New insights on the massive interacting binary UU Cassiopeiae

We present the results of our study of the close binary UU Cassiopeiae based on previously published multiwavelength photometric and spectroscopic data. Based on eclipse timings from the last 117 years, we find an improved orbital period of Po = 8.d519296(8). In addition, we find a long cycle of length T ∼ 270 d in the Ic-band data. There is no evidence for orbital period change over the last century, suggesting that the rate of mass loss from the system or mass exchange between the stars is small. Sporadic and rapid brightness drops of up to ΔV = 0.3 mag are detected throughout the orbital cycle, and infrared photometry clearly suggests the presence of circumstellar matter. We model the orbital light curve of 11 published datasets, fixing the mass ratio and cooler star temperature from previous spectroscopic work: q = 0.52 and Tc = 22 700 K. We find a system seen at an angle of 74° with a stellar separation of 52 R⊙, a temperature for the hotter star of Th = 30 200 K and, for the hotter and cooler stars, respectively, stellar masses of 17.4 and 9 M⊙, radii of 7.0 and 16.9 R⊙, and surface gravities log g = 3.98 and 2.94. We find an accretion disk surrounding the more massive star that has a radius of 21 R⊙ and a vertical thickness at its outer edge of 6.5 R⊙; the disk nearly occults the hotter star. Two active regions hotter than the surrounding disk are found, one located roughly in the expected position where the stream impacts the disk and the other on the opposite side of the disk. Changes are observed in parameters of the disk and spots in different datasets.

Thermal Experiments for Validation of 3-AMADEUS Cubesat

There has been an increasing interest in CubeSats missions due to its small size, low cost and flexibility to accommodate different payloads. It enables CubeSats to perform a range of various missions. One of the causes of failure in a satellite in space are the temperature peaks suffered during a full orbital cycle. Therefore, proper thermal control system design and test should be performed to guarantee the reliability of a spacecraft prior to launch.The present work aims to analyze the main heat transfer processes within a satellite to validate the 3-AMADEUS CubeSat and current methodologies used by CEiiA for nano and micro satellites. Hence, with the purpose of developing thermal models with higher reliability, an experiment was devised to be performed in a controlled environment. The experimental test consists in a study of the heat exchange between two aluminum plates through radiation, using infrared lamps as heat source. Three distance configuration and two lamp types are tested. This would emulate the heat transmission between different components within the satellite. The view factors are changed. In parallel, a finite element software (MSC Nastran) is used to carry out a numerical study of the same experiments. The temperature distribution results of both numerical and experimental solutions are then compared, and the results are discussed. Keywords: Radiation, View factors, Experimental

When the disc’s away, the stars will play: dynamical masses in the nova-like variable KR Aur with a pinch of accretion

ABSTRACT We obtained time-resolved optical photometry and spectroscopy of the nova-like variable KR Aurigae in the low state. The spectrum reveals a DAB white dwarf (WD) and a mid-M dwarf companion. Using the companion star’s i-band ellipsoidal modulation we refine the binary orbital period to be P = 3.906519 ± 0.000001 h. The light curve and the spectra show flaring activity due to episodic accretion. One of these events produced brightness oscillations at a period of 27.4 min, that we suggest to be related with the rotation period of a possibly magnetic WD at either 27.4 or 54.8 min. Spectral modelling provided a spectral type of M4–5 for the companion star and $T_{1}=27\, 148$ $\pm \, 496$ K, $\log \, g=8.90 \pm 0.07$, and $\log (\mathrm{He/H})= -0.79^{+0.07}_{-0.08}$ for the WD. By simultaneously fitting absorption- and emission-line radial velocity curves and the ellipsoidal light curve, we determined the stellar masses to be $M_1 = 0.94^{+0.15}_{-0.11}\, {\rm{M}_{\rm \odot}}$ and $M_2 = 0.37^{+0.07}_{-0.07}\,{\rm{M}_{\rm \odot}}$ for the WD and the M-dwarf companion, respectively, and an orbital inclination of $47^{+1^{\rm o}}_{-2^{\rm o}}$. Finally, we analyse time-resolved spectroscopy acquired when the system was at an i-band magnitude of 17.1, about 1.3 mag brighter than it was in the low state. In this intermediate state, the line profiles contain an emission S-wave delayed by ≃0.2 orbital cycle relative to the motion of the WD, similar to what is observed in SW Sextantis stars in the high state.

Onthe changes in the physical properties of the ionized region around the Weigelt structures in η Carinae over the 5.54-yr spectroscopic cycle

ABSTRACT We present HST/STIS observations and analysis of two prominent nebular structures around the central source of η Carinae, the knots C and D. The former is brighter than the latter for emission lines from intermediate- or high-ionization potential ions. The brightness of lines from intermediate- and high-ionization potential ions significantly decreases at phases around periastron. We do not see conspicuous changes in the brightness of lines from low-ionization potential (<13.6 eV) ions over the orbital period. Line ratios suggest that the total extinction towards the Weigelt structures is AV = 2.0. Weigelt C and D are characterized by an electron density of 106.9 cm−3 that does not significantly change throughout the orbital cycle. The electron temperature varies from 5500 (around periastron) to 7200 K (around apastron). The relative changes in the brightness of the He i lines are well reproduced by the variations in the electron temperature alone. We found that, at phases around periastron, the electron temperature seems to be higher for Weigelt C than that of D. The Weigelt structures are located close to the Homunculus equatorial plane, at a distance of about 1240 au from the central source. From the analysis of proper motion and age, the Weigelt complex can be associated with the equatorial structure called ‘Butterfly Nebula’ surrounding the central binary system.

CRTS J035010.7 + 323230, a new eclipsing polar in the cataclysmic variable period gap

ABSTRACT We report the discovery of a new eclipsing polar, CRTS J035010.7+323230 (hereafter CRTS J0350+3232). We identified this cataclysmic variable (CV) candidate as a possible polar from its multiyear Catalina Real-Time Transient Survey (CRTS) optical light curve. Photometric monitoring of 22 eclipses in 2015 and 2017 was performed with the 2.1-m Otto Struve Telescope at McDonald Observatory. We derive an unambiguous high-precision ephemeris. Strong evidence that CRTS J0350 + 3232 is a polar comes from optical spectroscopy obtained over a complete orbital cycle using the Apache Point Observatory 3.5-m telescope. High velocity Balmer and He ii λ4686Å emission-line equivalent width ratios, structures, and variations are typical of polars and are modulated at the same period, 2.37 h (142.3 min), as the eclipse to within uncertainties. The spectral energy distribution and luminosity is found to be comparable to that of AM Herculis. Pre-eclipse dips in the light curve show evidence for stream accretion. We derive the following tentative binary and stellar parameters assuming a helium composition white dwarf and a companion mass of 0.2 M⊙: inclination i = 74.68° ± 0.03°, semimajor axis a = 0.942 ± 0.024 R⊙, and masses and radii of the white dwarf and companion, respectively: M1 = 0.948 $^{+0.006}_{-0.012}$ M⊙, R1 = 0.00830 $^{+0.00012}_{-0.00006}$ R⊙, and R2 = 0.249 ± 0.002 R⊙. As a relatively bright (V ∼ 17–19 mag), eclipsing, period-gap polar, CRTS J0350 + 3232 will remain an important laboratory for the study of accretion and angular momentum evolution in polars.

V902 Monocerotis: A likely disc-accreting intermediate polar

Aims. We aim to confirm whether the eclipsing cataclysmic variable (CV) V902 Mon is an intermediate polar (IP), 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 2.2 m 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 confirmed V902 Mon as an IP based on detecting the spin period, which has a value of 2208 s, at multiple epochs. Spectroscopy of the donor star and Gaia parallax yield a distance of 3.5−0.9+1.3 kpc, suggesting an X-ray luminosity one or two orders of magnitude lower than the 1033 erg s−1 typical of previously known IPs. The X-ray to optical flux ratio is also very low. The inclination of the system is more than 79°, and is most likely a value of around 82°. We have refined the eclipse ephemeris, stable over 14 000 cycles. The Hα 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 XMM-Newton observation reveals a partially absorbed plasma model typical of magnetic CVs, that has a fluorescent iron line at 6.4 keV showing a large equivalent width of 1.4 keV. 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, although the radial velocity behaviour of the Hα 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.

Arabian Orbital Stratigraphy revisited – AROS 2015

ABSTRACT ‘Arabian Orbital Stratigraphy’ (AROS) is an R&D program aimed at dating Arabia’s transgressive-regressive (T-R) depositional sequences using the ‘Orbital Scale’ of Matthews and Al-Husseini (2010). The scale consists of time-rock units named ‘orbitons’, ‘dozons’ and ‘stratons’ that are tuned by orbital-forcing of glacio-eustasy. Orbitons have durations of 14.58 million years (Myr), and are bounded by regional sequence boundaries (SB, hiatus, unconformity, disconformity, lowstand deposits). Orbiton 1 was deposited between SB 1 at 16.166 million years before present (Ma) and SB 0 (zero) at 1.586 Ma. The interval between SB 0 and the Precambrian/Cambrian Boundary (PCB) consists of 37 orbitons; at least 30 can be identified in Arabia based on published data. SB 37 is predicted at 541.046 Ma (1.586 + 37 × 14.58 Myr), and correlates to the PCB, calibrated in Oman at 541.0 Ma. An orbiton consists of 36 stratons. Stratons are T-R sequences that tracked the long-eccentricity orbital cycle (E-cycle). The age of base Straton 1 is 0.371 Ma. Their durations can range between about 300 thousand years (Kyr) and 550 Kyr, but average 405 Kyr over several million years. The Phanerozoic Era consists of 1,336 stratons that are typically referred to as 4th-order sequences or cycle sets. Approximately 200 stratons are identified in this paper, and tentatively dated in the Orbital Scale. An orbiton also consists of three dozons, which are generally bounded by regional SBs. Dozons typically consist of 12 stratons (4.86 Myr). Examples of dozons are illustrated in this paper for the Permian–Triassic in Arabia. AROS predicts ages for Arabian and global T-R sequences that are deterministic, and they may be more accurate than those estimated by the Geological Time Scale GTS 2015. The paper proposes that the global T-R sequences should be recast in terms of stratons (E-cycles), and that stratons be used to calibrate biostratigraphy, magneto-stratigraphy and other global stratigraphic markers in future GTSs.

Transient Processes in a Binary System with a White Dwarf

Using the results of 3D gas dynamic numerical simulations we propose a mechanism that can explain the quiescent multihumped shape of light curves of WZ Sge short-period cataclysmic variable stars. Analysis of the obtained solutions shows that in the modeled system an accretion disk forms. In the outer regions of the disk four shock waves occur: two arms of the spiral tidal shock; “hot line”, a shock wave caused by the interaction of the circum-disk halo and the stream from the inner Lagrangian point; and the bow-shock forming due to the supersonic motion of the accretor and disk in the gas of the circum-binary envelope. In addition, in our solutions we observe a spiral precessional density wave in the disk. This wave propagates from inside the disk down to its outer regions and almost rests in the laboratory frame in one orbital period. As a results every next orbital period each shock wave passes through the outer part of the density wave. Supplying these shocks with extra-density the precessional density wave amplifies them, which leads to enhanced energy release at each shock and may be observed as a brightening (or hump) in the light curve. Since the velocity of the retrograde precession is a little lower that the orbital velocity of the system, the same shock wave at every next orbital cycle interacts with the density wave later than at the previous cycle. This causes the observed shift of the humps over binary phases. The number of the shock waves, interacting with the density wave determines the largest number of humps that may be observed in one orbital period of a WZ Sge type star.