583 research outputs found
The mass of the white dwarf in the old nova BT Mon
We present spectrophotometry of the eclipsing old nova BT Mon (Nova Mon
1939). By detecting weak absorption features from the secondary star, we find
its radial velocity semi-amplitude to be K_R = 205+/-5 km/s and its rotational
velocity to be vsin i = 138+/-5 km/s. We also measure the radial velocity
semi-amplitude of the primary star to be K_R = 170+/-10 km/s. From these
parameters we obtain a mass of 1.04+/-0.06 M_sun for the white dwarf primary
star and a mass of 0.87+/-0.06 M_sun for the G8V secondary star. The
inclination of the system is found to be 82.2+/-3.2 deg and we estimate that
the system lies at a distance of 1700+/-300pc. The high mass of the white dwarf
and our finding that BT Mon was probably a fast nova together constitute a new
piece of evidence in favour of the thermonuclear runaway model of classical
nova outbursts. The emission lines are single peaked throughout the orbital
cycle, showing absorption around phase 0.5, high velocity S-wave components and
large phase offsets in their radial velocity curves. In each of these respects,
BT Mon is similar to the SW Sex stars. We also find quasi-periodic flaring in
the trailed spectra, which makes BT Mon a candidate intermediate polar.Comment: 19 pages, LaTeX, 15 figures, accepted by MNRAS, 11 Sept 199
Ticarcillin hypersusceptibility in pseudomonas aeruginosa in cystic fibrosis
Background: A subpopulation of Pseudomonas aeruginosa (PsA) exists in cysticfibrosis (CF) patients that is hypersusceptible to ticarcillin, a carboxypenicillin, in vitro (Tichs strain) defined as a minimum inhibitory concentration (MIC) â€4ÎŒg/ml. Methods: In a retrospective cohort study, isolates of PsA from CF (23), non-cystic fibrosis bronchiectasis (NCFB) (17) and control (18) patients were analysed. MICs for each isolate were determined using agar dilution against six antibiotics and interpreted using EUCAST breakpoints. Prevalence of Tichs in each cohort was calculated. A point prevalence survey was conducted in CF to review the patientsâ clinical progress following PsA isolation. Results: Prevalence of the Tichs strain in PsA was 48%, 76% and 0% in the CF, NCFB and control cohorts respectively. A statistically significant difference in geometric mean MIC was seen between the Tichs and non-Tichs cohorts in CF for ticarcillin (as expected) and temocillin (p=0.041and p=0.036 respectively). A similar trend was observed in NCFB for ticarcillin (p=0.038) and temocillin (p=0.067), although statistical significance was not reached for the latter.In CF, the Tichs strain demonstrated lower MICs to all antibiotics tested apart from gentamicin compared to their non-Tichs counterparts. Those who had the Tichs strain in CF had fewer antibiotics (13.9 days versus 23.5 days, Tichs and non-Tichs respectively) although this result was not statistically significant p=0.202. Conclusion: Our data supports the existence of a Tichs strain of PsA in our CF and NCFB patient populations. This strain correlated with reduced MICs to temocillin in CF, to which PsA would normally be resistant, which may be of clinical relevance.</p
J-band spectroscopy of cataclysmic variables
We present time-resolved, J-band (1.025â1.340 ÎŒm) infrared spectra of the short-period dwarf novae (DNe) WZ Sge and VY Aqr, and single spectra of the short-period DN EF Peg and the nova-like variable PX And. There is some evidence in the spectra of VY Aqr and EF Peg that we have detected the secondary star, both in the continuum slope and also through the possible presence of spectral features. The spectra of WZ Sge and PX And, on the other hand, show no evidence for the secondary star, with upper limits for its contribution to the J-band light of 10 and 20 per cent respectively. The spectral type of the secondary in WZ Sge is constrained to be later than M7.5V. Using skew mapping, we have been able to derive a value for the radial velocity semi-amplitude of the secondary star in VY Aqr of KR=320±70 km sâ1, which in conjunction with KW from Thorstensen & Taylor gives a mass ratio of q=0.15±0.04
The mass of the white dwarf in the recurrent nova U Scorpii
We present spectroscopy of the eclipsing recurrent nova U Sco. The radial
velocity semi-amplitude of the primary star was found to be K_W = 93 \pm 10
kms^{-1} from the motion of the wings of the HeII\lambda4686\AA emission line.
By detecting weak absorption features from the secondary star, we find its
radial velocity semi-amplitude to be K_R = 170 \pm 10 kms^{-1}. From these
parameters, we obtain a mass of M_1 = 1.55 \pm 0.24M_\odot for the white dwarf
primary star and a mass of M_2 = 0.88 \pm 0.17M_\odot for the secondary star.
The radius of the secondary is calculated to be R_2 = 2.1\pm0.2R_\odot,
confirming that it is evolved. The inclination of the system is calculated to
be i = 82.7^\circ\pm2.9^\circ, consistent with the deep eclipse seen in the
lightcurves. The helium emission lines are double-peaked, with the blue-shifted
regions of the disc being eclipsed prior to the red-shifted regions, clearly
indicating the presence of an accretion disc. The high mass of the white dwarf
is consistent with the thermonuclear runaway model of recurrent nova outbursts,
and confirms that U Sco is the best Type Ia supernova progenitor currently
known. We predict that U Sco is likely to explode within \sim 700,000 years.Comment: 12 pages, 12 figures, accepted for publication in MNRA
A Radial Velocity Study of CTCV J1300-3052
We present time-resolved spectroscopy of the eclipsing, short period
cataclysmic variable CTCV J1300-3052. Using absorption features from the
secondary star, we determine the radial velocity semi-amplitude of the
secondary star to be K2 = 378 \pm 6 km/s, and its projected rotational velocity
to be v sin i = 125 \pm 7 km/s. Using these parameters and Monte Carlo
techniques, we obtain masses of M1 = 0.79 \pm 0.05 MSun for the white dwarf
primary and M2 = 0.198 \pm 0.029 MSun for the M-type secondary star. These
parameters are found to be in excellent agreement with previous mass
determinations found via photometric fitting techniques, supporting the
accuracy and validity of photometric mass determinations in short period CVs.Comment: Accepted for publication in MNRAS (24th January 2012). 10 pages, 9
figures (black and white
DE Canum Venaticorum : a bright, eclipsing red dwarfâwhite dwarf binary
Context. Close white dwarfâred dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarfâred dwarf binary with a relatively short (âŒ8.7 h) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study.
Aims. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters that we discuss in the framework of common-envelope evolution.
Methods. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average lowresolution spectrum of DE CVn, we constrain the temperature of the white dwarf and the spectral type of the red dwarf. The eclipse light curve is analysed and combined with the radial velocity curve of the red dwarf determined from time-resolved spectroscopy to derive constraints on the inclination and the masses of the components in the system.
Results. The derived ephemeris is HJDmin = 2 452 784.5533(1) + 0.3641394(2) Ă E. The red dwarf in DE CVn has a spectral type of M3V and the white dwarf has an effective temperature of 8 000 K. The inclination of the system is 86+3⊠â2 and the mass and radius of the red dwarf are 0.41 ± 0.06 M and 0.37+0.06 â0.007 R, respectively, and the mass and radius of the white dwarf are 0.51+0.06
â0.02 M and 0.0136+0.0008 â0.0002 R, respectively.
Conclusions. We found that the white dwarf has a hydrogen-rich atmosphere (DA-type). Given that DE CVn has experienced a common-envelope phase, we can reconstruct its evolution and we find that the progenitor of the white dwarf was a relatively lowmass star (M †1.6 M). The current age of this system is 3.3â7.3 Ă 109 years, while it will take longer than the Hubble time for DE CVn to evolve into a semi-detached system
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