National Astronomical Research Insititude of Thailand

Ban Mi, Thailand

National Astronomical Research Insititude of Thailand

Ban Mi, Thailand

Time filter

Source Type

Qian S.-B.,Chinese Academy of Sciences | Qian S.-B.,University of Chinese Academy of Sciences | Wang J.-J.,Chinese Academy of Sciences | Wang J.-J.,University of Chinese Academy of Sciences | And 10 more authors.
Astrophysical Journal, Supplement Series | Year: 2014

W UMa-type stars are contact systems where both cool components fill the critical Roche lobes and share a common convective envelope. Long and unbroken time-series photometry is expected to play an important role in their origin and activity. The newly discovered short-period W UMa-type star, CSTAR 038663, was monitored continuously by Chinese Small Telescope ARray (CSTAR) in Antarctica during the winters of 2008 and 2010. There were 15 optical flares recorded in the i band during the winter of 2010. This was the first time such flares were detected from a W UMa-type star. By analyzing the nearly unbroken photometric data from 2008, it is discovered that CSTAR 038663 is a W-type shallow contact binary system (f = 10.6(± 2.9)%) with a high mass ratio of q = 1.12(± 0.01), where the less massive component is slightly hotter than the more massive one. The asymmetric light curves are explained by the presence of a dark spot on the more massive component. Its temperature is about 800 K lower than the stellar photosphere and it covers 2.1% of the total photospheric surface. The lifetime of the dark spot is longer than 116 days. Using 725 eclipse times, we found that the observed-calculated (O-C) curve may show a cyclic variation that is explained by the presence of a close-in third body. Both the shallow contact configuration and the extremely high mass ratio suggest that CSTAR 038663 is presently evolving into a contact system with little mass transfer. The formation and evolution is driven by the loss of angular momentum via magnetic braking, and the close-in companion star is expected to play an important role, removing angular momentum from the central eclipsing binary. © 2014. The American Astronomical Society. All rights reserved.


Liu N.-P.,CAS Yunnan Astronomical Observatory | Liu N.-P.,Chinese Academy of Sciences | Liu N.-P.,University of Chinese Academy of Sciences | Qian S.-B.,CAS Yunnan Astronomical Observatory | And 14 more authors.
New Astronomy | Year: 2014

AQ Com is a W UMa-type binary star with a period of 0.28133 days that was discovered about fifty years ago. However, it was neglected for photometric investigation. Complete light curves in Rc and Ic bands are presented that show a positive O'Conell effect. The light maxima following the primary minima are higher than the other ones in both bands. Photometric solutions obtained with the W-D (Wilson and Devinney) method suggest that AQ Com is a contact binary with a contact degree of f=21.4(±6.2)%. It is found that the contact binary is a W-type system with a mass ratio of q=2.86 where the less massive component is hotter than the more massive one in a common convective envelope. The asymmetries of the light curves are explained by two dark spots on the more massive component. By combining several determined times of light minimum with the others compiled from the literature, it is detected that the Observed-Calculated (O-C) curve may display a cyclic change with a period of 8.5 years and an amplitude of 0.0016 days. The cyclic oscillation may be caused by the presence of a cool third stellar object at an orbital separation of about ∼4.2 AU. However, more data are needed to confirm the existence of the third body. © 2014 Elsevier B.V. All rights reserved.


Qian S.-B.,Chinese Academy of Sciences | Qian S.-B.,University of Chinese Academy of Sciences | Jiang L.-Q.,Chinese Academy of Sciences | Jiang L.-Q.,University of Chinese Academy of Sciences | And 17 more authors.
Astrophysical Journal Letters | Year: 2015

SDSS J001641-000925 is the first red dwarf contact binary star with an orbital period of 0.19856 days that is one of the shortest known periods among M-dwarf binary systems. The orbital period was detected to be decreasing rapidly at a rate of P∼ 8 s yr-1. This indicated that SDSS J001641-000925 was undergoing coalescence via a dynamical mass transfer or loss and thus this red dwarf contact binary is dynamically unstable. To understand the properties of the period change, we monitored the binary system photometrically from 2011 September 2 to 2014 October 1 by using several telescopes in the world and 25 eclipse times were determined. It is discovered that the rapid decrease of the orbital period is not true. This is contrary to the prediction that the system is merging driven by rapid mass transfer or loss. Our preliminary analysis suggests that the observed minus calculated (O-C) diagram shows a cyclic oscillation with an amplitude of 0.00255 days and a period of 5.7 yr. The cyclic variation can be explained by the light travel time effect via the presence of a cool stellar companion with a mass of M3 sin i′ ∼ 0.14 M⊙. The orbital separation between the third body and the central binary is about 2.8AU. These results reveal that the rarity of red dwarf contact binaries could not be explained by rapidly dynamical destruction and the presence of the third body helps to form the red dwarf contact binary. © 2015. The American Astronomical Society. All rights reserved.

Loading National Astronomical Research Insititude of Thailand collaborators
Loading National Astronomical Research Insititude of Thailand collaborators