I am an astrophysics Ph.D. student working under the supervision of Prof. Dan Maoz in the Astrophysics Department of Tel-Aviv University. During my Ph.D. I spent a couple of years with an ESO Studentship at the European Southern Observatory in Garching. Before that I got an M.Sc. (working with Prof. Lev Vaidman) and a B.Sc. in physics from Tel-Aviv University, and a B.A. in history from The Open University of Israel. I am also one of the organizers of the TAU AstroClub, a public outreach organization.
My main research interest is white dwarfs (WDs) and their immediate surroundings, which basically means that I am looking for stuff around WDs. The fact that more than 97% of all stars, our Sun included, end their lives as WDs, makes them an interesting research subject. The immediate surroundings of WDs are key to our understanding of a number of puzzles. Observations of WDs can reveal the presence of stellar, substellar, and stellar-remnant companions, planets, dust, atmospheric heavy elements, and planetary debris, each of relevance to several important questions. In my research I acquire and analyze new observational data, as well as publicly available archival data, in order to provide clues and maybe even answers to some of these questions. Scroll down to read about some of the things we have found.
Binary systems consisting of two WDs are important in a broad range of astrophysical contexts, from stellar evolution, through Type-Ia supernova (SN Ia) progenitors, to sources of gravitational waves. SNe Ia – supernova explosions of WDs – are a major source of heavy elements, and, as ‘standard candles’, they have provided one of the fundamental methods for estimating distances in the Universe. However, the nature of the progenitor systems of SNe Ia is still unclear. A progenitor scenario that has been long considered is the double-degenerate scenario, in which a double WD binary loses energy and angular momentum to gravitational waves, until merger and possible explosion as a SN Ia. If most SN Ia explosions are the result of double WD mergers, then the observed double WD merger rate should be high enough to account for the observed SN Ia rate. This motivates us to ask: are there enough double WDs to explain the observed SN Ia rate?
- Ferdinando Patat and Na'ama Hallakoun “Type Ia supernovae: where are they coming from and where will they lead us?" To appear in "The Impact of Binaries on Stellar Evolution", Beccari G. & Boffin H.M.J. (Eds.), 2018
From a sample of spectra of 439 WDs from the ESO-VLT Supernova-Ia Progenitor Survey (SPY), we measured the maximal changes in radial velocity (ΔRVmax) between epochs, and model the observed ΔRVmax statistics via Monte Carlo simulations, to constrain the population characteristics of double WDs. We then combined these constraints with those obtained by Badenes and Maoz 2012 for a sample of ~4000 WDs from the Sloan Digital Sky Survey (SDSS). We found that about 10% of WDs are double WDs with separations up to 4 AU, and that the Galactic WD merger rate per WD is about 10-11 per year. Integrated over the Galaxy lifetime, this implies that 8.5–11% of all WDs ever formed have merged with another WD. If most double WD mergers end as more-massive WDs, then some 10% of WDs are double WD-merger products, consistent with the observed fraction of WDs in a ‘high-mass bump’ in the WD mass function. The double WD merger rate is 4.5–7 times the Milky Way’s specific SN Ia rate. If most SN Ia explosions stem from the mergers of some double WDs (say, those with massive-enough binary components) then ∼15% of all WD mergers must lead to a SN Ia.
- Dan Maoz, Na'ama Hallakoun, and Carles Badenes “The separation distribution and merger rate of double white dwarfs: improved constraints" Monthly Notices of the Royal Astronomical Society, 476(2): 2584–2590, 2018
- Dan Maoz and Na'ama Hallakoun “The binary fraction, separation distribution, and merger rate of white dwarfs from SPY" Monthly Notices of the Royal Astronomical Society, 467(2): 1414–1425, 2017
- N. Hallakoun, D. Maoz, M. Kilic, T. Mazeh, A. Gianninas, E. Agol, K. J. Bell, S. Bloemen, W. R. Brown, J. Debes, S. Faigler, I. Kull, T. Kupfer, A. Loeb, B. M. Morris, and F. Mullally “SDSS J1152+0248: an eclipsing double white dwarf from the Kepler K2 campaign" Monthly Notices of the Royal Astronomical Society, 458(1): 845–854, 2016
The remains of the pre-WD-phase solar systems are revealed in the form of heavy element ‘pollution’ in WD atmospheres, excess emission from dust discs, and – only recently – in transits of planetary debris. In principle, WDs can host not only debris, but also whole planetary systems.
The first transiting planetesimal orbiting a WD was detected in
- N. Hallakoun, S. Xu, D. Maoz, T. R. Marsh, V. D. Ivanov, V. S. Dhillon, M. C. P. Bours, S. G. Parsons, P. Kerry, S. Sharma, K. Su, S. Rengaswamy, P. Pravec, P. Kušnirák, H. Kučáková, J. D. Armstrong, C. Arnold, N. Gerard, and L. Vanzi “Once in a blue moon: detection of ‘bluing’ during debris transits in the white dwarf WD 1145+017" Monthly Notices of the Royal Astronomical Society, 469(3): 3213–3224, 2017
- Na'ama Hallakoun, Dan Maoz, Eric Agol, Warren R. Brown, Patrick Dufour, Jay Farihi, Boris T. Gänsicke, Mukremin Kilic, Alekzander Kosakowski, Abraham Loeb, Tsevi Mazeh, and Fergal Mullally “Periodic optical variability and debris accretion in white dwarfs: a test for a causal connection" Monthly Notices of the Royal Astronomical Society, 476(1): 933–942, 2018
I am one of the organizers of the Tel-Aviv University Astronomy Club (AstroClub for short) — a public outreach organization, operated voluntarily by graduate students of the Department of Astrophysics of Tel-Aviv University. The activities are open to the general public, and include monthly lectures given by leading scientists, sidewalk observations, and open days at the Wise Observatory. I have also paticipated in the Hebrew translations of Galaxy Zoo and the Astronomy Picture of the Day.
ACP Scheduler is a commercial tool used to automatically schedule and execute observing plans for telescopes at the Wise Observatory. The observing plans can be entered manually using the Scheduler's GUI, or imported from Remote Telescope Markup Language (RTML) files. ScheduleRTML is a small python script that I wrote, to facilitate the writing of these RTML plans. It is available through GitHub.
My first name (Na'ama) has three syllables, the stress should be on the last one: "nah-ah-MAH". To pronounce my last name (Hallakoun) ignore the spelling and just say "hal-KON", this is what I do.