Secular Decrease Research Articles

The First Light Curve Modeling and Orbital Period Change Investigation of Nine Contact Binaries around the Short-period Cutoff

Abstract In this paper, we present the first light curve synthesis and orbital period change analysis of nine contact binaries around the short-period limit. It is found that all these systems are W-subtype contact binaries. One of them is a medium contact system while the others are shallow contact ones. Four of them manifest obvious O’Connell effect explained by a dark spot or hot spot on one of the component stars. Third light was detected in three systems. By investigating orbital period variations, we found that four of the targets display a secular period decrease while the others exhibit a long-term period increase. The secular period decrease is more likely caused by angular-momentum loss while the long-term period increase is due to mass transfer from the less massive component to the more massive one. Based on the statistic of 19 ultrashort-period contact binaries with known orbital period changes, we found that seven of them display long-term decrease (three of them also exhibit cyclic variations), ten of them manifest long-term increase while two of them only show cyclic variation, and that most of them are shallow contact binaries supporting the long timescale angular-momentum loss theory suggested by Stepien. For the three deep contact systems, we found that they are probably triple systems. The tertiary companion plays an essential role during their formation and evolution.

New multi-color photometric investigations of solar-like contact binary V680 Per

High-precision CCD photometric observations of the contact binary V680 Per were obtained in 2016. Its symmetric multi-color light curves were analyzed by using the Wilson–Devinney (2013) program. These photometric solutions suggest that V680 Per is an A-type W UMa contact binary with the mass ratio of q = 0.693 and a fill-out factor of f = 18.84% with a small temperature difference of 101 K. Based on all minimum times, the O − C curve was analyzed for the first time in this study. A cyclic oscillation (A3 = 0.00093 d, T3 = 4.92 yr) superimposed on a secular decrease (dP/dt = −8.16 × 10−8 d yr−1) was identified. The continuous decrease in period is possibly a result of mass transfer from the more massive component to the less massive one, or angular momentum loss due to a magnetic stellar wind. Because of this secular decrease, it is predicted that the degree of contact will become higher, and V680 Per will evolve into a deeper overcontact binary.

Investigation of near-contact semi-detached binary WUMi through observations and evolutionary models

W UMi is a near contact, semi-detached, double-lined eclipsing binary star with an orbital period of 1.7 d. Simultaneous analysis of new BV R multi-color light curves and radial velocity data yields the main astrophysical parameters of the binary and its component stars. We determined mass and radius to be M1 = 3.22 ± 0.08 M⊙, R1 = 3.63 ± 0.04 R⊙ for the primary star and M2 = 1.44 ± 0.05 M⊙, R2 = 3.09 ± 0.03 R⊙ for the secondary star. Based on analysis of mid-eclipse times, variation in the orbital period is represented by a cyclic term and a downward parabola. Mass loss from the system is suggested for a secular decrease (−0.02 s yr−1) in the period. Both the mechanisms of a hypothetical tertiary star orbiting around W UMi and the surface magnetic activity of the less massive cooler companion were used to interpret periodic changes. Observational parameters were found to be consistent with binary stellar evolution models produced in the non-conservative approach of MESA at a higher metallicity than the Sun and an age of about 400 Myr for the system. Evidence that the system is rich in metal was obtained from spectral and kinematic analysis as well as evolution models. W UMi, a high mass ratio system compared to classical semi-detached binaries, is an important example since it is estimated from binary evolutionary models that the system may reach its contact phase in a short time interval.

1SWASP J034439.97+030425.5: a short-period eclipsing binary system with a close-in stellar companion

First multi-wavelength photometric light curves (LCs) of the short-period eclipsing binary (EB) 1SWASP J034439.97+030425.5 (hereafter J0344) are presented and analyzed by using the 2013 version of the Wilson-Devinney (W-D) code. To explain the asymmetric LCs of J0344, a cool star-spot on the less massive component was employed. The photometric solutions suggest that J0344 is a W-subtype shallow contact EB with a contact degree of f = 4.9% ± 3.0% and a mass ratio of q = 2.456 ± 0.013. Moreover, an obvious third light was detected in our analysis. We calculated the average luminosity contribution of the third light to the total light, and that value reaches up to 49.78%. Based on the O − C method, the variations of the orbital period were studied for the first time. Our O − C diagram reveals a secular decrease superimposed on a cyclic oscillation. The orbital period decreases at a rate of dP/dt = −6.07 × 10−7 d yr−1, which can be explained by the mass transfer from the more massive component to the less massive one. Besides, its O − C diagram also shows a cyclic oscillation with an amplitude of 0.0030 d and a period about 7.08 yr, which can be explained by the presence of a third body with a minimum mass of M3min = 0.15 ± 0.02 M⊙. The third component may play an important role in the formation and evolution of J0344 by drawing angular momentum from the central system.

Trends in Parity and Breast Cancer Incidence in US Women Younger Than 40 Years From 1935 to 2015

During the past several decades, breast cancer incidence has been increasing for women younger than 40 years. The increase matches the decrease in parity, an established breast cancer risk factor, but secular trends in incidence have not been examined prior to the 1970s. To examine whether secular trends in parity explain the increase in breast cancer incidence among US women aged 25 to 39 years from 1935 to 2015. This population-based cohort study used population-based aggregate-level data from the Connecticut Tumor Registry (CTR) to examine breast cancer incidence and age-standardized rates among women aged 25 to 39 years from 1935 to 2015. National mean live births were calculated using birth data from the National Vital Statistics System (NVSS) from 1930 to 2015 (allowing for 5-year lag). Linear regression was used to compare a baseline model of year estimating age-adjusted breast cancer incidence rate with a model that adjusted for parity constructs. Breast cancer incidence rates among women aged 25 to 39 years from 1935 to 2015. Among women in Connecticut aged 25 to 39 years from 1935 to 2015, incidence of breast cancer for women aged 25 to 39 years increased 0.65% (95% CI, 0.53%-0.77%) per year, from 16.3 breast cancer diagnoses per 100 000 women in 1935 to 38.5 breast cancer diagnoses per 100 000 women in 2015. This increase began nearly 4 decades before the secular decrease in parity (mean [SD] parity peaked at 2.26 [0.87] live births per woman in 1966 and in 2010 had decreased to 1.41 [0.71] live births per woman). Age-specific parity trends explained only 0% to 4% of the variability in incidence over time. These findings suggest that breast cancer incidence for women aged 25 to 39 years has been significantly increasing since the 1930s and cannot be attributed to changes in parity over time.

Association between degree of exposure to the Hospital Value Based Purchasing Program and 30-day mortality: experience from the first four years of Medicare\u2019s pay-for-performance program

BackgroundThe Hospital Value Based Purchasing Program (HVBP) in the United States, announced in 2010 and implemented since 2013 by the Centers for Medicare and Medicaid Services (CMS), introduced payment penalties and bonuses based on hospital performance on patient 30-day mortality and other indicators. Evidence on the impact of this program is limited and reliant on the choice of program-exempt hospitals as controls. As program-exempt hospitals may have systematic differences with program-participating hospitals, in this study we used an alternative approach wherein program-participating hospitals are stratified by their financial exposure to penalty, and examined changes in hospital performance on 30-day mortality between hospitals with high vs. low financial exposure to penalty.MethodsOur study examined all hospitals reimbursed through the Medicare Inpatient Prospective Payment System (IPPS) – which include most community and tertiary acute care hospitals – from 2009 to 2016. A hospital’s financial exposure to HVBP penalties was measured by the share of its annual aggregate inpatient days provided to Medicare patients (“Medicare bed share”). The main outcome measures were annual hospital-level 30-day risk-adjusted mortality rates for acute myocardial infarction (AMI), heart failure (HF) and pneumonia patients. Using difference-in-differences models we estimated the change in the outcomes in high vs. low Medicare bed share hospitals following HVBP.ResultsIn the study cohort of 1902 US hospitals, average Medicare bed share was 61 and 41% in high (n = 540) and low (n = 1362) Medicare bed share hospitals, respectively. High Medicare bed share hospitals were more likely to have smaller bed size and less likely to be teaching hospitals, but ownership type was similar among both Medicare bed share groups.. Among low Medicare bed share (control) hospitals, baseline (pre-HVBP) 30-day mortality was 16.0% (AMI), 10.9% (HF) and 11.4% (pneumonia). In both high and low Medicare bed share hospitals 30-day mortality experienced a secular decrease for AMI, increase for HF and pneumonia; differences in the pre-post change between the two hospital groups were small (< 0.12%) and not significant across all three conditions.ConclusionsHVBP was not associated with a meaningful change in 30-day mortality across hospitals with differential exposure to the program penalty.

Incidence of myocardial infarction and associated mortality varies by latitude and season: findings from a Swedish Registry Study.

We investigated whether the incidence of death following myocardial infarction (MI) varied by season and latitude in the Swedish population. We studied deaths following MI from January 1987 to December 2009, using the Swedish National Cause of Death Register. County of residence was used to determine latitude and population density. An extension of Poisson regression was used to study the relationship between risk of death following MI with age, latitude, time (from 1987), population density and calendar days. Over the study period, there was a secular decrease in the incidence of MI-related death. In men, MI-related death incidence increased by 1.3% [95% confidence interval (CI)=1.1-1.5] per degree of latitude (northwards). In women, MI-related death incidence increased by 0.6% (95% CI=0.4-0.9) per degree of latitude. There was seasonal variation in the risk of MI-related death with peak values in the late winter and a nadir in the summer months in both the north and the south of Sweden. Findings were similar with incident MI as the outcome. The incidence of MI-related death varied markedly by season and latitude in Sweden, with summer months and more southerly latitude associated with lower rates than winter months and more northerly latitude.

Chaotic Rotation and Evolution of Asteroids and Small Planets in High-eccentricity Orbits around White Dwarfs

Abstract Observed planetary debris in white dwarf atmospheres predominately originate from the destruction of small bodies on highly eccentric (&gt;0.99) orbits. Despite their importance, these minor planets have coupled physical and orbital evolution, which has remained largely unexplored. Here, we present a novel approach for estimating the influence of fast chaotic rotation on the orbital evolution of high-eccentricity triaxial asteroids, and formally characterize the propagation of their angular rotation velocities and orbital elements as random time processes. By employing the impulse approximation, we demonstrate that the violent gravitational interactions during periastron passages transfer energy between the orbit and asteroid’s rotation. If the distribution of spin impulses were symmetric around zero, then the net result would be a secular decrease of the semimajor axis and a further increase of the eccentricity. We find evidence, however, that the chaotic rotation may be self regulated in such a manner that these effects are reduced or nullified. We discover that asteroids on highly eccentric orbits can break themselves apart—in a type of YORP-less (Yarkovsky–O’Keefe–Radzievskii–Paddack) rotational fission—without actually entering the Roche radius, with potentially significant consequences for the distribution of debris and energy requirements for gravitational scattering in metal-polluted white dwarf planetary systems. This mechanism provides a steady stream of material impacting a white dwarf without rapidly depleting the number of small bodies in the stellar system.

Detailed characterization of low activity comet 49P/Arend–Rigaux

Comet 49P/Arend–Rigaux is a well known low-activity Jupiter Family comet. Despite the low activity, we have witnessed outgassing activity in 1992, 2004, and 2012. In 2012 a broad tail-like feature (PA ∼ 270°, ∼2.3×105 km) and a narrow jet-like feature (PA ∼ 180°, ∼9.3×104 km) were seen simultaneously. Using Finson–Probstein (FP) dust dynamical models we determine: the grain sizes released in each event; the duration of activity; when the activity peaked; and the velocity of the dust particles, allowing us to make comparisons between the events. We find that the tail feature in 2012 is similar to the tail in 1992 with large grains (40–4000 μm) peaking in activity around perihelion with a long duration of outgassing greater than 150 days. The jet feature from 2012, however, is more similar to the 2004 event which we model with small grains (1–8 μm) with a short duration of activity on the order of one month. The main difference between these two features is that the 2004 event occurs prior to perihelion, while the 2012 event is post-perihelion. We use the grain sizes from the FP models to constrain ice sublimation models. Between 1985 and 2018 we cover six apparitions with 26 nights of our own observations, data from the literature, and data from the Minor Planet Center, which together, allow us to model the heliocentric light curve. We find that the models are consistent with H2O ice sublimation as the volatile responsible for driving activity over most of the active phases and a combination of H2O and CO2 ices are responsible for driving activity near perihelion. We measure the fractional active area over time for H2O and discover that the activity decreases from an average active area of ∼3% to ∼0.2%. This clear secular decrease in activity implies that the comet is becoming depleted of volatiles and is in the process of transitioning to either a dormant or dead state.

A Detailed Investigation on the Infrared-excess Binary EG Cassiopeiae

In this study, new data concerning the EB-type eclipsing binary EG Cas are presented as observed using three telescopes in China. A spectral type of F0V was determined from the low-precision spectrum. By solving the radial velocity and BV light curves, the absolute parameters of this system are preliminarily deduced. The results imply that EG Cas is a semi-detached binary with the secondary star filling its Roche lobe. An unequal height between the light maxima (i.e., ≲0.02 mag) of the light curves is modeled with the addition of a magnetic dark spot on the surface of the less-massive component. Analyzing the O − C curve a secular decrease at is identified in the orbital period, which corresponds to a mass-loss rate of in the case of non-conserved evolution of the binary. From the spectral energy distribution, an excess in the infrared occurs in the WISE W4 band, which may be attributed to the circumstellar envelope due to mass loss via the stellar magnetic wind. With the ongoing mass transfer and loss, this kind of F-type near-contact binary will eventually evolve into an A-subtype contact binary, as predicted by the thermal relaxation oscillation theory.

The origin of R CrA variability

Context. R CrA is the brightest member of the Coronet star-forming region and is the closest Herbig AeBe star with a spectrum dominated by emission lines. Its luminosity has been monitored since the end of the nineteenth century, but the origin of its variability, which shows a stable period of 65.767 ± 0.007 days, is still unknown. Aims. We studied photometric and spectroscopic data for this star to investigate the nature of the variability of R CrA. Methods. We exploited the fact that the near-infrared luminosity of the Herbig AeBe stars is roughly proportional to the total luminosity of the stars to derive the absorption, and then mass and age of R CrA. In addition, we modeled the periodic modulation of the light curve as due to partial attenuation of a central binary by a circumbinary disk. This model reproduces the observations very well. Results. We found that the central object in R CrA is a very young (1.5 ± 1.5 Myr) highly absorbed (AV = 5.47 ± 0.4 mag) binary; we obtain masses of MA = 3.02 ± 0.43 M⊙ and MB = 2.32 ± 0.35 M⊙ for the two components. We propose that the secular decrease of the apparent luminosity of R CrA is due to a progressive increase of the disk absorption. This might be related to precession of a slightly inclined disk caused by the recently discovered M-dwarf companion. This means that R CrA might be a triple system hosting a disk.

Orbital-Period Variations of the Eclipsing Binaries RY Aur, GG Cas, RS Lep, and RV Tri

Variations of the orbital periods of the eclipsing binaries RY Aur, GG Cas, RS Lep, and RV Tri are analyzed. The period variations in all of these systems can be represented as a superposition of a secular period decrease and cyclic variations that can be explained with the light-time effect due to the presence of a third body in the system. The secular period decrease could be due to magnetic braking.

Mass transfer and possible third-body effect on the period variations of the near-contact binary CN And

We present a period analysis of the near-contact binary CN And using all available times of light minima. It is revealed that the orbital period exhibits a long-term decrease as well as a small-amplitude cyclic oscillation. This result suggests that the secular period decrease at the rate of dP/dt = −1.4017 × 10−7 d yr−1 is caused by a combination of mass transfer and angular momentum loss due to magnetic braking. The periodic variation with an amplitude of A = 0.0036 d and a period of Pmod = 28.3542 yr should be rooted in the light-time effect of a third body, rather than cyclic magnetic activity.

Transition from Plume-driven to Plate-driven Magmatism in the Evolution of the Main Ethiopian Rift

Abstract New K–Ar ages, major and trace element concentrations, and Sr–Nd–Pb isotope data are presented for Oligocene to recent mafic volcanic rocks from the Ethiopian Plateau, the Main Ethiopian Rift (MER), and the Afar depression. Chronological and geochemical data from this study are combined with previously published datasets to reveal secular variations in magmatism throughout the entire Ethiopian volcanic region. The mafic lavas in these regions show variability in terms of silica-saturation (i.e. alkaline and sub-alkaline series) and extent of differentiation (mafic through intermediate to felsic). The P–T conditions of melting, estimated using the least differentiated basalts, reveal a secular decrease in the mantle potential temperature, from when the flood basalt magmas erupted (up to 1600 °C) to the time of the rift-related magmatism (&amp;lt;1500°C). Variations in the Sr–Nd–Pb isotopic compositions of the mafic lavas can account for the involvement of multiple end-member components. The relative contributions of these end-member components vary in space and time owing to changes in the thermal condition of the asthenosphere and the thickness of the lithosphere. The evolution of the Ethiopian rift is caused by a transition from plume-driven to plate-driven mantle upwelling, although the present-day mantle beneath the MER and the Afar depression is still warmer than normal asthenosphere.

Photometry study in period variation and orbital parameter of two W UMa eclipsing binaries: AV Crb and EK Aqr

We report new light curves of two eclipsing binaries of AV Crb and EK Aqr obtained in 2017 and 2018 using Holcomb and SARA telescopes. We obtain the updated ephemeris and find a continuous period decrease (AV Crb) and increase (EK Aqr), respectively. We used the 2015 version Wilson-Devinney method to analyze the light curves and asymmetries. The effective temperature of the primary components of the two eclipsing binaries are obtained from the Gaia DR2. We determine the orbital parameters of AV Crb and EK Aqr. The secular period decrease of -3.23(17)×10−7 days/yr suggests that in AV Crb mass transfer takes place from the primary component to the secondary at a ratedM1/dt of -3.67(17)×10−7M⊙/yr. We find a hot spot on the secondary component. The orbital period increase 3.33(21)×10−7 days/yr implies that EK Aqr is undergoing mass transfer from the secondary component to the primary at a rate of 3.33(21)×10−7M⊙/yr and we find a cool spot on the primary component. We conclude that AV Crb is a shallow contact eclipsing binary with a contact degree of 19.17(2.45)%, and EK Aqr is a deep contact binary with 56.86(1.13)% factor.

BVRCIC Observations, Analysis, and Spectra of The Most Extreme Mass Ratio (Totally Eclipsing) W UMa Binary, V1187 Herculis

CCD, BVRI primary light curves of V1187 Her were taken in 2017 May and 2018 May at the Dark Sky Observatory in North Carolina with the 0.81-m reflector of Appalachian State University. A spectrum was taken earlier at Dominion Astrophysical Observatory (DAO) with the 1.8 m telescope. The spectral type is F(8.5 ± 1)V, resulting in a surface temperature of 6250 ± 125 K (Cox ), so solar-type activity is expected. V1187 Her was previously identified as a low-amplitude, short-period, over-contact eclipsing binary (EW) with an orbital period of 0.310726 d. Strikingly, despite its low amplitude (∼0.15 mag), the early light curves show a total eclipse (eclipse duration: 31.5 minutes). This can only occur (in the absence of a strong third light) if the binary is an exceptionally extreme mass ratio binary, perhaps the most extreme known. Eight instances of minimum light were calculated. A 12-year period study reveals a secular period decrease in the orbital period with good confidence. The rate of period change is dP/dt = −1.5 × 10−07 d/yr, probably due to magnetic braking. Its Roche Lobe fill-out is found to be a hefty 84% along with a mass ratio of only ∼0.044; indeed, the most extreme known among solar-type (i.e., W UMa) binaries. It has a cool spot region. The secondary component has a temperature of K, which makes it a W-subtype binary (the less massive component is hotter). The inclination is only ∼67° despite its total eclipses. A q-search was conducted, which showed the 0.044 value was the best fit to the light curves. Additionally, follow-up observations were taken on 2018 May 4, which confirmed the mass ratio found from the earlier curves.

Secular decrease of wind power potential in India associated with warming in the Indian Ocean.

The Indian government has set an ambitious target for future renewable power generation, including 60 GW of cumulative wind power capacity by 2022. However, the benefits of these substantial investments are vulnerable to the changing climate. On the basis of hourly wind data from an assimilated meteorology reanalysis dataset covering the 1980-2016 period, we show that wind power potential may have declined secularly over this interval, particularly in western India. Surface temperature data confirm that significant warming occurred in the Indian Ocean over the study period, leading to modulation of high pressure over the ocean. A multivariable linear regression model incorporating the pressure gradient between the Indian Ocean and the Indian subcontinent can account for the interannual variability of wind power. A series of numerical sensitivity experiments confirm that warming in the Indian Ocean contributes to subsidence and dampening of upward motion over the Indian continent, resulting potentially in weakening of the monsoonal circulation and wind speeds over India.

A Model of the Mira–Type Star T UMi

Stellar evolution calculations were carried out from the main sequence to the final AGB stage of stars with initial masses from 1 to $2M_\odot$ and metallicity $Z=0.01$. Selected models of evolutionary sequences were used as initial conditions for solution of the equations of radiation hydrodynamics and time-dependent convection describing radial stellar pulsations. The study was aimed to construct the hydrodynamic models of Mira-type stars that show the secular decrease in the pulsation period commenced in 1970--th at $\Pi=315$ day. We show that such a condition for the period change is satisfied with evolutionary sequences from 1 to $1.2M_\odot$ and the best agreement with observations is obtained for models with initial mass $1.2M_\odot$. The pulsation period reduction is due to both the stellar radius decrease during the thermal pulse of the helium burning shell and mode switch from the fundamental mode to the first overtone. Theoretical estimates of the fundamental parameters of the star at the onset of pulsation period reduction are as follows: the mass is $M=0.93M_\odot$, the luminosity is $L = 4080L_\odot$, and the radius is $R=220R_\odot$. The mode switch occurs 35 years after the onset of period reduction.

Cyclic Orbital-period Variations in Eclipsing Binary Systems with Rapid Period Decreases: TU Her, TY Peg, and Y Psc

Cyclic variations of the orbital period superposed on a secular period decrease have been found for the Algol-type eclipsing binaries TU Her, TY Peg, and Y Psc. A superposition of two kinds of cyclic variations is observed for TU Her and Y Psc: with periods of 69.4 years and 30.0 years for TU Her, and 34.4 and 23.2 years for Y Psc. One type of oscillation, with a period of 74.3 years, was detected for TY Peg. The cyclic orbital-period variations of TY Peg and Y Psc can be successfully fitted using the light-time effect, and also with magnetic oscillations. In the case of TU Her, the light-time effect is able to explain only one of the cyclic variations, the one with the shorter period.

The First Photometric and Period Investigation of the Total Eclipse Binary System V0474 Cam

Three complete multi-band light curves of the W UMa-type binary V0474 Cam, which display a total eclipse, were obtained on four nights during two observing seasons from 2016 February 9 to 2017 February 24. By analyzing all obtainable times of light minimum, including 8 newly calculated, a downward parabolic change was found to be overlaid with a possible cyclic oscillation. The secular period decrease is determined to be days yr−1, which can be explained by the existence of angular momentum loss from the binary system via a magnetic stellar wind. The cyclic oscillation, with a 3.44-yr period and a 0.0015-days amplitude, could be explained more plausibly by the magnetic activity, although the light-travel time effect as result of the present of a third component cannot be excluded. According to the three complete light curves, the intrinsic variations are obvious, particularly in the deepness at primary minimum and in the phase around 0.75. The light curve of V0474 Cam is symmetric observed in February 2016, then it become asymmetric in December 2016 and February 2017. The W-D program was adopted to investigate the multi-band light curves and the results indicate V0474 Cam is a W-subtype binary (the less massive component is hotter). A mass ratio of q = 3.230 was derived by analyzing the symmetric light curves observed at February in 2016. After accepting the results derived from the symmetric light curves as the references, other two sets of asymmetrical light curves can be well resolved through adding a cool spot on the more massive component.