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* dp/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(sun) and M = 1.92 M(sun)). The position of this star in H-R diagram confirms that V2455 Cyg is a high amplitude Delta Scuti star.
The preliminary results of a three-site CCD photometric campaign are reported. The $δ$ Scuti variable V650 Tauri belonging to the Pleiades cluster was observed photometrically for 14 days on three continents during 2008 November. An overall run of 164 hr of data was collected. At least five significant frequencies for V650 Tauri have been detected.
Preliminary results on the discovery and follow-up observations of a new $δ$ Scuti pulsator in the Cygnus field are presented. The variability of the star HD 207331 was detected while testing a Strömgren spectrophotometer attached to the H.L. Johnson 1.5-m telescope at the San Pedro Mártir observatory, México. CCD photometric data acquired soon after confirmed its variability. A few hours of $uvby$ differential photoelectric photometry during three nights revealed at least two beating periods. A two-site observational campaign carried out during one week in 2009 confirms the multi-periodic nat…
We report on a multi-site photometric campaign on the high-amplitude $δ$ Scuti star V2367 Cyg in order to determine the pulsation modes. We also used high-dispersion spectroscopy to estimate the stellar parameters and projected rotational velocity. Time series multicolour photometry was obtained during a 98-d interval from five different sites. These data were used together with model atmospheres and non-adiabatic pulsation models to identify the spherical harmonic degree of the three independent frequencies of highest amplitude as well as the first two harmonics of the dominant mode. This was…
The results of an observational campaign on the new $δ$ Scuti pulsator \astrobj{HD~207331} are reported. The star was observed photometrically from August 26 to September 2, 2009 from the Observatorio San Pedro Mártir (0.84-m telescope, Mexico) and the Observatorio del Teide (0.80-m telescope, Spain). An overall run of 53.8 h of useful data was collected from the two sites. Four oscillation frequencies for \astrobj{HD~207331} have been found above a 99\% confidence level. These results confirm the multiperiodic pulsation nature of the star suggested in previous observations with sparse data. S…
We have obtained CCD photometry and medium-resolution spectroscopy of a number of $δ$ Scuti and $γ$ Doradus stars in the Kepler field-of-view as part of the ground-based observational efforts to support the \textit{Kepler} space mission. In this work we present the preliminary results of these observations.
The Hipparcos catalog contains stars suspected to be δ Scuti variables for which extensive ground-based observations and characterization of variability are necessary. Our aim was to characterize variability of 13 candidates to δ Scuti type stars. We obtained 24 215 CCD images and analyzed stellar light curves using the Period04 program. Twelve δ Scuti candidate stars have been characterized as pulsating with frequencies intrinsic to δ Scuti stars: HIP 2923, HIP 5526, HIP 5659, HIP 11090, HIP 17585, HIP 74155, HIP 101473, HIP 106219, HIP 107786, HIP 113487, HIP 115093, HIP 115856. Five of them…
We present a CCD photometric study of the star with ASAS ID 134738 + 0410.1 using V band observations obtained from the $IUCAA$ Girawali Observatory (IGO) 2-metre telescope, India. The star was selected from the $δ$ Scuti database of All Sky Automated Survey (ASAS) (Pojmanski 2002). Our analysis reveals that the star is not a $δ$ Scuti variable but is in fact a W UMa type contact binary with an orbital period of 0.2853067 day. Two new times of primary and secondary minima were determined from the observed data. A preliminary solution obtained using the Wilson-Devinney light curve modelling tec…
We present new results from optical photometric and spectroscopic observations of the eruptive pre-main sequence star V2493 Cyg (HBC 722). The object has continued to undergo significant brightness variations over the past few months and is an ideal target for follow-up observations. We carried out CCD BVRI photometric observations in the field of V2493 Cyg ("Gulf of Mexico") from August 1994 to April 2012, i.e. at the pre-outburst states and during the phases of the outburst. We acquired high, medium, and low resolution spectroscopy of V2493 Cyg during the outburst. To study the pre-outburst …
The multi-color CCD photometric study of 27 Delta Scuti stars is presented. By using approximately three years of photometric observations, we obtained the times of maxima and magnitude changes during the observation time interval for each star. The ephemerides of our Delta Scuti stars were calculated based on the Markov Chain Monte Carlo (MCMC) method using the observed times of maxima and the period of the stars' oscillations. We used the Gaia EDR3 parallaxes to calculate the luminosities and also the absolute magnitudes of these Delta Scuti stars. The fundamental physical parameters of all …
This study sums up a major part of the red giant V449 Cygni measurements for the years 1974 through 2022, obtained by visual and CCD GEOS observers, the Unione Astrofili Italiani, and various automatized telescopes. It appears that the light variations of V449 Cyg in the years 1970-1990 corresponded more to an L-type star according to the GCVS classification, with irregular amplitude variations, sometimes marked by a quasi-periodicity of about 100 days. Since the mid-1990s, these variations have become more regular, with an amplitude of about 0.7 magnitude in V, and a period of about 54,1 days…
We present the results of unfiltered and UBVR_cI_c band CCD photometry fast nova V2467Cyg. Our analysis of the data gives two distinct frequencies corresponding to periods of ~3.8h and ~35 min. The observed light curve of V2467 Cyg is typical for an intermediate polar.
A photometric variability study of a sample of northern field stars, which previously classified as either PMS or Herbig Ae/Be objects, has been undertaken with the purpose of detecting δ Scuti-type pulsations. Determination of physical parameters for these stars has also been carried out to locate them on the HR diagram and check the instability strip for this type of pulsators. Multichannel photomultiplier and CCD time series photometry in the uvby Strömgren and BVI Johnson bands were obtained during four consecutive years from 2007 to 2010. The light curves have been analysed, and a variabi…
Revisiting bright delta Scuti stars and their period-luminosity relation with TESS and Gaia DR3
University of Pennsylvania（宾夕法尼亚大学）；Sydney Institute for Astronomy, School of Physics, University of Sydney（悉尼大学物理学院天体物理研究所）；Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University（奥胡斯大学物理与天文系恒星天体物理中心）；Centre for Astrophysics, University of Southern Queensland（昆士兰南部大学天体物理中心）；Institute for Astronomy, University of Hawai‘i（夏威夷大学天体物理研究所）
CCD observations of 68 eclipsing binary systems, candidates for containing δ Scuti components, were obtained. Their light curves are analysed using the PERIOD04 software for possible pulsational behaviour. For the systems QY Aql, CZ Aqr, TY Cap, WY Cet, UW Cyg, HL Dra, HZ Dra, AU Lac, CL Lyn and IO UMa, complete light curves were observed due to the detection of a pulsating component. All of them, except QY Aql and IO UMa, are analysed with modern astronomical softwares in order to determine their geometrical and pulsational characteristics. Spectroscopic observations of WY Cet and UW Cyg were…
Metallic-line A (Am) stars are main-sequence stars of around twice the mass of the Sun that show element abundance peculiarities in their spectra. The radiative levitation and diffusive settling processes responsible for these abundance anomalies should also deplete helium from the region of the envelope that drives delta Scuti pulsations. Therefore, these stars are not expected to be delta Scuti stars, which pulsate in multiple radial and nonradial modes with periods of around 2 hours. As part of the NASA TESS Guest Investigator Program, we proposed photometric observations in 2-minute cadenc…
This paper presents a large amount of observations for the $δ$ Scuti star AN Lyncis carried out in 2001--2012. The extensive observations include two tri-continent campaigns coordinated in 2002 and 2011, respectively, and several single-site contributions throughout the period. The data in total have more than 104100 raw CCD frames and photoelectric records, which consist of 165 nights (about 816 hours) spanning over 3778 days. The final reduced light curves have more than 26500 data points (including those 3462 unpublished BYU data), from which we determined 306 new timings of maximum light. …
We present new multicolour (UBVRcIc) photometric observations of classical symbiotic stars, EG And, Z And, BF Cyg, CH Cyg, CI Cyg, V1329 Cyg, TX CVn, AG Dra, Draco C1, AG Peg and AX Per, carried out between 2007.1 and 2011.9. The aim of this paper is to present new data of our monitoring programme, to describe the main features of their light curves and to point problems for their future investigation. The data were obtained by the method of the classical photoelectric and CCD photometry.
We have conducted a 1.5 year-long variability study of the stars in the Cygnus OB2 association, the region in the northern hemisphere with the highest density of optically visible massive stars. The survey was conducted using four pointings in the Johnson $R$ and $I$ bands with a 35 cm Meade LX200-ACF telescope equipped with a 3.2 Mpixel SBIG ST10-XME CCD camera and includes 300+ epochs in each filter. A total of 1425 objects were observed with limiting magnitudes of 15 in $R$ and 14 in $I$. The photometry was calibrated using reference stars with existing $UBVJHK$ photometry. Bright stars hav…
New Multi-color $B$ $V$ $R_c$ $I_c$ photometric observation are presented for W UMa type eclipsing binary V1073 Cyg. The multi-color light curves analysis with the Wilson-Devinney(W-D) procedure acquired the absolute parameters of this system, showing that V1073Cyg is a shallow contact binary system with fill-out factor $f=0.124(\pm0.011)$. We collected all available times of light minima spanning 119 years including CCD data to construct the O-C curve and made detailed O-C analysis. The O-C diagram shows that the period change is complex. There exist a long-term continuous decrease and a cycl…
Spectroscopic iron-to-hydrogen ratios, radial velocities, atmospheric parameters, and new photometric analyses are presented for 41 RR Lyrae stars (and one probable high-amplitude delta Scuti star) located in the field-of-view of the Kepler space telescope. Thirty-seven of the RR Lyrae stars are fundamental-mode pulsators (i.e., RRab stars) of which 16 exhibit the Blazhko effect. Four of the stars are multiperiodic RRc pulsators oscillating primarily in the first-overtone mode. Spectroscopic [Fe/H] values for the 34 stars for which we were able to derive estimates range from -2.54 +/- 0.13 (NR…
Combining with our newest CCD times of light minimum of EM Cygni, all 45 available times of light minimum including 7 data with large scatters are compiled and the updated O-C analysis is made. The bestfit for the O-C diagram of EM Cygni is a quadratic-plus-sinusoidal fit. The secular orbital period decrease rate -2.5(\pm 0.3)x10^{-11} s s^{-1} means that magnetic braking effect with a rate of mass loss via stellar wind, 2.3x10^{-10}Msunyr^{-1}, is needed for explaining the observed orbital period decrease. Moreover, for explaining the significant cyclical period change with a period of \sim 1…
New CCD photometry is presented for the hot overcontact binary DK Cyg, together with reasonable explanations for the light and period variations. Historical light and velocity curves from 1962 to 2012 were simultaneously analyzed with the Wilson-Devinney (W-D) synthesis code. The brightness disturbances were satisfactorily modeled by applying a magnetic cool spot on the primary star. Based on 261 times of minimum light including 116 new timings and spanning more than 87 yrs, a period study reveals that the orbital period has varied due to a periodic oscillation superposed on an upward parabola…
Young double star V1318 Cyg, which is associated with a small isolated star-forming region around HAeBe star BD+40o4124, has very unusual photometric and spectral behavior. We present results of photometric and spectroscopic observations in the optical range. We carried out BVRI CCD photometric observations of V1318 Cyg from 2015 Sept. to 2017 July. For the same period we acquired medium- and low-resolution spectra. Observations were performed with the 2.6 m telescope. We analyze the historical light curve for V1318 Cyg and demonstrate that the southern component, V1318 Cyg S, after being rath…
We present new multicolour UBVRcIc photometric observations of symbiotic stars, EG And, Z And, BF Cyg, CH Cyg, CI Cyg, V1016 Cyg, V1329 Cyg, AG Dra, RS Oph, AG Peg, AX Per, and the newly discovered (August 2018) symbiotic star HBHA 1704-05, we carried out during the period from 2011.9 to 2018.75. Historical photographic and visual/V data were collected for HBHA 1704-05, FG Ser and AE Ara, AR Pav, respectively. The main aim of this paper is to present our original observations of symbiotic stars and to describe the most interesting features of their light curves. For example, periodic variation…
We present new multiband CCD photometry for WZ Cyg made on 22 nights in two observing seasons of 2007 and 2008. Our light-curve synthesis indicates that the system is in poor thermal contact with a fill-out factor of 4.8% and a temperature difference of 1447 K. Including our 40 timing measurements, a total of 371 times of minimum light spanning more than 112 yr were used for a period study. Detailed analysis of the $O$--$C$ diagram showed that the orbital period has varied by a combination with an upward parabola and a sinusoid. The upward parabola means the continuous period increase and indi…
We present the results of the $UBVI_C$ variability survey in the young open cluster NGC 6611 based on observations obtained during 34 nights spanning one year. In total, we found 95 variable stars. Most of these stars are classified as periodic and irregular pre-main sequence (PMS) stars. The analysis of the $JHK_S$ 2MASS photometry and four-colour IRAC photometry revealed 165 Class II young stellar sources, 20 of which are irregular variables and one is an eclipsing binary. These classifications, complemented by $JHK$ UKIDSS photometry and $riHα$ VPHAS photometry, were used to identify 24 can…
The Mt. Suhora M\,dwarf survey searching for pulsations in low mass main sequence stars has acquired CCD photometry of 46 M\,dwarf stars during the first year of the project (Baran et al 2011). As a by-product of this search hundreds field stars have been checked for variability. This paper presents our initial result of a search for periodic variables in field stars observed in the course of the survey. On the basis of the periodicity and the shape of the light curves, eight new variables has been detected, among which five are $δ$ Scuti stars and three likely RR Lyrae stars. Although variati…
Having a need to perform differential photometry for tens of thousands stars in a several square degrees field, we developed Astrokit program. The software corrects the star brightness variations caused by variations of atmospheric transparency: to this end, the program selects for each star an individual ensemble of reference stars having similar magnitudes and positions in the frame. With ten or more reference stars in the ensemble, the differences between their spectral types and the spectral type of the object studied become unimportant. Astrokit searches for variable stars using Robust Me…
The study of open clusters and their short period variable stars is fundamental in stellar evolution. Because the cluster members are formed in almost the same physical conditions, they share similar stellar properties such age and chemical composition. The assumption of common age, metallicity and distance impose strong constraints when modeling an ensemble of short period pulsators belonging to open clusters (e.g. Fox Machado et al., 2006). Very recently, Luo et al. (2009) carried out a search for variable stars in the direction of NGC 6811 with CCD photometry in B and V bands. They detected…
As extensive ground-based observations and characterisation of different variable stars are of the utmost importance in preparing optimal input catalogues for space missions, our aim was to search for new variable stars in selected fields of the northern sky. We obtained 24470 CCD images and analysed photometric time series of stars using the DAOPHOT based package Muniwin as the first step, and the Period04 package was used to further analyse the suspected new variable stars. The light curves and other observational results are presented for 3598 stars online. We found 81 new variable stars, a…
We present the results of spectroscopy and CCD photometry of the intermediate-luminosity red transient PSN J13100734+3410514 in the galaxy UGC 8246 performed in February and June 2014 with the Russian 6-meter telescope and SCORPIO spectral camera. Our CCD photometry was continued with the Special Astrophysical Observatory's 1-m telescope till November 2014. The star was discovered in late December 2013 at visual brightness 17.6 mag, which corresponded to the absolute magnitude Mv ~ -12.7, and was identified as a supernova impostor. Spectra taken at the visual brightness level of 19.5 mag show …
We present a CCD photometric survey for the search of variable stars in four open clusters namely Berkeley 69, King 5, King 7, and Berkeley 20. The time series observations were carried out for 1 and/or 2 nights for each of the clusters in the year 1998, which have led to identify nineteen variable stars in these clusters. Out of these 19 variable stars, five stars show delta Scuti like variability and two stars show W UMa type variability. In other stars, we could not find the periods and hence the type of variability due to the lack of sufficient data. The periods of delta Scuti type stars a…
We present stellar variability towards the young open cluster NGC\,6823. Time series $V$- and $I$-band CCD photometry led to identification and characterization of 88 variable stars, of which only 14 have been previously recognized. We ascertain the membership of each variable with optical $UBVI$ and infrared photometry, and with Gaia EDR3 parallax and proper motion data. Seventy two variable stars are found to be cluster members, of which 25 are main sequence stars and 48 are pre-main-sequence stars. The probable cluster members collectively suggest an isochrone age of the cluster to be about…
We carried out BVRI CCD photometric observations in the field of V582 Aur from 2009 August to 2013 February. We acquired high-, medium-, and low-resolution spectroscopy of V582 Aur during this period. To study the pre-outburst variability of the target and construct its historical light curve, we searched for archival observations in photographic plate collections. Both CCD and photographic observations were analyzed using a sequence of 14 stars in the field of V582 Aur calibrated in BVRI. The pre-outburst photographic observations of V582 Aur show low-amplitude light variations typical of T T…
We used Johnson UBV photometric CCD observations to identify pulsating and other variable stars in the young open cluster NGC 6231. The multi-color information was used to classify pulsating variables, perform frequency analysis, and - where possible - to compare observed to theoretical amplitude ratios for mode identification. The data reduction was performed with standard IRAF tools. Differential light curves have been obtained by identifying a set of suitable comparison stars and the frequency analysis was then conducted on the basis of Fourier methods. Our classification of pulsating stars…
During the last two years we have received long time-series photometric observations of bright (V mag < 8) main-sequence A- and B-type stars observed by the NASA TESS spacecraft and the Austria-Poland-Canada BRITE satellites. Using TESS observations of metallic-line A (Am) stars having peculiar element abundances, our goal is to determine whether and why these stars pulsate in multiple radial and non-radial modes, as do the delta Scuti stars in the same region of the H-R diagram. The BRITE data were requested to investigate pulsations in bright (V around 6 mag) A- and B-type stars in the Cygnu…
Context. RV Tauri-type variables are pulsating post-AGB stars that evolve rapidly through the instability strip after leaving the Asymptotic Giant Branch. Their light variability is dominated by radial pulsations. Members of the RVb subclass show an additional variability in form of a long-term modulation of the mean brightness, for which the most popular theories all assume binarity and some kind of circumstellar dust. Here we address if the amplitude modulations are consistent with the dust obscuration model. Aims. We measure and interpret the overall changes of the mean amplitude of the pul…
