456 research outputs found
The Quiescent Spectrum of the AM CVn star CP Eri
We used the 6.5m MMT to obtain a spectrum of the AM CVn star CP Eri in
quiescence. The spectrum is dominated by He I emission lines, which are clearly
double peaked with a peak-to-peak separation of ~1900 km/s. The spectrum is
similar to that of the longer period AM CVn systems GP Com and CE 315, linking
the short and the long period AM CVn systems. In contrast with GP Com and CE
315, the spectrum of CP Eri does not show a central 'spike' in the line
profiles, but it does show lines of SiII in emission. The presence of these
lines indicates that the material being transferred is of higher metallicity
than in GP Com and CE 315, which, combined with the low proper motion of the
system, probably excludes a halo origin of the progenitor of CP Eri. We
constrain the primary mass to M_1>0.27 M_sun and the orbital inclination to 33
degr < i < 80 degr. The presence of the He I lines in emission opens up the
possibility for phase resolved spectroscopic studies which allows a
determination of the system parameters and a detailed study of helium accretion
disks under highly varying circumstances.Comment: 12 pages, 2 figures, accepted for publication in ApJ Letter
The LMC supersoft X-ray binary RX J0513.9-6951
A detailed analysis of simultaneous photometric and spectroscopic observations of the optical counterpart of the LMC "supersoft" X-ray source RX J0513.9-6951 (identified with HV 5682) is presented. The spectrum is dominated by He II emission lines and H + He II blends; no He I is observed but several higher ionization emission features, especially O VI (3811, 3834, and 5290A) are prominent. Radial velocity measurements suggest a binary period of 0.76 days. If the small velocity amplitude, K~11 km/s, is interpreted as orbital motion, this implies that the binary system contains a somewhat evolved star plus a relatively massive compact object, viewed nearly pole-on. No orbital photometric variations were found, although irregular brightness changes of ~0.3 mag occurred. Unusual emission lines are observed which cannot be identified except as high velocity (4000 km/s) bipolar outflows or jets. These outflows are seen in H and He II at the same positive and negative velocities. They were relatively stable for periods of ~5 days, but their velocities appear to have been ~250 km/s smaller in 1992 than in 1993 or 1994
A Population of Faint Non-Transient Low Mass Black Hole Binaries
We study the thermal and viscous stability of accretion flows in Low Mass
Black Hole Binaries (LMBHBs). We consider a model in which an inner
advection-dominated accretion flow (ADAF) is surrounded by a geometrically thin
accretion disk, the transition between the two zones occurring at a radius
R_tr. In all the known LMBHBs, R_tr appears to be such that the outer disks
could suffer from a global thermal-viscous instability. This instability is
likely to cause the transient behavior of these systems. However, in most
cases, if R_tr were slightly larger than the estimated values, the systems
would be globally stable. This suggests that a population of faint persistent
LMBHBs with globally stable outer disks could be present in the Galaxy. Such
LMBHBs would be hard to detect because they would lack large amplitude
outbursts, and because their ADAF zones would have very low radiative
efficiencies, making the systems very dim. We present model spectra of such
systems covering the optical and X-ray bands.Comment: LateX, 37 pages, 11 figures; Accepted for publication in The
Astrophysical Journa
Infrared and Optical Spectroscopy of Type Ia Supernovae in the Nebular Phase
We present near-infrared (NIR) spectra for Type Ia supernovae at epochs of 13
to 338 days after maximum blue light. Some contemporary optical spectra are
also shown. All the NIR spectra exhibit considerable structure throughout the
J-, H- and K-bands. In particular they exhibit a flux `deficit' in the J-band
which persists as late as 175 days. This is responsible for the well-known red
J-H colour. To identify the emission features and test the Ni hypothesis
for the explosion and subsequent light curve, we compare the NIR and optical
nebular-phase data with a simple non-LTE nebular spectral model. We find that
many of the spectral features are due to iron-group elements and that the
J-band deficit is due to a lack of emission lines from species which dominate
the rest of the IR/optical spectrum. Nevertheless, some emission is unaccounted
for, possibly due to inaccuracies in the cobalt atomic data. For some
supernovae, blueshifts of 1000--3000 km/s are seen in infrared and optical
features at 3 months. We suggest this is due to clumping in the ejecta. The
evolution of the cobalt/iron mass ratio indicates that Co-decay
dominates the abundances of these elements. The absolute masses of iron-group
elements which we derive support the basic thermonuclear explosion scenario for
Type Ia supernovae. A core-collapse origin is less consistent with our data.Comment: 33 Latex pages, 12 Postscript figures: accepted by Monthly Notices of
the Royal Astronomical Societ
Early Life Socioeconomic Circumstance and Late Life Brain Hyperintensities : A Population Based Cohort Study
Funding: Image acquisition and image analysis for this study was funded by the Alzheimer's Research Trust (now Alzheimer's Research UK). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Acknowledgments The authors would like to thank the participants of the Aberdeen 1936 Birth Cohort (ABC36), without whom this research would not have been possible.Peer reviewedPublisher PD
Equal access, (Un)equal uptake: a longitudinal study of cataract surgery uptake in older people in England
The component masses of the cataclysmic variable V347 Puppis
We present time-resolved spectroscopy and photometry of the double-lined eclipsing cataclysmic variable V347 Pup (=LB 1800). There is evidence of irradiation on the inner hemisphere of the secondary star, which we correct for using a model to give a secondary-star radial velocity of KR= 198 ± 5 km sâ1. The rotational velocity of the secondary star in V347 Pup is found to be v sin i= 131 ± 5 km sâ1 and the system inclination is i= 840 ± 23. From these parameters we obtain masses of M1= 0.63 ± 0.04 Mâ for the white dwarf primary and M2= 0.52 ± 0.06 Mâ for the M0.5V secondary star, giving a mass ratio of q= 0.83 ± 0.05. On the basis of the component masses, and the spectral type and radius of the secondary star in V347 Pup, we find tentative evidence for an evolved companion. V347 Pup shows many of the characteristics of the SW Sex stars, exhibiting single-peaked emission lines, high-velocity S-wave components and phase-offsets in the radial velocity curve. We find spiral arms in the accretion disc of V347 Pup and measure the disc radius to be close to the maximum allowed in a pressureless disc
Elevated pre-treatment levels of plasma C-reactive protein are associated with poor prognosis after breast cancer: a cohort study
Time-Resolved HST Spectroscopy of Four Eclipsing Magnetic Cataclysmic Variables
Time-resolved HST UV eclipse spectrophotometry is presented for the magnetic
CVs V1309 Ori, MN Hya, V2301 Oph, and V1432 Aql. Separation of the light curves
into wavebands allows the multiple emission components to be distinguished.
Photospheric hot spots are detected in V1309 Ori and V2301 Oph. The emission-
line spectra of V1309 Ori and MN Hya are unusual, with the strength of N V 1240
and N IV 1718 suggesting an overabundance of nitrogen. Three epochs of
observation of the asynchronous V1432 Aql cover ~1/3 of a 50-day lap cycle
between the white dwarf spin and binary orbit. The light curves vary from epoch
to epoch and as a function of waveband. The dereddened UV spectrum is extremely
bright and the spectral energy distribution coupled with the duration of
eclipse ingress indicate that the dominant source of energy is a hot
(T~35,000K) white dwarf. Undiminished line emission through eclipse indicates
that the eclipse is caused by the accretion stream, not the secondary star. The
hot white dwarf, combined with its current asynchronous nature and rapid
timescale for relocking, suggests that V1432 Aql underwent a nova eruption in
the past 75-150 yr. The reversed sense of asynchronism, with the primary star
currently spinning up toward synchronism, is not necessarily at odds with this
scenario, if the rotation of the magnetic white dwarf can couple to the ejecta
during the wind phase of the eruption.Comment: To appear in ApJ Part 1; 25 pages, 12 figure
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