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Register a new user$tau$ Ori and $tau$ Lib: Two new massive heartbeat binaries
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We report the discovery of two massive eccentric systems with BRITE data, $tau$ Ori and $tau$ Lib, showing heartbeat effects close to the periastron passage. $tau$ Lib exhibits shallow eclipses that will soon vanish due to the apsidal motion in the system. In neither system, tidally excited oscillations were detected.
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We present new photometric and spectroscopic observations and analyses for the eclipsing binary systems V1241 Tau and GQ Dra. Our photometric light and radial velocity curves analyses combining with the TESS light curves show that both are conventional semi-detached binary systems. Their absolute parameters are also derived. We present the $O-C$ analyses of the systems and we propose the most possible orbital period modulating mechanisms. Furthermore, Fourier analyses are applied to the photometric residual data of the systems to check for the pulsational behavior of the components. We conclude that the primary component of the system GQ Dra is a $delta$ Sct type pulsator with a dominant pulsation frequency of 18.58 d$^{-1}$ based on our $B$ filter residual light curve although it can not be justified by 30-minute cadence TESS data. No satisfactory evidence of pulsational behaviour for V1241 Tau was verified. Finally, the evolutionary tracks of the components of both systems are calculated, while their locations within evolutionary diagrams are compared with other Algol-type systems.
V1184 Tau is a young variable for long time monitored at optical wavelengths. Its variability has been ascribed to a sudden and repetitive increase of the circumstellar extinction (UXor-type variable), but the physical origin of such variation, although hypothesized, has not been fully supported on observational basis. To get a new insight into the variability of V1184 Tau, we present new photometric and spectroscopic observations taken in the period 2008-2015. During these years the source has reached the same high brightness level that had before the remarkable fading of about 5 mag undergone in 2004. The optical spectrum is the first obtained when the continuum is at its maximum level. The observations are interpreted in the framework of extinction driven variability. We analyze light curves, optical and near-infrared colors, SED and optical spectrum. The emerging picture indicates that the source fading is due to an extinction increase of DeltaA_V about 5 mag, associated with a strong infrared excess, attributable to a thermal component at T=1000 K. From the flux of H(alpha) we derive a mass accretion rate between 10^-11 -5 10^-10 M_sun yr^-1 s, consistent with that of classical T Tauri stars of similar mass. The source SED was fitted for both the high and low level of brightness. A scenario consistent with the known stellar properties (such as spectral type, mass and radius) is obtained only if the distance to the source is of few hundreds of parsecs, in contrast with the commonly assumed value of 1.5 kpc. Our analysis partially supports that presented by Grinin (2009), according to which the circumstellar disk undergoes a periodical puffing, whose observational effects are both to shield the central star and to evidence a disk wind activity. However, since the mass accretion rate remains almost constant with time, the source is likely not subject to accretion bursts.
We analyze new, high quality multicolor light curves of four overcontact binaries: AK Her, HI Dra, V1128 Tau and V2612 Oph, and determine their orbital and physical parameters using the modeling program of G. Djurasevic and recently published results of radial velocity studies. The achieved precision in absolute masses is between 10 and 20%, and in absolute radii between 5 and 10%. All four systems are W UMa type binaries with bright or dark spots indicative of mass and energy transfer or surface activity. We estimate the distances and the ages of the systems using the luminosities computed through our analysis, and perform an O-C study for V1128 Tau, which reveals a complex period variation that can be interpreted in terms of mass loss/exchange and either the presence of the third body, or the magnetic activity on one of the components. We conclude that further observations of these systems are needed to deepen our understanding of their nature and variability.
(Abridged) We present CARMA observations of the thermal dust emission from the circumstellar disks around the young stars RYTau and DGTau at wavelengths of 1.3mm and 2.8mm. The angular resolution of the maps is as high as 0.15arcsec, or 20AU at the distance of the Taurus cloud, which is a factor of 2 higher than has been achieved to date at these wavelengths. The unprecedented detail of the resulting disk images enables us to address three important questions related to the formation of planets. (1) What is the radial distribution of the circumstellar dust? (2) Does the dust emission show any indication of gaps that might signify the presence of (proto-)planets? (3) Do the dust properties depend on the orbital radius? We find that modeling the disk surface density in terms of either a classical power law or the similarity solution for viscous disk evolution, reproduces the observations well. The 1.3mm image from RYTau shows two peaks separated by 0.2arcsec with a decline in the dust emission toward the stellar position, which is significant at about 2-4sigma. For both RYTau and DGTau, the dust emission at radii larger than 15 AU displays no significant deviation from an unperturbed viscous disk model. In particular, no radial gaps in the dust distribution are detected. Under reasonable assumptions, we exclude the presence of planets more massive than 5 Jupiter masses orbiting either star at distances between about 10 and 60 AU. The radial variation of the dust opacity slope, beta, was investigated by comparing the 1.3mm and 2.8mm observations. We find mean values of beta of 0.5 and 0.7 for DGTau and RYTau respectively. Variations in beta are smaller than 0.7 between 20 and 70 AU. These results confirm that the circumstellar dust throughout these disks differs significantly from dust in the interstellar medium.
We present new photometric observations of eclipsing binary systems V1241 Tau and GQ Dra. We use the following methodology: Initially, WD code is applied to the light curves, in order to determine the photometric elements of the systems. Then the residuals are analysed using Fourier Transformation techniques. The results show that one frequency can be barely attributed to the residual light variation of V1241 Tau, while there is no evidence of pulsation on the light curve of GQ Dra.
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