One million years until graceland: finding galactic Ia progenitors

AbstractDouble click to add an Abstract


The in-spiral and coalescence of double white dwarf (WD) binaries due to gravitational wave emission has several possible outcomes, all of them of the highest astronomical interest. When the combined mass exceeds the Chandrasekhar limit (\(M_{\rm Ch}\)), the merger could lead to a Type Ia Supernova (SN) (Iben et al., 1984; Webbink, 1984), although accretion induced collapse to a neutron star is also a possibility (Saio et al., 1998; Schwab et al., 2016). Recent work shows that the delay time distribution of SN Ia behaves like 1/t for t \(\gtrsim\) 1 Gyr, exactly as predicted by a population of binaries that merge through gravitational wave emission (Maoz et al., 2014). Sub-Chandrasekhar WD mergers have been linked to a new class of fast, faint transients with low ejected mass and unusual nucleosynthetic signatures (Bildsten 2007, Shen 2010), like SN2002bj (Poznanski 2009) and SN2005E (Perets 2010) or even possibly normal SN Ia (Kerkwijk 2010, Sim 2010). Although several binary WD systems have been discovered in the last years (e.g., Gianninas et al., 2015), the vast majority of the known pre-mergers have low mass He WD primaries, and combined masses well below \(M_{\rm Ch}\). Additionally, current empirical constraints on the merger rate are highly uncertain due to the very small number of known short period systems (Brown 2016).

Basic Idea

Compact binary WDs have large orbital velocities, with \(v_{\rm orb}\simeq 500\,{\rm km\,s}^{-1}(P_{\rm orb}/15\,{\rm min})^{-1/3}\) for an equal-mass \(0.6\,M_{\odot}\) WD binary. Such binaries should exhibit large radial velocities (RVs) that can be measured even in low resolution wide-field spectroscopic surveys. WD binaries with orbital periods of minutes to hours can thus be found with follow-up observations of targets with the largest RV variations.

The odds of detecting WD binaries at short orbital periods are good. If all type Ias are produced by C/O WD mergers, we expect a WD binary to merge within the Milky Way every \(\sim 10^{2}\,{\rm yr}\). The orbital decay time is \(200\,{\rm Myr}\) at an orbital period of 2 hours, therefore we estimate \(\sim 2\) million WDs with orbital periods under two hours within the galaxy. WDs at short orbital periods (under 15 minutes) may be tidally heated to surface temperatures \(T{\rm eff}\gtrsim 20,000\)K (Fuller et al., 2013), brightening them significantly and increasing the odds of detecting these systems in magnitude-limited surveys.

The SWARMS survey (Badenes et al., 2009; Mullally et al., 2009) was started in 2009 to identify pre-merging binary WDs in the large (\(\sim\)15,000 objects) database of WD spectra accumulated by the Sloan Digital Sky Survey. SWARMS uses the \(\sim\)15 minute sub-exposures to look for RV shifts (Figure 1). The typical time lag between sub-exposures (\(\sim\) half an hour to a few hours) is comparable to the orbital periods of pre-merging WDs, and the expected RV shifts (\(\gtrsim\) 100 km s\({}^{−1}\)) can be easily detected at the spectral resolution of SDSS, putting SWARMS in a good position to identify most of the pre-merging systems in this data base (see Badenes et al. 2009 for details). Unfortunately, followup of the SWARMS survey did not provide data of sufficient quality to measure RV curves, mainly due to bad weather and an aging spectrograph on the KPNO 4m. The time is ripe to revisit this program, especially given the large increase in spectroscopic white-dwarf samples.

Methods and Goals:

Our aim is to mine these samples to find and follow-up on candidate short-period WD binaries, ultimately deriving RV curves, component masses, periods, separations, and estimates of merger times. We will make use of multi spectroscopy available for many systems (better for systems with periods longer than typical exposure times, e.g., \(\sim\)15 minutes) to identify candidates with large RV variations. Additionally, single-epoch systems with very large RVs (\(\gtrsim 300\,{\rm km}\,{\rm s}^{-1}\)) are also indicative of binaries because it exceeds galactic orbital velocities. Very short period systems (\(P\lesssim 30\)) minutes will have significant orbital motion within the exposure time of the spectra which will broaden absorption lines. However, the RV shift can still be hundreds of \({\rm km}\,{\rm s}^{-1}\), which is still easily detectable.

The SWARMS sample was based on 19,000 spectroscopically confirmed WDs from SDSS DR7. New datasets have grown to include 14,000 new WDs with spectra from SDSS III BOSS observations in DR10 and DR12 (Kepler 2014, Kepler 2015) and several thousand new WDs from LAMOST (Zhao 2012, Cui 2012). SWARMS identified \(\sim 15\) good candidates, and we expect to more than double this sample with new data. Including systems with only single good epochs will increase the list further, and we expect to have dozens of candidates viable for follow-up observations.

Systems with the highest RV shifts, smallest uncertainties, and multiple epochs with RV shifts will represent our highest priority targets. Additionally, we plan to cross-reference our sample with those with GAIA distances and proper motions as they become available. Systems with large galactocentric velocities are good candidates for containing neutron star/black hole companions due to supernova kicks, and will be prioritized for follow-up.

After ranking the best candidates through these methods, we will utilize spectroscopic follow-up resources on large telescopes (Keck with PI Fuller’s preferred access, SALT with co-I Jha’s preferred access, and potentially Gemini through competitive US NOAO time). We will begin our reconnaissance with two short-exposure spectra to measure RV variations and confirm binarity, and then derive full radial-velocity curves for the confirmed systems.

Our work will contribute significantly to the known sample of massive pre-merging binary WDs, and will be a key ingredient in any updated calculation of the WD merger rate (Badenes 2012).

\label{fig:rvshift}Radial velocity shifts of absorption lines in spectra of SDSS J0926+5718, showing clear variations of \(\sim 500\,{\rm km}\,{\rm s}^{-1}\).

White dwarfs at short orbital periods may be tidally heated to surface temperatures \(T{\rm eff}\gtrsim 20,000\)K (Fuller et al., 2013), brightening them significantly and increasing the odds of detecting these systems in magnitude-limited surveys.

Phased radial velocity curve of the 12 minute binary WD SDSS J0651+2844 (Hermes et al., 2012).

Known compact WD binary systems from (Gianninas 2015).


  1. Carles Badenes, Fergal Mullally, Susan E. Thompson, Robert H. Lupton. FIRST RESULTS FROM THE SWARMS SURVEY. SDSS 1257\(\mathplus\)5428: A NEARBY MASSIVE WHITE DWARF BINARY WITH A LIKELY NEUTRON STAR OR BLACK HOLE COMPANION. The Astrophysical Journal 707, 971–978 IOP Publishing, 2009. Link

  2. Carles Badenes, Dan Maoz. THE MERGER RATE OF BINARY WHITE DWARFS IN THE GALACTIC DISK. The Astrophysical Journal 749, L11 IOP Publishing, 2012. Link

  3. Lars Bildsten, Ken J. Shen, Nevin N. Weinberg, Gijs Nelemans. Faint Thermonuclear Supernovae from AM Canum Venaticorum Binaries. The Astrophysical Journal 662, L95–L98 IOP Publishing, 2007. Link

  4. Warren R. Brown, Mukremin Kilic, Scott J. Kenyon, A. Gianninas. MOST DOUBLE DEGENERATE LOW-MASS WHITE DWARF BINARIES MERGE. ApJ 824, 46 American Astronomical Society, 2016. Link

  5. Xiang-Qun Cui, Yong-Heng Zhao, Yao-Quan Chu, Guo-Ping Li, Qi Li, Li-Ping Zhang, Hong-Jun Su, Zheng-Qiu Yao, Ya-Nan Wang, Xiao-Zheng Xing, Xin-Nan Li, Yong-Tian Zhu, Gang Wang, Bo-Zhong Gu, A-Li Luo, Xin-Qi Xu, Zhen-Chao Zhang, Gen-Rong Liu, Hao-Tong Zhang, De-Hua Yang, Shu-Yun Cao, Hai-Yuan Chen, Jian-Jun Chen, Kun-Xin Chen, Ying Chen, Jia-Ru Chu, Lei Feng, Xue-Fei Gong, Yong-Hui Hou, Hong-Zhuan Hu, Ning-Sheng Hu, Zhong-Wen Hu, Lei Jia, Fang-Hua Jiang, Xiang Jiang, Zi-Bo Jiang, Ge Jin, Ai-Hua Li, Yan Li, Ye-Ping Li, Guan-Qun Liu, Zhi-Gang Liu, Wen-Zhi Lu, Yin-Dun Mao, Li Men, Yong-Jun Qi, Zhao-Xiang Qi, Huo-Ming Shi, Zheng-Hong Tang, Qing-Sheng Tao, Da-Qi Wang, Dan Wang, Guo-Min Wang, Hai Wang, Jia-Ning Wang, Jian Wang, Jian-Ling Wang, Jian-Ping Wang, Lei Wang, Shu-Qing Wang, You Wang, Yue-Fei Wang, Ling-Zhe Xu, Yan Xu, Shi-Hai Yang, Yong Yu, Hui Yuan, Xiang-Yan Yuan, Chao Zhai, Jing Zhang, Yan-Xia Zhang, Yong Zhang, Ming Zhao, Fang Zhou, Guo-Hua Zhou, Jie Zhu, Si-Cheng Zou. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Research in Astronomy and Astrophysics 12, 1197–1242 IOP Publishing, 2012. Link

  6. J. Fuller, D. Lai. Dynamical tides in compact white dwarf binaries: helium core white dwarfs tidal heating and observational signatures. Monthly Notices of the Royal Astronomical Society 430, 274–287 Oxford University Press (OUP), 2013. Link

  7. A. Gianninas, Mukremin Kilic, Warren R. Brown, Paul Canton, Scott J. Kenyon. THE ELM SURVEY. VI. ELEVEN NEW DOUBLE DEGENERATES. ApJ 812, 167 IOP Publishing, 2015. Link

  8. J. J. Hermes, Mukremin Kilic, Warren R. Brown, D. E. Winget, Carlos Allende Prieto, A. Gianninas, Anjum S. Mukadam, Antonio Cabrera-Lavers, Scott J. Kenyon. RAPID ORBITAL DECAY IN THE 12.75-MINUTE BINARY WHITE DWARF J0651\(\mathplus\)2844. The Astrophysical Journal 757, L21 IOP Publishing, 2012. Link

  9. I. Jr. Iben, A. V. Tutukov. Supernovae of type I as end products of the evolution of binaries with components of moderate initial mass (M not greater than about 9 solar masses). The Astrophysical Journal Supplement Series 54, 335 IOP Publishing, 1984. Link

  10. S. O. Kepler, I. Pelisoli, D. Koester, G. Ourique, S. J. Kleinman, A. D. Romero, A. Nitta, D. J. Eisenstein, J. E. S. Costa, B. Kulebi, S. Jordan, P. Dufour, P. Giommi, A. Rebassa-Mansergas. New white dwarf stars in the Sloan Digital Sky Survey Data Release 10. Monthly Notices of the Royal Astronomical Society 446, 4078–4087 Oxford University Press (OUP), 2014. Link

  11. S. O. Kepler, I. Pelisoli, D. Koester, G. Ourique, A. D. Romero, N. Reindl, S. J. Kleinman, D. J. Eisenstein, A. D. M. Valois, L. A. Amaral. New white dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 12. Mon. Not. R. Astron. Soc. 455, 3413–3423 Oxford University Press (OUP), 2015. Link

  12. Marten H. van Kerkwijk, Philip Chang, Stephen Justham. SUB-CHANDRASEKHAR WHITE DWARF MERGERS AS THE PROGENITORS OF TYPE Ia SUPERNOVAE. The Astrophysical Journal 722, L157–L161 IOP Publishing, 2010. Link

  13. Dan Maoz, Filippo Mannucci, Gijs Nelemans. Observational Clues to the Progenitors of Type Ia Supernovae. Annual Review of Astronomy and Astrophysics 52, 107–170 Annual Reviews, 2014. Link

  14. F. Mullally, Carles Badenes, Susan E. Thompson, Robert Lupton. TWINS: THE TWO SHORTEST PERIOD NON-INTERACTING DOUBLE DEGENERATE WHITE DWARF STARS. The Astrophysical Journal 707, L51–L55 IOP Publishing, 2009. Link

  15. H. B. Perets, A. Gal-Yam, P. A. Mazzali, D. Arnett, D. Kagan, A. V. Filippenko, W. Li, I. Arcavi, S. B. Cenko, D. B. Fox, D. C. Leonard, D.-S. Moon, D. J. Sand, A. M. Soderberg, J. P. Anderson, P. A. James, R. J. Foley, M. Ganeshalingam, E. O. Ofek, L. Bildsten, G. Nelemans, K. J. Shen, N. N. Weinberg, B. D. Metzger, A. L. Piro, E. Quataert, M. Kiewe, D. Poznanski. A faint type of supernova from a white dwarf with a helium-rich companion. Nature 465, 322–325 Springer Nature, 2010. Link

  16. D. Poznanski, R. Chornock, P. E. Nugent, J. S. Bloom, A. V. Filippenko, M. Ganeshalingam, D. C. Leonard, W. Li, R. C. Thomas. An Unusually Fast-Evolving Supernova. Science 327, 58–60 American Association for the Advancement of Science (AAAS), 2009. Link

  17. Hideyuki Saio, Kenichi Nomoto. Inward Propagation of Nuclear-burning Shells in Merging C-O and He White Dwarfs. The Astrophysical Journal 500, 388–397 IOP Publishing, 1998. Link

  18. Josiah Schwab, Eliot Quataert, Daniel Kasen. The evolution and fate of super-Chandrasekhar mass white dwarf merger remnants. Monthly Notices of the Royal Astronomical Society 463, 3461–3475 Oxford University Press (OUP), 2016. Link

  19. Ken J. Shen, Dan Kasen, Nevin N. Weinberg, Lars Bildsten, Evan Scannapieco. THERMONUCLEAR .Ia SUPERNOVAE FROM HELIUM SHELL DETONATIONS: EXPLOSION MODELS AND OBSERVABLES. The Astrophysical Journal 715, 767–774 IOP Publishing, 2010. Link

  20. S. A. Sim, F. K. Röpke, W. Hillebrandt, M. Kromer, R. Pakmor, M. Fink, A. J. Ruiter, I. R. Seitenzahl. DETONATIONS IN SUB-CHANDRASEKHAR-MASS C+O WHITE DWARFS. The Astrophysical Journal 714, L52–L57 IOP Publishing, 2010. Link

  21. R. F. Webbink. Double white dwarfs as progenitors of R Coronae Borealis stars and Type I supernovae. The Astrophysical Journal 277, 355 IOP Publishing, 1984. Link

  22. Gang Zhao, Yong-Heng Zhao, Yao-Quan Chu, Yi-Peng Jing, Li-Cai Deng. LAMOST spectral survey An overview. Research in Astronomy and Astrophysics 12, 723–734 IOP Publishing, 2012. Link

[Someone else is editing this]

You are editing this file