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About 766 $\delta$ Scuti stars were observed by LAMOST by June 16, 2017. Stellar atmospheric parameters of 525 variables were determined, while spectral types were obtained for all samples. In the paper, those spectroscopic data are catalogued. We detect a group of 131 unusual and cool variable stars (UCVs) that are distinguished from the normal $\delta$ Scuti stars (NDSTs). On the H-R diagram and the $\log g-T$ diagram, the UCVs are far beyond the red edge of pulsational instability trip. Their effective temperatures are lower than 6700\,K with periods in the range from 0.09 to 0.22\,days. NDSTs have metallicity close to that of the Sun as expected, while UCVs are slightly metal poor than NDSTs. The two peaks on the distributions of the period and stellar atmospheric parameters are all caused by the existence of UCVs. When those UCVs are excluded, it is discovered that the effective temperature, the gravitational acceleration and the metallicity all are correlated with the pulsating period for NDSTs and their physical properties and evolutionary states are discussed. The detecting of those UCVs indicates that about 25\% of the known $\delta$ Scuti stars may be misclassified. However, if some of them are confirmed to be pulsating stars, they will be a new-type pulsator and their investigations will shed light on theoretical instability domains and on the theories of interacting between the pulsation and the convection of solar-type stars. Meanwhile, 88 $\delta$ Scuti stars are detected to be the candidates of binary or multiple systems., Comment: 15 pages, 16 figures, accepted for publication in MNRAS

The first complete VRcIc light curves of V608 Cas are presented and analyzed by using the 2010 version of the W-D code. The photometric results show that V608 Cas is a moderate mass-ratio (q = 0.373 +/- 0.005), shallow contact (f = 19.7 +/- 4.9%) binary. A cool spot is present on the massive component. The orbital period of V608 Cas may increase continuously according to the (0 - C) diagram, with a rate of dP/dt = +6.49 x 10(-7) days/year. The fundamental parameters of V608 Cas are estimated as: M-1 = 0.95 +/- 0.15M(circle dot), M-2 = 035 +/- 0.08M(circle dot), R-1 = 0.78 +/- 0.12R(circle dot), R-2 = 0.50 +/- 0.10R(circle dot), L-1 = 0.563 +/- 0.112L(circle dot), L-2 = 0.233 +/- 0.086L(circle dot), where the uncertainties mainly come from the uncertainty of the primary's effective temperature. (C) 2015 Elsevier B.V. All rights reserved.

1SWASP\,J162117.36$+$441254.2 was originally classified as an EW-type binary with a period of 0.20785\,days. However, it was detected to have undergone a stellar outburst on June 3, 2016. Although the system was latter classified as a cataclysmic variable (CV) and the event was attributed as a dwarf-nova outburst, the physical reason is still unknown. This binary has been monitored photometrically since April 19, 2016 and many light curves were obtained before, during and after the outburst. Those light and color curves observed before the outburst indicate that the system is a special CV. The white dwarf is not accreting material from the secondary and there are no accretion disks surrounding the white dwarf. By comparing the light curves obtained from April 19 to September 14, 2016, it was found that magnetic activity of the secondary is associated with the outburst. We show strong evidence that the $L_1$ region on the secondary was heavily spotted before and after the outburst and thus quench the mass transfer, while the outburst is produced by a sudden mass accretion of the white dwarf. These results suggest that J162117 is a good astrophysical laboratory to study stellar magnetic activity and its influences on CV mass transfer and mass accretion., 16 pages, 6 figures, accepted for publication in ApJ

We present CCD light curves of V710 Mon obtained in 2007 and 2013. By using the 2010 version of the W-D code, it is found that the star is a deep (59.5-62.7%) contact binary system, with an extreme mass ratio (0.143-0.183). The period of the system increases with a rate dP/dt = +1.95( +/- 0.06) x 10(-7) days/year. We propose that the system contains a post-main-sequence component which may be in an expanding phase. The time scale of the orbital increase nearly equals to the time for the post-main-sequence star to evolve into a subgiant. The age of the primary is estimated to be 5.34 Gyr. (c) 2014 Published by Elsevier B.V.

We present the photometric results of the eclipsing cataclysmic variable (CV) WZ Sge near the period minimum ($P_{min}$). Eight new mid-eclipse times were determined and the orbital ephemeris was updated. Our result shows that the orbital period of WZ Sge is decreasing at a rate of $\dot{P}=-2.72(\pm0.23)\times{10^{-13}}\,s s^{-1}$. This secular decrease, coupled with previous detection of its donor, suggest that WZ Sge is a pre-bounce system. Further analysis indicates that the observed period decrease rate is about $1.53$ times higher than pure gravitational radiation (GR) driving. We constructed the evolutionary track of WZ Sge, which predicts that $P_{min}$ of WZ Sge is $\sim77.98 (\pm0.90)$ min. If the orbital period decreases at the current rate, WZ Sge will evolve past its $P_{min}$ after $\sim25.3$ Myr. Based on the period evolution equation we find $\dot{M}_{2}\simeq4.04(\pm0.10)\times10^{-11}M_{\odot}yr^{-1}$, which is compatible with the current concept of CV evolution at ultrashort orbital periods., Comment: 8 pages, 5 figures

DV UMa is an eclipsing dwarf nova with an orbital period of $\sim2.06$ h, which lies just at the bottom edge of the period gap. To detect its orbital period changes we present 12 new mid-eclipse times by using our CCD photometric data and archival data. Combining with the published mid-eclipse times in quiescence, spanning $\sim30$ yr, the latest version of the $O-C$ diagram was obtained and analyzed. The best fit to those available eclipse timings shows that the orbital period of DV UMa is undergoing a cyclic oscillation with a period of $17.58(\pm0.52)$ yr and an amplitude of $71.1(\pm6.7)$ s. The periodic variation most likely arises from the light-travel-time effect via the presence of a circumbinary object because the required energy to drive the Applegate mechanism is too high in this system. The mass of the unseen companion was derived as $M_{3}\sin{i'}=0.025(\pm0.004)M_{\odot}$. If the third body is in the orbital plane (i.e. $i'=i=82.9^{\circ}$) of the eclipsing pair, it would match to a brown dwarf. This hypothetical brown dwarf is orbiting its host star at a separation of $\sim8.6$ AU in an eccentric orbit ($e=0.44$)., Comment: 16 pages, 6 figures

We present a timing analysis of the eclipsing post-common envelope binary (PCEB) DE CVn. Based on new CCD photometric observations and the published data, we found that the orbital period in DE CVn has a cyclic period oscillation with an amplitude of $28.08$ s and a period of $11.22$ years plus a rapid period decrease at a rate of $\dot{P}=-3.35\times10^{-11}ss^{-1}$. According to the evolutionary theory, secular period decreases in PCEBs arise from angular momentum losses (AMLs) driven by gravitational radiation (GR) and magnetic braking (MB). However, the observed orbital decay is too fast to be produced by AMLs via GR and MB, indicating that there could be other AML mechanism. We suggest that a circumbinary disk around DE CVn may be responsible for the additional AML. The disk mass was derived as a few$\times$$10^{-4}$-$10^{-3}$$M_{\odot}$ , which is in agreement with that inferred from previous studies in the order of magnitude. The cyclic change is most likely result of the gravitational perturbation by a circumbinary object due to the Applegate's mechanism fails to explain such a large period oscillation. The mass of the potential third body is calculated as $M_{3}\sin{i'}=0.011(\pm0.003)M_{\odot}$. Supposing the circumbinary companion and the eclipsing binary is coplanar, its mass would correspond to a giant planet. This hypothetical giant planet is moving in a circular orbit of radius $\sim5.75(\pm2.02)$ AU around its host star., Comment: 19 pages, 5 figures

SDSS J143547.87+373338.5 is a detached eclipsing binary that contains a white dwarf with a mass of 0.5 Mo and a fully convective star with a mass of 0.21 Mo. The eclipsing binary was monitored photometrically from 2009 March 24 to 2015 April 10, by using two 2.4-m telescopes in China and in Thailand. The changes in the orbital period are analyzed based on eight newly determined eclipse times together with those compiled from the literature. It is found that the observed-calculated (O-C) diagram shows a downward parabolic change that reveals a continuous period decrease at a rate of s s-1. According to the standard theory of cataclysmic variables, angular momentum loss (AML) via magnetic braking (MB) is stopped for fully convective stars. However, this period decrease is too large to be caused by AML via gravitational radiation (GR), indicating that there could be some extra source of AML beyond GR, but the predicted mass-loss rates from MB seem unrealistically large. The other possibility is that the O-C diagram may show a cyclic oscillation with a period of 7.72 years and a small amplitude of 0.000525. The cyclic change can be explained as the light-travel-time effect via the presence of a third body because the required energy for the magnetic activity cycle is much larger than that radiated from the secondary in a whole cycle. The mass of the potential third body is determined to be Mo when a total mass of 0.71 Mo for SDSS J143547.87+373338.5 is adopted. For orbital inclinations , it would be below the stable hydrogen-burning limit of M3 ∼ 0.072 Mo, and thus the third body would be a brown dwarf., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

By using our twelve new CCD times of light minimum of OY Carinae (OY Car) together with those collected from the literature, it is found that the O-C curve of OY Car shows a downward parabola with an amplitude of 27.8 s and a cyclic change of a period 14.0 yr. The period decrease is opposite to the hypothesis of mass transfer, and it cannot be explained by angular momentum loss via gravitational radiation. The Rappaport et al. (1983)’s magnetic braking (MB) prescription is adopted to explain the observed orbital period decrease. The cyclic change of period is analyzed with the light travel-time effect that originates from gravitational influence of a third body. The mass of the third star is determined to be M3sini‧=0.008097(±0.000014) M⊙=8.48(±0.02) MJup, suggesting that it may be a critical substellar object between brown dwarf and giant planet. If the orbital inclination of the third body equals 90°, the distance between the third body and the mass centre of the whole system is about 6.18(±0.45) AU. Fil: Han, Z. T. . Chinese Academy Of Sciences; República de China Fil: Qian, S. B.. Chinese Academy Of Sciences; República de China Fil: Fernandez Lajus, Eduardo Eusebio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Astrofísica de la Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina Fil: Liao, W. P.. Chinese Academy Of Sciences; República de China Fil: Zhang, J.. Chinese Academy Of Sciences; República de China