An investigation of a magnetic cataclysmic variable with a period of 14.1 ks

Magnetic cataclysmic variables （CVs） contain a white dwarf （WD） with a magnetic field strong enough to control the accretion flow from a late type secondary. In this paper, we identify a magnetic CV （CXOGSG J215544.4＋380116） from the Chandra archive data. The X-ray light curves show a significant period of 14.1 ks, and the X-ray spectra can be described by a multi-temperature hot thermal plasma, suggesting the source is a magnetic CV. The broad dip in the X-ray light curve is due to the eclipse of the primary magnetic pole, and the additional dip in the bright phase of the soft and medium bands may be caused by the accretion stream crossing our line of sight to the primary pole. Follow-up optical spectra show features of an M2-M4 dwarf dominating the red band and a WD which is responsible for the weak upturn in the blue band. The mass （~ 0.4 34⊙） and radius （~0.4 R⊙） for the M dwarf are obtained using CV evolution models and empirical relations between the orbital period and the mass/radius. The estimated low X-ray luminosity and accretion rate may suggest the source is a low-accretion-rate polar. In addition, Very Large Array observations reveal a possible radio counterpart to the X-ray source, but with a low significance. Further radio observations with high quality are needed to confirm the radio counterpart and explore the properties of this binary system.

A Study on White Dwarf Masses in Cataclysmic Variables Based on XMM-Newton and Suzaku Observations

The distribution of the mass of white dwarfs(WDs)is one of the fundamental questions in the field of cataclysmic variables(CVs).In this work,we make a systematical investigation on the WD masses in two subclass of CVs:intermediate polars(IPs)and non-magnetic CVs in the solar vicinity based on the fiux ratios of Fe XXVI-Lyαto Fe XXV-Heαemission lines(I_(7.0)/I_(6.7))from archival XMM-Newton and Suzaku observations.We first verify the(semi-empirical)relations between I_(7.0)/I_(6.7),the maximum emission temperature(T_(max))and the WD mass(M_(WD))with the mkcfiow model based on the apec description and the latest Atom DB.We then introduce a new spectral model to measure M_(WD)directly based on the above relations.A comparison shows that the derived M_(WD)is consistent with dynamically measured ones.Finally,we obtain the average WD masses of 58 CVs(including 36IPs and 22 non-magnetic CVs),which is the largest X-ray selected sample.The average WD masses are<M_(WD,IP)>=0.81±0.21 M☉and<M_(WD,DN)>=0.81±0.21M☉ for IPs and non-magnetic CVs,respectively.These results are consistent with previous works.

Simulation of the emission lines radiated from cataclysmic variables

Cataclysmic variables are special celestial bodies because they have particular light curves and spectra.The mechanisms for generating emission lines radiated from dwarf novae in their quiescent phases are studied.We assume that the incident radiation field which is emitted by a hot source（white dwarf and boundary layer）irradiates the gaseous layer evaporated from the accretion disk,and the emission lines are radiated from the gas.We model the fluxes of emission lines by using the photoionization code CLOUDY.Using this method,we input some reasonable parameters and get a series of simulated spectra.In order to find a simulated spectrum which is the best fit to an observed spectrum,we use a cross-correlation method to match them.After the calculation,we use the approximation that the parameters of the simulated spectrum can simulate the observed spectrum.Finally,we learn more about the physical conditions of the system.

Two Cataclysmic Variables Identified from ROSAT Bright Sources

This paper presents the results of optical spectroscopic observations of two ROSAT bright sources, 1RXS J020928.9+283243 and 1RXS J042332.8+745300. The low-dispersion spectra suggest the cataclysmic variable classification for the two objects. Further photometric observations are expected to reveal the variable features and to confirm the classifications.

Physical parameters and orbital period variation of a newly discovered cataclysmic variable GSC 4560-02157

GSC 4560-02157 is a new eclipsing cataclysmic variable with an orbital period of 0.265359 days. By using the published V- and R-band data together with our observations, we discovered that the O - C curve of GSC 4560-02157 may show a cyclic variation with a period of 3.51 years and an amplitude of 1.40 min. If this variation is caused by a light travel-time effect via the existence of a third body, then its mass can be derived as M3 sin i1≈ 91.08 Mjup, and it should be a low-mass star. In addition, several physical parameters were measured. The color of the secondary star was determined to be V - R = 0.77（±0.03） which corresponds to a spectral type of K2-3. The secondary star＇s mass was estimated as M2 = 0.73（±0.02） Mo by combing the derived V - R value around phase 0 with the assumption that it obeys the mass-luminosity relation for main sequence stars. This mass is consistent with the mass-period relation for CV donor stars. For the white dwarf, the eclipse durations and contacts of the white dwarf yield an upper limit on the white dwarf＇s radius corresponding to a lower limit on mass of M1 ≈ 0.501 M⊙. The overestimated radius and previously published spectral data indicate that the boundary layer may have a very high temperature.

Detection of a Quasiperiodic Phenomenon of a Binary Star System Using Convolutional Neural Network

Pattern recognition algorithms are commonly utilized to discover certain patterns,particularly in image-based data.Our study focuses on quasiperiodic oscillations(QPO)in celestial objects referred to as cataclysmic variables(CV).We are dealing with interestingly indistinct QPO signals,which we analyze using a power density spectrum(PDS).The confidence in detecting the latter using certain statistical approaches may come out with less significance than the truth.We work with real and simulated QPO data of a CV called MV Lyrae.Our primary statistical tool for determining confidence levels is sigma intervals.The aforementioned CV has scientifically proven QPO existence,but as indicated by our analysis,the QPO ended up falling below 1-σ,and such QPOs are not noteworthy based on the former approach.We intend to propose and ultimately train a convolutional neural network(CNN)using two types of QPO data with varying amounts of training dataset lengths.We aim to demonstrate the accuracy and viability of the classification using a CNN in comparison to sigma intervals.The resulting detection rate of our algorithm is very plausible,thus proving the effectiveness of CNNs in this scientific area.

Photometric analysis of the eclipsing polar MN Hya

As an eclipsing polar with a 3.39 h orbital period, MN Hya was going through a state change when we observed it during 2009-2016. Ten new mid-eclipse times, along with others obtained from literature, allow us to give a new ephemeris. The residuals of a linear fit show that period decreased during the phase of state change, which means angular momentum was lost during this phase. The associated X-ray observation indicates the mass accretion rate was about 3.6 x 10^-9 Mo yr^-1. The period decrease indicates that at least 60% of mass being transferred from the secondary was lost, maybe in the form of spherically symmetric stellar wind. In the high state, the data show the intensity of flickering reduced when the system had a higher accretion rate, and that flickering sticks out with a primary timescale of about 2 min, which implies the position of the threading point was about 30 white dwarf radii above its surface. The trend of light curves for the system in its high state follows that of the low state for a large fraction of the phase interval from phase 0 to phase 0.4 since, starting at phase 0.4, the cyclotron feature is visible, and the primary intensity hump of the light curves near phase 0.7 when the system is in the high state did not appear on the curve when it was in the low state. Those facts contradict predictions of the two-pole model.

Long-term photometric behavior of the eclipsing Z Cam-type dwarf nova AY Psc

New eclipse timings of the Z Cam-type dwarf nova AY Psc were measured and the orbital ephemeris was revised. In addition, based on long-term AAVSO data, the outburst behaviors were also explored. Our analysis suggests that normal outbursts are quasi-periodic, with an amplitude of 2.5（4-0.1） mag and a period of - 18.3（4-0.7） d. The amplitude vs. recurrence-time relation ofAY Psc is discussed, and we conclude that this relation may represent general properties of dwarf nova outbursts. The observed standstill ends with an outburst, which is inconsistent with the general picture of Z Cam- type stars. This unusual behavior was considered to be related to mass-transfer outbursts. Moreover, the average luminosity Is brighter during standstills than during outburst cycles. The changes in brightness mark variations in M2 due to the fact that the disk of AY Psc is nearly steady state.M2 value was limited to the range from 6.35 × 10-9 to 1.18 × 10-8 M yr-1. More detailed examination shows that there are a few small outbursts present during standstills. These events with amplitudes of - 0.5 - 0.9 mag are very similar to the stunted outbursts reported in some nova-like cataclysmic variables. We discussed several possible mechanisms and suggested that the most reasonable mechanism for these stunted outbursts is a changing mass-transfer rate.

A Photometry Campaign for IR Geminorum in Quiescence

We report a V band photometry of the SU UMa star IR Gem at quiescence in January 2002. The observations were made with two telescopes spaced ~ 160° apart in longitude. Several photometric modulations have been found. One gives a period of 98.50(13) min, exactly equal to the orbital period determined spectroscopically. Two others occasionally strengthen and seem to be positive and negative superhumps with periods of 103.6(4) and 95.4(4) min, 5.2 % longer and 3.1 % shorter than the orbital period, respectively. A signal at ~ 0.6 c/d in the power spectrum is roughly consistent with the expected period of nodal precession of the disk. There is a puzzling peak at 0.21(3) c/d corresponding to the ~ 4.3 d sine wave seen in the raw light curve. We suspect it to be a beat frequency between the frequencies of apsidal and nodal precessions of the disk. Quasi-periodic cycles with amplitudes 0.15–0.6 mag can be seen in the light curve. The mechanism underlying this modulation is not clear.

Spectroscopic and photometric observations of symbiotic nova PU Vul during 2009–2016

A new set of low-resolution spectral and UBVJHKL-photometric observations of the symbi- otic nova PU Vul is presented. The binary has been evolving after its symbiotic nova outburst in 1977 and now it is in the nebular stage. It is found that the third orbital cycle （after 1977） was characterized by great changes in associated light curves. Now, PU Vul exhibits a sine-wave shape in all the light curves （with an amplitude in the U band of about 0.7 mag）, which is typical for symbiotic stars in the quiescent state. Brightness variability due to pulsations of the cool component is now clearly visible in the VRI light curves. The amplitude of the pulsations increases from 0.5 mag in the V band to 0.8 mag in the I band. These two types of variability, as well as a very slow change in the physical parameters of the hot component due to evolution after the outburst of 1977, influence the spectral energy distribution （SED） of the system. The variability of emission lines is highly complex. Only hydrogen line fluxes vary with orbital phase. An important feature of the third orbital cycle is the first emergence of the OVI, 6828A Raman scattering line. We determine the temperature of the hot component by means of the Zanstra method applied to the He II, 4686A line. Our estimate is about 150000 K for the spectrum obtained near orbital maximum in 2014. The VO spectral index derived near pulsation minimum corresponds to M6 spectral class for the cool component of PU Vul.

CCD Time-Resolved Photometry of Four Newly Discovered CVs

We present time resolved optical light curves in R bands obtained from differential photometry on sequential CCD frams of 4 new discovered high galactic latitude CVs, which are discovered by our spectroscopic observations of the optical identification of ROSAT X ray sources. The analysis of the light curves shows repeatable periodicity in these objects. J020348 7+295921 exhibits 0 5m variation with orbital period of 258 min. J062518 2+733433 reveals a 0 3 mag modulation with orbital period of 254min. J230949 6+213523 shows probably both orbital period of 207 min and WD spin period of 25 min. J232953 9+062814 present short period of 32min, indicating a magnetic system.

A Spectroscopic Study of the SU UMa-type Dwarf Nova YZ Cnc during its 2002 Superoutburst

We report on time-resolved spectroscopic observations of the SU Ursae Majoris dwarf nova, YZ Cnc for over llh on two nights during its 2002 January superoutburst. The spectra on the first day only showed absorption-line profiles, while on the second day the lines showed “W” profiles with blue and red troughs. The radial velocity curve of the absorption troughs and emission peaks of H/3 has an amplitude of 49±10 km s^-1 and a phase offset of -0.07±0.04, which are very similar to those measured in quiescence. However, the γ velocity deviates strongly from the systemic velocity measured in quiescence, by some ±60 km s^-1. Large shifts of -70 km s^-1 in the orbital-averaged velocity and -0.09 in the phase are also found in our observations. All these features can be well explained by a precessing, eccentric disk.

Revisiting the X-ray emission of the asynchronous polar V1432 Aql

As the only eclipsing asynchronous polar,V1432 Aql provides an excellent laboratory to study the interaction between the accreted matter and the magnetic field.Here,we report an analysis of the X-ray data from the contemporaneous NuSTAR and Swift-XRT observations.The X-ray data present a profile with a low-intensity state for almost half an orbital period,a dip at 0.6 phase,and a peak at 0.75 phase,which suggests that there was only one accretion region during the observation and the claim is supported by the spectral analysis.The comparison with the previous data indicates that the X-ray data have an orbital modulation,as the case in BeppoSAX,rather than a spin one observed in ROSAT.We attribute the orbit and spin modulations to the different accretion geometries at work.The spectral analysis of the wide-band data presents a significant reflection effect,a commonly observed soft X-ray temperature,and the energy balance in V1432 Aql.Additionally,we obtained a low total accretion rate of 1.3×10~(-10)M yr~(-1)and a high specific accretion rate of 3.8 g cm~(-2)s~(-1)which explains the strong reflection from the surface of the white dwarf.However,due to its complex emission,a more physical understanding of its accretion geometry is still outstanding.

Near-infrared studies of nova V5584 Sgr in the pre-maximum and early decline phase

We present near-infrared spectroscopic and photometric observations of nova V5584 Sgr taken during the first 12 d following its discovery on Oct. 26.439 UT2009. The evolution of the spectra is shown from the initial P Cygni phase to an emission line phase. The prominent carbon lines seen in the JHK spectra closely match those observed in an Fe II class nova outburst. The spectra show first-overtone CO bands in emission between 2.29-2.40 μm. By examining WISE and other publicly available data, we show that the nova underwent a pronounced dust formation phase between February- April 2010.

1RXS J232953.9+062814: a New SU UMa Dwarf Nova below the Period Minimum

RXS 1232953.9+062814 was identified as a cataclysmic variable by Wei et al. (1999). Four low-resolution spectra of 1RXS J232953.9+062814 were obtained with the 2.16-rn telescope of the National Astronomical Observatories, of which two were at outburst, and two were at quiescence. The system is about 16.8 B and 16.5 V at quiescence, and 12.6 B and 12.6 V at outburst. The quiescent spectra were dominated by double-peaked Balmer emissions, which indicates a hydrogen-rich system with a high-inclination accretion disc. MgH and TiO absorption bands appeared in the quiescent spectrum which implies a companion with a spectral type of early M dwarf. If we take it as a MO dwarf, then the system is located at a distance of 350 pc with a proper motion velocity 150 km s-1. The superhump period of 0.046311 days was confirmed by our V photometry. The short period and the hydrogen-rich nature reveal that this system is another SU Ursae Majoris-type dwarf nova below the period minimum after V485 Centauri. 1RXS J23 2953.9+062814 is one of the most important systems for studying the evolutionary scenario of cataclysmic variables since it is much brighter than V485 Cen.

Damage of Flood-causing Rainstorm to Towns in Zhumadian City and Its Countermeasures for Disaster Reduction

Based on meteorological data of Zhumadian City in the past 56 years, the damage of flood-causing rainstorm to towns in Zhumadian City as well as its cataclysm form, influencing system, cataclysm characteristics and action mechanism were analyzed to discuss the characteristics and rules of damage caused by flood-causing rainstorm. Meanwhile, countermeasures against flood-causing rainstorm cataclysm in Zhumadian City were proposed to provide scientific references for early warning and monitoring of flood-causing rainstorm as well as flood control and disaster mitigation.

Empirical Study of Hybrid Optimization Strategy for Evolutionary Testing

Evolutionary testing (ET) is an effective test case generation technique which uses some meta-heuristic search algorithm, especially genetic algorithm, to generate test case automatically. However, the population prematurity problem may decrease the performance of ET. In this paper, a hybrid optimization strategy is proposed based on extended cataclysm which integrates both static configuration strategies and dynamic optimization strategy. Dynamic optimization strategy included the optimization of initial population and the dynamic population optimization based on extended cataclysm, where the diversity of population was monitored during the evolution process of ET, and once the population prematurity was detected, extended cataclysm operation was used to renew the diversity of the population. Experimental results show that the hybrid optimization strategy can improve the performance of ET.

家园 灾难

Sierra公司的一部《Homeworld（家园）》在向玩家们充分展现空间RTS巨大魅力的同时，更是勇夺了1999年紧出色RTS之一的头衔。而且谁也没有料到，在此之后的3个月后，Sierra公司再次发威，捧出了《Homeworld》最新的资料片——《Cataclysm(实难）》，不禁让所有的《家园》迷欣喜若狂。

Observatory science with eXTP

In this White Paper we present the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to Observatory Science targets. These include flaring stars, supernova remnants, accreting white dwarfs, low and high mass X-ray binaries, radio quiet and radio loud active galactic nuclei, tidal disruption events, and gamma-ray bursts. eXTP will be excellently suited to study one common aspect of these objects: their often transient nature. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Science, the eXTP mission is expected to be launched in the mid 2020s.

Beijing Review Observer:Japan’s Incredible Calmness and Strength OVERCOMING A CATACLYSM The Japanese begin to put their shattered economy back on track

Earthquake,tsunami,nuclear plantb reakdown.Each is a major catast rophe.But Japan has been hit by all of them.Homelessness,economic losses,release of radiation.Each is a huge challenge.Now Japan must face all three.How will Japan respond to the domino-like disaster