42 research outputs found
The period-gap cataclysmic variable CzeV404 Her: A link between SW Sex and SU UMa systems
Context: We present a new study of the eclipsing cataclysmic variable CzeV404
Her (Porb = 0.098 d) that is located in the period gap. Aims: This report
determines the origin of the object and the system parameters and probes the
accretion flow structure of the system. Methods: We conducted simultaneous
time-resolved photometric and spectroscopic observations of CzeV404 Her. We
applied our light-curve modelling techniques and the Doppler tomography method
to determine the system parameters and analyse the structure of the accretion
disk. Results: We found that the system has a massive white dwarf M_WD =
1.00(2) M_sun a mass ratio of q = 0.16, and a relatively hot secondary with an
effective temperature T_2 = 4100(50) K. The system inclination is i =
78.8{\deg}. The accretion disk spreads out to the tidal limitation radius and
has an extended hot spot or line region. The hot spot or line is hotter than
the remaining outer part of the disk in quiescence or in intermediate state,
but does not stand out completely from the disk flux in (super)outbursts.
Conclusions: We claim that this object represents a link between two distinct
classes of SU UMa-type and SW Sex-type cataclysmic variables. The accretion
flow structure in the disk corresponds to the SW Sex systems, but the physical
conditions inside the disk fit the behaviour of SU UMa-type objects
First apsidal motion and light curve analysis of 162 eccentric eclipsing binaries from LMC
We present an extensive study of 162 early-type binary systems located in the
LMC galaxy that show apsidal motion and have never been studied before. For the
ample systems, we performed light curve and apsidal motion modelling for the
first time. These systems have a median orbital period of 2.2 days and typical
periods of the apsidal motion were derived to be of the order of decades. We
identified two record-breaking systems. The first, OGLE LMC-ECL-22613, shows
the shortest known apsidal motion period among systems with main sequence
components (6.6 years); it contains a third component with an orbital period of
23 years. The second, OGLE LMC-ECL-17226, is an eccentric system with the
shortest known orbital period (0.9879 days) and with quite fast apsidal motion
period (11 years). Among the studied systems, 36 new triple-star candidates
were identified based on the additional period variations. This represents more
than 20% of all studied systems, which is in agreement with the statistics of
multiples in our Galaxy. However, the fraction should only be considered as a
lower limit of these early-type stars in the LMC because of our method of
detection, data coverage, and limited precision of individual times of
eclipses.Comment: 24 pages, 18 figures, 5 tables, published in 2020A&A...640A..33
A remarkable recurrent nova in M31: Discovery and optical/UV observations of the predicted 2014 eruption
The Andromeda Galaxy recurrent nova M31N 2008-12a had been caught in eruption eight times. The inter-eruption period of M31N 2008-12a is ~1 year, making it the most rapidly recurring system known, and a strong single-degenerate Type Ia Supernova progenitor candidate. Following the 2013 eruption, a campaign was initiated to detect the predicted 2014 eruption and to then perform high cadence optical photometric and spectroscopic monitoring using ground-based telescopes, along with rapid UV and X-ray follow-up with the Swift satellite. Here we report the results of a high cadence multicolour optical monitoring campaign, the spectroscopic evolution, and the UV photometry. We also discuss tantalising evidence of a potentially related, vastly-extended, nebulosity. The 2014 eruption was discovered, before optical maximum, on October 2, 2014. We find that the optical properties of M31N 2008-12a evolve faster than all Galactic recurrent novae known, and all its eruptions show remarkable similarity both photometrically and spectroscopically. Optical spectra were obtained as early as 0.26 days post maximum, and again confirm the nova nature of the eruption. A significant deceleration of the inferred ejecta expansion velocity is observed which may be caused by interaction of the ejecta with surrounding material, possibly a red giant wind. We find a low ejected mass and low ejection velocity, which are consistent with high mass-accretion rate, high mass white dwarf, and short recurrence time models of novae. We encourage additional observations, especially around the predicted time of the next eruption, towards the end of 2015
The field high-amplitude SX Phe variable BL Cam: results from a multisite photometric campaign. II. Evidence of a binary - possibly triple - system
Short-period high-amplitude pulsating stars of Population I ( Sct
stars) and II (SX Phe variables) exist in the lower part of the classical
(Cepheid) instability strip. Most of them have very simple pulsational
behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is
a unique object among them, being an extreme metal-deficient field
high-amplitude SX Phe variable with a large number of frequencies. Based on a
frequency analysis, a pulsational interpretation was previously given. aims
heading (mandatory) We attempt to interpret the long-term behaviour of the
residuals that were not taken into account in the previous Observed-Calculated
(O-C) short-term analyses. methods heading (mandatory) An investigation of the
O-C times has been carried out, using a data set based on the previous
published times of light maxima, largely enriched by those obtained during an
intensive multisite photometric campaign of BL Cam lasting several months.
results heading (mandatory) In addition to a positive (161 3) x 10
yr secular relative increase in the main pulsation period of BL Cam, we
detected in the O-C data short- (144.2 d) and long-term ( 3400 d)
variations, both incompatible with a scenario of stellar evolution. conclusions
heading (mandatory) Interpreted as a light travel-time effect, the short-term
O-C variation is indicative of a massive stellar component (0.46 to 1
M_{\sun}) with a short period orbit (144.2 d), within a distance of 0.7 AU
from the primary. More observations are needed to confirm the long-term O-C
variations: if they were also to be caused by a light travel-time effect, they
could be interpreted in terms of a third component, in this case probably a
brown dwarf star ( 0.03 \ M_{\sun}), orbiting in 3400 d at a
distance of 4.5 AU from the primary.Comment: 7 pages, 5 figures, accepted for publication in A&
M31N 2008-12a - the remarkable recurrent nova in M31: Pan-chromatic observations of the 2015 eruption
The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption ten times, including yearly eruptions from 2008-2014. With a measured recurrence period of days (we believe the true value to be half of this) and a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground and space-based follow-up programs. In this paper we present the 2015 detection; visible to near-infrared photometry and visible spectroscopy; and ultraviolet and X-ray observations from the Swift observatory. The LCOGT 2m (Hawaii) discovered the 2015 eruption, estimated to have commenced at Aug. UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities km s, possibly collimated outflows. Photometric and spectroscopic observations of the eruption provide strong evidence supporting a red giant donor. An apparently stochastic variability during the early super-soft X-ray phase was comparable in amplitude and duration to past eruptions, but the 2013 and 2015 eruptions show evidence of a brief flux dip during this phase. The multi-eruption Swift/XRT spectra show tentative evidence of high-ionization emission lines above a high-temperature continuum. Following Henze et al. (2015a), the updated recurrence period based on all known eruptions is d, and we expect the next eruption of M31N 2008-12a to occur around mid-Sep. 2016
Breaking the habit - the peculiar 2016 eruption of the unique recurrent nova M31N 2008-12a
Since its discovery in 2008, the Andromeda galaxy nova M31N 2008-12a has been observed in eruption every single year. This unprecedented frequency indicates an extreme object, with a massive white dwarf and a high accretion rate, which is the most promising candidate for the single-degenerate progenitor of a type-Ia supernova known to date. The previous three eruptions of M31N 2008-12a have displayed remarkably homogeneous multi-wavelength properties: (i) From a faint peak, the optical light curve declined rapidly by two magnitudes in less than two days; (ii) Early spectra showed initial high velocities that slowed down significantly within days and displayed clear He/N lines throughout; (iii) The supersoft X-ray source (SSS) phase of the nova began extremely early, six days after eruption, and only lasted for about two weeks. In contrast, the peculiar 2016 eruption was clearly different. Here we report (i) the considerable delay in the 2016 eruption date, (ii) the significantly shorter SSS phase, and (iii) the brighter optical peak magnitude (with a hitherto unobserved cusp shape). Early theoretical models suggest that these three different effects can be consistently understood as caused by a lower quiescence mass-accretion rate. The corresponding higher ignition mass caused a brighter peak in the free-free emission model. The less-massive accretion disk experienced greater disruption, consequently delaying re-establishment of effective accretion. Without the early refueling, the SSS phase was shortened. Observing the next few eruptions will determine whether the properties of the 2016 outburst make it a genuine outlier in the evolution of M31N 2008-12a
M31N 2008-12a - The REMARKABLE RECURRENT NOVA in M31: PANCHROMATIC OBSERVATIONS of the 2015 ERUPTION
© 2016. The American Astronomical Society. All rights reserved.The Andromeda Galaxy recurrent nova M31N 2008-12a had been observed in eruption 10 times, including yearly eruptions from 2008 to 2014. With a measured recurrence period of Prec = 351 ± 13 days (we believe the true value to be half of this) and a white dwarf very close to the Chandrasekhar limit, M31N 2008-12a has become the leading pre-explosion supernova type Ia progenitor candidate. Following multi-wavelength follow-up observations of the 2013 and 2014 eruptions, we initiated a campaign to ensure early detection of the predicted 2015 eruption, which triggered ambitious ground- and space-based follow-up programs. In this paper we present the 2015 detection, visible to near-infrared photometry and visible spectroscopy, and ultraviolet and X-ray observations from the Swift observatory. The LCOGT 2 m (Hawaii) discovered the 2015 eruption, estimated to have commenced at August 28.28 ± 0.12 UT. The 2013-2015 eruptions are remarkably similar at all wavelengths. New early spectroscopic observations reveal short-lived emission from material with velocities ∼13,000 km s-1, possibly collimated outflows. Photometric and spectroscopic observations of the eruption provide strong evidence supporting a red giant donor. An apparently stochastic variability during the early supersoft X-ray phase was comparable in amplitude and duration to past eruptions, but the 2013 and 2015 eruptions show evidence of a brief flux dip during this phase. The multi-eruption Swift/XRT spectra show tentative evidence of high-ionization emission lines above a high-temperature continuum. Following Henze et al. (2015a), the updated recurrence period based on all known eruptions is Prec = 174 ± 10 days, and we expect the next eruption of M31N 2008-12a to occur around 2016 mid-September
ExoClock Project III: 450 new exoplanet ephemerides from ground and space observations
The ExoClock project has been created with the aim of increasing the
efficiency of the Ariel mission. It will achieve this by continuously
monitoring and updating the ephemerides of Ariel candidates over an extended
period, in order to produce a consistent catalogue of reliable and precise
ephemerides. This work presents a homogenous catalogue of updated ephemerides
for 450 planets, generated by the integration of 18000 data points from
multiple sources. These sources include observations from ground-based
telescopes (ExoClock network and ETD), mid-time values from the literature and
light-curves from space telescopes (Kepler/K2 and TESS). With all the above, we
manage to collect observations for half of the post-discovery years (median),
with data that have a median uncertainty less than one minute. In comparison
with literature, the ephemerides generated by the project are more precise and
less biased. More than 40\% of the initial literature ephemerides had to be
updated to reach the goals of the project, as they were either of low precision
or drifting. Moreover, the integrated approach of the project enables both the
monitoring of the majority of the Ariel candidates (95\%), and also the
identification of missing data. The dedicated ExoClock network effectively
supports this task by contributing additional observations when a gap in the
data is identified. These results highlight the need for continuous monitoring
to increase the observing coverage of the candidate planets. Finally, the
extended observing coverage of planets allows us to detect trends (TTVs -
Transit Timing Variations) for a sample of 19 planets. All products, data, and
codes used in this work are open and accessible to the wider scientific
community.Comment: Recommended for publication to ApJS (reviewer's comments
implemented). Main body: 13 pages, total: 77 pages, 7 figures, 7 tables. Data
available at http://doi.org/10.17605/OSF.IO/P298