6,695 research outputs found
Multifrequency nature of the 0.75 mHz feature in the X-ray light curves of the nova V4743 Sgr
We present timing analyses of eight X-ray light curves and one optical/UV
light curve of the nova V4743 Sgr (2002) taken by CHANDRA and XMM on days after
outburst: 50 (early hard emission phase), 180, 196, 302, 371, 526 (super soft
source, SSS, phase), and 742 and 1286 (quiescent emission phase). We have
studied the multifrequency nature and time evolution of the dominant peak at
~0.75 mHz using the standard Lomb-Scargle method and a 2-D sine fitting method.
We found a double structure of the peak and its overtone for days 180 and 196.
The two frequencies were closer together on day 196, suggesting that the
difference between the two peaks is gradually decreasing. For the later
observations, only a single frequency can be detected, which is likely due to
the exposure times being shorter than the beat period between the two peaks,
especially if they are moving closer together. The observations on days 742 and
1286 are long enough to detect two frequencies with the difference found for
day 196, but we confidently find only a single frequency. We found significant
changes in the oscillation frequency and amplitude. We have derived blackbody
temperatures from the SSS spectra, and the evolution of changes in frequency
and blackbody temperature suggests that the 0.75-mHz peak was modulated by
pulsations. Later, after nuclear burning had ceased, the signal stabilised at a
single frequency, although the X-ray frequency differs from the optical/UV
frequency obtained consistently from the OM onboard XMM and from ground-based
observations. We believe that the late frequency is the white dwarf rotation
and that the ratio of spin/orbit period strongly supports that the system is an
intermediate polar.Comment: 17 pages, 22 figures, 7 tables, accepted for publication in MNRA
X-ray accretion signatures in the close CTTS binary V4046 Sgr
We present Chandra HETGS observations of the classical T Tauri star (CTTS)
V4046 Sgr. The He-like triplets of O VII, Ne IX, and Si XIII are clearly
detected. Similar to the CTTS TW Hya and BP Tau, the forbidden lines of O VII
and Ne IX are weak compared to the intercombination line, indicating high
plasma densities in the X-ray emitting regions. The Si XIII triplet, however,
is within the low-density limit, in agreement with the predictions of the
accretion funnel infall model with an additional stellar corona. V4046 Sgr is
the first close binary exhibiting these features. Together with previous
high-resolution X-ray data on TW Hya and BP Tau, and in contrast to T Tau, now
three out of four CTTS show evidence of accretion funnels.Comment: 5 pages, 5 figure
The supersoft X-ray source in V5116 Sgr I. The high resolution spectra
Classical novae occur on the surface of an accreting white dwarf in a binary
system. After ejection of a fraction of the envelope and when the expanding
shell becomes optically thin to X-rays, a bright source of supersoft X-rays
arises, powered by residual H burning on the surface of the white dwarf. While
the general picture of the nova event is well established, the details and
balance of accretion and ejection processes in classical novae are still full
of unknowns. The long-term balance of accreted matter is of special interest
for massive accreting white dwarfs, which may be promising supernova Ia
progenitor candidates. V5116 Sgr was observed as a bright and variable
supersoft X-ray source by XMM-Newton 610~days after outburst. The light curve
showed a periodicity consistent with the orbital period. During one third of
the orbit the luminosity was a factor of seven brighter than during the other
two thirds of the orbital period. In the present work we aim to disentangle the
X-ray spectral components of V5116 Sgr and their variability. We present the
high resolution spectra obtained with XMM-Newton RGS and Chandra LETGS/HRC-S in
March and August 2007. The grating spectrum during the periods of high-flux
shows a typical hot white dwarf atmosphere dominated by absorption lines of N
VI and N VII. During the low-flux periods, the spectrum is dominated by an
atmosphere with the same temperature as during the high-flux period, but with
several emission features superimposed. Some of the emission lines are well
modeled with an optically thin plasma in collisional equilibrium, rich in C and
N, which also explains some excess in the spectra of the high-flux period. No
velocity shifts are observed in the absorption lines, with an upper limit set
by the spectral resolution of 500 km/s, consistent with the expectation of a
non-expanding atmosphere so late in the evolution of the post-nova.Comment: 12 pages, 15 figures, 4 tables; accepted for publication in Astronomy
and Astrophysic
X-rays from accretion shocks in T Tauri stars: The case of BP Tau
We present an XMM-Newton observation of the classical T Tauri star BP Tau. In
the XMM-Newton RGS spectrum the O {\sc vii} triplet is clearly detected with a
very weak forbidden line indicating high plasma densities and/or a high UV flux
environment. At the same time concurrent UV data point to a small hot spot
filling factor suggesting an accretion funnel shock as the site of the X-ray
and UV emission. Together with the X-ray data on TW Hya these new observations
suggest such funnels to be a general feature in classical T Tauri stars.Comment: 4 pages, 4 figures, accepted by A&
Spatially resolved X-ray emission of EQ Pegasi
We present an analysis of an XMM-Newton observation of the M dwarf binary EQ
Pegasi with a special focus on the the spatial structure of the X-ray emission
and the analysis of light curves. Making use of data obtained with EPIC
(European Photon Imaging Camera) we were for the first time able to spatially
resolve the two components in X-rays and to study the light curves of the
individual components of the EQ Peg system. During the observation a series of
moderate flares was detected, where it was possible to identify the respective
flaring component.Comment: 6 pages, 11 figures, accepted by A&
GMRT Low Frequency Observations of Extrasolar Planetary Systems
Extrasolar planets are expected to emit detectable low frequency radio
emission. In this paper we present results from new low frequency observations
of two extrasolar planetary systems (Epsilon Eridani and HD 128311) taken at
150 MHz with the Giant Metrewave Radio Telescope (GMRT). These two systems have
been chosen because the stars are young (with ages < 1 Gyr) and are likely to
have strong stellar winds, which will increase the expected radio flux. The
planets are massive (presumably) gas giant planets in longer period orbits, and
hence will not be tidally locked to their host star (as is likely to be the
case for short period planets) and we would expect them to have a strong
planetary dynamo and magnetic field. We do not detect either system, but are
able to place tight upper limits on their low frequency radio emission, at
levels comparable to the theoretical predictions for these systems. From these
observations we have a 2.5sigma limit of 7.8 mJy for Epsilon Eri and 15.5 mJy
for HD 128311. In addition, these upper limits also provide limits on the low
frequency radio emission from the stars themselves. These results are discussed
and also the prospects for the future detection of radio emission from
extrasolar planets.Comment: 6 pages, 2 figures, accepted for publication in MNRA
Interplanetary sector structure, 1962 - 1966
Properties of interplanetary magnetic field observed by IMP-
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