The post-formation, initial entropy S
i of a gas giant planet is a key witness to its mass-assembly history and a crucial quantity for its early evolution. However, formation models are not yet able ...to predict reliably S
i, making unjustified the use solely of traditional, 'hot-start' cooling tracks to interpret direct-imaging results and calling for an observational determination of initial entropies to guide formation scenarios. Using a grid of models in mass and entropy, we show how to place joint constraints on the mass and initial entropy of an object from its observed luminosity and age. This generalizes the usual estimate of only a lower bound on the real mass, through hot-start tracks. Moreover, we demonstrate that with mass information, e.g. from dynamical-stability analyses or radial velocity, tighter bounds can be set on the initial entropy. We apply this procedure to 2M1207 b and find that its initial entropy is at least 9.2 k
B/baryon, assuming that it does not burn deuterium. For the planets of the HR 8799 system, we infer that they must have formed with S
i > 9.2 k
B/baryon, independent of uncertainties about the age of the star. Finally, a similar analysis for β Pic b reveals that it must have formed with S
i > 10.5 k
B/baryon, using the radial-velocity mass upper limit. These initial entropy values are, respectively, ca. 0.7, 0.5 and 1.5 k
B/baryon higher than the ones obtained from core-accretion models by Marley et al., thereby quantitatively ruling out the coldest starts for these objects and constraining warm starts, especially for β Pic b.
Context.
Clouds are ubiquitous in exoplanet atmospheres and they represent a challenge for the model interpretation of their spectra. When generating a large number of model spectra, complex cloud ...models often prove too costly numerically, whereas more efficient models may be overly simplified.
Aims.
We aim to constrain the atmospheric properties of the directly imaged planet HR 8799e with a free retrieval approach.
Methods.
We used our radiative transfer code petitRADTRANS for generating the spectra, which we coupled to the PyMultiNest tool. We added the effect of multiple scattering which is important for treating clouds. Two cloud model parameterizations are tested: the first incorporates the mixing and settling of condensates, the second simply parameterizes the functional form of the opacity.
Results.
In mock retrievals, using an inadequate cloud model may result in atmospheres that are more isothermal and less cloudy than the input. Applying our framework on observations of HR 8799e made with the GPI, SPHERE, and GRAVITY, we find a cloudy atmosphere governed by disequilibrium chemistry, confirming previous analyses. We retrieve that C/O = 0.60
−0.08
+0.07
. Other models have not yet produced a well constrained C/O value for this planet. The retrieved C/O values of both cloud models are consistent, while leading to different atmospheric structures: either cloudy or more isothermal and less cloudy. Fitting the observations with the self-consistent Exo-REM model leads to comparable results, without constraining C/O.
Conclusions.
With data from the most sensitive instruments, retrieval analyses of directly imaged planets are possible. The inferred C/O ratio of HR 8799e is independent of the cloud model and thus appears to be a robust. This C/O is consistent with stellar, which could indicate that the HR 8799e formed outside the CO
2
or CO iceline. As it is the innermost planet of the system, this constraint could apply to all HR 8799 planets.
The circumstellar disk of PDS 70 hosts two forming planets, which are actively accreting gas from their environment. The physical and chemical characteristics of these planets remain ambiguous due to ...their unusual spectral appearance compared to more evolved objects. In this work, we report the first detection of PDS 70 b in the Br
α
and
M
′ filters with VLT/NACO, a tentative detection of PDS 70 c in Br
α
, and a reanalysis of archival NACO
L
′ and SPHERE
H
23 and
K
12 imaging data. The near side of the disk is also resolved with the Br
α
and
M
′ filters, indicating that scattered light is non-negligible at these wavelengths. The spectral energy distribution (SED) of PDS 70 b is well described by blackbody emission, for which we constrain the photospheric temperature and photospheric radius to
T
eff
= 1193 ± 20 K and
R
= 3.0 ± 0.2
R
J
. The relatively low bolometric luminosity, log(
L
∕
L
⊙
) = −3.79 ± 0.02, in combination with the large radius, is not compatible with standard structure models of fully convective objects. With predictions from such models, and adopting a recent estimate of the accretion rate, we derive a planetary mass and radius in the range of
M
p
≈ 0.5–1.5
M
J
and
R
p
≈ 1–2.5
R
J
, independently of the age and post-formation entropy of the planet. The blackbody emission, large photospheric radius, and the discrepancy between the photospheric and planetary radius suggests that infrared observations probe an extended, dusty environment around the planet, which obscures the view on its molecular composition. Therefore, the SED is expected to trace the reprocessed radiation from the interior of the planet and/or partially from the accretion shock. The photospheric radius lies deep within the Hill sphere of the planet, which implies that PDS 70 b not only accretes gas but is also continuously replenished by dust. Finally, we derive a rough upper limit on the temperature and radius of potential excess emission from a circumplanetary disk,
T
eff
≲ 256 K and
R
≲ 245
R
J
, but we do find weak evidence that the current data favors a model with a single blackbody component.
Context.
The properties of protoplanetary discs determine the conditions for planet formation. In addition, planets can already form during the early stages of infall.
Aims.
We constrain physical ...quantities such as the mass, radius, lifetime, and gravitational stability of protoplanetary discs by studying their evolution from formation to dispersal.
Methods.
We perform a population synthesis of protoplanetary discs with a total of 50 000 simulations using a 1D vertically integrated viscous evolution code, studying a parameter space of final stellar mass from 0.05 to 5
M
⊙
. Each star-and-disc system is set up shortly after the formation of the protostar and fed by infalling material from the parent molecular cloud core. Initial conditions and infall locations are chosen based on the results from a radiation-hydrodynamic population synthesis of circumstellar discs. We also consider a different infall prescription based on a magnetohydrodynamic (MHD) collapse simulation in order to assess the influence of magnetic fields on disc formation. The duration of the infall phase is chosen to produce a stellar mass distribution in agreement with the observationally determined stellar initial mass function.
Results.
We find that protoplanetary discs are very massive early in their lives. When averaged over the entire stellar population, the discs have masses of ~0.3 and 0.1
M
⊙
for systems based on hydrodynamic or MHD initial conditions, respectively. In systems characterised by a final stellar mass ~1
M
⊙
, we find disc masses of ~0.7
M
⊙
for the “hydro” case and ~0.2
M
⊙
for the “MHD” case at the end of the infall phase. Furthermore, the inferred total disc lifetimes are long, ≈5–7 Myr on average. This is despite our choice of a high value of 10
−2
for the background viscosity
α
-parameter. In addition, we find that fragmentation is common in systems that are simulated using hydrodynamic cloud collapse, with more fragments of larger mass formed in more massive systems. In contrast, if disc formation is limited by magnetic fields, fragmentation may be suppressed entirely.
Conclusions.
Our work draws a picture quite different from the one often assumed in planet formation studies: protoplanetary discs are more massive and live longer. This means that more mass is available for planet formation. Additionally, when fragmentation occurs, it can affect the disc’s evolution by transporting large amounts of mass radially. We suggest that the early phases in the lives of protoplanetary discs should be included in studies of planet formation. Furthermore, the evolution of the central star, including its accretion history, should be taken into account when comparing theoretical predictions of disc lifetimes with observations.
The Millennium Run Observatory: first light Overzier, R; Lemson, G; Angulo, R. E ...
Monthly notices of the Royal Astronomical Society,
2013, Letnik:
428, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Simulations of galaxy evolution aim to capture our current understanding as well as to make predictions for testing by future experiments. Simulations and observations are often compared in an ...indirect fashion: physical quantities are estimated from the observational data and compared to models. However, many applications can benefit from a more direct approach, where the observing process is also simulated, so that the models are seen fully from the observer's perspective. To facilitate this, we have developed the Millennium Run Observatory (MRObs), a theoretical virtual observatory which uses virtual telescopes to 'observe' semi-analytic galaxy formation simulations based on the suite of Millennium Run (MR) dark matter simulations. The MRObs produces data that can be processed and analysed using the standard observational software packages developed for real observations. At present, we produce images in 40 filters covering the rest-frame ultraviolet to infrared for two stellar population synthesis models, for three different models of absorption by the intergalactic medium, and in two cosmologies (Wilkinson Microwave Anisotropy Probe year 1 and 7). Galaxy distributions for a large number of mock light cones can be 'observed' using models of major ground- and space-based telescopes. The data include light cone catalogues linked to structural properties of galaxies, pre-observation model images, mock telescope images and Source Extractor products that can all be traced back to the higher level dark matter, semi-analytic galaxy and light cone catalogues available in the MR data base. Here, we describe our methods and announce a first public release of simulated observations that emulate a large number of extragalactic surveys e.g. Sloan Digital Sky Survey, Canada-France-Hawaii Telescope Legacy Survey (CFHT-LS), Great Observatories Origins Deep Survey (GOODS), GOODS/Early Release Science (ERS), Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS) and Hubble Ultra Deep Field (HUDF). The MRObs browser, an online tool, further facilitates exploration of the simulated data. We demonstrate the benefits of a direct approach through a number of example applications: (1) deep galaxy number counts in the CANDELS survey; (2) observed properties of galaxy clusters; (3) structural parameters of galaxies; and (4) identification of dropout galaxies. The MRObs enhances the range of questions that can be asked of semi-analytic models, allowing observers and theorists to work towards each other with virtually complete freedom of where to meet.
Abstract Accretion rates ( M ̇ ) of young stars show a strong correlation with object mass ( M ); however, extension of the M ̇ – M relation into the substellar regime is less certain. Here, we ...present the Comprehensive Archive of Substellar and Planetary Accretion Rates (CASPAR), the largest compilation to date of substellar accretion diagnostics. CASPAR includes: 658 stars, 130 brown dwarfs, and 10 bound planetary mass companions. In this work, we investigate the contribution of methodological systematics to scatter in the M ̇ – M relation and compare brown dwarfs to stars. In our analysis, we rederive all quantities using self-consistent models, distances, and empirical line flux to accretion luminosity scaling relations to reduce methodological systematics. This treatment decreases the original 1 σ scatter in the log M ̇ – log M relation by ∼17%, suggesting that it makes only a small contribution to the dispersion. The CASPAR rederived values are best fit by M ̇ ∝ M 2.02 ± 0.06 from 10 M J to 2 M ⊙ , confirming previous results. However, we argue that the brown-dwarf and stellar populations are better described separately and by accounting for both mass and age. Therefore, we derive separate age-dependent M ̇ – M relations for these regions and find a steepening in the brown-dwarf M ̇ – M slope with age. Within this mass regime, the scatter decreases from 1.36 dex to 0.94 dex, a change of ∼44%. This result highlights the significant role that evolution plays in the overall spread of accretion rates, and suggests that brown dwarfs evolve faster than stars, potentially as a result of different accretion mechanisms.
Context.
Accreting planetary-mass objects have been detected at H
α
, but targeted searches have mainly resulted in non-detections. Accretion tracers in the planetary-mass regime could originate from ...the shock itself, making them particularly susceptible to extinction by the accreting material. High-resolution (
R
> 50 000) spectrographs operating at H
α
should soon enable one to study how the incoming material shapes the line profile.
Aims.
We calculate how much the gas and dust accreting onto a planet reduce the H
α
flux from the shock at the planetary surface and how they affect the line shape. We also study the absorption-modified relationship between the H
α
luminosity and accretion rate.
Methods.
We computed the high-resolution radiative transfer of the H
α
line using a one-dimensional velocity–density–temperature structure for the inflowing matter in three representative accretion geometries: spherical symmetry, polar inflow, and magnetospheric accretion. For each, we explored the wide relevant ranges of the accretion rate and planet mass. We used detailed gas opacities and carefully estimated possible dust opacities.
Results.
At accretion rates of
Ṁ
≲ 3 × 10
−6
M
J
yr
−1
, gas extinction is negligible for spherical or polar inflow and at most
A
H
α
≲ 0.5 mag for magnetospheric accretion. Up to
Ṁ
≈ 3 × 10
−4
M
J
yr
−1
, the gas contributes
A
H
α
≲ 4 mag. This contribution decreases with mass. We estimate realistic dust opacities at H
α
to be
κ
~ 0.01–10 cm
2
g
−1
, which is 10–10
4
times lower than in the interstellar medium. Extinction flattens the
L
H
α
–
Ṁ
relationship, which becomes non-monotonic with a maximum luminosity
L
H
α
~ 10
−4
L
⊙
towards
Ṁ
≈ 10
−4
M
J
yr
−1
for a planet mass ~10
M
J
. In magnetospheric accretion, the gas can introduce features in the line profile, while the velocity gradient smears them out in other geometries.
Conclusions.
For a wide part of parameter space, extinction by the accreting matter should be negligible, simplifying the interpretation of observations, especially for planets in gaps. At high
Ṁ
, strong absorption reduces the H
α
flux, and some measurements can be interpreted as two
Ṁ
values. Highly resolved line profiles (
R
~ 10
5
) can provide (complex) constraints on the thermal and dynamical structure of the accretion flow.
Abstract
Accretion signatures from bound brown dwarf and protoplanetary companions provide evidence for ongoing planet formation, and accreting substellar objects have enabled new avenues to study ...the astrophysical mechanisms controlling the formation and accretion processes. Delorme 1 (AB)b, a ∼30–45 Myr circumbinary planetary-mass companion, was recently discovered to exhibit strong H
α
emission. This suggests ongoing accretion from a circumplanetary disk, somewhat surprising given canonical gas disk dispersal timescales of 5–10 Myr. Here, we present the first NIR detection of accretion from the companion in Pa
β
, Pa
γ
, and Br
γ
emission lines from SOAR/TripleSpec 4.1, confirming and further informing its accreting nature. The companion shows strong line emission, with
L
line
≈ 1–6 × 10
−8
L
⊙
across lines and epochs, while the binary host system shows no NIR hydrogen line emission (
L
line
< 0.32–11 × 10
−7
L
⊙
). Observed NIR hydrogen line ratios are more consistent with a planetary accretion shock than with local line excitation models commonly used to interpret stellar magnetospheric accretion. Using planetary accretion shock models, we derive mass accretion rate estimates of
M
̇
pla
∼
3
–4 × 10
−8
M
J
yr
−1
, somewhat higher than expected under the standard star formation paradigm. Delorme 1 (AB)b’s high accretion rate is perhaps more consistent with formation via disk fragmentation. Delorme 1 (AB)b is the first protoplanet candidate with clear (signal-to-noise ratio ∼5) NIR hydrogen line emission.
ABSTRACT
Understanding how giant planets form requires observational input from directly imaged protoplanets. We used VLT/NACO and VLT/SPHERE to search for companions in the transition disc of 2MASS ...J19005804-3645048 (hereafter CrA-9), an accreting M0.75 dwarf with an estimated age of 1–2 Myr. We found a faint point source at ∼0.7-arcsec separation from CrA-9 (∼108 au projected separation). Our 3-epoch astrometry rejects a fixed background star with a 5σ significance. The near-IR absolute magnitudes of the object point towards a planetary-mass companion. However, our analysis of the 1.0–3.8$\,\mu$m spectrum extracted for the companion suggests it is a young M5.5 dwarf, based on both the 1.13-μm Na index and comparison with templates of the Montreal Spectral Library. The observed spectrum is best reproduced with high effective temperature ($3057^{+119}_{-36}$K) BT-DUSTY and BT-SETTL models, but the corresponding photometric radius required to match the measured flux is only $0.60^{+0.01}_{-0.04}$ Jovian radius. We discuss possible explanations to reconcile our measurements, including an M-dwarf companion obscured by an edge-on circum-secondary disc or the shock-heated part of the photosphere of an accreting protoplanet. Follow-up observations covering a larger wavelength range and/or at finer spectral resolution are required to discriminate these two scenarios.
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