The SWARMS Survey: The SWARMS Survey: Unveiling the Galactic Unveiling the Galactic population of Compact White Dwarf Binariespopulation of Compact White Dwarf Binaries
Carles Badenes
Weizmann Institute of Science /Tel-Aviv University Steve Bickerton (Princeton)
Fergal Mullally, Susan Thompson (NASA/Ames) Mukremin Kilic (CfA), Tom Matheson (NOAO)
Dan Maoz (TAU)Type Ia SN Progenitors WorkshopLeiden, September 22 2010
DD SN Ia ProgenitorsDD SN Ia Progenitors Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● The merging of binary WDs due to gravitational wave emission was suggested as SN Ia progenitor scenario in the 1980s [Webbink 84 ApJ 277, 355; Iben & Tutukov 84 ApJS 54, 335].
● The only scenario that naturally explains the lack of H in SN Ia spectra.
● Can produce both short and long delay times [Yungelson & Livio 99, ApJ 528, 108].
● Caveat: it is unclear whether WD mergers lead to SN Ia explosions or end in accretion induced collapse [Saio & Nomoto 85 A&A 150, 21] ignition if dM/dt>M⇒ crit (~10-5 M
⊙yr-1). Depends on the final accretion
phase multi-D simulations ⇒ [Rosswog talk].
● Might not need M1+M2=MCh [van Kerkwijk et
al. 10, arXiv:1006.4391].
K. ThorneT. Carnahan
Loren-Aguilar et al. 09 A&A 500, 1193
Where are the DD SN Ia Progenitors?Where are the DD SN Ia Progenitors? Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● [Nelemans talk]: Theoretical uncertainties are large. Observations are crucial.
● Are there enough WD+WD systems with M1+M2 > MCh & tMerge < tHubble ?
● Not a single such system is known (a few claims have been disproved).
● SPY Survey [Napiwotzki et al. 01 AN 322, 411]: ~1000 known WDs with B<16.5 using ESO VLT.
● SPY found ~100 DD systems [Napiwotzki et al. 04 ASP Conf. Ser. 318, 402], masses and periods only published for 26 systems [Nelemans et al. 05 A&A 440, 1087]. Of these, only 5 pre-mergers.
● Now we can do better...
The SWARMS SurveyThe SWARMS Survey Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
SN 1994D inNGC 4526 (P. Challis)
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● Strategy: Use the multiple exposures (≥3, ~15 min each) taken for all the spectra in the Sloan Digital Sky Survey (SDSS) to look for radial velocity (RV) shifts in White Dwarfs ⇒ ~15,000 WDs in the SDSS DR7 catalog [Eisenstein et al. 06, ApJS 167, 40 (E06); Kleinman et al. 10 in prep.] .● Goals:
● Find the double degenerate WD (DDWD) progenitors of Type Ia SNe (WD binaries with MA+MB≥MCh and tMerge<tHubble )
● Characterize the population of (pre-merging) compact white dwarf binaries in the Galaxy ⇒ binary fraction, mass ratio distribution, separation distribution... merger rates.
● First results: Badenes et al. 09, ApJ 707, 971; Mullally et al. 09, ApJL 707, L51.
S W A R M SS W A R M SSSloan loan WWhite dwhite dwAArf rf RRadial velocity data adial velocity data MMining ining SSurveyurvey
Time Resolved Spectroscopy in SDSSTime Resolved Spectroscopy in SDSS Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● SDSS was not designed to do time-resolved spectroscopy; this is a data mining project.
● Among the DR4 WDs, ~50% have 3 exposures and ~20% have 4.
● The maximum timescale that can be probed is below 6 hr in ~70% of the objects, but can go to weeks or longer in ~10% of the objects.
● Expected RV shifts are large (~100 km s-1) and can be measured using SDSS.
● Excellent training and complement for present and forthcoming synoptic surveys (PTF, PanSTARRS, LSST).
Pre-merging DDWDs
SDSS 1257+5428: DiscoverySDSS 1257+5428: Discovery Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● Classified as DA by E06; Mg=16.8.
● RV shift of ~8 Å (~490 km s-1) between exposures 0, 1 (taken 10/03/2003) and 2 (taken 10/04).
SDSS 1257+5428: Tight and MassiveSDSS 1257+5428: Tight and Massive Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● Follow-up observations: APO ARC 3.5m telescope on 02/2009.
● RV curve is well fit by a circular orbit with P=4.5550±0.0007 hr; KA=322.7±6.3 km s-1.
● System must be tight and/or have massive components.
SDSS 1257+5428: What is it?SDSS 1257+5428: What is it? Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● We can make a conservative mass estimate from high-order Balmer lines:
MMAA=0.92=0.92±±0.32 M0.32 M⊙⊙
● Together with the orbital parameters, this yields:
MMBBsin(i)=1.62sin(i)=1.62±±0.25 M0.25 M⊙⊙
● The companion is too massive to be another WD ⇒ probably a neutron star or black hole. At 29 ≤ D ≤ 58 pc, closest stellar remnant of a SN explosion.
● tCool=2.0±1.0 Gyr ⇒ old system!
● A WD companion cannot be discarded by the data.
SDSS 1257+5428: WD+WD Binary!SDSS 1257+5428: WD+WD Binary! Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● Companion is a WD [Marsh et al. 10 arXiv:1002.4677] ⇒ 120 spectra (followed since 2008).● Cold, low-mass WD (line cores) + Hot, rotating high mass WD (line wings) ⇒ no double core!● Effect is subtle, spectral 'disentangling' is very challenging.
Marsh et al. 10, arXiv:1002.4677
Marsh et al. 10, arXiv:1002.4677
SDSS 1257+5428: ... of some kindSDSS 1257+5428: ... of some kind Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● Will the system lead to a Type Ia explosion? Probably not (mass ratio is too low) ⇒ 5 HST orbits in Cycle 18.
● Rotation (~1 rpm) implies accretion!!
● Keck spectra [Kulkarni & van Kerkwijk 10, ApJ 719, 1123] Magnetic WD?⇒
Marsh et al. 10, arXiv:1002.4677
Kulkarni & van Kerkwijk 10, ApJ 719, 1123
SDSS 1436+5010SDSS 1436+5010 Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● Classified as DA by E06; Mg=18.2.
● RV shifts can be detected between consecutive SDSS exposures!
SDSS 1053+5200SDSS 1053+5200 Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● Classified as DA by E06; Mg=18.9.
● Cross-correlation works well for noisy spectra.
The Two Shortest Period DDWDsThe Two Shortest Period DDWDs Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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SDSS 1436+5010 SDSS 1053+5200
● SDSS 1436+5010 and 1053+5200 are the two detached DDWDs with the shortest periods known (1.15 and 0.96 hr). Their potential binarity had ben noted previously from their low masses (~0.19 M
⊙) [Kilic et al. 07, ApJ 660, 1451].
● Mullally et al. 09 ApJ 707, L51; Kilic et al. 10, ApJ 716, 122.
SWARMS vs SPYSWARMS vs SPY Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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SPY SWARMSLocation S (Paranal, Chile) N (APO, NM)Nobjects ~1,000 ~15,000 (DR7)
Resolution 18,500 (~2 km s-1) 1,800 (~120 km s-1 w/cc)Limiting mag. B≤16.5 g≲19Best suited for Systematic study of
DDWDsFinding pre-mergers and
SN Ia progenitors
● SWARMS complements and improves on the SPY survey [Napiwotzki et al. 01, Ast. Nach. 322, 411]. No control over original observations ⇒ luck is involved and completeness is hard to establish.
● Follow-up observations of individual candidates continue (4 nights on Kitt Peak 4m telescope in October).
● We anticipate more exciting discoveries, so stay tuned!
The SWARMS Treasure Chest: DDWDThe SWARMS Treasure Chest: DDWD Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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The SWARMS Treasure Chest: DAH+MThe SWARMS Treasure Chest: DAH+M Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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The SWARMS Treasure Chest: DA+MThe SWARMS Treasure Chest: DA+M Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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Characterizing the DDWD PopulationCharacterizing the DDWD Population Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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PRELIMINARY
K. ThorneT. Carnahan
● Beyond the identification of specific SN Ia progenitor candidates, SWARMS can be used to statistically characterize the DDWD population in the Milky Way.
● Distribution of RV shifts in the ~15,000 WDs ⇔ Monte Carlo simulations of DDWDs with different period and mass ratio distributions (see also [Maxted & Marsh 99, MNRAS 307, 122]).
● Selection effects and observational biases have to be dealt with carefully.
● End result: rate of WD mergers as a function of mass.
Not binaries Confirmed binaries
ConclusionsConclusions Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● SWARMS is well placed to find MCh DD SN Ia progenitors (if they exist) in particular, and pre-merger WD binaries in general. Multi-year project, fun for all the family.
● SDSS 1257+5428 is definitely an interesting DD WD, but its nature (and final fate) have not been fully established yet.
● SDSS 1436+5010 and SDSS 1053+5200 are the two detached DDWDs with the shortest periods known.
● Individual system follow-up will continue.
● Great prospects to statistically characterize the DDWD populationin the disk of the Milky Way.
● Stay tuned for more developments!
The Future: Spectral Variability in SDSSThe Future: Spectral Variability in SDSS Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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● The techniques developed for SWARMS have a wider applicability ⇒ time resolved spectroscopy with the largest spectroscopic data base!● Probe temporal scales between a few hours and a few months: chromospheric M-dwarf variability, sdB binaries, close binaries across all spectral types, quasar variability...
● Excellent training for future missions and surveys like Gaia (RVS) or LSST: data mining techniques, spectral characterization of transients, etc.
Largest data base for time Largest data base for time resolved spectroscopyresolved spectroscopy
SDSS Variability: CV?SDSS Variability: CV? Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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SDSS Variability: Diverse stuffSDSS Variability: Diverse stuff Carles BadenesCarles BadenesLeiden 09/22/10Leiden 09/22/10
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Hα (at z=0.18)
Hα (at z=0.18)
