192 research outputs found
Chemical abundances in quasar host galaxies and environments from narrow absorption line systems
We determined C, N and alpha-element relative abundances in the gas
surrounding six QSOs at an average redshift of ~ 2.4, by studying six
narrow associated absorption systems in UVES high-resolution spectra. We found
five systems with a metallicity (measured by C/H) consistent or above the solar
value. The ionization structure observed in the associated systems is clearly
different from that of the intervening ones, indicating that the associated
systems are influenced by the strong UV flux from the QSO. There is a possible
correlation (anticorrelation) between [N/C] ([Si/C]) and [C/H] of the studied
associated systems, and [N/C] >= 0 when [C/H] >= 0. We have compared these
observational results with the predictions of a model simulating the joint
evolution of QSOs and their spheroidal hosts. The agreement turns out to be
very good, in particular, the case envisaging massive haloes and high
star-formation rates recovers both the correlation between [N/C] and [C/H] and
the anticorrelation for [Si/C] vs. [C/H]. Narrow associated absorption systems
prove to be powerful tracers of the chemical abundances in gas belonging to
high redshift spheroidal galaxies. The outflow of this same gas, triggered by
the QSO feedback, is probably going to contribute to the early enrichment of
the surrounding intergalactic medium. A larger statistics, possibly increasing
the number of ionisation stages, chemical elements and the redshift range,
would allow us to put firm constraints on detailed chemical evolution models of
galaxies at high redshifts.Comment: 13 pages, 10 figures, submitted to MNRAS. Revised version after
referee comments. Some changes in the paper structure, critical revision of
errors, conclusions unchange
The High Time Resolution Universe Survey II: Discovery of 5 Millisecond Pulsars
We present the discovery of 5 millisecond pulsars found in the mid-Galactic
latitude portion of the High Time Resolution Universe (HTRU) Survey. The
pulsars have rotational periods from ~2.3 to ~7.5 ms, and all are in binary
systems with orbital periods ranging from ~0.3 to ~150 d. In four of these
systems, the most likely companion is a white dwarf, with minimum masses of
~0.2 Solar Masses. The other pulsar, J1731-1847, has a very low mass companion
and exhibits eclipses, and is thus a member of the "black widow" class of
pulsar binaries. These eclipses have been observed in bands centred near
frequencies of 700, 1400 and 3000 MHz, from which measurements have been made
of the electron density in the eclipse region. These measurements have been
used to examine some possible eclipse mechanisms. The eclipse and other
properties of this source are used to perform a comparison with the other known
eclipsing and "black widow" pulsars.
These new discoveries occupy a short-period and high-dispersion measure (DM)
region of parameter space, which we demonstrate is a direct consequence of the
high time and frequency resolution of the HTRU survey. The large implied
distances to our new discoveries makes observation of their companions unlikely
with both current optical telescopes and the Fermi Gamma-ray Space Telescope.
The extremely circular orbits make any advance of periastron measurements
highly unlikely. No relativistic Shapiro delays are obvious in any of the
systems, although the low flux densities would make their detection difficult
unless the orbits were fortuitously edge-on.Comment: 11 pages, 5 figures, 4 tables, for publication in MNRA
Formation of millisecond pulsars with CO white dwarf companions - II. Accretion, spin-up, true ages and comparison to MSPs with He white dwarf companions
Millisecond pulsars (MSPs) are mainly characterised by their spin periods,
B-fields and masses - quantities which are largely affected by previous
interactions with a companion star in a binary system. In this paper, we
investigate the formation mechanism of MSPs by considering the pulsar recycling
process in both intermediate-mass X-ray binaries (IMXBs) and low-mass X-ray
binaries (LMXBs). The IMXBs mainly lead to the formation of binary MSPs with a
massive carbon-oxygen (CO) or an oxygen-neon-magnesium white dwarf (ONeMg WD)
companion, whereas the LMXBs form recycled pulsars with a helium white dwarf
(He WD) companion. We discuss the accretion physics leading to the spin-up line
in the PPdot-diagram and demonstrate that such a line cannot be uniquely
defined. We derive a simple expression for the amount of accreted mass needed
for any given pulsar to achieve its equilibrium spin and apply this to explain
the observed differences of the spin distributions of recycled pulsars with
different types of companions. From numerical calculations we present further
evidence for significant loss of rotational energy in accreting X-ray MSPs in
LMXBs during the Roche-lobe decoupling phase (Tauris 2012) and demonstrate that
the same effect is negligible in IMXBs. We examine the recycling of pulsars
with CO WD companions via Case BB Roche-lobe overflow (RLO) of naked helium
stars in post common envelope binaries. We find that such pulsars typically
accrete of the order 0.002-0.007 M_sun which is just about sufficient to
explain their observed spin periods. We introduce isochrones of radio MSPs in
the PPdot-diagram to follow their spin evolution and discuss their true ages
from comparison with observations. Finally, we apply our results of the spin-up
process to the massive pulsar J1614-2230 (Paper I) and put new constraints on
the birth masses of a number of recycled pulsars. [Abridged]Comment: MNRAS in press, 32 pages, 14 figures, 4 tables, appendix. Version 2:
minor typos correcte
Revival of the magnetar PSR J1622-4950: observations with MeerKAT, Parkes, XMM-Newton, Swift, Chandra, and NuSTAR
New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and
NuSTAR) observations of PSR J1622-4950 indicate that the magnetar, in a
quiescent state since at least early 2015, reactivated between 2017 March 19
and April 5. The radio flux density, while variable, is approximately 100x
larger than during its dormant state. The X-ray flux one month after
reactivation was at least 800x larger than during quiescence, and has been
decaying exponentially on a 111+/-19 day timescale. This high-flux state,
together with a radio-derived rotational ephemeris, enabled for the first time
the detection of X-ray pulsations for this magnetar. At 5%, the 0.3-6 keV
pulsed fraction is comparable to the smallest observed for magnetars. The
overall pulsar geometry inferred from polarized radio emission appears to be
broadly consistent with that determined 6-8 years earlier. However, rotating
vector model fits suggest that we are now seeing radio emission from a
different location in the magnetosphere than previously. This indicates a novel
way in which radio emission from magnetars can differ from that of ordinary
pulsars. The torque on the neutron star is varying rapidly and unsteadily, as
is common for magnetars following outburst, having changed by a factor of 7
within six months of reactivation.Comment: Published in ApJ (2018 April 5); 13 pages, 4 figure
Insight into the proteome of the hyperthermophilic Crenarchaeon Ignicoccus hospitalis: the major cytosolic and membrane proteins
Ignicoccus hospitalis, a hyperthermophilic, chemolithoautotrophic Crenarchaeon, is the host of Nanoarchaeum equitans. Together, they form an intimate association, the first among Archaea. Membranes are of fundamental importance for the interaction of I. hospitalis and N. equitans, as they harbour the proteins necessary for the transport of macromolecules like lipids, amino acids, and cofactors between these organisms. Here, we investigated the protein inventory of I. hospitalis cells, and were able to identify 20 proteins in total. Experimental evidence and predictions let us conclude that 11 are soluble cytosolic proteins, eight membrane or membrane-associated proteins, and a single one extracellular. The quantitatively dominating proteins in the cytoplasm (peroxiredoxin; thermosome) antagonize oxidative and temperature stress which I. hospitalis cells are exposed to at optimal growth conditions. Three abundant membrane protein complexes are found: the major protein of the outer membrane, which might protect the cell against the hostile environment, forms oligomeric complexes with pores of unknown selectivity; two other complexes of the cytoplasmic membrane, the hydrogenase and the ATP synthase, play a key role in energy production and conversion
An extreme magneto-ionic environment associated with the fast radio burst source FRB 121102
Fast radio bursts are millisecond-duration, extragalactic radio flashes of unknown physical origin(1-3). The only known repeating fast radio burst source(4-6)-FRB 121102-has been localized to a star-forming region in a dwarf galaxy(7-9) at redshift 0.193 and is spatially coincident with a compact, persistent radio source(7,10). The origin of the bursts, the nature of the persistent source and the properties of the local environment are still unclear. Here we report observations of FRB 121102 that show almost 100 per cent linearly polarized emission at a very high and variable Faraday rotation measure in the source frame (varying from + 1.46 x 10(5) radians per square metre to + 1.33 x 10(5) radians per square metre at epochs separated by seven months) and narrow (below 30 microseconds) temporal structure. The large and variable rotation measure demonstrates that FRB 121102 is in an extreme and dynamic magneto-ionic environment, and the short durations of the bursts suggest a neutron star origin. Such large rotation measures have hitherto been observed(11,12) only in the vicinities of massive black holes (larger than about 10,000 solar masses). Indeed, the properties of the persistent radio source are compatible with those of a low-luminosity, accreting massive black hole(10). The bursts may therefore come from a neutron star in such an environment or could be explained by other models, such as a highly magnetized wind nebula(13) or supernova remnant(14) surrounding a young neutron star.</p
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