Abstract
We present a timing study of the short-period eclipsing cataclysmic variable (CV) HT Cas. Based on new eclipse times derived from our photometric monitoring and archival optical data, ...combined with historical timings, spanning ∼42 yr, we detect a secular decrease in the orbital period at a rate of
P
̇
=
−
1.32
×
10
−
12
ss
−
1
and a cyclic period wiggle with an amplitude of 79.3 s and a period of 30.28 yr. We find that neither gravitational radiation nor magnetic braking can explain the observed decrease rate, suggesting the presence of additional angular momentum loss (AML). The empirical consequential AML (eCAML) model developed by Schreiber et al. can well match the observed orbital decay in HT Cas, and the physical mechanism for eCAML is most likely attributable to the frictional AML following nova eruptions. As for the cyclic variation, the best explanation is the influence of an unseen companion in orbit around the binary. The derived orbital parameters reveal that the hypothetical third body could be a giant planet with mass of
M
3
≃ 14
M
Jup
that is moving on a highly eccentric orbit (
e
= 0.82). Taken together the results of the present study suggest that HT Cas is a unique triple system containing a high-eccentricity giant planet and it has the potential to become an ideal laboratory in which to test models of CV evolution.
About 3196 EA-type binaries (EAs) were observed by LAMOST by 2017 June 16 and their spectral types were derived. Meanwhile, the stellar atmospheric parameters of 2020 EAs were determined. In this ...paper, those EAs are cataloged and their physical properties and evolutionary states are investigated. The period distribution of EAs suggests that the period limit of tidal locking for the close binaries is about 6 days. It is found that the metallicity of EAs is higher than that of EW-type binaries (EWs), indicating that EAs are generally younger than EWs and they are the progenitors of EWs. The metallicities of long-period EWs ( days) are the same as those of EAs with the same periods, while their values of Log (g) are usually smaller than those of EAs. These support the evolutionary process that EAs evolve into long-period EWs through the combination of angular momentum loss (AML) via magnetic braking and case A mass transfer. For short-period EWs, their metallicities are lower than those of EAs, while their gravitational accelerations are higher. These reveal that they may be formed from cool short-period EAs through AML via magnetic braking with little mass transfer. For some EWs with high metallicities, they may be contaminated by material from the evolution of unseen neutron stars and black holes or they have third bodies that may help them to form rapidly through a short timescale of pre-contact evolution. The present investigation suggests that the modern EW populations may have formed through a combination of these mechanisms.
Abstract
Nickel-based complex oxides have served as a playground for decades in the quest for a copper-oxide analog of the high-temperature superconductivity. They may provide clues towards ...understanding the mechanism and an alternative route for high-temperature superconductors. The recent discovery of superconductivity in the infinite-layer nickelate thin films has fulfilled this pursuit. However, material synthesis remains challenging, direct demonstration of perfect diamagnetism is still missing, and understanding of the role of the interface and bulk to the superconducting properties is still lacking. Here, we show high-quality Nd
0.8
Sr
0.2
NiO
2
thin films with different thicknesses and demonstrate the interface and strain effects on the electrical, magnetic and optical properties. Perfect diamagnetism is achieved, confirming the occurrence of superconductivity in the films. Unlike the thick films in which the normal-state Hall-coefficient changes signs as the temperature decreases, the Hall-coefficient of films thinner than 5.5 nm remains negative, suggesting a thickness-driven band structure modification. Moreover, X-ray absorption spectroscopy reveals the Ni-O hybridization nature in doped infinite-layer nickelates, and the hybridization is enhanced as the thickness decreases. Consistent with band structure calculations on the nickelate/SrTiO
3
heterostructure, the interface and strain effect induce a dominating electron-like band in the ultrathin film, thus causing the sign-change of the Hall-coefficient.
Abstract Maternal heroin abuse has been shown to result in teratogenic neurobehavioral defects in the offspring, but the underlying mechanisms remain largely unknown. This study was designed to ...explore the role of neuronal apoptosis in the heroin-induced neurobehavioral defects of learning and memory. Pregnant BALB/c mice were treated with either heroin or saline. The animals in the heroin group received heroin subcutaneously at a dosage of 10 mg/kg/day on embryonic days (E) 9–18, while those in the saline group were treated as drug-naive. Offspring were grouped as prenatal heroin exposure (HER), prenatal saline exposure (SAL), and control (CON) groups, according to the maternal treatment regimen. Some of the mice were killed and their hippocampus harvested on postnatal day (P) 14, and the tissue subjected to reverse transcription polymerase chain reaction, Western blotting, and immunohistochemistry to reveal the mRNA and protein expressions of caspase-3, Bcl-2, and Bax. The Morris water maze was applied to assess the learning and memory capability of the mice at P30; poor maze performances were observed for the animals in the HER group. The results also showed that the mRNA and protein expressions of caspase-3 and Bax were significantly increased, while that of Bcl-2 was markedly decreased in the HER group compared with both the SAL and CON groups. The immunohistochemistry revealed significant caspase-3 immunoreactivity in the dentate gyrus and cornu ammonis (CA) 1 subareas of the hippocampal formation, whereas, no significant changes were seen in subarea CA3. These findings suggest that prenatal heroin exposure during the E9–18 period enhances neuronal apoptosis by altering the expressions of caspase-3, Bcl-2, and Bax in the mouse hippocampus, and leads to impairment in hippocampus-dependent learning and memory.
LAMOST views δ Scuti pulsating stars Qian, S-B; Li, L-J; He, J-J ...
Monthly Notices of the Royal Astronomical Society,
03/2018, Letnik:
475, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
About 766 δ Scuti stars were observed by LAMOST by 2017 June 16. 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 δ 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 d. 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. Detection of those UCVs indicates that about 25 per cent of the known δ 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 δ Scuti stars are detected to be the candidates of binary or multiple systems.
Abstract
We present an analysis of both Transiting Exoplanet Survey Satellite (TESS) and Zwicky Transient Facility (ZTF) observations of the eclipsing cataclysmic variable IPHAS J051814.34+294113.2 ...(IPHAS J0518). The TESS light curve shows numerous eclipses superimposed on two outbursts, and ZTF data show frequently outbursts recurring on average every 20.7 days and 12.9 days for long and short outbursts, respectively. This makes IPHAS J0518 to be identified as a possible Z Cam-type dwarf nova. Its quiescent magnitude is ∼16.7 in the
g
band. The orbital period is determined to be 4.95 hr. By combining the observed orbital period with the semiempirical relations of Knigge et al., we estimate the donor mass as
M
2
= 0.48
M
⊙
. The eclipse phase measurements are used to constrain the binary parameters. The orbital inclination is limited in the range of 75.°3 ≤
i
< 81.°7, and the mass ratio is derived as 0.33 <
q
≤ 0.73. Furthermore, we analysis the accretion disk eclipse and find that the total disk eclipse is possible during quiescence, whereas during outburst the disk would be only partially obscured. This indicates that the disk will become larger as the outburst proceeds. We also study the changes of the eclipse depth against the out-of-eclipse flux in IPHAS J0518. The results show evidence of the expansion in the disk size and the variations in the radial-temperature gradient during outburst.
We present a timing analysis of the eclipsing post-common envelope binary (PCEB) DE CVn. Based on new CCD photometric observations and 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 . 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 another 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 ×10−4-10−3 M , which is in agreement with that inferred from previous studies in the order of magnitude. The cyclic change is most likely the result of the gravitational perturbation by a circumbinary object due to the Applegate's mechanism failing to explain such a large period oscillation. The mass of the potential third body is calculated as . Supposing the circumbinary companion and the eclipsing binary are coplanar, its mass would correspond to a giant planet. This hypothetical giant planet is moving in a circular orbit of a radius of ∼5.75( 2.02) au around its host star.
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 2016 June 3. Although the ...system was later 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 2016 April 19, 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 2016 April 19 to those from September 14, it was found that magnetic activity of the secondary is associated with the outburst. We show strong evidence that the L1 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.
DV UMa is an eclipsing dwarf nova with an orbital period of ∼2.06 hr, 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. The latest version of the O-C diagram, combined with the published mid-eclipse times in quiescence, and spanning ∼30 years, 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 years and an amplitude of 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 . If the third body is in the orbital plane (i.e., ) of the eclipsing pair, this would indicate it is a brown dwarf. This hypothetical brown dwarf is orbiting its host star at a separation of ∼8.6 au in an eccentric orbit (e = 0.44).
PDF
