scholarly journals Fragmentation favoured in discs around higher mass stars

2020 ◽  
Vol 492 (4) ◽  
pp. 5041-5051 ◽  
Author(s):  
James Cadman ◽  
Ken Rice ◽  
Cassandra Hall ◽  
Thomas J Haworth ◽  
Beth Biller
Keyword(s):  
Gravitational Instability ◽  
High Mass ◽  
Low Mass Stars ◽  
Star Mass ◽  
Gravitational Instabilities ◽  
Mass Ratios ◽  
Particle Hydrodynamics ◽  
Low Mass ◽  
M Stars ◽  
Self Gravity

ABSTRACT We investigate how a protoplanetary disc’s susceptibility to gravitational instabilities and fragmentation depends on the mass of its host star. We use 1D disc models in conjunction with 3D smoothed particle hydrodynamics simulations to determine the critical disc-to-star mass ratios at which discs become unstable against fragmentation, finding that discs become increasingly prone to the effects of self-gravity as we increase the host star mass. The actual limit for stability is sensitive to the disc temperature, so if the disc is optically thin stellar irradiation can dramatically stabilize discs against gravitational instability. However, even when this is the case we find that discs around 2 M⊙ stars are prone to fragmentation, which will act to produce wide-orbit giant planets and brown dwarfs. The consequences of this work are twofold: that low-mass stars could in principle support high disc-to-star mass ratios, and that higher mass stars have discs that are more prone to fragmentation, which is qualitatively consistent with observations that favour high-mass wide-orbit planets around higher mass stars. We also find that the initial masses of these planets depends on the temperature in the disc at large radii, which itself depends on the level of stellar irradiation.

scholarly journals The Role of Discs in the Collapse and Fragmentation of Prestellar Cores

2016 ◽  
Vol 33 ◽  
Author(s):  
O. Lomax ◽  
A. P. Whitworth ◽  
D. A. Hubber
Keyword(s):  
Kinetic Energy ◽  
Smoothed Particle Hydrodynamics ◽  
Low Mass Stars ◽  
Gravitational Instabilities ◽  
Disc Material ◽  
Prestellar Cores ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Low Mass

AbstractDisc fragmentation provides an important mechanism for producing low-mass stars in prestellar cores. Here, we describe smoothed particle hydrodynamics simulations which show how populations of prestellar cores evolve into stars. We find the observed masses and multiplicities of stars can be recovered under certain conditions.First, protostellar feedback from a star must be episodic. The continuous accretion of disc material on to a central protostar results in local temperatures which are too high for disc fragmentation. If, however, the accretion occurs in intense outbursts, separated by a downtime of ~ 104yr, gravitational instabilities can develop and the disc can fragment.Second, a significant amount of the cores’ internal kinetic energy should be in solenoidal turbulent modes. Cores with less than a third of their kinetic energy in solenoidal modes have insufficient angular momentum to form fragmenting discs. In the absence of discs, cores can fragment but results in a top-heavy distribution of masses with very few low-mass objects.

scholarly journals Massive discs around low-mass stars

2020 ◽  
Vol 494 (3) ◽  
pp. 4130-4148 ◽  
Author(s):  
Thomas J Haworth ◽  
James Cadman ◽  
Farzana Meru ◽  
Cassandra Hall ◽  
Emma Albertini ◽  
...  
Keyword(s):  
Thermal Evolution ◽  
Solar Mass ◽  
Low Mass Stars ◽  
Star Mass ◽  
Smoothed Particle ◽  
Low Mass ◽  
Self Gravity ◽  
Stellar Masses ◽  
Smoothed Particle Hydrodynamic

ABSTRACT We use a suite of smoothed particle hydrodynamic simulations to investigate the susceptibility of protoplanetary discs to the effects of self-gravity as a function of star–disc properties. We also include passive irradiation from the host star using different models for the stellar luminosities. The critical disc-to-star mass ratio for axisymmetry (for which we produce criteria) increases significantly for low-mass stars. This could have important consequences for increasing the potential mass reservoir in a proto Trappist-1 system, since even the efficient Ormel et al. formation model will be influenced by processes like external photoevaporation, which can rapidly and dramatically deplete the dust reservoir. The aforementioned scaling of the critical Md/M* for axisymmetry occurs in part because the Toomre Q parameter has a linear dependence on surface density (which promotes instability) and only an $M_*^{1/2}$ dependence on shear (which reduces instability), but also occurs because, for a given Md/M*, the thermal evolution depends on the host star mass. The early phase stellar irradiation of the disc (for which the luminosity is much higher than at the zero age main sequence, particularly at low stellar masses) can also play a key role in significantly reducing the role of self-gravity, meaning that even solar mass stars could support axisymmetric discs a factor two higher in mass than usually considered possible. We apply our criteria to the DSHARP discs with spirals, finding that self-gravity can explain the observed spirals so long as the discs are optically thick to the host star irradiation.

scholarly journals Giant planets around AF and M stars

2013 ◽  
Vol 8 (S299) ◽  
pp. 64-65
Author(s):  
Julien Rameau ◽  
Gaël Chauvin ◽  
Anne-Marie Lagrange ◽  
Philippe Delorme ◽  
Justine Lannier
Keyword(s):  
Giant Planets ◽  
Early Type ◽  
Late Type ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Planetary Mass ◽  
Nearby Stars ◽  
Low Mass ◽  
M Stars ◽  
The One

AbstractWe present the results of two three-year surveys of young and nearby stars to search for wide orbit giant planets. On the one hand, we focus on early-type and massive, namely β Pictoris analogs. On the other hand, we observe late type and very low mass stars, i.e., M dwarfs. We report individual detections of new planetary mass objects. According to our deep detection performances, we derive the observed frequency of giant planets between these two classes of parent stars. We find frequency between 6 to 12% but we are not able to assess a/no correlation with the host-mass.

scholarly journals The CARMENES search for exoplanets around M dwarfs

2018 ◽  
Vol 620 ◽  
pp. A171 ◽  
Author(s):  
R. Luque ◽  
G. Nowak ◽  
E. Pallé ◽  
D. Kossakowski ◽  
T. Trifonov ◽  
...  
Keyword(s):  
Bimodal Distribution ◽  
Photometric Data ◽  
M Dwarfs ◽  
Visual Channel ◽  
Low Mass Stars ◽  
Short Period ◽  
Low Mass ◽  
Periodic Signals ◽  
M Stars ◽  
Host Stars

We announce the discovery of two planetary companions orbiting around the low-mass stars Ross 1020 (GJ 3779, M4.0V) and LP 819-052 (GJ 1265, M4.5V). The discovery is based on the analysis of CARMENES radial velocity (RV) observations in the visual channel as part of its survey for exoplanets around M dwarfs. In the case of GJ 1265, CARMENES observations were complemented with publicly available Doppler measurements from HARPS. The datasets reveal two planetary companions, one for each star, that share very similar properties: minimum masses of 8.0 ± 0.5 M⊕ and 7.4 ± 0.5 M⊕ in low-eccentricity orbits with periods of 3.023 ± 0.001 d and 3.651 ± 0.001 d for GJ 3779 b and GJ 1265 b, respectively. The periodic signals around 3 d found in the RV data have no counterpart in any spectral activity indicator. Furthermore, we collected available photometric data for the two host stars, which confirm that the additional Doppler variations found at periods of approximately 95 d can be attributed to the rotation of the stars. The addition of these planets to a mass-period diagram of known planets around M dwarfs suggests a bimodal distribution with a lack of short-period low-mass planets in the range of 2–5 M⊕. It also indicates that super-Earths (>5 M⊕) currently detected by RV and transit techniques around M stars are usually found in systems dominated by a single planet.

scholarly journals Very Low Mass Stars and Brown Dwarf Candidates in Orion OB1a and OB1b

2003 ◽  
Vol 211 ◽  
pp. 119-122
Author(s):  
Frederick M. Walter ◽  
William H. Sherry ◽  
Scott J. Wolk
Keyword(s):  
Ir Spectroscopy ◽  
Main Sequence ◽  
Brown Dwarf ◽  
Low Mass Stars ◽  
Space Density ◽  
Near Ir ◽  
Substellar Objects ◽  
Low Mass ◽  
M Stars

VRI images within the belt of Orion and the Ori OB1a association reveal a pre-main sequence locus extending to below our completeness limit of about V=21. We report here on followup JHK imaging and optical and near–IR spectroscopy of the faintest and reddest of the PMS candidates. We find that they are unreddened mid-to-late M “stars” which fall on a few million year isochrone. Masses are largely substellar, reaching as low as about 0.02 M⊙ (20 Jovian masses). The space density of the substellar objects is high.

scholarly journals What Causes the Low Binary Frequency in the Orion Nebula Cluster?

2004 ◽  
Vol 191 ◽  
pp. 104-108
Author(s):  
R. Köhler
Keyword(s):  
Statistical Significance ◽  
Formation Rate ◽  
High Mass ◽  
Cluster Center ◽  
Orion Nebula ◽  
Low Mass Stars ◽  
Cluster Radius ◽  
Companion Star ◽  
Binary Formation ◽  
Low Mass

AbstractWe report on the results of a binary survey in the outer parts of the Orion Nebula Cluster, 0.7 to 2 pc from the cluster center. The results should help to decide if the binary formation rate was lower in Orion than in Taurus-Auriga, or if many binaries formed initially, but were destroyed in close stellar encounters. We find that the binary frequency of low-mass stars does not depend on the distance to the cluster center. The companion star frequency of intermediate- to high-mass stars shows a trend to decrease with cluster radius, but the statistical significance of this trend is rather weak.

scholarly journals Fragmentation and dynamics in Massive Dense Cores in Cygnus-X

2010 ◽  
Vol 6 (S270) ◽  
pp. 53-56 ◽  
Author(s):  
T. Csengeri ◽  
S. Bontemps ◽  
N. Schneider ◽  
F. Motte
Keyword(s):  
Angular Resolution ◽  
High Density ◽  
High Mass ◽  
High Angular Resolution ◽  
Low Mass Stars ◽  
Dense Cores ◽  
Evolutionary Scenario ◽  
Low Mass ◽  
Molecular Tracers ◽  
Resolution Study

AbstractA systematic, high angular-resolution study of IR-quiet Massive Dense Cores (MDCs) of Cygnus-X in continuum and high-density molecular tracers is presented. The results are compared with the quasi-static and the dynamical evolutionary scenario. We find that the fragmentation properties are not compatible with the quasi-static, monolithic collapse scenario, nor are they entirely compatible with the formation of a cluster of mostly low-mass stars. The kinematics of MDCs shows individual velocity components appearing as coherent flows, which indicate important dynamical processes at the scale of the mass reservoir around high-mass protostars.

scholarly journals Search for radio jets from massive young stellar objects

2020 ◽  
Vol 645 ◽  
pp. A29
Author(s):  
Ü. Kavak ◽  
Á. Sánchez-Monge ◽  
A. López-Sepulcre ◽  
R. Cesaroni ◽  
F. F. S. van der Tak ◽  
...  
Keyword(s):  
Field Of View ◽  
Radio Continuum ◽  
High Mass ◽  
Mass Star ◽  
Low Mass Stars ◽  
Star Forming ◽  
Radio Jets ◽  
Star Forming Regions ◽  
Nonthermal Emission ◽  
Low Mass

Context. Recent theoretical and observational studies debate the similarities of the formation process of high- (>8 M⊙) and low-mass stars. The formation of low-mass stars is directly associated with the presence of disks and jets. Theoretical models predict that stars with masses up to 140 M⊙ can be formed through disk-mediated accretion in disk-jet systems. According to this scenario, radio jets are expected to be common in high-mass star-forming regions. Aims. We aim to increase the number of known radio jets in high-mass star-forming regions by searching for radio-jet candidates at radio continuum wavelengths. Methods. We used the Karl G. Jansky Very Large Array (VLA) to observe 18 high-mass star-forming regions in the C band (6 cm, ≈1′′.0 resolution) and K band (1.3 cm, ≈0′′.3 resolution). We searched for radio-jet candidates by studying the association of radio continuum sources with shock activity signs (e.g., molecular outflows, extended green objects, and maser emission). Our VLA observations also targeted the 22 GHz H2O and 6.7 GHz CH3OH maser lines. Results. We have identified 146 radio continuum sources, 40 of which are located within the field of view of both images (C and K band maps). We derived the spectral index, which is consistent with thermal emission (between − 0.1 and + 2.0) for 73% of these sources. Based on the association with shock-activity signs, we identified 28 radio-jet candidates. Out of these, we identified 7 as the most probable radio jets. The radio luminosity of the radio-jet candidates is correlated with the bolometric luminosity and the outflow momentum rate. About 7–36% of the radio-jet candidates are associated with nonthermal emission. The radio-jet candidates associated with 6.7 GHz CH3OH maser emission are preferentially thermal winds and jets, while a considerable fraction of radio-jet candidates associated with H2O masers show nonthermal emission that is likely due to strong shocks. Conclusions. About 60% of the radio continuum sources detected within the field of view of our VLA images are potential radio jets. The remaining sources could be compact H II regions in their early stages of development, or radio jets for which we currently lack further evidence of shock activity. Our sample of 18 regions is divided into 8 less evolved infrared-dark regions and 10 more evolved infrared-bright regions. We found that ≈71% of the identified radio-jet candidates are located in the more evolved regions. Similarly, 25% of the less evolved regions harbor one of the most probable radio jets, while up to 50% of the more evolved regions contain one of these radio-jet candidates. This suggests that the detection of radio jets in high-mass star-forming regions is more likely in slightly more evolved regions.

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

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.

scholarly journals The GAPS programme at TNG

2020 ◽  
Vol 642 ◽  
pp. A53
Author(s):  
C. Di Maio ◽  
C. Argiroffi ◽  
G. Micela ◽  
S. Benatti ◽  
A. F. Lanza ◽  
...  
Keyword(s):  
Magnetic Activity ◽  
Stellar Atmospheres ◽  
Activity Level ◽  
Mass Motion ◽  
Time Variability ◽  
Line Profiles ◽  
Low Mass Stars ◽  
Stellar Activity ◽  
Low Mass ◽  
M Stars

Context. Understanding stellar activity in M dwarfs is fundamental to improving our knowledge of the physics of stellar atmospheres and for planet search programmes. High levels of stellar activity (also frequently associated with flare events) can cause additional variations in the stellar emission that contaminate the signal induced by a planet and that need to be corrected. The study of activity indicators in active stars can improve our capability of modelling the signal generated by magnetic activity. Aims. In this work we present measurements of activity indicators at visible wavelength for a star with a high activity level, AD Leonis, observed with HARPS in 2006, and HARPS-N in 2018. Our aim is to understand the behaviour of stellar chromospheres of M stars, studying the more sensitive chromospheric activity indicators. We also focus on characterising their variability and on finding the correlations among these indicators to obtain information on the origin of the magnetic activity in low-mass stars. Methods. We performed a study of the main optical activity indicators (Ca II H&K, Balmer lines, Na I D1,2 doublet, He I D3, and other helium lines) measured for AD Leonis using the data provided by the HARPS-N high-resolution spectrograph at the Telescopio Nazionale Galileo in 2018, and by the HARPS instrument at La Silla observatory in 2006. Spectra were flux-calibrated in units of flux at the stellar surface. We measured excess flux of the selected activity indicators. The correlations between the different activity indicators as well as the temporal evolution of fluxes were analysed. A stellar flare was identified during the 2018 observing run and the Hα, Hβ, He I 4471 Å, and He I 5876 Å lines were analysed in detail by fitting the line profiles with two Gaussian components. Results. We found that the Ca II H&K flux excesses are strongly correlated with each other, but the Ca II H&K doublet is generally less correlated with the other indicators. Moreover, Hα is correlated with Na I doublet and helium lines. Analysing the time variability of flux of the studied lines, we found a higher level of activity of the star during the observations in 2018 than in 2006, while Ca II H&K showed more intense emission on spectra obtained during the observations in 2006. Thanks to a detailed analysis of selected line profiles, we investigated the flare evaluating the mass motion during the event.

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