273 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
Spectral analysis of the barium central star of the planetary nebula Hen 2-39
Barium stars are peculiar red giants characterized by an overabundance of
s-process elements along with an enrichment in carbon. These stars are
discovered in binaries with white dwarf companions. The more recently formed of
these stars are still surrounded by a planetary nebula. Precise abundance
determinations of the various s-process elements, especially, of the lightest,
short-lived radionuclide technetium will establish constraints for the
formation of s-process elements in asymptotic giant branch stars as well as
mass transfer through, for example, stellar wind, Roche-lobe overflow, and
common-envelope evolution. We performed a detailed spectral analysis of the
K-type subgiant central star of the planetary nebula Hen 2-39 based on
high-resolution optical spectra obtained with the Ultraviolet and Visual
Echelle Spectrograph at the Very Large Telescope using LTE model atmospheres.
We confirm the effective temperature of K for
the central star of the planetary nebula Hen 2-39. It has a photospheric carbon
enrichment of and a barium overabundance of
. We find a deficiency for most of the
iron-group elements (calcium to iron) and establish an upper abundance limit
for technetium (). The quality of the
available optical spectra is not sufficient to measure abundances of all
s-process elements accurately. Despite large uncertainties on the abundances as
well as on the model yields, the derived abundances are most consistent with a
progenitor mass in the range 1.75-3.00 and a metallicity of
. This result leads to the conclusion that the
formation of such systems requires a relatively large mass transfer that is
most easily obtained via wind-Roche lobe overflow.Comment: 26 pages, 18 figure
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
Binary Capture Rates for Massive Protostars
The high multiplicity of massive stars in dense, young clusters is
established early in their evolution. The mechanism behind this remains
unresolved. Recent results suggest that massive protostars may capture
companions through disk interactions with much higher efficiency than their
solar mass counterparts. However, this conclusion is based on analytic
determinations of capture rates and estimates of the robustness of the
resulting binaries. We present the results of coupled n-body and SPH
simulations of star-disk encounters to further test the idea that disk-captured
binaries contribute to the observed multiplicity of massive stars.Comment: 4 pages, 3 figures, accepted to ApJ
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