scholarly journals Imaging the water snowline in a protostellar envelope with H13CO+

2018 ◽  
Vol 613 ◽  
pp. A29 ◽  
Author(s):  
Merel L. R. van ’t Hoff ◽  
Magnus V. Persson ◽  
Daniel Harsono ◽  
Vianney Taquet ◽  
Jes K. Jørgensen ◽  
...  
Keyword(s):  
Central Star ◽  
Temperature Structure ◽  
Chemical Modeling ◽  
Emission Profile ◽  
Chemical Tracer ◽  
Close Proximity ◽  
Low Mass ◽  
Abundance Profile ◽  
Spherical Envelope ◽  
Good Tracer

Context. Snowlines are key ingredients for planet formation. Providing observational constraints on the locations of the major snowlines is therefore crucial for fully connecting planet compositions to their formation mechanism. Unfortunately, the most important snowline, that of water, is very difficult to observe directly in protoplanetary disks because of the close proximity of this snowline to the central star. Aims. Based on chemical considerations, HCO+ is predicted to be a good chemical tracer of the water snowline because it is particularly abundant in dense clouds when water is frozen out. This work aims to map the optically thin isotopolog H13CO+ toward the envelope of the low-mass protostar NGC 1333-IRAS2A, where the snowline is at a greater distance from the star than in disks. Comparison with previous observations of H218O show whether H13CO+ is indeed a good tracer of the water snowline. Methods. NGC 1333-IRAS2A was observed using the NOrthern Extended Millimeter Array (NOEMA) at ~0.′′9 resolution, targeting the H13CO+ J = 3 − 2 transition at 260.255 GHz. The integrated emission profile was analyzed using 1D radiative transfer modeling of a spherical envelope with a parametrized abundance profile for H13CO+. This profile was validated with a full chemical model. Results. The H13CO+ emission peaks ~ 2′′ northeast of the continuum peak, whereas H218O shows compact emission on source. Quantitative modeling shows that a decrease in H13CO+ abundance by at least a factor of six is needed in the inner ~360 AU to reproduce the observed emission profile. Chemical modeling indeed predicts a steep increase in HCO+ just outside the water snowline; the 50% decrease in gaseous H2O at the snowline is not enough to allow HCO+ to be abundant. This places the water snowline at 225 AU, further away from the star than expected based on the 1D envelope temperature structure for NGC 1333-IRAS2A. In contrast, DCO+ observations show that the CO snowline is at the expected location, making an outburst scenario unlikely. Conclusions. The spatial anticorrelation of H13CO+ and H218O emission provide proof of concept that H13CO+ can be used as a tracer of the water snowline.

scholarly journals Characterization of low-mass companion HD 142527 B

2018 ◽  
Vol 617 ◽  
pp. A37 ◽  
Author(s):  
V. Christiaens ◽  
S. Casassus ◽  
O. Absil ◽  
S. Kimeswenger ◽  
C. A. Gomez Gonzalez ◽  
...  
Keyword(s):  
Central Star ◽  
Primary Star ◽  
Dust Trap ◽  
Stellar Radius ◽  
Link Type ◽  
Hot Environment ◽  
T Tauri ◽  
Annular Gap ◽  
Medium Resolution ◽  
Low Mass

Context. The circumstellar disk of the Herbig Fe star HD 142527 is host to several remarkable features including a warped inner disk, a 120 au-wide annular gap, a prominent dust trap and several spiral arms. A low-mass companion, HD 142527 B, was also found orbiting the primary star at ~14 au. Aims. This study aims to better characterize this companion, which could help explain its impact on the peculiar geometry of the disk. Method. We observed the source with VLT/SINFONI in H + K band in pupil-tracking mode. Data were post-processed with several algorithms based on angular differential imaging (ADI). Results. HD 142527 B is conspicuously re-detected in most spectral channels, which enables us to extract the first medium-resolution spectrum of a low-mass companion within 0.″1 from its central star. Fitting our spectrum with both template and synthetic spectra suggests that the companion is a young M2.5 ± 1.0 star with an effective temperature of 3500 ± 100 K, possibly surrounded with a hot (1700 K) circum-secondary environment. Pre-main sequence evolutionary tracks provide a mass estimate of 0.34 ± 0.06 M⊙, independent of the presence of a hot environment. However, the estimated stellar radius and age do depend on that assumption; we find a radius of 1.37 ± 0.05 R⊙ (resp. 1.96 ± 0.10 R⊙) and an age of 1.8-0.5+1.2 Myr (resp. 0.75 ± 0.25 Myr) in the case of the presence (resp. absence) of a hot environment contributing in H + K. Our new values for the mass and radius of the companion yield a mass accretion rate of 4.1–5.8 × 10−9 M⊙ yr−1 (2–3% that of the primary). Conclusions. We have constrained the physical properties of HD 142527 B, thereby illustrating the potential for SINFONI+ADI to characterize faint close-in companions. The new spectral type makes HD 142527 B a twin of the well-known TW Hya T Tauri star, and the revision of its mass to higher values further supports its role in shaping the disk.

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.

scholarly journals Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Doradus

2018 ◽  
Vol 609 ◽  
pp. A63 ◽  
Author(s):  
M. Van de Sande ◽  
L. Decin ◽  
R. Lombaert ◽  
T. Khouri ◽  
A. de Koter ◽  
...  
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Central Star ◽  
High Mass ◽  
Circumstellar Envelope ◽  
Gaussian Profile ◽  
Macro Scale ◽  
Abundance Profile ◽  
Envelope Model

Context. The stellar outflows of low- to intermediate-mass stars are characterised by a rich chemistry. Condensation of molecular gas species into dust grains is a key component in a chain of physical processes that leads to the onset of a stellar wind. In order to improve our understanding of the coupling between the micro-scale chemistry and macro-scale dynamics, we need to retrieve the abundance of molecules throughout the outflow. Aims. Our aim is to determine the radial abundance profile of SiO and HCN throughout the stellar outflow of R Dor, an oxygen-rich AGB star with a low mass-loss rate. SiO is thought to play an essential role in the dust-formation process of oxygen-rich AGB stars. The presence of HCN in an oxygen-rich environment is thought to be due to non-equilibrium chemistry in the inner wind. Methods. We analysed molecular transitions of CO, SiO, and HCN measured with the APEX telescope and all three instruments on the Herschel Space Observatory, together with data available in the literature. Photometric data and the infrared spectrum measured by ISO-SWS were used to constrain the dust component of the outflow. Using both continuum and line radiative transfer methods, a physical envelope model of both gas and dust was established. We performed an analysis of the SiO and HCN molecular transitions in order to calculate their abundances. Results. We have obtained an envelope model that describes the dust and the gas in the outflow, and determined the abundance of SiO and HCN throughout the region of the stellar outflow probed by our molecular data. For SiO, we find that the initial abundance lies between 5.5 × 10-5 and 6.0 × 10-5 with respect to H2. The abundance profile is constant up to 60 ± 10 R∗, after which it declines following a Gaussian profile with an e-folding radius of 3.5 ± 0.5 × 1013 cm or 1.4 ± 0.2 R∗. For HCN, we find an initial abundance of 5.0 × 10-7 with respect to H2. The Gaussian profile that describes the decline starts at the stellar surface and has an e-folding radius re of 1.85 ± 0.05 × 1015 cm or 74 ± 2 R∗. Conclusions. We cannot unambiguously identify the mechanism by which SiO is destroyed at 60 ± 10 R∗. The initial abundances found are higher than previously determined (except for one previous study on SiO), which might be due to the inclusion of higher-J transitions. The difference in abundance for SiO and HCN compared to high mass-loss rate Mira star IK Tau might be due to different pulsation characteristics of the central star and/or a difference in dust condensation physics.

scholarly journals Radio Measurements of Possible Proto-Planetary Nebulae

1978 ◽  
Vol 76 ◽  
pp. 325-325
Author(s):  
C.R. Purton ◽  
P.A. Feldman
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Radio Spectrum ◽  
Ionized Gas ◽  
Mass Outflow ◽  
Calculated Mass ◽  
Low Mass ◽  
Spectrum Characteristic ◽  
Radio Measurements ◽  
Continuum Radio

A number of objects which may be proto-planetary nebulae are being studied. They were found through a radio search of early-type emission-line stars, and the radio emission is believed to originate in extensive circumstellar ionised gas. The objects have an infrared spectrum which indicates the presence of dust, and a continuum radio spectrum characteristic of prolonged mass outflow from the central star. Of the five objects discussed here, Vy2-2, Hbl2, HD167362, Hl-36 and V1016 Cygni, a distance is available for only the last: for that object the calculated mass of the ionized gas is 0.02 M0 (see Ahem et al, 1977). If this is typical of the five, then they may represent the early stages of the low-mass planetary nebulae discussed by Wood and Cahn (1977). References: (1) Ahern, F.A., Fitzgerald, P.M., Marsh, K.A., and Purton, C.R. 1977, Astron, & Astrophys., in press. (2) Wood, P.R., and Cahn, J.H. 1977, Astrophys. J. 211, 499.

scholarly journals Ejection of close-in super-Earths around low-mass stars in the giant impact stage

2020 ◽  
Vol 642 ◽  
pp. A23
Author(s):  
Yuji Matsumoto ◽  
Pin-Gao Gu ◽  
Eiichiro Kokubo ◽  
Shoichi Oshino ◽  
Masashi Omiya
Keyword(s):  
Surface Density ◽  
Dynamical Evolution ◽  
Central Star ◽  
Stellar Mass ◽  
Mass Relation ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Giant Impact ◽  
Low Mass ◽  
Strong Scattering

Context. Earth-sized planets were observed in close-in orbits around M dwarfs. While more and more planets are expected to be uncovered around M dwarfs, theories of their formation and dynamical evolution are still in their infancy. Aims. We investigate the giant impact stage for the growth of protoplanets, which includes strong scattering around low-mass stars. The aim is to clarify whether strong scattering around low-mass stars affects the orbital and mass distributions of the planets. Methods. We performed an N-body simulation of protoplanets by systematically surveying the parameter space of the stellar mass and surface density of protoplanets. Results. We find that protoplanets are often ejected after twice or three times the close-scattering around late M dwarfs. The ejection sets the upper limit of the largest planet mass. By adopting the surface density that linearly scales with the stellar mass, we find that as the stellar mass decreases, less massive planets are formed in orbits with higher eccentricities and inclinations. Under this scaling, we also find that a few close-in protoplanets are generally ejected. Conclusions. The ejection of protoplanets plays an important role in the mass distribution of super-Earths around late M dwarfs. The mass relation of observed close-in super-Earths and their central star mass is reproduced well by ejection.

Isolated dwarf galaxies in the Local Group

2018 ◽  
Vol 14 (S344) ◽  
pp. 81-85
Author(s):  
Clare R. Higgs ◽  
Alan W. McConnachie ◽  
Keyword(s):  
Globular Clusters ◽  
Local Group ◽  
Dwarf Galaxy ◽  
Apparent Size ◽  
Stellar Structure ◽  
Star Formation History ◽  
Wide Field ◽  
Formation History ◽  
Close Proximity ◽  
Low Mass

AbstractThe Solo (Solitary local) Dwarf Galaxy Survey is a volume limited sample of all nearby (< 3 Mpc) and isolated (> 300 kpc from the Milky Way or M31) dwarfs, with wide-field g and i imaging. This survey uses resolved stellar populations to parameterize these low mass systems. Comparison to the well studied satellite dwarfs characterizes the evolutionary impact of a large galaxy in close proximity. The deep, wide field nature of this survey also lends itself to searching for nearby substructures, both globular clusters and possible faint satellites.Current work is focused on the 16 closest Solo dwarfs, all within the virial radius (approximately 1 Mpc) of the Local Group. This subset has been characterized using consistent methods, despite their diversity in stellar mass and apparent size. The analysis highlights the extended stellar structure and morphology. We will examine trends with star formation history, and separation from a large host. This first subset emphasizes the survey’s unique challenges and advantages.The Solo Survey provides detailed look at the extended structure of dwarfs and characterizes the evolution of galaxies in the faint limit.

scholarly journals Jets in Molecular Clouds

1984 ◽  
Vol 110 ◽  
pp. 299-301
Author(s):  
Arieh Königl
Keyword(s):  
Molecular Clouds ◽  
Direct Evidence ◽  
Optical Emission ◽  
Central Star ◽  
Radio Continuum ◽  
Low Mass Stars ◽  
General Direction ◽  
Low Mass ◽  
Motion Measurements ◽  
Infrared Sources

There is now growing evidence that the cosmic jet phenomenon manifests itself in a remarkable way in regions of active star formation embedded in dense molecular clouds. The first indications for oppositely directed, supersonic outflows from young stars were provided by molecular line observations (most notably of CO) which detected spatially separated regions of redshifted and blueshifted emission in association with embedded infrared sources. About twenty sources of this kind have been identified so far, and more are continuously being discovered; they typically have radii ∼1018 cm, velocities ∼10–50 km s−1, dynamical ages ∼104 yr, and energies ∼1046-1047 erg s−1 (see Bally and Lada 1983 for a review). Statistical arguments indicate that energetic outflows of this type are probably a common feature in stellar evolution, and that they occur in both massive and low-mass stars. Direct evidence that the outflows in many cases are highly collimated was subsequently provided by the detection of high-velocity Herbig-Haro objects (optical emission clumps with typical masses ∼10−5M⊙) along the axes of the bipolar CO lobes. Proper-motion measurements are now available for a number of these objects (e.g., Herbig and Jones 1981), and they invariably reveal that the velocity vectors (of typical magnitudes 200–400 km s−1) point away from the central star. The clumps are often found to consist of many sub-condensations which move independently with disparate speeds, but which nevertheless travel in the same general direction with an angular spread ≲ 10°. Finally, radio continuum observations (e.g., Cohen et al. 1982) and deep CCD images (e.g., Mundt and Fried 1983) have shown that the collimation of the outflows is already well established on scales of ≲ 1015 cm.

scholarly journals Migrating low-mass planets in inviscid dusty protoplanetary discs

2020 ◽  
Vol 497 (2) ◽  
pp. 2425-2441
Author(s):  
He-Feng Hsieh ◽  
Min-Kai Lin
Keyword(s):  
Central Star ◽  
Small Scale ◽  
Dust Trapping ◽  
Drag Forces ◽  
Planetary Cores ◽  
Planet Migration ◽  
Low Mass ◽  
Future Work ◽  
Gas Drag ◽  
Protoplanetary Discs

ABSTRACT Disc-driven planet migration is integral to the formation of planetary systems. In standard, gas-dominated protoplanetary discs, low-mass planets or planetary cores undergo rapid inwards migration and are lost to the central star. However, several recent studies indicate that the solid component in protoplanetary discs can have a significant dynamical effect on disc–planet interaction, especially when the solid-to-gas mass ratio approaches unity or larger and the dust-on-gas drag forces become significant. As there are several ways to raise the solid abundance in protoplanetary discs, for example through disc winds and dust trapping in pressure bumps, it is important to understand how planets migrate through a dusty environment. To this end, we study planet migration in dust-rich discs via a systematic set of high-resolution, two-dimensional numerical simulations. We show that the inwards migration of low-mass planets can be slowed down by dusty dynamical corotation torques. We also identify a new regime of stochastic migration applicable to discs with dust-to-gas mass ratios of ≳0.3 and particle Stokes numbers ≳0.03. In these cases, disc–planet interaction leads to the continuous development of small-scale, intense dust vortices that scatter the planet, which can potentially halt or even reverse the inwards planet migration. We briefly discuss the observational implications of our results and highlight directions for future work.

scholarly journals 3D AMR simulations of G2 as an outflow

2016 ◽  
Vol 11 (S322) ◽  
pp. 243-244
Author(s):  
A. Ballone ◽  
M. Schartmann ◽  
A. Burkert ◽  
S. Gillessen ◽  
P.M. Plewa ◽  
...  
Keyword(s):  
Hydrodynamic Interaction ◽  
Central Star ◽  
Compact Source ◽  
Accretion Flow ◽  
Low Mass

AbstractWe study the evolution of G2 in a Compact Source Scenario, where G2 is the outflow from a low-mass central star moving on the observed orbit. This is done through 3D AMR simulations of the hydrodynamic interaction of G2 with the surrounding hot accretion flow. A comparison with observations is done by means of mock position-velocity (PV) diagrams. We found that a massive (Ṁw = 5× 10−7M⊙ yr−1) and slow (vw = 50 km s−1) outflow can reproduce G2’s properties. A faster outflow (vw = 400 km s−1) might also be able to explain the material that seems to follow G2 on the same orbit.

scholarly journals The post-common-envelope binary central star of the planetary nebula PN G283.7−05.1

2020 ◽  
Vol 642 ◽  
pp. A108 ◽  
Author(s):  
D. Jones ◽  
H. M. J. Boffin ◽  
J. Hibbert ◽  
T. Steinmetz ◽  
R. Wesson ◽  
...  
Keyword(s):  
Planetary Nebula ◽  
Main Sequence ◽  
Planetary Nebulae ◽  
Central Star ◽  
Radial Velocity Curve ◽  
Common Envelope ◽  
Low Mass ◽  
Red Giant ◽  
Model Temperature ◽  
Temperature Surface

We present the discovery and characterisation of the post-common-envelope central star system in the planetary nebula PN G283.7−05.1. Deep images taken as part of the POPIPlaN survey indicate that the nebula may possess a bipolar morphology similar to other post-common-envelope planetary nebulae. Simultaneous light and radial velocity curve modelling reveals that the newly discovered binary system comprises a highly irradiated M-type main-sequence star in a 5.9-hour orbit with a hot pre-white dwarf. The nebular progenitor is found to have a particularly low mass of around 0.4 M⊙, making PN G283.7−05.1 one of only a handful of candidate planetary nebulae that is the product of a common-envelope event while still on the red giant branch. In addition to its low mass, the model temperature, surface gravity, and luminosity are all found to be consistent with the observed stellar and nebular spectra through comparison with model atmospheres and photoionisation modelling. However, the high temperature (Teff ∼ 95 kK) and high luminosity of the central star of the nebula are not consistent with post-RGB evolutionary tracks.

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