43 results match your criteria Astrophysical Journal Letters[Journal]


Slowdown and Heating of Interstellar Neutral Helium by Elastic Collisions Beyond the Heliopause.

Astrophys J Lett 2021 Apr 26;911(2). Epub 2021 Apr 26.

Department of Mathematics and Statistics, University of Waikato, Hamilton, New Zealand.

Direct sampling of interstellar neutral (ISN) atoms close to the Sun enables studies of the very local interstellar medium (VLISM) around the heliosphere. The primary population of ISN helium atoms has, until now, been assumed to reflect the pristine VLISM conditions at the heliopause. Consequently, the atoms observed at 1 au by the Interstellar Boundary Explorer (IBEX) were used to determine the VLISM temperature and velocity relative to the Sun, without accounting for elastic collisions with other species outside the heliopause. Read More

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How Sublimation Delays the Onset of Dusty Debris Disk Formation Around White Dwarf Stars.

Astrophys J Lett 2021 Jun 2;913(2). Epub 2021 Jun 2.

Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ.

Although numerous white dwarf stars host dusty debris disks, the temperature distribution of these stars differs significantly from the white dwarf population as a whole. Dusty debris disks exist exclusively around white dwarfs cooler than 27,000 K. This is all the more enigmatic given that the formation processes of dusty debris disks should favor younger, hotter white dwarfs, which likely host more dynamically unstable planetary systems. Read More

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Thiols in the ISM: first detection of HC(O)SH and confirmation of CHSH.

Astrophys J Lett 2021 May 30;912(1). Epub 2021 Apr 30.

University of Maryland, College Park, ND 20742-2421, USA.

The chemical compounds carrying the thiol group (-SH) have been considered essential in recent prebiotic studies regarding the polymerization of amino acids. We have searched for this kind of compounds toward the Galactic Centre quiescent cloud G+0.693-0. Read More

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Cluster Analysis of Presolar Silicon Carbide Grains: Evaluation of Their Classification and Astrophysical Implications.

Astrophys J Lett 2021 Feb 29;907(2). Epub 2021 Jan 29.

Earth and Planets Laboratory, Carnegie Institution for Science, Washington, DC 20015, USA.

Cluster analysis of presolar silicon carbide grains based on literature data for C/C, N/N, Si/Si, and Si/Si including or not inferred initial Al/Al data, reveals nine clusters agreeing with previously defined grain types but also highlighting new divisions. Mainstream grains reside in three clusters probably representing different parent star metallicities. One of these clusters has a compact core, with a narrow range of composition, pointing to an enhanced production of SiC grains in asymptotic giant branch (AGB) stars with a narrow range of masses and metallicities. Read More

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February 2021

Explaining the Galilean Satellites' Density Gradient by Hydrodynamic Escape.

Astrophys J Lett 2020 Jul 15;897(2). Epub 2020 Jul 15.

Department of Earth and Planetary Sciences, UC Santa Cruz, 1156 High St, Santa Cruz, CA 95064, USA.

The Galilean satellites exhibit a monotonic decrease in density (and increase in ice mass fraction) with distance from Jupiter (Pollack & Fanale 1982). Whether this is because of the background conditions when they formed (Lunine & Stevenson 1982; Canup & Ward 2002; Mosqueira & Estrada 2003a; Ronnet et al. 2017), the process of accretion itself (Dwyer et al. Read More

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NuSTAR Observation of a Minuscule Microflare in a Solar Active Region.

Astrophys J Lett 2020 Apr 22;893(2). Epub 2020 Apr 22.

Santa Cruz Institute of Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA.

We present X-ray imaging spectroscopy of one of the weakest active region (AR) microflares ever studied. The microflare occurred at ~11:04 UT on 2018 September 9 and we studied it using the Nuclear Spectroscopic Telescope ARray (NuSTAR) and the Solar Dynamic Observatory's Atmospheric Imaging Assembly (SDO/AIA). The microflare is observed clearly in 2. Read More

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Laboratory Observations of Ultra-Low Frequency Analogue Waves Driven by the Right-Hand Resonant Ion Beam Instability.

Astrophys J Lett 2020 Mar 27;891(1). Epub 2020 Feb 27.

Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA.

The Right-Hand Resonant Instability (RHI) is one of several electromagnetic ion/ion beam instabilities responsible for the formation of parallel magnetized collisionless shocks and the generation of ultra-low frequency (ULF) waves in their foreshocks. This instability has been observed for the first time under foreshock-relevant conditions in the laboratory through the repeatable interaction of a preformed magnetized background plasma and a super-Alfvénic laser-produced plasma. This platform has enabled unprecedented volumetric measurements of waves generated by the RHI, revealing filamentary current structures in the transverse plane. Read More

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Accelerated Electrons Observed Down to <7 keV in a Solar Microflare.

Astrophys J Lett 2020 Mar 9;891(2). Epub 2020 Mar 9.

University of California at Berkeley, Berkeley, CA, USA.

We report the detection of emission from a nonthermal electron distribution in a small solar microflare (GOES class A5.7) observed by the , with supporting observation by the (). The flaring plasma is well accounted for by a thick-target model of accelerated electrons collisionally thermalizing within the loop, akin to the "coronal thick-target" behavior occasionally observed in larger flares. Read More

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Particle-in-cell Simulations of the Whistler Heat-flux Instability in Solar Wind Conditions.

Astrophys J Lett 2019 3;882(1). Epub 2019 Sep 3.

Centre for mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium.

In collision-poor plasmas from space, e.g., solar wind or stellar outflows, the heat flux carried by the strahl or beaming electrons is expected to be regulated by the self-generated instabilities. Read More

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September 2019

Comet C/2017 S3 (PanSTARRS): Outbursts and Disintegration.

Astrophys J Lett 2019 Oct;884(2)

Dept. of Climate and Space Sciences and Engineering, University of Michigan, 2455 Hayward Street, Ann Arbor, MI 48109-2143.

The Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyman-alpha camera on the SOlar and Heliospheric Observer (SOHO) satellite observed the hydrogen coma of comet C/2017 S3 (PanSTARRS) for the last month of its activity from 2018 July 4 to August 4 and what appears to have been its final disintegration just 11 days before its perihelion on August 15. The hydrogen coma indicated water production had a small outburst on July 8 at a heliocentric distance of 1.1AU and then a much larger one on July 20 at 0. Read More

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October 2019

Gas Accretion within the Dust Cavity in AB Aur.

Astrophys J Lett 2019 Jul 2;879(1). Epub 2019 Jul 2.

Observatorio Astronómico Nacional (OAN, IGN), Calle Alfonso XII 3 E-28014 Madrid, Spain.

AB Aur is a Herbig Ae star hosting a well-known transitional disk. Because of its proximity and low inclination angle, it is an excellent object to study planet formation. Our goal is to investigate the chemistry and dynamics of the molecular gas component in the AB Aur disk, and its relation with the prominent horseshoe shape observed in continuum mm emission. Read More

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TESS DISCOVERY OF A TRANSITING SUPER-EARTH IN THE MENSAE SYSTEM.

Astrophys J Lett 2018 Dec 30;868(2). Epub 2018 Nov 30.

Department of Physics, and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.

We report the detection of a transiting planet around Men (HD 39091), using data from the (). The solar-type host star is unusually bright ( = 5.7) and was already known to host a Jovian planet on a highly eccentric, 5. Read More

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December 2018

Multi-TeV Emission From the Vela Pulsar.

Astrophys J Lett 2018 Dec 11;869(1). Epub 2018 Dec 11.

North-West University, Private Bag X6001, Potchefstroom 2520, South Africa.

Pulsed emission from the Vela pulsar at energies above 3 TeV has recently been detected by the H.E.S. Read More

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December 2018

Cloud Coalescence: A Dynamical Instability Affecting Multiphase Environments.

Astrophys J Lett 2019 May 25;876(1). Epub 2019 Apr 25.

Department of Physics & Astronomy, University of Nevada, Las Vegas, NV, USA.

Mass and size distributions are the key characteristics of any astrophysical object, including the densest clumps comprising the cold phase of multiphase environments. In our recent papers, we showed how individual clouds of various sizes form and evolve in active galactic nuclei. In particular, we showed that large clouds undergo damped oscillations as a response to their formation process. Read More

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Extremely Cr- and Ti-rich presolar oxide grains in a primitive meteorite: Formation in rare types of supernovae and implications for the astrophysical context of solar system birth.

Astrophys J Lett 2018 Apr 18;856(2). Epub 2018 Mar 18.

Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Rd NW, Washington, DC 20015, USA;

We report the identification of 19 presolar oxide grains from the Orgueil CI meteorite with substantial enrichments in Cr, with Cr/Cr ratios ranging from 1.2 to 56 times the solar value. The most enriched grains also exhibit enrichments at mass 50, most likely due in part to Ti, but close-to-normal or depleted Cr/Cr ratios. Read More

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High-resolution SOFIA/EXES Spectroscopy of SO Gas in the Massive Young Stellar Object MonR2 IRS3: Implications for the Sulfur Budget.

Astrophys J Lett 2018 16;868(1). Epub 2018 Nov 16.

Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands.

Sulfur has been observed to be severely depleted in dense clouds leading to uncertainty in the molecules that contain it and the chemistry behind their evolution. Here, we aim to shed light on the sulfur chemistry in young stellar objects (YSOs) by using high-resolution infrared spectroscopy of absorption by the rovibrational band of SO obtained with the Echelon-Cross-Echelle Spectrograph on the Stratospheric Observatory for Infrared Astronomy. Using local thermodynamic equilibrium models we derive physical parameters for the SO gas in the massive YSO MonR2 IRS3. Read More

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November 2018

Thermal History of CB Chondrules and Cooling Rate Distributions of Ejecta Plumes.

Astrophys J Lett 2018 Mar 7;855(2). Epub 2018 Mar 7.

Physics, SUNY at Cortland, NY 13045, USA.

It has been proposed that some meteorites, CB and CH chondrites, contain material formed as a result of a protoplanetary collision during accretion. Their melt droplets (chondrules) and FeNi metal are proposed to have formed by evaporation and condensation in the resulting impact plume. We observe that the skeletal olivine (SO) chondrules in CB chondrites have a blebby texture and an enrichment in refractory elements not found in normal chondrules. Read More

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Discovery of Interstellar Isocyanogen (CNCN): Further Evidence that Dicyanopolyynes are Abundant in Space.

Astrophys J Lett 2018 Jul 13;861(2). Epub 2018 Jul 13.

Instituto de Física Fundamental, CSIC, C/ Serrano 123, 28006 Madrid, Spain.

It is thought that dicyanopolyynes could be potentially abundant interstellar molecules, although their lack of dipole moment makes it impossible to detect them through radioastronomical techniques. Recently, the simplest member of this chemical family, cyanogen (NCCN), was indirectly probed for the first time in interstellar space through the detection of its protonated form toward the dense clouds L483 and TMC-1. Here we present a second firm evidence of the presence of NCCN in interstellar space, namely the detection of the metastable and polar isomer isocyanogen (CNCN). Read More

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Variable Nature of Magnetically-Driven Ultra-Fast Outflows.

Astrophys J Lett 2018 Sep;864(2)

Research Center for Astronomy, Academy of Athens, Athens 11527, Greece.

Among a number of active galactic nuclei (AGNs) that drive ionized outflows in X-rays, a low-redshift ( = 0.184) quasar, PDS 456, is long known to exhibit one of the exemplary ultra-fast outflows (UFOs). However, the physical process of acceleration mechanism is yet to be definitively constrained. Read More

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September 2018

Discovery of the Ubiquitous Cation NS in Space Confirmed by Laboratory Spectroscopy.

Astrophys J Lett 2018 Jan;853

IRAP, Université de Toulouse, CNRS, UPS, CNES, Toulouse, France.

We report the detection in space of a new molecular species which has been characterized spectroscopically and fully identified from astrophysical data. The observations were carried out with the 30m IRAM telescopea. The molecule is ubiquitous as its =2→1 transition has been found in cold molecular clouds, prestellar cores, and shocks. Read More

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January 2018

First Detection of Interstellar SH.

Astrophys J Lett 2017 Dec;851

Laboratoire d'Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France.

We present the first detection of gas phase SH in the Horsehead, a moderately UV-irradiated nebula. This confirms the presence of doubly sulfuretted species in the interstellar medium and opens a new challenge for sulfur chemistry. The observed SH abundance is ~5×10, only a factor 4-6 lower than that of the widespread HS molecule. Read More

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December 2017

DETERMINING THE ELEMENTAL AND ISOTOPIC COMPOSITION OF THE PRESOLAR NEBULA FROM GENESIS DATA ANALYSIS: THE CASE OF OXYGEN.

Astrophys J Lett 2017 Dec 6;851(No 1). Epub 2017 Dec 6.

Department of Physics, CSUF, Fullerton CA 92831.

We compare element and isotopic fractionations measured in solar wind samples collected by NASA's Genesis mission with those predicted from models incorporating both the ponderomotive force in the chromosphere and conservation of the first adiabatic invariant in the low corona. Generally good agreement is found, suggesting that these factors are consistent with the process of solar wind fractionation. Based on bulk wind measurements, we also consider in more detail the isotopic and elemental abundances of O. Read More

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December 2017

STAR FORMATION AT = 2.481 IN THE LENSED GALAXY SDSS J1110+6459: STAR FORMATION DOWN TO 30 PARSEC SCALES.

Astrophys J Lett 2017 Jul 6;843(No 2). Epub 2017 Jul 6.

Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA.

We present measurements of the surface density of star formation, the star-forming clump luminosity function, and the clump size distribution function, for the lensed galaxy SGAS J111020.0+645950.8 at a redshift of =2. Read More

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Energy Dissipation in the Upper Atmospheres of Trappist-1 Planets.

Astrophys J Lett 2018 Mar 23;856(1). Epub 2018 Mar 23.

National Institute of Aerospace, 100 Exploration Way, Hampton, VA 23666, USA.

We present a method to quantify the upper-limit of the energy transmitted from the intense stellar wind to the upper atmospheres of three of the Trappist-1 planets (e, f, and g). We use a formalism that treats the system as two electromagnetic regions, where the efficiency of the energy transmission between one region (the stellar wind at the planetary orbits) to the other (the planetary ionospheres) depends on the relation between the conductances and impedances of the two regions. Since the energy flux of the stellar wind is very high at these planetary orbits, we find that for the case of high transmission efficiency (when the conductances and impedances are close in magnitude), the energy dissipation in the upper planetary atmospheres is also very large. Read More

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SEASONAL EVOLUTION OF TITAN'S STRATOSPHERE NEAR THE POLES.

Astrophys J Lett 2018 Feb;854(2)

Planetary Systems Laboratory, Goddard Space Flight Center, Greenbelt, MD 20771, USA.

In this paper we report the monitoring of seasonal evolution near Titan's poles. We find Titan's south pole to exhibit since 2010 a strong temperature decrease and a dramatic enhancement of several trace species such as complex hydrocarbons and nitriles (HCN and CH in particular) previously only observed at high northern latitudes (Coustenis et al. 2016 and references therein). Read More

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February 2018

Photoionization Modeling of Titan's Dayside Ionosphere.

Astrophys J Lett 2017 Dec 27;850(2). Epub 2017 Nov 27.

Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, USA.

Previous modeling studies of Titan's dayside ionosphere predict electron number densities that are roughly a factor of 2 higher than those observed by the RPWS/Langmuir probe. The issue can equivalently be described as the ratio between the calculated electron production rates and the square of the observed electron number densities resulting in roughly a factor of 4 higher effective recombination coefficient than expected from the ion composition and the electron temperature. Here we make an extended reassessment of Titan's dayside ionization balance, focusing on 34 flybys between TA and T120. Read More

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December 2017

Probing the Cold Dust Emission in the AB Aur Disk: A Dust Trap in a Decaying Vortex?

Astrophys J Lett 2017 Sep 28;846(1). Epub 2017 Aug 28.

IRAP, Université de Toulouse, CNRS, UPS, Toulouse, France.

One serious challenge for planet formation is the rapid inward drift of pebble-sized dust particles in protoplanetary disks. Dust trapping at local maxima in the disk gas pressure has received much theoretical attention but still lacks observational support. The cold dust emission in the AB Aur disk forms an asymmetric ring at a radius of about 120 au, which is suggestive of dust trapping in a gas vortex. Read More

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September 2017

Magnetic Nulls and Super-radial Expansion in the Solar Corona.

Astrophys J Lett 2017 May 8;840(2). Epub 2017 May 8.

National Center for Atmospheric Research, 3080 Center Green Drive, Boulder, CO 80301, USA.

Magnetic fields in the Sun's outer atmosphere-the corona-control both solar-wind acceleration and the dynamics of solar eruptions. We present the first clear observational evidence of coronal magnetic nulls in off-limb linearly polarized observations of pseudostreamers, taken by the Coronal Multichannel Polarimeter (CoMP) telescope. These nulls represent regions where magnetic reconnection is likely to act as a catalyst for solar activity. Read More

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The High Resolution Infrared Spectrum of HCl.

Astrophys J Lett 2016 Dec;833(2)

Molecular Physics Department, Instituto de Estructura de la Materia (IEM-CSIC). Serrano 123. 28006 Madrid, Spain.

The chloroniumyl cation, HCl, has been recently identified in space from 's spectra. A joint analysis of extensive vis-UV spectroscopy emission data together with a few high-resolution and high-accuracy millimiter-wave data provided the necessary rest frequencies to support the astronomical identification. Nevertheless, the analysis did not include any infrared (IR) vibration-rotation data. Read More

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December 2016

ALMA Observations of the Water Fountain Pre-Planetary Nebula IRAS 16342-3814: High-Velocity Bipolar Jets and an Expanding Torus.

Astrophys J Lett 2017 Jan;835(1)

Instituto de Ciencia de Materiales de Madrid, Sor Juana Ines de la Cruz, 3, Cantoblanco, 28049, Madrid, Spain.

We have mapped CO J=3-2 and other molecular lines from the "water-fountain" bipolar pre-planetary nebula (PPN) IRAS 16342-3814 with [Formula: see text] resolution using ALMA. We find (i) two very high-speed knotty, jet-like molecular outflows, (ii) a central high-density (> × 10 cm), expanding torus of diameter 1300 AU, and (iii) the circumstellar envelope of the progenitor AGB, generated by a sudden, very large increase in the mass-loss rate to > 3.5 × 10 yr in the past ~455 yr. Read More

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January 2017