1,253 research outputs found
The MUCHFUSS photometric campaign
Hot subdwarfs (sdO/Bs) are the helium-burning cores of red giants, which lost
almost all of their hydrogen envelopes. This mass loss is often triggered by
common envelope interactions with close stellar or even substellar companions.
Cool companions like late-type stars or brown dwarfs are detectable via
characteristic light curve variations like reflection effects and often also
eclipses. To search for such objects we obtained multi-band light curves of 26
close sdO/B binary candidates from the MUCHFUSS project with the BUSCA
instrument. We discovered a new eclipsing reflection effect system
(~d) with a low-mass M dwarf companion ().
Three more reflection effect binaries found in the course of the campaign were
already published, two of them are eclipsing systems, in one system only
showing the reflection effect but no eclipses the sdB primary is found to be
pulsating. Amongst the targets without reflection effect a new long-period sdB
pulsator was discovered and irregular light variations were found in two sdO
stars. The found light variations allowed us to constrain the fraction of
reflection effect binaries and the substellar companion fraction around sdB
stars. The minimum fraction of reflection effect systems amongst the close sdB
binaries might be greater than 15\% and the fraction of close substellar
companions in sdB binaries might be as high as . This would result in a
close substellar companion fraction to sdB stars of about 3\%. This fraction is
much higher than the fraction of brown dwarfs around possible progenitor
systems, which are solar-type stars with substellar companions around 1 AU, as
well as close binary white dwarfs with brown dwarf companions. This might be a
hint that common envelope interactions with substellar objects are
preferentially followed by a hot subdwarf phase.Comment: accepted for A&
Observations of microglitches in HartRAO radio pulsars
A detailed observation of microglitch phenomenon in relatively slow radio
pulsars is presented. Our analyses for these small amplitude jumps in pulse
rotation frequency () and/or spin down rate () combine the
traditional manual detection method (which hinges on careful visual inspections
of the residuals of pulse phase residuals) and a new, and perhaps more
objective, automated search technique (which exploits the power of the
computer, rather than the eyes, for resolving discrete events in pulsar spin
parameters). The results of the analyses of a sample of 26 radio pulsars reveal
that: (i) only 20 pulsars exhibit significant fluctuations in their arrival
times to be considered suitable for meaningful microglitch analyses; (ii) a
phenomenal 299 microglitch events were identified in and/or :
266 of these events were found to be simultaneously significant in and
, while 19 and 14 were noticeable only in and ,
respectively; (iii) irrespective of sign, the microglitches have fractional
sizes which cover about 3 orders of magnitude in and
( and ) with median values as
and , respectively.Comment: 12 pages, 3 figures, 2 Tables. Accepted for publication in Monthly
Notices of the Royal Astronomical Society Main Journa
GaBoDS: The Garching-Bonn Deep Survey -- II. Confirmation of EIS cluster candidates by weak gravitational lensing
We report the first confirmation of colour-selected galaxy cluster candidates
by means of weak gravitational lensing. Significant lensing signals were
identified in the course of the shear-selection programme of dark matter haloes
in the Garching-Bonn Deep Survey, which currently covers 20 square degrees of
deep, high-quality imaging data on the southern sky. The detection was made in
a field that was previously covered by the ESO Imaging Survey (EIS) in 1997. A
highly significant shear-selected mass-concentration perfectly coincides with
the richest EIS cluster candidate at z~0.2, thus confirming its cluster nature.
Several other shear patterns in the field can also be identified with cluster
candidates, one of which could possibly be part of a filament at z~0.45.Comment: 4 pages, 4 figures, submitted to A&A Letter
GaBoDS: The Garching-Bonn Deep Survey - III. Lyman-Break Galaxies in the Chandra Deep Field South
We present first results of our search for high-redshift galaxies in deep CCD
mosaic images. As a pilot study for a larger survey, very deep images of the
Chandra Deep Field South (CDFS), taken withWFI@MPG/ESO2.2m, are used to select
large samples of 1070 U-band and 565 B-band dropouts with the Lyman-break
method. The data of these Lyman-break galaxies are made public as an electronic
table. These objects are good candidates for galaxies at z~3 and z~4 which is
supported by their photometric redshifts. The distributions of apparent
magnitudes and the clustering properties of the two populations are analysed,
and they show good agreement to earlier studies. We see no evolution in the
comoving clustering scale length from z~3 to z~4. The techniques presented here
will be applied to a much larger sample of U-dropouts from the whole survey in
near future.Comment: 11 pages, 11 figures, replaced with version accepted by A&A. Minor
changes and tabular appendix with LBG catalogues. Version with full
resolution figures available at
http://www.astro.uni-bonn.de/~hendrik/2544.pd
Multi-wavelength photometric variation of PG1605+072
In a large coordinated attempt to further our understanding of the -mode
pulsating sdB star PG1605+072, the Multi-Site Spectroscopic Telescope (MSST)
collaboration has obtained simultaneous time-resolved spectroscopic and
photometric observations. The photometry was extended by additional WET data
which increased the time base. This contribution outlines the analysis of the
MSST photometric light curve, including the four-colour BUSCA data from which
chromatic amplitudes have been derived, as well as supplementary FUV spectra
and light curves from two different epochs. These results have the potential to
complement the interpretation of the published spectroscopic information.Comment: 6 pages, to be published in "Interpretation of asteroseismic data",
proceedings of the HELAS NA5 Workshop, eds. W. Dziembowski, M. Breger and M.
Thompson, Communications in Asteroseismology, 15
Non-Douglas-Kazakov phase transition of two-dimensional generalized Yang-Mills theories
In two-dimensional Yang-Mills and generalized Yang-Mills theories for large
gauge groups, there is a dominant representation determining the thermodynamic
limit of the system. This representation is characterized by a density the
value of which should everywhere be between zero and one. This density itself
is determined through a saddle-point analysis. For some values of the parameter
space, this density exceeds one in some places. So one should modify it to
obtain an acceptable density. This leads to the well-known Douglas-Kazakov
phase transition. In generalized Yang-Mills theories, there are also regions in
the parameter space where somewhere this density becomes negative. Here too,
one should modify the density so that it remains nonnegative. This leads to
another phase transition, different from the Douglas-Kazakov one. Here the
general structure of this phase transition is studied, and it is shown that the
order of this transition is typically three. Using carefully-chosen parameters,
however, it is possible to construct models with phase-transition orders not
equal to three. A class of these non-typical models are also studied.Comment: 11 pages, accepted for publication in Eur. Phys. J.
Parallax and Kinematics of PSR B0919+06 from VLBA Astrometry and Interstellar Scintillometry
Results are presented from a long-term astrometry program on PSR B0919+06
using the NRAO Very Long Baseline Array. With ten observations (seven epochs)
between 1994--2000, we measure a proper motion of 18.35 +/- 0.06 mas/yr in RA,
86.56 +/- 0.12 mas/yr in Dec, and a parallax of 0.83 +/- 0.13 mas (68%
confidence intervals). This yields a pulsar distance of 1.21 +/- 0.19 kpc,
making PSR B0919+06 the farthest pulsar for which a trigonometric parallax has
been obtained, and the implied pulsar transverse speed is 505 +/- 80 km/s.
Combining the distance estimate with interstellar scintillation data spanning
20 years, we infer the existence of a patchy or clumpy scattering screen along
the line of sight in addition to the distributed electron density predicted by
models for the Galaxy, and constrain the location of this scattering region to
within about 250 parsecs of the Sun. Comparison with the lines of sight towards
other pulsars in the same quadrant of the Galaxy permits refinement of our
knowledge of the local interstellar matter in this direction.Comment: 12 pages, includes 4 figures and 3 tables, uses AASTeX 5 (included);
ApJ submitte
Detection of X-ray Emission from the Very Old Pulsar J0108-1431
PSR J0108-1431 is a nearby, 170 Myr old, very faint radio pulsar near the
"pulsar death line" in the P-Pdot diagram. We observed the pulsar field with
the Chandra X-ray Observatory and detected a point source (53 counts in a 30 ks
exposure, energy flux (9+/-2)\times 10^{-15} ergs cm^{-2} s^{-1} in the 0.3-8
keV band) close to the radio pulsar position. Based on the large X-ray/optical
flux ratio at the X-ray source position, we conclude that the source is the
X-ray counterpart of PSR J0108-1431.The pulsar spectrum can be described by a
power-law model with photon index Gamma \approx 2.2 and luminosity L_{0.3-8
keV} \sim 2\times 10^{28} d_{130}^2 ergs s^{-1}, or by a blackbody model with
the temperature kT\approx 0.28 keV and bolometric luminosity L_{bol} \sim
1.3\times 10^{28} d_{130}^2 ergs s^{-1}, for a plausible hydrogen column
density NH = 7.3\times 10^{19} cm^{-2} (d_{130}=d/130 pc). The pulsar converts
\sim 0.4% of its spin-down power into the X-ray luminosity, i.e., its X-ray
efficiency is higher than for most younger pulsars. From the comparison of the
X-ray position with the previously measured radio positions, we estimated the
pulsar proper motion of 0.2 arcsec yr^{-1} (V_\perp \sim 130 d_{130} km
s^{-1}), in the south-southeast direction.Comment: 8 pages, 9 figures, accepted to ApJ; minor revisions in Sections 2.2
and 3.
The Frequency Evolution of Interstellar Pulse Broadening from Radio Pulsars
In this paper we report multi-frequency measurements of pulse broadening
times (tau_d) for nine medium dispersion measure (DM pc
cm) pulsars observed over a wide frequency range. The low frequency data
at 243, 325 and 610 MHz are new observations done with the Giant Metrewave
Radio Telescope (GMRT). The frequency dependence of tau_d for all but one (PSR
B1933+16) of our sources is consistent with the Kolmogorov spectrum of electron
density fluctuations in a turbulent medium. PSR B1933+16, however, shows a very
flat spectrum as previously observed for high DM pulsars. Our observations
combined with earlier published results enable us to study the spectral index
of tau_d over the whole observed DM range. While the spectral properties are
generally consistent with a Kolmogorov spectrum, pulsars seen along
line-of-sights towards the inner Galaxy or complex regions often show
deviations from this expected behaviour.Comment: 7 pages, 5 figures, accepted for publication in A&
BeppoSAX observation of PSR B1937+21
We present the results of a BeppoSAX observation of the fastest rotating
pulsar known: PSR B1937+21. The ~200 ks observation (78.5 ks MECS/34 ks LECS
on-source time) allowed us to investigate with high statistical significance
both the spectral properties and the pulse profile shape. The pulse profile is
clearly double peaked at energies > ~4 keV. Peak widths are compatible with the
instrumental time resolution and the second pulse lags the main pulse 0.52 in
phase, like is the case in the radio. In the 1.3-4 keV band we detect a ~45% DC
component; conversely the 4-10 keV pulsed fraction is consistent with 100%. The
on-pulse spectrum is fitted with an absorbed power-law of spectral index ~1.2,
harder than that of the total flux which is ~1.9. The total unabsorbed (2-10
keV) flux is F_{2-10} = 4.1 10^-13 cgs, implying a luminosity of L_X = 5.0
10^31 \Theta (d/3.6 kpc)^2 erg s^-1 and a X-ray efficiency of \eta = 4.5 10^-5
\Theta, where \Theta is the solid angle spanned by the emission beam. These
results are in agreement with those obtained by ASCA and a more recent
Rossi-XTE observation. The hydrogen column density N_H ~2 10^22 cm^-2 is ~10
times higher than expected from the radio dispersion measure and average
Galactic density of e-. Though it is compatible (within 2\sigma) with the
Galactic (HI derived) value of ~1 10^22 cm^-2, inspection of dust extinction
maps reveal that the pulsar falls in a highly absorbed region. In addition, 1.4
GHz radio map shows that the nearby (likely unrelated) HII source 4C21.53W is
part of a circular emission region ~4' across.Comment: 8 pages, 5 figures; accepted for publication in A&
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