BV(RI )c photometric study of three variable PMS stars in the field of V733 Cephei

This paper reports results from the first long-term BV(RI)c photometric CCD observations of three variable pre-main-sequence stars collected during the period from February 2007 to January 2020. The investigated stars are located in the field of the PMS star V733 Cep within the Cepheus OB3 association. All stars from our study show rapid photometric variability in all-optical passbands. In this paper, we describe and discuss the photometric behavior of these stars and the possible reasons for their variability. In the light variation of two of the stars, we found periodicity.

Photometric studies of two W UMa type variables in the field of distant open cluster NGC 6866

We present photometric analysis of the two W UMa type binaries identified in the field of distant open star cluster NGC 6866. Although these systems, namely ID487 and ID494, were reported by Joshi et al., a detailed study of these stars has not been carried out before. The orbital periods of these stars are found to be 0.415110±0.000001 day and 0.366709±0.000004 day, respectively. Based on the photometric and infrared colors, we find their respective spectral types to be K0 and K3. The photometric light vari- ations of both stars show the O＇Connell effect which can be explained by employing a dark spot on the secondary components. The V and I band light curves are analyzed using the Wilson-Devinney （WD） code and relations given by Gazeas which yield radii and masses for the binary components of star ID487 of R1 = 1.24 ± 0.01R,R2 = 1.11 4- 0.02Re, and M1 = 1.24 ± 0.02Me, M2 = 0.96 ±0.05Me and for star ID494 of R1 = 1.22 ± 0.02Re, R2 = 0.81 4- 0.01 Re, and M1 = 1.20 4- 0.06 Me, M2 = 0.47 4- 0.01 Me.

On the Identification of N-rich Metal-poor Field Stars with Future Chinese Space Station Telescope

During the long term evolution of globular clusters(GCs), some member stars are lost to the field. The recently found nitrogen-rich(N-rich) metal-poor field stars are promising candidates of these GC escapees, since N enhancement is the fingerprint of chemically enhanced populations in GCs. In this work, we discuss the possibility of identifying N-rich metal-poor field stars with the upcoming Chinese Space Station Telescope(CSST). We focus on the main survey camera with NUV, u, g, r, i, z, y filters and slitless spectrograph with a resolution about 200.The combination of UV sensitive equipment and prominent N-related molecular lines in the UV band bodes well for the identification: the color–color diagram of(u-g) versus(g-r) is capable of separating N-rich field stars from normal halo stars, if metallicity can be estimated without using the information on u-band photometry.Besides, the synthetic spectra show that a signal-to-noise ratio of 10 is sufficient to identify N-rich field stars. In the near future, a large sample of N-rich field stars found by CSST, combined with state-of-the-art N-body simulations will be crucial to deciphering GC-Galaxy co-evolution.

Variable stars in M37

The CCD photometric observations of open star cluster M37(NGC 2099) were carried out up to a limiting magnitude of V ～ 20 in both B and V filters to search for variable stars using a 2k×4k CCD and the 1.3 m telescope at the Vainu Bapu Observatory, Kavalur.A total of 314 stars were in the first observing run, out of which 60 were identified as variables.Eight out of the identified 60 variables are classified as W UMa binary stars.For model fitting, we used PHOEBE based on the W-D code to estimate the physical parameters of these newly detected W UMa binaries that theoretically best match the observed light curves.

The Fifth Edition of the General Catalogue of Variable Stars:experiences in the constellation Centaurus

We have recently announced that the General Catalogue of Variable Stars enters the stage of its fifth, purely electronic edition （GCVS 5.1）. We have included 1408 variable stars in the constellation Centaurus in this new version, GCVS 5.1. Working on this revision, we applied current possibilities from data mining, suggested new variability types for many variable stars and found new light elements for a large number of periodic variables. This paper describes the work completed during the preparation of GCVS 5.1 for Centaurus and discusses in detail a number of the most astrophysically significant cases.

The search for roAp stars: null results and new candidates from Strmgren-Crawford photometry

The rapidly oscillating Ap(roAp) stars exhibit pulsational photometric and/or radial velocity variations on time scales of several minutes, which are essential to test current pulsation models as well as our assumptions of atmospheric structure characteristics. In addition, their chemical peculiarity makes them very interesting for probing stellar formation and evolution in the presence of a global magnetic field. To date, a limited number of only 61 roAp stars is known to show photometric variability. On the other hand, a literature survey yields 619 unique stars that have unsuccessfully been searched for variability of this kind. Str o¨mgren-Crawford uvbyβ photometry of stars from both subgroups was used to investigate whether there is a selection bias for the investigated stars. We also present new photometric measurements(202 hours on 59 different nights) of 55 roAp candidates. We did not detect any new roAp star. Although our detection limits are comparable to other surveys, we also did not find pulsations in the known roAp star HD 12098, which may be a consequence of temporal amplitude changes. On the other hand, we do find some evidence for photometric variability of beta CrB at its spectroscopically derived pulsation period. From the uvbyβ photometry we conclude that the blue border of the roAp instability strip appears observationally well defined, whereas the red border is rather poorly known and studied.Within these boundaries, a total of 4646 candidates were identified which appear worth investigating for short-term pulsational variability.

Long-term V(RI) CCD photometry of pre-main-sequence stars in the association Cepheus OB3

Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are presented.These stars are located in the association Cepheus OB3,in the field of the young star V733 Cephei.Photometric observations,especially concerning the long-term variability of the stars,are missing in the literature.We present the first longterm V(RI)c monitoring for them,that cover 13 years.Results from our study indicate that all of the investigated stars manifest strong photometric variability.The presented paper is a part of our program for the photometric study of pre-main-sequence stars located in active star-forming regions.

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.

Discovery of Four Peculiar Variable Stars

Four stars, GSC 1258–0143, GSC 1986–1665, GSC 3045–0892 and GSC 2983–1597 were found to be new variables during a campaign of CCD photometric monitoring of short-period eclipsing binary stars. The variabilities of these new variables are reported. The main characteristics and probable classifications of the variables are discussed through a preliminary analysis on their light curves. Among these stars, GSC 1258–0143 is classified as a RR Lyr star of sub-type a. Its pulsation period is determined to be about 0.5206 days. The other three stars, are definite variables, but their periods and types of light variations remain unknown.

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.

Investigating variable stars in the open cluster NGC 1912 and its surrounding field

In this work,we studied the variable stars in the open cluster NGC 1912 based on the photometric observations and Gaia DR2 data.More than 3600 CCD frames in B,V,R filters were reduced,and we obtained the light curves that span about 63 hours.By analyzing these light curves,we detected 24 variable stars,including 16 periodic variable stars,seven eclipsing binaries and one star whose type is unclear.Among these 24 variable stars,11 are newly discovered,which are classified as sixγDoradus stars,oneδScuti star,three detached binaries and one contact binary.We also confirmed 13 previously known variable stars.Based on cluster members identified by Cantat-Gaudin et al.(2018),we inferred cluster memberships for these detected variable stars.Using Gaia DR2 data,we plotted a new color-magnitude diagram for NGC1912,and showed the nature of variable cluster members in kinematical properties and heliocentric distance.Among the 24 variable stars,seven variables are probable cluster members,which show homogeneity in kinematic characters and space position with the established cluster members.Four of the seven variable cluster members are the previously discovered stars,consisting of twoγDor stars and twoδSct stars.The remaining three variable cluster members,which are allγDor stars,are firstly detected in this work.The main physical parameters of these variable cluster members estimated from the color-magnitude diagram are log(age/yr)=8.75,[Fe/H]=-0.1,m-M=10.03 mag,and E(B-V)=0.307.

Photometry of δ Sct-type and Related Stars: Results of AD Ari, IP Vir and YZ Boo

Photometric results of three δ Scuti stars, AD Ari, IP Vir and YZ Boo from new observations obtained at the:Xinglong Station of the Beijing Astronom- ical Observatory (BAO) during 2000 aELd 2001 are reported. We present here the preliminary analyses. Detailed studies of these stars based on additional data will be published separately.

Study of variable stars associated with maser sources: G025.65+1.05

We report variation of K-band infrared(IR) emission in the vicinity of the G025.65+1.05 water and methanol maser source. New observational data were obtained with the 2.5 m telescope at the Caucasian Mountain Observatory(CMO) of Moscow State University on 2017–09–21 during a strong water maser flare. We found that the IR source situated close to the maser position had decreased brightness in comparison to archive data. This source is associated with a massive young stellar object(MYSO) corresponding to the compact IR source IRAS 18316–0602(RAFGL 7009 S). A similar decrease in K-brightness of the IR source close to the maser position was observed in March 2011 when the water maser experienced a period of increased activity. The dips in MYSO brightness can be related to the maser flare phases. Maser flares that are concurrent with dips in the IR emission can be explained if the lower IR radiation field enables a more efficient sink for the pumping cycle by allowing IR photons to escape the maser region.

Long-term photometric study of a faint W UMa binary in the direction of M31

We carry out a re-analysis of the photometric data in Rclc bands which were taken during the Nainital Microlensing Survey from 1998 to 2002 with the aim to detect gravitational microlensing events in the direction of M31. Here, we do photometric analysis of a faint W UMa binary CSS_JO04259.3＋410629 identified in the target field. The orbital period of this star is found to be 0.266402±0.000018 d. The photometric mass ratio, q, is found to be 0.28±0.01. The photometric light curves are investigated using the Wilson-Devinney （WD） code and absolute parameters are determined using empirical relations which provide masses and radii of the binary as M1 = 1.19±0.09M⊙, M2 = 0.33±0.02M⊙ and R1 = 1.02±0.04R⊙, R2 = 0.58±0.08Re respectively based on Rc band data. Quite similar values are found by analyzing/c band data. From the photometric light curve examination, the star is understood to be a low mass-ratio overcontact binary of A-subtype with a high fill-out factor of about 47%. The binary system is found to be located approximately at a distance of 2.64±0.03 kpc having a separation of 2.01 ±0.05 Re between the two components.

Abundances of 23 field RR Lyrae stars

We present stellar parameters and abundances of 15 elements （Na, Mg, A1, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Cu, Y and Ba） for 23 field RR Lyrae variables based on high-resolution （R ~ 60 000） and high signal-to-noise （S/N~ 200） spectra obtained using the High Dispersion Spectrograph on the Subaru Telescope. Six stars in the sample have more than one spectrum observed at different pulsation phases. The derived abundance ratios of [X/Fe] for 14 elements （except for Ba） do not vary during the pulsation cycle. An interesting curve of [Ba/Fe] versus phase is detected for the first time and it shows decreasing [Ba/Fe] with increasing temperature at a given metallicity. Combining with data in the literature, abundances of most RR Lyrae stars as a function of [Fe/H] follow the same trends as those of dwarf stars, but [Sc/Fe] and [Y/Fe] ratios of RR Lyrae stars at solar metallicity are lower than those of dwarf stars. The kinematics of RR Lyrae stars indicate that three comparatively metal-rich RR Lyrae stars might originate from the thick disk and they show higher [a/Fe] ratios than RR Lyrae stars with thin disk kinematics. Among 23 RR Lyrae stars, two special objects are found with abnormal abundances; TV Lib has high [a/Fe], [Sc/Fe], [Y/Fe] and [Ba/Fe] ratios while TW Her has solar [a/Fe] but significantly lower [Sc/Fe], [Y/Fe] and [Ba/Fe] ratios as compared with other RR Lyrae stars.

Photometric investigation on the W-subtype contact binary V1197 Her

Multi-color light curves of V1197 Her were obtained with the 2.4 meter optical telescope at the Thai National Observatory and the Wilson-Devinney(W-D)program was used to model the observational light curves.The photometric solutions reveal that V1197 Her is a W-subtype shallow contact binary system with a mass ratio of q=2.61 and a fill-out factor of f=15.7%.The temperature difference between the primary star and secondary star is only 140 K in spite of the low degree of contact,which means that V1197 Her is not only in geometrical contact configuration but is also already under thermal contact status.The orbital inclination of V1197 Her is as high as i=82.7?,and the primary star is completely eclipsed at the primary minimum.The totally eclipsing characteristic implies that the determined physical parameters are highly reliable.The masses,radii and luminosities of the primary star(star 1)and secondary star(star2)are estimated to be M1=0.30(1)M⊙,M2=0.77(2)M⊙,R1=0.54(1)R⊙,R2=0.83(1)R⊙,L1=0.18(1)L⊙and L2=0.38(1)L⊙.The evolutionary statuses of the two component stars are drawn in the Hertzsprung-Russell diagram,showing that the less massive but hotter primary star is more evolved than the secondary star.The period of V1197 Her is decreasing continuously at a rate of d P/dt=-2.58×10^-7 day·year^-1,which can be explained by mass transfer from the more massive star to the less massive one at a rate of dM2/dt=-1.61×10^-7 M⊙year^-1.The light curves of V1197 Her are reported to show the O’Connell effect.Thus,a cool spot is added to the more massive star to model the asymmetry in the light curves.

Time-resolved CCD photometry and time-series analysis of the RR Lyrae type star RR Gem

We present the results of a time-resolved photometric and time-series analysis of an RR Lyrae type star RR Gem. The main results are as follows: we found RR Gem’s pulsation period, 0.39689 d, and its V and I mean magnitudes, 11.277(V) and 11.063(I) mag respectively. We confirm its variability type as RRab/BL because it manifests the Blazhko effect, and it also exhibits asymmetric light curves(steep ascending branches), periods from 0.3 to 1.0 d and amplitudes from 0.3 to 2 mag in V. They are fundamental mode pulsators.

Photometric and Spectroscopic Study of Two Low Mass Ratio Contact Binary Systems:CRTS J225828.7-121122 and CRTSJ030053.5+230139

The study reports photometric and spectroscopic observations of two recently recognized contact binary systems.Both systems show total eclipses and analysis of the light curves indicates both have very low mass ratios of less than 0.3.We derive absolute parameters from color and distance based calibrations and show that,although both have low mass ratios,they are likely to be in a stable orbit and unlikely to merge.In other respects,both systems have characteristics similar to other contact binaries with the secondary larger and brighter than their main sequence counterparts and we also find that the secondary is considerably denser than the primary in both systems.

Carbon star CGCS 673 identified as a semi-regular variable star

This study reports that the carbon star CGCS 673 is a semi-regular(SR)variable star with a period of 135 d and an amplitude of 0.18mag in the V-band.The light curve obtained by this study correlates well with the SR classification as the photometric data obtained show noticeable periodicity in the light changes of CGCS 673 that is occasionally interrupted by a period of irregular variability.The derived period and colour index obtained from our data and those from professional databases indicate that the attributes of this star fall within the parameters of the SR class of variable stars.Following our notification of the discovery that this star is a variable source,CGCS 673 has received the AAVSO Unique Identifier of(AAVSO UID)000-BMZ-492.

Photometric and Spectroscopic Analysis of LBV Candidate J004341.84+411112.0 in M31

We study Luminous Blue Variable(LBV)candidate J004341.84+411112.0 in the Andromeda galaxy.We present optical spectra of the object obtained with the 6 m telescope of BTA SAO RAS.The candidate shows typical LBV features in its spectra:broad and strong hydrogen lines and the He I lines with P Cygni profiles.Its remarkable spectral resemblance to the well known LBV P Cygni suggests a common nature of the objects and supports LBV classification of J004341.84+411112.0.We estimate the temperature,reddening,radius and luminosity of the star using its spectral energy distribution.Obtained bolometric luminosity of the candidate(M_(bol)=-10.41±0.12 mag)is quite similar to those of known LBV stars in the Andromeda galaxy.We analyzed a ten year light curve of the object in R filter.The candidate demonstrates photometric variations of the order of 0.4 mag,with an overall brightness increasing trendΔR>0.1 mag.Therewith,the corresponding color variations of the object are fully consistent with LBV behavior when a star become cooler and brighter in the optical spectral range with a nearly constant bolometric luminosity.LBV-type variability of the object,similarity of its spectrum and estimated luminosity to those of known LBVs allow us to classify J004341.84+411112.0 as an LBV.