J/A+A/682/A169 Contact tracing of binary stars (Henneco+, 2024)
Contact tracing of binary stars: Pathways to stellar mergers.
Henneco J., Schneider F.R.N., Laplace E.
<Astron. Astrophys. 682, A169 (2024)>
=2024A&A...682A.169H 2024A&A...682A.169H (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Models ; Stars, masses ; Stars, ages
Keywords: methods: numerical - binaries: general - stars: evolution -
stars: low-mass - stars: massive
Abstract:
Stellar mergers are responsible for a wide variety of phenomena such
as rejuvenated blue stragglers, highly magnetised stars, spectacular
transients, iconic nebulae, and stars with peculiar surface chemical
abundances and rotation rates. Before stars merge, they enter a
contact phase. Here, we investigate which initial binary-star
configurations lead to contact and classical common-envelope (CE)
phases and assess the likelihood of a subsequent merger. To this end,
we computed a grid of about 6000 detailed one-dimensional binary
evolution models with initial component masses of 0.5-20.0M☉ at
solar metallicity. Both components were evolved, and rotation and
tides were taken into account. We identified five mechanisms that lead
to contact and mergers: runaway mass transfer, mass loss through the
outer Lagrange point L2, expansion of the accretor, orbital decay
because of tides, and non-conservative mass transfer. At least 40
percent of mass-transferring binaries with initial primary-star masses
of 5-20M☉ evolve into a contact phase; >12 percent and >19
percent likely merge and evolve into a CE phase, respectively. Because
of the non-conservative mass transfer in our models, classical CE
evolution from late Case-B and Case-C binaries is only found for
initial mass ratios qi<0.15-0.35. For larger mass ratios, we find
stable mass transfer. In early Case-B binaries, contact occurs for
initial mass ratios qi<0.15-0.35, while in Case-A mass transfer,
this is the case for all q_i in binaries with the initially closest
orbits and qi<0.35 for initially wider binaries. Our models predict
that most Case-A binaries with mass ratios of q<0.5 upon contact
mainly get into contact because of runaway mass transfer and accretor
expansion on a thermal timescale, with subsequent L2-overflow in more
than half of the cases. Thus, these binaries likely merge quickly
after establishing contact or remain in contact only for a thermal
timescale. On the contrary, Case-A contact binaries with higher mass
ratios form through accretor expansion on a nuclear timescale and can
thus give rise to long-lived contact phases before a possible merger.
Observationally, massive contact binaries are almost exclusively found
with mass ratios q>0.5, confirming our model expectations. Because of
non-conservative mass transfer with mass transfer efficiencies of
15-65 percent, 5-25 percent, and 25-50 percent in Case-A, -B, and -C
mass transfer, respectively (for primary-star masses above 3M☉),
our contact, merger, and classical CE incidence rates are conservative
lower limits. With more conservative mass transfer, these incidences
would increase. Moreover, in most binaries, the non-accreted mass
cannot be ejected, raising the question of the further evolution of
such systems. The non-accreted mass may settle into circumstellar and
circumbinary disks, but could also lead to further contact systems and
mergers. Overall, contact binaries are a frequent and fascinating
result of binary mass transfer of which the exact outcomes still
remain to be understood and explored further.
Description:
Using a grid of ∼6000 detailed binary evolution models including
rotation, tidal interactions, the evolution of both components, and
with component masses between 0.5 and 20.0M☉, we examine in
which regions of the initial binary parameter space we expect contact
phases, such as contact binaries and classical common-envelope (CE)
phases, to occur.We identify five mechanisms that lead to contact: the
expansion of the accretor, runaway mass transfer, L2-overflow, orbital
decay because of tides, and non-conservative mass transfer.
Table G.1 contains the results for all 5957 MESA models.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableg1.dat 102 5957 Contact tracing results of all 5957
binary MESA models
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Byte-by-byte Description of file: tableg1.dat
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Bytes Format Units Label Explanations
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1- 5 F5.2 Msun M1i Initial primary mass (M1_i)
7- 11 F5.2 Msun M2i Initial secondary mass (M2_i)
13- 17 F5.3 [Rsun] logai logarithm of the initial binary separation
(logai)
19- 24 F6.3 [d] logPi logarithm of the initial binary period
(logPi)
26- 30 F5.2 Msun M1f Final primary mass (M1_f)
32- 36 F5.2 Msun M2f Final secondary mass (M2_f)
38- 42 F5.3 [Rsun] logaf logarithm of the final binary separation
(logaf)
44- 49 F6.3 [d] logPf logarithm of the final binary period (logPf)
51- 56 F6.3 [yr] logAgef logarithm of the final age of the binary
system (logagef)
58 I1 --- AE [0/1] Accretor expansion (see Sect. 3.1) (AE)
60 I1 --- RMT [0/1] Runaway mass transfer (see Sect. 3.5)
(RMT)
62 I1 --- NCCE [0/1] Non-conservative mass transfer + cannot
eject (see Sect. 3.2) (NCCE)
64 I1 --- L2O [0/1] L2-overflow (see Sect. 3.3) (L2O)
66 I1 --- TDC [0/1] Tidally driven contact (see Sect. 3.4)
(TDC)
68 I1 --- NC [0/1] No contact (see Sect. 4) (NC)
70 I1 --- MTTP [0/1] Mass transfer after thermal pulse
(thermal pulses, see Sect. 4) (MTTP)
72 I1 --- NI [0/1] Numerical issues (see Sect. 4) (NI)
74- 82 A9 --- MTcases Array specifying the mass-transfer cases that
the system went through
[Case A, Case B, Case C] (mt_cases)
84- 92 A9 --- EVstage1 Final evolutionary stage of the primary
(ev_stage1) (1)
94-102 A9 --- EVstage2 Final evolutionary stage of the secondary
(ev_stage2) (1)
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Note (1): evolutionary stage as follows:
MS = before core-H exhaustion
post-MS = after core-H exhaustion and before core-He ignition
CHeB = after core-He ignition and before core-He exhaustion
post-CHeB = after core-He exhaustion
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Acknowledgements:
Jan Henneco, jan.henneco(at)protonmail.com
(End) Patricia Vannier [CDS] 01-Dec-2023