1,147 research outputs found
The mass ratio and the orbital parameters of the sdOB binary AA Doradus
The time sequence of 105 spectra covering one full orbital period of AA Dor
has been analyzed. Direct determination of Vsini for the sdOB component from 97
spectra outside of the eclipse for the lines MgII 4481 A and SiIV 4089 A
clearly indicated a substantially smaller value than estimated before. Detailed
modelling of line profile variations for 8 spectra during the eclipse for the
MgII 4481 A line, combined with the out-of-eclipse fits, gave Vsini =
31.8+/-1.8 km/s. The previous determinations of Vsini, based on the HeII 4686 A
line, appear to be invalid because of the large natural broadening of the line.
With the assumption of the solid-body, synchronous rotation of the sdOB
primary, the measured values of the semi-amplitude K1 and Vsini lead to the
mass ratio q = 0.213+/-0.013 which in turn gives K2 and thus the masses and
radii of both components. The sdOB component appears to be less massive than
assumed before, M1 = 0.25+/-0.05 Msol, but the secondary has its mass-radius
parameters close to theoretically predicted for a brown dwarf, M2 =
0.054+/-0.010 Msol and R2 = 0.089+/-0.005 Rsol. Our results do not agree with
the recent determination of Vuckovic et al. 2008 based on a K2 estimate from
line-profile asymmetries.Comment: Accepted by MNRA
A Low Rise Hospital Development on Restored Opencast Fill
An extensive low-rise hospital development has taken place since 1982 on a former opencast coal mining site 30 years after working and restoration. The clay and shale fill some 20 metres deep was placed without systematic compaction. Five separate site investigations have been carried out at different times during the last 20 years and a detailed engineering geological mapping exercise was completed in 1977. Drainage works and the main buildings in Scheme 1 and 2 have been monitored during and after construction. Significant settlements have occurred requiring some remedial work. A surcharge and inundation trial has been undertaken prior to the design and construction of Scheme 3. The response of the buildings and the drainage to ground movement is described and design recommendations made for future development
Variability in the extreme helium star LSS 5121
We report a photometric and spectroscopic study of the hot extreme helium
star LSS 5121. We found photometric variability, but no period was evident in
its periodogram. This is consistent with the previous proposal, based on
spectral line variations, that LSS 5121 is a non-radial pulsator similar to
other hot extreme helium stars.Comment: 5 pages, 6 figure
Orbital Characteristics of the Subdwarf-B and F V Star Binary EC~20117-4014(=V4640 Sgr)
Among the competing evolution theories for subdwarf-B (sdB) stars is the
binary evolution scenario. EC~20117-4014 (=V4640~Sgr) is a spectroscopic binary
system consisting of a pulsating sdB star and a late F main-sequence companion
(O'Donoghue et al. 1997), however the period and the orbit semi-major axes have
not been precisely determined. This paper presents orbital characteristics of
the EC 20117-4014 binary system using 20 years of photometric data. Periodic
Observed minus Calculated (O-C) variations were detected in the two highest
amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating
the binary system's precise orbital period (P = 792.3 days) and the
light-travel time amplitude (A = 468.9 s). This binary shows no significant
orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3
as an upper limit). This upper limit of the eccentricity is the lowest
among all wide sdB binaries with known orbital parameters. This analysis
indicated that the sdB is likely to have lost its hydrogen envelope through
stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB
stars. In addition to those results, the underlying pulsation period change
obtained from the photometric data was = 5.4 (0.7)
d d, which shows that the sdB is just before the end of the
core helium-burning phase
The binary properties of the pulsating subdwarf B eclipsing binary PG 1336-018 (NY Virginis)
Aims. We present an unbiased orbit solution and mass determination of the components of the eclipsing binary PG1336−018 as a critical test for the formation scenarios of subdwarf B stars.
Methods. We obtained high-resolution time series VLT/UVES spectra and high-speed multicolour VLT/ULTRACAM photometric
observations of PG1336−018, a rapidly pulsating subdwarf B star in a short period eclipsing binary.
Results. Combining the radial velocity curve obtained from the VLT/UVES spectra with the VLT/ULTRACAM multicolour
lightcurves, we determined numerical orbital solutions for this eclipsing binary. Due to the large number of free parameters and their strong correlations, no unique solution could be found, only families of solutions. We present three solutions of equal statistical
significance, two of which are compatible with the primary having gone through a core He-flash and a common-envelope phase described by the α-formalism. These two models have an sdB primary of 0.466 M and 0.389 M, respectively. Finally, we report the detection of the Rossiter-McLaughlin effect for PG1336−018
The Solar Neighborhood. XIX. Discovery and Characterization of 33 New Nearby White Dwarf Systems
We present spectra for 33 previously unclassified white dwarf systems
brighter than V = 17 primarily in the southern hemisphere. Of these new
systems, 26 are DA, 4 are DC, 2 are DZ, and 1 is DQ. We suspect three of these
systems are unresolved double degenerates. We obtained VRI photometry for these
33 objects as well as for 23 known white dwarf systems without trigonometric
parallaxes, also primarily in the southern hemisphere. For the 56 objects, we
converted the photometry values to fluxes and fit them to a spectral energy
distribution using the spectroscopy to determine which model to use (i.e. pure
hydrogen, pure helium, or metal-rich helium), resulting in estimates of
effective temperature and distance. Eight of the new and 12 known systems are
estimated to be within the NStars and Catalogue of Nearby Stars (CNS) horizons
of 25 pc, constituting a potential 18% increase in the nearby white dwarf
sample. Trigonometric parallax determinations are underway via CTIOPI for these
20 systems.
One of the DCs is cool so that it displays absorption in the near infrared.
Using the distance determined via trigonometric parallax, we are able to
constrain the model-dependent physical parameters and find that this object is
most likely a mixed H/He atmosphere white dwarf similar to other cool white
dwarfs identified in recent years with significant absorption in the infrared
due to collision-induced absorptions by molecular hydrogen.Comment: 33 pages, 10 figures, accepted for publication in the Astronomical
Journa
Fortnightly Fluctuations in the O-C Diagram of CS 1246
Dominated by a single, large-amplitude pulsation mode, the rapidly-pulsating
hot subdwarf B star CS 1246 is a prime candidate for a long-term O-C diagram
study. We collected nearly 400 hours of photometry with the PROMPT telescopes
over a time span of 14 months to begin looking for secular variations in the
pulse timings. Interestingly, the O-C diagram is dominated by a strong
sinusoidal pattern with a period of 14.1 days and an amplitude of 10.7
light-seconds. Underneath this sine wave is a secular trend implying a decrease
in the 371.7-s pulsational period of Pdot = -1.9 x 10^-11, which we attribute
to the evolution of the star through the H-R diagram. The sinusoidal variation
could be produced by the presence of a low-mass companion, with m sin i ~ 0.12
Msun, orbiting the subdwarf B star at a distance of 20 Rsun. An analysis of the
combined light curve reveals the presence of a low-amplitude first harmonic to
the main pulsation mode.Comment: Accepted for publication in MNRAS. 11 pages, 8 figures, 5 table
An evolutionary study of the pulsating subdwarf B eclipsing binary PG1336-018 (NY Vir)
The formation of subdwarf B (sdB) stars is not well understood within the
current framework of stellar single and binary evolution. In this study, we
focus on the formation and evolution of the pulsating sdB star in the very
short-period eclipsing binary PG1336-018. We aim at refining the formation
scenario of this unique system, so that it can be confronted with observations.
We probe the stellar structure of the progenitors of sdB stars in short-period
binaries using detailed stellar evolution calculations. Applying this to
PG1336-018 we reconstruct the common-envelope phase during which the sdB star
was formed. The results are interpreted in terms of the standard
common-envelope formalism (the alpha-formalism) based on the energy equation,
and an alternative description (the gamma-formalism) using the angular momentum
equation. We find that if the common-envelope evolution is described by the
alpha-formalism, the sdB progenitor most likely experienced a helium flash. We
then expect the sdB mass to be between 0.39 and 0.48 Msun, and the sdB
progenitor initial mass to be below ~2 Msun. However, the results for the
gamma-formalism are less restrictive, and a broader sdB mass range (0.3 - 0.8
Msun) is possible in this case. Future seismic mass determination will give
strong constraints on the formation of PG1336-018 and, in particular, on the CE
phase.Comment: 9 pages, 7 figures, 2 tables, accepted for publication in A&
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