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J.P. Magué & B. Ménard

[1]
Title: The close circumstellar environment of Betelgeuse - V. Rotation velocity and molecular envelope properties from ALMA
Comments: 18 pages, 19 figures, accepted for publication in A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We observed Betelgeuse using ALMA's extended configuration in band 7 (f~340 GHz, {\lambda}~0.88 mm), resulting in a very high angular resolution of 18 mas. Using a solid body rotation model of the 28SiO(v=2,J=8-7) line emission, we show that the supergiant is rotating with a projected equatorial velocity of v_eq sin i = 5.47 +/- 0.25 km/s at the equivalent continuum angular radius R_star = 29.50 +/- 0.14 mas. This corresponds to an angular rotation velocity of {\omega} sin i = (5.6 +/- 1.3) x 10^(-9) rad/s. The position angle of its north pole is PA = 48.0 +/- 3.5{\deg}. The rotation period of Betelgeuse is estimated to P/sin i = 36 +/- 8 years. The combination of our velocity measurement with previous observations in the ultraviolet shows that the chromosphere is co-rotating with the star up to a radius of ~10 au (45 mas or 1.5x the ALMA continuum radius). The coincidence of the position angle of the polar axis of Betelgeuse with that of the major ALMA continuum hot spot, a molecular plume, and a partial dust shell (from previous observations) suggests that focused mass loss is currently taking place in the polar region of the star. We propose that this hot spot corresponds to the location of a particularly strong "rogue" convection cell, which emits a focused molecular plume that subsequently condenses into dust at a few stellar radii. Rogue convection cells therefore appear to be an important factor shaping the anisotropic mass loss of red supergiants.

[2]
Title: Peering beyond the horizon with standard sirens and redshift drift
Authors: Raul Jimenez (1,2), Alvise Raccanelli (1), Licia Verde (1,2), Sabino Matarrese (3,4,5,6) ((1) ICC Barcelona, (2) ICREA, (3) Università di Padova, (4) INFN Padova, (5) INAF Padova, (6) GSSI)
Comments: 10 pages, 1 figure, 2 tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

An interesting test on the nature of the Universe is to measure the global spatial curvature of the metric in a model independent way, at a level of $|\Omega_k|<10^{-4}$, or, if possible, at the cosmic variance level of the amplitude of the CMB fluctuations $|\Omega_k|\approx10^{-5}$. A limit of $|\Omega_k|<10^{-4}$ would yield stringent tests on several models of inflation. Further, improving the constraint by an order of magnitude would help in reducing "model confusion" in standard parameter estimation. Moreover, if the curvature is measured to be at the value of the amplitude of the CMB fluctuations, it would offer a powerful test on the inflationary paradigm and would indicate that our Universe must be significantly larger than the current horizon. On the contrary, in the context of standard inflation, measuring a value above CMB fluctuations will lead us to conclude that the Universe is not much larger than the current observed horizon; this can also be interpreted as the presence of large fluctuations outside the horizon. However, it has proven difficult, so far, to find observables that can achieve such level of accuracy, and, most of all, be model-independent. Here we propose a method that can in principle achieve that; this is done by making minimal assumptions and using distance probes that are cosmology-independent: gravitational waves, redshift drift and cosmic chronometers. We discuss what kind of observations are needed in principle to achieve the desired accuracy.

[3]
Title: Declining rotation curves at $z=2$: A natural phenomenon in $Λ$CDM cosmology
Comments: 6 pages, 4 figures, submitted to ApJ Letters, www.magneticum.org
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Selecting disk galaxies from the cosmological, hydrodynamical simulation Magneticum Pathfinder we show that almost half of our poster child disk galaxies at $z=2$ show significantly declining rotation curves and low dark matter fractions, very similar to recently reported observations. These galaxies do not show any anomalous behavior, reside in standard dark matter halos and typically grow significantly in mass until $z=0$, where they span all morphological classes, including disk galaxies matching present day rotation curves and observed dark matter fractions. Our findings demonstrate that declining rotation curves and low dark matter fractions in rotation dominated galaxies at $z=2$ appear naturally within the $\Lambda$CDM paradigm and reflect the complex baryonic physics, which plays a role at the peak epoch of star-formation. In addition, we find that dispersion dominated galaxies at $z=2$, which host a significant gas disk, exhibit similar shaped rotation curves as the disk galaxy population, rendering it difficult to differentiate between these two populations with currently available observation techniques.

[4]
Title: Revisiting the bulge-halo conspiracy II: Towards explaining its puzzling dependence on redshift
Authors: Francesco Shankar (1), Alessandro Sonnenfeld (2), Philip Grylls (1), Lorenzo Zanisi (1), Carlo Nipoti (3), Kyu-Hyun Chae (4), Mariangela Bernardi (5), Carlo Enrico Petrillo (6), Marc Huertas-Company (7), Gary A. Mamon (8), Stewart Buchan (1) ((1) University of Southampton, (2) Kavli IPMU, University of Tokyo, (3) Bologna University, (4) Sejong University, (5) University of Pennsylvania, (6) University of Groningen, (7) LERMA, Observatoire de Paris, (8) Institut d'Astrophysique de Paris)
Comments: 14 pages, 8 figures. MNRAS, accepted. Main result of the paper in Figure 2
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We carry out a systematic investigation of the total mass density profile of massive (Mstar~3e11 Msun) early-type galaxies and its dependence on redshift, specifically in the range 0<z<1. We start from a large sample of SDSS early-type galaxies with stellar masses and effective radii measured assuming two different profiles, de Vaucouleurs and S\'{e}rsic. We assign dark matter haloes to galaxies via abundance matching relations with standard LCDM profiles and concentrations. We then compute the total, mass-weighted density slope at the effective radius gamma', and study its redshift dependence at fixed stellar mass. We find that a necessary condition to induce an increasingly flatter gamma' at higher redshifts, as suggested by current strong lensing data, is to allow the intrinsic stellar profile of massive galaxies to be S\'{e}rsic and the input S\'{e}rsic index n to vary with redshift approximately as n(z)~(1+z)^(-1). This conclusion holds irrespective of the input Mstar-Mhalo relation, the assumed stellar initial mass function, or even the chosen level of adiabatic contraction in the model. Secondary contributors to the observed redshift evolution of gamma' may come from an increased contribution at higher redshifts of adiabatic contraction and/or bottom-light stellar initial mass functions. The strong lensing selection effects we have simulated seem not to contribute to this effect. A steadily increasing S\'{e}rsic index with cosmic time is supported by independent observations, though it is not yet clear whether cosmological hierarchical models (e.g., mergers) are capable of reproducing such a fast and sharp evolution.

[5]
Title: Dynamical equivalence, the origin of the Galactic field stellar and binary population, and the initial radius--mass relation of embedded clusters
Comments: 6 pages, 2 figures; accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)

In order to allow a better understanding of the origin of Galactic field populations, dynamical equivalence of stellar-dynamical systems has been postulated by Kroupa and Belloni et al. to allow mapping of solutions of the initial conditions of embedded clusters such that they yield, after a period of dynamical processing, the Galactic field population. Dynamically equivalent systems are defined to initially and finally have the same distribution functions of periods, mass ratios and eccentricities of binary stars. Here we search for dynamically equivalent clusters using the {\sc mocca} code. The simulations confirm that dynamically equivalent solutions indeed exist. The result is that the solution space is next to identical to the radius--mass relation of Marks \& Kroupa, $\left( r_h/{\rm pc} \right)= 0.1^{+0.07}_{-0.04}\, \left( M_{\rm ecl}/{\rm M}_\odot \right)^{0.13\pm0.04}$. This relation is in good agreement with the observed density of molecular cloud clumps. According to the solutions, the time-scale to reach dynamical equivalence is about 0.5~Myr which is, interestingly, consistent with the lifetime of ultra-compact HII regions and the time-scale needed for gas expulsion to be active in observed very young clusters as based on their dynamical modelling.

[6]
Title: CO excitation in the Seyfert galaxy NGC 34: stars, shock or AGN driven?
Comments: Accepted for publication in MNRAS. 10 pages, 6 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present a detailed analysis of the X-ray and molecular gas emission in the nearby galaxy NGC 34, to constrain the properties of molecular gas, and assess whether, and to what extent, the radiation produced by the accretion onto the central black hole affects the CO line emission. We analyse the CO Spectral Line Energy Distribution (SLED) as resulting mainly from Herschel and ALMA data, along with X-ray data from NuSTAR and XMM-Newton. The X-ray data analysis suggests the presence of a heavily obscured AGN with an intrinsic luminosity of L$_{\rm{1-100\,keV}} \simeq 4.0\times10^{42}$ erg s$^{-1}$. ALMA high resolution data ($\theta \simeq 0.2''$) allows us to scan the nuclear region down to a spatial scale of $\approx 100$ pc for the CO(6-5) transition. We model the observed SLED using Photo-Dissociation Region (PDR), X-ray-Dominated Region (XDR), and shock models, finding that a combination of a PDR and an XDR provides the best fit to the observations. The PDR component, characterized by gas density ${\rm log}(n/{\rm cm^{-3}})=2.5$ and temperature $T=30$ K, reproduces the low-J CO line luminosities. The XDR is instead characterised by a denser and warmer gas (${\rm log}(n/{\rm cm^{-3}})=4.5$, $T =65$ K), and is necessary to fit the high-J transitions. The addition of a third component to account for the presence of shocks has been also tested but does not improve the fit of the CO SLED. We conclude that the AGN contribution is significant in heating the molecular gas in NGC 34.

[7]
Title: A Universal Transition in Atmospheric Diffusion for Hot Subdwarfs Near 18,000 K
Comments: Accepted for publication in The Astrophysical Journal. 9 pages, 1 table, 10 figures. Figure 2 is shown at low resolution due to file size limits
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In the color-magnitude diagrams (CMDs) of globular clusters, when the locus of stars on the horizontal branch (HB) extends to hot temperatures, discontinuities are observed at colors corresponding to ~12,000 K and ~18,000 K. The former is the "Grundahl jump" that is associated with the onset of radiative levitation in the atmospheres of hot subdwarfs. The latter is the "Momany jump" that has remained unexplained. Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we have obtained ultraviolet and blue spectroscopy of six hot subdwarfs straddling the Momany jump in the massive globular cluster omega Cen. By comparison to model atmospheres and synthetic spectra, we find that the feature is due primarily to a decrease in atmospheric Fe for stars hotter than the feature, amplified by the temperature dependence of the Fe absorption at these effective temperatures.

[8]
Title: Photonuclear Reactions in Lightning Discovered from Detection of Positrons and Neutrons
Authors: Teruaki Enoto (1), Yuuki Wada (2 and 3), Yoshihiro Furuta (2), Kazuhiro Nakazawa (2), Takayuki Yuasa (4), Kazufumi Okuda (2), Kazuo Makishima (3), Mitsuteru Sato (5), Yousuke Sato (6), Toshio Nakano (3), Daigo Umemoto (3), Harufumi Tsuchiya (7) ((1) Kyoto University, (2) The University of Tokyo, (3) RIKEN, (4) Singapore, (5) Hokkaido University, (6) Nagoya University, (7) JAEA)
Comments: This manuscript was submitted to Nature Letter on July 30, 2017, and the original version that has not undergo the peer review process. See the accepted version at Nature website, published on the issue of November 23, 2017 with the revised title "photonuclear reaction triggered by lightning discharge"
Journal-ref: Nature Letter, the issue of November 23, 2017
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Atmospheric and Oceanic Physics (physics.ao-ph)

Lightning and thundercloud are the most dramatic natural particle accelerators on the Earth. Relativistic electrons accelerated by electric fields therein emit bremsstrahlung gamma rays, which have been detected at ground observations, by airborne detectors, and as terrestrial gamma-ray flashes (TGFs) from space. The energy of the gamma rays is sufficiently high to potentially invoke atmospheric photonuclear reactions 14N(gamma, n)13N, which would produce neutrons and eventually positrons via beta-plus decay of generated unstable radioactive isotopes, especially 13N. However, no clear observational evidence for the reaction has been reported to date. Here we report the first detection of neutron and positron signals from lightning with a ground observation. During a thunderstorm on 6 February 2017 in Japan, a TGF-like intense flash (within 1 ms) was detected at our monitoring sites 0.5-1.7 km away from the lightning. The subsequent initial burst quickly subsided with an exponential decay constant of 40-60 ms, followed by a prolonged line emission at about 0.511 megaelectronvolt (MeV), lasting for a minute. The observed decay timescale and spectral cutoff at about 10 MeV of the initial emission are well explained with de-excitation gamma rays from the nuclei excited by neutron capture. The centre energy of the prolonged line emission corresponds to the electron-positron annihilation, and hence is the conclusive indication of positrons produced after the lightning. Our detection of neutrons and positrons is unequivocal evidence that natural lightning triggers photonuclear reactions. No other natural event on the Earth is known to trigger photonuclear reactions. This discovery places lightning as only the second known natural channel on the Earth after the atmospheric cosmic-ray interaction, in which isotopes, such as 13C, 14C, and 15N, are produced.

[9]
Title: Tracing the Assembly History of NGC 1395 through its Globular Cluster System
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We used deep Gemini-South/GMOS g'r'i'z' images to study the globular cluster (GC) system of the massive elliptical galaxy NGC 1395, located in the Eridanus supergroup. The photometric analysis of the GC candidates reveals a clear colour bimodality distribution, indicating the presence of "blue" and "red" GC subpopulations. While a negative radial colour gradient is detected in the projected spatial distribution of the red GCs, the blue GCs display a shallow colour gradient. The blue GCs also display a remarkable shallow and extended surface density profile, suggesting a significant accretion of low-mass satellites in the outer halo of the galaxy. In addition, the slope of the projected spatial distribution of the blue GCs in the outer regions of the galaxy, is similar to that of the X-ray halo emission. Integrating up to 165 kpc the profile of the projected spatial distribution of the GCs, we estimated a total GC population and specific frequency of 6000$\pm$1100 and $S_N$=7.4$\pm$1.4, respectively. Regarding NGC 1395 itself, the analysis of the deep Gemini/GMOS images shows a low surface brightness umbrella-like structure indicating, at least, one recent merger event. Through relations recently published in the literature, we obtained global parameters, such as $M_\mathrm{stellar}=9.32\times10^{11}$ M$\odot$ and $M_h=6.46\times10^{13}$ M$\odot$. Using public spectroscopic data, we derive stellar population parameters of the central region of the galaxy by the full spectral fitting technique. We have found that, this region, seems to be dominated for an old stellar population, in contrast to findings of young stellar populations from the literature.

[10]
Title: Exo-lightning radio emission: the case study of HAT-P-11b
Comments: Accepted to the Conference Proceedings of the 8th International Workshop on Planetary, Solar and Heliospheric Radio Emissions (PRE 8), held in Seggauberg near Leibnitz/Graz, Austria, October 25-27, 2016. 12 pages, 2 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR); Atmospheric and Oceanic Physics (physics.ao-ph); Geophysics (physics.geo-ph)

Lightning induced radio emission has been observed on solar system planets. Lecavelier des Etangs et al. [2013] carried out radio transit observations of the exoplanet HAT-P-11b, and suggested a tentative detection of a radio signal. Here, we explore the possibility of the radio emission having been produced by lightning activity on the exoplanet, following and expanding the work of Hodos\'an et al. [2016a]. After a summary of our previous work [Hodos\'an et al. 2016a], we extend it with a parameter study. The lightning activity of the hypothetical storm is largely dependent on the radio spectral roll-off, $n$, and the flash duration, $\tau_\mathrm{fl}$. The best-case scenario would require a flash density of the same order of magnitude as can be found during volcanic eruptions on Earth. On average, $3.8 \times 10^6$ times larger flash densities than the Earth-storms with the largest lightning activity is needed to produce the observed signal from HAT-P-11b. Combined with the results of Hodos\'an et al. [2016a] regarding the chemical effects of planet-wide thunderstorms, we conclude that future radio and infrared observations may lead to lightning detection on planets outside the solar system.

[11]
Title: The SUrvey for Pulsars and Extragalactic Radio Bursts II: New FRB discoveries and their follow-up
Comments: 21 pages, 8 figures and accepted for publication in MNRAS
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We report the discovery of four Fast Radio Bursts (FRBs) in the ongoing SUrvey for Pulsars and Extragalactic Radio Bursts (SUPERB) at the Parkes Radio Telescope: FRBs 150610, 151206, 151230 and 160102. Our real-time discoveries have enabled us to conduct extensive, rapid multi-messenger follow-up at 12 major facilities sensitive to radio, optical, X-ray, gamma-ray photons and neutrinos on time scales ranging from an hour to a few months post-burst. No counterparts to the FRBs were found and we provide upper limits on afterglow luminosities. None of the FRBs were seen to repeat. Formal fits to all FRBs show hints of scattering while their intrinsic widths are unresolved in time. FRB 151206 is at low Galactic latitude, FRB 151230 shows a sharp spectral cutoff, and FRB 160102 has the highest dispersion measure (DM = $2596.1\pm0.3$ pc cm$^{-3}$) detected to date. Three of the FRBs have high dispersion measures (DM >$1500$ pc cm$^{-3}$), favouring a scenario where the DM is dominated by contributions from the Intergalactic Medium. The slope of the Parkes FRB source counts distribution with fluences $>2$ Jyms is $\alpha=-2.2^{+0.6}_{-1.2}$ and still consistent with a Euclidean distribution ($\alpha=-3/2$). We also find that the all-sky rate is $1.7^{+1.5}_{-0.9}\times10^3$FRBs/($4\pi$ sr)/day above $\sim2$ Jyms and there is currently no strong evidence for a latitude-dependent FRB sky-rate.

[12]
Title: Discovery of 21 New Changing-look AGNs in Northern Sky
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The rare case of changing-look (CL) AGNs, with the appearance or disappearance of broad Balmer emission lines within a few years, challenges our understanding of the AGN unified model. We present a sample of 21 new CL AGNs at $0.08<z<0.58$. The new sample doubles the number of such objects known to date. These new CL AGNs were discovered by several ways, from repeat spectra in the SDSS, repeat spectra in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and SDSS, and from photometric variability and new spectroscopic observations. The estimated upper limits of transition timescale of the CL AGNs in this sample span from 0.9 to 13 years in rest-frame. The continuum flux in the optical and mid-infrared becomes brighter when the CL AGNs turn on, or vice versa. Variations of more than 0.2 mag in the mid-infrared $W1$ band, from the Wide-field Infrared Survey Explorer (WISE), were detected in 15 CL AGNs during the transition. The optical and mid-infrared variability is not consistent with the scenario of variable obscuration in 10 CL AGNs at higher than $3\sigma$ confidence level. We confirm a bluer-when-brighter trend in the optical. However, the mid-infrared colors $W1-W2$ become redder when the objects become brighter in the $W1$ band, possibly due to a stronger hot dust contribution in the $W2$ band when the AGN activity becomes stronger. The physical mechanism of type transition is important for understanding the evolution of AGNs.

[13]
Title: Resolving the Internal Structure of Circum-Galactic Medium using Gravitationally Lensed Quasars
Comments: 13 pages, 8 figures, 3 tables, accepted for publication in ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We study the internal structure of the Circum-Galactic Medium (CGM), using 29 spectra of 13 gravitationally lensed quasars with image separation angles of a few arcseconds, which correspond to 100 pc to 10 kpc in physical distances. After separating metal absorption lines detected in the spectra into high-ions with ionization parameter (IP) $>$ 40 eV and low-ions with IP $<$ 20 eV, we find that i) the fraction of absorption lines that are detected in only one of the lensed images is larger for low-ions ($\sim$16%) than high-ions ($\sim$2%), ii) the fractional difference of equivalent widths ($EW$s) between the lensed images is almost same (${\rm d}EW$ $\sim$ 0.2) for both groups although the low-ions have a slightly larger variation, and iii) weak low-ion absorbers tend to have larger ${\rm d}EW$ compared to weak high-ion absorbers. We construct simple models to reproduce these observed properties and investigate the distribution of physical quantities such as size and location of absorbers, using some free parameters. Our best models for absorbers with high-ions and low-ions suggest that i) an overall size of the CGM is at least $\sim$ 500 kpc, ii) a size of spherical clumpy cloud is $\sim$ 1 kpc or smaller, and iii) only high-ion absorbers can have diffusely distributed homogeneous component throughout the CGM. We infer that a high ionization absorber distributes almost homogeneously with a small-scale internal fluctuation, while a low ionization absorber consists of a large number of small-scale clouds in the diffusely distributed higher ionized region. This is the first result to investigate the internal small-scale structure of the CGM, based on the large number of gravitationally lensed quasar spectra.

[14]
Title: The MASIV Survey IV: relationship between intra-day scintillation and intrinsic variability of radio AGNs
Comments: 18 pages, 13 figures, 5 tables, resubmitted to MNRAS after minor revision
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

We investigate the relationship between 5 GHz interstellar scintillation (ISS) and 15 GHz intrinsic variability of compact, radio-selected AGNs drawn from the Microarcsecond Scintillation-Induced Variability (MASIV) Survey and the Owens Valley Radio Observatory (OVRO) blazar monitoring program. We discover that the strongest scintillators at 5 GHz (modulation index, $m_5 \geq 0.02$) all exhibit strong 15 GHz intrinsic variability ($m_{15} \geq 0.1$). This relationship can be attributed mainly to the mutual dependence of intrinsic variability and ISS amplitudes on radio core compactness at $\sim 100\, \mu$as scales, and to a lesser extent, on their mutual dependences on source flux density, arcsec-scale core dominance and redshift. However, not all sources displaying strong intrinsic variations show high amplitude scintillation, since ISS is also strongly dependent on Galactic line-of-sight scattering properties. This observed relationship between intrinsic variability and ISS highlights the importance of optimizing the observing frequency, cadence, timespan and sky coverage of future radio variability surveys, such that these two effects can be better distinguished to study the underlying physics. For the full MASIV sample, we find that Fermi-detected gamma-ray loud sources exhibit significantly higher 5 GHz ISS amplitudes than gamma-ray quiet sources. This relationship is weaker than the known correlation between gamma-ray loudness and the 15 GHz variability amplitudes, most likely due to jet opacity effects.

[15]
Title: Iwahashi Zenbei's Sunspot Drawings in 1793 in Japan
Comments: 2017/11/16 accepted for publication in Solar Physics
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); History and Philosophy of Physics (physics.hist-ph)

Three Japanese sunspot drawings associated with Iwahashi Zenbei (1756-1811) are shown here from contemporary manuscripts and woodprint documents with the relevant texts. We revealed the observational date of one of the drawings to be 26 August 1793, and the overall observations lasted for over a year. Moreover, we identified the observational site for the dated drawing at Fushimi in Japan. We then compared his observations with group sunspot number and raw group count from Sunspot Index and Long-term Solar Observations (SILSO) to reveal its data context, and concluded that these drawings filled the gaps in understanding due to the fragmental sunspots observations around 1793. These drawings are important as a clue to evaluate astronomical knowledge of contemporary Japan in the late 19 th century and are valuable as a non-European observation, considering that most sunspot observations up to mid-19 th century are from Europe.

[16]
Title: Examination of artifact in vector magnetic field SDO/HMI measurements
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In this paper, we came to conclusion that there is a significant systematic error in the SDO/HMI vector magnetic data, which reveals itself in a significant deviation of the lines of the knot magnetic fields from the radial direction. The value of this deviation demonstrates a clear dependence on the distance to the disk center. This paper suggests a method for correction of the vector magnetograms that eliminates the detected systematic error.

[17]
Title: Planet-driven spiral arms in protoplanetary disks: I. Formation mechanism
Authors: Jaehan Bae (1), Zhaohuan Zhu (2) ((1) Carnegie DTM, (2) UNLV)
Comments: 16 pages, 14 figures, submitted to the ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Protoplanetary disk simulations show that a single planet can excite more than one spiral arm, possibly explaining recent observations of multiple spiral arms in some systems. In this paper, we explain the mechanism by which a planet excites multiple spiral arms in a protoplanetary disk. Contrary to previous speculations, the formation of both primary and additional arms can be understood as a linear process when the planet mass is sufficiently small. A planet resonantly interacts with epicyclic oscillations in the disk, launching spiral wave modes around the Lindblad resonances. When a set of wave modes is in phase, they can constructively interfere with each other and create a spiral arm. More than one spiral arm can form because such constructive interference can occur for different sets of wave modes, with the exact number and launching position of spiral arms dependent on the planet mass as well as the disk temperature profile. Non-linear effects become increasingly important as the planet mass increases, resulting in spiral arms with stronger shocks and thus larger pitch angles. This is found in common for both primary and additional arms. When a planet has a sufficiently large mass ($\gtrsim$ 3 thermal masses for $(h/r)_p=0.1$), only two spiral arms form interior to its orbit. The wave modes that would form a tertiary arm for smaller mass planets merge with the primary arm. Improvements in our understanding of the formation of spiral arms can provide crucial insights into the origin of observed spiral arms in protoplanetary disks.

[18]
Title: Discovery of molecular and atomic clouds associated with the gamma-ray supernova remnant Kesteven 79
Comments: 12 pages, 6 figures, 2 tables, submitted to The Astrophysical Journal (ApJ)
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

We carried out $^{12}$CO($J$ = 1-0) observations of the Galactic gamma-ray supernova remnant (SNR) Kesteven 79 using the Nobeyama Radio Observatory 45 m radio telescope, which has an angular resolution of $\sim20$ arcsec. We identified molecular and atomic gas interacting with Kesteven 79 whose radial velocity is $\sim80$ km s$^{-1}$. The interacting molecular and atomic gases show good spatial correspondence with the X-ray and radio shells, which have an expanding velocity structure with $\Delta V\sim4$ km s$^{-1}$. The molecular gas associated with the radio and X-ray peaks also exhibits a high-intensity ratio of CO 3-2/1-0 $>$ 0.8, suggesting a kinematic temperature of $\sim100$ K, owing to heating by the supernova shock. We determined the kinematic distance to the SNR to be $\sim5.5$ kpc and the radius of the SNR to be $\sim8$ pc. The average interstellar proton density inside of the SNR is $\sim360$ cm$^{-3}$, of which atomic protons comprise only $\sim10$ $\%$. Assuming a hadronic origin for the gamma-ray emission, the total cosmic-ray proton energy above 1 GeV is estimated to be $\sim5 \times 10^{48}$ erg.

[19]
Title: Planet-driven spiral arms in protoplanetary disks: II. Implications
Authors: Jaehan Bae (1), Zhaohuan Zhu (2) ((1) Carnegie DTM, (2) UNLV)
Comments: 14 pages, 10 figures, Figure 2 size reduced to meet the requirement, submitted to the ApJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

In Paper I (Bae & Zhu 2017), we explained how a planet excites multiple spiral arms in a protoplanetary disk. To examine whether various characteristics of observed spiral arms can be used to constrain the masses of unseen planets and their positions within their disks, we carry out two-dimensional simulations varying planet mass and disk gas temperature. A larger number of spiral arms form with a smaller planet mass and a lower disk temperature. For a range of disk temperature characterized by the disk aspect ratio $0.04 \leq (h/r)_p \leq 0.15$, three or fewer spiral arms are excited interior to a planet's orbit when $M_p/M_* \gtrsim 3\times10^{-4}$ and two spiral arms when $M_p/M_* \gtrsim 3\times10^{-3}$. Exterior to a planet's orbit, multiple spiral arms can form only in cold disks with $(h/r)_p \lesssim 0.06$. Constraining the planet mass with the pitch angle of spiral arms requires accurate disk temperature measurements that might be challenging even with ALMA. However, the property that the pitch angle of planet-driven spiral arms decreases away from the planet can be a powerful diagnostic to determine whether the planet is located interior or exterior to the observed spirals. The arm-to-arm separations increase as a function of planet mass, consistent with previous studies; however, we find that the exact slope depends on disk temperature as well as the radial location where the arm-to-arm separations are measured. We apply these diagnostics to the spiral arms seen in MWC 758 and Elias 2-27. Finally, we discuss the possibility that Jupiter's core creates multiple pressure bumps in the solar nebula through spiral shocks, and show how it can help explain meteoritic properties.

[20]
Title: Causal propagation of signal in strangeon matter
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The state equation of strangeon matter is very stiff due to the non-relativistic nature of and the repulsing interaction between the particles, and pulsar masses as high as $\sim 3M_\odot$ would be expected. However, an adiabatic sound speed, $c_s=\sqrt{\partial P/\partial \rho}$, is usually superluminal for strangeon matter, and dynamic response of strangeon star (e.g., binary merger) could not be tractable in calculation. We examine signal propagation in strangeon matter, and calculate the propagation speed, $c_{\rm signal}$, in reality. It is found that as the causality condition is satisfied, i.e., $c_{\rm signal}<c$, and the signal speed as a function of stellar radius is presented.

[21]
Title: Peculiar Motions of Galaxy Clusters in the Regions of Superclusters of galaxies
Comments: 16 pages, 6 figures, 3 tables, published in the Astrophysical Bulletin, 2017
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

We present results of the study of peculiar motions of 57 clusters and groups of galaxies in the regions of the Corona Borealis (CrB), Bootes (Boo), Z5029/A1424, A1190, A1750/A1809 superclusters of galaxies and 20 galaxy clusters located beyond massive structures ($0.05<z<0.10$). Using the SDSS (Data Release 8) data, a sample of early-type galaxies was compiled in the systems under study, their fundamental planes were built, and relative distances and peculiar velocities were determined. Within the galaxy superclusters, significant peculiar motions along the line of sight are observed with rms deviations of $652\pm50$~km s$^{-1}$---in CrB, $757\pm70$~km s$^{-1}$---in Boo. For the most massive A2065 cluster in the CrB supercluster, no peculiar velocity was found. Peculiar motions of other galaxy clusters can be caused by their gravitational interaction both with A\,2065 and with the A2142 supercluster. It has been found that there are two superclusters projected onto each other in the region of the Bootes supercluster with a radial velocity difference of about 4000~km s$^{-1}$. In the Z5029/A1424 supercluster near the rich Z5029 cluster, the most considerable peculiar motions with a rms deviation of $1366\pm170$~km s$^{-1}$ are observed. The rms deviation of peculiar velocities of 20 clusters that do not belong to large-scale structures is equal to $0\pm20$~km s$^{-1}$. The whole sample of the clusters under study has the mean peculiar velocity equal to $83\pm130$~km s$^{-1}$ relative to the cosmic microwave background.

[22]
Title: 12C/13C isotopic ratios in red-giant stars of the open cluster NGC 6791
Comments: Accepted for publication in MNRAS, 9 pages, 4 figures, 2 tables
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Carbon isotope ratios, along with carbon and nitrogen abundances, are derived in a sample of 11 red-giant members of one of the most metal-rich clusters in the Milky Way, NGC 6791. The selected red-giants have a mean metallicity and standard deviation of [Fe/H]=+0.39+-0.06 (Cunha et al. 2015). We used high resolution H-band spectra obtained by the SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE). The advantage of using high-resolution spectra in the H-band is that lines of CO are well represented and their line profiles are sensitive to the variation of 12C/13C. Values of the 12C/13C ratio were obtained from a spectrum synthesis analysis. The derived 12C/13C ratios varied between 6.3 and 10.6 in NGC 6791, in agreement with the final isotopic ratios from thermohaline-induced mixing models. The ratios derived here are combined with those obtained for more metal poor red-giants from the literature to examine the correlation between 12C/13C, mass, metallicity and evolutionary status.

[23]
Title: The formation rate of short gamma-ray bursts and gravitational waves
Authors: G. Q. Zhang, F. Y. Wang (NJU)
Comments: 29 pages, 8 figures, 2 tables, accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

In this paper, we study the luminosity function and formation rate of short gamma-ray bursts (sGRBs). Firstly, we derive the $E_p-L_p$ correlation using 16 sGRBs with redshift measurements and determine the pseudo redshifts of 284 Fermi sGRBs. Then, we use the Lynden-Bell c$^-$ method to study the luminosity function and formation rate of sGRBs without any assumptions. A strong evolution of luminosity $L(z)\propto (1+z)^{4.47}$ is found. After removing this evolution, the luminosity function is $\Psi (L) \propto L_0 ^ {- 0.29 \pm 0.01}$ for dim sGRBs and $\psi (L) \propto L_0 ^ {- 1.07 \pm 0.01}$ for bright sGRBs, with the break point $8.26 \times 10^{50}$ erg s$^{-1}$. We also find that the formation rate decreases rapidly at $z<1.0$, which is different with previous works. The local formation rate of sGRBs is 7.53 events Gpc$^{-3}$ yr$^{-1}$. Considering the beaming effect, the local formation rate of sGRBs including off-axis sGRBs is $203.31^{+1152.09}_{-135.54}$ events Gpc$^{-3}$ yr$^{-1}$. We also estimate that the event rate of sGRBs detected by the advanced LIGO and Virgo is $0.85^{+4.82}_{-0.56}$ events yr$^{-1}$ for NS-NS binary.

[24]
Title: A universal relation for the propeller mechanisms in magnetic rotating stars at different scales
Authors: Sergio Campana (1), Luigi Stella (2), Sandro Mereghetti (3), Domitilla de Martino (4) ((1) INAF-Brera, (2) INAF-Monteporzio, (3) INAF-IASF Milano, (4) INAF-Napoli)
Comments: 11 pages, 3 figures. Accepted for publication in A&A
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Accretion of matter onto a magnetic, rotating object can be strongly affected by the interaction with its magnetic field. This occurs in a variety of astrophysical settings involving young stellar objects, white dwarfs, and neutron stars. As matter is endowed with angular momentum, its inflow toward the star is often mediated by an accretion disc. The pressure of matter and that originating from the stellar magnetic field balance at the magnetospheric radius: at smaller distances the motion of matter is dominated by the magnetic field, and funnelling towards the magnetic poles ensues. However, if the star, and thus its magnetosphere, is fast spinning, most of the inflowing matter will be halted at the magnetospheric radius by centrifugal forces, resulting in a characteristic reduction of the accretion luminosity. The onset of this mechanism, called the propeller, has been widely adopted to interpret a distinctive knee in the decaying phase of the light curve of several transiently accreting X-ray pulsar systems. By comparing the observed luminosity at the knee for different classes of objects with the value predicted by accretion theory on the basis of the independently measured magnetic field, spin-period, mass, and radius of the star, we disclose here a general relation for the onset of the propeller which spans about eight orders of magnitude in spin period and ten in magnetic moment. The parameter-dependence and normalisation constant that we determine are in agreement with basic accretion theory.

[25]
Title: Enceladus's crust as a non-uniform thin shell: I Tidal deformations
Authors: Mikael Beuthe
Comments: 71 pages, 12 figures, 5 tables
Journal-ref: Icarus 302 (2018) 145-174
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Geophysics (physics.geo-ph); Space Physics (physics.space-ph)

The geologic activity at Enceladus's south pole remains unexplained, though tidal deformations are probably the ultimate cause. Recent gravity and libration data indicate that Enceladus's icy crust floats on a global ocean, is rather thin, and has a strongly non-uniform thickness. Tidal effects are enhanced by crustal thinning at the south pole, so that realistic models of tidal tectonics and dissipation should take into account the lateral variations of shell structure. I construct here the theory of non-uniform viscoelastic thin shells, allowing for depth-dependent rheology and large lateral variations of shell thickness and rheology. Coupling to tides yields two 2D linear partial differential equations of the 4th order on the sphere which take into account self-gravity, density stratification below the shell, and core viscoelasticity. If the shell is laterally uniform, the solution agrees with analytical formulas for tidal Love numbers; errors on displacements and stresses are less than 5% and 15%, respectively, if the thickness is less than 10% of the radius. If the shell is non-uniform, the tidal thin shell equations are solved as a system of coupled linear equations in a spherical harmonic basis. Compared to finite element models, thin shell predictions are similar for the deformations due to Enceladus's pressurized ocean, but differ for the tides of Ganymede. If Enceladus's shell is conductive with isostatic thickness variations, surface stresses are approximately inversely proportional to the local shell thickness. The radial tide is only moderately enhanced at the south pole. The combination of crustal thinning and convection below the poles can amplify south polar stresses by a factor of 10, but it cannot explain the apparent time lag between the maximum plume brightness and the opening of tiger stripes. In a second paper, I will study tidal dissipation in a non-uniform crust.

[26]
Title: Revised Models of Interstellar Nitrogen Isotopic Fractionation
Comments: Accepted for publication in MNRAS, 3 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Nitrogen-bearing molecules in cold molecular clouds exhibit a range of isotopic fractionation ratios and these molecules may be the precursors of $^{15}$N enrichments found in comets and meteorites. Chemical model calculations indicate that atom-molecular ion and ion-molecule reactions could account for most of the fractionation patterns observed. However, recent quantum-chemical computations demonstrate that several of the key processes are unlikely to occur in dense clouds. Related model calculations of dense cloud chemistry show that the revised $^{15}$N enrichments fail to match observed values. We have investigated the effects of these reaction rate modifications on the chemical model of Wirstr\"{o}m et al. (2012) for which there are significant physical and chemical differences with respect to other models. We have included $^{15}$N fractionation of CN in neutral-neutral reactions and also updated rate coefficients for key reactions in the nitrogen chemistry. We find that the revised fractionation rates have the effect of suppressing $^{15}$N enrichment in ammonia at all times, while the depletion is even more pronounced, reaching $^{14}$N/$^{15}$N ratios of >2000. Taking the updated nitrogen chemistry into account, no significant enrichment occurs in HCN or HNC, contrary to observational evidence in dark clouds and comets, although the $^{14}$N/$^{15}$N ratio can still be below 100 in CN itself. However, such low CN abundances are predicted that the updated model falls short of explaining the bulk $^{15}$N enhancements observed in primitive materials. It is clear that alternative fractionating reactions are necessary to reproduce observations, so further laboratory and theoretical studies are urgently needed.

[27]
Title: High-Energy Neutrino Astronomy: where do we stand, where do we go?
Comments: Talk given at the occasion of the 50th anniversary of the Baksan Laboratory
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

With the identification of a diffuse flux of astrophysical ("cosmic") neutrinos in the TeV-PeV energy range, IceCube has opened a new window to the Universe. However, the corresponding cosmic landscape is still uncharted: so far, the observed flux does not show any clear association with known source classes. In the present talk, I sketch the way from Baikal-NT200 to IceCube and summarize IceCube's recent astrophysics results. Finally, I describe the present projects to build even larger detectors: GVD in Lake Baikal, KM3NeT in the Mediterranean Sea and IceCube-Gen2 at the South Pole. These detectors will allow studying the high-energy neutrino sky in much more detail than the present arrays permit.

[28]
Title: CMB constraints on running non-Gaussianity
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We develop a complete set of tools for CMB forecasting, simulation and estimation of primordial running bispectra, arising from a variety of curvaton and single-field (DBI) models of Inflation. We validate our pipeline using mock CMB running non-Gaussianity realizations and test it on real data by obtaining experimental constraints on the $f_{\rm NL}$ running spectral index, $n_{\rm NG}$, using WMAP 9-year data. Our final bounds (68\% C.L.) read $-0.3< n_{\rm NG}<1.7$, $-0.3< n_{\rm NG}<1.3$, $-0.9<n_{\rm NG}<1.0$ for the single-field curvaton, two-field curvaton and DBI scenarios, respectively. We show forecasts and discuss potential improvements on these bounds, using Planck and future CMB surveys.

[29]
Title: Extragalactic diffuse gamma-rays from dark matter annihilation: revised prediction and full modelling uncertainties
Comments: 21 pages + appendix, 10 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

Recent high-energy data from Fermi-LAT on the diffuse gamma-background (DGRB) have been used to set among the best constraints on annihilating TeV cold dark matter (DM) candidates. In order to assess the robustness of these limits, we revisit and update the calculation of the isotropic extragalactic gamma-ray intensity from DM annihilation. The emission from halos with masses $\geq10^{10}\,M_{\odot}$ provides a robust lower bound on the predicted intensity. The intensity including smaller halos whose properties are extrapolated from their higher mass counterparts is typically 5 times higher, and boost from subhalos yields an additional factor ~1.5. We also rank the uncertainties from all ingredients and provide a detailed error budget in table 1. Overall, our fiducial intensity is a factor 5 lower than the one derived by the Fermi-LAT collaboration for their latest analysis. This indicates that the limits set on extragalactic DM annihilations could be relaxed by the same factor. We also calculate the expected intensity for self-interacting dark matter (SIDM) in massive halos and find the emission reduced by a factor 3 compared to the collisionless counterpart. The next release of the CLUMPY code will provide all the tools necessary to reproduce and ease future improvements of this prediction.

[30]
Title: Tomography of cool giant and supergiant star atmospheres. I. Validation of the method
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Cool giant and supergiant star atmospheres are characterized by complex velocity fields originating from convection and pulsation processes which are not fully understood yet. The velocity fields impact the formation of spectral lines, which thus contain information on the dynamics of stellar atmospheres. The tomographic method allows to recover the distribution of the component of the velocity field projected on the line of sight at different optical depths in the stellar atmosphere. The computation of the contribution function to the line depression aims at correctly identifying the depth of formation of spectral lines in order to construct numerical masks probing spectral lines forming at different optical depths. The tomographic method is applied to 1D model atmospheres and to a realistic 3D radiative hydrodynamics simulation performed with CO5BOLD in order to compare their spectral line formation depths and velocity fields. In 1D model atmospheres, each spectral line forms in a restricted range of optical depths. On the other hand, in 3D simulations, the line formation depths are spread in the atmosphere mainly because of temperature and density inhomogeneities. Comparison of CCF profiles obtained from 3D synthetic spectra with velocities from the 3D simulation shows that the tomographic method correctly recovers the distribution of the velocity component projected on the line of sight in the atmosphere.

[31]
Authors: Pedro Figueira
Comments: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 2016
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

This chapter describes briefly the key aspects behind the derivation of precise radial velocities. I start by defining radial velocity precision in the context of astrophysics in general and exoplanet searches in particular. Next I discuss the different basic elements that constitute a spectrograph, and how these elements and overall technical choices impact on the derived radial velocity precision. Then I go on to discuss the different wavelength calibration and radial velocity calculation techniques, and how these are intimately related to the spectrograph's properties. I conclude by presenting some interesting examples of planets detected through radial velocity, and some of the new-generation instruments that will push the precision limit further.

[32]
Title: Searching for X-ray Pulsations from Neutron Stars Using NICER
Comments: 4 pages, to appear in Proceedings of IAU Symposium 337: Pulsar Astrophysics - The Next 50 Years
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The Neutron Star Interior Composition Explorer (NICER) presents an exciting new capability for exploring the modulation properties of X-ray emitting neutron stars, including large area, low background, extremely precise absolute event time stamps, superb low-energy response and flexible scheduling. The Pulsation Searches and Multiwavelength Coordination working group has designed a 2.5 Ms observing program to search for emission and characterize the modulation properties of about 30 known or suspected neutron star sources across a number of source categories. A key early goal will be to search for pulsations from millisecond pulsars that might exhibit thermal pulsations from the surface suitable for pulse profile modeling to constrain the neutron star equation of state. In addition, we will search for pulsations from transitional millisecond pulsars, isolated neutron stars, low-mass X-ray binaries (LMXBs), accretion-powered millisecond pulsars, central compact objects and other sources. We present our science plan and initial results from the first months of the NICER mission, including the discovery of pulsations from the millisecond pulsar J1231-1411.

[33]
Title: Super-Flaring Active Region 12673 Has One of the Fastest Magnetic Flux Emergence Ever Observed
Comments: Accepted to the Research Notes of the AAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The flux emergence rate of AR 12673 is greater than any values reported in the literature of which we are aware.

[34]
Title: Reduced Order Modelling in searches for continuous gravitational waves - I. barycentering time delays
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

The frequencies and phases of emission from extra-solar sources, as measured by Earth-bound observers, are modulated due to the Doppler motions of the observer with respect to the source, and through relativistic effects. These modulations depend critically on the sky-location of the source. Precise knowledge of the modulations is required if wanting to coherently track the phase of a source over long observation times, for example in pulsar timing, or searches for continuous gravitational wave sources. The modulations can be modelled as a sky-location and time dependent time delay that converts arrival times at the observer to the inertial frame of the source. In many cases this inertial frame can be the solar system barycentre (SSB). We study the use of Reduced Order Modelling for speeding up the calculation of the time delay between an observer and the SSB for any sky-location and for coherent observations spanning one year. We find that the time delay model can be decomposed into just four basis vectors, which can be used to reconstruct the time delay for any sky-location to sub-nanosecond accuracy. When compared to the standard routines for time delay calculation used in gravitational wave searches, the use of the reduced basis can lead to a speed-up factor of 30 times. We have also studied the components of equivalent time delays for sources in binary systems. For these, assuming eccentricities less than 0.25, we can reconstruct the delays to within 100s of nanoseconds, with best case speed-ups of a factor of 10, or factors of two when having to interpolate the basis to different orbital periods or time stamps. In long-duration phase-coherent searches for sources with large sky-position uncertainties, or binary parameter uncertainties, these speed-ups could allow enhancements in their scopes without large additional computational burdens.

[35]
Title: Rotationally modulated photometric variations in B supergiants?
Authors: Alexandre David-Uraz (1 and 2), Gregg Wade (3), Anthony Moffat (4), Stan Owocki (1), Véronique Petit (1), the BRITE team ((1) University of Delaware, (2) Florida Institute of Technology, (3) Royal Military College of Canada, (4) Université de Montréal)
Comments: 6 pages, 3 figures, to be published in the proceedings of the 3rd BRITE Science Conference held in Saint-Michel-des-Saints (QC, Canada), 2017 August 7-10 -- Proceedings of the Polish Astronomical Society
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

In this contribution, we present BRITE observations of the early-B supergiants $\epsilon$ Ori and $\kappa$ Ori. We perform a preliminary analysis of the data acquired over the first two Orion observing runs. We evaluate whether they are compatible with co-rotating bright spots and discuss the challenges of such an approach.

[36]
Title: Modelling the atmospheric composition of warm exoplanets
Comments: Submitted to Experimental Astronomy, ARIEL Special Issue
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Since the discovery of the first extrasolar planet more than twenty years ago, we have discovered more than three thousand planets orbiting stars other than the Sun. Current observational instruments (on board the Hubble Space Telescope, Spitzer, and on ground-based facilities) allowed the scientific community to obtain important information on the physical and chemical properties of these planets. However, for a more in-depth characterisation of these worlds, more powerful telescopes are needed. Thanks to the high sensitivity of their instruments, the next generation of space observatories (e.g. James Webb Space Telescope, ARIEL) will provide observations of unprecedented quality, allowing us to extract far more information than what was previously possible. Such high quality observations will provide constraints on theoretical models of exoplanet atmospheres and lead to a greater understanding of the physics and chemistry. Important modelling efforts have been carried out during the past few years, showing that numerous parameters and processes (such as the element abundances, temperature, mixing, etc.) are likely to effect the atmospheric composition of exoplanets and subsequently the observable spectra. In this manuscript, we review the different parameters that can influence the molecular composition of exoplanet atmospheres. We also consider future developments that are necessary to improve atmospheric models, driven by the need to interpret the available observations and show how ARIEL is going to improve our view and characterisation of exoplanet atmospheres.

[37]
Title: Neutrino Mass Priors for Cosmology from Random Matrices
Comments: 16+2 pages, two column, 7 figures, 2 tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

Cosmological measurements of structure are placing increasingly strong constraints on the sum of the neutrino masses, $\Sigma m_\nu$, through Bayesian inference. Because these constraints depend on the choice for the prior probability $\pi(\Sigma m_\nu)$, we argue that this prior should be motivated by fundamental physical principles rather than the ad hoc choices that are common in the literature. The first step in this direction is to specify the prior directly at the level of the neutrino mass matrix $M_\nu$, since this is the parameter appearing in the Lagrangian of the particle physics theory. Thus by specifying a probability distribution over $M_\nu$, and by including the known squared mass splittings, we predict a theoretical probability distribution over $\Sigma m_\nu$ that we interpret as a Bayesian prior probability $\pi(\Sigma m_\nu)$. We find that $\pi(\Sigma m_\nu)$ peaks close to the smallest $\Sigma m_\nu$ allowed by the measured mass splittings, roughly $0.06 \, {\rm eV}$ ($0.1 \, {\rm eV}$) for normal (inverted) ordering, due to the phenomenon of eigenvalue repulsion in random matrices. We consider three models for neutrino mass generation: Dirac, Majorana, and Majorana via the seesaw mechanism; differences in the predicted priors $\pi(\Sigma m_\nu)$ allow for the possibility of having indications about the physical origin of neutrino masses once sufficient experimental sensitivity is achieved. We present fitting functions for $\pi(\Sigma m_\nu)$, which provide a simple means for applying these priors to cosmological constraints on the neutrino masses or marginalizing over their impact on other cosmological parameters.

[38]
Title: Simulating the galaxy cluster "El Gordo": gas motion, kinetic Sunyaev-Zel'dovich signal, and X-ray line features
Authors: Congyao Zhang (1, 2), Qingjuan Yu (2), Youjun Lu (3, 4) ((1) MPA, (2) KIAA, (3) NAOC, (4) UCAS)
Comments: 10 pages, 6 figures, submitted to ApJ
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

The massive galaxy cluster "El Gordo" (ACT-CL J0102--4915) is a rare merging system with a high collision speed suggested by multi-wavelength observations and the theoretical modeling. Zhang et al. (2015) propose two types of mergers, a nearly head-on merger and an off-axis merger with a large impact parameter, to reproduce most of the observational features of the cluster, by using numerical simulations. The different merger configurations of the two models result in different gas motion in the simulated clusters. In this paper, we predict the kinetic Sunyaev-Zel'dovich (kSZ) effect, the relativistic correction of the thermal Sunyaev-Zel'dovich (tSZ) effect, and the X-ray spectrum of this cluster, based on the two proposed models. We find that (1) the amplitudes of the kSZ effect resulting from the two models are both on the order of $\Delta T/T\sim10^{-5}$; but their morphologies are different, which trace the different line-of-sight velocity distributions of the systems; (2) the relativistic correction of the tSZ effect around $240 {\rm\,GHz}$ can be possibly used to constrain the temperature of the hot electrons heated by the shocks; and (3) the shift between the X-ray spectral lines emitted from different regions of the cluster can be significantly different in the two models. The shift and the line broadening can be up to $\sim 25{\rm\,eV}$ and $50{\rm\,eV}$, respectively. We expect that future observations of the kSZ effect and the X-ray spectral lines (e.g., by ALMA, XARM) will provide a strong constraint on the gas motion and the merger configuration of ACT-CL J0102--4915.

[39]
Title: Reconstruction of a direction-dependent primordial power spectrum from Planck CMB data
Comments: 32 pages, 22 figures, 6 tables
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

We consider the possibility that the primordial curvature perturbation is direction-dependent. To first order this is parameterised by a quadrupolar modulation of the power spectrum and results in statistical anisotropy of the cosmic microwave background, which can be quantified using the bipolar spherical harmonic representation. We compute these for the Planck Release 2 SMICA map and use them to infer the quadrupole modulation of the primordial power spectrum which, going beyond previous work, we allow to be scale-dependent. Uncertainties are estimated from Planck FFP9 simulations. Consistent with the Planck collaboration's findings, we find no evidence for a constant quadrupole modulation, nor one scaling with wave number as a power law. However our non-parametric reconstruction suggests several spectral features. When a constant quadrupole modulation is fitted to data limited to the wave number range $0.005 \leq k/\mathrm{Mpc}^{-1} \leq 0.008$, we find that its preferred direction is aligned with the cosmic hemispherical asymmetry. To determine the statistical significance we construct two different test statistics and test them on our reconstructions from data, against reconstructions of realisations of noise only. With a test statistic sensitive only to the amplitude of the modulation, the reconstructions are unusual at $2.5\sigma$ significance in the full wave number range, but at $2.2\sigma$ when limited to the intermediate wave number range $0.008 \leq k/\mathrm{Mpc}^{-1} \leq 0.074$. With the second test statistic, sensitive also to direction, the reconstructions are unusual with $4.6\sigma$ significance, dropping to $2.7 \sigma$ for the intermediate wave number range. Our approach is easily generalised to include other data sets such as polarisation, large-scale structure and forthcoming 21-cm line observations which will enable these anomalies to be investigated further.