Transcript Document 7707414

Spectroscopic Binaries in
Planetary Nebulae
Howard E. Bond
Space Telescope Science Institute
2005 June 29
Planetary Nebulae as Astronomical Tools
Three Arguments that Many PNe
are Ejected from Binary Stars
1. Large majority of PNe have highly nonspherical or bipolar shapes
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Simplest explanation: PN ejection through
common-envelope (CE) interactions,
or at least the ejection process is strongly
influenced by companions (tidal spin-up,
dynamo generation of magnetic field)
Three Arguments…
2. An observed high incidence of very close
binary PNNi
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Photometric monitoring shows that ~10% of
PNNi are binaries with periods of a few hours
to a few days (Bond & Grauer 1980’s; Bond
& Livio 1990; Bond 2000)
These close systems must have emerged from
common-envelope interactions
Common-envelope Interactions
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Occur in binaries initially wide enough for
one component to become RG or AGB star
before interacting with MS companion
Companion is engulfed, spirals in, and may
eject the envelope, leaving a much closer
binary: MS star + hot core.
Hot core can ionize ejected envelope,
producing a PN around the close binary
Common-envelope Interactions
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Final orbital period depends on efficiency
with which orbital energy goes into ejecting
material from the system…
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…denoted CE
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High CE results in long final period
Low CE results in short period, or merger
More discussion will be in following talk
(De Marco)
Three Arguments…
3. The 10% of very close pairs may just be
the short-period tail of a much larger
fraction of binary PNNi
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Population-synthesis studies suggest this is
true for a wide range of CE values
e.g., Yungelson et al. (1993), next slide
Yungelson et al. (1993) Population Synthesis
Predicted orbital period distribution of binary PNNi
Yungelson et al. (1993) Population Synthesis
Predicted orbital period distribution of binary PNNi
Post-CE systems
Yungelson et al. (1993) Population Synthesis
Predicted orbital period distribution of binary PNNi
Gap due to binaries
moving to shorter P
Post-CE systems
Yungelson et al. (1993) Population Synthesis
Predicted orbital period distribution of binary PNNi
Gap due to binaries
moving to shorter P
Post-CE systems
Wide binaries that never interact
Yungelson et al. (1993) Population Synthesis
Predicted orbital period distribution of binary PNNi
Gap due to binaries
moving to shorter P
Post-CE systems
Wide binaries that never interact
A digression on the next slide
A digression…
• Ciardullo, Bond, et al. (1999 AJ 118, 488)
carried out an HST “snapshot” survey for the
expected population of visual binaries in PNe
• We found 10 likely and 6 possible resolved
binaries, out of 113 examined.
HST WFPC2 images
These wide companions are useful for deriving distances to the
PNe (MS fitting), but are unlikely to affect PN ejection
Outcome of CE interaction
depends on CE
High CE  long periods
Low CE  short periods & mergers
Yungelson et al. 1993
…but only short-period systems
can be found photometrically
Systems that can be found photometrically
The photometric
search method
depends on
heating effects in
close binaries,
so…
Artist: Dana Berry
…the shortperiod systems
could just be the
tip of an iceberg
of longer-period
binaries…
…the shortperiod systems
could just be the
tip of an iceberg
of longer-period
binaries…
Short periods
LONG
PERIODS
…and if so, the total fraction of
binary central stars is very high,
and PNe are fundamentally a
binary-star phenomenon!
Testing the “iceberg” hypothesis
• Requires radial-velocity (RV)
measurements, in order to find wider
binaries that lack heating effects
• Results to be reported here—
– De Marco, Bond, Harmer, & Fleming: WIYN
3.5m telescope at Kitt Peak
– Afsar & Bond: SMARTS 1.5m telescope at
Cerro Tololo
WIYN 3.5-m Program
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Hydra spectrograph, 2002-04.
Dispersion 0.33 A/pix; resolution ~7500
RV precision ~3-3.7 km/s
Scheduling optimized for periods of days to
months
• Results of 2002-03 observations were
reported by De Marco, Bond, Harmer, &
Fleming (ApJ 602,L93,2004)
RV variations are often unequivocal:
RV = 33 km/s in 21 days
RV = 27 km/s in 21 days
WIYN result: 10 out of 11 PNNi
have variable RVs! Probability RV
is variable
SMARTS 1.5-m Program
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Cassegrain spectrograph, 2003-04.
Dispersion 0.77 A/pix; resolution ~2000
RV precision ~10 km/s
Scheduling (as with WIYN) optimized for
periods of days to months
• Part of PhD thesis of Melike Afsar, Ege
University (Turkey) & STScI
SMARTS: again many RV variables
P > 0.99
SMARTS: again many RV variables
Found var. in
WIYN pgm.
RV survey results
• WIYN (~3.5 km/s): 10 out of 11 PNNi
variable
• SMARTS ( ~10 km/s): 7 out of 19
• Sorensen & Pollacco (Asymm PNe III,
2003) ( ~5 km/s?) found 13 out of 33
PNNi have variable RV’s (incl. NGC 6891,
also found by WIYN & SMARTS)
Caveats
• Measurements are difficult in some PNNi
due to few suitable absorption lines (free of
nebular contamination, etc) and low RV
amplitudes
• Wind variations could produce line-profile
variations that mimic RV variability
– But we tried to select against PNNi with strong
UV P Cygni profiles
Searching for periods
• Finding orbital periods would strengthen
the case for binarity, but we have not been
able to fit a binary period to any of our
objects…
…with one possible exception
f(m) = 0.006, implying m2>0.13Msun if m1=0.6Msun
Searching for periods
• Finding orbital periods would strengthen
the case for binarity, but we have not been
able to fit a binary period to any of our
objects…with the possible exception of IC
4593…
• But our observations cover 2-3 years
sparsely, which is highly non-optimum for
finding periods that now appear to be short
(few days)
What next?
• We need an intensive campaign on a few objects
with a large telescope, high resolution, and high
S/N…
• …in order to distinguish between binary orbital
motion and wind-profile variations
• Bond & De Marco had successful 5-night run in
May 2005 with Kitt Peak 4m echelle spectrograph.
– Concentrated on IC 4593, BD+33 2642, LS IV-12 111,
NGC 6210
• Stay tuned for results!
Other implications of binaries in
PNe
• May explain existence of PNe in globular
clusters
– Post-AGB remnants of low-mass stars evolve
too slowly to produce ionized PNe
– But binaries can merge or transfer matter before
the PN stage, producing higher-mass remnants
• PNe at the bright end of the PNLF may be
descended from binaries (Ciardullo poster)
The PN in M15 (HST)
Other implications of binaries in
PNe, contd.
• Most of the classes of compact binaries are
probably descended from binary PNNi via
common envelopes:
– Pre-cataclysmic red-dwarf/white-dwarf binaries
like V471 Tau
– Cataclysmic variables
– Low-mass X-ray binaries
– SN Ia progenitors
Other implications of binaries in
PNe, contd.
• Knowing the overall orbital period
distribution of PNNi would help constrain
the typical value of CE, which is needed in
population-synthesis calculations.
Summary
• ~10% of PNNi are very short-period
binaries (hours to a few days) that must
have been ejected from CE interactions
• Resolved visual binary PNNi occur about as
often as expected
• RV observations are now suggesting that a
large population of spectroscopic binaries
exists among PNNi, making the total binary
fraction very high
Summary contd.
• However, additional spectroscopic
observations with large telescopes are
needed to verify the suspected high
spectroscopic binary fraction
• At present, it appears very plausible that
binary-star ejection is a major
formation channel for planetary
nebulae
Thanks to collaborators!
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Orsola De Marco
Di Harmer
Andrew Fleming
Melike Afsar
Robin Ciardullo
Al Grauer
Telescope operators, funding agencies,
SMARTS Consortium, STScI DDRF!
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