skip to main content


Title: I–Love–Q relations for realistic white dwarfs
ABSTRACT

The space-borne gravitational wave interferometer, Laser Interferometer Space Antenna, is expected to detect signals from numerous binary white dwarfs. At small orbital separation, rapid rotation and large tidal bulges may allow for the stellar internal structure to be probed through such observations. Finite-size effects are encoded in quantities like the moment of inertia (I), tidal Love number (Love), and quadrupole moment (Q). The universal relations among them (I–Love–Q relations) can be used to reduce the number of parameters in the gravitational-wave templates. We here study I–Love–Q relations for more realistic white dwarf models than used in previous studies. In particular, we extend previous works by including (i) differential rotation and (ii) internal temperature profiles taken from detailed stellar evolution calculations. We use the publicly available stellar evolution code mesa to generate cooling models of both low- and high-mass white dwarfs. We show that differential rotation causes the I–Q relation (and similarly the Love–Q relation) to deviate from that of constant rotation. We also find that the introduction of finite temperatures causes the white dwarf to move along the zero-temperature mass sequence of I–Q values, moving towards values that suggest a lower mass. We further find that after only a few Myr, high-mass white dwarfs are well described by the zero-temperature model, suggesting that the relations with zero temperature may be good enough in most practical cases. Low-mass, He-core white dwarfs with thick hydrogen envelopes may undergo long periods of H burning which sustain the stellar temperature and allow deviations from the I–Love–Q relations for longer times.

 
more » « less
Award ID(s):
1806776
NSF-PAR ID:
10130060
Author(s) / Creator(s):
 ;  ;  
Publisher / Repository:
Oxford University Press
Date Published:
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
492
Issue:
1
ISSN:
0035-8711
Page Range / eLocation ID:
p. 978-992
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ABSTRACT

    White dwarf binaries with orbital periods below 1 h will be the most numerous sources for the space-based gravitational wave detector Laser Interferometer Space Antenna (LISA). Based on thousands of individually resolved systems, we will be able to constrain binary evolution and provide a new map of the Milky Way and its close surroundings. In this paper we predict the main properties of populations of different types of detached white dwarf binaries detected by LISA over time. For the first time, we combine a high-resolution cosmological simulation of a Milky Way-mass galaxy (taken from the FIRE project) with a binary population synthesis model for low- and intermediate-mass stars. Our Galaxy model therefore provides a cosmologically realistic star formation and metallicity history for the Galaxy and naturally produces its different components such as the thin and thick disc, the bulge, the stellar halo, and satellite galaxies and streams. Thanks to the simulation, we show how different Galactic components contribute differently to the gravitational wave signal, mostly due to their typical age and distance distributions. We find that the dominant LISA sources will be He–He double white dwarfs (DWDs) and He–CO DWDs with important contributions from the thick disc and bulge. The resulting sky map of the sources is different from previous models, with important consequences for the searches for electromagnetic counterparts and data analysis. We also emphasize that much of the science-enabling information regarding white dwarf binaries, such as the chirp mass and the sky localization, becomes increasingly rich with long observations, including an extended mission up to 8 yr.

     
    more » « less
  2. null (Ed.)
    ABSTRACT Compact white dwarf (WD) binaries are important sources for space-based gravitational-wave (GW) observatories, and an increasing number of them are being identified by surveys like Extremely Low Mass (ELM) and Zwicky Transient Facility (ZTF). We study the effects of non-linear dynamical tides in such binaries. We focus on the global three-mode parametric instability and show that it has a much lower threshold energy than the local wave-breaking condition studied previously. By integrating networks of coupled modes, we calculate the tidal dissipation rate as a function of orbital period. We construct phenomenological models that match these numerical results and use them to evaluate the spin and luminosity evolution of a WD binary. While in linear theory the WD’s spin frequency can lock to the orbital frequency, we find that such a lock cannot be maintained when non-linear effects are taken into account. Instead, as the orbit decays, the spin and orbit go in and out of synchronization. Each time they go out of synchronization, there is a brief but significant dip in the tidal heating rate. While most WDs in compact binaries should have luminosities that are similar to previous traveling-wave estimates, a few per cent should be about 10 times dimmer because they reside in heating rate dips. This offers a potential explanation for the low luminosity of the CO WD in J0651. Lastly, we consider the impact of tides on the GW signal and show that the Laser Interferometer Space Antenna (LISA) and TianGO can constrain the WD’s moment of inertia to better than $1{{\ \rm per\ cent}}$ for centi-Hz systems. 
    more » « less
  3. Abstract

    Compact-object binaries including a white dwarf component are unique among gravitational-wave sources because their evolution is governed not just by general relativity and tides, but also by mass transfer. While the black hole and neutron star binaries observed with ground-based gravitational-wave detectors are driven to inspiral due to the emission of gravitational radiation—manifesting as a “chirp-like” gravitational-wave signal—the astrophysical processes at work in double white dwarf (DWD) systems can cause the inspiral to stall and even reverse into an outspiral. The dynamics of the DWD outspiral thus encode information about tides, which tell us about the behavior of electron-degenerate matter. We carry out a population study to determine the effect of the strength of tides on the distributions of the DWD binary parameters that the Laser Interferometer Space Antenna (LISA) will be able to constrain. We find that the strength of tidal coupling parameterized via the tidal synchronization timescale at the onset of mass transfer affects the distribution of gravitational-wave frequencies and frequency derivatives for detectably mass-transferring DWD systems. Using a hierarchical Bayesian framework informed by binary population synthesis simulations, we demonstrate how this parameter can be inferred using LISA observations. By measuring the population properties of DWDs, LISA will be able to probe the behavior of electron-degenerate matter.

     
    more » « less
  4. Context. The collection of high-quality photometric data by space telescopes, such as the completed Kepler mission and the ongoing TESS program, is revolutionizing the area of white-dwarf asteroseismology. Among the different kinds of pulsating white dwarfs, there are those that have He-rich atmospheres, and they are called DBVs or V777 Her variable stars. The archetype of these pulsating white dwarfs, GD 358, is the focus of the present paper. Aims. We report a thorough asteroseismological analysis of the DBV star GD 358 (TIC 219074038) based on new high-precision photometric data gathered by the TESS space mission combined with data taken from the Earth. Methods. We reduced TESS observations of the DBV star GD 358 and performed a detailed asteroseismological analysis using fully evolutionary DB white-dwarf models computed accounting for the complete prior evolution of their progenitors. We assessed the mass of this star by comparing the measured mean period separation with the theoretical averaged period spacings of the models, and we used the observed individual periods to look for a seismological stellar model. We detected potential frequency multiplets for GD 358, which we used to identify the harmonic degree ( ℓ ) of the pulsation modes and rotation period. Results. In total, we detected 26 periodicities from the TESS light curve of this DBV star using standard pre-whitening. The oscillation frequencies are associated with nonradial g (gravity)-mode pulsations with periods from ∼422 s to ∼1087 s. Moreover, we detected eight combination frequencies between ∼543 s and ∼295 s. We combined these data with a huge amount of observations from the ground. We found a constant period spacing of 39.25 ± 0.17 s, which helped us to infer its mass ( M ⋆  = 0.588 ± 0.024  M ⊙ ) and constrain the harmonic degree ℓ of the modes. We carried out a period-fit analysis on GD 358, and we were successful in finding an asteroseismological model with a stellar mass ( M ⋆ = 0.584 −0.019 +0.025   M ⊙ ), compatible with the stellar mass derived from the period spacing, and in line with the spectroscopic mass ( M ⋆  = 0.560 ± 0.028  M ⊙ ). In agreement with previous works, we found that the frequency splittings vary according to the radial order of the modes, suggesting differential rotation. Obtaining a seismological model made it possible to estimate the seismological distance ( d seis  = 42.85 ± 0.73 pc) of GD 358, which is in very good accordance with the precise astrometric distance measured by Gaia EDR3 ( π  = 23.244 ± 0.024,  d Gaia  = 43.02 ± 0.04 pc). Conclusions. The high-quality data measured with the TESS space telescope, used in combination with data taken from ground-based observatories, provides invaluable information for conducting asteroseismological studies of DBV stars, analogously to what happens with other types of pulsating white-dwarf stars. The currently operating TESS mission, together with the advent of other similar space missions and new stellar surveys, will give an unprecedented boost to white dwarf asteroseismology. 
    more » « less
  5. ABSTRACT

    Studying the kinematics and mass modelling of galaxies from H i 21 cm data provides valuable insights into the properties of both the baryonic components and the dark matter halo in nearby galaxies. Despite many observational studies, mass modelling of galaxies remains challenging due to different limitations. For example, most of the previous studies involving mass modelling are based on rotation curves derived from 2D velocity fields from H i or H α spectroscopic observation which are often affected by beam smearing and projection effect. However, kinematic modelling done by fitting the ‘Tilted ring model’ to 3D data cube is not affected by these issues. In this study, we present and compare 3D kinematic modelling of a pilot sample of 11 galaxies from the GMRT archive atomic gas survey (GARCIA) using two different publicly available pipelines. We model the observed H i rotation curve using 3.6-μm infrared data and SDSS r-band data for stellar contribution, H i surface density profile for gas, and Navarro–Frenk–White profile for dark matter halo; and employ the Markov chain Monte Carlo optimization method for parameter estimation. Further, to validate our analysis, we revisit important scaling relations, e.g. the Mgas–Mstar relation, Mstar–Mhalo relation, Mgas–Mhalo relation and Baryonic Tully–Fisher relation. The scaling relations from our analysis are broadly consistent with that reported in the literature. A larger sample of galaxies from GARCIA in the near future will allow studying these scaling relations in greater details.

     
    more » « less