MUSE integral field unit observation of the compact objects in the globular cluster NGC 6397

Manuel PICHARDO MARCANO

Supervised by

Natalie WEBB

Sebastien GUILLOT

Toulouse
June 16, 2016

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.

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:.
    • Neutron stars binaries sources for LIGO
    • White dwarf degenerate sources for eLISA

Field CVs and GC CVs

GC CVs

  • Primordial and Dynamically formed
  • Dearth of outbursts
  • Mainly magnetic?
  • Period distribution?
  • 8 spectra from 4 GCs

Field CVs

  • Main Sequence binary evolution
  • 40% show outburst
  • 25% magnetic
  • $75 \text{ min} \lesssim \text{P}_{\text{orb}}\lesssim 10 \text{ hrs} $
  • Hundreds of spectra

Lack data and understanding CVs in GCs

MUSE

Integral Field Unit (IFU)

  • Data cube:
    • $ \text{FoV:}(1^ \prime \times 1 ^ \prime )$
    $(0.\!\!^{\prime\prime}2 \times 0.\!\!^{\prime\prime}2 \times 1.25 \, \unicode{x212B} $)
    $4800-9300 \, \unicode{x212B} $
  • MUSE Commissioning
    • July 26th to August 3rd, 2014
    • Very short exposures (25-60 s)
    • Total 95 minutes
NGC 6397
Credit: ESO's

Data reduction

Pre-processing to remove instrumental signatureCredit: MUSE Pipeline User Manual
Post-processing for observation calibration and produce data cubes
Credit: MUSE Pipeline User Manual

The Data
White Image

H$\alpha - $continuum

(H$\alpha$ - continuum) + Chandra X-ray Contours

Very Noisy Data

Detected CVs

Obtained spectra from CVs in NGC 6397. IDs from (Bogdanov et al., 2010)

Spectroscopically confirmed CVs in NGC 6397

(1) Grindlay et al. 1995; (2) Edmonds et al. 1999; (3) Kaluzny & Thomson 2003

Spectral Analysis

CVs and LMXB

  • CVs:
    • Mass ratio:
      • From the H$\alpha$ double peaked emission (Casares 2016)
    • Radial Velocity:
      • Cross-correlation two observing nights
    • Outbursts:
      • Compare to Hubble observations (Cohn et al. 2010). Variability in R magnitude
  • LMXB:
    • Hint of detection. Limit on the H$\alpha$ flux

Results

  • Primordial CVs
    • 'Faint' undetected CVs H$\alpha$
    • Primordial in the outer regions?
  • Periods:
    • Too short exposures (100 secs first night)
    • Secondary Mass - Period relation:
      • Big error bars mass ratio determination
      • No TiO and turnoff point: $0.5 \text{ M}_\odot \lesssim \text{M}_{\text{sec}} \lesssim 0.8 \text{ M}_\odot$
  • Outbursts:.
    • Expected at least one (biased and empirical estimate)
    • Very rare in globular clusters. Suggests magnetic in nature
  • Magnetism:
    • No ionised helium (He II)
    • Strongest He II outside range (4686 Å)

Conclusions

We have demonstrated how an IFU like MUSE can be used to efficiently study the population of compact objects in globular clusters. Deeper observation are needed but we exposed some hints that the population of field CVs and CVs in GCs are different

Future Work

  • Follow up Observations
    • Submitted proposal for observing time
      • Determine NS atmosphere
      • Study CV with large field-of-view
  • Data analysis:
    • Optima spectra extraction
    • Short term variability
    • Analysis available spectra
  • Reproducibility:
    • Continuous analysis
    • Cloud Computing

Thank you.