scholarly journals Polarized Emission and the Discovery of New Magnetic CVs

2004 ◽  
Vol 190 ◽  
pp. 22-32
Author(s):  
Gary D. Schmidt
Keyword(s):  
Gravitational Radiation ◽  
Accretion Rate ◽  
Cataclysmic Variables ◽  
Selection Effects ◽  
Optical Polarization ◽  
Angular Momentum Loss ◽  
Cyclotron Emission ◽  
Magnetic Cataclysmic Variables ◽  
Current Sample ◽  
Cool White Dwarfs

AbstractRecent quasar surveys have identified several new magnetic cataclysmic variables accreting at remarkably low rates, ~10−13M⊙ yr−1. The new discoveries raise questions regarding selection effects that may influence the current sample and the traditional evolutionary conclusions that have been drawn. This paper reviews the techniques that have been used to identify polars, including a summary of the optical polarization as a function of accretion rate and magnetic field strength. The new, low-ṁ systems accrete without a shock and cooling is dominated by optical cyclotron emission in very well-defined harmonics. These binaries, which have been found to accrete at far below the rate corresponding to angular momentum loss by gravitational radiation, also appear to contain unusually cool white dwarfs, suggesting that they are either at an advanced age or in unusual evolutionary states.

scholarly journals The Characteristics of Magnetic CVs in the Period Gap

2004 ◽  
Vol 190 ◽  
pp. 15-21 ◽  
Author(s):  
Gaghik Tovmassian ◽  
Sergey Zharikov ◽  
Ronald Mennickent ◽  
Jochen Greiner
Keyword(s):  
Mass Transfer ◽  
Orbital Period ◽  
Accretion Rate ◽  
Cataclysmic Variables ◽  
Magnetic Systems ◽  
Transfer Rates ◽  
Significant Difference ◽  
Magnetic Cataclysmic Variables

AbstractWe have observed several magnetic cataclysmic variables located in the range between 2 and 3 hours, known as the period gap. This work was prompted by the recent discovery of RXJ1554.2+2721. It has 2.54 hours orbital period and shows almost pure cyclotron continuum in a low luminosity state, similar to HS1023+3900, HS0922+1333 and RBS206. These are low accretion rate polars (LARPs) known to have mass transfer rates of order of a few 10-13M⊙/year. The aim of the study was to find out, if magnetic systems filling the period gap are in any way different from their counterparts outside that range of periods. The only significant difference we encounter is a much higher number of asynchronous magnetic systems towards longer periods than below the gap.

scholarly journals Physical Interpretation of Dwarf Nova Primary Effective Temperatures

2004 ◽  
Vol 194 ◽  
pp. 192-193
Author(s):  
Dean M. Townsley ◽  
Lars Bildsten
Keyword(s):  
Gravitational Radiation ◽  
Accretion Rate ◽  
Thermal State ◽  
Cataclysmic Variables ◽  
Theoretical Work ◽  
Dwarf Novae ◽  
Radiation Losses ◽  
Accretion Rates ◽  
The Masses ◽  
The Impact

AbstractWe have undertaken a theoretical study of the impact of the accumulating envelopes on the thermal state of the underlying white dwarf (WD). This has allowed us to find the equilibrium WD core temperatures, the classical nova ignition masses and the thermal luminosities for WDs accreting at rates of 10–11 – 10–8M⊙ yr–1. These accretion rates are most, appropriate to WDs in cataclysmic variables (CVs) of (Porb ≲ 7 hr), many of which accrete sporadically as Dwarf Novae. Over twenty Dwarf Novae have been observed in quiescence, when the accretion rate is low and the WD photosphere is detected and Teff measured. Comparing our theoretical work to these observations allows us to constrain the WD mass and the time averaged accretion rate, ⟨Ṁ⟩. If ⟨Ṁ⟩ is that given by gravitational radiation losses alone, then the WD masses are > 0.8 M⊙. An alternative conclusion is that the masses are closer to 0.6M⊙ and ⟨Ṁ⟩ is 3-4 times larger than that expected from gravitational radiation losses.

scholarly journals 2PBC J0658.0–1746: a hard X-ray eclipsing polar in the orbital period gap

2019 ◽  
Vol 489 (1) ◽  
pp. 1044-1053 ◽  
Author(s):  
F Bernardini ◽  
D de Martino ◽  
K Mukai ◽  
M Falanga ◽  
N Masetti
Keyword(s):  
Orbital Period ◽  
Accretion Rate ◽  
Timing Analysis ◽  
Spectral Energy Distribution ◽  
Cataclysmic Variables ◽  
Spectral Energy ◽  
X Ray ◽  
Mass Accretion Rate ◽  
Cyclotron Emission ◽  
Long Time

Abstract The hard X-ray source 2PBC J0658.0–1746 was proposed as an eclipsing magnetic cataclysmic variable of the polar type, based on optical follow-ups. We present the first spectral and timing analysis at X-ray energies with XMM–Newton, complemented with archival X-ray, optical, infrared (IR) photometry, and spectroscopy. The X-ray emission shows bright and faint phases and total eclipses recurring every 2.38 h, consistent with optical properties. This firmly identifies 2PBC J0658.0–1746 as an eclipsing polar, the second hard X-ray selected in the orbital period gap. The X-ray orbital modulation changes from cycle-to-cycle and the X-ray flux is strongly variable over the years, implying a non-stationary mass accretion rate both on short and long time-scales. The X-ray eclipses allow to refine the orbital ephemeris with period 0.09913398(4) d, and to constrain the binary inclination $79^{\circ}\lesssim i \lesssim 90^{\circ}$ and the mass ratio 0.18$\lt M_2/M_{\mathrm{ WD}}\lt $0.40. A companion mass M$_{2}=0.2-0.25\rm \, M_{\odot }$ with a radius R$_{2}=0.24-0.26\rm \, R_{\odot }$ and spectral type ∼M4, at D$=209^{+3}_{-2}\rm \, pc$, is derived. A lower limit to the white dwarf mass of $\sim 0.6\, \rm \, M_{\odot }$ is obtained from the X-ray spectrum. An upper limit to the magnetic colatitude, $\beta \lesssim 50^{\circ}$, and a shift in azimuth, $\psi \sim 14^{\circ}$, of the main accreting pole are also estimated. The optical/IR spectral energy distribution shows large excess in the mid-IR due to lower harmonics of cyclotron emission. A high-state mass accretion rate $\rm \, \sim 0.4-1\times 10^{-10}\, M_{\odot }\, yr^{-1}$, lower than that of cataclysmic variables above the gap and close to that of systems below it, is estimated. With 2PBC J0658.0–1746, the number of hard X-ray-selected polars increases to 13 members, suggesting that they are not as rare as previously believed.

scholarly journals Idling magnetic white dwarf in the synchronizing polar BY Cam. The Noah-2 project

Open Physics ◽  
2008 ◽  
Vol 6 (3) ◽  
Author(s):  
Ivan Andronov ◽  
Kirill Antoniuk ◽  
Vitalii Breus ◽  
Lidia Chinarova ◽  
Wonyong Han ◽  
...  
Keyword(s):  
Limit Of Detection ◽  
Spectral Energy Distribution ◽  
Cataclysmic Variables ◽  
Principal Component ◽  
Wavelength Dependence ◽  
Mean Value ◽  
Spectral Energy ◽  
Nearby Star ◽  
Cyclotron Emission ◽  
Magnetic Cataclysmic Variables

AbstractA multi-color study of the variability of the magnetic cataclysmic variable BY Cam is presented. The observations were obtained at the Korean 1.8 m and Ukrainian 2.6 m, 1.2 m and 38 cm telescopes in 2003–2005, 56 observational runs cover 189 hours. The variations of the mean brightness in different colors are correlated with a slope dR/dV = 1:29(4), where the number in brackets denotes the error estimates in the last digits. For individual runs, this slope is much smaller ranging from 0.98(3) to 1.24(3), with a mean value of 1.11(1). Near the maximum, the slope becomes smaller for some nights, indicating more “blue” spectral energy distribution, whereas the night-to-night variability has an “infrared” character. For the simultaneous UBVRI photometry, the slopes increase with wavelength from dU/dR = 0:23(1) to dI/dR = 1:18(1). Such wavelength dependence is the opposite of that observed in non-magnetic cataclysmic variables, in agreement with the model of cyclotron emission. The principal component analysis shows two components of variablitity with different spectral energy distributions (with a third at the limit of detection), which possibly correspond to different regions of emission. The highest peak in the scalegram analysis corresponds to the 200 min spin variability, its quarter and to the 30 min and 8 min QPOs. The amplitudes of these components are dependent on wavelength and luminosity state. The light curves were fitted by a statistically optimal trigonometrical polynomial (up to 4th order) to take into account a 4-hump structure. The dependences of these parameters on the phase of the beat period and on mean brightness are discussed. The amplitude of spin variations increases with an increasing wavelength and with decreasing brightness. The linear ephemeris based on 46 mean minima for 2003–2005 is HJD 2453213:010(3) + 0:137123(3)E: The extensive tables of the original observations and of results of analysis are published in an electronic form. The nearby star GSC 4081–1562 was found to be an eclipsing red variable.

scholarly journals ROSAT observations of non-magnetic CVs

1996 ◽  
Vol 158 ◽  
pp. 273-276 ◽  
Author(s):  
A. van Teeseling ◽  
F. Verbunt ◽  
K. Beuermann
Keyword(s):  
Boundary Layer ◽  
Accretion Disk ◽  
White Dwarf ◽  
Accretion Rate ◽  
Cataclysmic Variables ◽  
Rotation Velocity ◽  
X Rays ◽  
X Ray ◽  
Orbital Modulation ◽  
Magnetic Cataclysmic Variables

In non-magnetic cataclysmic variables the accreted matter forms an accretion disk around the white dwarf. In the boundary layer between the white dwarf and the accretion disk the accreted matter decelerates from Keplerian velocities to the rotation velocity of the white dwarf. If the accretion rate is high the boundary layer would be optically thick and cool (T ~ 105K), and if the accretion rate is low the boundary layer would be optically thin and hot (T ~ 108K) (Pringle & Savonije 1979).There are several observational problems with this simple picture: a soft X-ray component could only be detected so far in 5 dwarf novae in outburst and not in any nova-like variable. Also in high-accretion-rate systems there is a hot optically thin X-ray source, which has, however, an X-ray luminosity which is much less than the UV luminosity of the system (van Teeseling & Verbunt 1994). Finally, there is evidence for orbital modulation in the X-rays from some systems (e.g. van Teeseling et al. 1995).

scholarly journals From Common Envelope to Pre-Cataclysmic Variables: An Observational Test of Common Envelope Evolution

1996 ◽  
Vol 158 ◽  
pp. 453-456
Author(s):  
M. J. Sarna
Keyword(s):  
Gravitational Radiation ◽  
Planetary Nebula ◽  
Cataclysmic Variables ◽  
Orbital Energy ◽  
Dwarf Star ◽  
Common Envelope ◽  
Evolutionary Scenario ◽  
Angular Momentum Loss ◽  
Red Giant ◽  
Detached Binaries

The generally accepted evolutionary scenario for cataclysmic variables (CVs) is common envelope (CE) evolution (Iben & Livio 1993) proposed by Paczyñski (1976). The secondary spirals towards the giant’s compact core converting orbital energy into kinetic energy of the giant’s envelope and the envelope is ejected. The dynamics of the red dwarf and red giant envelope interaction have been studied by several groups (Livio & Soker 1988; Taam & Bodenheimer 1991). After the ejection of the red giant envelope the post common envelope detached binaries (PCEBs) are formed. These can be divided into three groups:• Hot subdwarf with a red dwarf star inside a planetary nebula.• Hot subdwarf with a red dwarf star without a planetary nebula.• Hot white dwarf with a red dwarf star without a planetary nebula. Next, due to angular momentum loss by magnetic braking and/or gravitational radiation, the red dwarf component fills its Roche lobe and a cataclysmic variable is formed.

scholarly journals Simulating AXAF Grating Spectra of Accreting White Dwarfs

1998 ◽  
Vol 15 (3) ◽  
pp. 339-347 ◽  
Author(s):  
Allyn F. Tennant ◽  
Kinwah Wu ◽  
Stephen L. O'Dell ◽  
Martin C. Weisskopf
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Accretion Rate ◽  
Cataclysmic Variables ◽  
High Energy ◽  
High Spectral Resolution ◽  
X Ray ◽  
Transmission Grating ◽  
Magnetic Cataclysmic Variables ◽  
Very High

AbstractWe present simulated AXAF spectra of accreting white dwarfs, using parameters appropriate for magnetic cataclysmic variables. The very high spectral resolution that can be obtained with the High-Energy Transmission Grating of AXAF can resolve the keV X-ray emission lines that characterise the temperature, density and velocity profiles of the shock-heated emission regions of these systems. These simulations demonstrate that actual spectra will allow us to place constraints on the white-dwarf mass and the accretion rate of the systems. The high-resolution spectra also allow the measurement of the velocity of the accretion flow in regions close to the white-dwarf surface.

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