5,105 research outputs found
What is the closest black hole to the Sun?
We examine the distance of the two galactic microquasars GRO J1655-40 and
A0620-00, which are potentially the two closest black holes to the Sun. We aim
to provide a picture as wide and complete as possible of the problem of
measuring the distance of microquasars in our Galaxy. The purpose of this work
is to fairly and critically review in great detail every distance method used
for these two microquasars in order to show that the distances of probably all
microquasars in our galaxy are much more uncertain than currently admitted.
Moreover, we show that many confirmations of quantitative results are often
entangled and rely on very uncertain measurements. We also present a new
determination of the maximum distance of GRO J1655-40 using red clump giant
stars, and show that it confirms our earlier result of a distance less than 2
kpc instead of 3.2 kpc. Since it then becomes more likely that GRO J1655-40
could originate from the stellar cluster NGC 6242, located at 1.0 kpc, we
review the distance estimations of A0620-00, which is so far the closest black
hole with an average distance of about 1.0 kpc. We show that the distance
methods used for A0620-00 are also problematic. Finally, we present a new
analysis of spectroscopic and astrometric archival data on this microquasar,
and apply the maximum-distance method of Foellmi et al. (2006). It appears that
A0620-00 could indeed be even closer to the Sun than currently estimated, and
consequently would be the closest known black hole to the Sun.Comment: Accepted for publication in New Astronomy. 27 pages, 7 figures, Added
new column in Table 1. Corrected definition of mass ratio in Equ 1
Exploring the Energetics of Intracluster Gas with a Simple and Accurate Model
The state of the hot gas in clusters of galaxies is investigated with a set
of model clusters, created by assuming a polytropic equation of state
(Gamma=1.2) and hydrostatic equilibrium inside gravitational potential wells
drawn from a dark matter simulation. Star formation, energy input, and
nonthermal pressure support are included. To match the gas fractions seen in
non-radiative hydrodynamical simulations, roughly 5% of the binding energy of
the dark matter must be transferred to the gas during cluster formation; the
presence of nonthermal pressure support increases this value. In order to match
X-ray observations, scale-free behavior must be broken. This can be due to
either variation of the efficiency of star formation with cluster mass M_500,
or the input of additional energy proportional to the formed stellar mass M_F.
These two processes have similar effects on X-ray scalings. If 9% of the gas is
converted into stars, independent of cluster mass, then feedback energy input
of 1.2e-5*M_Fc^2 (or ~1.0 keV per particle) is required to match observed
clusters. Alternatively, if the stellar mass fraction varies as M_500^-0.26
then a lower feedback of 4e-6*M_Fc^2 is needed, and if the stellar fraction
varies as steeply as M_500^-0.49 then no additional feedback is necessary. The
model clusters reproduce the observed trends of gas temperature and gas mass
fraction with cluster mass, as well as observed entropy and pressure profiles;
thus they provide a calibrated basis with which to interpret upcoming SZ
surveys. One consequence of the increased gas energy is that the baryon
fraction inside the virial radius is less than roughly 90% of the cosmic mean,
even for the most massive clusters.Comment: Accepted by ApJ; 28 pages, 12 figure
The Active Quiescence of HR Del (Nova Del 1967)
This new UV study of the ex-nova HR Del is based on all of the data obtained
with the IUE satellite, and includes the important series of spectra taken in
1988 and 1992 that have not been analyzed so far. After the correction for the
reddening (EB-V)=0.16), adopting a distance d =850 pc, we have derived a mean
UV luminosity close to Luv ~ 56 Lsun, the highest value among classical novae
in "quiescence". Also the "average" optical absolute magnitude Mv=+2.30 is
indicative of a bright object. The UV continuum luminosity, the HeII 1640 A
emission line luminosity, and the optical absolute magnitude all give a mass
accretion rate Mdot very close to 1.4*10**(-7) Msun/yr, if one assumes that the
luminosity of the old nova is due to a non-irradiated accretion disk. The
continuum distribution is well fitted with either a black body of 33,900 K, or
a power-law F(lambda) ~ lambda**(-2.20). We show that the "quiescent" optical
magnitude at mv ~ 12 comes from the hot component and not from the companion
star. Since most IUE observations correspond to the "quiescent" magnitude at mv
~ 12, the same as in the pre-eruption stage, we infer that the pre-nova, for at
least 70 years prior to eruption, was also very bright at near the same Luv,
Mv, Mdot and T values as derived in the present study for the ex-nova. The wind
components in the P Cyg profiles of the CIV 1550 A and NV 1240 A resonance
lines are strong and variable on short timescales, with vedge up to -5000 km/s,
a remarkably high value. The phenomenology in the short-time variations of the
wind indicates the presence of an inhomogeneous outflow. We discuss the nature
of the strong UV continuum and wind features and the implications of the
presence of a "bright" state a long time before and after outburst on our
present knowledge of the pre-nova and post-nova behavior.Comment: 15 pages, 10 figures, accepted for Astronomy and Astrophysic
Optical novae: the major class of supersoft X-ray sources in M 31
We searched for X-ray counterparts of optical novae detected in M 31 and M
33. We combined an optical nova catalogue from the WeCAPP survey with optical
novae reported in the literature and correlated them with the most recent X-ray
catalogues from ROSAT, XMM-Newton and Chandra, and - in addition - searched for
nova correlations in archival data. We report 21 X-ray counterparts for novae
in M 31 - mostly identified as supersoft sources (SSS) by their hardness ratios
- and two in M 33. Our sample more than triples the number of known optical
novae with supersoft X-ray phase. Most of the counterparts are covered in
several observations allowing us to constrain their X-ray light curves.
Selected brighter sources were classified by their XMM-Newton EPIC spectra. We
use the well determined start time of the SSS state in two novae to estimate
the hydrogen mass ejected in the outburst to ~10^{-5}M_sun and ~10^{-6}M_sun,
respectively. The supersoft X-ray phase of at least 15% of the novae starts
within a year. At least one of the novae shows a SSS state lasting 6.1 years
after the optical outburst. Six of the SSSs turned on between 3 and 9 years
after the optical discovery of the outburst and may be interpreted as recurrent
novae. If confirmed, the detection of a delayed SSS phase turn-on may be used
as a new method to classify novae as recurrent. At the moment, the new method
yields a ratio of recurrent novae to classical novae of 0.3 which is in
agreement (within the errors) with previous works.Comment: 16 pages, 7 figures, A&A revised version, 1 nova in M33 added,
restructured discussion, summary and conclusion
Reply to Letter to Editor: Potent Anticoagulants are Associated with a Higher All-cause Mortality Rate after Hip and Knee Arthroplasty
Evaluation of MLH1 variants of unclear significance
Inactivating mutations in the MLH1 gene cause the cancer predisposition Lynch syndrome, but for small coding genetic variants it is mostly unclear if they are inactivating or not. Nine such MLH1 variants have been identified in South American colorectal cancer (CRC) patients (p.Tyr97Asp, p.His112Gln, p.Pro141Ala, p.Arg265Pro, p.Asn338Ser, p.Ile501del, p.Arg575Lys, p.Lys618del, p.Leu676Pro), and evidence of pathogenicity or neutrality was not available for the majority of these variants. We therefore performed biochemical laboratory testing of the variant proteins and compared the results to protein in silico predictions on structure and conservation. Additionally, we collected all available clinical information of the families to come to a conclusion concerning their pathogenic potential and facilitate clinical diagnosis in the affected families. We provide evidence that four of the alterations are causative for Lynch syndrome, four are likely neutral and one shows compromised activity which can currently not be classified with respect to its pathogenic potential. The work demonstrates that biochemical testing, corroborated by congruent evolutionary and structural information, can serve to reliably classify uncertain variants when other data are insufficient.Barretos Cancer Hospital was partially funded by FINEP‐CT‐INFRA, Grant Number: 02/2010, Radium Hospital Foundation (Oslo, Norway), Helse Sør‐Øst (Norway); Deutsche Forschungsgemeinschaft, Grant Number: PL688/2‐1info:eu-repo/semantics/publishedVersio
X-ray emission from classical and recurrent-novae observed with ROSAT
We have analysed 350 pointed and serendipitous observations of 108 different
classical and recurrent novae in outburst and in quiescence, contained in the
ROSAT archive. One aim was to search for super-soft X-ray sources and we found
only 3 of them among post-novae. Thus, the super-soft X-ray phase of novae is
relatively short lived (up to 10 years) and is observed only for up to 20% of
novae.
Most classical and recurrent novae instead emit hard X-rays (in the ROSAT
band) in the first months after the outburst, with peak X-ray luminosity of a
few times 10(33) erg/s. The emission, which we attribute to shocks in the nova
ejecta, lasts at least 2 years and even much longer under special circumstances
(like preexisting circumstellar material, or a prolonged wind phase).
We also investigate X-ray emission due to accretion in quiescent novae. Only
11 out of 81 Galactic classical and recurrent novae were detected. The average
X-ray uminosity is not higher than for dwarf novae, and some novae are variable
in X-rays on time scales of years.Comment: tex file of the text and 8 figure
Neck fracture of a cementless forged titanium alloy femoral stem following total hip arthroplasty: a case report and review of the literature
<p>Abstract</p> <p>Introduction</p> <p>Fractures of the neck of the femoral component have been reported in uncemented total hip replacements, however, to our knowledge, no fractures of the neck of a cementless forged titanium alloy femoral stem coated in the proximal third with hydroxy-apatite have been reported in the medical literature.</p> <p>Case presentation</p> <p>This case report describes a fracture of the neck of a cementless forged titanium alloy stem coated in the proximal third with hydroxy-apatite.</p> <p>Conclusion</p> <p>The neck of the femoral stem failed from fatigue probably because of a combination of factors described analytically below.</p
Cementless total hip replacement: past, present, and future
Cementless total hip replacement (THR) is rapidly being accepted as the surgery for arthritic diseases of the hip joint. The bone-ingrowth rate in porous-type cementless implants was about 90% over 10 years after surgery, showing that biological fixation of cementless THR was well maintained on both the stem and cup sides. As for the stress shielding of the femur operated using a distal fixation-type stem, severe bone resorption was observed. The severe bone resorption group showed continuous progression for more than 10 years after surgery. Stem loosening directly caused by stress shielding has been considered less likely; however, close attention should be paid to bone resorption-associated disorders including femoral fracture. Cementless cups have several specific problems. It is difficult to decide whether a cup should be placed in the physiological position for the case of acetabular dysplasia by bone grafting or at a relatively higher position without bone grafting. The bone-ingrowth rate was lower in the group with en bloc bone grafting, and the reactive line was frequently noted in the bone-grafted region. Although no data indicated that en bloc bone grafting directly led to poor outcomes, such as loosening, cup placement at a higher site without bone grafting is now selected by most operators. The polyethylene liner in a cementless cup is thinned due to the metal cup thickness; however, it has been suggested that the apparent relation between the cup size and the wear rate was absent as long as a cementless cup is used. Comparative study indicated cementless THR was inferior with regard to the yearly polyethylene wear rate and incidence of osteolysis on both the stem and cup sides. Meta-analysis study on the survival rate between cement and cementless THR reported that cemented THR was slightly superior. It should be considered that specific problems for cementless THR, especially with regard to polyethylene wear, do occur
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