| 1. |
- Dominguez, R., et al.
(författare)
-
Are hierarchically formed embedded star clusters surviving gas expulsion depending on their initial conditions?
- 2021
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 508:4, s. 5410-5424
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the dissolution process of young embedded star clusters with different primordial mass segregation levels using fractal distributions by means of N-body simulations. We combine several star clusters in virial and subvirial global states with Plummer and uniform density profiles to mimic the gas. The star clusters have masses of M-stars = 500 M-circle dot that follow an initial mass function where the stars have maximum distance from the centre of r = 1.5 pc. The clusters are placed in clouds that at the same radius have masses of M-cloud = 2000 M-circle dot, resulting in star formation efficiency of 0.2. We remove the background potential instantaneously at a very early phase, mimicking the most destructive scenario of gas expulsion. The evolution of the fraction of bound stellar mass is followed for a total of 16 Myr for simulations with stellar evolution and without. We compare our results with previous works using equal-mass particles where an analytical physical model was used to estimate the bound mass fraction after gas expulsion. We find that independent of the initial condition, the fraction of bound stellar mass can be well predicted just right after the gas expulsion but tends to be lower at later stages, as these systems evolve due to the stronger two-body interactions resulting from the inclusion of a realistic initial mass function. This discrepancy is independent of the primordial mass segregation level.
|
|
| 2. |
- Farias Osses, Juan Pablo, 1987, et al.
(författare)
-
Gas expulsion in highly substructured embedded star clusters
- 2018
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 476:4, s. 5341-5357
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the response of initially substructured, young, embedded star clusters to instantaneous gas expulsion of their natal gas. We introduce primordial substructure to the stars and the gas by simplistically modelling the star formation process so as to obtain a variety of substructure distributed within our modelled star-forming regions. We show that, by measuring the virial ratio of the stars alone (disregarding the gas completely), we can estimate how much mass a star cluster will retain after gas expulsion to within 10 per cent accuracy, no matter how complex the background structure of the gas is, and we present a simple analytical recipe describing this behaviour. We show that the evolution of the star cluster while still embedded in the natal gas, and the behaviour of the gas before being expelled, is crucial process that affect the time-scale on which the cluster can evolve into a virialized spherical system. Embedded star clusters that have high levels of substructure are subvirial for longer times, enabling them to survive gas expulsion better than a virialized and spherical system. By using a more realistic treatment for the background gas than our previous studies, we find it very difficult to destroy the young clusters with instantaneous gas expulsion. We conclude that gas removal may not be the main culprit for the dissolution of young star clusters.
|
|
| 3. |
- Farias Osses, Juan Pablo, 1987, et al.
(författare)
-
Hunting for Runaways from the Orion Nebula Cluster
- 2020
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 900:1
-
Tidskriftsartikel (refereegranskat)abstract
- We use Gaia DR2 to hunt for runaway stars from the Orion Nebula Cluster (ONC). We search a region extending 45 degrees around the ONC and out to 1 kpc to find sources that have overlapped in angular position with the cluster in the last similar to 10 Myr. We find similar to 17,000 runaway/walkaway candidates that satisfy this 2D traceback condition. Most of these are expected to be contaminants, e.g., caused by Galactic streaming motions of stars at different distances. We thus examine six further tests to help identify real runaways, namely: (1) possessing young stellar object (YSO) colors and magnitudes based on Gaia optical photometry; (2) having IR excess consistent with YSOs based on 2MASS and Wide-field Infrared Survey Explorer photometry; (3) having a high degree of optical variability; (4) having closest approach distances well-constrained to within the cluster half-mass radius; (5) having ejection directions that avoid the main Galactic streaming contamination zone; and (6) having a required radial velocity (RV) for 3D overlap of reasonable magnitude (or, for the 7% of candidates with measured RVs, satisfying 3D traceback). Thirteen sources, not previously noted as Orion members, pass all these tests, while another twelve are similarly promising, except they are in the main Galactic streaming contamination zone. Among these 25 ejection candidates, ten with measured RVs pass the most restrictive 3D traceback condition. We present full lists of runaway/walkaway candidates, estimate the high-velocity population ejected from the ONC, and discuss its implications for cluster formation theories via comparison with numerical simulations.
|
|
| 4. |
- Farias Osses, Juan Pablo, 1987, et al.
(författare)
-
On the formation of runaway stars BN and x in the Orion Nebula Cluster
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 612
-
Tidskriftsartikel (refereegranskat)abstract
- We explore scenarios for the dynamical ejection of stars BN and x from source I in the Kleinmann-Low nebula of the Orion Nebula Cluster (ONC), which is important because it is the closest region of massive star formation. This ejection would cause source I to become a close binary or a merger product of two stars. We thus consider binary-binary encounters as the mechanism to produce this event. By running a large suite of N-body simulations, we find that it is nearly impossible to match the observations when using the commonly adopted masses for the participants, especially a source I mass of 7 M-circle dot. The only way to recreate the event is if source I is more massive, that is, similar to 20 M-circle dot. However, even in this case, the likelihood of reproducing the observed system is low. We discuss the implications of these results for understanding this important star-forming region.
|
|
| 5. |
|
|
| 6. |
- Farias Osses, Juan Pablo, 1987, et al.
(författare)
-
Star cluster formation from turbulent clumps. II. Gradual star cluster formation
- 2019
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 483:4, s. 4999-5019
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the dynamical evolution of star clusters during their formation, assuming that they are born from a turbulent starless clump of a given mass that is embedded within a parent self-gravitating molecular cloud characterized by a particular mass surface density. In contrast to the standard practice of most N-body studies, we do not assume that all stars are formed at once. Rather, we explore the effects of different star formation rates on the global structure and evolution of young embedded star clusters, also considering various primordial binary fractions and mass segregation levels. Our fiducial clumps studied in this paper have initial masses of M cl = 3000M ⊙ , are embedded in ambient cloud environments of σ cloud = 0.1 and 1 g cm -2 , and gradually form stars with an overall efficiency of 50 per cent until the gas is exhausted. We investigate star formation efficiencies per free-fall time in the range ϵ ff = 0.01-1, and also compare to the instantaneous case (ϵ ff = α) of Paper I. We show that most of the interesting dynamical processes that determine the future of the cluster, happen during the early formation phase. In particular, the ejected stellar population is sensitive to the duration of star cluster formation: for example, clusters with longer formation times produce more runaway stars, since these clusters remain in a dense state for longer, thus favouring occurrence of dynamical ejections. We also show that the presence of radial age gradients in star clusters depends sensitively on the star formation efficiency per free-fall time, with observed values being matched best by our slowest forming clusters with ϵ ff ≲0.03.
|
|
| 7. |
- Farias Osses, Juan Pablo, 1987, et al.
(författare)
-
Star cluster formation from turbulent clumps – III. Across the mass spectrum
- 2023
-
Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 523:2, s. 2083-2110
-
Tidskriftsartikel (refereegranskat)abstract
- We study the formation and early evolution of star clusters that have a wide range of masses and background cloud mass surface densities, ∑cloud, which help set the initial sizes, densities, and velocity dispersions of the natal gas clumps. Initial clump masses of 300, 3000, and 30 000 M☉ are considered, from which star clusters are born with an assumed 50 per cent overall star formation efficiency and with 50 per cent primordial binarity. This formation is gradual, i.e. with a range of star formation efficiencies per free-fall time from 1 to 100 per cent, so that the formation time can range from 0.7 Myr for low-mass, high-∑cloud clumps to ∼30 Myr for high-mass, low-∑cloud clumps. Within this framework of the turbulent clump model, for a given ∑cloud, clumps of higher mass are of lower initial volume density, but their dynamical evolution leads to higher bound fractions and causes them to form much higher density cluster cores and maintain these densities for longer periods. This results in systematic differences in the evolution of binary properties, degrees of mass segregation, and rates of creation of dynamically ejected runaways. We discuss the implications of these results for observed star clusters and stellar populations.
|
|
| 8. |
- Farias Osses, Juan Pablo, 1987
(författare)
-
Th Dynamics of Star Cluster Formation
- 2018
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A major question in astrophysics is how star clusters form. These objects are important, since they are the birth sites of most stars, perhaps including our own Sun. There are different theoretical models of cluster formation and our main goal is to examine how they may affect the dynamical evolution of the stars in the system, including those stars that are ejected from the cluster. In particular, we set up cluster formation models with global initial conditions of the Turbulent Clump Model, which has been proposed as a description of gas structures within molecular clouds. We then investigate how global star formation efficiency from such a natal gas clump, overall clump density, degree of primordial mass segregation, degree of primordial binarity and binary population properties affect the subsequent dynamical evolution. In a second paper, after a major code development that allows modeling of gradual star formation, we investigate how the rate of star cluster formation affects its dynamical evolution, which is the first time such a study has been conducted for realistic clusters that have realistic binary properties. We show througth this thesis that star clusters that formed fast, i.e., during about one free-fall time, show quite different properties than star clusters that forms in a slow quasi-equilibirum fashion. Quickly-formed clusters tend to expand much faster compared to slow-formed clusters, thus requiring higher initial densities to agree with observations. Creation of the runaway stellar population is also sensitive to the rate of cluster formation. Future directions of this work, adding greater degrees of realism are also discussed. Finally, we carry out an example study of how the observed properties of a particular set of runaway stars can constrain properties of the dynamical ejection event, with implications for the closest region of massive star formation in the Orion Nebula Cluster.
|
|
| 9. |
- Farias Osses, Juan Pablo, 1987
(författare)
-
The Dynamics of Star Cluster Formation
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- How do star clusters form? We care, since these are the birth sites of most stars, perhaps including our own Sun. There are a great variety of different theoretical models of cluster formation and our main goal in this thesis is to examine the implications of these for the dynamical evolution of a cluster's stellar population, including the ejected stars. In contrast to the majority of previous cluster formation studies, the focus of this work is on detailed modeling, using the Nbody6 code, of stellar dynamics, including binaries, with the structure, kinematics and star formation of the natal gas cloud explored with simple analytic prescriptions. In particular, we adopt the Turbulent Clump Model of pressure-truncated singular polytropic spheres, which sets global and local initial conditions of the newly formed stars. In a first paper, exploring a fiducial 3,000 solar mass clump, we investigated the effects of overall clump density, global star formation efficiency, degree of primordial mass segregation, degree of primordial binarity and binary population properties on the dynamical evolution of the cluster. Here, like most previous works, we assumed stars are formed very quickly, i.e., approximated as instantaneously, compared to the free-fall time of the clump. In our next work, after implementing a major code development to Nbody6 that allows modeling of gradual formation of stars, we investigated how the timescale of cluster formation, parameterized via the star formation efficiency per free-fall time, affects its early dynamical evolution. This is the first time that such a study, including a realistic binary population, has been carried out. We showed that star clusters that form rapidly expand more quickly after they emerge from the gas, while slowly-formed clusters evolve into a much more stable configuration during the gas rich phase. We also showed how the stellar population is affected by the timescale of formation, including the frequency of runaway/walkaway stars, stellar age gradients and primordial binary processing. We have then carried out preliminary explorations of a broad range of star-forming clump parameters, i.e., with masses from 300 to 30,000 solar masses and background cloud mass surface densities from 0.1 to 1 g cm². For the largest clusters simulated, we make use of a GPU-enabled version of the code. Further improvements to the modeling that have been implemented include global elongation of the clump so that nonspherical, including very filamentary, initial conditions can be studied. Models with internal spatial and kinematic substructure for the birth locations of the stars, based on hydrodynamic simulations of supersonic turbulence, have also been studied. In parallel, we have also carried out two projects that focus on observed systems related to dynamical ejections within the Orion Nebula Cluster (ONC). First, we examined a particular set of runaway stars associated with the Orion KL massive star forming region and carried out a systematic exploration of N-body simulations to understand the properties of the dynamical ejection that produced them. Second, we have performed a census of runaway stars from the ONC using Gaia data, estimating the total unbound population from the cluster. We have compared these results with our cluster formation simulations leading to new constraints on the star formation rate and dynamical age of the system.
|
|
| 10. |
- Fedriani, Rubén, 1991, et al.
(författare)
-
The SOFIA Massive (SOMA) Star Formation Survey. IV. Isolated Protostars
- 2023
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 942:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present similar to 10-40 mu m SOFIA-FORCAST images of 11 isolated protostars as part of the SOFIA Massive (SOMA) Star Formation Survey, with this morphological classification based on 37 mu m imaging. We develop an automated method to define source aperture size using the gradient of its background-subtracted enclosed flux and apply this to build spectral energy distributions (SEDs). We fit the SEDs with radiative transfer models, developed within the framework of turbulent core accretion (TCA) theory, to estimate key protostellar properties. Here, we release the sedcreator python package that carries out these methods. The SEDs are generally well fitted by the TCA models, from which we infer initial core masses M ( c ) ranging from 20-430 M (circle dot), clump mass surface densities sigma(cl) similar to 0.3-1.7 g cm(-2), and current protostellar masses m (*) similar to 3-50 M (circle dot). From a uniform analysis of the 40 sources in the full SOMA survey to date, we find that massive protostars form across a wide range of clump mass surface density environments, placing constraints on theories that predict a minimum threshold sigma(cl) for massive star formation. However, the upper end of the m (*)-sigma(cl) distribution follows trends predicted by models of internal protostellar feedback that find greater star formation efficiency in higher sigma(cl) conditions. We also investigate protostellar far-IR variability by comparison with IRAS data, finding no significant variation over an similar to 40 yr baseline.
|
|
| 11. |
- Moser, Emily, et al.
(författare)
-
The High-mass Protostellar Population of a Massive Infrared Dark Cloud
- 2020
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 897:2
-
Tidskriftsartikel (refereegranskat)abstract
- We conduct a census of the high-mass protostellar population of the similar to 70,000Minfrared dark cloud (IRDC) G028.37+00.07, identifying 35 sources based on their 70 mu m emission, as reported in the Herschel Hi-GAL catalog of Molinari et al. We perform aperture photometry to construct spectral energy distributions, which are then fit with the massive protostar models of Zhang & Tan. We find that the sources span a range of isotropic luminosities from similar to 20 to 4500L. The most luminous sources are predicted to have current protostellar masses ofm(*) similar to 10Mforming from cores of massM(c) similar to 40 to 400M. The least luminous sources in our sample are predicted to be protostars with masses as low as similar to 0.5Mforming from cores withM(c) similar to 10M, which are the minimum values explored in the protostellar model grid. The detected protostellar population has a total estimated protostellar mass ofM(*) similar to 100M. Allowing for completeness corrections, which are constrained by comparison with an ALMA study in part of the cloud, we estimate a star formation efficiency per freefall time of similar to 3% in the IRDC. Finally, analyzing the spatial distribution of the sources, we find relatively low degrees of central concentration of the protostars. The protostars, including the most massive ones, do not appear to be especially centrally concentrated in the protocluster as defined by the IRDC boundary.
|
|
