1. Testing the White Dwarf M-R Relation with HST Observations of Sirius-type Binaries M.A. Barstow, H. Bond, M.R. Burleigh, S.L. Casewell, J. Farihi, J.B. Holberg, I. Hubeny, S.R.G. Joyce www.le.ac.uk Department of Physics & Astronomy

2. Importance of the M-R relation Estimates of cooling age depend on it –Ages of clusters and limits on age of Universe Underpins late stages of stellar evolution –Interstellar gas & dust production Behaviour of matter under extreme conditions Understanding of SN Ia progenitors Hansen et al 2007

3. Introduction Sirius B, the closest known white dwarf –Previous results Improved observation techniques New results for Sirius B and an extended sample Remaining issues? Hubble 2020, 20-24 April 2015

4. Mass &/or Radius Measurements Possible Data… Parallax –D Astrometry –M Photometry –(R/D) 2 Spectroscopy –T eff, g, Z Hubble 2020, 20-24 April 2015

5. Some history Sirius B first white dwarf discovered –Bessel, 1844, MNRAS, 6, 136, resolved by A.G. Clarke 1862 –spectrum by W.S Adams, 1915 (PASP, 27, 237) –others… Lassell, Strüve, Burnham, Hall, Barnard Observations very difficult! –due to overwhelming brightess of Sirius A –J.B. Oke 1963, Kodaira 1967 (PASJ, 19, 172) Greenstein, Oke & Shipman 1971 –T eff = 32000±1000K, log g = 8.65±0.10 –R = 0.0078±0.0002 R , V grav =86±16 km/s First space-age measurements in 2005 –Barstow et al. 2005 (MNRAS, 362, 1134)

6. Hubble 2020, 20-24 April 2015

8. G430L G750M

9. 2005 results Hubble 2020, 20-24 April 2015 g, (R/D) 2 V gr, (R/D) 2

10. New observations Sirius B (again), 56 Per, HR2133B, HR1348B, HD217411B, 14AurCb WFC3, STIS G430L and G750M –Different slit sizes to address systematics in flux, wavelength zero point and scattered light 56 Per separation too small for spectra HR1348, scattered light issue, to be resolved Hubble 2020, 20-24 April 2015

11. 56 Per Hubble 2020, 20-24 April 2015

12. HD217411 Hubble 2020, 20-24 April 2015 Holberg et al. 2014, arXiv:1407.4332arXiv:1407.4332

13. Hubble 2020, 20-24 April 2015 1993 2004 2011

14. Revised Parameters for Sirius B Hubble 2020, 20-24 April 2015 Param.ValueError New Results mVmVmVmV8.480.028.500.01 T eff (K) 25,1933725,48367 log g 8.5560.0108.6420.005 π (") 0.379210.00158 V gr (km/s) 77.40.880.424.83

15. Hubble 2020, 20-24 April 2015 g, (R/D) 2 V gr, (R/D) 2

16. Hubble 2020, 20-24 April 2015

18. Conclusions Potentially improved accuracy of M-R –Differentiation between models Systematic issues to resolve –Sirius B - V gr doesn’t agree with log g –Slit location Need improved parallaxes (Gaia) Need more orbital data – HST, Gaia, JWST, HDST… continuity for ~50 yrs Hubble 2020, 20-24 April 2015