Exploring the formation by core accretion and the luminosity evolution of directly imaged planets

Context. A low-mass companion to the two-solar mass star HIP 65426 has recently been detected by SPHERE at around 100 au from its host. Explaining the presence of super-Jovian planets at large separations, as revealed by direct imaging, is currently an open question. Aims. We want to derive statistical constraints on the mass and initial entropy of HIP 65426 b and to explore possible formation pathways of directly imaged objects within the core-accretion paradigm, focusing on HIP 65426 b. Methods. Constraints on the planet’s mass and post-formation entropy are derived from its age and luminosity combined with cooling models. For the first time, the results of population synthesis are also used to inform the results. Then a formation model that includes N-body dynamics with several embryos per disc is used to study possible formation histories and the properties of possible additional companions. Finally, the outcomes of two- and three-planet scattering in the post-disc phase are analysed, taking tides into account for small-pericentre orbits. Results. The mass of HIP 65426 b is found to be mp = 9.9−1.8+1.1 MJ using the hot population and mp = 10.9−2.0+1.4 MJ with the cold-nominal population. We find that core formation at small separations from the star followed by outward scattering and runaway accretion at a few hundred astronomical units succeeds in reproducing the mass and separation of HIP 65426 b. Alternatively, systems having two or more giant planets close enough to be on an unstable orbit at disc dispersal are likely to end up with one planet on a wide HIP 65426 b-like orbit with a relatively high eccentricity (≳ 0.5). Conclusions. If this scattering scenario explains its formation, HIP 65426 b is predicted to have a high eccentricity and to be accompanied by one or several roughly Jovian-mass planets at smaller semi-major axes, which also could have a high eccentricity. This could be tested by further direct-imaging as well as radial-velocity observations.

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Be it therefore resolved: cosmological simulations of dwarf galaxies with 30 solar mass resolution

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2887 ◽

2019 ◽

Vol 490 (3) ◽

pp. 4447-4463 ◽

Cited By ~ 25

Author(s):

Coral Wheeler ◽

Philip F Hopkins ◽

Andrew B Pace ◽

Shea Garrison-Kimmel ◽

Michael Boylan-Kolchin ◽

...

Keyword(s):

Star Formation ◽

Surface Brightness ◽

Local Group ◽

Dwarf Galaxies ◽

Stellar Rotation ◽

Solar Mass ◽

Dynamical Mass ◽

Low Mass ◽

Star Formation Histories ◽

First Time

ABSTRACT We study a suite of extremely high-resolution cosmological Feedback in Realistic Environments simulations of dwarf galaxies ($M_{\rm halo} \lesssim 10^{10}\rm \, M_{\odot }$), run to z = 0 with $30\, \mathrm{M}_{\odot }$ resolution, sufficient (for the first time) to resolve the internal structure of individual supernovae remnants within the cooling radius. Every halo with $M_{\rm halo} \gtrsim 10^{8.6}\, \mathrm{M}_{\odot }$ is populated by a resolved stellar galaxy, suggesting very low-mass dwarfs may be ubiquitous in the field. Our ultra-faint dwarfs (UFDs; $M_{\ast }\lt 10^{5}\, \mathrm{M}_{\odot }$) have their star formation (SF) truncated early (z ≳ 2), likely by reionization, while classical dwarfs ($M_{\ast }\gt 10^{5}\, \mathrm{M}_{\odot }$) continue forming stars to z < 0.5. The systems have bursty star formation histories, forming most of their stars in periods of elevated SF strongly clustered in both space and time. This allows our dwarf with M*/Mhalo > 10−4 to form a dark matter core ${\gt}200\rm \, pc$, while lower mass UFDs exhibit cusps down to ${\lesssim}100\rm \, pc$, as expected from energetic arguments. Our dwarfs with $M_{\ast }\gt 10^{4}\, \mathrm{M}_{\odot }$ have half-mass radii (R1/2) in agreement with Local Group (LG) dwarfs (dynamical mass versus R1/2 and stellar rotation also resemble observations). The lowest mass UFDs are below surface brightness limits of current surveys but are potentially visible in next-generation surveys (e.g. LSST). The stellar metallicities are lower than in LG dwarfs; this may reflect pre-enrichment of the LG by the massive hosts or Pop-III stars. Consistency with lower resolution studies implies that our simulations are numerically robust (for a given physical model).

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Infalling Streamer-Disk-Outflow System in a Nearby High-mass Star Formation Region

10.21203/rs.3.rs-402900/v1 ◽

2021 ◽

Author(s):

Xi Chen ◽

Zhiyuan Ren ◽

Da-Lei Li ◽

Tie Liu ◽

Ke Wang ◽

...

Keyword(s):

Direct Detection ◽

Theoretical Models ◽

Young Stellar Objects ◽

High Mass ◽

Similar Process ◽

Mass Star ◽

Solar Mass ◽

Low Mass Stars ◽

Stellar Objects ◽

Low Mass

Abstract Theoretical models and numerical simulations suggest that high mass star (with mass > 8 solar mass) can be formed either via monolithic collapse of a massive core or competitive accretion, but the dominant mechanism is currently unclear. Although recent high resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have detected physical and kinematic features, such as disks, outflows and filamentary structures surrounding the high mass young stellar objects (HMYSO), direct detection of the infalling gas towards the HMYSO is still the key to distinguish the different scenarios. Chemically fresh gas inflows have been detected towards low-mass stars being formed, which are consistent with the accretion-disk-outflow process. In this work we report the detection of a chemically fresh inflow which is feeding HMYSO growth in the nearby high mass star-forming region G352.63-1.07. High quality images of the dust and molecular lines from both ALMA and the Submillimeter Array (SMA) have consistently revealed a gravitationally-controlled gas inflow towards a rotating structure (disk or torus) around the HMYSO. The HMYSO is also observed to have an outflow, but it can be clearly separated from the inflow. These kinematic features provide observational evidence to support the conjecture that high-mass stars can be formed in a similar process to that observed in the low-mass counterparts. The chemically fresh infalling streamers could also be related with the disk configuration, fragmentation and accretion bursts that occur in both simulations and observations.

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A centrally concentrated sub-solar-mass starless core in the Taurus L1495 filamentary complex

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psz051 ◽

2019 ◽

Vol 71 (4) ◽

Cited By ~ 3

Author(s):

Kazuki Tokuda ◽

Kengo Tachihara ◽

Kazuya Saigo ◽

Phillipe André ◽

Yosuke Miyamoto ◽

...

Keyword(s):

Star Formation ◽

Initial Conditions ◽

Volume Density ◽

Mass Star ◽

Brown Dwarf ◽

Solar Mass ◽

Star Forming ◽

The Core ◽

Order Of Magnitude ◽

Low Mass

Abstract The formation scenario of brown dwarfs is still unclear because observational studies to investigate its initial condition are quite limited. Our systematic survey of nearby low-mass star-forming regions using the Atacama Compact Array (aka the Morita array) and the IRAM 30-m telescope in 1.2 mm continuum has identified a centrally concentrated starless condensation with a central H2 volume density of ∼106 cm−3, MC5-N, connected to a narrow (width ∼0.03 pc) filamentary cloud in the Taurus L1495 region. The mass of the core is $\sim {0.2\!-\!0.4}\, M_{\odot }$, which is an order of magnitude smaller than typical low-mass pre-stellar cores. Taking into account a typical core to star formation efficiency for pre-stellar cores (∼20%–40%) in nearby molecular clouds, brown dwarf(s) or very low-mass star(s) may be going to be formed in this core. We have found possible substructures at the high-density portion of the core, although much higher angular resolution observation is needed to clearly confirm them. The subsequent N2H+ and N2D+ observations using the Nobeyama 45-m telescope have confirmed the high-deuterium fractionation (∼30%). These dynamically and chemically evolved features indicate that this core is on the verge of proto-brown dwarf or very low-mass star formation and is an ideal source to investigate the initial conditions of such low-mass objects via gravitational collapse and/or fragmentation of the filamentary cloud complex.

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The high latitude low mass star forming region Cometary Globule 12: two compact cores and a C18O hot spot

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307002086 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 420-420

Author(s):

L. K. Haikala ◽

M. Juvela ◽

J. Harju ◽

K. Lehtinen ◽

K. Mattila ◽

...

Keyword(s):

Galactic Plane ◽

Hot Spot ◽

Mass Star ◽

Intermediate Mass ◽

Solar Mass ◽

Stellar Cluster ◽

Star Forming ◽

Continuum Source ◽

Nir Imaging ◽

Low Mass

AbstractCometary globule CG 12 lies at the distance of 630 pc more than 200 pc above the Galactic plane. The cloud's structure could be due to the passage of a supernova blast wave. Curiously, the cometary tail points at the galactic plane which would put the putative supernova even farther above the Galactic plane than the globule. The globule contains a low/intermediate mass stellar cluster with at least 9 members (Williams et al. 1977). The head of CG 12 has been observed using NIR imaging (NTT SOFI), mm continuum (SEST SIMBA) and sub mm (APEX) and mm (SEST) spectroscopy (Haikala & Olberg 2006, Haikala et al.). The molecular material is distributed in a North-South 10' long elongated lane with two compact maxima separated by 3'. Strong C18O (3-2), (2-1) and (1-0) emission is detected in both maxima and both have an associated compact 1.2 mm continuum source. The Northern core, CG 12 N, is cold and is possibly still pre-stellar. A dense and compact core is observed in DCO+ and CS emission in the direction of the Southern core, CG 12 S. A remarkable C18O hot spot was detected in CG 12 S. This is the first detection of such a compact, warm object in a low mass star forming region. The hot spot can be modelled with a 60″ to 80″ diameter (~0.2 pc) hot (80 K ≲ Tex≲ 100 K) 1.6 solar mass clump (Haikala et al. 2006). The hot spot lies at the edge of a dense cloud core and on the axis of a highly collimated bipolar molecular outflow (White 1993). The driving source of the outflow is most probably embedded in the dense core. NIR imaging reveals a bright cone like feature with a faint counter cone in the centre of CG 12 S. The size of the CG 12 compact head, 1.1 pc by 1.8 pc, and the C18O mass larger than 100 solar masses are comparable to those of other nearby low/intermediate mass star formation regions.

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The K2-HERMES Survey: age and metallicity of the thick disc

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2861 ◽

2019 ◽

Vol 490 (4) ◽

pp. 5335-5352 ◽

Cited By ~ 13

Author(s):

Sanjib Sharma ◽

Dennis Stello ◽

Joss Bland-Hawthorn ◽

Michael R Hayden ◽

Joel C Zinn ◽

...

Keyword(s):

Selection Function ◽

Population Synthesis ◽

Low Mass Stars ◽

Mass Scaling ◽

Elemental Abundances ◽

Thick Disc ◽

Promising Tool ◽

Low Mass ◽

The Mean ◽

First Time

ABSTRACT Asteroseismology is a promising tool to study Galactic structure and evolution because it can probe the ages of stars. Earlier attempts comparing seismic data from the Kepler satellite with predictions from Galaxy models found that the models predicted more low-mass stars compared to the observed distribution of masses. It was unclear if the mismatch was due to inaccuracies in the Galactic models, or the unknown aspects of the selection function of the stars. Using new data from the K2 mission, which has a well-defined selection function, we find that an old metal-poor thick disc, as used in previous Galactic models, is incompatible with the asteroseismic information. We use an importance-sampling framework, which takes the selection function into account, to fit for the metallicities of a population synthesis model using spectroscopic data. We show that spectroscopic measurements of [Fe/H] and [α/Fe] elemental abundances from the GALAH survey indicate a mean metallicity of log (Z/Z⊙) = −0.16 for the thick disc. Here Z is the effective solar-scaled metallicity, which is a function of [Fe/H] and [α/Fe]. With the revised disc metallicities, for the first time, the theoretically predicted distribution of seismic masses show excellent agreement with the observed distribution of masses. This indirectly verifies that the asteroseismic mass scaling relation is good to within five per cent. Assuming the asteroseismic scaling relations are correct, we estimate the mean age of the thick disc to be about 10 Gyr, in agreement with the traditional idea of an old α-enhanced thick disc.

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A giant exoplanet orbiting a very-low-mass star challenges planet formation models

Science ◽

10.1126/science.aax3198 ◽

2019 ◽

Vol 365 (6460) ◽

pp. 1441-1445 ◽

Cited By ~ 22

Author(s):

J. C. Morales ◽

A. J. Mustill ◽

I. Ribas ◽

M. B. Davies ◽

A. Reiners ◽

...

Keyword(s):

Near Infrared ◽

Planet Formation ◽

Giant Planet ◽

Mass Star ◽

Low Mass Stars ◽

Migration Rates ◽

Low Mass ◽

And Migration ◽

Core Accretion ◽

Planet Accretion

Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought.

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Bipolar molecular outflow of the very low-mass star Par-Lup3-4

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038128 ◽

2020 ◽

Vol 640 ◽

pp. A13

Author(s):

A. Santamaría-Miranda ◽

I. de Gregorio-Monsalvo ◽

N. Huélamo ◽

A. L. Plunkett ◽

Á. Ribas ◽

...

Keyword(s):

Spectral Energy Distribution ◽

Spectral Energy ◽

Molecular Gas ◽

Mass Star ◽

Low Mass Stars ◽

Molecular Outflow ◽

Outflow Rate ◽

Low Mass ◽

First Time ◽

Mass Sources

Context. Very low-mass stars are known to have jets and outflows, which is indicative of a scaled-down version of low-mass star formation. However, only very few outflows in very low-mass sources are well characterized. Aims. We characterize the bipolar molecular outflow of the very low-mass star Par-Lup3-4, a 0.12 M⊙ object known to power an optical jet. Methods. We observed Par-Lup3-4 with ALMA in Bands 6 and 7, detecting both the continuum and CO molecular gas. In particular, we studied three main emission lines: CO(2–1), CO(3–2), and 13CO(3–2). Results. Our observations reveal for the first time the base of a bipolar molecular outflow in a very low-mass star, as well as a stream of material moving perpendicular to the primary outflow of this source. The primary outflow morphology is consistent with the previously determined jet orientation and disk inclination. The outflow mass is 9.5 × 10−7 M⊙, with an outflow rate of 4.3 × 10−9 M⊙ yr−1. A new fitting to the spectral energy distribution suggests that Par-Lup3-4 may be a binary system. Conclusions. We have characterized Par-Lup3-4 in detail, and its properties are consistent with those reported in other very low-mass sources. This source provides further evidence that very low-mass sources form as a scaled-down version of low-mass stars.

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How does the mass and activity history of the host star affect the population of low-mass planets?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab897 ◽

2021 ◽

Vol 504 (2) ◽

pp. 2034-2050

Author(s):

Daria Kubyshkina ◽

Aline A Vidotto

Keyword(s):

Mass Star ◽

Intermediate Mass ◽

Solar Mass ◽

Planetary Evolution ◽

The Past ◽

Strongly Connected ◽

History Of ◽

Low Mass ◽

Host Stars ◽

Atmospheric Mass

ABSTRACT The evolution of the atmospheres of low- and intermediate-mass planets is strongly connected to the physical properties of their host stars. The types and the past activities of planet-hosting stars can, therefore, affect the overall planetary population. In this paper, we perform a comparative study of sub-Neptune-like planets orbiting stars of different masses and different evolutionary histories. We discuss the general patterns of the evolved population as a function of parameters and environments of planets. As a model of the atmospheric evolution, we employ the own framework combining planetary evolution in Modules for Experiments in Stellar Astrophysics (mesa) with the realistic prescription of the escape of hydrogen-dominated atmospheres. We find that the final populations look qualitatively similar in terms of the atmospheres survival around different stars, but qualitatively different, with this difference accentuated for planets orbiting more massive stars. We show that a planet has larger chances of keeping its primordial atmosphere in the habitable zone of a solar-mass star compared to M or K dwarfs and if it starts the evolution having a relatively compact envelope. We also address the problem of the uncertain initial temperatures (luminosities) of planets and show that this issue is only of particular importance for planets exposed to extreme atmospheric mass losses.

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Comparison of Low-Mass and High-Mass Star Formation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316007432 ◽

2015 ◽

Vol 11 (S315) ◽

pp. 154-162 ◽

Cited By ~ 1

Author(s):

Jonathan C. Tan

Keyword(s):

Star Formation ◽

Massive Star ◽

Initial Conditions ◽

Cluster Formation ◽

Theoretical Models ◽

High Mass ◽

Mass Star ◽

Massive Star Formation ◽

Low Mass ◽

Core Accretion

AbstractI review theoretical models of star formation and how they apply across the stellar mass spectrum. Several distinct theories are under active study for massive star formation, especiallyTurbulent Core Accretion,Competitive AccretionandProtostellar Mergers, leading to distinct observational predictions. These include the types of initial conditions, the structure of infall envelopes, disks and outflows, and the relation of massive star formation to star cluster formation. Even for Core Accretion models, there are several major uncertainties related to the timescale of collapse, the relative importance of different processes for preventing fragmentation in massive cores, and the nature of disks and outflows. I end by discussing some recent observational results that are helping to improve our understanding of these processes.

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