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Register a new userDynamo effect in the double periodic variable DQ Velorum
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Added by
Ruben San Martin-Perez
Publication date
2018
fields
Physics
and research's language is
English
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DQ Velorum is a galactic double periodic variable (DPV), this system is a semi-detached binary comprised of a B-type gainer and an A-type donor star plus an extended accretion disc around the gainer. The system also presents an orbital period of $6.08337$~days and a long period of $189$~days whose origin is still under debate. Here we studied the possibility that this period may be driven by a magnetic dynamo investigating the entire evolution of the system. The model matches in a very good way the current state of the system and it can potentially be used to describe the evolution of DQ Velorum. It also predicts an increase of the dynamo number of the donor during epochs of high mass transfer in this system, and a theoretical long/orbital period ratio very close to the observed one at the present system age.
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We report the discovery of 3 new Double Periodic Variables based on the analysis of ASAS-SN light curves: GSD J11630570-510306, V593 Sco and TYC 6939-678-1. These systems have orbital periods between 10 and 20 days and long cycles between 300 and 600 days.
We have performed a new search for DPVs of short period in the ASAS catalog (Pojmanski, G., 1997), focusing on those stars with orbital periods between 2 to 3 days which also show variations in their brightness. From a total of 244 objects, we have found another candidate to DPV, one whose mean brightness is gradually decreasing. By fitting a 3rd order polynomial to the mean magnitude and then moving it to zero for a second analysis, a gradual decrease over 2500 days was revealed. During the last 1000 days of this decrease, a 42% increase in the variation between the minimum and maximum values of the magnitude was observed. We determined the orbital period by using the PDM IRAF software (Stellingwerf 1978) and estimated the errors for the orbital period and long cycle by visual inspection of the light curves phased with trial periods near the minimum of the periodogram given by PDM.
HD170582 is an interacting binary of the Double Periodic Variable (DPV) type, showing ellipsoidal variability with a period of 16.87 days along with a long photometric cycle of 587 days. It was recently studied by Mennickent et al. (2015), who found a slightly evolved B-type star surrounded by a luminous accretion disc fed by a Roche-lobe overflowing A-type giant. Here we extend their analysis presenting new spectroscopic data and studying the Balmer emission lines. We find orbitally modulated double-peak Halpha and Hbeta emissions whose strength also vary in the long-term. In addition, Doppler maps of the emission lines reveal sites of enhanced line emission in the 1st and 4th velocity quadrants, the first one consistent with the position of one of the bright zones detected by the light curve analysis. We find a difference between Doppler maps at high and low stage of the long cycle; evidence that the emission is optically thicker at high state in the stream-disc impact region, possibly reflecting a larger mass transfer rate. We compare the system parameters with a grid of synthetic binary evolutionary tracks and find the best fitting model. The system is found to be semi-detached, in a conservative Case-B mass transfer stage, with age 7.68E7 yr and mass transfer rate 1.6E-6 Msun/yr. For 5 well-studied DPVs, the disc luminosity scales with the primary mass and is much larger than the theoretical accretion luminosity.
We present ~47,000 periodic variables found during the analysis of 5.4 million variable star candidates within a 20,000 square degree region covered by the Catalina Surveys Data Release-1 (CSDR1). Combining these variables with type-ab RR Lyrae from our previous work, we produce an on-line catalog containing periods, amplitudes, and classifications for ~61,000 periodic variables. By cross-matching these variables with those from prior surveys, we find that > 90% of the ~8,000 known periodic variables in the survey region are recovered. For these sources we find excellent agreement between our catalog and prior values of luminosity, period and amplitude, as well as classification. We investigate the rate of confusion between objects classified as contact binaries and type-c RR Lyrae (RRcs) based on periods, colours, amplitudes, metalicities, radial velocities and surface gravities. We find that no more than few percent of these variables in these classes are misidentified. By deriving distances for this clean sample of ~5,500 RRcs, we trace the path of the Sagittarius tidal streams within the Galactic halo. Selecting 146 outer-halo RRcs with SDSS radial velocities, we confirm the presence of a coherent halo structure that is inconsistent with current N-body simulations of the Sagittarius tidal stream. We also find numerous long-period variables that are very likely associated within the Sagittarius tidal streams system. Based on the examination of 31,000 contact binary light curves we find evidence for two subgroups exhibiting irregular lightcurves. One subgroup presents significant variations in mean brightness that are likely due to chromospheric activity. The other subgroup shows stable modulations over more than a thousand days and thereby provides evidence that the OConnell effect is not due to stellar spots.
In this paper we study the effects of hemispheric imbalance of magnetic helicity density on breaking the equatorial reflection symmetry of the dynamo generated large-scale magnetic field. Our study employs the axisymmetric dynamo model which takes into account the nonlinear effect of magnetic helicity conservation. We find that the evolution of the net magnetic helicity density, in other words, the magnetic helicity imbalance, on the surface follows the evolution of the parity of the large-scale magnetic field. Random fluctuations of the $alpha$-effect and the helicity fluxes can inverse the causal relationship, i.e., the magnetic helicity imbalance or the imbalance of magnetic helicity fluxes can drive the magnetic parity breaking. We also found that evolution of the net magnetic helicity of the small-scale fields follows the evolution of the net magnetic helicity of the large-scale fields with some time lag. We interpret this as an effect of the difference of the magnetic helicity fluxes out of the Sun from the large and small scales.
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