437 research outputs found
Characterization of exoplanets from their formation III: The statistics of planetary luminosities
This paper continues a series in which we predict the main observable
characteristics of exoplanets based on their formation. In Paper I we described
our global planet formation and evolution model. In Paper II we studied the
planetary mass-radius relationship. Here we present an extensive study of the
statistics of planetary luminosities during both formation and evolution. Our
results can be compared with individual directly imaged (proto)planets as well
as statistical results from surveys. We calculated three synthetic planet
populations assuming different efficiencies of the accretional heating by gas
and planetesimals. We describe the temporal evolution of the planetary
mass-luminosity relation. We study the shock and internal luminosity during
formation. We predict a statistical version of the post-formation mass versus
entropy "tuning fork" diagram. We find high nominal post-formation luminosities
for hot and cold gas accretion. Individual formation histories can still lead
to a factor of a few spread in the post-formation luminosity at a given mass.
However, if the gas and planetesimal accretional heating is unknown, the
post-formation luminosity may exhibit a spread of as much as 2-3 orders of
magnitude at a fixed mass covering cold, warm, and hot states. As a key result
we predict a flat log-luminosity distribution for giant planets, and a steep
increase towards lower luminosities due to the higher occurrence rate of
low-mass planets. Future surveys may detect this upturn. During formation an
estimate of the planet mass may be possible for cold gas accretion if the gas
accretion rate can be estimated. Due to the "core-mass effect" planets that
underwent cold gas accretion can still have high post-formation entropies. Once
the number of directly imaged exoplanets with known ages and luminosities
increases, the observed distributions may be compared with our predictions.Comment: 44 pages, 26 figures (journal format). A&A in print. Language
correction only relative to V
A comparison of the neutron detection efficiency and response characteristics of two pixelated PSD-capable organic scintillator detectors with different photo-detection readout methods
We characterize the performance of two pixelated neutron detectors: a
PMT-based array that utilizes Anger logic for pixel identification and a
SiPM-based array that employs individual pixel readout. The SiPM-based array
offers improved performance over the previously developed PMT-based detector
both in terms of uniformity and neutron detection efficiency. Each detector
array uses PSD-capable plastic scintillator as a detection medium. We describe
the calibration and neutron efficiency measurement of both detectors using a
Cs source for energy calibration and a Cf source for
calibration of the neutron response. We find that the intrinsic neutron
detection efficiency of the SiPM-based array is ()\%, which
is almost twice that of the PMT-based array, which we measure to be ()\%
Mapping Global Star Formation in the Interacting Galaxy Pair Arp32
A multi-wavelength set of photometric data including UV (GALEX), optical, near-IR, infrared (Spitzer) and radio (VLA 20cm) images and spectroscopic observations are used to map the dust-obscured and unobscured star formation in the galaxy pair Arp 32. The system consists of an actively starforming galaxy and another one with depressed star formation. The most active galaxy has disrupted morphology and different sites of star formation. Spectroscopic data show hints of nuclear activity in its core, intense star formation in limited regions of the galaxy as well as an underlying population of stars witnessing a past episode of star formation. Current star formation rates are estimated from UV and bolometric IR luminosities
High signal-to-noise spectral characterization of the planetary-mass object HD 106906 b
We spectroscopically characterize the atmosphere of HD 106906b, a young
low-mass companion near the deuterium burning limit. The wide separation from
its host star of 7.1" makes it an ideal candidate for high S/N and
high-resolution spectroscopy. We aim to derive new constraints on the spectral
type, effective temperature, and luminosity of HD106906b and also to provide a
high S/N template spectrum for future characterization of extrasolar planets.
We obtained 1.1-2.5 m integral field spectroscopy with the VLT/SINFONI
instrument with a spectral resolution of R~2000-4000. New estimates of the
parameters of HD 106906b are derived by analyzing spectral features, comparing
the extracted spectra to spectral catalogs of other low-mass objects, and
fitting with theoretical isochrones. We identify several spectral absorption
lines that are consistent with a low mass for HD 106906b. We derive a new
spectral type of L1.51.0, one subclass earlier than previous estimates.
Through comparison with other young low-mass objects, this translates to a
luminosity of log()= and an effective temperature of
Teff= K. Our new mass estimates range between (hot start) and (cold start).
These limits take into account a possibly finite formation time, i.e., HD
106906b is allowed to be 0--3 Myr younger than its host star. We exclude
accretion onto HD 106906b at rates yr based on the fact that we observe no hydrogen (Paschen-,
Brackett-) emission. This is indicative of little or no circumplanetary
gas. With our new observations, HD 106906b is the planetary-mass object with
one of the highest S/N spectra yet. We make the spectrum available for future
comparison with data from existing and next-generation (e.g., ELT and JWST)
spectrographs.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy &
Astrophysics. Fully reduced spectra will be made available for download on
CD
Evolutionary models of cold and low-mass planets: Cooling curves, magnitudes, and detectability
Future instruments like NIRCam and MIRI on JWST or METIS at the ELT will be
able to image exoplanets that are too faint for current direct imaging
instruments. Evolutionary models predicting the planetary intrinsic luminosity
as a function of time have traditionally concentrated on gas-dominated giant
planets. We extend these cooling curves to Saturnian and Neptunian planets. We
simulate the cooling of isolated core-dominated and gas giant planets with
masses of 5 Earthmasses to 2 Jupitermasses. The luminosity includes the
contribution from the cooling and contraction of the core and of the H/He
envelope, as well as radiogenic decay. For the atmosphere we use grey,
AMES-Cond, petitCODE, and HELIOS models. We consider solar and non-solar
metallicities as well as cloud-free and cloudy atmospheres. The most important
initial conditions, namely the core-to-envelope ratio and the initial
luminosity are taken from planet formation simulations based on the core
accretion paradigm. We first compare our cooling curves for Uranus, Neptune,
Jupiter, Saturn, GJ 436b, and a 5 Earthmass-planet with a 1% H/He envelope with
other evolutionary models. We then present the temporal evolution of planets
with masses between 5 Earthmasses and 2 Jupitermasses in terms of their
luminosity, effective temperature, radius, and entropy. We discuss the impact
of different post formation entropies. For the different atmosphere types and
initial conditions magnitudes in various filter bands between 0.9 and 30
micrometer wavelength are provided. Using black body fluxes and non-grey
spectra, we estimate the detectability of such planets with JWST. It is found
that a 20 (100) Earthmass-planet can be detected with JWST in the background
limit up to an age of about 10 (100) Myr with NIRCam and MIRI, respectively.Comment: Language corrected version and improved arrangements of figures,
online data at:
http://www.space.unibe.ch/research/research_groups/planets_in_time/numerical_data/index_eng.htm
Simulated annealing for generalized Skyrme models
We use a simulated annealing algorithm to find the static field configuration
with the lowest energy in a given sector of topological charge for generalized
SU(2) Skyrme models. These numerical results suggest that the following
conjecture may hold: the symmetries of the soliton solutions of extended Skyrme
models are the same as for the Skyrme model. Indeed, this is verified for two
effective Lagrangians with terms of order six and order eight in derivatives of
the pion fields respectively for topological charges B=1 up to B=4. We also
evaluate the energy of these multi-skyrmions using the rational maps ansatz. A
comparison with the exact numerical results shows that the reliability of this
approximation for extended Skyrme models is almost as good as for the pure
Skyrme model. Some details regarding the implementation of the simulated
annealing algorithm in one and three spatial dimensions are provided.Comment: 14 pages, 6 figures, added 2 reference
Improved Fast Neutron Spectroscopy via Detector Segmentation
Organic scintillators are widely used for fast neutron detection and
spectroscopy. Several effects complicate the interpretation of results from
detectors based upon these materials. First, fast neutrons will often leave a
detector before depositing all of their energy within it. Second, fast neutrons
will typically scatter several times within a detector, and there is a
non-proportional relationship between the energy of, and the scintillation
light produced by, each individual scatter; therefore, there is not a
deterministic relationship between the scintillation light observed and the
neutron energy deposited. Here we demonstrate a hardware technique for reducing
both of these effects. Use of a segmented detector allows for the
event-by-event correction of the light yield non-proportionality and for the
preferential selection of events with near-complete energy deposition, since
these will typically have high segment multiplicities.Comment: Accepted for publication in Nuclear Instruments and Methods in
Physics Research Section
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