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The F0 V star 9 Aur A exhibits an irregular variability of amplitude $approx $0.1 magnitude at optical wavelengths. The variations are too slow for it to be a $delta$ Scuti-type star. There is no evidence for a close, interacting companion or ring of dust, either from infrared, ultraviolet, or speckle data. The photometric variability of 9 Aur A is similar to two other early F dwarf stars: $gamma$ Doradus and HD 96008. 9 Aur B appears to be an M dwarf, 9 Aur C is an early- to mid-K dwarf star, and 9 Aur E, if it is a member of the system, probably is a normal white dwarf. 9 Aur D is most likely an unrelated and distant K giant. [See note added in press regarding a fourth member of this class of ``variables without a cause, and short term variations of the radial velocity of 9 Aur.]
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The young star AB Aurigae is surrounded by a complex combination of gas-rich and dust dominated structures. The inner disk which has not been studied previously at sufficient resolution and imaging dynamic range seems to contain very little gas inside a radius of least 130 astronomical units (AU) from the star. Using adaptive-optics coronagraphy and polarimetry we have imaged the dust in an annulus between 43 and 302 AU from the star, a region never seen before. An azimuthal gap in an annulus of dust at a radius of 102 AU, along with a clearing at closer radii inside this annulus, suggests the formation of at least one small body at an orbital distance of about 100 AU. This structure seems consistent with crude models of mean motion resonances, or accumulation of material at two of the Lagrange points relative to the putative object and the star. We also report a low significance detection of a point source in this outer annulus of dust. This source may be an overdensity in the disk due to dust accreting onto an unseen companion. An alternate interpretation suggests that the objects mass is between 5 and 37 times the mass of Jupiter. The results have implications for circumstellar disk dynamics and planet formation.
(Abriged) We present the results of millimeter observations and a suitable chemical and radiative transfer model of the AB Aur (HD 31293) circumstellar disk and surrounding envelope. The integral molecular content of this system is studied by observing CO, C$^{18}$O, CS, HCO$^+$, DCO$^+$, H$_2$CO, HCN, HNC, and SiO rotational lines with the IRAM 30-m antenna, while the disk is mapped in the HCO$^+$(1-0) transition with the Plateau de Bure interferometer. Using a flared disk model with a vertical temperature gradient and an isothermal spherical envelope model with a shadowed midplane and two unshielded cones together with a gas-grain chemical network, time-dependent abundances of observationally important molecules are calculated. Then a 2D non-LTE line radiative transfer code is applied to compute excitation temperatures of several rotational transitions of HCO$^+$, CO, C$^{18}$O, and CS molecules. We synthesize the HCO$^+$(1-0) interferometric map along with single-dish CO(2-1), C$^{18}$O(2-1), HCO$^+$(1-0), HCO$^+$(3-2), CS(2-1), and CS(5-4) spectra and compared them with the observations. Our disk model successfully reproduces observed interferometric HCO$^+$(1-0) data, thereby constraining the following disk properties: (1) the inclination angle $iota=17^{+6}_{-3}degr$, (2) the position angle $phi=80pm30degr$, (3) the size $R_mathrm{out}=400pm200$ AU, (4) the mass $M_mathrm{disk}=1.3cdot10^{-2} M_{sun}$ (with a factor of $sim7$ uncertainty), and (5) that the disk is in Keplerian rotation. Furthermore, indirect evidence for a local inhomogeneity of the envelope at $ga600$ AU is found...
V455 Aur is a detached eclipsing binary containing two F-stars in a 3.15-d orbit with a small eccentricity. Its eclipses were discovered in data from the Hipparcos satellite and a spectroscopic orbit was obtained by Griffin (2001, 2013). Griffin found a long-term variation of the systemic velocity of the eclipsing system due to a third body in a highly eccentric orbit (e = 0.73) with a period of 4200 d. We have used these data, the light curve of V455 Aur from the TESS satellite, and the Gaia EDR3 parallax to determine the physical properties of the components of the system to high precision. We find the eclipsing stars to have masses of 1.289 +/- 0.006 Msun and 1.232 +/- 0.005 Msun, radii of 1.389 +/- 0.011 Rsun and 1.318 +/- 0.014 Rsun and effective temperatures of 6500 +/- 200 and 6400 +/- 200 K. Light from the tertiary component is directly detected for the first time, in the form of a third light of l_3 = 0.028 +/- 0.002 in the solution of the TESS light curve. From this l_3, theoretical spectra and empirical calibrations we estimate the star to have a mass of 0.72 +/- 0.05 Msun, a radius of 0.74 +/- 0.05 Rsun and a temperature of 4300 +/- 300 K. The inclination of the outer orbit is 53 +/- 3 degrees, so the two orbits in the system are not coplanar. We show that a measured spectroscopic light ratio of the two eclipsing stars could lower the uncertainties in radius from 1% to 0.25%. A detailed spectroscopic analysis could also yield precise temperatures and chemical abundances of the system, thus making V455 Aur one of the most precisely measured eclipsing systems known.
Recent exo-planetary surveys reveal that planets can orbit and survive around binary stars. This suggests that some fraction of young binary systems which possess massive circumbinary disks (CB) may be in the midst of planet formation. However, there are very few CB disks detected. We revisit one of the known CB disks, the UY Aurigae system, and probe 13CO 2-1, C18O 2-1, SO 5(6)-4(5) and 12CO 3-2 line emission and the thermal dust continuum. Our new results confirm the existence of the CB disk. In addition, the circumstellar (CS) disks are clearly resolved in dust continuum at 1.4 mm. The spectral indices between the wavelengths of 0.85 mm and 6 cm are found to be surprisingly low, being 1.6 for both CS disks. The deprojected separation of the binary is 1.26 based on our 1.4 mm continuum data. This is 0.07 (10 AU) larger than in earlier studies. Combining the fact of the variation of UY Aur B in $R$ band, we propose that the CS disk of an undetected companion UY Aur Bb obscures UY Aur Ba. A very complex kinematical pattern inside the CB disk is observed due to a mixing of Keplerian rotation of the CB disk, the infall and outflow gas. The streaming gas accreting from the CB ring toward the CS disks and possible outflows are also identified and resolved. The SO emission is found to be at the bases of the streaming shocks. Our results suggest that the UY Aur system is undergoing an active accretion phase from the CB disk to the CS disks. The UY Aur B might also be a binary system, making the UY Aur a triple system.
In this work $textit{n}$-transfer and incomplete fusion cross sections for $^{9}$Be + $^{197}$Au system are reported over a wide energy range, E$_{c.m.}$ $approx$ 29-45 MeV. The experiment was carried out using activation technique and off-line gamma counting. The transfer process is found to be the dominant mode as compared to all other reaction channels. Detailed coupled reaction channel (CRC) calculations have been performed for $textit{n}$-transfer stripping and pickup cross sections. The measured 1$textit{n}$-stripping cross sections are explained with CRC calculations by including the ground state and the 2$^{+}$ resonance state (E = 3.03 MeV) of $^{8}$Be. The calculations for 1$textit{n}$-pickup, including only the ground state of $^{10}$Be agree reasonably well with the measured cross sections, while it overpredicts the data at subbarrier energies. For a better insight into the role of projectile structure in the transfer process, a comprehensive analysis of 1$textit{n}$-stripping reaction has been carried out for various weakly bound projectiles on $^{197}$Au target nucleus. The transfer cross sections scaled with the square of total radius of interacting nuclei show the expected Q-value dependence of 1$textit{n}$-stripping channel for weakly bound stable projectiles.
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