اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدHydrodynamic Winds From Twin-Star Binaries
32
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Stellar winds shape the evolution of stars through the loss of mass. In binary systems, they also shape the stars evolution by modifying the orbit. In this paper, we use hydrodynamic simulations to study the emergence of nearly-isothermal winds from identical-twin binaries. We vary the degree to which model stars fill their Roche lobes and the temperature of the wind. Initialized at rest on the stellar surfaces, winds accelerate away from the binary components through a sonic surface to supersonic outward velocities. In cases where the binary fills its Roche lobe, a shared subsonic region surrounds both components. We find that mass loss rates from close twin-star binaries are enhanced relative to the expectation from two single-object winds. This binary enhancement is best modeled as a function of the ratio of wind velocity to orbital velocity. Similarly, we find that the specific angular momentum with which winds emerge can vary between that of the binary components and that of the outer Lagrange points depending on the ratio of wind velocity to orbital velocity. Given that mass and angular momentum loss can be modeled as simple functions of wind velocity, our results may be broadly applicable to the evolution of close, equal-mass binaries. One particularly important potential application is to massive, close binaries which may be progenitors of binary black hole mergers through the chemically-homogeneous evolution channel.
قيم البحث
اقرأ أيضاً
Massive stars feature highly energetic stellar winds that interact whenever two such stars are bound in a binary system. The signatures of these interactions are nowadays found over a wide range of wavelengths, including the radio domain, the optical
band, as well as X-rays and even gamma-rays. A proper understanding of these effects is thus important to derive the fundamental parameters of the components of massive binaries from spectroscopic and photometric observations.
We propose a formation mechanism for twin blue stragglers (BSs) in compact binaries that involves mass transfer from an evolved outer tertiary companion on to the inner binary via a circumbinary disk. We apply this scenario to the observed double BS
system Binary 7782 in the old open cluster NGC 188, and show that its observed properties are naturally reproduced within the context of the proposed model. We predict the following properties for twin BSs: (1) For the outer tertiary orbit, the initial orbital period should lie between 220 days $lesssim$ P$_{rm out}$ $lesssim$ 1100 days, assuming initial masses for the inner binary components of $m_{rm 1} = 1.1$ M$_{odot}$ and $m_{rm 2} =$ 0.9 M$_{odot}$ and an outer tertiary mass of $m_{rm 3} = 1.4$ M$_{odot}$. After Roche-lobe overflow, the outer star turns into a white dwarf (WD) of mass 0.43 to 0.54,MSun. There is a correlation between the mass of this WD and the outer orbital period: more massive WDs will be on wider orbits. (3) The rotational axes of both BSs will be aligned with each other and the orbital plane of the outer tertiary WD. (4) The BSs will have roughly equal masses, independent of their initial masses (since the lower mass star accretes the most). The dominant accretor should, therefore, be more enriched by the accreted material. Hence, one of the BSs will appear to be more enriched by either He, C and O or by s-process elements, if the donor started Roche lobe overflow on, respectively, the red giant or asymptotic giant branch. (5) Relative to old clusters, twin BSs in close binaries formed from the proposed mechanism should be more frequent in the Galactic field and open clusters with ages $lesssim$ 4-6 Gyr, since then the donor will have a radiative envelope. (6) The orbit of the binary BS will have a small semi-major axis (typically $aplt 0.3$,au) and be close to circular ($e aplt 0.2$).
In the Milky Way, $sim$18 Wolf-Rayet+O (WR+O) binaries are known with estimates of their stellar and orbital parameters. Whereas black hole+O (BH+O) binaries are thought to evolve from the former, only one such system is known in the Milky Way. To re
solve this disparity, it was suggested that upon core collapse, the WR stars receive large kicks such that most of the binaries are disrupted. We reassess this issue, with emphasis on the uncertainty in the formation of an accretion disk around wind-accreting BHs in BH+O binaries, which is key to identifying such systems. We follow the methodology of previous work and apply an improved analytic criterion for the formation of an accretion disk around wind accreting BHs. We then use stellar models to predict the properties of the BH+O binaries which are expected to descend from the observed WR+O binaries, if the WR stars would form BHs without a natal kick. We find that disk formation depends sensitively on the O stars wind velocity, the specific angular momentum carried by the wind, the efficiency of angular momentum accretion by the BH, and the spin of the BH. We show that the assumption of a low wind velocity may lead to predicting that most of the BH+O star binaries will have an extended X-ray bright period. However, this is not the case when typical wind velocities of O stars are considered. We find that a high spin of the BH can boost the duration of the X-ray active phase as well as the X-ray brightness during this phase, producing a strong bias for detecting high mass BH binaries in X-rays with high BH spin parameters. We conclude that large BH formation kicks are not required to understand the sparsity of X-ray bright BH+O stars in the Milky Way. Probing for a population of X-ray silent BH+O systems with alternative methods can inform us about BH kicks and the conditions for high energy emission from high mass BH binaries. (Abridged)
X-ray and UV line emission in X-ray binaries can be accounted for by a hot corona. Such a corona forms through irradiation of the outer disk by radiation produced in the inner accretion flow. The same irradiation can produce a strong outflow from the
disk at sufficiently large radii. Outflowing gas has been recently detected in several X-ray binaries via blue-shifted absorption lines. However, the causal connection between winds produced by irradiation and the blue-shifted absorption lines is problematic, particularly in the case of GRO J1655-40. Observations of this source imply wind densities about two orders of magnitude higher than theoretically predicted. This discrepancy does not mean that these `thermal disk-winds cannot explain blue-shifted absorption in other systems, nor that they are unimportant as a sink of matter. Motivated by the inevitability of thermal disk-winds and wealth of data taken with current observatories such as Chandra, XMM-Newton and Suzaku, as well as the future AstroH mission, we decided to investigate the requirements to produce very dense winds. Using physical arguments, hydrodynamical simulations and absorption line calculations, we found that modification of the heating and cooling rates by a factor of a few results in an increase of the wind density of up to an order of magnitude and the wind velocity by a factor of about two. Therefore, the mass loss rate from the disk can be one, if not even two orders of magnitude higher than the accretion rate onto the central object. Such a high mass loss rate is expected to destabilize the disk and perhaps provides a mechanism for state change.
We want to test if self-similar magneto-hydrodynamic (MHD) accretion-ejection models can explain the observational results for accretion disk winds in BHBs. In our models, the density at the base of the outflow, from the accretion disk, is not a free
parameter, but is determined by solving the full set of dynamical MHD equations without neglecting any physical term. Different MHD solutions were generated for different values of (a) the disk aspect ratio ($varepsilon$) and (b) the ejection efficiency ($p$). We generated two kinds of MHD solutions depending on the absence (cold solution) or presence (warm solution) of heating at the disk surface. The cold MHD solutions are found to be inadequate to account for winds due to their low ejection efficiency. The warm solutions can have sufficiently high values of $p (gtrsim 0.1)$ which is required to explain the observed physical quantities in the wind. The heating (required at the disk surface for the warm solutions) could be due to the illumination which would be more efficient in the Soft state. We found that in the Hard state a range of ionisation parameter is thermodynamically unstable, which makes it impossible to have any wind at all, in the Hard state. Our results would suggest that a thermo-magnetic process is required to explain winds in BHBs.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
