78 research outputs found
Spectral observations of X Persei: Connection between H-alpha and X-ray emission
We present spectroscopic observations of the Be/X-ray binary X Per obtained
during the period 1999 - 2018. Using new and published data, we found that
during "disc-rise" the expansion velocity of the circumstellar disc is 0.4 -
0.7 km/s. Our results suggest that the disc radius in recent decades show
evidence of resonant truncation of the disc by resonances 10:1, 3:1, and 2:1,
while the maximum disc size is larger than the Roche lobe of the primary and
smaller than the closest approach of the neutron star. We find correlation
between equivalent width of H-alpha emission line () and the X-ray
flux, which is visible when . The
correlation is probably due to wind Roche lobe overflow.Comment: Accepted for publication in Astronomy & Astrophysic
Buckling behavior of multilayer cylindrical shells composed of functionally graded nanocomposite layers under lateral pressure in thermal environments
In this study, the stability behavior of multilayer cylindrical shells made of functionally graded nanocomposite layers (FG-NCLs) subjected to the lateral pressure in thermal environments is investigated. It is postulated that nanocomposite layers forming layered cylindrical shells are made of single-walled carbon nanotube (SWCNT)-reinforced polymers that have four types of profiles based on the uniform and linear distributions of mechanical properties. The material properties of SWCNTs are assumed to be dependent on location as well as temperature and are obtained from molecular dynamics simulations. The governing equations are derived as partial differential equations within shear deformation theory (SDT) and solved in a closed form, using the Galerkin procedure, to determine the lateral critical pressure (LCP) in thermal environments. The numerical representations relate to the buckling behavior of multilayer cylindrical shells made of functionally graded nanocomposite layers under the uniform lateral pressure for different CNT patterns and temperatures within SDT and Kirchhoff-Love theory (KLT)
UBVRI observations of the flickering of RS Ophiuchi at Quiescence
We report observations of the flickering variability of the recurrent nova RS
Oph at quiescence on the basis of simultaneous observations in 5 bands (UBVRI).
RS Oph has flickering source with (U-B)_0=-0.62 \pm 0.07, (B-V)_0=0.15 \pm
0.10, (V-R)_0=0.25 \pm 0.05. We find for the flickering source a temperature
T_fl = 9500 \pm 500 K, and luminosity L_fl = 50 - 150 L_sun (using a distance
of d=1.6kpc). We also find that on a (U-B) vs (B-V) diagram the flickering of
the symbiotic stars differs from that of the cataclysmic variables. The
possible source of the flickering is discussed. The data are available upon
request from the authors and on the web
www.astro.bas.bg/~rz/RSOph.UBVRI.2010.MNRAS.tar.gz.Comment: 7 pages, MNRAS (accepted
Disks Surviving the Radiation Pressure of Radio Pulsars
The radiation pressure of a radio pulsar does not necessarily disrupt a
surrounding disk. The position of the inner radius of a thin disk around a
neutron star can be estimated by comparing the electromagnetic energy density
generated by the neutron star with the kinetic energy density of the disk.
Inside the light cylinder, the near zone electromagnetic field is essentially
the dipole magnetic field, and the inner radius is the conventional Alfven
radius. Far outside the light cylinder, in the radiation zone, and the
electromagnetic energy density is where is the
Poynting vector. Shvartsman (1970) argued that a stable equilibrium can not be
found in the radiative zone because the electromagnetic energy density
dominates over the kinetic energy density, with the relative strength of the
electromagnetic stresses increasing with radius. In order to check whether this
is true also near the light cylinder, we employ global electromagnetic field
solutions for rotating oblique magnetic dipoles (Deutsch 1955). Near the light
cylinder the electromagnetic energy density increases steeply enough with
decreasing to balance the kinetic energy density at a stable equilibrium.
The transition from the near zone to the radiation zone is broad. The radiation
pressure of the pulsar can not disrupt the disk for values of the inner radius
up to about twice the light cylinder radius if the rotation axis and the
magnetic axis are orthogonal. This allowed range beyond the light cylinder
extends much further for small inclination angles. We discuss implications of
this result for accretion driven millisecond pulsars and young neutron stars
with fallback disks.Comment: Accepted by Astrophysical Journal, final version with a minor
correctio
Searching for the Physical Drivers of Eigenvector-1: From Quasars to Nano-Quasars
We point out an analogy between two accreting white dwarfs with jets (CH Cyg
and MWC 560) and powerful quasars. In spite of the enormous difference in the
mass of the central object (a factor about 10^7), the emission lines are
strikingly similar to those of I Zw1 (the prototype "Narrow Line Seyfert 1"
nucleus whose spectrum is widely used as an FeII template for almost all
quasars). The spectral similarity give us the unique possibility to consider
the optical Eigenvector-1 diagram using objects less massive by a factor of
millions. Our results reinforce the interpretation of the "Eigenvector-1
correlations" found for low redshift quasars as driven mainly by the source
luminosity to central compact object mass ratio(L/M). The accreting white
dwarfs CH Cyg and MWC 560, their jets and emission lines, may well represent
the low energy, non relativistic end of the accretion phenomena, which
encompass the most powerful quasars and the microquasars. The remarkable
similarities suggest that they may be legitimately considered "nano-quasars".Comment: 5 pages, 2 figures, accepted by the Astrophysical Journal (Letters
Possible changes of state and relevant timescales for a neutron star in LS I +61{\deg}303
The properties of the short, energetic bursts recently observed from the
gamma-ray binary LS I +61{\deg}303, are typical of those showed by high
magnetic field neutron stars, and thus provide a strong indication in favor of
a neutron star being the compact object in the system. Here, we discuss the
transitions among the states accessible to a neutron star in a system like LS I
+61{\deg}303, such as the ejector, propeller and accretor phases, depending on
the NS spin period, magnetic field and rate of mass captured. We show how the
observed bolometric luminosity (>= few x 1E35 erg/s), and its broad-band
spectral distribution, indicate that the compact object is most probably close
to the transition between working as an ejector all along its orbit, and being
powered by the propeller effect when it is close to the orbit periastron, in a
so-called flip-flop state. By assessing the torques acting onto the compact
object in the various states, we follow the spin evolution of the system,
evaluating the time spent by the system in each of them. Even taking into
account the constraint set by the observed gamma-ray luminosity, we found that
the total age of the system is compatible with being ~5-10 kyr, comparable to
the typical spin-down ages of high-field neutron stars. The results obtained
are discussed in the context of the various evolutionary stages expected for a
neutron star with a high mass companion.Comment: 12 pages, 6 figures. Accepted for publication in Ap
Average UV Quasar Spectra in the Context of Eigenvector 1: A Baldwin Effect Governed by Eddington Ratio?
We present composite UV spectra for low redshift Type 1 AGN binned to exploit
the information content of the Eigenvector 1 (E1) parameter space. Composite
spectra allow a decomposition of the CIV1549 line profile - one of the
strongest high-ionization lines. The simplest CIV decomposition into narrow
(NLR), broad (BLR) and very broad (VBLR) components suggests that different
components have an analog in Hb with two major exceptions. VBLR emission is
seen only in population B (FWHM(Hb)>4000 km/s) sources. A blue
shifted/asymmetric BLR component is seen only in pop. A (FWHM(Hb)<4000 km/s)
HIL such as CIV. The blueshifted component is thought to arise in a wind or
outflow. Our analysis suggests that such a wind can only be produced in pop. A
(almost all radio-quiet) sources where the accretion rate is relatively high.
Comparison between broad UV lines in radio-loud (RL) and radio-quiet (RQ)
sources shows few significant differences. Clear evidence is found for a narrow
CIV component in most radio-loud sources. We find also some indirect
indications that the black hole (BH) spin, rather than BH mass or accretion
rate is a key trigger in determining whether an object will be RL or RQ. We
find a ten-fold decrease in EW CIV with Eddington ratio (decreasing from ~1 to
\~0.01) while NV shows no change. These trends suggest a luminosity-independent
"Baldwin effect" where the physical driver may be the Eddington ratio.Comment: 39 pages, 6 figures. To appear in Ap
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