Compact Binaries in the globular cluster NGC 6397

Manuel Pichardo Marcano

Supervised by

Thomas J. Maccarone

Collaborators:

L. E. Rivera Sandoval, N. Webb, S. Guillot

October, 2019

Compact Binaries

Cataclysmic Variable/ Low-mass X-ray Binary

  • White dwarf / Neutron star as primary:
  • MS star companion
  • Accretion (usually) via a disk:
    • Disk instability outbursts. Increase several magnitudes
Credit: Rob Hynes.

Redback System

Powerful radiation and the pulsar's "wind" strongly heat the facing side of the star. Credit: NASA.

Binaries in Globular Clusters

  • Globular Clusters
    • The binary population drives the dynamical evolution of GCs
  • Cataclysmic Variables:
    • Potentially very different from field CVs
    • A lot of open questions
  • Neutron Stars:
    • Known distance binary in GC
    • Estimate equation of state (mass-radius relation)
  • Gravitational Waves:.
    • White dwarf degenerate sources for LISA

Binaries in NGC 6397

Known X-ray sources

  • Cataclysmic Variables
    • 15 CV Candidates
  • Millisecond Pulsars (MSPs):
    • One radio confirmed and one candidate
  • Neutron Stars:
    • One qLMXB and possibly ultracompact
HST UV image of NGC 6397

Hubble Space Telescope

Wide Field Planetary Camera 2

  • March-April 2005:
    • 126 Orbits
    • F814W, F606W and F336W
    • Exp time:500-700 s
  • March-April 2005:
    • 126 Orbits
    • F814W, F606W and F336W
    • Exp time:500-700 s
NGC 6397
NGC 6397

Light Curves

U18

Candidate MSP. Possible redback system.

U18

Candidate MSP. Possible redback system.

New Candidate RedBack

    • $P_{orb} = \text{ 1.98 days}$
    • Narrow H$\alpha$ emission
      • FWHM ~ 170 km/s
    • From Husser et al. 2016
      • $\Delta v_{rad} \ge$ 145.9 km/s
HST CMD of NGC 6397

New Candidate RedBack

    • "Median" masses:
      • Inclination 60°
      • NS 1.35 $M_\odot$

    • $M_{donor} \approx 0.5 M_\odot$
Figure from Strader et al. (2019)

Future Work

  • Follow up Observations
    • Radio data NGC 6397
    • Other clusters with Hubble
    • MUSE Adaptive Optics and extended range
  • Variability:
    • Find more periods
  • MUSE Datacube:
    • Systematically search for emission:
      • Helium emitters (AM CVn ?)
      • Planetary Nebula
      • Active Binaries

Gracias

Department of Physics and Astronomy