Observational Constraints on Physics of White Dwarfs
from Visual BinariesHoward E. Bond
Pennsylvania State University (Professor of Practice)Space Telescope Science Institute (Astronomer Emeritus)
Current Challenges in the Physics of White-Dwarf Stars Santa Fe 2017 June 13
Alan Dyer
Alan Dyer
Sirius
Alan Dyer
Sirius
Procyon
Alan Dyer
Sirius
Procyon
o2 (40) Eridani
HST & Ground-based Imaging & Astrometry of WDs in 4 Visual Binaries …
• Procyon B
• Sirius B
• 40 Eridani B
• Stein 2051B
HST & Ground-based Imaging & Astrometry of WDs in 4 Visual Binaries …
• Procyon B
• Sirius B
• 40 Eridani B
• Stein 2051B40 Eri and Stein have evolved as single stars;
less clear for Procyon & Sirius
Collaborators• Procyon & Sirius:
• Martin Barstow, Matt Burleigh, Sarah Casewell, Pierre Demarque, Ron Gilliland, Terry Girard, Don Gudehus, Jay Holberg, Simon Joyce, Vera Kozhurina-Platais, Irving Lindenblad, Brian Mason, Ed Nelan, Gail Schaefer, Miranda Seitz-McLeese, David Arnett, Patrick Young, Federico Spada
• 40 Eri:
• Brian Mason, William Hartkopf, Korie Miles, Pierre Bergeron, Antoine Bedard
Collaborators• Stein 2051B:
• Kailash Sahu (PI, STScI), Jay Anderson, Stefano Casertano, Pierre Bergeron, Ed Nelan, Laurent Pueyo, Tom Brown, Andrea Bellini, Zolt Levay, Josh Sokol, Martin Dominik, Annalisa Calamida, Noe Kains
• See Poster 11 !
The Companions of Sirius & Procyon
The Companions of Sirius & Procyon• Friedrich W. Bessel (1844)
• proper motions of Sirius & Procyon show perturbations from linear
• “Light is no real property of mass. The existence of numberless visible stars can prove nothing against the existence of numberless invisible ones.”
• The faint companions were finally seen for Sirius (1862, Alvan Clark) & Procyon (1896, Schaeberle)
• Both are white dwarfs
Mass-Radius Relation WD radius decreases with mass and with mean molecular weight
Provencal et al. 2001: WDs in visual binaries,
common p.m., and field
Poor agreement with theory!
Chandrasekhar limit ~1.4 Msun
Procyon• 8th brightest star in sky
• F5 IV-V + DQZ (helium atmosphere; lines of C, Mg, Fe)
• P = 40.84 yr
• 2nd nearest & 3rd brightest WD
• HST images at 19 epochs, 1995-2016. WFPC2/WFC3. Astrometric precision ~0″.003
• plus 55 ground-based measures 1896-1995, nearly all visual micrometer
• Bond+ 2015 ApJ, 813, 106
Nov 1997, sep = 4″.706∆V ~ 10.5
HST observations & orbit fit
Gnd-based used in fit
Gnd-based rejected
HST data & expected pos’n
Orbit fit
HST observations & orbit fit
• P = 40.840 yr • a = 4″.3075 • e = 0.39785 • MA = 1.478 ± 0.012 M⊙ • MB = 0.592 ± 0.006 M⊙
Procyon B in theoretical HR diagram
Procyon B in theoretical HR diagram
evolutionary sequences from Bergeron, Fontaine,Tremblay, Kowalski
Procyon B in theoretical HR diagram
Expected mass agrees almost perfectly with measured.
Cooling age 1.37 Gyr
Procyon B in mass-radius relation
radius from Provencal+ 2002
mass is dynamical massfrom HST orbit
qH = 10-10
Procyon B in mass-radius relation
“iron box” from Provencal+ 1997
qH = 10-10
Procyon Results• Theoretical cooling tracks & mass-radius relation
agree with CO core and HST dynamical mass
• Freed from the “iron box”!
• Cooling age 1.37 Gyr
• Final mass 0.59 M⊙. Initial mass was ~1.9-2.2 M⊙, depending on properties of Procyon A.
Puzzles of Procyon B• Source of metals accreting onto DQZ WD?
• planetesimals around B would have been destroyed during RG/AGB phase.
• Planetesimals or debris disk around A? …
• … or surrounding the entire binary?
• Why no obvious past interaction with A?
• periastron separation was only ~5.1 AU in progenitor binary
• why is the eccentricity still ~0.40?
Sirius• Brightest star in sky
• A1 Vm + DA2 (pure H atmosphere)
• P = 50.13 yr
• Nearest & brightest WD
• HST images at 17 epochs, 1997-2016. WFPC2/WFC3. Astrometric precision ~0″.003
• plus >2300 ground-based measures 1862-2016, mostly visual micrometer or photographic
• Bond+, 2017, ApJ, 840, 70 Oct 2003, sep = 6″.089∆V ~ 9.9
Sirius• Brightest star in sky
• A1 V + DA2 (pure H atmosphere)
• P = 50.13 yr
• Nearest & brightest WD
• HST images at 17 epochs, 1997-2016. WFPC2/WFC3. Astrometric precision ~0″.003
• plus >2300 ground-based measures 1862-2016, mostly visual micrometer or photographic
• Bond+, 2017, ApJ, 840, 70 Oct 2003, sep = 6″.089∆V ~ 9.9
Sirius• Brightest star in sky
• A1 V + DA2 (pure H atmosphere)
• P = 50.13 yr
• Nearest & brightest WD
• HST images at 17 epochs, 1997-2016. WFPC2/WFC3. Astrometric precision ~0″.003
• plus >2300 ground-based measures 1862-2016, mostly visual micrometer or photographic
• Bond+, 2017, ApJ, 840, 70 Oct 2003, sep = 6″.089∆V ~ 9.9
The Hubble ultra-shallow field
Sirius: all observations 1862-2016
Sirius: visual obs. omitted
HST observations & orbit fit
HST observations & orbit fit
HST observations & orbit fit
HST observations & orbit fit
• P = 50.1284 yr • a = 7″.4957 • e = 0.59142 • MA = 2.063 ± 0.023 M⊙ • MB = 1.018 ± 0.011 M⊙
Sirius B in mass-radius relationra
dius
from
HST
spe
ctro
scop
ic
anal
ysis
dynamical massfrom HST orbit
Sirius B in theoretical HR diagram
Sirius B in theoretical HR diagram
Expected mass 1.019 M⊙; dynamical mass 1.018 ± 0.011 M⊙
Sirius B in theoretical HR diagram
Cooling age 126 Myr
Sirius Results• Excellent agreement of theoretical cooling tracks & mass-
radius relation for CO core with the HST dynamical mass
• Final mass 1.018 M⊙
• Cooling age 126 Myr.
• Based on IFMR of Cummings+ (2016), initial mass was ~5.0-5.6 M⊙. MS lifetimes ~100 Myr ⇒
• Total age of Sirius B = 226 ± 10 Myr
Consistency Check with Age of Sirius A• Two evolution codes:
• Tycho (Arnett group)
• YREC (Demarque group)
• Different treatments of convection
• Both require Sirius A to be slightly metal-poor (~0.85 Z⊙)
• Age of A is ~237-247 Myr, with uncertainty of ~ ±15 Myr.
• Consistent with age of Sirius B of 226 ± 10 Myr ! 😀
Puzzles of Sirius B• Why no obvious past interaction with A?
• periastron separation was only ~1.6 AU in original binary—smaller than radius of AGB progenitor!
• how was common envelope avoided?
• why is the eccentricity still ~0.59?
omicron-22
Eridani B (40 Eri B)
• Triple system
• 40 Eri B: first white dwarf to be recognized
• H. N. Russell: In 1910, “The first person who knew of the existence of white dwarfs was Mrs. Fleming; the next two, an hour or two later, Prof. Pickering and I. … Pickering smiled and said ‘It is just such discrepancies which lead to the increase of our knowledge.’ ”
• Orbited by 40 Eri C
• 5th nearest & 2nd brightest WD—and easiest to observe!
A: dK1
C: dM4.5
B: WD, DA4
omicron-22
Eridani B (40 Eri B)
• Heintz (1974) found P = 252 yr and MB = 0.43 ± 0.02 M⊙ from observations covering ~half the orbit. Does it have an Fe core??
• Grav redshift (Koester & Weidemann 1991) implies 0.53 ± 0.04 M⊙
• Shipman+ (1997) used new Hipparcos parallax to revise Heintz to 0.501 ± 0.011 M⊙
• Holberg+ (2012): based on this low a mass “we find strong evidence for the existence of a ‘thin’ H envelope.”
A: dK1
C: dM4.5
B: WD, DA4
40 Eri B in M-R Plane: “Thin” H Envelope?
40 Eri B in M-R Plane: “Thin” H Envelope?
Caveat: most recent observations used in Heintz dynamical mass were made in 1973!
The US Navy to the Rescue!
USNO 26-inch refractor (1873), Washington DC
40 Eri B from downtown Washington DC
USNO 26-inch refractor (1873), speckle camera, 2017 Feb 17courtesy Brian Mason
A
BC
40 Eri B Updated Orbit• Brian Mason et al., in prep
• New observations revise period from 252 to 230 yr, small changes in other elements:
• Revised mass = 0.573 ± 0.018 M⊙
• Updated Teff & radius from Bedard, Bergeron, & Fontaine (poster)
40 Eri B in M-R Plane: Still Thin H Envelope!
40 Eri B: DA tracks predict too high mass
40 Eri B: DB tracks predict observed mass!
Stein 2051 System• d = 5.58 pc, ~60th nearest star system
• dM4 + DC (helium-atmosphere WD, continuous spectrum)
• 6th-nearest WD; nearest & brightest DC
• Sahu et al. predicted passage of B in front of 18-mag background star, early 2014, impact parameter 0.1 arcsec!
• Opportunity to measure mass of B via relativistic deflection
• reprise of 1919 solar eclipse that made Einstein a celebrity!
• K. Sahu et al., 2017, Science, 356, 1046
HST WFC3 image, Oct. 2013A-B sep = 10″.1
B (DC)
A (dM4)
Stein 2051 System• d = 5.58 pc, ~60th nearest star system
• dM4 + DC (helium-atmosphere WD, continuous spectrum)
• 6th-nearest WD; nearest & brightest DC
• Sahu et al. predicted passage of B in front of 18-mag background star, early 2014, impact parameter 0.1 arcsec!
• Opportunity to measure mass of B via relativistic deflection
• reprise of 1919 solar eclipse that made Einstein a celebrity!
• K. Sahu et al., 2017, Science, 356, 1046
HST WFC3 image, Oct. 2013A-B sep = 10″.1
B (DC)
A (dM4)
General Relativistic Deflection of Background Star Image:“Astrometric Microlensing”
STScI Office of Public Outreach
Close Encounter of the Relativistic Kind
STScI Office of Public Outreach
Stein 2051B Close Encounter
Sahu
et a
l. 20
17
Stein 2051B Close Encounter
STScI Office of Public Outreach
Stein 2051B Deflections & Model Fit
K. Sahu et al., Science, in press.
Stein 2051B Max Deflection ~2 mas
K. Sahu et al., Science, in press.
Stein 2051B Max Deflection ~2 mas
Stein 2051B Max Deflection ~2 mas
Stein 2051B Max Deflection ~2 mas
Stein 2051B Max Deflection ~2 mas
Stein 2051B Max Deflection ~2 mas
Stein 2051B Max Deflection ~2 mas
Stein 2051B Max Deflection ~2 mas
2 mas = diameter of US quarter at distance of State College (~1550 mi)
Parameters of Stein 2051B from Astrometric Microlensing• Fit to deflections & known distances of WD (5.5
pc) and background star (2.0 kpc) ⇒
• mass = 0.675 ± 0.051 M⊙
• Broadband photometry & model atmospheres ⇒
• Teff = 7122 ± 181 K, R = 0.0114 ± 0.0004 R⊙
Stein 2051B in theoretical HR diagram
expected mass = 0.67; measured = 0.675 ± 0.051 M⊙ cooling age 1.9 ± 0.4 Gyr
Stein 2051B in mass-radius relation
Summary• Precise dynamical masses for WDs in visual binaries
• Sirius B, Procyon B, 40 Eri B
• Mass measurement for Stein 2051B from relativistic deflection of background star
• Theory provides excellent agreement in mass-radius plane
• 40 Eri B has a thin H layer
• Puzzles of Sirius & Procyon…
• Did Sirius B and Procyon B interact with companions?
• High orbital eccentricities
Mass-radius Relation for WDs inShort-Period Eclipsing Binaries
Post-common-envelope binaries; Parsons+ 2016
Summary Mass-radius Diagram
Thank you!supported by grants from STScI
