اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدDoppler tomography of the circumstellar disk of {pi} Aquarii
110
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The work is aimed at a study of the circumstellar disk of the bright classical binary Be star {pi} Aqr. We analysed variations of a double-peaked profile of the H{alpha} emission line in the spectrum of {pi} Aqr that was observed in many phases during ~40 orbital cycles in 2004--2013. We applied the Discrete Fourier Transform (DFT) method to search for periodicity in the peak intensity (V/R) ratio. Doppler tomography was used to study the structure of the disk around the primary. The dominant frequency in the power spectrum of the H{alpha} V/R ratio is 0.011873 day^-1 that correspond to a period of 84.2(2) days and is in agreement with the earlier determined orbital period of the system, Porb=84.1 days. The V/R ratio shows a sinusoidal variation phase-locked with the orbital period. Doppler maps of all our spectra show a non-uniform structure of the disk around the primary: a ring with the inner and outer radii at Vin~ 450 km/s and Vout~ 200km/s, respectively, along with an extended stable region (spot) at V_x ~ 225 km/s and V_y~100 km/s. The disk radius of ~ 65 Rsun = 0.33 AU was estimated assuming Keplerian motion of a particle on a circular orbit at the disk outer edge.
قيم البحث
اقرأ أيضاً
We present Doppler and modulation tomography of the X-ray nova XTE J1118+480 with data obtained during quiescence using the 10-m Keck II telescope. The hot spot where the gas stream hits the accretion disc is seen in H-Alpha, H-Beta, He I Lambda-5876
, and Ca II Lambda-8662, thus verifying the presence of continued mass transfer within the system. The disc is clearly seen in H-Alpha and Ca II Lambda-8662. We image the mass-donor star in narrow absorption lines of Na I Lambda-Lambda-5890, 5896, 8183, 8195 and Ca II Lambda-8662, implying an origin from the secondary itself rather than the interstellar medium. We also detect deviations in the centroid of the double peak of H-Alpha akin to those found by Zurita et al. 2002 suggesting disc eccentricity.
Grid-based hydrodynamics simulations of circumstellar disks are often performed in the curvilinear coordinate system, in which the center of the computational domain coincides with the motionless star. However, the center of mass may be shifted from
the star due to the presence of any non-axisymmetric mass distribution. As a result, the system exerts a gravity force on the star, causing the star to move in response, which can affect the evolution of the circumstellar disk. We aim at studying the effects of stellar motion on the evolution of protostellar and protoplanetary disks. In protostellar disks, a non-axisymmetric distribution of matter in the form of spiral arms or massive clumps can form due to gravitational instability. Protoplanetary disks can also feature non-axisymmetric structures caused by a high-mass planet or a large-scale vortex. We use 2D grid-based hydrodynamic simulations to explore the effect of stellar motion. We adopt a non-inertial polar coordinate system centered on the star, in which the stellar motion is taken into account by calculating the indirect potential caused by the non-axisymmetric disk, a high-mass planet, or a large-scale vortex. We found that the stellar motion has a moderate effect on the evolution history in protostellar disks, reducing somewhat the disk size and mass, while having a profound effect on the collapsing envelope, changing its inner shape from an initially axisymmetric to a non-axisymmetric configuration. Protoplanetary disk simulations show that the stellar motion slightly reduces the width of the gap opened by a high-mass planet, decreases the planet migration rate, and strengthens the large-scale vortices formed at the viscosity transition. We conclude that the inclusion of the indirect potential is recommended in grid-based hydrodynamics simulations of circumstellar disks which use the curvilinear coordinate system.
Stars form with gaseous and dusty circumstellar envelopes, which rapidly settle into disks that eventually give rise to planetary systems. Understanding the process by which these disks evolve is paramount in developing an accurate theory of planet f
ormation that can account for the variety of planetary systems discovered so far. The formation of Earth-like planets through collisional accumulation of rocky objects within a disk has mainly been explored in theoretical and computational work in which post-collision ejecta evolution is typically ignored, although recent work has considered the fate of such material. Here we report observations of a young, Sun-like star (TYC 8241 2652 1) where infrared flux from post-collisional ejecta has decreased drastically, by a factor of about 30, over a period of less than two years. The star seems to have gone from hosting substantial quantities of dusty ejecta, in a region analogous to where the rocky planets orbit in the Solar System, to retaining at most a meagre amount of cooler dust. Such a phase of rapid ejecta evolution has not been previously predicted or observed, and no currently available physical model satisfactorily explains the observations.
We present results of high-resolution imaging toward HL Tau by the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We have obtained 1.3 and 2.7 mm dust continua with an angular resolution down to 0.13 arc second. Through model fitti
ng to the two wavelength data simultaneously in Bayesian inference using a flared viscous accretion disk model, we estimate the physical properties of HL Tau, such as density distribution, dust opacity spectral index, disk mass, disk size, inclination angle, position angle, and disk thickness. HL Tau has a circumstellar disk mass of 0.13 solar mass, a characteristic radius of 79 AU, an inclination of 40 degree, and a position angle of 136 degree. Although a thin disk model is preferred by our two wavelength data, a thick disk model is needed to explain the high mid- and far-infrared emission of the HL Tau spectral energy distribution. This could imply large dust grains settled down on the mid plane with fine dust grains mixed with gas. The HL Tau disk is likely gravitationally unstable and can be fragmented between 50 and 100 AU of radius. However, we did not detect dust thermal continuum supporting the protoplanet candidate claimed by a previous study using observations of the Very Large Array at 1.3 cm.
The debris disk surrounding $beta$ Pictoris has a gas composition rich in carbon and oxygen, relative to solar abundances. Two possible scenarios have been proposed to explain this enrichment. The preferential production scenario suggests that the ga
s produced may be naturally rich in C and O, while the alternative preferential depletion scenario states that the enrichment has evolved to the current state from a gas with solar-like abundances. In the latter case, the radiation pressure from the star expels the gas outwards, leaving behind species less sensitive to stellar radiation such as C and O. Nitrogen is also not sensitive to radiation pressure due to its low oscillator strength, which would make it also overabundant under the preferential depletion scenario. As such, the abundance of N in the disk may provide clues to why C and O are overabundant. We aim to measure the N column density in the direction of $beta$ Pic, and use this information to disentangle these different scenarios explaining the C and O overabundance. Using far-UV spectroscopic data collected by the HSTs Cosmic Origins Spectrograph (COS) instrument, we analyse the spectrum and characterise the NI triplet by modelling the absorption lines. We measure the N column density in the direction of $beta$ Pic for the first time, and find it to be $log(N_{mathrm{NI}}/1,mathrm{cm}^2) = 14.9pm0.7$. The N gas is found to be consistent with solar abundances and Halley dust. The solar N abundance supports the preferential production hypothesis, in which the composition of gas in $beta$,Pic is the result of photodesorption from icy grains rich in C and O or collisional vaporisation of C and O rich dust in the disk. It does not support the hypothesis that C and O are overabundant due to the insensitivity of C and O to radiation pressure thereby leaving them to accumulate in the disk.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
