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Monthly Notices of the Royal Astronomical Society

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https://www.readbyqxmd.com/read/27559304/the-winds-from-hl-tau
#1
P D Klaassen, J C Mottram, L T Maud, A Juhasz
Outflowing motions, whether a wind launched from the disc, a jet launched from the protostar, or the entrained molecular outflow, appear to be a ubiquitous feature of star formation. These outwards motions have a number of root causes, and how they manifest is intricately linked to their environment as well as the process of star formation itself. Using the Atacama Large Millimeter/submillimeter Array (ALMA) Science Verification data of HL Tau, we investigate the high-velocity molecular gas being removed from the system as a result of the star formation process...
July 21, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27279787/forming-supermassive-black-hole-seeds-under-the-influence-of-a-nearby-anisotropic-multifrequency-source
#2
John A Regan, Peter H Johansson, John H Wise
The photodissociation of H2 by a nearby anisotropic source of radiation is seen as a critical component in creating an environment in which a direct collapse black hole may form. Employing radiative transfer we model the effect of multifrequency (0.76-60 eV) radiation on a collapsing halo at high redshift. We vary both the shape of the spectrum which emits the radiation and the distance to the emitting galaxy. We use blackbody spectra with temperatures of T = 10(4) K and 10(5) K and a realistic stellar spectrum...
July 1, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27279786/direct-collapse-to-supermassive-black-hole-seeds-comparing-the-amr-and-sph-approaches
#3
Yang Luo, Kentaro Nagamine, Isaac Shlosman
We provide detailed comparison between the adaptive mesh refinement (AMR) code enzo-2.4 and the smoothed particle hydrodynamics (SPH)/N-body code gadget-3 in the context of isolated or cosmological direct baryonic collapse within dark matter (DM) haloes to form supermassive black holes. Gas flow is examined by following evolution of basic parameters of accretion flows. Both codes show an overall agreement in the general features of the collapse; however, many subtle differences exist. For isolated models, the codes increase their spatial and mass resolutions at different pace, which leads to substantially earlier collapse in SPH than in AMR cases due to higher gravitational resolution in gadget-3...
July 1, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27279785/new-methods-to-constrain-the-radio-transient-rate-results-from-a-survey-of-four-fields-with-lofar
#4
D Carbone, A J van der Horst, R A M J Wijers, J D Swinbank, A Rowlinson, J W Broderick, Y N Cendes, A J Stewart, M E Bell, R P Breton, S Corbel, J Eislöffel, R P Fender, J-M Grießmeier, J W T Hessels, P Jonker, M Kramer, C J Law, J C A Miller-Jones, M Pietka, L H A Scheers, B W Stappers, J van Leeuwen, R Wijnands, M Wise, P Zarka
We report on the results of a search for radio transients between 115 and 190 MHz with the LOw-Frequency ARray (LOFAR). Four fields have been monitored with cadences between 15 min and several months. A total of 151 images were obtained, giving a total survey area of 2275 deg(2). We analysed our data using standard LOFAR tools and searched for radio transients using the LOFAR Transients Pipeline. No credible radio transient candidate has been detected; however, we are able to set upper limits on the surface density of radio transient sources at low radio frequencies...
July 1, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27279784/modelling-galaxy-clustering-halo-occupation-distribution-versus-subhalo-matching
#5
Hong Guo, Zheng Zheng, Peter S Behroozi, Idit Zehavi, Chia-Hsun Chuang, Johan Comparat, Ginevra Favole, Stefan Gottloeber, Anatoly Klypin, Francisco Prada, Sergio A Rodríguez-Torres, David H Weinberg, Gustavo Yepes
We model the luminosity-dependent projected and redshift-space two-point correlation functions (2PCFs) of the Sloan Digital Sky Survey (SDSS) Data Release 7 Main galaxy sample, using the halo occupation distribution (HOD) model and the subhalo abundance matching (SHAM) model and its extension. All the models are built on the same high-resolution N-body simulations. We find that the HOD model generally provides the best performance in reproducing the clustering measurements in both projected and redshift spaces...
July 1, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27279783/the-minimum-mass-of-detectable-planets-in-protoplanetary-discs-and-the-derivation-of-planetary-masses-from-high-resolution-observations
#6
Giovanni P Rosotti, Attila Juhasz, Richard A Booth, Cathie J Clarke
We investigate the minimum planet mass that produces observable signatures in infrared scattered light and submillimetre (submm) continuum images and demonstrate how these images can be used to measure planet masses to within a factor of about 2. To this end, we perform multi-fluid gas and dust simulations of discs containing low-mass planets, generating simulated observations at 1.65, 10 and 850 μm. We show that the minimum planet mass that produces a detectable signature is ∼15 M⊕: this value is strongly dependent on disc temperature and changes slightly with wavelength (favouring the submm)...
July 1, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27279782/low-radio-frequency-eclipses-of-the-redback-pulsar-j2215-5135-observed-in-the-image-plane-with-lofar
#7
J W Broderick, R P Fender, R P Breton, A J Stewart, A Rowlinson, J D Swinbank, J W T Hessels, T D Staley, A J van der Horst, M E Bell, D Carbone, Y Cendes, S Corbel, J Eislöffel, H Falcke, J-M Grießmeier, T E Hassall, P Jonker, M Kramer, M Kuniyoshi, C J Law, S Markoff, G J Molenaar, M Pietka, L H A Scheers, M Serylak, B W Stappers, S Ter Veen, J van Leeuwen, R A M J Wijers, R Wijnands, M W Wise, P Zarka
The eclipses of certain types of binary millisecond pulsars (i.e. 'black widows' and 'redbacks') are often studied using high-time-resolution, 'beamformed' radio observations. However, they may also be detected in images generated from interferometric data. As part of a larger imaging project to characterize the variable and transient sky at radio frequencies <200 MHz, we have blindly detected the redback system PSR J2215+5135 as a variable source of interest with the Low-Frequency Array (LOFAR). Using observations with cadences of two weeks - six months, we find preliminary evidence that the eclipse duration is frequency dependent (∝ν(-0...
July 1, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27279781/modelling-accretion-disc-and-stellar-wind-interactions-the-case-of-sgr-a
#8
I M Christie, M Petropoulou, P Mimica, D Giannios
Sgr A* is an ideal target to study low-luminosity accreting systems. It has been recently proposed that properties of the accretion flow around Sgr A* can be probed through its interactions with the stellar wind of nearby massive stars belonging to the S-cluster. When a star intercepts the accretion disc, the ram and thermal pressures of the disc terminate the stellar wind leading to the formation of a bow shock structure. Here, a semi-analytical model is constructed which describes the geometry of the termination shock formed in the wind...
July 1, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27274704/the-different-baryonic-tully-fisher-relations-at-low-masses
#9
Chris B Brook, Isabel Santos-Santos, Greg Stinson
We compare the Baryonic Tully-Fisher relation (BTFR) of simulations and observations of galaxies ranging from dwarfs to spirals, using various measures of rotational velocity V rot. We explore the BTFR when measuring V rot at the flat part of the rotation curve, V flat, at the extent of H i gas, V last, and using 20 per cent (W 20) and 50 per cent (W 50) of the width of H i line profiles. We also compare with the maximum circular velocity of the parent halo, [Formula: see text], within dark matter only simulations...
June 11, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27274703/tapering-the-sky-response-for-angular-power-spectrum-estimation-from-low-frequency-radio-interferometric-data
#10
Samir Choudhuri, Somnath Bharadwaj, Nirupam Roy, Abhik Ghosh, Sk Saiyad Ali
It is important to correctly subtract point sources from radio-interferometric data in order to measure the power spectrum of diffuse radiation like the Galactic synchrotron or the Epoch of Reionization 21-cm signal. It is computationally very expensive and challenging to image a very large area and accurately subtract all the point sources from the image. The problem is particularly severe at the sidelobes and the outer parts of the main lobe where the antenna response is highly frequency dependent and the calibration also differs from that of the phase centre...
June 11, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27284270/fr-ii-radio-galaxies-at-low-frequencies-i-morphology-magnetic-field-strength-and-energetics
#11
Jeremy J Harwood, Judith H Croston, Huib T Intema, Adam J Stewart, Judith Ineson, Martin J Hardcastle, Leith Godfrey, Philip Best, Marisa Brienza, Volker Heesen, Elizabeth K Mahony, Raffaella Morganti, Matteo Murgia, Emanuela Orrú, Huub Röttgering, Aleksandar Shulevski, Michael W Wise
Due to their steep spectra, low-frequency observations of Fanaroff-Riley type II (FR II) radio galaxies potentially provide key insights in to the morphology, energetics and spectrum of these powerful radio sources. However, limitations imposed by the previous generation of radio interferometers at metre wavelengths have meant that this region of parameter space remains largely unexplored. In this paper, the first in a series examining FR IIs at low frequencies, we use LOFAR (LOw Frequency ARray) observations between 50 and 160 MHz, along with complementary archival radio and X-ray data, to explore the properties of two FR II sources, 3C 452 and 3C 223...
June 1, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27453685/the-%C3%AE-ray-afterglows-of-tidal-disruption-events
#12
Xian Chen, Germán Arturo Gómez-Vargas, James Guillochon
A star wandering too close to a supermassive black hole (SMBH) will be tidally disrupted. Previous studies of such 'tidal disruption event' (TDE) mostly focus on the stellar debris that are bound to the system, because they give rise to luminous flares. On the other hand, half of the stellar debris in principle are unbound and can stream to a great distance, but so far there is no clear evidence that this 'unbound debris stream' (UDS) exists. Motivated by the fact that the circum-nuclear region around SMBHs is usually filled with dense molecular clouds (MCs), here we investigate the observational signatures resulting from the collision between an UDS and an MC, which is likely to happen hundreds of years after a TDE...
May 21, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27346980/collision-velocity-of-dust-grains-in-self-gravitating-protoplanetary-discs
#13
Richard A Booth, Cathie J Clarke
We have conducted the first comprehensive numerical investigation of the relative velocity distribution of dust particles in self-gravitating protoplanetary discs with a view to assessing the viability of planetesimal formation via direct collapse in such environments. The viability depends crucially on the large sizes that are preferentially collected in pressure maxima produced by transient spiral features (Stokes numbers, St ∼ 1); growth to these size scales requires that collision velocities remain low enough that grain growth is not reversed by fragmentation...
May 21, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27346979/an-apodized-kepler-periodogram-for-separating-planetary-and-stellar-activity-signals
#14
Philip C Gregory
A new apodized Keplerian (AK) model is proposed for the analysis of precision radial velocity (RV) data to model both planetary and stellar activity (SA) induced RV signals. A symmetrical Gaussian apodization function with unknown width and centre can distinguish planetary signals from SA signals on the basis of the span of the apodization window. The general model for m AK signals includes a linear regression term between RV and the SA diagnostic log (R'hk), as well as an extra Gaussian noise term with unknown standard deviation...
May 21, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27346978/line-driven-ablation-of-circumstellar-discs-i-optically-thin-decretion-discs-of-classical-oe-be-stars
#15
Nathaniel Dylan Kee, Stanley Owocki, J O Sundqvist
The extreme luminosities of massive, hot OB stars drive strong stellar winds through line-scattering of the star's UV continuum radiation. For OB stars with an orbiting circumstellar disc, we explore here the effect of such line-scattering in driving an ablation of material from the disc's surface layers, with initial focus on the marginally optically thin decretion discs of classical Oe and Be stars. For this we apply a multidimensional radiation-hydrodynamics code that assumes simple optically thin ray tracing for the stellar continuum, but uses a multiray Sobolev treatment of the line transfer; this fully accounts for the efficient driving by non-radial rays, due to desaturation of line-absorption by velocity gradients associated with the Keplerian shear in the disc...
May 21, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27274702/cluster-mass-profile-reconstruction-with-size-and-flux-magnification-on-the-hst-stages-survey
#16
Christopher A J Duncan, Catherine Heymans, Alan F Heavens, Benjamin Joachimi
We present the first measurement of individual cluster mass estimates using weak lensing size and flux magnification. Using data from the HST STAGES (Space Telescope A901/902 Galaxy Evolution Survey) survey of the A901/902 supercluster we detect the four known groups in the supercluster at high significance using magnification alone. We discuss the application of a fully Bayesian inference analysis, and investigate a broad range of potential systematics in the application of the method. We compare our results to a previous weak lensing shear analysis of the same field finding the recovered signal-to-noise of our magnification-only analysis to range from 45 to 110 per cent of the signal-to-noise in the shear-only analysis...
March 21, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27274701/the-iron-dispersion-of-the-globular-cluster-m2-revised
#17
C Lardo, A Mucciarelli, N Bastian
M2 has been claimed to possess three distinct stellar components that are enhanced in iron relative to each other. We use equivalent width measurements from 14 red giant branch stars from which Yong et al. detect a ∼0.8 dex wide, trimodal iron distribution to redetermine the metallicity of the cluster. In contrast to Yong et al., which derive atmospheric parameters following only the classical spectroscopic approach, we perform the chemical analysis using three different methods to constrain effective temperatures and surface gravities...
March 21, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/27013768/the-interstellar-chemistry-of-h2c3o-isomers
#18
Jean-Christophe Loison, Marcelino Agúndez, Núria Marcelino, Valentine Wakelam, Kevin M Hickson, José Cernicharo, Maryvonne Gerin, Evelyne Roueff, Michel Guélin
We present the detection of two H2C3O isomers, propynal and cyclopropenone, toward various starless cores and molecular clouds, together with upper limits for the third isomer propadienone. We review the processes controlling the abundances of H2C3O isomers in interstellar media showing that the reactions involved are gas-phase ones. We show that the abundances of these species are controlled by kinetic rather than thermodynamic effects.
March 11, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/26924856/polycyclic-aromatic-hydrocarbons-and-molecular-hydrogen-in-oxygen-rich-planetary-nebulae-the-case-of-ngc-6720
#19
N L J Cox, P Pilleri, O Berné, J Cernicharo, C Joblin
Evolved stars are primary sources for the formation of polycyclic aromatic hydrocarbons (PAHs) and dust grains. Their circumstellar chemistry is usually designated as either oxygen-rich or carbon-rich, although dual-dust chemistry objects, whose infrared spectra reveal both silicate- and carbon-dust features, are also known. The exact origin and nature of this dual-dust chemistry is not yet understood. Spitzer-IRS mid-infrared spectroscopic imaging of the nearby, oxygen-rich planetary nebula NGC 6720 reveals the presence of the 11...
February 11, 2016: Monthly Notices of the Royal Astronomical Society
https://www.readbyqxmd.com/read/26997679/the-abundance-of-28-si-32-s-29-si-32-s-28-si-34-s-and-30-si-32-s-in-the-inner-layers-of-the-envelope-of-irc-10216
#20
J P Fonfría, J Cernicharo, M J Richter, M Fernández-López, L Velilla Prieto, J H Lacy
We present high spectral resolution mid-IR observations of SiS towards the C-rich AGB star IRC+10216 carried out with the Texas Echelon-cross-Echelle Spectrograph mounted on the NASA Infrared Telescope Facility. We have identified 204 ro-vibrational lines of (28)Si(32)S, 26 of (29)Si(32)S, 20 of (28)Si(34)S, and 15 of (30)Si(32)S in the frequency range 720 - 790 cm(-1). These lines belong to bands v = 1 - 0, 2 - 1, 3 - 2, 4-3, and 5-4, and involve rotational levels with Jlow ≲ 90. About 30 per cent of these lines are unblended or weakly blended and can be partially or entirely fitted with a code developed to model the mid-IR emission of a spherically symmetric circumstellar envelope composed of expanding gas and dust...
August 13, 2015: Monthly Notices of the Royal Astronomical Society
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