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Register a new userThe magnetic system SMSS J1606-1000 as a period bouncer
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We report the discovery of a rare close binary system, SMSS J160639.78-100010.7, comprised of a magnetic white dwarf with a field of about 30 MG and a brown dwarf. We measured an orbital period of 92 min which is consistent with the photometric period. Minimum and maximum light occur at the orbital quadratures Phi=0.25 and 0.75, respectively, and cannot be caused by reflection on the brown dwarf, but, instead, by a spot on the synchronously rotating magnetic white dwarf. The brown dwarf does not fill its Roche lobe and the system may be in a low-accretion state or, more likely, in a detached state following episodes of mass transfer. SMSS J160639.78-100010.7 is the nearest known magnetic white dwarf plus brown dwarf system.
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We observed the 2012-2013 superoutburst of the newly identified transient SSS J122221.7-311523 and found that this object showed successive two superoutbursts. Superhumps grew in amplitude during the second superoutburst and showed a characteristic pattern of period change reflecting the growth of the superhump. Assuming that the periods of superhumps during the growing stage [0.07721(1) d] and post-superoutburst stage [0.07673(3) d], represent the dynamical precession rates at the radius of the 3:1 resonance and the radius immediately after the superoutburst, respectively, we found that this object has a very small mass ratio q=M2/M1 < 0.05. The possible orbital period from quiescent data suggests q=0.045, one of the smallest among hydrogen-rich cataclysmic variables. The long orbital period and low q make this object a perfect candidate for a period bouncer. We suggest that the peculiar pattern of double superoutburst is a result of a low q and may be characteristic to period bouncers.
We report on photometric observations of two dwarf novae, OT J075418.7+381225 and OT J230425.8+062546, which underwent superoutburst in 2013 (OT J075418) and in 2011 (OT J230425). Their mean period of the superhump was 0.0722403(26) d (OT J074518) and 0.067317(35) d (OT J230425). These objects showed a very long growing stage of the superhump (stage A) and a large period decrease in stage A-B transition. The long stage A suggests slow evolution of the superhump due to very small mass ratios of these objects. The decline rates during the plateau phase in the superoutburst of these objects were lower than those of SU UMa-type DNe with a similar superhump period. These properties were similar to those of SSS J122221.7-311523, the best candidate for the period bouncer. Therefore, these two DNe are regarded as good candidates for the period bouncer. We estimated the number density of period bouncers roughly from our observations in the recent five years. There is a possibility that these WZ Sge-type dwarf novae with unusual outburst properties can account for the missing population of the period bouncer expected from the evolutionary scenario.
We report the identification of the bright (V${sim}13.3$ mag) star FY Sct as a long period detached eclipsing binary using a combined ASAS-SN and ASAS light curve spanning 2000-2018. The orbital period is P${sim}2.57$ years and the primary eclipse lasts ${sim}73$ days. The eclipse profile is suggestive of a disk eclipsing binary rather than a stellar component. We also detect ${sim}0.4$ mag pulsations with a period of P${sim78}$ d. The next eclipse begins on September, 28, 2018. Further photometric and spectroscopic observations are encouraged, particularly when the system is in eclipse.
Building on previous work, a new search of the SuperWASP archive was carried out to identify eclipsing binary systems near the short-period limit. 143 candidate objects were detected with orbital periods between 16000 and 20000 s, of which 97 are new discoveries. Period changes significant at 1 sigma or more were detected in 74 of these objects, and in 38 the changes were significant at 3 sigma or more. The significant period changes observed followed an approximately normal distribution with a half-width at half-maximum of ~0.1 s/yr. There was no apparent relationship between period length and magnitude or direction of period change. Amongst several interesting individual objects studied, 1SWASP J093010.78+533859.5 is presented as a new doubly eclipsing quadruple system, consisting of a contact binary with a 19674.575 s period and an Algol-type binary with a 112799.109 s period, separated by 66.1 AU, being the sixth known system of this type.
We report the discovery of SMSS J160540.18-144323.1, a new ultra-metal poor halo star discovered with the SkyMapper telescope. We measure [Fe/H] = -6.2 +- 0.2 (1D LTE), the lowest ever detected abundance of iron in a star. The star is strongly carbon-enhanced, [C/Fe] = 3.9 +- 0.2, while other abundances are compatible with an alpha-enhanced solar-like pattern with [Ca/Fe] = 0.4 +- 0.2, [Mg/Fe] = 0.6 +- 0.2, [Ti/Fe] = 0.8 +- 0.2, and no significant s- or r-process enrichment, [Sr/Fe] < 0.2 and [Ba/Fe] < 1.0 (3{sigma} limits). Population III stars exploding as fallback supernovae may explain both the strong carbon enhancement and the apparent lack of enhancement of odd-Z and neutron-capture element abundances. Grids of supernova models computed for metal-free progenitor stars yield good matches for stars of about 10 solar mass imparting a low kinetic energy on the supernova ejecta, while models for stars more massive than roughly 20 solar mass are incompatible with the observed abundance pattern.
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