The eclipsing AM CVn star, SDSS J0926+3624 Tom Marsh Department of - - PowerPoint PPT Presentation

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The eclipsing AM CVn star, SDSS J0926+3624 Tom Marsh Department of - - PowerPoint PPT Presentation

Jun 26, 2023 98 likes •395 views

The eclipsing AM CVn star, SDSS J0926+3624 Tom Marsh Department of Physics, University of Warwick Co-Is: Vik Dhillon, Stu Littlefair, Paul Groot, Pasi Hakala, Gijs Nelemans, Gavin Ramsay, Gijs Roelofs, Danny Steeghs Tom Marsh, University of

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The eclipsing AM CVn star, SDSS J0926+3624

Tom Marsh

Department of Physics, University of Warwick

Co-Is: Vik Dhillon, Stu Littlefair, Paul Groot, Pasi Hakala, Gijs Nelemans, Gavin Ramsay, Gijs Roelofs, Danny Steeghs

Tom Marsh, University of Warwick Slide 1 / 29

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Outline

  • 1. The discovery of SDSS J0926+3624
  • 2. ULTRACAM observations:
  • Phenomenology: superhumps and QPOs
  • Eclipses, parameters.
  • Testing Patterson’s ǫ-q relation
  • Timing
  • 3. Conclusions

Tom Marsh, University of Warwick Slide 2 / 29

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The discovery of SDSS0926+3624

  • Anderson et al (2005)

discovered 4 new AM CVn stars in the SDSS.

  • SDSS J0926+3624 is

eclipsing, the first and currently the only eclipsing AM CVn known.

  • P = 28 minutes
  • g ′ = 19.3 out of

eclipse with eclipses lasting ∼ 1 minute.

Tom Marsh, University of Warwick Slide 3 / 29

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The discovery of SDSS0926+3624

  • Anderson et al (2005)

discovered 4 new AM CVn stars in the SDSS.

  • SDSS J0926+3624 is

eclipsing, the first and currently the only eclipsing AM CVn known.

  • P = 28 minutes
  • g ′ = 19.3 out of

eclipse with eclipses lasting ∼ 1 minute.

Tom Marsh, University of Warwick Slide 4 / 29

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ULTRACAM: a high-speed CCD photometer

ULTRA at Cass on the 4.2m WHT

Tom Marsh, University of Warwick Slide 5 / 29

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SDSS0926+3624 with 4.2m WHT & ULTRACAM

Tom Marsh, University of Warwick Slide 6 / 29

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Superhumps – I.

Gross changes of the light curve from night-to-night caused by superhumps, a changing, tidal distortion of the outer disc that occurs for q = M2/M1 < 0.3 (Whitehurst 1987).

Tom Marsh, University of Warwick Slide 7 / 29

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Superhumps – II.

Superhump cycle time: PCyc = POrbPSH PSH − POrb , = 2.26 ± 0.26 days.

Tom Marsh, University of Warwick Slide 8 / 29

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QPO

No high frequency

  • scillations, but a QPO

with a period around 50 seconds.

Tom Marsh, University of Warwick Slide 9 / 29

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QPO

No high frequency

  • scillations, but a QPO

with a period around 50 seconds. Peak-to-peak amplitude up to ∼ 10%

Tom Marsh, University of Warwick Slide 10 / 29

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Eclipse analysis in CVs

Stream dynamics and Roche geometry ⇒the orbital inclination i and the mass ratio q = M2/M1 Accretor’s eclipse gives R1/a. M-R relation and Kepler’s 3rd law ⇒M1 and M2. Smak (1979); Cook & Warner (1984); Wood et al (1986) q = 0.2, i = 80◦ q = 0.1, i = 83.9◦

Tom Marsh, University of Warwick Slide 11 / 29

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Example models

q = 0.15 q = 0.03

Tom Marsh, University of Warwick Slide 12 / 29

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Example data, courtesy Stu Littlefair

P = 144 min, q = 0.215

P = 67 min, q = 0.05

Tom Marsh, University of Warwick Slide 13 / 29

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SDSS0926, mean data, night-by-night

In SDSS0926, the bright-spot starts its eclipse after the white dwarf has come out

  • f eclipse. q is clearly

small. Disc radius variable from night-to-night (tidal instability of

  • uter disc).

Tom Marsh, University of Warwick Slide 14 / 29

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Light curve fits

White dwarf ∼ 70% of flux; disc and bright-spot ∼ 15% each. Typical of quiescent systems.

Tom Marsh, University of Warwick Slide 15 / 29

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Distorted outer disc

From night 1 to night 2, the bright-spot’s distance from the white dwarf changes from 0.33a to 0.42a.

Tom Marsh, University of Warwick Slide 16 / 29

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Fit parameters

Many parameter fits; uncertainties best derived using Markov Chain Monte Carlo (MCMC method, not equivalent to the “Monte Carlo” method).

Tom Marsh, University of Warwick Slide 17 / 29

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Fit parameters

Many parameter fits; uncertainties best derived using Markov Chain Monte Carlo (MCMC method, not equivalent to the “Monte Carlo” method).

Tom Marsh, University of Warwick Slide 18 / 29

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Fit parameters

Many parameter fits; uncertainties best derived using Markov Chain Monte Carlo (MCMC method, not equivalent to the “Monte Carlo” method).

Tom Marsh, University of Warwick Slide 19 / 29

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Fit parameters

Many parameter fits; uncertainties best derived using Markov Chain Monte Carlo (MCMC method, not equivalent to the “Monte Carlo” method).

Tom Marsh, University of Warwick Slide 20 / 29

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Fit parameters

Many parameter fits; uncertainties best derived using Markov Chain Monte Carlo (MCMC method, not equivalent to the “Monte Carlo” method).

Tom Marsh, University of Warwick Slide 21 / 29

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Fit parameters

Many parameter fits; uncertainties best derived using Markov Chain Monte Carlo (MCMC method, not equivalent to the “Monte Carlo” method).

Tom Marsh, University of Warwick Slide 22 / 29

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Fit parameters

Many parameter fits; uncertainties best derived using Markov Chain Monte Carlo (MCMC method, not equivalent to the “Monte Carlo” method).

Tom Marsh, University of Warwick Slide 23 / 29

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Component masses

Donor mass ∼ 0.025 M⊙ Smaller than reported earlier (∼ 0.029 M⊙), and thus closer to fully degenerate 0.020 M⊙. I have not resolved why yet.

Tom Marsh, University of Warwick Slide 24 / 29

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Patterson’s ǫ–q relation for superhumps

Whitehurst (1987): at small q = M2/M1, outer disk distorts and precesses → superhumps. Patterson (2001) presented evidence for an empirical relation between ǫ = (PSH − Porb)/Porb and q.

Potentially simple way to measure q in AM CVn stars, but poorly constrained at very small q.

Tom Marsh, University of Warwick Slide 25 / 29

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Patterson’s ǫ–q relation for superhumps

SDSS0926 lies within ∼ 15% of Patterson’s (2001) relation and is by far the most secure calibrator at small q

Tom Marsh, University of Warwick Slide 26 / 29

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Timing

Mean eclipse time over 3 nights has RMS uncertainty ≈ 0.2 sec. Time delay due to GWR-driven orbital evolution

  • ver 10 years ∼ 5 sec.

⇒predicted evolution will be detectable within ∼ 5 years. Any enhancement from magnetic braking should be

  • bvious.

Tom Marsh, University of Warwick Slide 27 / 29

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Conclusions

  • 1. The first eclipsing AM CVn star, SDSS 0926+3624, does not

disappoint and has already the most secure parameters of any AM CVn star.

  • 2. Patterson’s (2001) ǫ–q relation survives SDSS0926

remarkably unscathed.

  • 3. Future observations can (a) map out the shape of a

superhumping disc, (b) firm up the parameters, (c) directly measure the period evolution, and (d) test whether magnetic braking operates in AM CVn stars.

  • 4. An eclipsing system in hand is worth ten in the fynbos; let’s

find some more!

Tom Marsh, University of Warwick Slide 28 / 29