A candidate magnetic helium core white dwarf binary in the globular cluster NGC 6397

Manuel Pichardo Marcano (AMNH)

Liliana Rivera Sandoval, Thomas J. Maccarone, Diogo Belloni, Craig Heinke, Arash Bahramian, Rene Rohrmann, Leandro Althaus

  • HST Archive
  • 7 Globular Clusters
  • Many Exposures
  • Different properties
    • Metallicity
    • Core-collapsed
    • Non core-collapsed

SCOVaS: Survey for Compact Objects and Variables

  

NGC 6397

  • WFPC-2
  • March-April 2005:
    • 126 orbits
    • F814W, F606W and F336W
    • Exp time: 500-700 s

He WDs in NGC 6397

 Strickler et al. (2009)

  • Binary Evolution:
    •  Mass-transfer episodes
    • Many in Binary systems
  • Extremely           low-mass WDs:
    • He WD
    • M < ∼ 0.3 M☉
  • 24 Candidates in NGC 6397

0.175 M⊙

 0.45  M⊙

He WD Candidate

 Pichardo Marcano et al. (in prep)

HACKS CMD

 Data: Libralato et al. (2022)

He WD Candidate

Tracks from Althaus et al. (2009)

0.16 M☉

 0.22  M⊙

0.52 M⊙

  • 18.4 hours

He WD Candidate

He WD Candidate

 Pichardo Marcano et al. (in prep)

MUSE spectrum

Data from Husser et al. (2016), Kamman et al. (2016)

Magnetic He WD Candidate

  • Vrad > 150 km/s (MUSE)
  • Not Detected in X-rays
    • Lx < 1028 ergs/s
  • Roche-lobe filling stripped star?
    • M~ 2 x 10-4 ☉
  • 18.4 hours

Rotational Period

Magnetic He WD Candidate

 Pichardo Marcano et al. (in prep)

  • 18.4 hours

  • 0.16 M☉

  • 0.24 R☉
  • 0.11 Gyr
  • Teff 7586 K
  • log g = 4.9

Magnetic He WD Candidate

Extra

Helium-Core White Dwarfs

Z. Li et al. (2009)

  • Binary Evolution:
    •  Mass-transfer episodes
    • Many in Binary systems
  • Extremely           low-mass WDs:
    • He WD
    • M < ∼ 0.3 M☉
  • 24 Candidates in NGC 6397

Magnetic He WD Candidate

 Pichardo Marcano et al. (in prep)

Lightcurve in F336W Filter

  • 18.4 hours

Magnetic He WD Candidate

 Pichardo Marcano et al. (in prep)

  • 0.16 M☉

  • 0.24 R☉
  • 0.11 Gyr
  • Teff 7586 K
  • log g = 4.9

Preliminary Results

NGC 6397

  • WFPC-2
  • March-April 2005:
    • 126 orbits
    • F814W, F606W and F336W
    • Exp time: 500-700 s

Magnetic He WD Candidate

Tracks from Althaus et al. (2009)

0.16 M☉

Blue Variables

Magnetic He WD

  • Vrad > 100 km/s (MUSE)
  • Not Detected in X-rays
  • Rotation Period 
    • 18.4 hours

Pichardo Marcano et. al (in prep)

Magnetic He WD

Pichardo Marcano et. al (in prep)

  • 18.4 hours

Magnetic He WD Candidate

SCOVaS: Survey for Studying Compact Objects and Variables

  

  • Focus: Cataclysmic Variables (CVs) with HST
  • First Survey for CVs in GCs Unbiased in the X-ray
    • X-ray faint CVs
    • Orbital Periods
  • Spatial Distribution:
    • Looking at the dense Core of Clusters
    • Next: Search in the Outskirts
  • Optical Counterpart X-ray/Radio Sources in GCs

Detached White Dwarf-Red Dwarf

Pichardo Marcano et. al (in prep)

  • Not Detected in X-rays
  • Potential Porb 
    • 5.21 hours

Pichardo Marcano et. al (in prep)

Detached White Dwarf-Red Dwarf

NGC 6397

  • Pipeline to find interesting objects:
    • CMD Position and Periodicity/Variability Searches
  • We were able to recover all known CV Candidates
  • Found Orbital Period Redback Pulsar
  • Detached White Dwarf-Red Dwarf
  • Many more variables to analyze...

M 92

  • New variables in the core:
    • SX Phe, RR Lyrae, AB, ....
  • Search for Optical Counterparts of X-ray sources:
    • 1 Pulsar, 4-5 CVs
  • Many more variables to analyze...

Other work with Accreting WDs

  • Follow-up eROSITA transient:

  • TESS time series analysis

    • Atel: Pichardo Marcano (2020)

    • Paper: Schwope, [...], Pichardo Marcano, et al. (2021)

Caltech

Preliminary Results

M 92

  • WFPC-2
  • 2008-01-25 to 2008-01-30:
    • 76 Exposures
    • F555W
    • Exp time: 10 s

M 92

HST vs Ground-based

Yepez et al. (2020)

Ground-based Data

HST Data

New Variables in the Core

SX Phe

 

  • Good Distance indicator:
    • Strong P-L relation
  • Less common than RR Lyrae
  • Blue Straggler
    • Product of Binary evolution

P = 1.38 hr

Pichardo Marcano et. al (in prep)

Compact Binaries Surveys

2- SCOVaS: Survey for Compact Objects and Variables

Pichardo Marcano et al. (2021a)

Pichardo Marcano et al. (in prep.)

1- TACOS: TESS AM CVn Outbursts Survey

Pichardo Marcano et al. (2021b)

Compact Binaries Surveys

Extra Slides

PTF1 J0719+4858:

  • Similar to Dwarf Novae:
    • Hameury et al. (2020)
    • Rivera Sandoval et al. (2021)

Color Evolution

Pichardo Marcano et al. (2021)

Transiting Exoplanet Survey Satellite (TESS)

Empirical Relationships

  1. Trec prop Porb^7.35
  2. Tdur prop Porb^4.54
  3. Delta mag prop Porb
  4. Long-term
  5. Ground-Based:
    1. PTF
    2. CRTS

Levitan et al. 2015

See also Duffy et al. 2021

Outbursts

Pichardo Marcano et al. (2021)

Long-term monitoring

Pichardo Marcano et al. (2021)

  • Orbital Periods:
    • 2-minute cadence
  • Limits on Recurrence Time
  • "Normal Outburts"

AM Canum Venaticorum AM CVn

  • White dwarf + White dwarf

  • White dwarf + He Star

  • Orbital Period: 5-70 minutes

Caltech

Summary

  • GOTO:
    • Time-domain astronomy
      • ZTF, ATLAS, TESS, HST
    • Experience Transients
      • Expand my expertise
  • Common interest with Warwick Scientists
    • Compact Binaries:
      • Accreting WDs
  • Experience Spectroscopy:
    • IFU: MUSE, VIMOS
    • GEMINI