Dor Variables Research Articles

WASP 0346-21: An EL CVn-type Eclipsing Binary with Multiperiodic Pulsations in a Triple System

Very Large Telescope/UVES spectroscopic and Transiting Exoplanet Survey Satellite (TESS) photometric observations for WASP 0346-21 allow the direct determination of its physical properties, along with the detection of a circumbinary object and oscillating signals. The high-resolution spectra yielded the radial velocities of all three stars and the atmospheric parameters of T eff,A = 7225 ± 42 K, [M/H] = 0.30 ± 0.03 dex, and v A sini = 78 ± 5 km s−1 of the primary component. The combined analysis of these observations resulted in the fundamental parameters of the eclipsing components and the third light of l 3 = 0.043 ± 0.004, which is consistent with the light contribution of the tertiary star observed in the echelle spectra. WASP 0346-21 A resides within the overlapping main-sequence domain of δ Sct and γ Dor variables, while the secondary component of M B = 0.185 ± 0.013 M ⊙, R B = 0.308 ± 0.023 R ⊙, T eff,B = 10,655 ± 146 K, and L B = 1.09 ± 0.17 L ⊙ matches well with the low-mass white dwarf (WD) model for Z = 0.01, corresponding to the thick disk population classified by the Galactic kinematics. Multifrequency analyses were performed on the residual TESS data after removing the binarity effects. The low frequencies around 26.348 day−1 and 17.683 day−1 are δ Sct pulsations originating from WASP 0346-21 A, and the high frequencies of 97.996 day−1 and 90.460 day−1 are considered to be extremely low-mass WD oscillations. These results demonstrate that WASP 0346-21 is a hierarchical triple system, consisting of an EL CVn binary with multiperiodic pulsations in each component and a distant outer tertiary.

Nine Bright γ Doradus Variables Discovered with Ground-based Photometry

Abstract We have used precise photometric and high-dispersion spectroscopic observations to study nine candidate γ Doradus (γ Dor) stars, identified as optically variable comparison stars in our photometric studies of Sun-like stars. In this paper, we confirm these nine candidates as new γ Dor variables. All exhibit sinusoidal variability with amplitudes between 6 and 65 mmag in Johnson B and periods from 0.28 to 1.13 days. All lie in the same region of the H-R diagram as our previously confirmed γ Dor stars. Of the nine systems, one is a single-lined spectroscopic binary (SB1), two are double-lined spectroscopic binaries (SB2), and the remaining six are single stars. We present orbits for the three binary systems: HD 34415, HD 144839, and HD 182735. Their periods are 6400 days or 17.5 yr (adopted), 995 ± 7 days, and 1052.4 ± 0.2 days, respectively. We compare our photometric periods with those we derive for six of the nine stars observed with the Transiting Exoplanet Survey Satellite to strengthen the confirmation of these new γ Dor variables. Finally, because the distribution of γ Dor stars in the H-R diagram overlaps with the red edge of the δ Scuti (δ Sct) instability strip, we use our ground-based photometric results for the 73 γ Dor stars confirmed with our Automatic Photoelectric Telescopes over the past two decades to look at the incidence of hybrid δ Sct/γ Dor stars; these are highly valuable targets for asteroseismology.

Rapidly oscillating TESS A–F main-sequence stars: are the roAp stars a distinct class?

ABSTRACT From sector 1–44 TESS observations, 19 new rapidly oscillating Ap (roAp) stars, 103 ostensibly non-peculiar stars with roAp-like frequencies, and 617 δ Scuti stars with independent frequencies typical of roAp stars were found. Examination of all chemically peculiar stars observed by TESS resulted in the discovery of 199 Ap stars that pulsate as δ Sct or γ Dor variables. The fraction of pulsating Ap stars is the same as the fraction of pulsating chemically normal stars. There is no distinct separation in frequency or radial order between chemically peculiar δ Sct stars and roAp stars. In fact, all the features that originally distinguished roAp from δ Sct stars in the past have disappeared. There is no reason to assume that the high frequencies in roAp stars are driven by a different mechanism from the high frequencies in chemically normal stars. However, chemically peculiar stars are far more likely to pulsate with high frequencies. The term ‘roAp’ should be dropped: all roAp stars are normal δ Scuti stars.

More than two hundred and fifty thousand spectroscopic binary or variable star candidates discovered by LAMOST

About 786.4 thousand stars were observed by LAMOST twice or more during the first stage of its spectroscopic survey. The radial velocity differences for about 256 thousand targets are larger than 10 km s−1 and they are possible spectroscopic binary or variable candidates (SBVCs). It is shown that most SBVCs are slightly metal poorer than the Sun. There are two peaks in the temperature distribution of SBVCs around 5760 K and 4870 K, while there are three peaks in the distribution of the gravitational acceleration at 2.461, 4.171 and 4.621 cm s−2. The locations of SBVCs on the [Fe/H]-T, [Fe/H]-log g, log g-T and H-R diagrams are investigated. It is found that the detected SBVCs could be classified into four groups. The first group has higher log g ∼4.621 and lower T ∼ 4870 K which are mainly cool red dwarf binaries. The second group of SBVCs has log g around 4.171 cm s−2 that includes binaries and pulsating stars such as δ Sct and γ Dor variables. The gravitational accelerations of the third group of SBVCs are higher and some of them are below the zero-age main sequence. They may be contact binaries in which the primary components are losing energy to the secondaries in the common envelopes and are at a special stellar evolutionary stage. The last group is composed of giants or supergiants with log g around 2.461 cm s−2 that may be evolved pulsating stars. One target (C134624.29+333921.2) is confirmed as an eclipsing binary with a period of 0.65 days. A preliminary analysis suggests that it is a detached binary with a mass ratio of 0.46. The primary fills its critical Roche lobe by about 89%, indicating that mass transfer will occur between the two components.

Physical properties of γ Doradus pulsating stars and their relationship with long-period δ Scuti variables

We present LAMOST data on 168 γ Doradus (γ Dor) pulsating stars including stellar atmospheric parameters of 137 variables and spectral types for all of the samples. The distributions of period (P), temperature (T), gravitational acceleration (log(g)) and metallicity [Fe/H] are shown. It is found that most γ Dor variables are main-sequence stars with early F spectral types and temperatures from 6880 K to 7280 K. They are slightly more metal poor than the Sun with a metallicity range from −0.4 to 0. On the H-R and log g–T diagrams, both the γ Dor and δ Scuti (δ Sct) stars occupy in the same region and some are beyond the borders predicted by current stellar pulsation theories. It is discovered that the physical properties of γ Dor stars are similar to those of long-period δ Sct (P > 0.3 d) stars. The stellar atmospheric parameters are all correlated with the pulsation period for short-period δ Sct variables (P < 0.3 d), but there are no such relations for γ Dor or long-period δ Sct stars. These results reveal that γ Dor and long-period δ Sct are the same group of pulsating stars and they are different from short-period δ Sct variables. Meanwhile, 33 γ Dor stars are identified as candidates of binary or multiple systems.

The first comprehensive catalog of γ Dor pulsators and their characteristics

We present the first comprehensive catalog of the γ Doradus type pulsating stars. This catalog covers observational properties of all γ Dor variables obtained until January 2017. The photometric and physical properties of 109 well−knownγ Dor pulsators, 18 hybrid stars, 13 anomalous γ Dor stars, and 22 γ Dor stars in eclipsing plus 1 non–eclipsing SB2 binary systems are presented as separate tables. In addition, 291 candidate γ Dor variables discovered by CoRot, 307 candidate γ Dor, 205 hybrid and 11 candidate γ Dor in binaries discovered by Kepler were also presented. Distribution of the genuine single γ Dor pulsators in the Ppuls-Teff, Amplitude-Teff, Amplitude-Ppuls and L-Teff diagrams are presented and discussed. We find following correlations for the γ Dor pulsators in the eclipsing binaries: Ppuls ∝ Porb0.27,Ppuls ∝ Q0.45, and Ppuls ∝ r−0.44, where (Q) is the pulsation constant and r is the fractional radius of the pulsating component in the binary system. The correlation coefficients are not high enough due to limited sample and scattering in the data.

THE SPECTROSCOPIC ORBITS OF FIVE γ DORADUS STARS

ABSTRACT We have determined the spectroscopic orbits of five γ Dor variables, HD 776, HD 6568, HD 17310, HD 19684, and HD 62196. Their orbital periods range from 27.8 to 1163 days and their eccentricities from 0.01 to 0.65. Of the five systems, only HD 19684 shows lines of its binary companion, but those lines are always so weak and blended with the lines of the primary that we were unable to measure them satisfactorily. The velocity residuals of the orbital fits were searched for periodicities associated with pulsation. No clear, convincing case for velocity periodicities in the residuals was found in four of the five stars. However, for HD 17310 we identified a period of 2.13434 days, a value in agreement with the largest amplitude period previously found photometrically for that star. The velocity residuals of HD 62196 have a long-term trend suggesting that it is a triple system.

The Kepler view of γ Doradus stars

Visual classification of over 10 000 stars in the Kepler data base has revealed a class of stars with almost monoperiodic light variations and characteristic beating. A subset of these stars have a larger light amplitude and asymmetric light curves with larger variation in maximum brightness than in minimum brightness. The beating is mostly a result of two dominant, closely spaced frequencies. A third group of stars shows multiple low frequencies of comparable amplitudes. All three types of star fall in the region of the Hertzsprung–Russell diagram where γ Dor stars are found and we therefore identify them as γ Dor variables. However, stars with migrating star-spots also have symmetric light curves with beats, so it is likely that the sample is contaminated by non-pulsating stars of this type. If we assume that the dominant frequency in stars with beats is the rotational frequency, the resulting distribution of equatorial rotational velocities matches that of field stars of similar temperature and luminosity. We therefore conclude that the pulsation periods of these stars must be close to their rotational periods. The third group with multiple frequencies may be slowly rotating γ Dor stars. This investigation is closely related to the presence of low frequencies in δ Scuti stars which we briefly discuss.

Linear analyses for the stability of radial and non-radial oscillations of massive stars

In order to understand the periodic and semi-periodic variations of luminous O- B- A-type stars, linear nonadiabatic stability analyses for radial and nonradial oscillations have been performed for massive evolutionary models ($8M_\odot - 90M_\odot$). In addition to radial and nonradial oscillations excited by the kappa-mechanism and strange-mode instability, we discuss the importance of low-degree oscillatory convection (nonadiabatic g$^-$) modes. Although their kinetic energy is largely confined to the convection zone generated by the Fe opacity peak near $2\times10^5$K, the amplitude can emerge to the photosphere and should be observable in a certain effective temperature range. They have periods longer than those of the radial strange modes so that they seem to be responsible for some of the long-period microvariations of LBVs (S Dor variables) and $\alpha$ Cyg variables. Moreover, monotonously unstable radial modes are found in some models whose initial masses are greater than or equal to $60M_\odot$ with $Z=0.02$. The monotonous instability probably corresponds to the presence of an optically thick wind. The instability boundary roughly coincides with the Humphreys-Davidson limit.

HD 8801: A Unique Single Am Star with γ Doradus and δ Scuti Pulsations

We have discovered the first example of a star pulsating intrinsically with both γ Doradus and δ Scuti frequencies. The star, HD 8801, is an Am metallic-line star that appears to be single. Since the vast majority of Am stars are members of binary systems with periods less than 1000 days and also do not pulsate, HD 8801 possesses a very unusual, if not unique, combination of physical properties. Our photometry, acquired with an automatic telescope at Fairborn Observatory, resolves six independent pulsation periods between 0.048 and 0.404 days. The two longest periods lie within the range of γ Dor variables, while the four shorter periods are within the range of δ Sct stars. Eleven radial velocities, obtained over an 11 month period, have a mean of 0.8 ± 0.3 km s-1, providing no evidence for a spectroscopic companion. The star is on the main sequence and lies within both the γ Dor and δ Sct instability strips. Pulsation constants computed for the six periods agree with pulsation constants computed for other γ Dor and δ Sct variables. HD 8801 is also the first confirmed case of a metallic-line star pulsating with γ Dor frequencies. Its projected rotational velocity of 55 km s-1 is typical for Am stars, which, as a group, rotate more slowly than normal A stars. HD 8801's slow rotation compared to normal A stars does not appear to arise from either a binary companion or evolutionary expansion and thus remains a puzzle. The coexistence of metallicism and pulsation in several main-sequence stars near the red edge of the δ Sct strip contradicts recent models that predict pulsations only in more evolved stars.

High-resolution spectroscopy of two LBV cycles of HR Car

Luminous Blue Variables (LBVs or S Dor Variables) are showing characteristic variability of very long timescales of a decade and more. During their expansion and contraction phases, they move across a wide part of the H-R diagram with dramatic changes of their stellar wind characteristics, radius and temperature. We present results of our long-term spectroscopic monitoring campaigns for the galactic star HR Car with optical spectra taken over 13 years and two minimum and maximum phases observed during this time.

Light variations of massive stars (α Cyg variables)

We discuss photometric monitoring (VBLUW system) of three B(e) supergiants. All three objects appear to be variable. They are subject to two (R 66 and R 126 in the LMC) and three (S 18 in the SMC) types of light oscillations which range from a few days to years, and are probably due to pulsations. We argue that a classication as Cyg variables is justied. Their classication as mixed B(e)/S Dor variables is less certain, though not impossible. Also based on other cases, a strong B(e){S Dor variable connection seems to be present.

The multiperiodicity of the γ Doradus stars HD 224945 and HD 224638 as detected from a multisite campaign

We discuss new photometric data collected on the Dor variables HD 224945 and HD 224638. Multiperiodicity was detected in both stars, thanks to the clear spectral window of a multisite campaign that involved ve observatories. HD 224945 shows the shortest period among the Dor stars, i.e., 0.3330 d. The pulsation behaviour is very dierent: HD 224945 displays a set of frequencies spread over an interval much larger than that of HD 224638. We clearly found evidence for amplitude variations in the excited modes by comparing data from dierent years. HD 224945 and HD 224638 are among the best examples of Dor stars that show multimode pulsations, which make them very interesting from an asteroseismological point of view.

δ Scuti Variables with Periods Longer than 0.25 Days

AbstractVariables listed as δ Scuti-type pulsators in the R00 catalogue (Rodriguez et al., 2000) with periods longer than 0.d25 are examined on a star-by-star basis, in order to discriminate their true nature (δ Scuti, RR Lyr or γ Dor-type). From this study, it seems that three stars (DH Peg, UY Cam and YZ Cap) are RR Lyr pulsators rather than δ Scuti variables. Moreover, two variables (AD Ari and DE Oct) seem to be γ Dor variables with the shortest periods known to date (0.d2699 and 0.d2778, respectively).

A Proposed Pulsation Driving Mechanism for γ Doradus Variable Stars

AbstractWe propose a pulsation driving mechanism for γ Doradus variable stars. This mechanism requires that the local convective timescale at the base of the envelope convection zone be comparable to or longer than the pulsation period. This mechanism explains both the red and blue edges of the γ Dor instability strip. We predict that some candidate γ Dor stars summarized by Handler (1999) may actually be too hot or too cool to be γ Dor variables.

P Cygni in a short S Doradus phase. Spectroscopic and photometric evidences

We studied the long-term spectral and photometric behaviour of P Cygni over the 13.8 year interval from March 1985 to January 1999. The UBV photometry reveals a slow (7.4-year), low-amplitude (0.1 mag) variation in V in which the star becomes redder when it brightens and vice versa. It underwent a possible maximum in the winter of 1985 (between JD 2 446 000 and JD 2 446 200), a minimum in the winter of 1989 (between JD 2 447 500 and JD 2 447 700), a maximum in the fall of 1992 (between JD 2 448 800 and JD 2 449 000), and a minimum in the spring of 1996 (between JD 2 450 100 and JD 2 450 300) The properties of this variation are typical for weak-active S Dor variables in \short S Dor phase (van Genderen 2001). Simultaneous spectroscopic observations show changes in the H equivalent width (corrected for the eect of the changing continuum) in positive correlation with the 7.4-year photometric oscillation in the V -band brightness. This result is interpreted as an indication that in P Cygni an increase in the stellar brightness, during the 7.4-year SD phase, is likely accompanied by an increase in the mass-loss rate. In this behaviour P Cygni is similar to S Dor and R71. From simple considerations, it is concluded that the 7.4-year SD cycle is probably a combination of an increasing radius/decreasing eective temperature and an expanding pseudo-photosphere.

S Doradus variables in the Galaxy and the Magellanic Clouds

The goal in writing this paper is ve fold: (1) to summarize the scientic achievements in the 20th century on S Dor variables (or LBVs); (2) to present an inventory of these variables in the Galaxy and the Magellanic Clouds with a description of their physical state and instability properties; (3) to emphasize the photometric achievements of the various types of instabilities. Generally this seems to be a neglected item resulting in a number of misunderstandings continuously wandering through literature; (4) to investigate the structure of the S Dor-area on the HR-diagram; (5) to estimate the total numbers of S Dor variables in the three stellar systems. The position of the strong active S Dor variables in minimum brightness obey the following linear relation on the HR-diagram:logL=L =1 :37 logTe 0:03: The relatively small dispersion of less active and supposed ex- and dormant S Dor variables with respect to this relation is twice as large at the blue side than at the red side. This might be caused by evolution to the WR stage and/or to high rotation. S Dor variables can be subject to ve types of instabilities: the very rare genuine eruptive episodes (the \SD-eruptions), two dierent brightening phases caused by slow pulsations (the \SD-phases): one on a time scale of years, the other on a time scale of decades at a more or less constant luminosity and two types of microvariations: one on a time scale of weeks, the other on a time scale of about 100 d. So far, no periodicities of light curve characteristics of any of these instabilities have ever been found. The durations of active and non-active stages are estimated for about half of the sample based on scattered magnitude estimations such as from historical records, and on modern monitoring campaigns. It would be a misunderstanding to believe that all S Dor variables should be always spectacular. It is estimated that most of them will not be spectacular at all for at least 70% of their lifetime as an S Dor variable.

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.

The Long-Term Variability of Luminous Blue Variables

AbstractThe stars known as Luminous Blue Variables include two very distinctive subgroups - the S Dor-type variables which basically define what we call an LBV and the much rarer ‘giant eruption’ LBV’s which include famous stars like η Car and P Cyg. The distinctive characteristics and long term variability of these two groups is reviewed. The lesser 1890 eruption of η Car is shown to have been much more significant than previously believed and resembles the second peak seen in the historic light curve of P Cyg. Because so many, if not all, stars in certain parts of the HR diagram appear to be luminous, blue, and variable, I suggest returning to our previous designation - S Dor variables and η Car variables for these two important groups of stars.

Asteroseismology from MUSICOS multi-site campaigns

For the MUSICOS international project (MUlti-SIte COntinuous Spectroscopy), the instrument concept and multi-site operational constraints for microvariability and asteroseismology are discussed. Operations and results from previous MUSICOS international campaigns in 1989, 1992, 1994, 1996 involving Pic du Midi, Haute-Provence, South Africa, La Palma, Kitt Peak, ESO La Silla, Hawaii, Anglo-Australian, Xinglong and other observatories are presented. Some MUSICOS asteroseismology highlights on micro-variability and non-radial pulsations on Be, δ Scuti, O and B, γ Dor variables are reviewed. Perspectives for solar-type asteroseismology with multi-site networks in support to space asteroseismology missions such as COROT, are discussed.