Scuti Pulsations Research Articles

Modelling of the fast rotatingδScuti star Altair

We present an asteroseismic study of the fast rotating star HD 187642 (Altair), recently discovered to be a 0 Scuti pulsator. We have computed models taking into account rotation for increasing rotational velocities. We investigate the relation between the fundamental radial mode and the first overtone in the framework of Petersen diagrams. The effects of rotation on such diagrams, which become important at rotational velocities above 150 km s -1 , as well as the domain of validity of our seismic tools are discussed. We also investigate the radial and non-radial modes in order to constrain models fitting the five most dominant observed oscillation modes.

Spectroscopic monitoring of the Herbig Ae star HD 104237

We present the results of multisite observations spanning two years of the pre-main-sequence Herbig Ae star HD 104237. The star was observed in high resolution spectroscopy (R ≥ 35 000) for a total of 157.3 h of effective expo- sure time, over 42 nights, corresponding to a data base of 1888 individual echelle spectra. We confirm that the HD 104237 system includes a spectroscopic binary, whose primary component HD 104237 A is pulsating. The resulting high quality radial velocity curve allows us to detect for the first time by spectroscopic means multiperiodic oscillations in a pre-main sequence star. Five different modes are detected with very high confidence, with frequencies ranging between 28.5 and 35.6 d −1 , typical of δ Scuti pulsations; an additional 3 frequencies have been extracted from the data, but with a lower level of confidence. The pattern of frequencies indicates that at least some of the detected modes are non-radial. The precise orbit determination and the measurement of the double line spectroscopic binary observed around periastron enabled us to determine a mass ratio of 1.29 ± 0.02 between the primary and the secondary; based on the primary mass of 2.2 ± 0.1 Mwe conclude that the spectroscopic secondary HD 104237 b should have a mass of 1.7 ± 0.1 Mand lie outside the pre-main sequence instability strip towards later spectral types. A search for pulsations in the radial velocity curve of the much weaker secondary component was not con- clusive at this stage. The location of the primary in the HR diagram and its position with respect to recent pre-main sequence evolutionary tracks and isochrones implies a location of the secondary indicative of spectral type K3.

HD 207651: A Triple System with Scuti and Ellipsoidal Variations But No Doradus Pulsations

We examine HD 207651 as a possible example of a star exhibiting both γ Doradus and δ Scuti type pulsations. We find photometric periods of 0.06479 and 0.06337 days with peak-to-peak amplitudes in Johnson B of 21 and 13 mmag, respectively, clearly indicating δ Scuti pulsations. Additional light variation with a period of 0.73540 days and an even larger amplitude of 31 mmag is within the range of γ Doradus pulsation periods but results instead from the ellipticity effect. HD 207651 has a composite spectrum with a weak, narrow absorption line superposed near the center of each broad metal line. The broad-lined component is the primary of a short-period, single-lined binary, which has a period of 1.4708 days, twice the period of the ellipsoidal variations seen in the photometry. We determine the primary to be an A8 giant and estimate the unseen secondary of the short-period binary to be a mid-M dwarf. The narrow-lined star, an F7: dwarf, shows velocity variability with a period of months or perhaps years. It is thus a more distant companion to the binary, making HD 207651 a triple system. All light variations come from the A8 giant primary star. Since the 0.73540 day variation results from the ellipticity effect, HD 207651 is not an example of a star that exhibits both δ Scuti and γ Doradus pulsations. The growing number of confirmed γ Doradus stars that also occur within the δ Scuti instability strip but fail to show additional δ Scuti variability makes it increasingly unlikely that the two types of pulsation can coexist in the same star.

Radial velocity study of the roAp starαCircinus

We present results of 548 high-dispersion spectra of the roAp star a Circinus over a five-night period. The pulsational radial velocities measured from the rare-earth elements, Nd III, Ha and Hβ are easily measured and occur at the photometric period. The amplitude is largest in Nd III and Ha, is lower in the rare earths and Hβ, and cannot be measured in other metal lines. This behaviour can be understood in terms of an increase of pulsational amplitude with height in the atmosphere coupled with abundance stratification. The radial velocities show a significant variation at the rotational period of 4.463 d and a marginally significant periodicity at a frequency of 8.16 cycle d - 1 . The latter may be a very low-amplitude δ Scuti pulsation.

Scuti pulsations in Pictoris

The discovery of very low-amplitude periodic brightness variations of β Pictoris is reported. Three frequencies in the approximate range 47-53 d - 1 could be extracted from four observing runs spanning a week. The character of the variations, together with the high incidence of δ Scuti pulsations in mid A type stars, suggests that β Pic is a member of this class of variable stars.

The pulsational characteristics of the Bootis type star BD Phe (HD 11413)

We have investigated the pulsational characteristics of the λ Bootis type star BD Phe. Detailed asteroseismological investigations have so far only been carried out for four members of this group of stars, with the number of identified frequencies in these stars ranging from four to seven. We present 30 h of UBVRI time-series photometry, together with 14 h of high-dispersion high signal-to-noise ratio spectroscopy of BD Phe. At least seven frequencies were detected. Since these are all present in independent sets of observations, we argue that the frequencies are fairly well determined despite our limited data. We present a very tentative discussion of the possible pulsation modes. Our results may be useful in the context of recently published δ Scuti pulsation models, which take into account the effects of diffusion.

V351 Ori as a Target for the Wet

AbstractWe present time series observations of the Herbig Ae star V351 Ori. This star presents light variations on short time scale (a few hours), typical of the δ Scuti pulsation. The new data are briefly described and the possibility to observe V351 Ori with the WET is discussed.

Six New γ Doradus Stars

ABSTRACTWe present high‐resolution spectroscopy and precision photometry of six new γ Doradus stars, one of which was independently discovered by another group. This brings the total number of confirmed γ Doradus variables to 30. All six of these variables fall in the spectral class range F0–F2; all but one are subgiants. The six stars have between one and five photometric periods in the range 0.3–1.2 days. We find no evidence for higher frequency δ Scuti pulsations in any of these six stars. Our spectroscopic observations reveal HD 108100 to be the first confirmed γ Doradus variable with composite broad and narrow line profiles suggesting the presence of a circumstellar shell or disk. HD 221866 has the most asymmetric absorption lines of the six stars in this paper and also the largest photometric amplitude. Most of the 30 confirmed γ Doradus variables lie in a fairly tight region of the H‐R diagram on or just above the main sequence that partially overlaps the cool edge of the δ Scuti instability strip. However, three stars, including two of the new variables in this paper, are subgiants that lie well within the δ Scuti strip. Among the 30 confirmed γ Doradus variables, we find no correlation between the photometric periods and intrinsic color, absolute magnitude, or luminosity.

Four New δ Scuti Pulsators from a Variability Survey of 131 Stars

ABSTRACTIn a photometric variability survey of 131 stars with B≲14 mag, we have found four new δ Scuti stars. We were sensitive to oscillation amplitudes as low as a few millimagnitudes (mmag). The detection rate of short‐period (P<0.1 days) pulsating variable stars, which may be relevant for planned large‐variability surveys such as the Global Astrometric Interferometer for Astrophysics, the Panoramic Optical Imager, and even the Large‐Aperture Synoptic Survey Telescope, was therefore 3%. All four new variable stars have low pulsation amplitude (tens of mmag), and one has a very short period (0.0198 days). This star is one of the fastest known δ Scuti pulsators. The short period of this variable star makes it observationally tractable, and it may therefore be a particularly good candidate for asteroseismological studies. All four new variable stars will add to the cadre of low‐amplitude and relatively short period δ Scuti stars that are potentially useful for learning about the structure of stars on or near the main sequence, slightly more massive than the Sun.

On the relationship between the δ Scuti and γ Doradus pulsators

We searched for δ Scuti-type pulsations amongst known and candidate γ Doradus stars. The motivations for such a project come from the need to understand the relationship of these two classes of pulsator better, from the present poor knowledge of the hot border of the γ Doradus phenomenon, and from the exciting prospects for asteroseismology should stars be found which have both types of pulsation excited. We acquired 270 h of observations and monitored a total of 26 stars. One target, HD 209295, turned out to be a member of both classes of pulsating star, but this object is peculiar in the sense that it is a close binary. We classify six of our targets as new bona fide γ Doradus stars, whereas nine more are good γ Doradus candidates, and three turned out to be ellipsoidal variables. One of our programme stars was found to be a δ Scuti star, with no additional γ Doradus variations. Furthermore, one star was already known to be a bona fide γ Doradus star, and we could not find an unambiguous explanation for the variability of five more stars. The analysis of our data together with improved knowledge of stars from the literature enabled us to revise the blue border of the γ Doradus phenomenon towards cooler temperatures. This new blue edge is much better defined than the previous one and extends from a temperature of about 7550 K on the ZAMS to 7400 K one magnitude above it. Five bona fide γ Doradus stars we observed are located inside the δ Scuti instability strip, but none of them exhibited observable δ Scuti pulsations. We therefore suggest that γ Doradus stars are less likely to be δ Scuti pulsators compared with other normal stars in the same region of the lower instability strip. In addition, we show that there is a clear separation between the pulsation constants Q of δ Scuti and γ Doradus stars. The γ Doradus stars known to date all have Q>0.23 d.

Mode characterisation inδScuti stars

We present new spectroscopic observations of four bright Scuti pulsators. Line indices of the Balmer lines can be used to establish mode identications using the ratio R between such line index amplitudes and photometric amplitudes. For the well known radial pulsator Pup an absolute value of the amplitude ratio of the radial mode was found to R =0 :43, consistent with earlier values of R 0:5 reported for other Scuti stars. In GN And we recover the recently reported newly excited mode, while the former dominant mode was not recovered. We conrm that V1208 Aql is a non-radial pulsator, containing two modes of dierent degree. In V1208 Aql we report a previously unseen mode behavior: the phases of both modes are reversed between the core and wings of the H line, suggesting the presence of more undetected modes. For AV Cet we nd that the dominant mode is a previously undetected one. We suggest the undertaking of new photometric observations of Pup, GN And, V1208 Aql and AV Cet to determine the frequencies and amplitudes of the pulsations.

δ Scuti Variables in the HR Diagram

The location of the δ Scuti variables in the HR diagram is discussed on the basis of HIPPARCOS parallaxes and uvbyβ photometry together with the R00 catalogue (Rodríguez et al., 2000). In particular, the properties of the α Scuti-type pulsators with nonsolar surface abundances (SX Phe, λ Boo, ρ Pup, δ Del and classical Am stars subgroups) are examined.The latter four classes of stars are spectroscopically defined subclasses with surface abundance anomalies. Although the stars ρ Pup and δ Del are also pulsators, the groups named after these stars should not be regarded as pulsation subclasses of δ Scuti stars. The abundance anomalies in these stars affect the pulsation properties, e.g., the classical Am stars are constant in light or show only small pulsation amplitudes (e.g., HD 1097). These four groups are only a small selection from the bewildering zoo of stars with unusual surface abundances in this temperature region and represent the groups with δ Scuti pulsation.

Pulsation in the pre-main-sequence Herbig Ae star HD 142666

Asteroseismology of pre-main-sequence δ Scuti stars has the potential not only to provide unprecedented constraints on models of these stars, but also to allow for the possibility of detecting evolutionary period changes, thus providing a direct measure of the pre-main-sequence evolutionary time-scale. In the last two years, the published number of such stars known has doubled from four to eight. Searches are now being conducted amongst the Herbig Ae stars, which are considered to be excellent candidates. We announce the discovery of δ Scuti pulsation in one Herbig Ae star, HD 142666, which lies within Marconi & Palla's theoretically predicted instability strip for pre-main-sequence stars, making this the ninth known pre-main-sequence δ Scuti star. We also demonstrate a lack of δ Scuti pulsation in another such star, HD 142527.

On the δ Scuti variability in the pre-main sequence Herbig Ae star HR 5999

A reanalysis of photometric data for the bright, southern Herbig Ae star HR 5999 obtained by Praderie et al. (1991) at ESO in 1985 shows Scuti pulsation with the same period, 4.812 d 1 , and semi-amplitude, 6 mmag, found by Kurtz & Marang (1995) in data obtained from SAAO in 1994. HR 5999 is, therefore, a potential candidate to test Breger & Pamyatnykh's (1998) predictions of evolutionary period changes 10 to 100 times faster in pre- main sequence Scuti stars than in post-main sequence stars. We argue that the low frequency, low amplitude 2 CVn variability of HR 6000 with a period near 2 d, and its long-term variability are no hindrance to using it as a comparison star for study of the Scuti variability of HR 5999. With a separation of 44 arcsec between HR 5999 and HR 6000, and similar brightnesses for the two stars, we urge the use of small telescopes with CCD photometers to obtain the long-term data necessary for the study of period change. We point out that this can be done under less-than-ideal photometric conditions and urban lighting with CCD photometers on small telescopes which are widely available at small observatories, at universities and at the home observatories of serious amateur astronomers.

δScuti and related stars: Analysis of the R00 Catalogue

We present a comprehensive analysis of the properties of the pulsating δ Scuti and related variables based mainly on the content of the recently published catalogue by Rodriguez et al. ([CITE], hereafter R00). In particular, the primary observational properties such as visual amplitude, period and visual magnitude and the contributions from the Hipparcos, OGLE and MACHO long-term monitoring projects are examined. The membership of these variables in open clusters and multiple systems is also analyzed, with special attention given to the δ Scuti pulsators situated in eclipsing binary systems. The location of the δ Scuti variables in the H-R diagram is discussed on the basis of HIPPARCOS parallaxes and uvbyβ photometry. New borders of the classical instability are presented. In particular, the properties of the δ Scuti pulsators with nonsolar surface abundances (SX Phe, λ Boo, ρ Pup, δ Del and classical Am stars subgroups) are examined. The Hipparcos parallaxes show that the available photometric uvbyβ absolute magnitude calibrations by Crawford can be applied correctly to δ Scuti variables rotating faster than 100 km s with normal spectra. It is shown that systematic deviations exist for the photometrically determined absolute magnitudes, which correlate with and . The photometric calibrations are found to fit the λ Boo stars, but should not be used for the group of evolved metallic-line A stars. The related γ Dor variables and the pre-main-sequence δ Scuti variables are also discussed. Finally, the variables catalogued with periods longer than 025 are examined on a star-by-star basis in order to assign them to the proper δ Scuti, RR Lyrae or γ Dor class. A search for massive, long-period δ Scuti stars similar to the triple-mode variable AC And is also carried out.

A Survey for Pulsating Ap Stars from Naini Tal

Pulsation is ubiquitous among chemically normal A-type stars, but comparatively rare among chemically peculiar Am and Ap stars of the same temperature range. The conventional explanation for this is that diffusion produces the surface abundance anomalies in the Am and Ap stars, and also drains He from the He-II ionisation zone, thus quenching the κ-mechanism that drives δ Scuti pulsation. The pulsating Am and Ap stars exhibit dichotomous pulsation characteristics. The Am stars (and related stars) exhibit low-overtone δ Scuti pulsation, with amplitudes ranging from a few mmag to 0.1 mag. The pulsating Ap stars exhibit high-overtone pulsation with periods in the range 6-16 min and Johnson B semi-amplitudes typically ≤ 5 mmag. These stars are referred to as rapidly oscillating Ap stars, or ‘roAp’ stars (the see review by Martinez &amp; Kurtz 1995).

Second Overtone Pulsators among δ Scuti Stars

We investigate the modal stability of stellar models at masses and luminosity levels corresponding to post-main-sequence luminous δ Scuti pulsators. The envelope models have been computed at fixed mass value (M/M☉ = 2.0), luminosity level [log (L/L☉) = 1.7], and chemical composition (Y = 0.28, Z = 0.02). According to a nonlinear approach to radial oscillations, the present investigation for the first time predicts the occurrence of stable second overtone pulsators . More generally, we found that when moving inside the instability strip from lower to higher effective temperatures, the models show a stable limit cycle in three different pulsation modes: fundamental and first and second overtones. The shapes of both light and velocity curves are presented and discussed, providing a useful tool for the identification of second overtone pulsators among the known groups of radially pulsating stars. Comparison with observations shows that our nonlinear, nonlocal, and time-dependent convective models provide light curves in agreement with observed values, suggesting that second overtone pulsators have already been observed, though misclassified as fundamental pulsators. In a limited region of the instability strip we also found some models presenting mixed-mode features, i.e., radial pulsators that show a stable limit cycle in more than one pulsational mode. The period ratios of mixed-mode pulsators obtained by perturbing the first and the second overtone radial eigenfunctions are in agreement with observed values. This result is a crucial point for understanding the pulsation properties of δ Scuti stars, since it provides sound evidence that these variables during their evolution off the main sequence are pure or mixed-mode radial pulsators. Finally, the physical structure and the dynamical properties of second overtone pulsators are discussed in detail. The role played by the nodal lines in the destabilization of second overtone pulsators is also pointed out.

Lithium Abundances in delta Scuti Stars and Their Relationship with the Lithium Dip

view Abstract Citations (24) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lithium Abundances in delta Scuti Stars and Their Relationship with the Lithium Dip Russell, Stephen C. Abstract Several years ago it was suggested that mass loss from δ Scuti stars may transform them into the lithium "dip,, stars seen in open clusters like Coma Berenices and the Hyades. Although there is evidence to indicate that this is unlikely, there has never been a study made of the lithium abundances in δ Scuti stars themselves. This paper reports the results of a survey of lithium in these stars. Lithium was detected in about half of the stars studied, with only upper limits being determined for the others. For those stars with measurable lithium there is evidence for a moderate depletion at the cooler temperatures. For those stars with no measurable lithium, the upper limits are consistent with only moderate depletion in all except one or two cases. There is no correlation between lithium depletion and a star's rotational velocity, mass, gravity, period of pulsation, or metallicity. There is, therefore, no support for the suggestion that mass loss on the main sequence due to δ Scuti pulsation may be responsible for the lithium dip stars. However, the data cannot exclude the possibility that mass loss may be responsible for a degree of lithium depletion in δ Scuti stars. Interestingly, though most elements are in solar ratio to iron, there is evidence for a pronounced carbon abundance deficiency in all of the stars with measurable carbon. Publication: The Astrophysical Journal Pub Date: October 1995 DOI: 10.1086/176261 Bibcode: 1995ApJ...451..747R Keywords: STARS: DELTA SCUTI; STARS: ABUNDANCES; STARS: EVOLUTION; STARS: MASS LOSS full text sources ADS | data products SIMBAD (24)

Metallicism and pulsation: the discovery of large-amplitude δ Scuti pulsation in a high-metallicity ρ Puppis star, HD 40765

Metallicism and pulsation: the discovery of large-amplitude δ Scuti pulsation in a high-metallicity ρ Puppis star, HD 40765

Long-Term Amplitude and Period Variations of δ Scuti Stars: A Sign of Chaos?

AbstractOn short time-scales of under a year, the vast majority of δ Scuti stars studied in detail show completely regular multiperiodic pulsation. Nonradial pulsation is characterized by the excitation of a large number of modes with small amplitudes. Reports of short-term irregularity or nonperiodicity in the literature need to be examined carefully, since insufficient observational data can lead to an incorrect impression of irregularity. Some interesting cases of reported irregularities are examined.A few δ Scuti stars, such as 21 Mon, have shown stable variations with sudden mode switching to a new frequency spectrum. This situation might be an indication of deterministic chaos. However, the observational evidence for mode switching is still weak.One the other hand, the case for the existence of long-term amplitude and period changes is becoming quite convincing. Recently found examples of nonradial pulsators with long-term changes are 4 CVn, 44 Tau, τ Peg and HD 2724. (We note that other δ Scuti pulsators such as X Cae and θ2 Tau, have shown no evidence for amplitude variations over the years.) Neither the amplitude nor the period changes are periodic, although irregular cycles with time scales between a few and twenty years can be seen. While the amplitude changes can be very large, the period changes are quite small. This property is common in nonlinear systems which lead to chaotic behavior. There exists observational evidence for relatively sudden period jumps changing the period by about 10−5 and/or slow period changes near dP/dt ≤ 10−9. These period changes are an order of magnitude larger than those expected from stellar evolution.The nonperiodic long-term changes are interpreted in terms of resonances between different nonradial modes. It is shown that a large number of the nonradial acoustic modes can be in resonance with other modes once the mode interaction terms, different radial orders and rotational m-mode splitting are considered. These resonances are illustrated numerically by the use of pulsation model. Observational evidence is presented that these interaction modes exist in the low-frequency domain.