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Register a new userFUSE Observational Evidence of the Boundary Layer of MY Lyrae in the High State
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We carry out a spectral analysis of the archival FUSE spectrum of the VY Scl nova-like cataclysmic variable MV Lyrae obtained in the high state. We find that standard disk models fail to fit the flux in the shorter wavelengths of FUSE (< 950$A). An improved fit is obtained by including a modeling of the boundary layer at the inner edge of the disk. The result of the modeling shows that in the high state the disk has a moderate accretion rate of about 2.E09 solar mass per year, a low inclination, a boundary layer with a temperature of around 100,000K, and size 0.20Rwd, and the white dwarf is possibly heated up to a temperature of 50,000K or higher.
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We observed persistent high-frequency oscillations of the boundary layer near an accreting, weakly-magnetized star in global 3D MHD simulations. The tilted dipole magnetic field is not strong enough to open a gap between the star and the disk. Instead, it forms a highly-wrapped azimuthal field near the surface of the star which slows down rotation of the disk matter, while a small tilt of the field excites oscillations of the boundary layer with a frequency below the Keplerian frequency. This mechanism may be responsible for the high-frequency oscillations in accreting neutron stars, white dwarfs and classical T Tauri stars.
A high percentage of the astrophysically important RR Lyrae stars show a periodic amplitude and/or phase modulation of their pulsation cycles. More than a century after its discovery, this Blazhko effect still lacks acceptable theoretical understanding. In one of the plausible models for explaining the phenomenon, the modulation is caused by the effects of a magnetic field. So far, the available observational data have not allowed us to either support nor rule out the presence of a magnetic field in RR Lyrae stars. We intend to determine whether RR Lyrae stars are generally characterized by the presence of a magnetic field organized on a large scale. With the help of the FORS1 instrument at the ESO VLT we performed a spectropolarimetric survey of 17 relatively bright southern RR Lyrae stars, both Blazhko stars and non-modulated stars, and determined their mean longitudinal magnetic field with a typical error bar < 30 G. All our measurements of the mean longitudinal magnetic field resulted in null detections within 3 sigma. From our data we can set an upper limit for the strength of the dipole component of the magnetic fields of RR Lyrae stars to ~ 130 G. Because of the limitations intrinsic to the diagnostic technique, we cannot exclude the presence of higher order multipolar components. The outcome of this survey clarifies that the Blazhko modulation in the pulsation of RR Lyrae stars is not correlated with the presence of a strong, quasi-dipolar magnetic field.
We present spectral properties of an accretion disk model, in which a Keplerian accretion disk is flanked by a sub-Keplerian halo component terminating at a standing shock. The post-shock region (which may be considered to be the boundary layer of a black hole) reprocesses the soft photons emitted from the Keplerian accretion disk. We show that switching of states (from hard to soft and vice versa) could be accomplished by a change in the accretion rate of the Keplerian disk component. Our consideration, for the first time, resolves a long-standing problem of identifying the illusive `Compton cloud responsible for the switching of states.
We present a kinematical study of 314 RR~Lyrae stars in the solar neighbourhood using the publicly available photometric, spectroscopic, and {it Gaia} DR2 astrometric data to explore their distribution in the Milky Way. We report an overdensity of 22 RR~Lyrae stars in the solar neighbourhood at a pericenter distance of between 5--9,kpc from the Galactic center. Their orbital parameters and their chemistry indicate that these 22 variables share the kinematics and the [Fe/H] values of the Galactic disc, with an average metallicity and tangential velocity of [Fe/H]=$-0.60$,dex and $v_{theta} = 241$,km,s$^{-1}$, respectively. From the distribution of the Galactocentric spherical velocity components, we find that these 22 disc-like RR~Lyrae variables are not consistent with the {it Gaia} Sausage ({it Gaia}-Enceladus), unlike almost half of the local RR~Lyrae stars. Chemical information from the literature shows that the majority of the selected pericenter peak RR~Lyrae variables are $alpha$-poor, a property shared by typically much younger stars in the thin disc. Using the available photometry we rule out a possible misclassification with the known classical and anomalous Cepheids. The similar kinematic, chemical, and pulsation properties of these disc RR~Lyrae stars suggest they share a common origin. In contrast, we find the RR~Lyrae stars associated with the {it Gaia}-Enceladus based on their kinematics and chemical composition show a considerable metallicity spread in the old population ($sim$~1,dex).
We present spectroscopic observations of the massive multiple system HD,167971, located in the open cluster NGC,6604. The brighter component of the triple system is the overcontact eclipsing binary MY,Ser with an orbital period of 3.32,days. The radial velocities and the previously published UBV data obtained by citet{may10} and the UBVRI light curves by citet{dav88} are analysed for the physical properties of the components. We determine the following absolute parameters: for the primary star M$_p$=32.23$pm$0.54 M$_{odot}$, R$_p$=14.23$pm$0.75 R$_{odot}$; and for the secondary star M$_s$=30.59$pm$0.53 M$_{odot}$, R$_s$=13.89$pm$0.75 R$_{odot}$. Photoelectric times of minimum light are analyzed under the consideration of the light-time orbit. The center-of-mass of the eclipsing binary is orbiting around the common center-of-gravity of the triple system with a period of 21.2$pm$0.7,yr and with a projected semi-major axis of 5.5$pm$0.7,AU. The mass function for the third star was calculated as 0.370$pm$0.036 M$_{odot}$. The light contributions of the third star to the triple system in the UBV pass-bands were derived and the intrinsic magnitudes and colors were calculated individually for the three stars. The components of the eclipsing pair were classified as O7.5 {sc iii} and O9.5 {sc iii}. The intrinsic color indices for the third star yield a spectral type of (O9.5-B0) {sc iii-i}. {bf This classification leads to constrain the inclination of the third-body orbit, which should be about 30$^{o}$, and therefore its mass should be about 29 M$_{odot}$. MY,Ser is one of the rare massive O-type triple system at a distance of 1.65$pm$0.13,kpc, the same as for the NGC,6604 embedded in the Ser,OB2 association.}
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