341 research outputs found
On the mass of the neutron star in V395 Car/2S 0921-630
We report high-resolution optical spectroscopy of the low-mass X-ray binary
V395 Car/2S 0921-630 obtained with the MIKE echelle spectrograph on the
Magellan-Clay telescope. Our spectra are obtained near superior conjunction of
the mass donor star and we exploit the absorption lines originating from the
back-side of the K-type object to accurately derive its rotational velocity.
Using K0-K1 III templates, we find vsini=32.9 +/- 0.8 km/s. We show that the
choice of template star and the assumed limb darkening coefficient has little
impact on the derived rotational velocity. This value is a significant revision
downwards compared to previously published values. We derive new system
parameter constraints in the light of our much lower rotational velocity. We
find M_1=1.44 +/- 0.10 Msun, M_2=0.35 +/- 0.03 Msun, and q=0.24 +/- 0.02 where
the errors have been estimated through a Monte-Carlo simulation. A possible
remaining systematic effect is the fact that we may be over-estimating the
orbital velocity of the mass donor due to irradiation effects. However, any
correction for this effect will only reduce the compact object mass further,
down to a minimum mass of M_1=1.05 +/- 0.08 Msun. There is thus strong evidence
that the compact object in this binary is a neutron star of rather typical mass
and that the previously reported mass values of 2-4Msun were too high due to an
over-estimate of the rotational broadening.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
Advanced lightweight 316L stainless steel cellular lattice structures fabricated via selective laser melting
PublishedJournal ArticleThis paper investigates the manufacturability and performance of advanced and lightweight stainless steel cellular lattice structures fabricated via selective laser melting (SLM). A unique cell type called gyroid is designed to construct periodic lattice structures and utilise its curved cell surface as a self-supported feature which avoids the building of support structures and reduces material waste and production time. The gyroid cellular lattice structures with a wide range of volume fraction were made at different orientations, showing it can reduce the constraints in design for the SLM and provide flexibility in selecting optimal manufacturing parameters. The lattice structures with different volume fraction were well manufactured by the SLM process to exhibit a good geometric agreement with the original CAD models. The strut of the SLM-manufactured lattice structures represents a rough surface and its size is slightly higher than the designed value. When the lattice structure was positioned with half of its struts at an angle of 0° with respect to the building plane, which is considered as the worst building orientation for SLM, it was manufactured with well-defined struts and no defects or broken cells. The compression strength and modulus of the lattice structures increase with the increase in the volume fraction, and two equations based on Gibson-Ashby model have been established to predict their compression properties. © 2013 Elsevier Ltd.This work has been supported by the TSB funded project is entitled âSAVING â Sustainable product development via design optimisation and AdditiVe manufacturINGâ and is a collaboration between the Simpleware Ltd., Delcam PLC, University of Exeter, 3T RPD, Crucible Industrial Design Ltd., EOS Electro Optical Systems Ltd. and Plunkett Associates Ltd. The characterization experiments in this study were supported by the founds of State Key Laboratory of Material Processing and Die & Mould Technology in Huazhong University of Science and Technology, China (Grant Nos. 2012-P02 and 2013-09). The authors thank Dr. Chang Hong and Dr. Wear Lesley for assistance with Micro-CT, SEM and optical microscope measurements
Is the Relation Between the Solar Wind Dynamic Pressure and the Magnetopause Standoff Distance so Straightforward?
We present results of global magnetohydrodynamic simulations which reconsider the relationship between the solar wind dynamic pressure (Pd) and magnetopause standoff distance (RSUB). We simulate the magnetospheric response to increases in the dynamic pressure by varying separately the solar wind density or velocity for northward and southward interplanetary magnetic field (IMF). We obtain different values of the power law indices N in the relation RSUB- ÂŒPd- 1/N depending on which parameter, density, or velocity, has been varied and for which IMF orientation. The changes in the standoff distance are smaller (higher N) for a density increase for southward IMF and greater (smaller N) for a velocity increase. An enhancement of the solar wind velocity for a southward IMF increases the magnetopause reconnection rate and Region 1 current that move the magnetopause closer to the Earth than it appears in the case of density increase for the same dynamic pressure.Plain Language SummaryThe magnetopause is the boundary between the near- Earth space, which is governed by the magnetic field produced in the Earthâs core, and interplanetary space populated by the plasma emitted from the Sun called the solar wind. It is well known that the position of this boundary is defined by the balance of the pressures from both sides of the magnetopause and in a unique way depends on the velocity and density of the plasma in the interplanetary space. In this work, we reexamine the relationship between the magnetopause position and parameters of the solar wind by means of computer modeling. It is shown that the relationship between solar wind velocity and density and magnetopause position is more complex than originally thought. It is suggested that the pressure balance condition through the magnetopause depends on the continuing magnetic reconnection between the interplanetary and magnetospheric magnetic field lines and that the consequences of the reconnection change the relationship between the solar wind dynamic pressure and magnetopause boundary location.Key PointsWe reconsider the relation between the solar wind dynamic pressure and magnetopause standoff distanceThe magnetopause reacts differently to density, and velocity increases for the same dynamic pressureA new scaling law for magnetopause standoff distance is proposedPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154966/1/grl60461_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154966/2/grl60461.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154966/3/grl60461-sup-0001-Supporting_Information_SI-S01.pd
The massive neutron star or low-mass black hole in 2S0921-630
We report on optical spectroscopy of the eclipsing Halo LMXB 2S0921-630, that
reveals the absorption line radial velocity curve of the K0III secondary star
with a semi-amplitude K_2=92.89 +/- 3.84 km/s, a systemic velocity
=34.9 +/- 3.3 \kms and an orbital period P_orb of 9.0035 +/- 0.0029 day
(1-sigma). Given the quality of the data, we find no evidence for the effects
of X-ray irradiation. Using the previously determined rotational broadening of
the mass donor, and applying conservative limits on the orbital inclination, we
constrain the compact object mass to be 2.0-4.3 Msolar (1-sigma), ruling out a
canonical neutron star at the 99% level. Since the nature of the compact object
is unclear, this mass range implies that the compact object is either a
low-mass black hole with a mass slightly higher than the maximum neutron star
mass (2.9 Msolar) or a massive neutron star. If the compact object is a black
hole, it confirms the prediction of the existence of low-mass black holes,
while if the object is a massive neutron star its high mass severely constrains
the equation of state of nuclear matter.Comment: Accepted by ApJ
Fatty-acid amide hydrolase polymorphisms and post-traumatic stress disorder after penetrating brain injury
The past few years have seen an increase in the clinical awareness of post-traumatic stress disorder (PTSD), one of the most disabling and least understood behavioral disorders. Although the biological bases of PTSD are poorly understood, fatty-acid amide hydrolase (FAAH) activity has been linked with arousability and aversive-memories extinction, that is, two key features of PTSD. In this study, we investigated the association between the FAAH genetic polymorphisms and PTSD development and maintenance. We assessed PTSD frequency in a group of male Vietnam war veterans who suffered combat-related penetrating traumatic brain injury, that is, a relatively homogeneous population regarding the nature of the events that led to PTSD. We showed that rs2295633, a single-nucleotide polymorphism of FAAH, was significantly associated with PTSD diagnosis in subjects without lesions in the ventromedial prefrontal cortex. Moreover, the presence of the C allele was associated with more severe re-experiencing of trauma and more negative reported childhood experiences. In conclusion, our data suggest that FAAH has an important role in PTSD through modulation of aversive memories and point to both a novel therapeutic target and a possible risk marker for this condition
Geosynchronous magnetopause crossings and their relationships with magnetic storms and substorms
The paper investigates the strengthening of magnetospheric activity related to geosynchronous magnetopause crossings (GMCs). We make a list of GMC events using the empirical magnetopause model (Lin et al., 2010) and hourly averaged OMNI data and find which solar wind and magnetospheric conditions accompany and follow the GMCs. The GMCs are mostly caused by the impact of interplanetary coronal mass ejections (ICMEs) and/or interplanetary shocks often with a strong increase in the density and a moderate increase in velocity. The average solar wind density during the first GMC hour is higher than 20 cmâ3 in 70 % cases, while the velocity is higher than 500 km/s in 56 % cases. The hourly interplanetary magnetic field (IMF) BZ is negative in 87 % cases. The average over all events SMU (SML), Kp, and PC indices reach maxima (minima) in 1 hour after the GMC beginning, while the delay of the minimum of the Dst index is usually 3â8 hours. These average time delays do not depend on the strength of the storms and substorms. The SML (Dst) minimum is less than -500 nT (-30 nT) in the next 24 hours in 95 % (99 %) cases, i.e. the GMC events are mostly followed by magnetic storms and substorms. We compare solar wind and magnetospheric conditions for GMCs connected with ICMEs and stream interaction regions (SIRs). Our study confirms that the ICME-related events are characterized by stronger ring current and auroral activity than the SIR-related events. The difference might be explained by the different behavior of the solar wind velocity
Suzaku observations of Jovian diffuse hard X-ray emission
We report on results of systematic analyses of the entire three X-ray data sets of Jupiter taken by Suzaku in 2006, 2012, and 2014. Jovian diffuse hard X-ray emission was discovered by Suzaku in 2006 when the solar activity went toward its minimum. The diffuse emission was spatially consistent with the Jovian inner magnetosphere and was spectrally fitted with a flat power-law function suggesting non-thermal emission. Thus, a scenario in which ultra-relativistic (tens of MeV) electrons in the Jovian inner magnetosphere inverse-Comptonize solar visible photons into X-ray bands has been hypothetically proposed. We focused on the dependence of the Jovian diffuse hard X-ray emission on the solar activity to verify this scenario. The solar activity in 2012 and 2014 was around the maximum of the 24th solar cycle. By combining the imaging and spectral analyses for the three data sets, we successfully separated the contribution of the diffuse emission from the emission of Jupiterâs body (i.e., the aurora and disk emission). The 1â5âkeV luminosity of the diffuse emission has been stable and did not vary significantly, and did not simply depend on the solar activity, which is also known to affect the high-energy electron distribution in the Jovian inner magnetosphere scarcely. The luminosity of the body emission both in 0.2â1 and 1â5âkeV, in contrast, probably depended on the solar activity and varied by a factor of 2â5. These results strongly supported the inverse-Compton scattering scenario by the ultra-relativistic electrons. In this paper, we estimate spatial and spectral distributions of the inverse-Compton scattering X-rays by Jovian magnetospheric high-energy electrons with reference to the DivineâGarrett model and found a possible agreement in an inner region (âČ10âRJ) for the X-ray observations
Multiwavelength campaign on Mrk 509. VI. HST/COS observations of the far-ultraviolet spectrum
We present medium resolution (R~20,000) HST/COS ultraviolet spectra covering
1155-1760 A of the Seyfert 1 Mrk 509 obtained simultaneously with a
Chandra/LETGS spectrum as part of a multiwavelength campaign in 2009 that
included observations with XMM-Newton, SWIFT, and Integral. Our high S/N
spectrum detects additional complexity in the absorption troughs from a variety
of sources in Mrk 509, including the outflow from the active nucleus, the ISM
and halo of the host galaxy, and infalling clouds or stripped gas from a merger
that are illuminated by the AGN. Variability between the STIS and COS
observation of the -400 km/s component allows us to set an upper limit on its
distance of < 250 pc. Similarly, variability of a component at +150 km/s
between two prior FUSE observations limits its distance to < 1.5 kpc. The UV
absorption only partially covers the emission from the AGN nucleus. Covering
fractions are lower than those previously seen with STIS, and are comparable to
those seen with FUSE. Given the larger apertures of COS and FUSE compared to
STIS, we favor scattered light from an extended region near the AGN as the
explanation for the partial covering. As observed in prior X-ray and UV
spectra, the UV absorption has velocities comparable to the X-ray absorption,
but the bulk of the ultraviolet absorption is in a lower ionization state with
lower total column density than the gas responsible for the X-ray absorption.
We conclude that the outflow from the active nucleus is a multiphase wind.Comment: 21 pages, 9 figures. Accepted for publication in Astronomy &
Astrophysics, 26 May 201
Searching for Saturn's X-rays during a rare Jupiter Magnetotail Crossing using Chandra
Every 19 years, Saturn passes through Jupiter's 'flapping' magnetotail. Here,
we report Chandra X-ray observations of Saturn planned to coincide with this
rare planetary alignment and to analyse Saturn's magnetospheric response when
transitioning to this unique parameter space. We analyse three Director's
Discretionary Time (DDT) observations from the High Resolution Camera (HRC-I)
on-board Chandra, taken on November 19, 21 and 23 2020 with the aim to find
auroral and/or disk emissions. We infer the conditions in the kronian system by
looking at coincident soft X-ray solar flux data from the Geostationary
Operational Environmental Satellite (GOES) and Hubble Space Telescope (HST)
observations of Saturn's ultraviolet (UV) auroral emissions. The large
Saturn-Sun-Earth angle during this time would mean that most flares from the
Earth-facing side of the Sun would not have impacted Saturn. We find no
significant detection of Saturn's disk or auroral emissions in any of our
observations. We calculate the 3 upper band energy flux of Saturn
during this time to be 0.9 - 3.04 10 erg cm s
which agrees with fluxes found from previous modelled spectra of the disk
emissions. We conclude by discussing the implications of this non-detection and
how it is imperative that the next fleet of X-ray telescope (such as Athena and
the Lynx mission concept) continue to observe Saturn with their improved
spatial and spectral resolution and very enhanced sensitivity to help us
finally solve the mysteries behind Saturn's apparently elusive X-ray aurora.Comment: 8 pages, 3 figures, accepted for publication in MNRA
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