118 research outputs found
Planet formation from the ejecta of common envelopes
The close binary system NN Serpentis must have gone through a common envelope
phase before the formation of its white dwarf. During this phase, a substantial
amount of mass was lost from the envelope. The recently detected orbits of
circumbinary planets are likely inconsistent with planet formation before the
mass loss.We explore whether new planets may have formed from the ejecta of the
common envelope and derive the expected planetary mass as a function of
radius.We employed the Kashi & Soker model to estimate the amount of mass that
is retained during the ejection event and inferred the properties of the
resulting disk from the conservation of mass and angular momentum. The
resulting planetary masses were estimated from models with and without
radiative feedback. We show that the observed planetary masses can be
reproduced for appropriate model parameters. Photoheating can stabilize the
disks in the interior, potentially explaining the observed planetary orbits on
scales of a few AU. We compare the expected mass scale of planets for 11
additional systems with observational results and find hints of two
populations, one consistent with planet formation from the ejecta of common
envelopes and the other a separate population that may have formed earlier. The
formation of the observed planets from the ejecta of common envelopes seems
feasible. The model proposed here can be tested through refined observations of
additional post-common envelope systems. While it appears observationally
challenging to distinguish between the accretion on pre-existing planets and
their growth from new fragments, it may be possible to further constrain the
properties of the protoplanetary disk through additional observations of
current planetary candidates and post-common envelope binary systems.Comment: 12 pages, 8 figures, 3 tables. Accepted at A&
The quest for companions to post-common envelope binaries IV: The 2:1 mean-motion resonance of the planets orbiting NN Serpentis
We present 69 new mid-eclipse times of the young post-common envelope binary
(PCEB) NN Ser, which was previously suggested to possess two circumbinary
planets. We have interpreted the observed eclipse-time variations in terms of
the light-travel time effect caused by two planets, exhaustively covering the
multi-dimensional parameter space by fits in the two binary and ten orbital
parameters. We supplemented the fits by stability calculations for all models
with an acceptable chi-square. An island of secularly stable 2:1 resonant
solutions exists, which coincides with the global chi-square minimum. Our
best-fit stable solution yields current orbital periods P_o = 15.47 yr and P_i
= 7.65 yr and eccentricities e_o = 0.14 and e_i = 0.22 for the outer (o) and
inner (i) planets, respectively. The companions qualify as giant planets, with
masses of 7.0 M_Jup and 1.7 M_Jup for the case of orbits coplanar with that of
the binary. The two-planet model that starts from the present system parameters
has a lifetime greater than 10^8 yr, which significantly exceeds the age of NN
Ser of 10^6 yr as a PCEB. The resonance is characterized by libration of the
resonant variable Theta_1 and circulation of omega_i-omega_o, the difference
between the arguments of periapse of the two planets. No stable non-resonant
solutions were found, and the possibility of a 5:2 resonance suggested
previously by us is now excluded at the 99.3% confidence level.Comment: 8 pages, 8 figure
Spectroscopic binaries in the Solar Twin Planet Search program: from substellar-mass to M dwarf companions
Previous studies on the rotation of Sun-like stars revealed that the
rotational rates of young stars converge towards a well-defined evolution that
follows a power-law decay. It seems, however, that some binary stars do not
obey this relation, often by displaying enhanced rotational rates and activity.
In the Solar Twin Planet Search program we observed several solar twin
binaries, and found a multiplicity fraction of in the whole
sample; moreover, at least three of these binaries (HIP 19911, HIP 67620 and
HIP 103983) clearly exhibit the aforementioned anomalies. We investigated the
configuration of the binaries in the program, and discovered new companions for
HIP 6407, HIP 54582, HIP 62039 and HIP 30037, of which the latter is orbited by
a M brown dwarf in a 1-month long orbit. We report the orbital
parameters of the systems with well-sampled orbits and, in addition, the lower
limits of parameters for the companions that only display a curvature in their
radial velocities. For the linear trend binaries, we report an estimate of the
masses of their companions when their observed separation is available, and a
minimum mass otherwise. We conclude that solar twin binaries with low-mass
stellar companions at moderate orbital periods do not display signs of a
distinct rotational evolution when compared to single stars. We confirm that
the three peculiar stars are double-lined binaries, and that their companions
are polluting their spectra, which explains the observed anomalies.Comment: 13 pages, 7 figures, accepted for publication in MNRA
The D/H Ratio in the Interstellar Medium toward the White Dwarf PG0038+199
We determine the D/H ratio in the interstellar medium toward the DO white
dwarf PG0038+199 using spectra from the Far Ultraviolet Spectroscopic Explorer
(FUSE), with ground-based support from Keck HIRES. We employ curve of growth,
apparent optical depth and profile fitting techniques to measure column
densities and limits of many other species (H2, NaI, CI, CII, CIII, NI, NII,
OI, SiII, PII, SIII, ArI and FeII) which allow us to determine related ratios
such as D/O, D/N and the H2 fraction. Our efforts are concentrated on measuring
gas-phase D/H, which is key to understanding Galactic chemical evolution and
comparing it to predictions from Big Bang nucleosynthesis. We find column
densities log N(HI) = 20.41+-0.08, log N(DI)=15.75+-0.08 and log N(H2) =
19.33+-0.04, yielding a molecular hydrogen fraction of 0.14+-0.02 (2 sigma
errors), with an excitation temperature of 143+-5K. The high HI column density
implies that PG0038+199 lies outside of the Local Bubble; we estimate its
distance to be 297 (+164,-104)pc (1 sigma). D/[HI+2H2] toward PG0038+199 is
1.91(+0.52,-0.42) e-5 (2 sigma). There is no evidence of component structure on
the scale of Delta v > 8 km/s based on NaI, but there is marginal evidence for
structure on smaller scales. The D/H value is high compared to the majority of
recent D/H measurements, but consistent with the values for two other
measurements at similar distances. D/O is in agreement with other distant
measurements. The scatter in D/H values beyond ~100pc remains a challenge for
Galactic chemical evolution.Comment: 59 pages, 7 tables, 18 figures (1 standalone), accepted by ApJ v2
minor typos correcte
The temporal evolution of neutron-capture elements in the Galactic discs
Important insights into the formation and evolution of the Galactic disc(s)
are contained in the chemical compositions of stars. We analysed
high-resolution and high signal to noise HARPS spectra of 79 solar twin stars
in order to obtain precise determinations of their atmospheric parameters, ages
(0.4 Gyr) and chemical abundances (0.01~dex) of 12
neutron-capture elements (Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, and Dy).
This valuable dataset allows us to study the [X/Fe]-age relations over a time
interval of 10 Gyr and among stars belonging to the thin and thick discs.
These relations show that i) the -process has been the main channel of
nucleosynthesis of -capture elements during the evolution of the thin disc;
ii) the thick disc is rich in -process elements which suggests that its
formation has been rapid and intensive. %; iii) a chemical continuity between
the thin and thick discs is evident in the abundances of Ba. In addition, the
heavy (Ba, La, Ce) and light (Sr, Y, Zr) -process elements revealed details
on the dependence between the yields of AGB stars and the stellar mass or
metallicity. Finally, we confirmed that both [Y/Mg] and [Y/Al] ratios can be
employed as stellar clocks, allowing ages of solar twin stars to be estimated
with an average precision of 0.5~Gyr
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