (i.e. frequency difference between consecutive quadrupole and radial modes), which is sensitive to the core structure and hence to the evolutionary stage of the star. Determining global stellar parameters such as the age using mode frequencies at a given moment of the magnetic activity cycle could lead to biased results. Our estimations show that in general these errors are lower than other systematic uncertainties, but in some circumstances they can be as high as 10% in age and of a few percent in mass and radius. In addition, the frequency shifts caused by the magnetic activity are also frequency dependent. In the solar case this is a smooth function that will mostly be masked by the filtering of the so-called surface effects. However the observations of other stars suggest that there is an oscillatory component with a period close to the one corresponding to the acoustic depth of the He II zone. This could give rise to a misdetermination of some global stellar parameters, such as the helium abundance. Our computations show that the uncertainties introduced by this effect are lower than the 3% level.

arXiv:1906.10579v1 [pdf, other]
Planet formation and stability in polar circumbinary discs
Comments: 9 pages, 9 figures; accepted for publication in Astronomy & Astrophysics

Context. Dynamical studies suggest that most of the circumbinary discs (CBDs) should be coplanar, i.e. the rotation vectors of the binary and the disc are aligned. However, some theoretical works show that under certain conditions a CBD can become polar, i.e the rotation vector is orthogonal with respect to the binary orbital plane. Interestingly, very recent observations showed that polar CBDs exist in Nature (e.g. HD 98800). Aims. We test the predictions of CBD alignment around eccentric binaries based on linear theory. In particular, we compare prograde and retrograde CBD configurations. Then, we thoroughly characterise the orbital behaviour and stability of misaligned (P-type) particles. Methods. The evolution of the CBD alignment for various configurations is modelled through three-dimensional hydrodynamical simulations. For the orbital characterisation and the analysis stability, we relied on long-term N-body integrations and structure and chaos indicators, such as $\Delta e$ and MEGNO. Results. We confirm previous analytical predictions on CBD alignment, but find an unexpected symmetry breaking between prograde and retrograde configurations. More specifically, we observe polar alignment for a retrograde misaligned CBD that was expected to become coplanar with respect to the binary disc plane. Therefore, the likelihood of becoming polar for a highly misaligned CBD is higher than previously thought. Regarding the stability of circumbinary P-type planets (aka Tatooines), polar orbits are stable over a wide range of binary parameters. In particular, for binary eccentricities below 0.4, the orbits are stable for any value of the binary mass ratio. In the absence of gas, planets with masses below $10^{-5}$ $M_{\odot}$ have negligible effects on the binary orbit. Finally, we predict that Polar Tatooines should be searched around mildly eccentric equal-mass binaries.

arXiv:1906.10585v1 [pdf, other]
Observational evidence for bar formation in disk galaxies via cluster-cluster interaction
Comments: 12 pages, 3 figures, 1 supplementary information, published in Nature Astronomy

Bars are an elongated structure that extends from the centre of galaxies, and about one-third of disk galaxies are known to possess bars. These bars are thought to form either through a physical process inherent in galaxies, or through an external process such as galaxy-galaxy interactions. However, there are other plausible mechanisms of bar formation that still need to be observationally tested. Here we present the observational evidence that bars can form via cluster-cluster interaction. We examined 105 galaxy clusters at redshift $0.015 < z < 0.060$ that are selected from the Sloan Digital Sky Survey data, and identified 16 interacting clusters. We find that the barred disk-dominated galaxy fraction is about 1.5 times higher in interacting clusters than in clusters with no clear signs of ongoing interaction (42% versus 27%). Our result indicates that bars can form through a large-scale violent phenomenon, and cluster-cluster interaction should be considered an important mechanism of bar formation.

arXiv:1906.10589v1 [pdf, other]
Measuring Limb Darkening of Stars in high magnification Microlensing Events by the Finite Element Method

Very high-magnification microlensing events provide chances to measure limb darkening of distant stars. We use the Finite Element Method (FEM) as an inversion tool for discretization and inversion of the magnification-limb darkening integral equation. This method makes no explicit assumption about the shape of brightness profile more than the flatness of the profile near the centre of the stellar disk. From the simulation, we investigate the accuracy and stability of this method and we use regularization techniques to stabilize it. Finally, we apply this method to the single lens, high magnification transit events of OGLE-2004-BLG-254 ($SAAO_I$), MOA-2007-BLG-233/OGLE-2007-BLG-302 ($OGLE_I, MOA_R$), MOA-2010-BLG-436 ($MOA_R$), MOA-2011-BLG-93 ($Canopus_V$), MOA-2011-BLG-300/OGLE-2011-BLG-0990 ($Pico_I$) and MOA-2011-BLG-325/OGLE-2011-BLG-1101 ($LT_I$) in which light curves have been observed with a high cadence near the peak \citep{Ch}. The result of this analysis is almost consistent with the standard modeling of limb darkening. The advantage of FEM is to extract limb darkening of stars without any assumption about the model.

arXiv:1906.10594v1 [pdf, other]
Towards the Baikal Open Laboratory in Astroparticle Physics

The open science framework defined in the German-Russian Astroparticle Data Life Cycle Initiative (GRADLCI) has triggered educational and outreach activities at the Irkutsk State University (ISU), which is actively participated in the two major astroparticle facilities in the region: TAIGA observatory and Baikal-GVD neutrino telescope. We describe the ideas grew out of this unique environment and propose a new open science laboratory based on education and outreach as well as on the development and testing new methods and techniques for the multimessenger astronomy.

arXiv:1906.10595v1 [pdf, other]
Spectro-timing analysis of MAXI J1535-571 using AstroSat
Comments: 8 pages, 8 figures; Accepted in MNRAS

We report the results of the analysis of an AstroSat observation of the Black Hole candidate MAXI J1535-571 during its Hard Intermediate state. We studied the evolution of the spectral and timing parameters of the source during the observation. The observation covered a period of $\sim$5 days and consisted of 66 continuous segments, corresponding to individual spacecraft orbits. Each segment was analysed independently. The source count rate increased roughly linearly by $\sim$30 %. We modelled the spectra as a combination of radiation from a thermal disk component and a power-law. The timing analysis revealed the presence of strong Quasi Periodic Oscillations with centroid frequency $\nu_{\rm{QPO}}$ fluctuating in the range 1.7-3.0 Hz. We found a tight correlation between the QPO centroid frequency $\nu_{\rm{QPO}}$ and the power-law spectral index $\Gamma$, while $\nu_{\rm{QPO}}$ appeared not to be correlated with the linearly-increasing flux itself. We discuss the implications of these results on physical models of accretion.

arXiv:1906.10598v1 [pdf, other]
Phase tracking based on GPGPU and applications in Planetary radio Science

This paper introduces a phase tracking method for planetary radio science research based on GPGPU (General Purpose Computing on GPU) technology. Different from phase counting method based on phase-locked loop(PLL) Circuits applied by traditional Doppler data processing this method fits signal model expressed by Taylor series into baseband tracking data. The differential evolution(DE) algorithm is employed in polynomial fitting. Because the fitting of the original tracking data requires a large amount of calculation,We use GPGPU chips to accelerate data processing. Dual K80s graphics chips is applied in data processing and can achieve real-time data processing. The phase expression obtained by fitting is Taylor polynomial which can be used to calculate instantaneous phase,frequency,derivative of frequency and the total count phase of different integration scales. These observables can be conveniently used in planetary radio science research about planetary occultation and planetary gravity fields.

arXiv:1906.10600v1 [pdf, other]
Even-to-Odd Barium Isotope Ratio in Selected Galactic Halo Stars
Comments: 16 pages, 5 figures, and 4 tables. Published in Astron. Letters, vol. 45, p. 341-352 (2019)

We have updated the Ba II model atom by taking into account the H I impact excitation with the rate coefficients from the quantum-mechanical calculations of Belyaev and Yakovleva (2018). Using high-resolution stellar spectra and the non-local thermodynamic equilibrium (non-LTE) line formation for Ba II, we have determined the fraction of barium isotopes with an odd mass number (fodd}) in four Galactic halo giants with well-known atmospheric parameters. We use a method based on the requirement that the abundances from the Ba II 4554 A resonance and Ba II 5853, 6496 A subordinate lines be equal. An accuracy of 0.04 dex in determining the barium abundance from individual lines has been achieved. In three stars (HD 2796, HD 108317, and HD 122563) fodd >= 0.4. This suggests that >= 80 % of the barium observed in these stars was synthesized in the r-process. In HD 128279 fodd = 0.27 exceeds the fraction of odd barium isotopes in the Solar system, but only slightly. The dominance of the r-process at the formation epoch of our sample stars is confirmed by the presence of a europium overabundance relative barium, with [Eu/Ba] > 0.3. We have calculated the non-LTE abundance corrections for five Ba II lines and investigated their dependence on atmospheric parameters in the ranges of effective temperatures from 4500 to 6500 K, surface gravities log g from 0.5 to 4.5, and metallicities [Fe/H] from 0 to -3.

arXiv:1906.10617v1 [pdf, other]
Galactic Tide and Local Stellar Perturbations on the Oort Cloud: Creation of Interstellar Comets
Comments: Submitted to A&A. 13 pages, 13 figures

Comets in the Oort cloud evolve under the influence of internal and external perturbations, such as giant planets, stellar passages, and the galactic tidal field. We aim to study the dynamical evolution of the comets in the Oort cloud, accounting for external perturbations (passing stars and the galactic tide). We first construct an analytical model of stellar encounters. We find that individual perturbations do not modify the dynamics of the comets in the cloud unless very close (< 0.5pc) encounters occur. Using proper motions, parallaxes, and radial velocities from Gaia DR2, we construct an astrometric catalogue of 14,659 stars that are within 50pc from the Sun. For all these stars we calculate the time and the closest distance to the Sun. We find that the cumulative effect of relatively distant ($\leq1$ pc) passing stars can perturb the comets in the Oort cloud. Finally, we study the dynamical evolution of the comets in the Oort cloud under the influence of multiple stellar encounters within 2.5pc from the Sun and the galactic tidal field over $\pm10$Myr. We considered two models for the Oort cloud, compact (a $\leq$0.25 pc) and extended (a$\leq0.5$ pc). We find that the cumulative effect of stellar encounters is the major perturber of the Oort cloud for a compact configuration while for the extended, the galactic tide is the major perturber. In both cases, the effect of passing stars and the galactic tide raises the semi-major axis of $\sim1.1$\% of the comets at the edge of the cloud up to interstellar regions ($a >0.5$pc). This leads to the creation of transitional interstellar comets, which might become interstellar objects due to external perturbations. This raises the question about the existence of a cloud of objects in the interstellar space which might overlap with our Oort cloud if we consider that other planetary systems face similar processes for the ejection of comets.

arXiv:1906.10629v1 [pdf, other]
Optical Reddening, Integrated HI Optical Depth, Total Hydrogen Column Density

Despite the vastly different angular scales on which they are measured, the integrated $\lambda$21 cm \HI\ optical depth measured interferometrically, \WHI, is a good proxy for the optical reddening derived from IR dust emission, with %\WHI\ $\equiv \int\tau({\rm \HI}) ~{\rm dv} = (13.8\pm0.7)$\EBV$^{(1.10\pm0.03)}$ \kms\ \WHI\ $\propto$ \EBV$^{1.10}$ for 0.04 mag $\la$ \EBV\ $\la$ 4 mag. For \EBV\ $\la 0.04$ mag or \WHI\ $< 0.7$ \kms, less-absorbent warm and ionized gases assert themselves and $\tau$(HI) is a less reliable tracer of \EBV. The \WHI-\EBV\ relationship can be inverted to give a broken power-law relationship between the total hydrogen column density N(H) and \WHI\ such that knowledge of \WHI\ alone predicts N(H) with an accuracy of a factor 1.5 ($\pm 0.18$ dex) across two orders of magnitude variation of \WHI. The \WHI-N(H) relation is invariant under a linear rescaling of the reddening measure used in the analysis and does not depend on knowing properties of the HI such as the spin temperature.

arXiv:1906.10630v1 [pdf, other]
Timing Properties of Shocked Accretion Flows around Neutron Stars -- II. Viscous Disks and Boundary Layers
Comments: 5 Pages, 1 Figure. Submitted in The Astrophysical Journal on June 22, 2019

We use Smoothed Particle Hydrodynamics to study viscous accretion flows around a weakly magnetic neutron star. We show the formation of multiple ''boundary" layers in presence of both cooling and viscosity. We find that with the introduction of a small viscosity in a sub-Keplerian flow, much like the wind accretion in HMXBs such as Cir X-1, only a single Normal Boundary Layer (NBOL) forms to adjust the rotational velocity component. With the increase of viscosity, the region extends radially and beyond some critical value, a RAdiative KEplerian Disk/layer (RAKED) forms between the sub-Keplerian flow and the NBOL. When viscosity is increased further only NBOL and RAKED remain. In all such cases, the CENtrifugal pressure dominated BOundary Layer (CENBOL) is formed, away from the star, as in the case of black holes. This is the first self-consistent study where such a transition from sub-Keplerian flows has been reported for neutron stars. We also identify the connection between accretion and ejection of matter, following the Two-Component Advective Flow for black holes, for neutron stars. The results are crucial in the understanding of the formation of disks, boundary layers and outflows in wind dominated neutron star systems.

arXiv:1906.10650v1 [pdf, other]
CHANG-ES XIX: Galaxy NGC 4013 -- a diffusion-dominated radio halo with plane-parallel disk and vertical halo magnetic fields
Comments: 24 pages, 27 figures, accepted for publication in A&A

Using the Continuum HAloes in Nearby Galaxies - an EVLA Survey (CHANG-ES) radio continuum data from the Karl G. Jansky Very Large Array (VLA) in two frequency bands (C-band, L-band), we analyzed the radio properties, including polarization and the transport processes of the CR electrons (CREs), in the edge-on spiral galaxy NGC 4013. Supplementary LOw-Frequency ARray (LOFAR) data at 150MHz are used to study the low-frequency properties of this galaxy and X-ray (Chandra, XMM-Newton) data are used to investigate the central region. The central point source dominates the radio continuum in both CHANG-ES bands, but no clear AGN classification is possible at this time. The scale height analysis shows that Gaussian fits, with halo scale heights of 1.2 kpc in C-band, 2.0 kpc in L-band, and 3.1 kpc at 150 MHz, better represent the intensity profiles than do exponential fits. The radio continuum halo of NGC 4013 in C-band is rather small, while the low-frequency LOFAR data reveal a large halo. The polarization data reveal plane-parallel, regular magnetic fields within the entire disk and vertical halo components out to heights of about 6 kpc indicating the presence of an axisymmetric field having a radial component pointing outwards. The mean magnetic field strength of the disk of NGC 4013 of 6.6 $\mu$G (using the revised equipartition formula) is rather small. The interaction and the low star formation rate (SFR) across the disk of NGC 4013 probably influence the appearance of its radio continuum. Several observable quantities give consistent evidence that the CR transport in the halo of NGC 4013 is diffusive: the frequency dependence of the synchrotron scale height, the disk/halo flux density ratio, the vertical profile of the synchrotron spectral index, the small propagation speed measured modeled with spinnaker, and the low temperature of the X-ray emitting hot gas.

arXiv:1906.10660v1 [pdf, other]
UVIT view of dwarf irregular galaxy IC 2574 : Is the star formation triggered due to expanding H$~$I shells?
Comments: 19 pages, 9 figures, Revised version submitted to Astrophysical Journal

Star forming dwarf galaxies in the local volume are diverse and are ideal test beds to understand details of star formation in a variety of environments. Here, we present a deep FUV imaging study of a nearby dwarf irregular galaxy IC 2574 using the Ultraviolet Imaging Telescope (UVIT). We identified 419 FUV bright regions with radii between 15 - 285 pc in the galaxy and found that 28.6\% of them to be located in H~I shells, 12.6\% inside holes and 60.1\% to be away from the holes. The H~I column density is found to be more than $10^{21} cm^{-2}$ for 82.3\% of the identified regions. 30 out of the 48 H~I holes show triggered star formation in their shells while 16 holes do not show any related FUV emission. Cross-matching with H$\alpha$ emission, we found that 23 holes have both FUV and H$\alpha$ emission in their shells signifying very recent trigger. Therefore, star formation in the galaxy has been partly triggered due to the expanding H~I holes whereas in majority of the sites it is driven by other mechanisms. Irrespective of the location, larger star forming complexes were found to have multiple sub-structures. We report two resolved components for the remnant cluster of the super giant shell and estimated their masses. The star formation rate of IC 2574 is found to be 0.57 $M_{\odot}$/yr, which is slightly higher compared to the average value of other nearby dwarf irregular galaxies.