A search for variable stars and compact binaries in globular clusters with HST

Manuel Pichardo Marcano

Liliana Rivera Sandoval, Thomas J. Maccarone

Background

• From Santo Domingo, Dominican Rep.
• B.S. Utah State University
• M.S. Université Toulouse III-Paul Sabatier
• Ph.D. Candidate Texas Tech University

Cataclysmic Variable

• White dwarf primary

• "Main-sequence" donor

• Roche-lobe overflow

• Accretion disk (non-magnetic)

• Disk instability:

  • Dwarf novae

  • 2-8 mag outburst

Formation of CVs

1. Main sequence binary
2. Roche lobe overflow
3. Common Envelope
   • α = E_bin/ΔE_orbit
4. Detached binary
5. Cataclysmic Variable

Evolution of the CV

• Magnetic Breaking
  • Porb > 3 hr
• Period Gap
  • Fully convective donor
• Gravitational Wave Rad
  •  Porb < 2 hr
• Period Minimum
  • Brown dwarf
• Period Bouncers
  • Increase Porb

Knigge (2006)

Evolution of the CV

• Tracer evolution
• Donor mass
• Ṁ

Abril et. al (2019)

Variability Search

My God, It's Full of Stars

NASA, ESA, H. Richer and J. Heyl (University of British Columbia), and J. Anderson and J. Kalirai (STScI)

Looking of CVs in GCs

NASA, ESA, H. Richer and J. Heyl (University of British Columbia), and J. Anderson and J. Kalirai (STScI)

Finding CVs in GCs

HST Optical (3' x 2')

NASA, T. Brown and S. Casertano (STScI)

HST NUV (2.7' x 2.7')

Dieball et. al (2016)

Chandra (3.65 ' x 3.65')

NASA/CXC/Northwestern Univ/J.Fregeau

1. X-rays and 2. (F)UV excess

Color-Magnitude Diagram

NGC 6752

Lugger et. al  (2017)

• CMDs:
  • Identify blue objects
  • Hα excess
• Variability:
  • Flickering
  • Ellipsoidal Modulations
  • Outbursts

Finding CVs in GCs

• Advantages:

  • Avoid crowding

• Disadvantages:

  • Small FoV (FUV)
  • L_x ≥ 10²⁹ ergs/s

CVs in GCs

• Few of CVs per cluster

• X-ray biased sample:

  • L_x > 10²⁹ergs/s

• Dearth of DNe:

  • Only 17 confirmed

• Core-collapsed:

  • Bimodal population

• Non core-collapsed:

  • 1 faint population

• Period distribution?

  • 16 know periods

Unbiased X-ray search

SSCOVaS: Survey for Studying Compact Objects and Variables Stars

• 7 Globular Clusters
• Core and Outskirts
• Different properties
  • Metallicity
  • Core-collapsed
  • Non core-collapse

Other Binaries

• Low-mass X-ray Binary
• Millisecond Pulsars
• Active Binaries

Chandra and Radio follow-up

NASA/CXC/Northwestern Univ/J.Fregeau

Preliminary Results

NGC 6397

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

A new candidate Redback MSP

A new candidate Redback MSP

HUGS catalogue. (Piotto et al. 2015, Nardiello et al. 2018)

Pichardo Marcano et. al (submitted)

X-ray

HST F336W

Radio

A new candidate Redback MSP

Pichardo Marcano et. al (submitted)

• Porb 1.96 days
• Longest Porb for Redback in GCs
• Missed MSP in Pulsar Searchers

Other Interests

• AM CVns
  • TESS follow up (P.I. Rivera Sandoval)
• Multi-wavelenght/messenger:
  • Learn from you radio and γ-ray astronomers!
• Follow up interesting sources/outburts
  • Amateurs astronomers from the region

¡Gracias!

Extra Slides

CV Population in the field

Pala et. al (2019)

• Dwarf Novae (59 %):
  • U Gem
  • SU UMa
  • WZ Sge

Finding CVs in GCs

HST Optical (3' x 2')

NASA, T. Brown and S. Casertano (STScI)

HST NUV (2.7' x 2.7')

Dieball et. al (2016)

Chandra (3.65 ' x 3.65')

NASA/CXC/Northwestern Univ/J.Fregeau

1. X-rays and 2. (F)UV excess

Location, Location, Location

CVs in Globular Clusters

47 Tuc

NGC 6752

Location, Location, Location

47 Tuc

L.E. Rivera Sandoval et al.  (2018)

CVs in Globular Clusters

43 CVs

16 CVs

NGC 6752

Lugger et. al  (2017)

Evolution of the CV

• Magnetic Breaking
  • Porb > 3 hr
• Period Gap
  • Fully convective donor
• Gravitational Wave Rad
  •  Porb < 2 hr
• Period Minimum
  • Brown dwarf
• Period Bouncers
  • Increase Porb

Knigge (2006)