The multi-band CCD photometric investigation of short-period eclipsing binary V1044 Her

We present new CCD photometric observations of V1044 Her obtained on May 22, 23 and 24, 2015. From our data, we derived five new light curve minimum times. Combining our new results with previously available CCD light minimum times, we derived an updated ephemeris and discovered that the period of this binary system exhibits an oscillation. The cyclic variation may be caused by the light-time effect via the presence of a third body or magnetic activity cycle. We calculated the corresponding period of the third body to be 14.1 ± 1.4 years or magnetic cycle to be 12.2 ± 0.7 years. We analyzed our new asymmetric light curves to obtain photometric solutions and starspot parameters using the Wilson and Devinney program. The final results show that V1044 Her is a contact binary system with a degree of contact factor f = 3.220( ± 0.002)%.     

Photometric Study of the W Uma-Type Eclipsing Binary System GSC 4832.400

We present a photometric analysis of the eclipsing binary systemGSC4832.400 based on 732 photometric observations obtained on sixteen clear nights during 1999–2000 in the V-Johnson and yb-Strömgren filters. The observed times of the minima yielded a linear ephemeris showing that the system has a constant period of 0.313150 ± 0.000002days. The light curve corresponds to a circular orbit for the system and clearly shows that GSC4832.400 has the defining characteristics of a W UMa-type eclipsing binary. It also shows a small O'Connell effect, which could be due to the presence of a hot spot in the primary star. A preliminary photometric solution based on the assumption of an over contact systemsatis factorily reproduced the observed light curve.     

How semiregular are irregular variables?

We investigate the question whether there is a real difference in the light change between stars classified as semiregular (SRV) or irregular (Lb) variables by analysing photometric light curves of 12 representatives of each class. Using Fourier analysis we try to find a periodic signal in each light curve and determine the S/N of this signal. For all stars, independent of their variability class we detect a period above the significance threshold. No difference in the measured S/N between the two classes could be found. We propose that the Lb stars can be seen as an extension of the SRVs towards shorter periods and smaller amplitudes. This is in agreement with findings from other quantities which also showed no marked difference between the two classes (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The first light curve solutions and period study of two contact binary systems: V1370 Tau and QQ Boo

The first light curve solutions of the binary systems V1370 Tau and QQ Boo are presented. The periodic changes are calculated, and a new ephemeris presented for each of these two binary systems. O-C analysis is performed using the MCMC method in OCFit code. The changing rate of period was measured as dP/dt= 0.2423 days/year for V1370 Tau and dP/dt= -0.1363 days/year for QQ Boo. The light curve solutions suggest that V1370 Tau is a weak-contact eclipsing binary system with a photometric mass ratio q = 0.829, and that the corresponding fillout factor is 11.06%. Furthermore, it is suggested that the QQ Boo binary system is also a weak-contact W UMa eclipsing binary with a photometric mass ratio q = 0.831, and that its fillout factor equals 10.26%. The light curve solutions require cold spots. Utilizing the Wilson-Devinney code the photometric and geometric parameters of the systems are determined. The distance of both V1370 Tau and QQ Boo are calculated according to the estimated absolute parameters as 159.95 ± 23 pc and 309.03 ± 25 pc, respectively, which are in a good agreement with the distance values derived from the Gaia DR2 parallax within one standard deviation. Moreover, the positions of their components on the H-R diagram are represented.     

Is the semi‐regular variable RU Vulpeculae undergoing a helium‐shell flash?

The semi‐regular variable star RU Vulpeculae (RU Vul) is being observed visually since 1935. Its pulsation period and amplitude are declining since ∼1954. A leading hypothesis to explain the period decrease in asymptotic giant branch (AGB) stars such as RU Vul is an ongoing flash of the He‐burning shell, also called a thermal pulse (TP), inside the star. In this paper, we present a CCD photometric light curve of RU Vul, derive its fundamental parameters, and test if the TP hypothesis can describe the observed period decline. We use CCD photometry to determine the present‐day pulsation period and amplitude in three photometric bands, and high‐resolution optical spectroscopy to derive the fundamental parameters. The period evolution of RU Vul is compared to predictions by evolutionary models of the AGB phase. We find that RU Vul is a metal‐poor star with a metallicity [M/H] = –1.59 ± 0.05 and an effective surface temperature of T_eff = 3634 ± 20 K. The low metallicity of RU Vul and its kinematics indicate that it is an old, low‐mass member of the thick disc or the halo population. The present day pulsation period determined from our photometry is ∼108 d, the semiamplitude in the V ‐band is 0.39 ± 0.03 mag. The observed period decline is found to be well matched by an evolutionary AGB model with stellar parameters comparable to those of RU Vul. We conclude that the TP hypothesis is in good agreement with the observed period evolution of RU Vul. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New classification and basic stellar parameters of SU Equulei

The variable star SU Equulei was classified as a close binary with an eclipse light curve previously categorized as WUMa type. The aim of this paper is a review of this old classification on the basis of new observations and a new determination of variable star ephemeris as well as the determination of SU Equ spectral type and distance. New photometric observations in different colours allow a precise determination of the period of variability and yield more accurate light curves allowing a re‐classification of the type of variability. We find the best period of variability to be half the old value. The shape of the light curve is inconsistent with an eclipse curve but consistent with an RR Lyrae type c classification. From the B, V, and R colours we deduce a new spectral classification. SU Equulei is an RRc Lyrae type variable of spectral class A8 at a distance of ≈12.4 kpc instead of a late‐type eclipsing binary (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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

Long-term BV RI 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.     

Photometric analysis of the eclipsing binary 2MASS 19090585+4911585

We report on observations of the eclipsing binary 2MASS 19090585+4911585 with the 25 cm auxiliary telescope of the University Observatory Jena. We show that a nearby brighter star (2MASS 19090783+4912085) was previously misclassified as the eclipsing binary and find 2MASS 19090585+4911585 to be the true source of variation. We present photometric analysis of VRI light curves. The system is an overcontact binary of W UMa type with an orbital period of (0.288374 ± 0.000010) d (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Discovery of cyclic spot activity on the G8 giant HD 208472

We present and analyze 17 consecutive years of UBVRI time‐series photometry of the spotted giant component of the RS CVn binary HD 208472. Our aim is to determine the morphology and the evolution of its starspots by using periodsearch techniques and two‐spot light‐curve modelling. Spots on HD208472 always occur on hemispheres facing the observer during orbital quadrature and flip their location to the opposite hemisphere every approximately six years. The times when the spots change their preferential hemisphere correspond to times when the light curve amplitudes are the smallest and when abrupt changes of the photometric periods are observed. During these times the star is also close to a relative maximum brightness, suggesting a vanishing overall spottedness at each end of the previous cycle and the start of a new one. We find evidence for a 6.28±0.06‐yr brightness cycle, which we interpret to be a stellar analog of the solar 11‐year sunspot cycle. We also present clear evidence for a brightening trend, approximated with a 21.5±0.5‐yr period, possibly due to a stellar analog of the solar Gleissberg cycle. From the two‐spot modelling we also determine an upper limit for the differential‐rotation coefficient of α = ΔP/P of 0.004±0.010, which would be fifty times weaker than on the Sun (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Rotation Of Comet C/1995 O1 Hale–Bopp From Inner Coma Photometry

We present a further investigation of the periodogram resulting from the photometric data by Rodríguez et al. (1997) for comet C/1995 O1 Hale–Bopp and interpret that the main period in the data is 11.23 ± 0.01 h, but not 7.19 days. The latter is now attributed to an alias of the 11.23-h period. Assuming that the periodicity observed in the photometry is the solar day, the 11.23-h period is consistent with estimates of the sidereal rotation period by Farnham et al. (1998), and Jorda et al. (1997–1999) provided that the obliquity of the comet‘s equatorial plane to its orbital plane is larger than 75° and 80°, respectively. This result is in agreement with estimates of the obliquity by Sekanina (1997–1999) and Jorda et al. (1998). A weaker periodic signal in the light curve could be 5.48 ± 0.01 h, but we suggest that this is an alias of a 3.25 ± 0.01 h period of unknown origin. This revised version was published online in July 2006 with corrections to the Cover Date.     

The Rotational Periods of Three C-Type Asteroids 431, 521 and 524

The determination for asteroids’ spin parameters is very important for the physical study of asteroids and their evolution. Sometimes, the low amplitude of light curves and kinds of systematic errors in photometric data prevent the determination of the asteroids’ spin period. To solve such a problem, we introduced the de-correlation methods developed in searching for exoplanetary transit signal into the asteroid’s data reduction in this paper. By applying the principle of Collier Cameron (MNRAS 373:799–810, 2006) and Tamuz et al. (MNRAS 356:1466–1470, 2005)’s, we simulated the systematic effects in photometric data of asteroid, and removed those simulated errors from photometric data. Therefore the S/N of intrinsic signals of three selected asteroids are enhanced significantly. As results, we derived the new spin periods of 18.821 ± 0.011 h, 28.202 ± +0.071 h for (431) and (521) respectively, and refined the spin period of (524) as 14.172 ± 0.016 h.     

Analysis of a “flickering” Geminid fireball

Abstract— In the early morning hours of December 13, 2002, a bright Geminid fireball with an absolute magnitude of ?9.2 ± 0.5 was observed from Southern Saskatchewan, Canada. The fireball displayed distinct small‐scale oscillations in brightness, or flickering, indicative of the parent meteoroid being both non‐spherical and rotating. Using the light curve derived from a calibrated radiometer, we determine a photometric mass of 0.429 ± 0.15 kg for the meteoroid, and we estimate from its initial rotation rate of some 6 Hz that the meteoroid was ejected from the parent body (3200) Phaethon some 2500 ± 500 years ago. We find that 70% of Geminid fireballs brighter than magnitude ?3 display distinct flickering effects, a value that is in stark contrast to the 18% flickering rate exhibited by sporadic fireballs. The high coincidence of flickering and the deep atmospheric penetration of Geminid fireballs are suggestive of Geminid meteoroids having a highly resilient structure, a consequence, we suggest, of their having suffered a high degree of thermal processing. The possibility of Gemind material surviving atmospheric ablation and being sampled is briefly discussed, but the likelihood of collecting and identifying any such material is admittedly very small.     

A photometric study of a weak-contact binary: V873 Per

We present a photometric study of a weak-contact binary V873 Per. New observations in BVR filter bands showed asymmetric light curves to be a negative type of the O’Connell effect, which can be described by magnetic activity of a cool spot on the more massive component. Our photometric solutions showed that V873 Per is a W-type with a mass ratio of q = 2.504(±0.0029), confirming the results of Samec et al. (2009). The derived contact degree was found to be f = 18.10%(±1.36%). Moreover, our analysis found the cyclic variation with the period of about 4 yr that could be due to existence of the third companion in the system or the mechanism of magnetic activity cycle in the binary. While available data indicated that the long-term orbital period tends to be stable rather than decreasing.     

Pole orientation of asteroid 44 Nysa via photometric astrometry,including a discussion of the method's application and its limitations

The results of photometric astrometry, a method of determining the orientation of a rotation axis, as applied to asteroid 44 Nysa are presented. The pole orientation of Nysa was found to be λ₀ = 100°, β₀ = +60° with an uncertainty of 10°. The sidereal period is 0^d.26755902 ± 0.00000006, and the rotation prograde. Refinements to, and limitations of, the application of the method of photometric astrometry are discussed. In light of the results presented herein, we believe that all photometric astrometry pole determinations of the past should be redone.     

Seven years photometry of the W UMa‐type eclipsing binary V2612 Oph

We present the first long‐term Johnson UBVR observations and comprehensive photometric analysis of the W UMa‐type eclipsing binary V2612 Oph. Observations in the time interval between 2003 and 2009 enabled us to reveal the seasonal and long‐term variations of the light curve. Hence, we found that the mean brightness level of the light curve shows a variation with a period of 6.7 years. Maximum and minimum brightness levels of the light curve exhibit a variation from year to year which we attribute to a solar‐like activity. The O – C variation of eclipse timings of the system shows a decreasing parabolic trend and reveals a period decrease at a rate of P = 6.27×10^‐7 day yr^‐1 with an additional low‐amplitude sinusoidal variation that has a similar period as the long‐term brightness variations. Our light curve analysis shows that the system is a W‐subtype W UMa eclipsing binary. We calculated masses and radii of the primary and secondary components as M₁ = 1.28 M_⊙, M₂ = 0.37 M_⊙ and R₁ = 1.31 R_⊙, R₂ = 0.75 R_⊙, respectively. The derived absolute photometric parameters allow us to calculate a distance of 140 pc, which confirms that the system is a foreground star in the sky field of the Galactic open cluster NGC 6633. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A photometric investigation of the asteroid (89) Julia

New photometric data of the light curve of the minor planet (89) Julia were obtained on nine nights during the 1972 opposition using the 60cm telescope at OHP. A synodic period of 11^h23^m14^s ± 7^s and an amplitude of 0.25mag were derived from the measurements. The light curve is rather unsymmetric and no plausible explanation for this has been offered so far. The measurements have been carried out in instrumental V′; the data obtained in B′ and U′ supplement all conclusions from V′ data concerning the rotation of Julia.     

A photometric study of the W UMa-type binary DF Canum Venaticorum

We present new photometric observations for the eclipsing binary DF CVn, and determined five light minimum times. By using the Wilson–Devinney code, two sets of photometric solutions were deduced from our observations in 2009. The asymmetric light curves obtained on 2009 March 5 were modeled by a dark spot on the more massive component. The results indicate that DF CVn is a W-type weak-contact binary, with a mass ratio of q ～ 0.28 and an overcontact degree of f ～ 20%. From the O ? C curve of minimum times, it is found that there exists a cyclic variation, whose period and semi-amplitude are P₃ = 17.2(±0.9) year and A = 0.^d0070(±0.^d0008), respectively. This kind of cyclic oscillation may possibly result from the light-time effect due to the presence of an unseen third body. This kind of additional body may extract angular momentum from the central system. The low-amplitude changes of the light curves on a short-time scale (e.g., half a month) may be attributed to the dark spot activity, which may result in angular momentum loss via magnetic breaking. With angular momentum loss, the weak-contact binary DF CVn will evolve into a deep-contact configuration.     

On nova Scorpii 2007 N.1 (V1280 Sco)

We present the results of our photometric and spectroscopic observations of Nova Sco 2007 N.1 (V1280 Sco). The photometric data was represented by a single data point in the light curve since the observation was carried out only for one night. The spectra cover two different phases of the object’s evolution during the outburst, i.e. pre-maximum and post-maximum. Measurements of the P-Cygni profile on Na I ‘D’ line (5889 Å) was derived as the velocity of shell expansion, yielding 1567.43±174.14 km s^?1. We conclude that V1280 Sco is a fast Fe II-type nova.     

A CCD photometric study of the late type contact binary EK Comae Berenices

We present CCD photometric observations of the W UMa type contact binary EK Comae Berenices using the 2 m telescope of IUCAA Girawali Observatory, India. The star was classified as a W UMa type binary of subtype-W by Samec et al. (1996). The new V band photometric observations of the star reveal that shape of the light curve has changed significantly from the one observed by Samec et al. (1996). A detailed analysis of the light curve obtained from the high-precision CCD photometric observations of the star indicates that EK Comae Berenices is not a W-type but an A-type totally eclipsing W UMa contact binary. The photometric mass ratio is determined to be 0.349 ± 0.005. A temperature difference of ΔT = 141 ± 10 K between the components and an orbital inclination of i[°] = 89.800 ± 0.075 were obtained for the binary system. Absolute values of masses, radii and luminosities are estimated by means of the standard mass-luminosity relation for zero age main-sequence stars. The star shows O’Connell effect, asymmetries in the light curve shape around the primary and secondary maximum. The observed O’Connell effect is explained by the presence of a hot spot on the primary component.     

Light‐curve inversions with truncated least‐squares principal components: Tests and application to HD 291095 = V1355 Orionis

We present a new inversion code that reconstructs the stellar surface spot configuration from the light curve of a rotating star. Our code employs a method that uses the truncated least‐squares estimation of the inverse problem's objects principal components. We use spot filling factors as the unknown objects. Various test cases that represent a rapidly‐rotating K subgiant are used for the forward problem. Tests are then performed to recover the artificial input map and include data errors and input‐parameter errors. We demonstrate the robustness of the solution to false input parameters like photospheric temperature, spot temperature, gravity, inclination, unspotted brightness and different spot distributions and we also demonstrate the insensitivity of the solution to spot latitude. Tests with spots peppered over the entire stellar surface or with phase gaps do not produce fake active longitudes. The code is then applied to ten years of V and I ‐band light curve data of the spotted sub‐giant HD291095. A total of 22 light curves is presented. We find that for most of the time its spots were grouped around two active longitudes separated on average by 180°. Switches of the dominant active region between these two longitudes likely occurred about every 3.15±0.23 years while the amplitude modulation of the brightness occurred with a possible period of 3.0±0.15 years. For the first time, we found evidence that the times of the activity flips coincide with times of minimum light as well as minimum photometric amplitude, i.e. maximum spottedness. From a comparison with simultaneous Doppler images we conclude that the activity flips likely take place near the rotational pole of the star. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)