High-amplitude Delta Scuti Research Articles

The Photometric Analysis and Classification of High Amplitude δ Scuti: AE Ursae Majoris

AE UMa, a Population I high amplitude Delta Scuti (HADS), was observed for 4 nights through 14-21 March 2022. 454 Visual CMOS observations and 11 new times of maxima were obtained over a period of ~19.4 hours in total. Using python coding and Fourier analysis, a fundamental frequency ƒ0 = 11.6251 cd-1 was established and further observation of amplitudes of light maxima led to beat phenomenon period Pb = 0.29360 d. Subsequently, the first overtone frequency ƒ1 = 15.0316 cd-1 was calculated and the period ratio = 0.7734 was found to be relatively unchanged from Szeidl (1974). Thereafter, the period ratio-metallicity correlation determined by Hintz et al. (1997b) was used to estimate the metallicity [Fe/H] of AE UMa. I concluded that AE UMa is incorrectly classified as a Pop. II HADS (SX Phoenicis) and should be grouped with Pop. I HADS.

Asteroseismic inferences from the study of non-linearities in δ Sct stars

Many pulsating star light curves must be interpreted strictly within the framework of a non-linear theory. The detection of non-linear interactions between pulsation modes has increased due to the ultra-precise photometric data provided by space missions. For this reason, it is now possible and essential to continue the effort of building data-driven non-linear pulsation models. The analysis of non-linear stellar light curves has become a fundamental challenge in asteroseismology in the era of space missions. In this article, a diagnostic method is presented. It is based on an observational characterization of the non-linear behavior of high-amplitude delta Scuti (HADS) stars. It diagnoses the nature of non-linear pulsations in δ Sct stars of lower amplitudes. It potentially provides an extra hint for identifying a radial mode and determine its radial order n. Additionally, it could show signatures of moderate to rapid rotation in these stars. Overall, this article shows the capabilities for making asteroseismic inferences from studying combination frequencies in δ Sct stars.

Frequency Analysis of KIC 1573174: Shedding Light on the Nature of HADS Stars

We propose that KIC 1573174 is a quadruple-mode δ Scuti star with pulsation amplitudes between those of the high-amplitude Delta Scuti star group and average low-amplitude pulsators. The radial modes detected in this star provide a unique opportunity to exploit asteroseismic techniques up to their limits. Detailed frequency analysis is given for the light curve from the Kepler mission. The variation of the light curve is dominated by the strongest mode with a frequency of F0 = 7.3975 day−1, as shown by Fourier analysis of long cadence data (Q1–Q17, spanning 1460 days), indicating that the target is a δ Scuti star. The other three independent modes with F1 = 9.4397 day−1, F2 = 12.1225 day−1, and F3 = 14.3577 day−1, have ratios of P 1/P 0, P 2/P 0, and P 3/P 0 estimated as 0.783, 0.610, and 0.515, which indicate that KIC 1573174 is a quadruple-mode δ Scuti star. A different approach has been used to determine the O − C through the study of phase modulation. The change of period (1/P)dP/dt is obtained resulting in −1.14 × 10−6 yr−1 and −4.48 × 10−6 yr−1 for F0 and F1 respectively. Based on frequency parameters (i.e., F0, F1, F2, and F3), a series of theoretical models were conducted by employing the stellar evolution code MESA. The ratio of observed f 1/f 2 is larger than that of the model, which may be caused by the rotation of the star. We suggest high-resolution spectral observation is highly desired in the future to further constrain models.

New triple-mode high-amplitude Delta Scuti variables

Abstract I present a detection of four new triple-mode high-amplitude Delta Scuti variables, pulsating in the fundamental, first, and second overtone modes. This is a new addition to the ten known cases in the Galaxy. I used the data of ASAS-SN and analyzed them using the WinEfk code by V. P. Goranskij. Light elements and parameters of the light curves were obtained.

ON THE NATURE OF THE HADS STAR V2455 CYG

Using uvby − β photoelectric photometry obtained with the 0.84 m telescope of the Observatorio Astrónomico Nacional de San Pedro Mártir, México, we determined some of the physical characteristics, such as effective temperature and surface gravity of the high amplitude Delta Scuti star V2455 Cyg (=HD 204615). Newly determined times of maximum light gathered at the Observatorio Astrónomico Nacional de Tonantzintla, México with small 10 inch telescopes equipped with CCD cameras were combined with times of maxima in the literature, and used to study the secular variation of the pulsational period of the star.

TYC 3637-1152-1 – A high amplitude δ Scuti star with peculiar pulsational properties

In some δ Scuti stars, only one or two radial modes are excited (usually the fundamental mode and/or first overtone mode) and the observed peak-to-peak amplitudes exceed 0.3 mag (V). These stars are known as High Amplitude Delta Scuti (HADS) variables.We here present a detailed photometric and spectroscopic analysis of the HADS star TYC 3637-1152-1. We have derived a metallicity close to solar, a spectral type of F4 V and an age of logt=9.1. Employing archival time series data from different sources, two frequencies f0 = 10.034 c/d and f1 = 12.681 c/d and their harmonics and linear combinations were identified. The period ratio of f0/f1=0.791 puts this star into a peculiar position in the Petersen diagram, from which we conclude that TYC 3637-1152-1 is a unique object with peculiar pulsational properties that indicate a transitional state between HADS stars pulsating in the fundamental and first overtone modes and stars pulsating in higher overtones.

New variable stars from the photographic archive: semi-automated discoveries, attempts at automatic classification and the new field 104 Her

Using 172 plates taken with the 40-cm astrograph of the Sternberg Astronomical Institute (Lomonosov Moscow University) in 1976–1994 and digitized with a resolution of 2400 dpi, we discovered and studied 275 new variable stars. We present the list of our new variables with all necessary information concerning their brightness variations. As in our earlier studies, the new discoveries show a rather large number of high-amplitude Delta Scuti variables, predicting that many stars of this type remain not detected in the whole sky. We also performed automated classification of the newly discovered variable stars based on the Random Forest algorithm. The results of the automated classification were compared to traditional classification and showed that automated classification was possible even with noisy photographic data. However, further improvement of automated techniques is needed, which is especially important when considering the very large numbers of new discoveries expected from all-sky surveys.

First light curve analysis of the high-amplitude Delta Scuti star GSC 4552–1498

We carried out observation of the HADS (High-Amplitude Delta Scuti) variable GSC 4552–1498 through three filters. Our goal was to consider its periodic behavior using our photometry data in addition to previous observations. A new ephemeris and determination of oscillation modes of the star based on Fourier analysis are presented. The Two color diagram of the star as a function of its phase is shown. Finally, some of the star's physical parameters including mass, radius and luminosity are calculated.

CzeV293 and CzeV581—Two new high-amplitude double-mode delta Scuti stars

We report on the discovery of two high-amplitude double-mode delta Scuti stars in constellations of Hercules and Auriga. The stars were observed photometrically in five and two seasons, respectively. Frequency analysis revealed that both stars show complex pulsation behaviour with two independent modes and several combination peaks. Placing the stars into the Petersen diagram allowed us to identify the pulsation modes as the fundamental and the first overtone. Both stars follow the general trend for F/1O pulsators in the short-period part of the Petersen diagram and turned out to be classical members of HADS group of variables. Using empirical formulae we roughly estimate visual absolute magnitude, intrinsic (B−V)0 colour index and temperature of the target stars.

Photometry and the determination of oscillation modes for high amplitude Delta Scuti (HADS) variable GSC 1566-2802

CCD photometry observation of a newly discovered, high amplitude Delta Scuti star GSC 1566-2802, with a visible filter, is presented. The observations were carried out at Alborz Observatory located in Mahdasht, Karaj, Iran.The main goal of this project was to update our knowledge of the periodic variations of the target star. This paper covers three analyses, first calculating a new ephemeris and plotting a new light curve based on 19 times of maxima; then a Fourier analysis of the observed data points which results in determining probable oscillation modes, as well as computing its physical parameters which guide us to its harmonics and pulsation modes.

On the period variations of several low declination high amplitude delta Scuti variables

A 16-inch Schmidt-Cassegrain telescope on the campus of Naresuan University of Thailand and several similar-size telescopes in China equipped with CCD cameras were used to observe 14 high amplitude delta Scuti stars: GP And, CY Aqr, BS Aqr, YZ Boo, AD CMi, VZ Cnc, EH Lib, DY Her, V927 Her, KZ Hya, BE Lyn, V1162 Ori, DY Peg, and CW Ser, between the years 1999 and 2010. Data were also collected from scientific journals and sources on the Internet for these variable stars. Times of light maximum of these delta Scuti stars were then either determined from the observations or obtained from the literature to analyze the pulsation period variations. For the 14 delta Scuti stars we concluded that 7 stars (BS Aqr, CY Aqr, AD CMi, EH Lib, KZ Hya, BE Lyn and DY Peg) are binary or multiple systems. 10 delta Scuti stars are found with periods increasing with rates between 5.86×10−9 and 2.34×10−6 per year and the other 4 stars (BS Aqr, DY Her, BE Lyn and DY Peg) show periods decreasing with rates of about 10−9 to 10−8 per year.

HIGH-AMPLITUDE δ-SCUTIS IN THE LARGE MAGELLANIC CLOUD

We present 2323 High-Amplitude \delta-Scuti (HADS) candidates discovered in the Large Magellanic Cloud (LMC) by the SuperMACHO survey (Rest et al. 2005). Frequency analyses of these candidates reveal that several are multimode pulsators, including 119 whose largest amplitude of pulsation is in the fundamental (F) mode and 19 whose largest amplitude of pulsation is in the first overtone (FO) mode. Using Fourier decomposition of the HADS light curves, we find that the period-luminosity (PL) relation defined by the FO pulsators does not show a clear separation from the PL-relation defined by the F pulsators. This differs from other instability strip pulsators such as type c RR Lyrae. We also present evidence for a larger amplitude, subluminous population of HADS similar to that observed in Fornax (Poretti et al. 2008).

44 Tau: Discrimination between MS and post-MS models

Inhalt (u.a.): M. BREGER: Delta Scuti stars: Observational aspects; M.S. Cunha: Theory of rapidly oscillating Ap stars; M. SACHKOV et al.: Vertical structure of pulsations in roAp stars; G. HOUDEK: Theoretical asteroseismology of solar-like oscillations; B.L. POPIELSKI: Core modes as a seismic probe of mixing beyond the convective core; M. GODART: Temperature gradients in the core overshooting region; W.A. DZIEMBOWSKI – J. DASZYŃSKA-DASZKIEWICZ – A.A. PAMYATNYKH: Interpretation of the Be star HD 163868 oscillation spectrum based on the MOST observations; D. KILKENNY: Pulsating Hot Subdwarfs – An Observational Review; M.H. MONTGOMERY: Mapping Convection using Pulsating White Dwarf Stars; M. ROTH: The Network Activities in HELAS; I. KUDZEJ et al.: A New Slovak Observatory 500 km from Vienna; W.W. WEISS: Microsatellites; G. KOPACKI – S. FRANDSEN: RR Lyrae stars in M4

A Pulsational Distance to ω Centauri Based on Near‐Infrared Period‐Luminosity Relations of RR Lyrae Stars

We present new Near-Infrared (J,K) magnitudes for 114 RR Lyrae stars in the globular cluster Omega Cen (NGC 5139) which we combine with data from the literature to construct a sample of 180 RR Lyrae stars with J and K mean magnitudes on a common photometric system. This is presently the largest such sample in any stellar system. We also present updated predictions for J,K-band Period-Luminosity relations for both fundamental and first-overtone RR Lyrae stars, based on synthetic horizontal branch models with metal abundance ranging from Z=0.0001 to Z=0.004. By adopting for the Omega Cen variables with measured metal abundances an alpha-element enhancement of a factor of 3 (about 0.5 dex) with respect to iron we find a true distance modulus of 13.70 (with a random error of 0.06 and a systematic error of 0.06), corresponding to a distance d=5.5 Kpc (with both random and systematic errors equal to 0.03 Kpc). Our estimate is in excellent agreement with the distance inferred for the eclipsing binary OGLEGC-17, but differ significantly from the recent distance estimates based on cluster dynamics and on high amplitude Delta Scuti stars.

The role of rotation on Petersen diagrams. The $\mathsf{\Pi_{1/0}\,(\Omega)}$ period ratios

The present work explores the theoretical effects of rotation in calculating the period ratios of double-mode radial pulsating stars with special emphasis on high-amplitude delta Scuti stars (HADS). Diagrams showing these period ratios vs. periods of the fundamental radial mode have been employed as a good tracer of non-solar metallicities and are known as Petersen diagrams (PD).In this paper we consider the effect of moderate rotation on both evolutionary models and oscillation frequencies and we show that such effects cannot be completely neglected as it has been done until now. In particular it is found that even for low-to-moderate rotational velocities (15-50 km/s), differences in period ratios of some hundredths can be found. The main consequence is therefore the confusion scenario generated when trying to fit the metallicity of a given star using this diagram without a previous knowledge of its rotational velocity.

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.

Dwarf Cepheid Radii and the Distance Scale

AbstractBaade-Wesselink radii for dwarf Cepheids (High Amplitude Delta Scuti stars) can give luminosities and distances independent of the classical Cepheid distance scale. Using optical and IR photometry together with precision radial velocities, the authors have obtained radii and luminosities for 7 stars, and combined these with two from the literature, obtaining results consistent with the luminosities of the 3 dwarf Cepheids with good Hipparcos parallaxes. Classical Cepheids and dwarf Cepheids appear to fit the same PL and PR relations. The results imply ‘bright’ RR Lyrae absolute magnitudes giving an LMC distance modulus of 18.51-18.54, in agreement with the distance derived from classical Cepheids.