arXiv subjects

Jason Jackiewicz

Publications and source records attributed to Jason Jackiewicz.

46 records · Page 3Linked to original sources

arXiv2013

Red Giants in Eclipsing Binary and Multiple-Star Systems: Modeling and Asteroseismic Analysis of 70 Candidates from Kepler Data

Red-giant stars are an incredible source of information for testing models of stellar evolution, as asteroseismology has opened up a window into their interiors. Such insights are a direct result of the unprecedented data from space missions Kepler and CoRoT as well as recent theoretical advances. Eclipsing binaries are also fundamental astrophysical objects, and when coupled with asteroseismology, binaries would provide two independent methods to obtain masses and radii and exciting opportunities to develop highly constrained stellar models. The possibility of discovering pulsating red giants in eclipsing binary systems is therefore an important goal that could potentially offer very robust characterization of these systems. Hitherto, only 1 case has been discovered with Kepler. We cross-correlated the detected red-giant and eclipsing-binary catalogs from Kepler data to find candidate systems. Light-curve modeling and mean asteroseismic properties are combined to yield measurements of periods, masses, radii, temperatures, eclipse timing variations, core rotation rates, and red-giant evolutionary state. After elimination of false positives, out of the 70 systems common to the red-giant and eclipsing-binary catalogs we find 13 new strong candidates that are pulsating red giants in eclipsing binaries, and 10 more that are pulsating red giants in hierarchical triple systems. The systems span a range of orbital eccentricities, periods, and spectral types for the red-giant companion. One case even suggests a system composed of two red-giants. The discovery of pulsating red giants in multiple systems provides exciting test beds for precise astrophysical modeling, and follow-up spectroscopic observations of the candidate systems are encouraged.

astro-ph.SR↗

arXiv2012

Sequential Chomospheric Brightening: An Automated Approach to Extracting Physics from Ephemeral Brightening

We make a comparison between small scale chromospheric brightenings and energy release processes through examining the temporal evolution of sequential chromospheric brightenings (SCBs), derive propagation velocities, and propose a connection of the small-scale features to solar flares. Our automated routine detects and distinguishes three separate types of brightening regularly observed in the chromosphere: plage, flare ribbon, and point brightenings. By studying their distinct dynamics, we separate out the flare-associated bright points commonly known as SCBs and identify a propagating Moreton wave. Superimposing our detections on complementary off-band images, we extract a Doppler velocity measurement beneath the point brightening locations. Using these dynamic measurements, we put forward a connection between point brightenings, the erupting flare, and overarching magnetic loops. A destabilization of the pre-flare loop topology by the erupting flare directly leads to the SCBs observed.

astro-ph.SR↗

arXiv2012

Properties of Sequential Chromospheric Brightenings and Associated Flare Ribbons

We report on the physical properties of solar sequential chromospheric brightenings (SCBs) observed in conjunction with moderate-sized chromospheric flares with associated CMEs. To characterize these ephemeral events, we developed automated procedures to identify and track subsections (kernels) of solar flares and associated SCBs using high resolution H-alpha images. Following the algorithmic identification and a statistical analysis, we compare and find the following: SCBs are distinctly different from flare kernels in their temporal characteristics of intensity, Doppler structure, duration, and location properties. We demonstrate that flare ribbons are themselves made up of subsections exhibiting differing characteristics. Flare kernels are measured to have a mean propagation speed of 0.2 km/s and a maximum speed of 2.3 km/s over a mean distance of 5 x 10^3 km. Within the studied population of SCBs, different classes of characteristics are observed with coincident negative, positive, or both negative and positive Doppler shifts of a few km/s. The appearance of SCBs precede peak flare intensity by ~12 minutes and decay ~1 hour later. They are also found to propagate laterally away from flare center in clusters at 41 km/s or 89 km/s. Given SCBs distinctive nature compared to flares, we suggest a different physical mechanism relating to their origin than the associated flare. We present a heuristic model of the origin of SCBs.

astro-ph.SR↗

arXiv2012

The Classificiation of Kepler B star Variables

The light curves of 252 B-star candidates in the Kepler data base are analyzed in a similar fashion to that done by Balona et al. (2011) to further characterize B star variability, increase the sample of variable B stars for future study, and to identify stars whose power spectra include particularly interesting features such as frequency groupings. Stars are classified as either constant light emitters, $β$ Cep stars, slowly pulsating B stars, hybrid pulsators, binaries or stars whose light curves are dominated by rotation (Bin/Rot), hot subdwarfs, or white dwarfs. One-hundred stars in our sample were found to be either light contants or to be variable at a level of less than 0.02 mmag. We increase the number of candidate B-star variables found in the Kepler data base by Balona et al. (2011) in the following fashion: $β$ Cep stars from 0 to 10, slowly pulsating B stars from 8 to 54, hybrid pulsators from 7 to 21, and Bin/Rot stars from 23 to 82. For comparison purposes, approximately 51 SPBs and 6 hybrids had been known prior to 2007. The number of $β$ Cep stars known prior to 2004 was 93. A secondary result of this study is the identification of an additional 11 pulsating white dwarf candidates, four of which possess frequency groupings.

astro-ph.SR↗

arXiv2007

Many body exchange effects close to the s-wave Feshbach resonance in two-component Fermi systems: Is a triplet superfluid possible?

We suggest that the exchange fluctuations close to a Feshbach resonance in a two-component Fermi gas can result in an effective p-wave attractive interaction. On the BCS side of a Feshbach resonance, the magnitude of this effective interaction is comparable to the s-wave interaction, therefore leading to a possible spin-triplet superfluid in the range of temperatures of actual experiments. We also show that the particle-hole exchange fluctuations introduce an effective scattering length which does not diverge, as the standard mean-field one does. Finally, using the effective interaction quantities we are able to model the molecular binding energy on the BEC side of the resonance.

cond-mat.other↗

arXiv2007

Fermi liquid behavior and Luttinger's theorem close to a diverging scattering length

Based on the results obtained in a previous paper (S. Gaudio et al., cond-mat/0505309}, we derive the thermodynamic properties of a Fermi gas, deep into the quantum degenerate regime. We show that, if Luttinger's theorem holds, a first order phase transition occurs in the normal phase as a function of the interaction strength, U. We also show that a volume change occurs at finite temperatures from the BEC to the BCS side of a diverging s-wave scattering length, in the normal phase. The transition has an end point above the BCS critical temperature. Also we show that a paramagnetic system in equilibrium, close to the divergence of the scattering length, on the negative side, screens out any applied magnetic field.

cond-mat.str-el↗

arXiv2005

Pairing symmetry signatures of T1 in superconducting ferromagnets

We study the nuclear relaxation rate 1/T1 as a function of temperature for a superconducting-ferromagnetic coexistent system using a p-wave triplet model for the superconducting pairing symmetry. This calculation is contrasted with a singlet s-wave one done previously, and we see for the s-wave case that there is a Hebel-Slichter peak, albeit reduced due to the magnetization, and no peak for the p-wave case. We then compare these results to a nuclear relaxation rate experiment on UGe2 to determine the possible pairing symmetry signatures in that material. It is seen that the experimental data is inconclusive to rule out the possibility of s-wave pairing in $UGe_{2}$.

cond-mat.str-el↗

arXiv2004

Physical properties of ferromagnetic-superconducting coexistent system

We studied the nuclear relaxation rate 1/T1 of a ferromagnetic-superconducting system from the mean field model proposed in Ref.14. This model predicts the existence of a set of gapless excitations in the energy spectrum which will affect the properties studied here, such as the density of states and, hence, 1/T1. The study of the temperature variation of 1/T1(for T<Tc) shows that the usual Hebel-Slichter peak exists, but will be reduced because of the dominant role of the gapless fermions and the background magnetic behavior. We have also presented the temperature dependence of ultrasonic attenuation and the frequency dependence of electromagnetic absorption within this model. We are successful in explaining certain experimental results.

cond-mat.supr-con↗

arXiv2004

Quantum fluctuation driven first order phase transition in weak ferromagnetic metals

In a local Fermi liquid (LFL), we show that there is a line of weak first order phase transitions between the ferromagnetic and paramagnetic phases due to purely quantum fluctuations. We predict that an instability towards superconductivity is only possible in the ferromagnetic state. At T=0 we find a point on the phase diagram where all three phases meet and we call this a quantum triple point (QTP). A simple application of the Gibbs phase rule shows that only these three phases can meet at the QTP. This provides a natural explanation of the absence of superconductivity at this point coming from the paramagnetic side of the phase diagram, as observed in the recently discovered ferromagnetic superconductor, $UGe_{2}$.

cond-mat.str-el↗

arXiv2003

A model for coexistent superconductivity and ferromagnetism

We explore various temperature dependencies and thermodynamic quantities of a mean field model of a ferromagnetic-superconducting system. The starting point for this model is based on an s-wave pairing scheme in the singlet channel of the superconducting state and a spontaneously broken symmetry phase in the ferromagnetic state. We show numerically and analytically that a state of coexistence reveals itself and is favored energetically over other possible states, and a simple phase diagram is developed. Finally, a comparison of the specific heat with experiment is shown.

cond-mat.supr-con↗