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Register a new userImpact of Pulsation Activity on the Light Curves of Symbiotic Variables
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We used long-term visual amateur observations of several symbiotic variables for detection of periods that may be caused by pulsation. The examples of multiple periodicities are discussed individually in each case.
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Outbursts in two classes of interacting binary systems, the symbiotic stars (SSs) and the cataclysmic variables (CVs), show a number of similarities in spite of very different orbital periods. Typical values for SSs are in the order of years, whereas for CVs they are of a few hours. Both systems undergo unpredictable outbursts, characterized by a brightening in the optical by 1 - 3 and 7 - 15 mag for SSs and CVs, respectively. By modelling the multiwavelength SED of selected examples from both groups of these interacting binaries, I determine their basic physical parameters at a given time of the outburst evolution. In this way I show that the principal difference between outbursts of these objects is their violence, whereas the ionization structure of their ejecta is basically very similar. This suggests that the mechanism of the mass ejection by the white dwarfs in these systems is also similar.
We present results of period analysis of ASAS, MACHO and OGLE light curves of 79 symbiotic stars classified as S and D-type. The light curves of 58 objects show variations with the orbital period. In case of 34 objects, orbital periods are estimated for the first time, what increases the number of symbiotic stars with known orbital periods by about 64 %. The light curves of 46 objects show, in addition to the long-term or/and orbital variations, short-term variations with time scales of 50-200 days most likely due to stellar pulsations of the cool giant component. We also report eclipse-like minima and outbursts present in many of the light curves.
In the standard view of massive star evolution, luminous blue variables (LBVs) are transitional objects between the most massive O-type stars and Wolf-Rayet (WR) stars. With short lifetimes, these stars should all be found near one another. A recent study of LBVs in the Large Magellanic Cloud (LMC) found instead that LBVs are considerably more isolated than either O-type stars or WRs, with a distribution intermediate between that of the WRs and red supergiants (RSGs). A similar study, using a more restricted sample of LBVs, reached the opposite conclusion. Both studies relied upon the distance to the nearest spectroscopically identified O-type star to define the degree of isolation. However, our knowledge of the spectroscopic content of the LMC is quite spotty. Here we re-examine the issue using carefully defined photometric criteria to select the highest mass unevolved stars (bright blue stars, or BBSs), using spatially complete photometric catalogs of the LMC, M31, and M33. Our study finds that the LBVs are no more isolated than BBSs or WRs. This result holds no matter which sample of LBVs we employ. A statistical test shows that we can rule out the LBVs having the same distribution as the RSGs, which are about 2x more isolated. We demonstrate the robustness of our results using the second-closest neighbor. Furthermore, the majority of LBVs in the LMC are found in or near OB associations as are the BBS and WRs; the RSGs are not. We conclude that the spatial distribution of LBVs therefore is consistent with the standard picture of massive star evolution.
We have detected asymmetry in the symbiotic star CH Cyg through the measurement of precision closure-phase with the IONIC beam combiner, at the IOTA interferometer. The position of the asymmetry changes with time and is correlated with the phase of the 2.1-yr period found in the radial velocity measurements for this star. We can model the time-dependent asymmetry either as the orbit of a low-mass companion around the M giant or as an asymmetric, 20% change in brightness across the M giant. We do not detect a change in the size of the star during a 3 year monitoring period neither with respect to time nor with respect to wavelength. We find a spherical dust-shell with an emission size of 2.2+/-0.1 D* FWHM around the M giant star. The star to dust flux ratio is estimated to be 11.63+/-0.3. While the most likely explanation for the 20% change in brightness is non-radial pulsation we argue that a low-mass companion in close orbit could be the physical cause of the pulsation. The combined effect of pulsation and low-mass companion could explain the behaviour revealed by the radial-velocity curves and the time-dependent asymmetry detected in the closure-phase data. If CH Cyg is a typical long secondary period variable then these variations could be explained by the effect of an orbiting low-mass companion on the primary star.
Using recently established empirical calibrations for the impact of chromospheric activity on the radii, effective temperatures, and estimated masses of active low-mass stars and brown dwarfs, we reassess the shape of the initial mass function (IMF) across the stellar/substellar boundary in the Upper Sco star-forming region (age 5-10 Myr). We adjust the observed effective temperatures to warmer values using the observed strength of the chromospheric H$alpha$ emission, and redetermine the estimated masses of objects using pre--main-sequence evolutionary tracks in the H-R diagram. The effect of the activity-adjusted temperatures is to shift the objects to higher masses by 3-100%. While the slope of the resulting IMF at substellar masses is not strongly changed, the peak of the IMF does shift from ~0.06 to ~0.11 Msun. Moreover, for objects with masses <~0.2 Msun, the ratio of brown dwarfs to stars changes from ~80% to ~33%. These results suggest that activity corrections are essential for studies of the substellar mass function, if the masses are estimated from spectral types or from effective temperatures.
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