XX Cyg Research Articles

ANALYSIS OF A SHORT PERIODIC PULSATOR: SX PHOENICIS STAR XX CYG

Photometric observations were made of the SX Phoenicis star XX Cyg between September and October 2019, using the 1.88-m Kottamia reflector telescope in Egypt. We used 340 CCD observations with blue-visible-red (BVR) filters to derive light curves. In addition, we obtained 9540 visual magnitudes for XX Cyg from the literature to prepare an observed-minus-calculated (O-C) diagram. 85 new times of maximum for XX Cyg are presented. We did not detect a bump in the descending portion of the light curve of maximum light for XX Cyg. However, we did detect a secular bump in the phased light curves, which changes with phase in some SuperWASP observations. We found the change in period of XX Cyg to be dP/dt = 15.5 × 10-5 s/yr, with its amplitude decreasing at a rate of 0.7 mmag/year. Stellar parameters of XX Cyg and its position in the instability strip of the Hertzsprung Russell stellar evolution diagram are presented.

STELLAR PULSATIONS AND PERIOD CHANGES IN THE SX PHOENICIS STAR XX CYGNI

Time-series photometric observations were made for the SX Phoenicis star XX Cyg between 2007 and 2011 at the Xinglong Station of National Astronomical Observatories of China. With the light curves derived from the new observations, we do not detect any secondary maximum in the descending portion of the light curves of XX Cyg, as reported in some previous work. Frequency analysis of the light curves confirms a fundamental frequency f 0 = 7.4148 cycles day–1 and up to 19 harmonics, 11 of which are newly detected. However, no secondary mode of pulsation is detected from the light curves. The O–C diagram, produced from 46 newly determined times of maximum light combined with those derived from the literature, reveals a continuous period increase with the rate of (1/P)(dP/dt) = 1.19(13) × 10–8 yr-1. Theoretical rates of period change due to the stellar evolution were calculated with a modeling code. The result shows that the observed rate of period change is fully consistent with period change caused by evolutionary behavior predicted by standard theoretical models.

Period Changes in SX Phoenicis Stars. III. XX Cygni

ABSTRACTXX Cyg is a high-amplitude δ Scuti star which has been extensively studied because of its changing period. We present 64 new times of maxima that have been combined with 174 times of maxima from literature, in order to give an updated ephemeris and O - C plot for XX Cyg. Its period, currently found to be 0.134865117(3) days, is shown to be increasing continuously, which has lead to a new calculated value of (1/P)(dP/dt) = 1.33(7)·10-8 yr-1.

Binarity and multiperiodicity in high-amplitude δ Scuti stars

We have carried out a photometric and spectroscopic survey of bright high-amplitude δ Scuti (HADS) stars. The aim was to detect binarity and multiperiodicity (or both) in order to explore the possibility of combining binary star astroph ysics with stellar oscillations. Here we present the first results for ten, predominantly southern , HADS variables. We detected the orbital motion of RS Gru with a semi-amplitude of �6.5 km s 1 and 11.5 days period. The companion is inferred to be a low-mass dwarf star in a close orbit around RS Gru. We found multiperiodicity in RY Lep both from photometric and radial velocity data and detected orbital motion in the radial velocities with hints of a possible peri od of 500‐700 days. The data also revealed that the amplitude of the secondary frequency is variable on the time-scale of a few years, whereas the dominant mode is stable. Radial velocities of AD CMi revealed cycle-tocycle variations which might be due to non-radial pulsations. We confirmed the multiperiodic nature of BQ Ind, while we obtained the first radial velocity c urves of ZZ Mic and BE Lyn. The radial velocity curve and the O‐C diagram of CY Aqr are consistent with the long-period binary hypothesis. We took new time series photometry on XX Cyg, DY Her and DY Peg, with which we updated their O‐C diagrams.

A photometric monitoring of bright high-amplitudeδScuti stars

We present new photometric data for seven high-amplitude delta Scuti stars. The observations were acquired between 1996 and 2002, mostly in the Johnson photometric system. For one star (GW UMa), our observations are the first since the discovery of its pulsational nature from the Hipparcos data.The primary goal of this project was to update our knowledge on the period variations of the target stars. For this, we have collected all available photometric observations from the literature and constructed decades-long O-C diagrams of the stars. This traditional method is useful because of the single-periodic nature of the light variations. Text-book examples of slow period evolution (XX Cyg, DY Her, DY Peg) and cyclic period changes due to light-time effect (LITE) in a binary system (SZ Lyn) are updated with the new observations. For YZ Boo, we find a period decrease instead of increase. The previously suggested LITE-solution of BE Lyn (Kiss & Szatmary 1995) is not supported with the new O-C diagram. Instead of that, we suspect the presence of transient light curve shape variations mimicking small period changes.

Period Changes in SX Phoenicis Stars. II. XX Cygni

ABSTRACTWe have conducted photometric monitoring of the SX Phoenicis star XX Cyg in order to study the changes in pulsation period of this object. We have combined 20 new times of maximum light for XX Cyg with those from the literature to prepare an O - C diagram for XX Cyg. The results suggest that contrary to earlier work, XX Cyg exhibits a continuous period increase, rather than sudden jumps in the period. We measure the change in period of XX Cyg to be (1/P)(dP/dt) = 1.13(2) × 10-8 yr-1. This is in reasonably good agreement with the theoretical predictions of Rodríguez et al. of (1/P)(dP/dt) = 6.2 × 10-8 yr-1 change expected from theoretical considerations. We marginally detect a bump in the descending portion of the light curve of XX Cyg, as reported by previous authors.

Amplitude and Period Changes in the δ Sct Star AN Lyncis

AbstractWe report a study of time-dependent behaviour of the light variations in the δ Set star AN Lyn, based on an analysis of new time-series CCD observations and existing data. The amplitude of the main frequency increased from 1994 to 2000 at a rate of 0.006 mmag/yr. The light variation of AN Lyn can be explained currently by amplitude variability mixed with multiperiodic pulsation. With the extended data base, results on XX Cyg are also reported.

AMPLITUDE AND PERIOD CHANGES IN THE SX PHOENICIS STAR XX CYGNI

The new time-resolved CCD photometry of XX Cyg was presented. We investigate the time-dependent behaviour of the light variations by reanalyzing the data in the literature. XX Cyg was demonstrated beyond any doubt again to be a monoperiodic pulsator. Its light curves can be well reproduced by the sinusoids with the fundamental frequency f 0 = 7.41481 ± 0.00001 cycle d-1(P 0 = 0d . 1348652 ± 0.0000001) and its first nine harmonics. Fourier, wavelet and O–C analyses based on all the available data reveals the amplitude and period variations during the years 1974 to 2000.The general trend of the amplitude changes is decreasing at a rate of one percent milli-magnitudes per year. The parabolic analysis on the updated 101 times of maximum light suggests a slowly continuous increasing at a rate of 1.3 × 10-3 days per million years in the period.

FOURIER DECOMPOSITION OF THE LIGHT CURVES OF THREE DWARF CEPHEIDS: CY AQUARII, XX CYGNI, AND V798 CYGNI

ABSTRACT The three dwarf Cepheid variable stars CY Aquarii, XX Cygni, and V798 Cygni were examined with CCD time series ensemble photometry. The Fourier decomposition of the light curves showed no evidence that any of the three stars was a double-mode variable. CY Aqr was fit with a nine term harmonic series with a residual error of 10 mmag. XX Cyg was fit with a ten term harmonic series with a residual error of 10 mmag. V798 Cyg was fit with a four term harmonic series with a residual error of 7 mmag. In addition, we examined a set of double-mode dwarf Cepheids with the same Fourier decomposition techniques. We present evidence that these double-mode dwarf Cepheids fill the gap in the amplitude ratio distribution reported by Antonello et al.(1986) and Poretti et al.(1990.

PHOTOMETRIC OBSERVATIONS OF THE DWARF CEPHEID XX CYGNI.

ABSTRACT Photometric observations were made during the summer of 1984 of the short-period dwarf Cepheid XX Cyg. The light curves of XX Cyg taken with B and V filters are presented, as well as current estimates of various parameters inferred from them. Among these parameters are an accurate determination of the period and the change in visual light output. In addition, the light curves suggest a small migrating bump that slowly changes in shape and position over many periods, and may even disappear altogether.

THE NATURE OF THE DWARF CEPHEID XX CYG.

ABSTRACT Photometry of XX Cyg in the uvby and β systems has been secured and analyzed. A reddening value, E(b - y) = + 0.m057, is derived from the photometry. Intrinsic (b - y) and c1 values are used to determine a mean effective temperature, eff> = 7530 K, and a mean surface gravity, = 3.66. XX Cyg is found to be a metal-poor dwarf cepheid with [Fe/H] = -0.49. A radius of 2.4 Rsun has been found from the Wesselink method. The radius and effective temperature indicate that bol> = + 1.7. A mass of 1.0 Msun is found from the radius and effective gravity. The radial-velocity data yield a mean radial velocity of -108 km s-1 and a total velocity range of 37 km s-1.