Variable Star Status of Two Stars:V204 and I-I-39 in M3

The star 1-1-42 （=vZ1390）, a cluster member in M3, located near the red edge of the instability strip of the horizontal branch, was discovered by Roberts and Sandage as a low amplitude variable, it was designated as V204 in the ＂second catalogue of variable stars in globular clusters＂, but its coordinates given in all versions of this catalogue are wrong since 1955. We argue that V204 is indeed a low amplitude HB variable star, located near to the red edge of the instability strip, with a period of 0.74785d and an amplitude of about 0.04 mag in V. We also find that the red cluster member star 1-1-39 is a low amplitude variable with a period of 1.16^d and amplitude of about 0.03 mag in V which might be pulsating at the second overtone.

Golden Ratio Sinusoidal Sequences and the Multimode Pulsation of the δ Sct Star V784 Cassiopeiae

Non periodic ordered sequences obtained by production rules in formal grammars are applied to the analysis of the multi-periodicity of the δ-Scuti type variable star V784 Cas. An artificial light curve for V784 Cas is generated by a non deterministic derivation in a context-sensitive grammar by concatenation of two sinusoidal fragments following certain word sequences. The two basic building blocks represent temporal segments in a golden ratio and the number of long and short segments in a word are also in a golden ratio.

Long-term photometric behavior of the PMS stars V977 Cep and V982 Cep in the vicinity of NGC 7129

Long-term BVRI photometric light curves of the pre-main sequence stars V977 Cep and V982 Cep during the period from 2000 October to 2016 August are presented. The stars are located in the vicinity of the reflection nebula NGC 7129. Our photometric data show that both stars exhibit strong photometric variability in all optical passbands, which is typical for Classical T Tauri stars. Using our observational data we analyze the reasons for the observed brightness variations. In the case of V977 Cep we identify previously unknown periodicity in its light curve.

Spectroscopic and photometric studies of a candidate pulsating star in an eclipsing binary:V948 Her

Eclipsing binary stars with a pulsating component are powerful tools that allow us to probe the stellar interior structure and the evolutionary statuses with a good accuracy. Therefore, in this study, spectroscopic and photometric examinations of an eclipsing binary system V948 Her are presented. The primary component of the system is classified to be a candidate 3 Scuti variable in the literature. The fundamental stellar, atmospheric and orbital parameters, and the surface abundance of the star were determined and the pulsation behaviour was investigated in this study. The orbital parameters were derived by the analysis of radial velocity and SuperWASP light curves. The spectral classification was found to be F2V. The initial atmospheric parameters of the primary component were derived by analysis of the spectral energy distribution and hydrogen lines. The final atmospheric parameters and chemical abundances of the primary component were obtained by using the method of spectrum synthesis. As a result, the final atmospheric parameters were determined as Teff= 7100±200 K, log 9= 4.34±0.1 cgs and ζ = 2.2 4± 0.2 km s^-1. The surface abundance was found to be similar to solar. The fundamental stellar parameters of both components were also obtained to be M = 1.722 4±0.123, 0.762 4± 0.020 Me, R = 1.655 4± 0.034,M,R= 0.689 ± 0.016 R for primary and secondary components, respectively. The pulsation characteristic of the primary component was examined using SuperWASP data and the pulsation period was found to be ~0.038 d. The position of the primary pulsating component was also obtained inside the instability strip of δ Sct stars. The primary component of V948 Her was defined to be a Sct variable.

V2551 Cyg:a pulsating star with enigmatic peculiarities

Intensive photometric and spectral observations of the variable star V2551 Cyg are presented.The light curve shape reveals that the target is a pulsating star, contrary to its previous classification as an eclipsing binary. The period and amplitude of the light curve, the amplitudes of color changes and the radial velocity curve of V2551 Cyg are similar to those of a high-amplitude δ Scuti variable. The target seems to pulsate with the fundamental mode. However, V2551 Cyg exhibits several important peculiarities：（i） the decreasing branch of its light curve is steeper than the increasing one;（ii） the radial velocity curve has a flat section in the phase range 0.7-1.2 and short increase of the negative radial velocity at phase 0.7;（iii） the rotational velocity is quite big for a HADS star;（iv） the Fourier coefficients of V2551 Cyg are quite different from those of HADS stars. The target classification is difficult due to these peculiarities.

A long-term UBVRI photometric study of the pre-main sequence star V350 Cep

Results from UBVRI optical photometric observations of the pre-main se- quence star V350 Cep during the period 2004-2014 are presented. The star was dis- covered in 1977 due to its remarkable increase in brightness by more than 5 mag （R）. In previous studies, V350 Cep was considered to be a potential FUor or EXor eruptive variable. Our data suggest that during the period of observations the star maintains its maximum brightness with low amplitude photometric variations. Our conclusion is that V350 Cep was probably an intermediate object between FUors and EXors, similar to V1647 Ori.

New CCD photometric investigation of high amplitude δ Scuti star V2455 Cyg

New V-band CCD observations of variable star V2455 Cyg were performed during two nights in September 2017. According to all times of maximum light and new maxima, the O-C curve was analyzed.The period changes of V2455 Cyg were investigated and the rate of increasing period was obtained to be(1/P) d P/dt = 1.99 × 10^-7 yr-1. Frequency analysis indicated that V2455 Cyg pulsates with the radial p mode and the fundamental frequency is 10.61574 d-1. Physical parameters of V2455 Cyg at mean temperature were determined(e.g., R = 2.52 R⊙and M = 1.92 M⊙). The position of this star in the H-R diagram confirms that V2455 Cyg is a high amplitude δ Scuti star.

Spectral study of V565 Mon: probable FU Ori-like or chemically peculiar star

We present a detailed spectroscopic study of pre-main sequence star V565 Mon,which is the illuminating star of the Parsamian 17 cometary nebula.Observations were performed with the 2.6 m telescope in Byurakan Astrophysical Observatory on 2018 February 15.Radial velocities and equivalent widths of the most prominent lines of V565 Mon are presented.We build the spectral energy distribution and estimate the main parameters of the star,for example the obtained bolometric luminosity of V565 Mon is L_(V565)≈130 L_(⊙).Considering all features of V565 Mon,we come to the conclusion that this young intermediate-mass star belongs to some intermediate class between T Tau and HAeBe stars.Very unusual for a young star is the presence of strong absorption BaⅡlines in the spectrum.Possible explanations on this issue are discussed.Hence,we think that V565 Mon is a unique example,which can help to understand some open questions involved in the problem of nucleosynthesis in young stars.

The determination of white dwarf parameters in dwarf novae by optical spectral modeling

This paper presents the results of a model analysis of optical spectra and determination of the parameters of three individual SU UMa and WZ Sge type dwarf novae.The moderate resolution spectra of TY Psc,FL Psc and V455 And were obtained at the 6-m BTA of the SAO RAS in the low state of these systems with the determination of white dwarf radiation.The theoretical spectra were calculated using the grid models of hydrogen dwarf atmospheres of white dwarfs by varying the parameters(T_(eff) and log g) to reach the best agreement with the observed ones.We highlight different effects of the parameters on the shape and intensity of the HI lines.Therefore,it is possible to unambiguously determine T_(eff) and log g from the analysis of observations.The fundamental parameters of white dwarfs(M and R) were found by comparing the parameters of atmospheres with theoretical models of the internal structure.The obtained parameters of the primaries of TY Psc,FL Psc and V455 And are consistent with the average values for SU UMa and WZ Sge systems.As a result,we demonstrate the efficiency of the method for determining the parameters of such systems based on the analysis of a limited set of observed optical spectra.

Simultaneous photometric and spectral analysis of a new outburst of V1686 Cyg

We present an analysis of the optical observations of Herbig Ae/Be(HAeBe)star V1686 Cyg,which is associated with a small isolated star-forming region around HAeBe star BD+40?4124.We observed this star as a part of our project investigating young eruptive stars.Observations were conducted on the 2.6-m telescope of Byurakan Observatory from 2015 to 2017.In this period,we obtained direct images of V1686 Cyg and 14 medium-and low-resolution spectra.In the course of observations,we noticed that this star underwent an atypical brightness outburst.After data reduction,we found that the full rise and decline in the brightness of V1686 Cyg had an amplitude of almost 3 magnitudes and lasted about 3 months.We were also able to track changes in the stellar spectrum during the outburst,which are correlated with the photometric variations.

Linear nonadiabatic pulsation models of the double-mode Cepheid V371 Per

A recently found double-mode Cepheid with the shortest known period in our Galaxy and abnormal period ratio, V371 Per, is investigated by linear nonadiabatic pulsation models. V371 Per is likely to be crossing the instability strip for the first time, because the mass derived from pulsation models is larger than the evolution mass for the second or higher crossing objects. This result seems to support the conclusion obtained from spectroscopic observation. We also found that models with observed period and period ratio of V371 Per need to have mass and Teff in a narrow range which shifts as heavy element abundance Z changes. We have checked the agreement between Teffranges estimated observationally and derived from pulsation models using observational Z. We found that those ranges overlap marginally. We need more spectroscopic estimations of Teff and [Fe/H], and more photometric monitoring to estimate the evolutional period change for confirmation of our result.

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.