Roche Lobe Size Research Articles

Size of the accretion disc in the recurrent nova T CrB

AbstractWe present high‐resolution (0.06 Å px) spectroscopic observations of the recurrent nova T Coronae Borealis obtained during the last 1.5 years (September 2022–January 2024), with the 2.0‐m RCC telescope of the Rozhen National Astronomical Observatory, Bulgaria. Double‐peaked emission is visible in the line after the end of the superactive state. We subtract the red giant contribution and measure the distance between the peaks () of the line. For the period July 2023–January 2024, we find that is in range km s. Assuming that the emission is from the accretion disc around the white dwarf, we find average radius of the accretion disc R, which is approximately equal to the Roche lobe size of the white dwarf. Our results indicate that tidal torque plays an important role but that the disc can extend up to the Roche lobe of the accreting star.

Thick accretion disk configurations around a compact object in the brane-world scenario

We have studied the equipotential surfaces of a thick accretion disk around a Casadio–Fabbri–Mazzacurati compact object in the brane-world scenario, which possesses a mass parameter together with a parameterized post-Newtonian (PPN) parameter. With the increase in the PPN parameter, the size of the thick accretion disk decreases, but the corresponding Roche lobe size increases. Thus, the larger PPN parameter yields the larger region of existing bound disk structures, where the fluid is not accreted into the central wormhole. Moreover, with the increase in the PPN parameter, the position of the Roche lobe gradually moves away from the central compact object, and the thickness of the region enclosed by the Roche lobe decreases near the compact object but increases in the region far from the compact object. Our results also show that the pressure gradient in the disk decreases with the PPN parameter. These effects of the PPN parameter on the thick accretion disk could help one to further understand compact objects in the brane-world scenario.

Evolutionary increase of the orbital separation and change of the Roche lobe size in SS433

We present results of long-term photometric monitoring of SS433 which proves a secular evolutionary increase of the orbital period of SS433 at a rate of (1.14±0.25)×10−7 s s−1. Using a physical model of non-conservative mass transfer in SS433 through a supercritical accretion disc around the compact companion, we reliably confirm that the binary mass ratio in SS433, q=MX/MV is ≳0.8. For an optical star mass MV∼10M⊙ the compact object in SS433 is a black hole with mass MBH≳8M⊙. We discuss evolutionary implications of the found orbital period increase in SS433 – a secular change in the orbital separation and a size of the Roche lobe of the optical star. We show that for the mass-loss rate ṀV∼10−4−3×10−5M⊙ per year and an optical star mass MV∼10−15M⊙ the found orbital period increase implies the corresponding orbital separation increase while the Roche lobe size can shrink or expand around a mean constant value depending on the optical star mass-loss rate which may be modulated with the precessional period.

The Hubble Space Telescope PanCET Program: Exospheric Mg ii and Fe ii in the Near-ultraviolet Transmission Spectrum of WASP-121b Using Jitter Decorrelation

Abstract We present Hubble Space Telescope (HST) near-ultraviolet (NUV) transits of the hot Jupiter WASP-121b, acquired as part of the PanCET program. Time-series spectra during two transit events were used to measure the transmission spectra between 2280 and 3070 Å at a resolution of 30,000. Using HST data from 61 Space Telescope Imaging Spectrograph visits, we show that data from HST’s Pointing Control System can be used to decorrelate the instrument systematic errors (jitter decorrelation), which we used to fit the WASP-121b light curves. The NUV spectra show very strong absorption features, with the NUV white light curve found to be larger than the average optical and near-infrared value at 6σ confidence. We identify and spectrally resolve absorption from the Mg ii doublet in the planetary exosphere at a 5.9σ confidence level. The Mg ii doublet is observed to reach altitudes of R pl/R star = 0.284 ± 0.037 for the 2796 Å line and 0.242 ± 0.0431 for the 2804 Å line, which exceeds the Roche lobe size as viewed in transit geometry (R eqRL/R star = 0.158). We also detect and resolve strong features of the Fe ii UV1 and UV2 multiplets, and observe the lines reaching altitudes of R pl/R star ≈ 0.3. At these high altitudes, the atmospheric Mg ii and Fe ii gas is not gravitationally bound to the planet, and these ionized species may be hydrodynamically escaping or could be magnetically confined. Refractory Mg and Fe atoms at high altitudes also indicate that these species are not trapped into condensate clouds at depth, which places constraints on the deep interior temperature.

PROBING THE MASSES AND RADII OF DONOR STARS IN ECLIPSING X-RAY BINARIES WITH THESWIFTBURST ALERT TELESCOPE

Physical parameters of both the mass donor and compact object can be constrained in X-ray binaries with well-defined eclipses, as our survey of wind-fed supergiant X-ray binaries (SGXBs) IGR J16393-4643, IGR J16418-4532, IGR J16479-4514, IGR J18027-2016 and XTE J1855-026 reveals. Using the orbital period and Kepler's third law, we express the eclipse half-angle in terms of radius, inclination angle and the sum of the masses. Pulse-timing and radial velocity curves can give masses of both the donor and compact object as in the case of the "double-lined" binaries IGR J18027-2016 and XTE J1855-026. The eclipse half angles are 15 (+3,-2), 31.7 (+0.7,-0.8), 32 +/- 2, 34 +/- 2 and 33.6 +/- 0.7 degrees for IGR J16393-4643, IGR J16418-4532, IGR J16479-4514, IGR J18027-2016 and XTE 1855-026, respectively. In wind-fed systems, the primary not exceeding the Roche-lobe size provides an upper limit on system parameters. In IGR J16393-4643, spectral types of B0 V or B0-5 III are found to be consistent with the eclipse duration and Roche-lobe, but the previously proposed donor stars in IGR J16418-4532 and IGR J16479-4514 were found to be inconsistent with the Roche-lobe size. Stars with spectral types O7.5 I and earlier are possible. For IGR J18027-2016, the mass and radius of the donor star lie between 18.6--19.4 $M_\odot$ and 17.4--19.5 $R_\odot$. We constrain the neutron star mass between 1.37--1.43 $M_\odot$. We find the mass and radius of the donor star in XTE J1855-026 to lie between 19.6--20.2 $M_\odot$ and 21.5--23.0 $R_\odot$. The neutron star mass was constrained to 1.77--1.82 $M_\odot$. Eclipse profiles are asymmetric in IGR J18027-2016 and XTE J1855-026, which we attribute to accretion wakes.

LONG-TERM EVOLUTION OF DOUBLE WHITE DWARF BINARIES ACCRETING THROUGH DIRECT IMPACT

We calculate the long-term evolution of angular momentum in double white dwarf binaries undergoing direct impact accretion over a broad range of parameter space. We allow the rotation rate of both components to vary, and account for the exchange of angular momentum between the spins of the white dwarfs and the orbit, while conserving the total angular momentum. We include gravitational, tidal, and mass transfer effects in the orbital evolution, and allow the Roche radius of the donor star to vary with both the stellar mass and the rotation rate. We examine the long-term stability of these systems, focusing in particular on those systems that may be progenitors of AM CVn or Type Ia Supernovae. We find that our analysis yields an increase in the predicted number of stable systems compared to that in previous studies. Additionally, we find that by properly accounting for the effects of asynchronism between the donor and the orbit on the Roche-lobe size, we eliminate oscillations in the orbital parameters which are found in previous studies. Removing these oscillations can reduce the peak mass transfer rate in some systems, keeping them from entering an unstable mass transfer phase.

Hαobservations of theγ-ray-emitting Be/X-ray binary LSI+61°303: orbital modulation, disk truncation, and long-term variability

We report 138 spectral observations of the H-alpha emission line of the radio- and gamma-ray-emitting Be/X-ray binary LSI+61303 obtained during the period of September 1998 -- January 2013. From measuring various H-alpha parameters, we found that the orbital modulation of the H-alpha is best visible in the equivalent width ratio EW(B)/EW(R), the equivalent width of the blue hump, and in the radial velocity of the central dip. The periodogram analysis confirmed that the H-alpha emission is modulated with the orbital and superorbital periods. For the past 20 years the radius of the circumstellar disk is similar to the Roche lobe size at the periastron. It is probably truncated by a 6:1 resonance. The orbital maximum of the equivalent width of H-alpha emission peaks after the periastron and coincides on average with the X-ray and gamma-ray maxima. All the spectra are available upon request from the authors and through the CDS.

PSR J1723–2837: AN ECLIPSING BINARY RADIO MILLISECOND PULSAR

We present a study of PSR J1723-2837, an eclipsing, 1.86 ms millisecond binary radio pulsar discovered in the Parkes Multibeam survey. Radio timing indicates that the pulsar has a circular orbit with a 15 hr orbital period, a low-mass companion, and a measurable orbital period derivative. The eclipse fraction of ~15% during the pulsar's orbit is twice the Roche lobe size inferred for the companion. The timing behavior is significantly affected by unmodeled systematics of astrophysical origin, and higher-order orbital period derivatives are needed in the timing solution to account for these variations. We have identified the pulsar's (non-degenerate) companion using archival ultraviolet, optical, and infrared survey data and new optical photometry. Doppler shifts from optical spectroscopy confirm the star's association with the pulsar and indicate a pulsar-to-companion mass ratio of 3.3 +/- 0.5, corresponding to a companion mass range of 0.4 to 0.7 Msun and an orbital inclination angle range of between 30 and 41 degrees, assuming a pulsar mass range of 1.4-2.0 Msun. Spectroscopy indicates a spectral type of G for the companion and an inferred Roche-lobe-filling distance that is consistent with the distance estimated from radio dispersion. The features of PSR J1723-2837 indicate that it is likely a "redback" system. Unlike the five other Galactic redbacks discovered to date, PSR J1723-2837 has not been detected as a gamma-ray source with Fermi. This may be due to an intrinsic spin-down luminosity that is much smaller than the measured value if the unmeasured contribution from proper motion is large.

Diagnostics of SS433 with the RXTE

We present our analysis of the extensive monitoring of SS433 by the RXTE observatory collected over the period 1996–2005. The difference between energy spectra taken at different precessional and orbital phases shows the presence of strong photoabsorption ( cm-2) near the optical star, probably due to its powerful, dense wind. Therefore the size of the secondary deduced from analysis of X-ray orbital eclipses might be significantly larger than its Roche lobe size, which must be taken into account when evaluating the mass ratio from analysis of X-ray eclipses. Assuming that a precessing accretion disk is geometrically thick, we recover the temperature profile in the X-ray emitting jet that best fits the observed precessional variations in the X-ray emission temperature. The hottest visible part of the X-ray jet is located at a distance of , or ~ cm from the central compact object, and has a temperature of about keV. We discovered appreciable orbital X-ray eclipses at the “crossover” precessional phases (jets are in the plane of the sky, disk is edge-on), which under model assumptions put a lower limit on the size of the optical component and an upper limit on a mass ratio of binary companions , if the X-ray opaque size of the star is not larger than .

Density Diagnostics of the Hot Plasma in AE Aquarii withXMM‐Newton

We report on XMM-Newton observations of the magnetic CV AE Aqr. High-resolution spectroscopy of the He-like triplet of N and O with the RGS has enabled us to measure the electron number density of the plasma as ~1011 cm-3. Incorporating this with the emission measure, we estimate the geometrical scale of the plasma emitting these lines to be lp (2-3) × 1010 cm. Since the density and the scale are both incompatible with the standard postshock accretion column of an mCV, the plasma cannot be a product of mass accretion onto the white dwarf. The widths of the H-like Kα emission lines of N and O (=1250-1600 km s-1) are of similar magnitude to the thermal velocity dispersion of the hottest part of the plasma, where kTmax is 4.6 keV. It is known that Balmer series and UV emission lines also show a similar velocity dispersion. In addition, like these lines, the X-ray emission lines are found to show dramatic flaring activity. These facts strongly suggest that all these broad emission lines from X-ray to optical wave bands are produced in the course of adiabatic cooling of the plasma once heated up to Tmax in the deep gravitational potential of the white dwarf. This interpretation can resolve the problem of the absence of the high-velocity component in the Hα emission line spectrum by a scenario where the plasma that is expelled due to the propeller action is still too hot to emit the Hα line within a region of r < lp (roughly equal to the Roche lobe size) from the white dwarf where the high-velocity component is expected to originate.

Mass Accumulation Efficiency in Helium Shell Flashes for Various White Dwarf Masses

We have calculated the mass accumulation efficiency during helium shell flashes on white dwarfs (WDs) of mass 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, and $1.35 M_{\odot}$ for the helium accretion rates $\log\dot M_{\rm He} (M_{\odot}$ yr$^{-1}) = -7.4$ to -5.8. This efficiency is a crucial factor for binary evolutions of Type Ia supernovae. For less massive WDs ($< 0.8 M_{\odot}$) no wind mass loss occurs and all the accreted mass accumulates on the WD if the Roche lobe size is large enough. The efficiency takes the minimum values in between 1.1 and 1.2 $M_{\odot}$ WD for a given mass accretion rate and increases in both less and more massive WDs. The mass accumulation efficiency is larger than 0.5 for $\log\dot M_{\rm He} \geq -6.72$ in all the WD masses.

A Limit Cycle Model For Long‐Term Optical Variations of V Sagittae: The Second Example of Accretion Wind Evolution

V Sagittae shows quasi-periodic optical high (soft X-ray-off) and low (soft X-ray-on) states with the total period of ~300 days. A binary model is presented to explain orbital light curves for both the high and low states, as well as the transition mechanism between them. The binary model consists of a white dwarf (WD), a disk around the WD, and a lobe-filling main-sequence companion. In the optical low state, the mass-transfer rate to the WD is small and the size of the disk is as small as its Roche lobe size. In the optical high state, the mass-transfer rate to the WD exceeds the critical rate of ~1 × 10-6 M☉ yr-1 and the WD blows an optically thick, massive wind. Surface layers of the disk are blown in the wind, and the disk surface extends to the companion or over. As a result, optical luminosity of the disk increases by a magnitude because of its large irradiation effect. The massive wind completely obscures soft X-rays. This corresponds to the optical high/soft X-ray off state. The transition between optical high and low states is driven by an attenuation of the mass transfer from the secondary. During the optical high state, the wind from the WD hits the companion and strips off its surface layer. The mass transfer from the companion gradually reduces and stops. As the mass supply stops, the WD wind weakens and eventually stops. The disk shrinks to a Roche lobe size, and the optical magnitude drops. This phase corresponds to the optical low/soft X-ray on state. Then a rapid mass transfer resumes. The mass of the WD envelope increases and blows a wind again. This cycle is repeated like a limit cycle. During this intermittent wind phase, the WD can grow in mass at the critical rate and eventually reach the Chandrasekhar mass limit. This process is called wind evolution, which is a key evolutionary process in a recently developed evolutionary scenario of Type Ia supernovae. This evolutionary process was first confirmed in the LMC supersoft X-ray source RX J0513.9-6951, although it commonly occurs in the supersoft X-ray sources when the mass-transfer rate exceeds the critical rate. Thus, V Sge is the second example of accretion wind evolution.

A Theoretical Light‐Curve Model for the Recurrent Nova V394 Coronae Australis

A theoretical light curve for the 1987 outburst of V394 Coronae Australis (V394 CrA) is modeled to obtain various physical parameters of this recurrent nova. We then apply the same set of parameters to a quiescent phase and confirm that these parameters give a unified picture of the binary. Our V394 CrA model consists of a very massive white dwarf (WD), with an accretion disk (ACDK) having a flaring-up rim, and a lobe-filling, slightly evolved, main-sequence star (MS). The model includes irradiation effects of the MS and the ACDK by the WD. The early visual light curve (t ~ 1-10 days after the optical maximum) is well reproduced by a thermonuclear runaway model on a very massive WD close to the Chandrasekhar limit (1.37 ± 0.01 M☉). The ensuing plateau phase (t ~ 10-30 days) is also reproduced by the combination of a slightly irradiated MS and a fully irradiated flaring-up disk with a radius ~1.4 times the Roche lobe size. The best-fit parameters are the WD mass ~1.37 M☉, the companion mass ~1.5 M☉ (0.8-2.0 M☉ is acceptable), the inclination angle of the orbit i ~ 65°-68°, and the flaring-up rim ~0.30 times the disk radius. The envelope mass at the optical peak is estimated to be ~6 × 10-6 M☉, which indicates an average mass accretion rate of ~1.5 × 10-7 M☉ yr-1 during the quiescent phase between the 1949 and 1987 outbursts. In the quiescent phase, we properly include the accretion luminosity of the WD and the viscous luminosity of the ACDK as well as the irradiation effects of the ACDK and MS by the WD. The observed light curve can be reproduced with a disk size of 0.7 times the Roche lobe size and a rather slim thickness of 0.05 times the accretion disk size at the rim. About 0.5 mag sinusoidal variation of the light curve requires a mass accretion rate higher than ~1.0 × 10-7 M☉ yr-1, which is consistent with the above estimation from the 1987 outburst. These newly obtained quantities are exactly the same as those predicted in a new progenitor model of Type Ia supernovae.

A Theoretical Light-Curve Model for the 1999 Outburst of U Scorpii.

A theoretical light curve for the 1999 outburst of U Scorpii is presented in order to obtain various physical parameters of the recurrent nova. Our U Sco model consists of a very massive white dwarf (WD) with an accretion disk and a lobe-filling, slightly evolved, main-sequence star (MS). The model includes a reflection effect by the companion and the accretion disk together with a shadowing effect on the companion by the accretion disk. The early visual light curve (with a linear phase of t approximately 1-15 days after maximum) is well reproduced by a thermonuclear runaway model on a very massive WD close to the Chandrasekhar limit (MWD=1.37+/-0.01 M middle dot in circle), in which optically thick winds blowing from the WD play a key role in determining the nova duration. The ensuing plateau phase (t approximately 15-30 days) is also reproduced by the combination of a slightly irradiated MS and a fully irradiated flaring-up disk with a radius approximately 1.4 times the Roche lobe size. The cooling phase (t approximately 30-40 days) is consistent with a low-hydrogen content of X approximately 0.05 of the envelope for the 1.37 M middle dot in circle WD. The best-fit parameters are the WD mass of MWD approximately 1.37 M middle dot in circle, the companion mass of MMS approximately 1.5 M middle dot in circle (0.8-2.0 M middle dot in circle is acceptable), the inclination angle of the orbit (i approximately 80&j0;), and the flaring-up edge, the vertical height of which is approximately 0.30 times the accretion disk radius. The duration of the strong wind phase (t approximately 0-17 days) is very consistent with the BeppoSAX supersoft X-ray detection at t approximately 19-20 days because supersoft X-rays are self-absorbed by the massive wind. The envelope mass at the peak is estimated to be approximately 3x10-6 M middle dot in circle, which is indicates an average mass accretion rate of approximately 2.5x10-7 M middle dot in circle yr-1 during the quiescent phase between 1987 and 1999. These quantities are exactly the same as those predicted in a new progenitor model of Type Ia supernovae.

The ASCA Observation Campaign of SS433

Here we present a very short review of the ASCA observation campaign of the enigmatic galactic jet system SS433. The campaign started in 1994 just after the launch, and ended in 1996. Various phases of the 162.5-day precession and 13-day orbital motion were sampled. With ASCA, the Doppler-shifted pairs from various ion species from Si to Ni were resolved for the first time (Kotani et al. 1994). The Doppler-shift parameters were determined with an accuracy comparable to optical spectroscopy (Kawai 1995). No velocity gradient was found between the X-ray emission region of the jet and the optical. The distance between them was constrained to be less than 1015 cm. Line intensity ratios of Fe XXVI/Fe XXV give the base temperature of the jet to be 20 keV (Kotani et al. 1996). The variation of the apparent base temperature of the jet can be explained in terms of the partial occultation of the jet by a precessing accretion disk (Kotani et al. 1997a). From the variation, the disk radius and the disk height in unit of the X-ray jet length were estimated to be 0.23 ± 0.10 and 0.0232 ± 0.0049, respectively. (These are an improved version of the values in Kotani et al. (1997a).) SS433 is also known as an eclipsing binary. Because the emission from each jet with ASCA, it is possible to know how much of which jet is occulted by the companion star during an eclipse. Relative size of the companion star gives Roche lobe size and thus mass ratio MX/MC = 0.22+0.09-0.16 (Kotani 1997b). With the help of Doppler modulation, compact star mass is constrained. However, the values of Doppler modulation reported from optical observations largely scatters. D'Odorico et al. (1991) reported 112 km s−1 and this gives MX = 0.68+0.43-0.53 M⊙, i.e., a white dwarf, while Fabrika and Bychkova (1990) reported 175 km s−1, which gives 2.6+1.6-2.0 M⊙. (This error includes systematic errors of the X-ray data, and will be reduced in future analysis.) On the other hand, the absolute size of the system were determined with a satisfactory precision. For example, the X-ray jet length was determined to be 2×1013 cm, ten times larger than previous estimations (Kotani et al. 1997c). Other physical parameters of the jet can be derived from the X-ray jet length. Mass outflow rate and the kinetic luminosity of both jet were determined to be 8 × 10−6 M⊙ yr−1 and 1.6 × 1040 erg s−1 (Kotani et al. 1997d), implicating a highly super critical accretion. Most of these values are first precise measurements and/or “radical” revisions of previous estimations. The new picture of SS433 drawn here is far stormy and highly energetic.

Critical Mass for Merging in Double White Dwarfs

We examine whether or not double white dwarfs are ultimately merging into one body. It has been argued that such a double white dwarf system forms from some intermediate-mass binary stars and will merge due to the gravitational radiation which decreases the separation of binary. After filling the inner critical Roche lobe, the less massive component begins to transfer its mass to the more massive one. When the mass transfer rate exceeds a some critical value, a common envelope is formed. If the common envelope is hydrostatic, the mass transfer is tuned up to be a some value which depends only on the white dwarf mass, radius, and the Roche lobe size. The mass transfer from the less massive to the more massive components leads the separation to increase. On the other hand, the gravitational radiation effect reduces the separation. Which effect wins determines the fate of double white dwarfs, that is, whether merging or not merging. Since the formula of the gravitational radiation effect is well known, we have studied the mass accretion rate in common envelope phase of double white dwarfs assuming the Roche lobe size is as small as 0.03 R⊙ or 0.1 R⊙.

Mass loss during nova outbursts

The mass-loss process during nova outbursts is studied for a 1.3 solar mass white dwarf. A sequence consisting of steady mass-loss solutions and static solutions for the dwarf are constructed, and the mass accmulation ratio is calculated using this sequence. The amount of processed helium is estimated, and the accumulation ratio is determined for the case of infinitely large sizes of the Roche lobe. It is found that a complete nova cycle for such a dwarf is followed by a sequence consisting of static and steady mass-loss solutions. Once a hydrogen shell flash occurs, an optically thick wind always follows it. The occurrence of the wind is independent of the initial envelope mass. The mass accumulation ratio depends on the mass transfer rate from the companion. If the size of the outer critical Roche lobe is as small as as few solar radii or less, the mass accumulation ratio depends also on the Roche lobe size.