122 research outputs found
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
FK Comae Berenices, King of Spin: The COCOA-PUFS Project
COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast
spinning, heavily spotted, yellow giant FK Com (HD117555; G4 III). This single
star is thought to be a recent binary merger, and is exceptionally active by
measure of its intense ultraviolet and X-ray emissions, and proclivity to
flare. COCOA-PUFS was carried out with Hubble Space Telescope in the UV
(120-300 nm), using mainly its high-performance Cosmic Origins Spectrograph,
but also high-precision Space Telescope Imaging Spectrograph; Chandra X-ray
Observatory in the soft X-rays (0.5-10 keV), utilizing its High-Energy
Transmission Grating Spectrometer; together with supporting photometry and
spectropolarimetry in the visible from the ground. This is an introductory
report on the project.
FK Com displayed variability on a wide range of time scales, over all
wavelengths, during the week-long main campaign, including a large X-ray flare;
"super-rotational broadening" of the far-ultraviolet "hot-lines" (e.g., Si IV
139 nm (T~80,000 K) together with chromospheric Mg II 280 nm and C II 133 nm
(10,000-30,000 K); large Doppler swings suggestive of bright regions
alternately on advancing and retreating limbs of the star; and substantial
redshifts of the epoch-average emission profiles. These behaviors paint a
picture of a highly extended, dynamic, hot (10 MK) coronal magnetosphere around
the star, threaded by cooler structures perhaps analogous to solar prominences,
and replenished continually by surface activity and flares. Suppression of
angular momentum loss by the confining magnetosphere could temporarily postpone
the inevitable stellar spindown, thereby lengthening this highly volatile stage
of coronal evolution.Comment: to be published in ApJ
Absolute dimensions and apsidal motion of the eclipsing binaries V889 Aquilae and V402 Lacertae
Context. Double-lined eclipsing binaries allow the direct determination of masses and radii, which are key for testing stellar models. With the launch of the TESS mission, many well-known eclipsing binaries have been observed at higher photometric precision, permitting the improvement of the absolute dimension determinations. Aims. Using TESS data and newly obtained spectroscopic observations, we aim to determine the masses and radii of the eccentric eclipsing binary systems V889 Aql and V402 Lac, together with their apsidal motion parameters. Methods. We simultaneously modelled radial velocity curves and times of eclipse for each target to precisely determine the orbital parameters of the systems, which we used to analyse the light curves and then obtain their absolute dimensions. We compared the obtained values with those predicted by theoretical models. Results. We determined masses and radii of the components of both systems with relative uncertainties lower than 2%. V889 Aql is composed of two stars with masses 2:17±0:02 M⊙ and 2:13±0:01 M⊙ and radii 1:87±0:04 R⊙ and 1:85±0:04 R⊙.We find conclusive evidence of the presence of a third body orbiting V889 Aql with a period of 67 yr. Based on the detected third light and the absence of signal in the spectra, we suggest that this third body could in turn be a binary composed of two ±1.4 M⊙ stars. V402 Lac is composed of two stars with masses 2:80 ± 0:05 M⊙ and 2:78 ± 0:05 M⊙ and radii 2:38 ± 0:03 R⊙ and 2:36 ± 0:03 R⊙. The times of minimum light are compatible with the presence of a third body for this system too, although its period is not yet fully sampled. In both cases we have found a good agreement between the observed apsidal motion rates and the model predictions
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