759 research outputs found
Simultaneous Doppler maps of IP Peg in outburst
IP Pegasi is an eclipsing dwarf nova lying above the period gap with an orbital period of 3.8h. It is the first cataclysmic variable to show evidence of spiral arms in its accretion disc. We present new time-resolved echelle spectroscopic observations of IP Peg, covering the 3900-7700 Angstrom range. This allows us to produce simultaneous Doppler Maps in 9 emission lines
IP Pegasi in outburst: Echelle spectroscopy & Modulation Doppler Tomography
We analyse a unique set of time-resolved echelle spectra of the dwarf nova IP
Peg, obtained at ESO's NTT with EMMI. The dataset covers the wavelength range
of 4000-7500A and shows Balmer, HeI, HeII and heavier elements in emission. IP
Peg was observed one day after the peak of an outburst. The trailed spectra,
spectrograms and Doppler maps show characteristics typical of IP Pegasi during
the early stages of its outburst. The high-ionisation line of HeII 4686A is the
most centrally located line and has the greatest radial extension compared to
the HeI lines. The Balmer lines extend from close to the white dwarf up to
approximately 0.45 times R_L, with the outer radius gradually increasing when
moving from H delta to H alpha. The application, for the first time, of the
modulation Doppler tomography technique, maps any harmonically varying
components present in the system configuration. We find, as expected, that part
of the strong secondary star emission in Balmer and HeI lines is modulated
predominantly with the cosine term, consistent with the emission originating
from the irradiated front side of the mass-donor star, facing the accreting
white dwarf. For the Balmer lines the level of the modulation, compared to the
average emission, decreases when moving to higher series. Emission from the
extended accretion disk appears to be only weakly modulated, with amplitudes of
at most a few percent of the non-varying disk emission. We find no evidence of
modulated emission in the spiral arms, which if present, is relatively weak at
that our signal-to-noise ratio was good enough to put a lower detection limit
of any modulated emission at 5--6%. Only in one arm of the HeII 4686A line, is
there a possibility of modulated emission, but again, we cannot be sure this is
not caused by blending with the nearby Bowen complex of lines.Comment: 20 pages, 8 figures, submitted to Journal of Astronomical Dat
Photometric study of selected cataclysmic variables II. Time-series photometry of nine systems
We present time-series photometry of nine cataclysmic variables: EI UMa,
V844Her, V751 Cyg, V516 Cyg, GZ Cnc, TY Psc, V1315 Aql, ASAS J002511+1217.12,
V1315 Aql and LN UMa. The observations were conducted at various observatories,
covering 170 hours and comprising 7,850 data points in total.
For the majority of targets we confirm previously reported periodicities and
for some of them we give, for the first time, their spectroscopic orbital
periods. For those dwarf-nova systems which we observed during both quiescence
and outburst, the increase in brightness was followed by a decrease in the
amount of flickering. Quasi-periodic oscillations have either been discovered,
or were confirmed. For the eclipsing system V1315 Aql we have covered 9
eclipses, and obtained a refined orbital ephemeris. We find that, during its
long baseline of observations, no change in the orbital period of this system
has occurred. V1315 Aql also shows eclipses of variable depth.Comment: 30 pages, 16 figures, 4 tables. Submitted to JA
RR Pictoris: an old nova showing superhumps and QPOs
We present time-resolved V-photometry of the old nova RR Pic. Apart from the
hump-like variability, the light curves show the strong flickering and random
variation typical for RR Pic. We do not find any convincing evidence for the
previously reported eclipse. The extrapolated eclipse phase coincides with a
broad minimum, but comparing the overall shape of the light curve suggests that
the eclipse should actually be located around phase 0.2. The orbital period
which we derive from these data agrees well with the old one, any uncertainty
is too small to account for the possible phase shift. Apart from the 3.48h
period, which is usually interpreted as the orbital one, we find an additional
period at P=3.78h, which we interpret as the superhump period of the system;
the corresponding precession period at 1.79d is also present in the data. We
also find indications for the presence of a 13min quasi-periodic oscillation.Comment: 9 pages, 7 figures + 1 Appendix figure, accepted by MNRA
Unsung heroes: who supports social work students on placement?
Since the introduction of the three year degree programme in 2003, social work education has undergone a number of significant changes. The time students spend on placement has been increased to two hundred days, and the range of placement opportunities and the way in which these placements have been configured has significantly diversified. A consistent feature over the years, however, has been the presence of a Practice Educator (PE) who has guided, assessed and taught the student whilst on placement. Unsurprisingly, the role of the PE and the pivotal relationship they have with the student has been explored in the past and features in social work literature.
This paper, however, concentrates on a range of other relationships which are of significance in providing support to students on placement. In particular it draws on research to discuss the role of the university contact tutor, the place of the wider team in which the student is sited, and the support offered by family, friends and others.
Placements and the work undertaken by PE’s will continue to be integral to the delivery of social work education. It is, however, essential to recognise and value the often over looked role of others in providing support to students on placement
Spawning induction of first-generation (F1) greater amberjack Seriola dumerili in the Canary Islands, Spain using GnRHa delivery systems
The development of a sustainable aquaculture industry requires the closing of the life-cycle
of a potential species in captivity, and the establishment of breeding selection programs using
hatchery-produced breeding stocks. The greater amberjack Seriola dumerili is a cosmopolitan pelagic
species that has been considered as a good candidate for the species diversification of aquaculture
production in the Mediterranean region. However, commercial production is still very limited
due to bottlenecks in reproduction, larval rearing and management control during grow out.
The aim of the present study was to examine the reproductive development of hatchery-produced
greater amberjack and to develop a spawning induction protocol based on the use of gonadotropin
releasing hormone agonist (GnRHa) in a controlled-release delivery system. The results showed that
hatchery-produced greater amberjack undergo normal gametogenesis and can be induced to undergo
maturation, ovulation and spawning after multiple administrations of GnRHa implants, over an
extended spawning period lasting from May to September in the Canary Islands, Spain. The use of
GnRHa-delivery systems resulted in multiple spawns of fertilized and viable eggs. Egg production
was high and egg quality adequate for the implementation of larval rearing for commercial purposes.
The handling required to administer the GnRHa implants during the prolonged spawning season
did not result in any negative effect on the welfare and reproductive performance of the fish based on
evaluation of several biochemical parameters. The developed reproduction control method shows
great potential to advance the commercial production of greater amberjack, by enabling the use of
hatchery-produced broodstocks for further breeding selection.Postprin
V2051 Ophiuchi after superoutburst : out-of-plane material and the superhump light source
Aims. We performed a detailed spectroscopic analysis of the dwarf nova V2051 Oph at the end of its 1999 superoutburst. We studied and interpreted the simultaneous behaviour of various emission lines.
Methods. We obtained high-resolution echelle spectroscopic data at ESO’s NTT with EMMI, covering the spectral range of 4000–7500 Å. The analysis was performed using standard IRAF tools. The indirect imaging technique of Doppler tomography was applied, in order to map the accretion disc and distinguish between the different emission sources.
Results. The spectra are characterised by strong Balmer emission, together with lines of He i and the iron triplet Fe ii 42. All lines are double-peaked, but the blue-to-red peak strength and central absorption depth vary. The primary’s velocity was found to be 84.9 kms−1. The spectrograms of the emission lines reveal the prograde rotation of a disc-like emitting region and, for the Balmer and He i lines, an enhancement of the red-wing during eclipse indicates a bright spot origin. The modulation of the double-peak separation shows a highly asymmetric disc with non-uniform emissivity. This is confirmed by the Doppler maps, which apart from the disc and bright spot emission also indicate an additional region of enhanced emission in the 4th quadrant (+Vx, −Vy), which we associate with the superhump light source. Given the behaviour of the iron triplet and its distinct differences from the rest of the lines, we attribute its existence to an extended gas region above the disc. Its origin can be explained through the fluorescence mechanism
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