scholarly journals Constraints on observing brightness asymmetries in protoplanetary disks at solar system scale

2018 ◽  
Vol 611 ◽  
pp. A90 ◽  
Author(s):  
Robert Brunngräber ◽  
Sebastian Wolf
Keyword(s):  
Solar System ◽  
Flux Ratio ◽  
Angular Separation ◽  
Circumstellar Disks ◽  
Theoretical Models ◽  
Central Star ◽  
Resolving Power ◽  
Nearby Star ◽  
Significance Level ◽  
Infrared Wavelength

We have quantified the potential capabilities of detecting local brightness asymmetries in circumstellar disks with the Very Large Telescope Interferometer (VLTI) in the mid-infrared wavelength range. The study is motivated by the need to evaluate theoretical models of planet formation by direct observations of protoplanets at early evolutionary stages, when they are still embedded in their host disk. Up to now, only a few embedded candidate protoplanets have been detected with semi-major axes of 20–50 au. Due to the small angular separation from their central star, only long-baseline interferometry provides the angular resolving power to detect disk asymmetries associated to protoplanets at solar system scales in nearby star-forming regions. In particular, infrared observations are crucial to observe scattered stellar radiation and thermal re-emission in the vicinity of embedded companions directly. For this purpose we performed radiative transfer simulations to calculate the thermal re-emission and scattered stellar flux from a protoplanetary disk hosting an embedded companion. Based on that, visibilities and closure phases are calculated to simulate observations with the future beam combiner MATISSE, operating at the L, M and N bands at the VLTI. We find that the flux ratio of the embedded source to the central star can be as low as 0.5 to 0.6% for a detection at a feasible significance level due to the heated dust in the vicinity of the embedded source. Furthermore, we find that the likelihood for detection is highest for sources at intermediate distances r ≈ 2–5 au and disk masses not higher than ≈10−4 M⊙.

Extreme Adaptive Optics

2018 ◽  
Vol 56 (1) ◽  
pp. 315-355 ◽  
Author(s):  
Olivier Guyon
Keyword(s):  
Adaptive Optics ◽  
Thermal Emission ◽  
Contrast Ratio ◽  
Angular Separation ◽  
Circumstellar Disks ◽  
Spectroscopic Characterization ◽  
Central Star ◽  
High Contrast ◽  
Direct Imaging ◽  
Segmented Mirror

Over the last two decades, several thousand exoplanets have been identified, and their study has become a high scientific priority. Direct imaging of nearby exoplanets and the circumstellar disks in which they form and evolve is challenging due to the high contrast ratio and small angular separation relative to the central star. Exoplanets are typically within 1 arcsec of, and between 4 and 10 orders of magnitude fainter than, the stars they orbit. To meet these challenges, ground-based telescopes must be equipped with extreme adaptive optics (ExAO) systems optimized to acquire high-contrast images of the immediate surrounding of nearby bright stars. Current ExAO systems have the sensitivity to image thermal emission from young massive planets in near-IR, while future systems deployed on Giant Segmented Mirror Telescopes will image starlight reflected by lower-mass rocky planets. Thanks to rapid progress in optical coronagraphy, wavefront control, and data analysis techniques, direct imaging and spectroscopic characterization of habitable exoplanets will be within reach of the next generation of large ground-based telescopes.

scholarly journals Millimetre/Sub-millimetre Observations of Circumstellar Disks

2011 ◽  
Vol 7 (S280) ◽  
pp. 103-113
Author(s):  
Anne Dutrey
Keyword(s):  
Planet Formation ◽  
Circumstellar Disks ◽  
Current Understanding ◽  
Resolving Power ◽  
Nearby Star ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions

AbstractTTauri disks located in nearby star-forming regions (e.g. Taurus-Auriga at 140 pc) are thought to be the site of planet formation, since proto-planetary disks orbiting around active (still accreting) TTauri stars should contain, in many cases, enough gas to form giant gaseous planets. As such, circumstellar disks are ideal laboratories to study planet formation, provided the gas and dust observations have enough sensitivity and resolving power. I will focus in these proceedings, on recent results of molecular observations which unveil the physical conditions of gas disks and reveal the weakness of our current understanding and modeling.

scholarly journals HST Imaging of New Edge-on Circumstellar Disks in Nearby Star-forming Regions

2013 ◽  
Vol 8 (S299) ◽  
pp. 99-103
Author(s):  
K.R. Stapelfeldt ◽  
G. Duchêne ◽  
M. Perrin ◽  
S. Wolff ◽  
J.E. Krist ◽  
...  
Keyword(s):  
Structural Parameters ◽  
Scattered Light ◽  
Spectral Energy Distribution ◽  
Circumstellar Disks ◽  
Central Star ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Ancillary Data ◽  
Nearby Star ◽  
Space Telescope

AbstractEdge-on, optically thick circumstellar disks have been previously imaged at subarcsecond resolution around about a dozen nearby young stellar objects. In these systems the central star is occulted from direct view, bright star image artifacts are absent, and the disk reflected light is clearly seen. Comparison of Hubble Space Telescope (HST) edge-on disk images with scattered light models has allowed key disk structural parameters and dust grain properties to be determined. Edge-on disks have been systematically undercounted to date: while 10% of young stars should statistically be occulted by their disk, the observed frequency is much less. Thus there is a significant potential for discovering and imaging new examples. Spitzer Space Telescope legacy science programs have provided the first good spectral energy distribution (SED) measurements for the previously known edge-on disks. These can be used as templates to identify new candidates in far-infrared survey datasets.We report on the results of our HST program to image twenty-one edge-on disk candidates mostly selected from their SEDs. Eleven are well-resolved with radii ranging from 30-400 AU, nine for the first time and six showing highly collimated jets. Outstanding individual sources include a large and symmetric new template object, a highly flattened disk not accreting onto its central star, and an asymmetric disk with a misaligned jet which likely traces tidal perturbations in a binary system. Follow-up work to obtain ancillary data and perform scattered light modeling of the most symmetric disks is now being pursued. The results of this program will guide a new round of searches for these rare but important snapshots of protoplanetary disk evolution.

scholarly journals Gaia view of low-mass star formation

2017 ◽  
Vol 12 (S330) ◽  
pp. 309-312
Author(s):  
C. F. Manara ◽  
T. Prusti ◽  
J. Voirin ◽  
E. Zari
Keyword(s):  
Circumstellar Disks ◽  
Central Star ◽  
High Energy ◽  
Young Star ◽  
Mass Star ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Kinematic Modelling ◽  
Low Mass

AbstractUnderstanding how young stars and their circumstellar disks form and evolve is key to explain how planets form. The evolution of the star and the disk is regulated by different processes, both internal to the system or related to their environment. The former include accretion of material onto the central star, wind emission, and photoevaporation of the disk due to high-energy radiation from the central star. These are best studied spectroscopically, and the distance to the star is a key parameter in all these studies. Here we present new estimates of the distance to a complex of nearby star-forming clouds obtained combining TGAS distances with measurement of extinction on the line of sight. Furthermore, we show how we plan to study the effects of the environment on the evolution of disks with Gaia, using a kinematic modelling code we have developed to model young star-forming regions.

scholarly journals Circumstellar Disks around Young Solar-type Stars

2004 ◽  
Vol 219 ◽  
pp. 385-389 ◽  
Author(s):  
Inga Kamp ◽  
Fatima Sammar
Keyword(s):  
Radiation Field ◽  
Uv Radiation ◽  
Circumstellar Disks ◽  
Central Star ◽  
Time Dependent ◽  
Solar Chromosphere ◽  
Starting Point ◽  
Solar Type ◽  
Time Dependent Behaviour ◽  
Dependent Behaviour

The chemistry of circumstellar disks around young (a few 10 Myr) solar-type stars is mainly driven by the strong UV radiation field of the central star. As a starting point for a detailed UV radiation field, the rocket and satellite observations of the solar chromosphere are used and scaled according to the time-dependent behaviour of stellar activity. The disk chemistry as well as dust and gas temperatures are then derived self-consistently from the model. The results of these calculations can be used for the identification of the most promising gas tracers as well as for the interpretation of present and future observations.

Cosmic Pathways to Life: From Interstellar Molecules to the First Traces of Life

2018 ◽  
Vol 14 (S345) ◽  
pp. 1-14
Author(s):  
Manuel Güdel ◽  
Bruce G. Elmegreen ◽  
L. Viktor Tóth
Keyword(s):  
Central Star ◽  
Life Forms ◽  
Disk Accretion ◽  
Nearby Star ◽  
Long Period ◽  
Cosmic Evolution ◽  
Stellar Radiation ◽  
Solid Bodies ◽  
Gaseous Envelope ◽  
Central Stars

AbstractThe present-day Earth with its innumerable life forms is a product of cosmic evolution starting with the formation of our galaxy and the dense gas clouds within it, and proceeding through the contraction of one of those clouds about 4.6 Gyr ago, first into filaments and then one or more protostellar disks, planets, and central stars, one of which was our Sun. Radioactive debris from a massive nearby star was included. The planets themselves formed through coagulation, accretion, and fragmentation of solid bodies. Habitability depends on a delicate balance between disk accretion by gravity and dispersal by the central star, which determine the size of the planet and its gaseous envelope, combined with a long period of stellar radiation, which has to disperse this envelope but leave a hospitable secondary atmosphere. The final step toward life involves even more complexity as self-replicating bio-molecules form with ever increasing stability.

scholarly journals The lifecycle of molecular clouds in nearby star-forming disc galaxies

2019 ◽  
Vol 493 (2) ◽  
pp. 2872-2909 ◽  
Author(s):  
Mélanie Chevance ◽  
J M Diederik Kruijssen ◽  
Alexander P S Hygate ◽  
Andreas Schruba ◽  
Steven N Longmore ◽  
...  
Keyword(s):  
Star Formation ◽  
Flux Ratio ◽  
Molecular Gas ◽  
H Ii Regions ◽  
Dynamical Processes ◽  
Nearby Star ◽  
Star Forming ◽  
Spatially Resolved ◽  
Stellar Feedback ◽  
Disc Galaxies

ABSTRACT It remains a major challenge to derive a theory of cloud-scale ($\lesssim100$ pc) star formation and feedback, describing how galaxies convert gas into stars as a function of the galactic environment. Progress has been hampered by a lack of robust empirical constraints on the giant molecular cloud (GMC) lifecycle. We address this problem by systematically applying a new statistical method for measuring the evolutionary timeline of the GMC lifecycle, star formation, and feedback to a sample of nine nearby disc galaxies, observed as part of the PHANGS-ALMA survey. We measure the spatially resolved (∼100 pc) CO-to-H α flux ratio and find a universal de-correlation between molecular gas and young stars on GMC scales, allowing us to quantify the underlying evolutionary timeline. GMC lifetimes are short, typically $10\!-\!30\,{\rm Myr}$, and exhibit environmental variation, between and within galaxies. At kpc-scale molecular gas surface densities $\Sigma _{\rm H_2}\ge 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$, the GMC lifetime correlates with time-scales for galactic dynamical processes, whereas at $\Sigma _{\rm H_2}\le 8\,\rm {M_\odot}\,{{\rm pc}}^{-2}$ GMCs decouple from galactic dynamics and live for an internal dynamical time-scale. After a long inert phase without massive star formation traced by H α (75–90 per cent of the cloud lifetime), GMCs disperse within just $1\!-\!5\,{\rm Myr}$ once massive stars emerge. The dispersal is most likely due to early stellar feedback, causing GMCs to achieve integrated star formation efficiencies of 4–10 per cent. These results show that galactic star formation is governed by cloud-scale, environmentally dependent, dynamical processes driving rapid evolutionary cycling. GMCs and H ii regions are the fundamental units undergoing these lifecycles, with mean separations of $100\!-\!300\,{{\rm pc}}$ in star-forming discs. Future work should characterize the multiscale physics and mass flows driving these lifecycles.

scholarly journals The Single-mode Complex Amplitude Refinement (SCAR) coronagraph

2020 ◽  
Vol 635 ◽  
pp. A55 ◽  
Author(s):  
E. H. Por ◽  
S. Y. Haffert
Keyword(s):  
High Resolution ◽  
Adaptive Optics ◽  
Flux Ratio ◽  
Single Mode ◽  
Complex Amplitude ◽  
Phase Plate ◽  
Spectral Bandwidth ◽  
Nearby Star ◽  
Integral Field Spectrograph ◽  
Pupil Plane

Context. The recent discovery of an Earth-mass exoplanet around the nearby star Proxima Centauri provides a prime target for the search for life on planets outside our solar system. Atmospheric characterization of these planets has been proposed by blocking the starlight with a stellar coronagraph and using a high-resolution spectrograph to search for reflected starlight off the planet. Aims. Due to the large flux ratio and small angular separation between Proxima b and its host star (≲10−7 and ≲2.2λ/D respectively; at 750 nm for an 8 m-class telescope) the coronagraph requires high starlight suppression at extremely-low inner working angles. Additionally, it must operate over a broad spectral bandwidth and under residual telescope vibrations. This allows for efficient use of spectroscopic post-processing techniques. We aim to find the global optimum of an integrated coronagraphic integral-field spectrograph. Methods. We present the Single-mode Complex Amplitude Refinement (SCAR) coronagraph that uses a microlens-fed single-mode fiber array in the focal plane downstream from a pupil-plane phase plate. The mode-filtering property of the single-mode fibers allows for the nulling of starlight on the fibers. The phase pattern in the pupil plane is specifically designed to take advantage of this mode-filtering capability. Second-order nulling on the fibers expands the spectral bandwidth and decreases the tip-tilt sensitivity of the coronagraph. Results. The SCAR coronagraph has a low inner working angle (∼1λ/D) at a contrast of < 3 × 10−5 for the six fibers surrounding the star using a sufficiently-good adaptive optics system. It can operate over broad spectral bandwidths (∼20%) and delivers high throughput (> 50% including fiber injection losses). Additionally, it is robust against tip-tilt errors (∼0.1λ/D rms). We present SCAR designs for both an unobstructed and a VLT-like pupil. Conclusions. The SCAR coronagraph is a promising candidate for exoplanet detection and characterization around nearby stars using current high-resolution imaging instruments.

scholarly journals Dust Around Young Stars: How Related to Solar System Dust?

1995 ◽  
Vol 10 ◽  
pp. 351-392 ◽  
Author(s):  
Martha S. Hanner
Keyword(s):  
Solar System ◽  
Interplanetary Space ◽  
Circumstellar Disks ◽  
Theoretical Work ◽  
Interplanetary Dust ◽  
Young Stars ◽  
Dust Particles ◽  
Interplanetary Dust Particles ◽  
Technical Advances ◽  
Dust Disks

Study of the dust in circumstellar disks around young stars is currently an extremely active area in astronomy. There is little doubt that accretion disks are a natural part of protostellar evolution. Much recent observational and theoretical work is giving us a clearer picture of the physical conditions in dust disks and their evolutionary progression. IRAS observations revealed that many main-sequence stars, such as p Pictoris, have circumstellar disks. But whether these disks are related to planetary formation is not yet understood.A portion of the dust in disks around young stars ultimately may be incorporated into planetary systems. Thus, study of the dust in our own solar system complements the remote sensing of protostellar regions and aids in reconstructing the evolutionary history of the dust. Since comets formed in the cold outer regions of the solar nebula, they may contain intact interstellar grains. As the comets lose material during passage through the warm inner solar system, some of these grains will be released into interplanetary space. Technical advances now allow analysis of individual micrometer or smaller grains in interplanetary dust particles and primitive meteorite samples. Isotopic anomalies and patterns of crystal growth in these particles are yielding tantalizing clues about the interstellar material incorporated into these solar system samples.

The early Solar System and the rotation of the Sun

1984 ◽  
Vol 313 (1524) ◽  
pp. 39-45 ◽  
Keyword(s):  
Angular Momentum ◽  
Solar System ◽  
Magnetic Coupling ◽  
Central Star ◽  
The Sun ◽  
Early Solar System ◽  
Low Mass Stars ◽  
Hydrogen Burning ◽  
Low Mass ◽  
Solid Bodies

In most discussions of the formation of the Solar System, the early Sun is assumed to have possessed the bulk of the angular momentum of the system, and a closely surrounding disc of gas was spun out, which, through magnetic coupling, acquired a progressively larger proportion of the total angular momentum. There are difficulties with this model in accounting for the inclined axis of the Sun, the magnitude of the magnetic coupling required, and the nucleogenetic variations recently observed in the Solar System. Another possibility exists, namely that of a slowly contracting disc of interstellar material, leading to the formation of both a central star and a protoplanetary disc. In this model one can better account for the tilt of the Sun’s axis and the lack of mixing necessary to account for the nucleogenetic evidence. The low angular momentum of the Sun and of other low mass stars is then seen as resulting from a slow build-up as a degenerate dwarf, acquiring orbital material at a low specific angular momentum. When the internal temperature reaches the threshold for hydrogen burning, the star expands to the Main Sequence and is now a slow rotator. More massive stars would spin quickly because they had to acquire orbiting material after the expansion, and therefore at a high specific angular momentum. A process of gradual inward spiralling may also allow materials derived from different sources to accumulate into solid bodies, and be placed on a great variety of orbits in the outer reaches of the system, setting up the cometary cloud of uneven nucleogenetic composition.

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