Scuti Pulsations Research Articles

TV Mon - post mass transfer Algol type binary with δ Scuti pulsations in primary component

TV Mon - post mass transfer Algol type binary with δ Scuti pulsations in primary component

Quadratic Frequency Dispersion in the Oscillations of Intermediate-mass Stars

Asteroseismology, the study of stellar vibration, has met with great success, shedding light on stellar interior structure, rotation, and magnetism. Prominently known as δ Scutis, the intermediate-mass main-sequence oscillators that often exhibit rapid rotation and possess complex internal stratification are important targets of asteroseismic study. δ Scuti pulsations are driven by the κ (opacity) mechanism, resulting in a set of acoustic modes that can be challenging to interpret. Here, we apply machine learning to identify new patterns in the pulsation frequencies of δ Scuti stars, discovering resonances spaced according to quadratic functions of integer mode indices. This unusual connection between mode frequencies and indices suggests that rotational influence may play an important role in determining the frequencies of these acoustic oscillations.

Asteroseismology of the mild Am δ Sct star HD 118660 : TESS photometry and modelling

Abstract We present the results of an asteroseismic study of HD 118660 (TIC 171729860), being a chemically peculiar (mild Am) star exhibiting δ Scuti (δ Sct) pulsations. It is based on the analysis of two sectors of time-series photometry from the space mission TESS and seismic modelling. It yielded the detection of 15 and 16 frequencies for TESS sectors 23 and 50, respectively. The identified pulsation modes include four radial (ℓ = 0) and five dipolar (ℓ = 1) ones. The radial modes are overtones with order n ranging from 3 and 6. Such high values of n are theoretically not expected for stars with the effective temperature of HD 118660 ($\rm T_{\rm eff}\approx 7550 \rm K$ ) located near the red edge of the δ Sct instability strip. To estimate the asteroseismic parameters, we have generated a grid of stellar models assuming a solar metallicity (Z = 0.014) and different values for the convective overshooting parameter (0.1 ≤ αov ≤ 0.3). We conclude that the analysis of the radial modes is insufficient to constrain αov and Z for δ Sct stars. The value for the equatorial velocity of HD 118660 derived from the seismic radius and the rotational frequency is consistent with values found in the literature.

The δ Scuti stars of the Cep–Her Complex – I. Pulsator fraction, rotation, asteroseismic large spacings, and the νmax relation

ABSTRACT We identify delta Scuti ($\delta$ Sct) pulsators amongst members of the recently discovered Cep–Her Complex using light curves from the Transiting Exoplanet Survey Satellite (TESS). We use Gaia colours and magnitudes to isolate a subsample of provisional Cep–Her members that are located in a narrow band on the colour–magnitude diagram compatible with the zero-age main sequence. The $\delta$ Sct pulsator fraction amongst these stars peaks at 100 per cent and we describe a trend of higher pulsator fractions for younger stellar associations. We use four methods to measure the frequency of maximum amplitude or power, $\nu _{\rm max}$, to minimize methodological bias, and we demonstrate their sound performance. The $\nu _{\rm max}$ measurements display a correlation with effective temperature, but with a scatter that is too large for the relation to be useful. We find two ridges in the $\nu _{\rm max}$–$T_{\rm eff}$ diagram, one of which appears to be the result of rapid rotation causing stars to pulsate in low-order modes. We measure the $\nu _{\rm max}$ values of $\delta$ Sct stars in four other clusters or associations of similar age (Trumpler 10, the Pleiades, NGC 2516, and Praesepe) and find similar behaviour with $T_{\rm eff}$. Using échelle diagrams, we measure the asteroseismic large spacing, $\Delta \nu$, for 70 stars, and find a correlation between $\Delta \nu$, rotation, and luminosity that allows rapid rotators seen at low inclinations to be distinguished from slow rotators. We find that rapid rotators are more likely than slow rotators to pulsate, but they do so with less regular pulsation patterns. We also investigate the reliability of Gaia’s vbroad measurement for A-type stars, finding that it is mostly accurate but underestimates $v\sin i$ for slow rotators ($v\sin i \lt 50$ km s−1) by 10–15 per cent.

Analysis of KIC 7023917: Spotted Low-mass Ratio Eclipsing Binary with δ Scuti Pulsations

Times of minima of eclipsing binary KIC 7023917 show quasiperiodic anti-symmetric deviations from the calculated one with an amplitude of up to 10 minutes and a period of 200–300 days. These changes correlate with the observed variations of the light-curve maxima (amplitude and phase separation). We used photometric data obtained by Kepler and TESS missions to analyze the times of minima and determine system parameters. The phases and amplitudes of the maxima were measured to study the O’Connell effect. As an additional source of information, we performed ground-based multicolor photometric observation and determined the radial velocities of the system from our spectroscopic measurements. We could explain long-term variations of the light-curve shape and times of the eclipses using the cold star spot located on the secondary component and the modification of its size. Based on our modelling, the system consists of a primary main-sequence star of spectral type A7 and an evolved, oversized secondary component with a mass ratio of only 0.1 due to past mass transfer. Calculation of absolute parameters gives us the mass of the primary component about 1.8 M ☉ and 0.2 M ☉ for the secondary one, and radii of 2.2 R ☉ of the primary star and 0.9 R ☉ of secondary one, respectively. The studied low-mass ratio eclipsing binary is probably a progenitor of the variable star of EL CVn type. A multiple-period photometric variability was disclosed in the TESS data ranging from half to two hours due to δ Scuti-type pulsations of the primary component.

A New Catalog of 100,000 Variable TESS A-F Stars Reveals a Correlation between δ Scuti Pulsator Fraction and Stellar Rotation

δ Scuti variables are found at the intersection of the classical instability strip and the main sequence on the Hertzsprung–Russell diagram. With space-based photometry providing millions of light curves of A-F type stars, we can now probe the occurrence rate of δ Scuti pulsations in detail. Using the 30 minutes cadence light curves from NASA's Transiting Exoplanet Survey Satellite's first 26 sectors, we identify variability in 103,810 stars within 5–24 cycles per day down to a magnitude of T = 11.25. We fit the period–luminosity relation of the fundamental radial mode for δ Scuti stars in the Gaia G band, allowing us to distinguish classical pulsators from contaminants for a subset of 39,367 stars. Out of this subset, over 15,918 are found on or above the expected period–luminosity relation. We derive an empirical red edge to the classical instability strip using Gaia photometry. The center where the pulsator fraction peaks at 50%–70%, combined with the red edge, agrees well with previous work in the Kepler field. While many variable sources are found below the period–luminosity relation, over 85% of sources inside of the classical instability strip derived in this work are consistent with being δ Scuti stars. The remaining 15% of variables within the instability strip are likely hybrid or γ Doradus pulsators. Finally, we discover strong evidence for a correlation between pulsator fraction and spectral line broadening from the Radial Velocity Spectrometer on board the Gaia spacecraft, confirming that rotation has a role in driving pulsations in δ Scuti stars.

The β Pictoris b Hill sphere transit campaign

The β Pictoris system is the closest known stellar system with directly detected gas giant planets, an edge-on circumstellar disc, and evidence of falling sublimating bodies and transiting exocomets. The inner planet, β Pictoris c, has also been indirectly detected with radial velocity (RV) measurements. The star is a known δ Scuti pulsator, and the long-term stability of these pulsations opens up the possibility of indirectly detecting the gas giant planets through time delays of the pulsations due to a varying light travel time. We search for phase shifts in the δ Scuti pulsations consistent with the known planets β Pictoris b and c and carry out an analysis of the stellar pulsations of β Pictoris over a multi-year timescale. We used photometric data collected by the BRITE-Constellation, bRing, ASTEP, and TESS to derive a list of the strongest and most significant δ Scuti pulsations. We carried out an analysis with the open-source python package maelstrom to study the stability of the pulsation modes of β Pictoris in order to determine the long-term trends in the observed pulsations. We did not detect the expected signal for β Pictoris b or β Pictoris c. The expected time delay is 6 s for β Pictoris c and 24 s for β Pictoris b. With simulations, we determined that the photometric noise in all the combined data sets cannot reach the sensitivity needed to detect the expected timing drifts. An analysis of the pulsational modes of β Pictoris using maelstrom showed that the modes themselves drift on the timescale of a year, fundamentally limiting our ability to detect exoplanets around β Pictoris via pulsation timing.

HIP 65426 is a High-frequency Delta Scuti Pulsator in Plausible Spin–Orbit Alignment with its Directly Imaged Exoplanet

HIP 65426 hosts a young giant planet that has become the first exoplanet directly imaged with JWST. Using time-series photometry from the Transiting Exoplanet Survey Satellite (TESS), we classify HIP 65426 as a high-frequency δ Scuti pulsator with a possible large-frequency separation of Δν = 7.23 ± 0.02 cycles day−1. We check the TESS data for pulsation-timing variations and use the nondetection to estimate a 95% dynamical mass upper limit of 12.8 M Jup for HIP 65426 b. We also identify a low-frequency region of signal that we interpret as stellar latitudinal differential rotation with two rapid periods of 7.85 ± 0.08 hr and 6.67 ± 0.04 hr. We use our TESS rotation periods together with published values of radius and vsini to jointly measure the inclination of HIP 65426 to i⋆=107−11+12 °. Our stellar inclination is consistent with the orbital inclination of HIP 65426 b ( 108−3+6 °) at the 68% percent level based on our orbit fit using published relative astrometry. The lack of significant evidence for spin–orbit misalignment in the HIP 65426 system supports an emerging trend consistent with preferential alignment between imaged long-period giant planets and their host stars.

HR 10 as seen by CHEOPS and TESS. Revealing delta Scuti pulsations, granulation-like signal and hint for transients

HR 10 has only recently been identified as a binary system. Previously thought to be an A-type shell star, it appears that both components are fast-rotating A-type stars, each presenting a circumstellar envelope. Although showing complex photometric variability, spectroscopic observations of the metallic absorption lines reveal variation explained by the binarity, but not indicative of debris-disc inhomogeneities or sublimating exocomets. On the other hand, the properties of the two stars make them potential delta Scuti pulsators. The system has been observed in two sectors by the TESS satellite, and was the target of three observing visits by CHEOPS. Thanks to these new data, we aim to further characterise the stellar properties of the two components. In particular, we aim to decipher the extent to to which the photometric variability can be attributed to a stellar origin. In complement, we searched in the lightcurves for transient-type events that could reveal debris discs or exocomets. We analysed the photometric variability of both the TESS and CHEOPS datasets in detail. We first performed a frequency analysis to identify and list all the periodic signals that may be related to stellar oscillations or surface variability. The signals identified as resulting from the stellar variability were then removed from the lightcurves inorder to search for transient events in the residuals. We report the detection of delta Scuti pulsations in both the TESS and CHEOPS data, but we cannot definitively identify which of the components is the pulsating star. In both datasets, we find flicker noise with the characteristics of a stellar granulation signal. However, it remains difficult to firmly attribute it to actual stellar granulation from convection, given the very thin surface convective zones predicted for both stars. Finally, we report probable detection of transient events in the CHEOPS data, without clear evidence of their origin.

The Hybrid Debris Disk Host Star HD 21997 is a High-frequency Delta Scuti Pulsator

HD 21997 is host to a prototypical “hybrid” debris disk characterized by debris disk-like dust properties and a CO gas mass comparable to a protoplanetary disk. We use Transiting Exoplanet Survey Satellite time series photometry to demonstrate that HD 21997 is a high-frequency delta Scuti pulsator. If the mode identification can be unambiguously determined in future works, an asteroseismic age of HD 21997 may become feasible.

Identifying 850 δ Scuti pulsators in a narrow Gaia colour range with TESS 10-min full-frame images

ABSTRACT We use TESS 10-min full-frame images (Sectors 27–55) to study a sample of 1708 stars within 500 pc of the Sun that lie in a narrow colour range in the centre of the δ Scuti instability strip (0.29 < GBP − GRP < 0.31). Based on the Fourier amplitude spectra, we identify 848 δ Scuti stars, as well as 47 eclipsing or contact binaries. The strongest pulsation modes of some δ Scuti stars fall on the period–luminosity relation of the fundamental radial mode but many correspond to overtones that are approximately a factor of two higher in frequency. Many of the low-luminosity δ Scuti stars show a series of high-frequency modes with very regular spacings. The fraction of stars in our sample that show δ Scuti pulsations is about 70 per cent for the brightest stars (G < 8), consistent with results from Kepler. However, the fraction drops to about 45 per cent for fainter stars and we find that a single sector of TESS data only detects the lowest amplitude δ Scuti pulsations (around 50 ppm) in stars down to about G = 9. Finally, we have found four new high-frequency δ Scuti stars with very regular mode patterns, and have detected pulsations in λ Mus that make it the fourth-brightest δ Scuti in the sky (G = 3.63). Overall, these results confirm the power of TESS and Gaia for studying pulsating stars.

TIC 184 743 498: the first tri-axial stellar pulsator

ABSTRACT We have discovered a δ Scuti pulsator in a tight binary (P = 1.053 d) with nine pulsation modes whose frequencies are between 38 and 56 d−1. Each of these modes exhibits amplitude modulations and π-rad phase shifts twice per orbital cycle. Five of these modes exhibit amplitude and phase shifts that are readily explained by dipole pulsations along an axis that is aligned with the binary’s tidal axis. The novelty of the system lies in the remaining four pulsation modes, which we show are dipole pulsations along an axis that is perpendicular to both the tidal axis and the binary’s orbital angular momentum axis. There are additionally two pulsation modes whose amplitudes and phases do not change significantly with orbital phase; they are explained as dipole modes along an axis aligned with the orbital/rotation axis. Hence, we propose that TIC 184 743 498 is a tri-axial pulsator, the first of its kind.

Physical and geometrical properties of an Algol type eclipsing binary with a [formula omitted] Scuti pulsator: HD 221072

In this study, we obtained physical and geometrical parameters of an Algol type eclipsing binary hosting a δ Scuti pulsator. Based on the Transiting Exoplanet Survey Satellite (TESS) observations of HD 221072 system published in Sectors 24, 57, and 58, we obtained the photometric solution of the eclipsing binary. The light curve modelling reveals that it is a detached system with masses and radii of the primary and secondary components as M1=1.772±0.003M⊙, M2=1.753±0.003M⊙ and R1=4.157±0.002R⊙, R2=2.369±0.002R⊙, respectively. After removing of the binary model from the TESS data, frequency analysis is applied to the light residuals. The Fourier spectrum shows that it can be divided in two sectors. One of them is located below the f<6d−1 limit and it is purely related with the orbital frequency. Because of the locations of the components on the Hertzsprung–Russell diagram there is a possibility of the secondary component pulsating too. According to the Q pulsation constant obtained for primary and secondary component, we can say that the primary component pulsating with the frequencies larger than f>6d−1 and it is the δ Scuti pulsator in the eclipsing system.

FX UMa: A New Heartbeat Binary System with Linear and Nonlinear Tidal Oscillations and δ Sct Pulsations

We present a detailed analysis of an eclipsing double-lined binary FX UMa based on TESS photometry and newly acquired spectroscopic observations. The radial velocities and atmospheric parameters for each component star are obtained from the SONG high-resolution spectra. Combined with the radial-velocity measurements, our light-curve modeling yields absolute masses and radii of the two components. The Fourier amplitude spectrum of the residual light curve reveals a total of 103 frequencies with signal-to-noise ratio (S/N) ≥ 4, including 12 independent frequencies, 17 multiples of the orbital frequency (Nf orb), and 74 combination frequencies. Ten Nf orb peaks with S/N > 10 have very high amplitudes and are likely due to tidally excited oscillations (TEOs). The remaining Nf orb peaks (4 ≤ S/N ≤ 10) may be originated from the imperfect removal, or they are actually real TEOs. Four anharmonic frequencies can pair up and sum to give exact harmonics of the orbital frequency, suggesting the existence of nonlinear tidal processes in the eccentric binary system FX UMa. Eight independent frequencies in the range of 20–32 day−1 are typical low-order pressure modes of δ Scuti pulsators.

Photometric variability of blue straggler stars in M67 with TESS and K2

ABSTRACT Blue straggler stars (BSSs) are formed through mass transfers or mergers in binaries. The recent detections of white dwarf (WD) companions to BSSs in M67 suggested a mass transfer pathway of formation. In search of a close companion to five BSSs in M67 that are known to be spectroscopic binaries, we study the light curves from K2 and TESS data. We use PHOEBE to analyse the light curves and estimate the properties of the companions. We detect variability in WOCS 1007, and the light curve is dominated by ellipsoidal variation. Using the light curve and radial velocity measurements, we estimate its orbital period to be 4.212 ± 0.041 d and e = 0.206 ± 002. The mass of the companion is estimated to be 0.22 ± 0.05 M⊙ with a radius of 0.078 ± 0.027 R⊙, confirming it to be an LM WD with Teff = 14300 ± 1100 K. The estimated mass of the BSS, 1.95 ± 0.26 M⊙, is similar to that estimated from isochrones. The BSS in WOCS 1007 shows δ Scuti pulsations, although it is slightly deformed and likely to be formed through an efficient mass transfer. Though we detect a light curve for WOCS 4003 showing grazing eclipse with ellipsoidal variation, the estimated parameters are inconclusive. Apart from the 0.44 d period, we found smaller eclipses with a period of 1.1 d, suggesting a compact triple system. In the cases of WOCS 4003, WOCS 5005, and WOCS 1025, no eclipses or pulsations are detected, confirming the absence of any short-period inner binary with high inclination in these BSSs.

Variable Blue Straggler Stars in the Open Cluster NGC 6819 Observed in the Kepler “Superstamp” Field

NGC 6819 is an open cluster of age 2.4 Gyr that was in the NASA Kepler spacecraft’s field of view from 2009 to 2013. The central part of the cluster was observed in a 200 × 200 pixel “superstamp” during these four years in 30 minute cadence photometry, providing a unique, high-precision, long time-series data set. The cluster contains “blue straggler” stars, i.e., stars on the main sequence above the cluster turnoff that should have left the main sequence to become red giants. We present light curves and pulsation frequency analyses derived from custom photometric reductions for five confirmed cluster members—four blue stragglers and one star near the main-sequence turnoff. Two of these stars show a rich spectrum of δ Scuti pulsation modes, with 236 and 124 significant frequencies identified, respectively, while two stars show mainly low-frequency modes, characteristic of γ Doradus variable stars. The fifth star, a known active X-ray binary, shows only several harmonics of two main frequencies. For the two δ Scuti stars, we use a frequency separation–mean density relation to estimate their mean densities, and then use these values along with their effective temperature to derive their stellar masses and radii. For the two stars showing low frequencies, we searched for period-spacing sequences that may be representative of gravity-mode or Rossby-mode sequences, but found no clear sequences. The common age for the cluster members, considered along with the frequencies, will provide valuable constraints for asteroseismic analyses, and may shed light on the origin of the blue stragglers.

TESS Observations of the Pleiades Cluster: A Nursery for δ Scuti Stars

We studied 89 A- and F-type members of the Pleiades open cluster, including five escaped members. We measured projected rotational velocities () for 49 stars and confirmed that stellar rotation causes a broadening of the main sequence in the color–magnitude diagram. Using time-series photometry from NASA’s TESS Mission (plus one star observed by Kepler/K2), we detected δ Scuti pulsations in 36 stars. The fraction of Pleiades stars in the middle of the instability strip that pulsate is unusually high (over 80%), and their range of effective temperatures agrees well with theoretical models. On the other hand, the characteristics of the pulsation spectra are varied and do not correlate with stellar temperature, calling into question the existence of a useful relation for δ Scutis, at least for young main-sequence stars. By including δ Scuti stars observed in the Kepler field, we show that the instability strip is shifted to the red with increasing distance by interstellar reddening. Overall, this work demonstrates the power of combining observations with Gaia and TESS for studying pulsating stars in open clusters.

An Ap Star Catalog Based on LAMOST DR9

We present a sample of 2700 Ap stars in the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) DR9 catalog. The candidates are first selected to be in a temperature range typical of Ap stars by using the BP − RP color index from Gaia DR3. Then the 5200 Å flux depression features characteristic of Ap stars are visually checked in LAMOST DR9 spectra. The detailed spectral features are given by applying a modified spectral classification program, MKCLASS. The stellar parameters of these Ap stars, such as the T eff, , [Fe/H], [Si/H], and , are either extracted from a hot star catalog or derived through empirical relations and then a statistical analysis is carried out. The evolutionary stages are also discussed. Finally, we discuss the rotation and pulsation features of those that have TESS or Kepler light curves. Among these Ap stars, we find seven new rotation variables, one new roAp star, and a new δ Scuti pulsation of a previously known roAp star.

δ Scuti pulsations in the bright Pleiades eclipsing binary HD 23642

ABSTRACT We announce the discovery of pulsations in HD 23642, the only bright eclipsing system in the Pleiades, based on light curves from the Transiting Exoplanet Survey Satellite (TESS). We measure 46 pulsation frequencies and attribute them to δ Scuti pulsations in the secondary component. We find four ℓ = 1 doublets, three of which have frequency splittings consistent with the rotation rate of the star. The dipole mode amplitude ratios are consistent with a high stellar inclination angle and the stellar rotation period agrees with the orbital period. Together, these suggest that the spin axis of the secondary is aligned with the orbital axis. We also determine precise effective temperatures and a spectroscopic light ratio, and use the latter to determine the physical properties of the system alongside the TESS data and published radial velocities. We measure a distance to the system in agreement with the Gaia parallax, and an age of 170 ± 20 Myr based on a comparison to theoretical stellar evolutionary models.

Detection of δ Scuti Pulsators in the Eclipsing Binaries Observed by TESS

Based on 2 minute cadence TESS data from sectors 1–50, we report the results of the systematic extraction of δ Scuti–type pulsations in the 6431 eclipsing binaries with orbital periods shorter than 13 days. A total number of 242 pulsators were found in those systems, including 143 new discoveries. We examined their pulsation properties based on the H-R diagram and the relationships between the dominant pulsation period P dom, orbital period P orb, and effective temperature T eff. As a consequence, 216 targets are likely δ Scuti stars (123 new), 11 likely γ Doradus–δ Scuti hybrid stars (8 new), 5 likely β Cephei stars (4 new), 4 likely δ Scuti–γ Doradus hybrid stars (3 new), 3 likely Maia stars (3 new), 2 likely pulsating red giants (1 new), and a new unclassified star. As for the six new δ Scuti pulsators in eclipsing binaries with P orb < 0.65 days, we found that three of them significantly exceed the upper limits of the P dom/P orb ratio. This may indicate that P dom and P orb are uncorrelated for them. Finally, we statistically analyzed the dominant pulsation periods of the 216 δ Scuti stars in eclipsing binaries. Those stars concentrate around 225 μHz and the proportion of stars in the high-frequency region is significantly higher than that of single stars, which could be ascribed to the mass-transfer process.