Evolutionary Period Changes Research Articles

Non-evolutionary effects on period change in Magellanic Cepheids

Context. Period change studies offer a novel way to probe the evolution and dynamics of Cepheids. While evolutionary period changes have been well studied both observationally and theoretically, non-evolutionary period changes lack a systematic and quantitative description. Here, we deal with one such aspect of non-evolutionary period changes related to a crucial property, namely, the binarity-based nature of a Cepheid. With the advent of long-term photometry surveys covering Magellanic fields, the census of classical Cepheids in binary (or multiple) systems outside the Milky Way is timely. This may have implications for crucial aspects such as the period-luminosity relationship calibrations and our understanding of the nature of Cepheid companions. Aims. The overall objective is to have a quantitative understanding of the full picture of non-evolutionary period changes in Cepheids to develop a formalism to disentangle it from the secular evolutionary period change. In the first paper in the series, we aim to conduct a systematic search for non-evolutionary period changes to look for Cepheids in likely binary configurations and quantify their incidence rates in the Magellanic Clouds. Methods. We collected more than a decade-long time-series photometry from the publicly available, Optical Gravitational Lensing Experiment (OGLE) survey, with more than 7200 Cepheids altogether from the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). Our sample contains both fundamental-mode and first-overtone mode Cepheids. Then, we calculate d the observed minus calculated (O–C) diagrams to reveal the light-travel time effect (LTTE). Finally, we calculated the minimum companion masses of the Cepheids and compared them with the predictions from Cepheid population synthesis results. Results. In our search, out of an overall sample of more than 7200 Cepheids, we found 52 candidate Cepheid binary systems in the LMC (30 fundamental and 22 first-overtone mode) and 145 in the SMC (85 fundamental and 60 first-overtone mode). The majority of the sample is characterized by orbital periods of 2000–4000 d and eccentricities of 0.2–0.5. Moreover, we report two candidates in each galaxy with the Cepheid likely existing with a giant companion. The incidence rate ratio for SMC to LMC calculated from our sample is in agreement with binary Cepheid population synthesis predictions. Conclusions. In our attempt to quantify the non-evolutionary period change connected with the LTTE, our systematic search has enriched the Cepheid binary sample by a factor of about 2 in both galaxies. The future spectroscopic follow-up can confirm the binarity nature of our sample and constrain the orbital parameters.

Evolutionary Period Changes for 52 Cataclysmic Variables, and the Failure for the Most-fundamental Prediction of the Magnetic Braking Model

The evolution of cataclysmic variables (CVs) is driven by period changes ( Ṗ ), for which the long-venerable consensus is the magnetic braking model (MBM). The MBM has its only distinctive assumption being a power-law “recipe” describing the angular momentum loss (AML) in the binary, producing a single unique evolutionary track with Ṗ as a function of the orbital period. This required prediction can be used to test the most-fundamental assumption of MBM, but it has never been tested previously. In this paper, I collect Ṗ measures for 52 CVs of all types. First, 44% of the CVs have positive Ṗ , with such being impossible in MBM. Second, even among the CVs with negative Ṗ , their Ṗ measures are always more negative than required by MBM, with an average deviation of 110×. Third, three CVs have large chaotic variations in Ṗ that are impossible for MBM, proving that some unknown mechanism exists and is operating that dominates for these systems. Fourth, the MBM does not account for the long-term effects on evolution arising from the large sudden period decreases seen across many nova events, with this unaccounted effect dominating for the majority of nova systems and changing the sign of the overall evolutionary Ṗ . Fifth, three recurrent novae are observed to suddenly change Ṗ by an order of magnitude across a nova event, with this being impossible in the MBM. In all, the required MBM Ṗ predictions all fail for my 52 CVs, usually by orders of magnitude, so the MBM AML-recipe is wrong by orders of magnitude.

Amplitude and frequency variability of the pulsating DB white dwarf stars KUV 05134+2605 and PG 1654+160 observed with the Whole Earth Telescope

We have acquired new time series photometry of the two pulsating DB white dwarf stars KUV 05134+2605 and PG 1654+160 with the Whole Earth Telescope. Additional single-site photometry is also presented. We use all these data plus all available archival measurements to study the temporal behaviour of the pulsational amplitudes and frequencies of these stars for the first time. We demonstrate that both KUV 05134+2605 and PG 1654+160 pulsate in many modes, the amplitudes of which are variable in time; some frequency variability of PG 1654+160 is also indicated. Beating of multiple pulsation modes cannot explain our observations; the amplitude variability must therefore be intrinsic. We cannot find stable modes to be used for determinations of the evolutionary period changes of the stars. Some of the modes of PG 1654+160 appear at the same periods whenever detected. The mean spacing of these periods (≈40 s) suggests that they are probably caused by non-radial gravity-mode pulsations of spherical degree ℓ = 1. If so, PG 1654+160 has a mass around 0.6 M⊙. The time-scales of the amplitude variability of both stars (down to two weeks) are consistent with theoretical predictions of resonant mode coupling, a conclusion which might however be affected by the temporal distribution of our data.

A search for period changes inδScuti stars with the super-LOTIS sky patrol system

We have observed a sample of Delta Scuti stars discovered by the ROTSE collaboration in 1999 with Super-LOTIS in order to characterize changes in their pulsation periods over a time baseline of roughly three years. Achieving these goals required the creation of an automated astrometric and photometric data reduction pipeline for the Super-LOTIS camera. Applying this pipeline to data from a June 2002 observing campaign, we detect pulsations in 18 objects, and find that in two cases the periods have changed significantly over the three years between the ROTSE and Super-LOTIS observations. Since theory predicts that evolutionary period changes should be quite small, sources of non-evolutionary period changes due to the interactions of pulsations modes are discussed.

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.

Studies of classical cepheids

Abstract We present a review of recent results of our photometric and spectroscopic studies of classical Cepheids. We have accumulated the world's richest set of original, accurate photometric observations and radial-velocity measurements for Galactic Cepheids. Our observations are available to the community in electronic form via ftp. A Cepheid data bank has been prepared, including original and published data. Using these data, improved period-luminosity relations have been derived. A catalogue of Cepheid light curve parameters, luminosities, and distances has been compiled. Indications of evolutionary period changes have been found in our extensive studies of the most rapidly evolving Cepheids. We have discovered a number of new spectroscopic-binary Cepheids, and determined orbital elements for several stars. Our estimate of the lower limit on the incidence of spectroscopic binary Cepheids is 22%. A new period-radius relation has been derived from Baade-Wesselink radii for 62 Cepheids.

Long‐Term Changes in Mira Stars. II. A Search for Evolutionary Period Changes in Mira Stars

ABSTRACTThe (O - C) diagrams of Mira stars are dominated by the effects of random, cycle‐to‐cycle fluctuations in period. Nevertheless, it is possible to average these effects over many stars with similar properties and compare the average apparent period change with that predicted by evolutionary models. The average rate of period change for a 1.0 M⊙ model, averaged over the Mira phase, is +28 × 10-6 days day−1 if the pulsation is in the fundamental mode, and +11 × 10-6 days day−1 if it is in the first overtone mode (as most Mira star pulsation is now believed to be). The observed changes are not inconsistent with these results, in the sense that (1) positive period changes outnumber negative ones and (2) the average period change of all of the M type Miras is +16 × 10-6 days day−1; the median value is +14.5 × 10-6 days day−1. Of the seven M type Miras with[V - 12 μm] colors greater than 13.5, six had positive period changes. There is some evidence that C type Miras have larger period changes than M and S types.

Effects of metal abundances on the evolutionary period changes of classical Cepheids

Theoretical values of the evolutionary period changes of classical Cepheids are calculated as functions of not only periods but also chemical abundances. It is found that the theoretical values of period changes marginally depend on metal abundances. Comparison with observed period changes of galactic Cepheids shows reasonable agreement. Small-amplitude Cepheids are discussed combined with their evolutionary states.

Evolutionary period changes in the rapidly oscillating AP stars

Preliminary computations of the asymptotic p-mode frequency spacings, and their time derivatives, are presented for a grid of evolutionary models of the rapidly oscillating Ap ('roAp') stars. It is shown how the frequency spacings depend on stellar mass, metallicity, and evolutionary stage. The frequency spacings observed in two of the roAp stars indicate that they either are main-sequence objects or have evolved off of the main sequence, depending on how the pulsation spectrum is interpreted. A way to remove this ambiguity is suggested: secular evolutionary changes in the pulsation frequencies may be measurable if the roAp stars have evolved off of the main sequence. In principle, this determination may be made for the roAp star HR 1217 with existing data.

Evolutionary period changes in variable helium-rich white dwarfs

view Abstract Citations (37) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evolutionary Period Changes in Variable Helium-rich White Dwarfs Kawaler, S. D. ; Winget, D. E. ; Iben, I., Jr. ; Hansen, C. J. Abstract The authors investigate the rates of pulsation period change in realistic, theoretical evolutionary models of pulsating DB white dwarf (DBV) stars and their presumed progenitors, the pulsating PG 1159 (DOV) stars. The expected rates of period change are computed by solving the equations of linear, adiabatic, nonradial oscillation for nonrotating models of hydrogen-deficient white dwarfs. The value of d(ln P)/dt varies over the range (3 - 5)x10-14s-1 for models of DOV stars. Values for DBV stars range from 3x10-16s-1 at Teff = 30,000K to 5x10-17s-1 at Teff = 20,000K. Period changes of this order should be measurable in DBV stars over a few observing seasons. The effects of varying stellar mass and chemical composition on the numerical results are also examined. Publication: The Astrophysical Journal Pub Date: March 1986 DOI: 10.1086/164013 Bibcode: 1986ApJ...302..530K Keywords: Stellar Composition; Stellar Evolution; Stellar Oscillations; Variable Stars; White Dwarf Stars; Helium; Stellar Luminosity; Stellar Mass; Stellar Models; Stellar Temperature; Astrophysics; STARS: EVOLUTION; STARS: INTERIORS; STARS: PULSATION; STARS: WHITE DWARFS full text sources ADS | data products SIMBAD (3)

Evolutionary period changes in rotating hot pre-white dwarf stars

view Abstract Citations (15) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evolutionary period changes in rotating hot pre-white dwarf stars. Kawaler, S. D. ; Winget, D. E. ; Hansen, C. J. Abstract The splitting of high order nonradial g-modes due to slow rotation in models of hot prewhite dwarf stars of 0.60 solar mass are calculated. The effects of rotational spin-up, produced by gravitational contraction, on the rate of evolutionary period change for the cases of uniform and differential rotation are investigated. For models in the luminosity range of PG 1159 - 035 (L of about 100 solar luminosities), it is found that rotation rates of a few thousand seconds for modes with m less than about -2 produce values of d(ln P)/dt that are consistent with the measurement of the rate of period change of the 516-second period of PG 1159 - 035. Publication: The Astrophysical Journal Pub Date: November 1985 DOI: 10.1086/163656 Bibcode: 1985ApJ...298..752K Keywords: Computational Astrophysics; Pulsars; Stellar Evolution; Stellar Rotation; White Dwarf Stars; Angular Velocity; Periodic Variations; Stellar Models; Astrophysics full text sources ADS | data products SIMBAD (2)

Observations of evolutionary changes in the pulsation period of cepheids

In spite of the fact that Cepheid variables pulsate quite regularly their pulsation period remains constant only in the first approximation. The pulsation period is subject to variations because of stellar evolution. The calculations made by Hofmeister (1965) predicted that the evolutionary period changes of classical Cepheids should be observed on a time scale of several decades or longer. No detailed analysis of the observed period changes has been made since Hofmeister's fundamental theoretical work.

Period changes of Cepheid variables

Secular period changes of one hundred northern Cepheids are investigated with the help of O−C diagrams. With the classical Cepheids the rate of observed period changes is in good agreement with that determined from stellar evolution theory. The period noise cannot mask the evolutionary period changes especially in longer period Cepheids for which the occurrence of parabolic O−C graphs is unusually frequent.