Manuel Pichardo Marcano (Fisk/Vanderbilt)

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

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

Surveys

1- SCOVaS: Survey for Compact Objects and Variables

Pichardo Marcano et al. (2021a,2023, in prep.)

2- TACOS: TESS AM CVn Outbursts Survey

Pichardo Marcano et al. (2021b)

NASA

3- MARES: Magnetic Remnants in Symbiotics

Pichardo Marcano et al. (in prep.)

Cataclysmic Variables

• White dwarf primary

• "Main-sequence" donor

• Roche-lobe overflow

• Accretion disk (non-magnetic)

• Highly Variables:

  • Dwarf novae

    • 2-8 mag outburst

    • 10-100 increase in L

Cataclysmic Variables

R. Hynes

X-ray

Cataclysmic Variables

• Magnetic CVs:
  • High B Field (Polars)
  • Weaker B Field  (IPs)
• Non-Magnetic:
  • Accretion disk
    • DN Outburst

Intermediate Polar (IPs)

Polars

"Disk" CVs

CVs in the HR Diagram

Abril et. al (2019)

CV Population in the field

Pala et. al (2019)

• Dwarf Novae (59 %):
  • Transients/Outbursts:
    • U Gem
    • SU UMa
    • WZ Sge
• Novalike:
  • Persistently Bright

 Mroz et. al (2016) Image: (J. Skowron, K. Ulaczyk / Warsaw University Observatory)

Variability Search

Variability Search

Looking of CVs in GCs

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

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

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)

Finding CVs in X-rays and UV

• Advantages of X-ray Searches:

  • Avoid crowding

• Disadvantages:

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

Summary CVs in GCs

• Few of CVs per cluster

• X-ray biased sample:

  • Lx > 10²⁹ergs/s

• Predicted "Hidden" Population:

  • Belloni et al. (2016, 2017a, 2017b)

• Dearth of DNe:

  • Only 17 confirmed

• Core-collapsed:

  • Bimodal population

• Period distribution?

  • ~15 known periods

All Magnetics ?

See Belloni & Rivera Sandoval (2020) and Rivera Sandoval et al. (2024)

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

SCOVaS: Survey for Compact Objects and Variables

Preliminary Results

NGC 6397

• Closest Core Collapse
• Second Closest
  • 2.4 kpc
  • 15 CV candidates
  • 2 Pulsars

Preliminary Results

NGC 6397

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

Preliminary Results

NGC 6397

• 126 Orbits (F336W)
• Lomb–Scargle
• False Alarm Probability < 10^-8
• Not in the MS

Preliminary Results

NGC 6397

We haven't found new

X-ray faint CVs

Spoiler Alert!

Preliminary Results

NGC 6397

We haven't found new

X-ray faint CVs

Spoiler Alert!

Other Binaries

Credits: NASA/Rivera Sandoval

Main et al 2018 (Nature)

Redback 'spider' Pulsar

Redback  Pulsar

A new candidate Redback Pulsar

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

Pichardo Marcano et. al (2021a)

X-ray

HST F336W

Radio

Zhao et al. (2020), including Pichardo Marcano

A new candidate Redback MSP

Pichardo Marcano et. al (2021a)

• Porb 1.96 days
• Longest Porb for Redback in GCs
• Missed MSP in Pulsar Searchers
  • Confirmed by Zhang et al. (2022)

Blue Variables

Blue Variables

He WD Candidate

 Pichardo Marcano et al. (2023)

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. (2023)

MUSE spectrum

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

Magnetic He WD Candidate

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

• 18.4 hours 

Rotational Period

ESO/L. Calçada

 Pichardo Marcano et al. (2023)

Second Periodic WD Candidate

 Pichardo Marcano et al. (in prep.)

Data: Piotto et al.(2015)/ Nardiello et al. (2018)

• 5.3 hours 

Variable and No Hα Excess

• Not Detected in X-rays
• 0.2 Δmag in F336W
  
• No Hα in Excess
  
• Periodicity

  • 5.3 hours 

 Pichardo Marcano et al. (in prep.)

Light Curves of Known CV Candidates

High and Low state?

Nova-like Candidate

U19

U21

Nova-like Candidate

Ṁ changes?

 Pichardo Marcano et al. (in prep.)

Light Curves Variable WD Candidates

NF1 from Cool et al. 1998

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
• First Magnetic He Core WD in GCs
• Second Magnetic WD?
• Many more variables to analyze...

Where are all the CVs?

Surveys

1- SCOVaS: Survey for Compact Objects and Variables

Pichardo Marcano et al. (2021a,2023, in prep.)

2- TACOS: TESS AM CVn Outbursts Survey

Pichardo Marcano et al. (2021b)

NASA

3- MARES: Magnetic Remnants in Symbiotics

Pichardo Marcano et al. (in prep.)

AM Canum Venaticorum AM CVn

• White dwarf + White dwarf

• White dwarf + He Star

• Orbital Period: 5-70 minutes

• Rare: 70 Galactic field

Transiting Exoplanet Survey Satellite TESS

TESS Cadence and Coverage

• Primary mission:
  • 2-min selected targets
  • 30-min full-frame images (FFI).
• Extended:
  • 20 sec selected targets
  • 10-min FFI
• Second extended mission
  • 200-second FFI

Disk AM CVns

High state (high Ṁ)

• Hot ionized disk

~20

~10

~40-60 (?)

Low state (low Ṁ)

• Cold stable disk

Caltech

Caltech

• P_orb 20 to ~ 60 minutes (?)

• Superoutburts (SO) and "Normal" outbursts (NO)

• Disk instability model (DIM)

  •  Constant Mass transfer rate

  • Tidal-thermal disk instability model

    • SO: Superhumps (periodic brightness variation )

Outbursting Systems

Tidal radius

3:1 Resonance radius

Accretion disk

Precessing eccentric disc

Kley et al. 2008

Kimura 2020

Caltech

• P_orb 20 to ~ 60 minutes (?)

• Superoutburts (SO) and "Normal" outbursts (NO)

• Disk instability model (DIM)

  •  Constant Mass transfer rate

  • Tidal-thermal disk instability model

    • SO: Superhumps (periodic brightness variation )

Outbursting Systems

Better LC → Better Constraints

Place Constraints

Tidal radius

3:1 Resonance radius

Accretion disk

1. T_rec ∝ P_orb^7.35
2. T_dur ∝ P_orb^4.45
3. Δ mag ∝ Porb
4. Ground-Based:
   1. PTF/CRTS
   2. LINEAR
   3. ZTF

Levitan et al. 2015

See also Duffy et al. 2021

Better LC → Better Constraints

Constraint Empirical Relationships

Outbursts

Pichardo Marcano et al. (2021)

SO duration

Compare to CVs (SS Cyg)

Pichardo Marcano et al. (2021)

SO duration

Mariko Kimura (2020)

ASASSN-14cc

Pichardo Marcano et al. (2021)

9–18 d

kato et al. (2015)

• 2 Super Outbursts:
  • P_orb 22.5 min
  • Variable in length
    • Compare Kato+'15 and Duffy+'21
• Superhump period
  • 10 minute cadence

~7 d

• Precursor
  • TESS (Duffy et al. 2021)
• 5/6 have Precursor
  • Except ASASSN-14cc

PTF1 J0719+4858

Pichardo Marcano et al. (2021)

ZTF

TESS

Precursor

Type of Super Outbursts

Osaki et al. (2005)

High Mass Ratio

DIM

Cataclysmic Variables

See also Duffy et al. (2021)

High Mass Ratio

High Mass Ratio

High Mass Ratio

 eccentric disc develops rapidly

Type of Echo Outbursts

SDSS J1043+5632

• P_orb = 28.5 min
• WZ Sge like
  • Precursors
  • EMT (Hameury+'20)
  • Reflection:
    • Hot Massive WD

• P_orb = 26.7 min
• Compare to TCP J21040470+4631129
  • EMT (Hameury+'20)
• Helium "SU UMa"
  • EMT+TTI (Kotko+'12)

SO

rebrightening

SO

rebrightening

• Color Evolution

PTF1 J0719+4858

Pichardo Marcano et al. (2021)

ZTF

SO

NO

SO

NO

rebrightening

rebrightening

Color Evolution

PTF1 J0719+4858

SS Cyg

Cataclysmic Variable

• Similar to Dwarf Novae

  • Hameury et al. (2020)

• Similar SDSS J1411+4812
  • Rivera Sandoval et al. (2021)
• Compare to SDSS 1137
  • Rivera Sandoval et al. (2021)

Pichardo Marcano et al. (2021)

Color Evolution

PTF1 J0719+4858

• Similar to Dwarf Novae

  • Hameury et al. (2020)

• Similar SDSS J1411+4812
  • Rivera Sandoval et al. (2021)
• Compare to SDSS 1137
  • Rivera Sandoval et al. (2021)

Pichardo Marcano et al. (2021)

SDSS J113732+405458

 Enhanced mass transfer

Rivera Sandoval et al. (2021)

P_orb = 26.7 min

P_orb ~ 60 min

• Color Evolution

SDSS J1043+5632

Pichardo Marcano et al. (2021)

ZTF

TESS

SDSSJ1043+5632

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

Color Evolution

Long-term monitoring

• Observed 357 days
• Recurrence Time:
  • 203 days
• P_orb = 30.14 min :
  • 2-minute cadence
• "Normal Outburts"

Sector 5

Sector 12

Normal Outbursts

V803 Cen

• V803 Cen
  • Porb = 26.9 min
  • "Cycle"
  • Low Ṁ
• PTF1 J2219+3135:
  • New Porb= 27.7 min
  • Agrees with Trec
  • Permanent Superhumper?

Normal Outbursts

V803 Cen

• V803 Cen
  • Porb = 26.9 min
  • "Cycle"
  • Low Ṁ

Permanent Superhumper?

Osaki (1996)

Normal Outbursts

V803 Cen

• V803 Cen
  • Porb = 26.9 min
  • "Cycle"
  • Low Ṁ

Permanent Superhumper?

Osaki (1996)

Superoutburst duration vs P_orb

Pichardo Marcano et al. (2021)

TACOS Summary

• Precursors and "Normal" Outbursts:
  • Relatively Common
  • Short Duration (missed by ground-based)
• Echo Outbursts:
  • Different morphology
  • Enhanced Mass Transfer
• Superoutburst durations overestimated
• Two new candidate orbital periods
  • Constraint on T_rec vs. P_orb
• Color Evolution

Extra

Evolution of the CV

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

Knigge (2006)

Cataclysmic Variables

• Highly Variable and Hydrogen Rich

JD - 2458636

Hα

DN

Hα:

3-2 H transition

Cataclysmic Variables

• Highly Variable and Hydrogen Rich
• Many types of Behaviour

High and Low States

Super Outburts

M 92

HST vs Ground-based

Yepez et al. (2020)

Ground-based Data

HST Data

Preliminary Results

M 92

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

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

F555W

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...

Extra

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⊙

Location, Location, Location

CVs in Globular Clusters

47 Tuc

NGC 6752

• Most Lx < 10²⁹ ergs/s
  • ~100 L☉ of the Sun
• > 90% are period bouncers
  • Old systems
• Dearth of dwarf novae:
  • Low Accretors -> Rare Outburts
• Population beyond half-light radius

Simulation results

Belloni et al. (2016, 2017a, 2017b)

Simulation results

Variability Search in GCs

The results of our extensive survey provide new evidence ... that ordinary DNe are indeed very rare in GCs.

Pietrukowicz et. al (2008)

Hourihane et. al (2011)

• Only 17 confirmed DNe
• 7 GCs

Modiano et. al (2020)

Variability Search in GCs

[...] this would suggest MCVs are somehow enhanced in globular cluster cores, providing yet more evidence that stellar evolution in globulars is affected by close encounters.

Grindlay (1999)

Hourihane et. al (2011)

• DNe is suppressed due to truncation of the accretion disk.

Modiano et. al (2020)

Evolution of the CV

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

Knigge (2006)

Cataclysmic Variables

• Magnetic CVs:
  • High B Field (Polars)
  • Weaker B Field  (IPs)
• Non-Magnetic:
  • Accretion disk
    • DN Outburst

Intermediate Polar (IPs)

Polars

"Disk" CVs

Magnetic He WD Candidate

 Pichardo Marcano et al. (2023)

• 18.4 hours

• 0.16 M☉

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

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...

Also interested in:

• TESS:
  • Transients
  • Crowding
  • Symbiotics
• Halo vs Thick Disk:
  • Halo CVs
  • Halo AM CVns?

Data from Peters (2008)

Color-Magnitude Diagram

Lugger et. al  (2017)

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

NGC 6752

Bright CVs

Faint CVs

Color-Magnitude Diagram

47 Tuc

L.E. Rivera Sandoval et al.  (2018)

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

What do we know from theory and simulations?

A new candidate Redback Pulsar

Pichardo Marcano et. al (2021a)

X-ray

HST F336W

Radio

Zhao et al. (2020), including Pichardo Marcano

Mass-transfer rates vs orbital period

Caltech

• White dwarf + White dwarf

• White dwarf + He Star

• Outbursting:

  • P_orb 20 to ~ 60 minutes (?)

• Superoutburts (SO) and "Normal" outbursts (NO)

  • SO: Superhumps (periodic brightness variation )

Outbursting Systems

Outbursts

Pichardo Marcano et al. (2021)

• Precursor
  • TESS (Duffy et al. 2021)
• Echo Outbursts
• DIM with Enhanced Mass Transfer  (e.g. Hameury & Lasota 2021)

TESS AM CVn Outbursts Survey

Pichardo Marcano et al. (2021)

ZTF

TESS

Long-term monitoring

Pichardo Marcano et al. (2021)

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

Superoutburst duration vs P_orb

Pichardo Marcano et al. (2021)

TACOS Summary

• Precursors and "Normal" Outbursts:
  • Relatively Common
  • Short Duration (missed by ground-based)
• Echo Outbursts:
  • Different morphology
  • Enhanced Mass Transfer
• Superoutburst durations overestimated
• Two new candidate orbital periods
• Color Evolution

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

SCOVaS: Survey for Compact Objects and Variables

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

Preliminary Results

NGC 6397

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

Preliminary Results

NGC 6397

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

A new candidate Redback Pulsar

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

Pichardo Marcano et al. (2021a)

X-ray

HST F336W

Radio

Zhao et al. , including Pichardo Marcano (2020)

A new candidate Redback MSP

Pichardo Marcano et. al (2021a)

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

Blue Variables

He WD Candidate

 Pichardo Marcano et al. (2023)

MUSE spectrum

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

Light Curves of Known CV Candidates

High and Low state?

Novalike?

Pichardo Marcano et. al (in prep)

Ṁ changes?

Pichardo Marcano et. al (in prep)

Light Curves of Known CV Candidates

Magnetic He WD Candidate

Pichardo Marcano et. al (in prep)

Magnetic He WD

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

  • 18.4 hours 

Pichardo Marcano et. al (in prep)

Detached White Dwarf-Red Dwarf

Pichardo Marcano et. al (in prep)

• Not Detected in X-rays
• Potential P_orb

  • 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...

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

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