221 research outputs found
Probing the accretion processes in soft X-ray selected polars
High-energy data of accreting white dwarfs give access to the regime of the
primary accretion-induced energy release and the different proposed accretion
scenarios. We perform XMM-Newton observations of polars selected due to their
ROSAT hardness ratios close to -1.0 and model the emission processes in
accretion column and accretion region. Our models consider the
multi-temperature structure of the emission regions and are mainly determined
by mass-flow density, magnetic field strength, and white-dwarf mass. To
describe the full spectral energy distribution from infrared to X-rays in a
physically consistent way, we include the stellar contributions and establish
composite models, which will also be of relevance for future X-ray missions. We
confirm the X-ray soft nature of three polars.Comment: Accepted for publication in Acta Polytechnica, Proceedings of "The
Golden Age of Cataclysmic Variables and Related Objects II
Probing the Accretion Processes in Soft X-Ray Selected Polars
High-energy data of accreting white dwarfs give access to the regime of the primary accretion-induced energy release and the different proposed accretion scenarios. We perform XMM-Newton observations of polars selected due to their ROSAT hardness ratios close to -1.0 and model the emission processes in accretion column and accretion region. Our models consider the multi-temperature structure of the emission regions and are mainly determined by mass-flow density, magnetic field strength, and white-dwarf mass. To describe the full spectral energy distribution from infrared to X-rays in a physically consistent way, we include the stellar contributions and establish composite models, which will also be of relevance for future X-ray missions. We confirm the X-ray soft nature of three polars
XMM-Newton observations of the X-ray soft polar QS Telescopii
Context. On the basis of XMM-Newton observations, we investigate the energy
balance of selected magnetic cataclysmic variables, which have shown an extreme
soft-to-hard X-ray flux ratio in the ROSAT All-Sky Survey.
Aims. We intend to establish the X-ray properties of the system components,
their flux contributions, and the accretion geometry of the X-ray soft polar QS
Tel. In the context of high-resolution X-ray analyses of magnetic cataclysmic
variables, this study will contribute to better understanding the accretion
processes on magnetic white dwarfs.
Methods. During an intermediate high state of accretion of QS Tel, we have
obtained 20 ks of XMM-Newton data, corresponding to more than two orbital
periods, accompanied by simultaneous optical photometry and phase-resolved
spectroscopy. We analyze the multi-wavelength spectra and light curves and
compare them to former high- and low-state observations.
Results. Soft emission at energies below 2 keV dominates the X-ray light
curves. The complex double-peaked maxima are disrupted by a sharp dip in the
very soft energy range (0.1-0.5 keV), where the count rate abruptly drops to
zero. The EPIC spectra are described by a minimally absorbed black body at 20
eV and two partially absorbed MEKAL plasma models with temperatures around 0.2
and 3 keV. The black-body-like component arises from one mainly active, soft
X-ray bright accretion region nearly facing the mass donor. Parts of the plasma
emission might be attributed to the second, virtually inactive pole. High
soft-to-hard X-ray flux ratios and hardness ratios demonstrate that the
high-energy emission of QS Tel is substantially dominated by its X-ray soft
component.Comment: Accepted for publication in Astronomy and Astrophysics. 7 pages, 4
figures, 2 table
XMM-Newton observations of the low-luminosity cataclysmic variable V405 Pegasi
V405 Peg is a low-luminosity cataclysmic variable (CV) that was identified as
the optical counterpart of the bright, high-latitude ROSAT all-sky survey
source RBS1955. The system was suspected to belong to a largely undiscovered
population of hibernating CVs. Despite intensive optical follow-up its subclass
however remained undetermined.
We want to further classify V405 Peg and understand its role in the CV zoo
via its long-term behaviour, spectral properties, energy distribution and
accretion luminosity.
We perform a spectral and timing analysis of \textit{XMM-Newton} X-ray and
ultra-violet data. Archival WISE, HST, and Swift observations are used to
determine the spectral energy distribution and characterize the long-term
variability.
The X-ray spectrum is characterized by emission from a multi-temperature
plasma. No evidence for a luminous soft X-ray component was found. Orbital
phase-dependent X-ray photometric variability by occurred without
significant spectral changes. No further periodicity was significant in our
X-ray data. The average X-ray luminosity during the XMM-Newton observations was
L_X, bol simeq 5e30 erg/s but, based on the Swift observations, the
corresponding luminosity varied between 5e29 erg/s and 2e31 erg/son timescales
of years.
The CV subclass of this object remains elusive. The spectral and timing
properties show commonalities with both classes of magnetic and non-magnetic
CVs. The accretion luminosity is far below than that expected for a standard
accreting CV at the given orbital period. Objects like V405 Peg might represent
the tip of an iceberg and thus may be important contributors to the Galactic
Ridge X-ray Emission. If so they will be uncovered by future X-ray surveys,
e.g. with eROSITA.Comment: A&A, in pres
Spectroscopic classification and Gaia DR2 parallaxes of new nearby white dwarfs among selected blue proper motion stars
AIMS: With our low-resolution spectroscopic observing program for selected
blue proper motion stars, we tried to find new white dwarfs (WDs) in the solar
neighbourhood. METHODS: We used the LSPM catalogue with a lower proper motion
limit of 150mas/yr and the UCAC2 for proper motions down to about 90mas/yr. The
LSPM and UCAC2 photometry was combined with Two Micron All Sky Survey (2MASS)
near-infrared (NIR) photometry. Targets selected according to their blue
optical-to-NIR and NIR colours were observed mainly at Calar Alto. The spectra
were classified by comparison with a large number of already known comparison
objects, including WDs, simultaneously observed within our program. Gaia DR2
parallaxes and colours were used to confirm or reject spectroscopic WD
candidates and to derive improved effective temperatures. RESULTS: We found ten
new WDs at distances between 24.4pc and 79.8pc, including six hot DA WDs: GD
221 (DA2.0), HD 166435 B (DA2.2), GD 277 (DA2.2), 2MASS J19293865+1117523
(DA2.4), 2MASS J05280449+4105253 (DA3.6), and 2MASS J05005185-0930549 (DA4.2).
The latter is rather bright (G~12.6) and with its Gaia DR2 parallax of ~14mas
it appears overluminous by about 3mag compared to the WD sequence in the Gaia
DR2 colour-magnitude diagram. It may be the closest extremely low mass (ELM) WD
to the Sun. We further classified 2MASS J07035743+2534184 as DB4.1. With its
distance of 25.6pc it is the second nearest known representative of its class.
With GD 28 (DA6.1), LP 740-47 (DA7.5), and LSPM J1919+4527 (DC10.3) three
additional cool WDs were found. Gaia DR2 parallaxes showed us that four of our
candidates but also two previously supposed WDs (WD 1004+665 and LSPM
J1445+2527) are in fact distant Galactic halo stars with high tangential
velocities. Among our rejected WD candidates, we identified a bright
(G=13.4mag) G-type carbon dwarf, LSPM J0937+2803, at a distance of 272pc.Comment: 14 pages, 13 figures, accepted for publication in Astronomy and
Astrophysic
V902 Monocerotis: a likely disc-accreting intermediate polar
Aims: We aim to confirm whether the eclipsing cataclysmic variable V902 Mon
is an Intermediate Polar, to characterise its X-ray spectrum and flux, and to
refine its orbital ephemeris and spin period. Methods: We performed
spectrographic observations of V902 Mon in 2016 with the 2.2m Calar Alto
telescope, and X-ray photometry and spectroscopy with XMM-Newton in October
2017. This data was supplemented by several years of AAVSO visual photometry.
Results: We have confirmed V902 Mon as an IP based on detecting the spin
period, with a value of 2,208s, at multiple epochs. Spectroscopy of the donor
star and Gaia parallax yield a distance of 3.5+1.3-0.9, kpc, suggesting an
X-ray luminosity one or two orders of magnitude lower than the 10^33 erg/s
typical of previously known IPs. The X-ray to optical flux ratio is also very
low. The inclination of the system is more than 79deg, with a most likely value
of around 82deg. We have refined the eclipse ephemeris, stable over 14,000
cycles. The Halpha line is present throughout the orbital cycle and is clearly
present during eclipse, suggesting an origin distant from the white dwarf, and
shows radial velocity variations at the orbital period. The amplitude and
overall recessional velocity seem inconsistent with an origin in the disc. The
\emph{XMM-Newton} observation reveals a partially absorbed plasma model typical
of magnetic CVs, with a fluorescent iron line at 6.4keV showing a large
equivalent width of 1.4keV. Conclusions: V902 Mon is an IP, and probably a
member of the hypothesized X-ray underluminous class of IPs. It is likely to be
a disc accretor, though the radial velocity behaviour of the Halpha line
remains puzzling. The large equivalent width of the fluorescent iron line, the
small FX/Fopt ratio, and the only marginal detection of X-ray eclipses suggests
that the X-ray emission arises from scattering.Comment: 10 pages, 12 figure
Transmission spectroscopy of the inflated exo-Saturn HAT-P-19b
We observed the Saturn-mass and Jupiter-sized exoplanet HAT-P-19b to refine
its transit parameters and ephemeris as well as to shed first light on its
transmission spectrum. We monitored the host star over one year to quantify its
flux variability and to correct the transmission spectrum for a slope caused by
starspots. A transit of HAT-P-19b was observed spectroscopically with OSIRIS at
the Gran Telescopio Canarias in January 2012. The spectra of the target and the
comparison star covered the wavelength range from 5600 to 7600 AA. One
high-precision differential light curve was created by integrating the entire
spectral flux. This white-light curve was used to derive absolute transit
parameters. Furthermore, a set of light curves over wavelength was formed by a
flux integration in 41 wavelength channels of 50 AA width. We analyzed these
spectral light curves for chromatic variations of transit depth. The transit
fit of the combined white-light curve yields a refined value of the
planet-to-star radius ratio of 0.1390 pm 0.0012 and an inclination of 88.89 pm
0.32 degrees. After a re-analysis of published data, we refine the orbital
period to 4.0087844 pm 0.0000015 days. We obtain a flat transmission spectrum
without significant additional absorption at any wavelength or any slope.
However, our accuracy is not sufficient to significantly rule out the presence
of a pressure-broadened sodium feature. Our photometric monitoring campaign
allowed for an estimate of the stellar rotation period of 35.5 pm 2.5 days and
an improved age estimate of 5.5^+1.8_-1.3 Gyr by gyrochronology.Comment: 14 pages, 9 figures, Accepted for publication in A&
A giant X-ray dust scattering ring around the black hole transient MAXI J1348-630 discovered with SRG/eROSITA
We report the discovery of a giant dust scattering ring around the Black Hole
transient MAXI J1348-630 with SRG/eROSITA during its first X-ray all-sky
survey. During the discovery observation in February 2020 the ring had an outer
diameter of 1.3 deg, growing to 1.6 deg by the time of the second all sky
survey scan in August 2020. This makes the new dust ring the by far largest
X-ray scattering ring observed so far. Dust scattering halos, in particular the
rings found around transient sources, offer the possibility of precise distance
measurements towards the original X-ray sources. We combine data from
SRG/eROSITA, XMM-Newton, MAXI, and Gaia to measure the geometrical distance of
MAXI J1348-630. The Gaia data place the scattering dust at a distance of 2050
pc, from the measured time lags and the geometry of the ring, we find MAXI
J1348-630 at a distance of 3390 pc with a statistical uncertainty of only 1.1%
and a systematic uncertainty of 10% caused mainly by the parallax offset of
Gaia. This result makes MAXI J1348-630 one of the black hole transients with
the best determined distances. The new distance leads to a revised mass
estimate for the black hole of 11+-2 solar masses, the transition to the soft
state during the outburst occurred when the bolometric luminosity of MAXI
J1348-630 had reached 1.7% of its Eddington luminosity.Comment: 10 pages, 10 figures, 3 tables, accepted for publication in A&
The giant planet orbiting the cataclysmic binary DP Leonis
Planets orbiting post-common envelope binaries provide fundamental
information on planet formation and evolution, especially for the yet nearly
unexplored class of circumbinary planets. We searched for such planets in \odp,
an eclipsing short-period binary, which shows long-term eclipse-time
variations. Using published, reanalysed, and new mid-eclipse times of the white
dwarf in DP\,Leo, obtained between 1979 and 2010, we find agreement with the
light-travel-time effect produced by a third body in an elliptical orbit. In
particular, the measured binary period in 2009/2010 and the implied radial
velocity coincide with the values predicted for the motion of the binary and
the third body around the common center of mass. The orbital period, semi-major
axis, and eccentricity of the third body are P_c = 28.0 +/- 2.0 yrs, a_c = 8.2
+/- 0.4 AU, and e_c = 0.39 +/- 0.13. Its mass of M_c sin(i_c) = 6.1 +/- 0.5 M_J
qualifies it as a giant planet. It formed either as a first generation object
in a protoplanetary disk around the original binary or as a second generation
object in a disk formed in the common envelope shed by the progenitor of the
white dwarf. Even a third generation origin in matter lost from the present
accreting binary can not be entirely excluded. We searched for, but found no
evidence for a fourth body.Comment: Accepted by A&
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