scholarly journals Structure, kinematics, and ages of the young stellar populations in the Orion region

2019 ◽  
Vol 628 ◽  
pp. A123 ◽  
Author(s):  
E. Zari ◽  
A. G. A. Brown ◽  
P. T. de Zeeuw
Keyword(s):  
Star Formation ◽  
Clustering Algorithm ◽  
Age Distribution ◽  
Three Dimensional ◽  
Star Formation History ◽  
Dimensional Structure ◽  
Mean Velocity ◽  
Fitting Procedure ◽  
Sequence Of Events ◽  
Kinematic Modelling

We present a study of the three dimensional structure, kinematics, and age distribution of the Orion OB association, based on the second data release of the Gaia satellite (Gaia DR2). Our goal is to obtain a complete picture of the star formation history of the Orion complex and to relate our findings to theories of sequential and triggered star formation. We selected the Orion population with simple photometric criteria, and we constructed a three dimensional map in galactic Cartesian co-ordinates to study the physical arrangement of the stellar clusters in the Orion region. The map shows structures that extend for roughly 150 pc along the line of sight, divided in multiple sub-clusters. We separated different groups by using the density-based clustering algorithm DBSCAN. We studied the kinematic properties of all the groups found by DBSCAN first by inspecting their proper motion distribution, and then by applying a kinematic modelling code based on an iterative maximum likelihood approach, which we used to derive their mean velocity, velocity dispersion, and isotropic expansion. We derived ages and extinction values for all the groups by using an isochrone fitting procedure. We confirm the presence of an old population (∼15 Myr) towards the 25 Ori region, and we find that groups with ages of 12 − 15 Myr are present also towards the Belt region. We notice the presence of a population of ∼10 Myr also in front of the Orion A molecular cloud. Our findings suggest that star formation in Orion does not follow a simple sequential scenario, but instead consists of multiple events, which caused kinematic and physical sub-structure. To fully explain the detailed sequence of events, specific simulations and further radial velocity data are needed.

scholarly journals The Gaia-ESO Survey: Age spread in the star forming region NGC 6530 from the HR diagram and gravity indicators

2019 ◽  
Vol 623 ◽  
pp. A159 ◽  
Author(s):  
L. Prisinzano ◽  
F. Damiani ◽  
V. Kalari ◽  
R. Jeffries ◽  
R. Bonito ◽  
...  
Keyword(s):  
Star Formation ◽  
Cluster Formation ◽  
Age Distribution ◽  
T Tauri Stars ◽  
Star Formation History ◽  
Dimensional Structure ◽  
Cluster Membership ◽  
T Tauri ◽  
Stellar Ages ◽  
Fundamental Stellar Parameters

Context. In very young clusters, stellar age distribution is empirical proof of the duration of star cluster formation and thus it gives indications of the physical mechanisms involved in the star formation process. Determining the amount of interstellar extinction and the correct reddening law are crucial steps to derive fundamental stellar parameters and in particular accurate ages from the Hertzsprung-Russell diagram. Aims. In this context, we seek to derive accurate stellar ages for NGC 6530, the young cluster associated with the Lagoon Nebula to infer the star formation history of this region. Methods. We used the Gaia-ESO survey observations of the Lagoon Nebula, together with photometric literature data and Gaia DR2 kinematics, to derive cluster membership and fundamental stellar parameters. Using spectroscopic effective temperatures, we analysed the reddening properties of all objects and derived accurate stellar ages for cluster members. Results. We identified 652 confirmed and 9 probable members. The reddening inferred for members and non-members allows us to distinguish foreground objects, mainly main-sequence stars, and background objects, mainly giants, and to trace the three-dimensional structure of the nebula. This classification is in agreement with the distances inferred from Gaia DR2 parallaxes for these objects. Finally, we derive stellar ages for 382 confirmed cluster members for which we obtained the individual reddening values. In addition, we find that the gravity-sensitive γ index distribution for the M-type stars is correlated with stellar age. Conclusions. For all members with Teff <  5500 K, the mean logarithmic age is 5.84 (units of years) with a dispersion of 0.36 dex. The age distribution of stars with accretion or discs, i.e. classical T Tauri stars with excess (CTTSe), is similar to that of stars without accretion and without discs, i.e. weak T Tauri stars with photospheric emission (WTTSp). We interpret this dispersion as evidence of a real age spread since the total uncertainties on age determinations, derived from Monte Carlo simulations, are significantly smaller than the observed spread. This conclusion is supported by evidence of the decrease of the gravity-sensitive γ index as a function of stellar ages. The presence of a small age spread is also supported by the spatial distribution and kinematics of old and young members. In particular, members with accretion or discs, formed in the last 1 Myr, show evidence of subclustering around the cluster centre, in the Hourglass Nebula and in the M8-E region, suggesting a possible triggering of star formation events by the O-type star ionization fronts.

scholarly journals A new look at Sco OB1 association with Gaia DR2

2020 ◽  
Vol 495 (1) ◽  
pp. 1349-1359 ◽  
Author(s):  
L Yalyalieva ◽  
G Carraro ◽  
R Vazquez ◽  
L Rizzo ◽  
E Glushkova ◽  
...  
Keyword(s):  
Open Cluster ◽  
Three Dimensional ◽  
Star Formation History ◽  
Optical Data ◽  
Dimensional Structure ◽  
Fundamental Parameters ◽  
Time Estimates ◽  
Young Open Cluster ◽  
Pms Stars ◽  
Gaia Dr2

ABSTRACT We present and discuss photometric optical data in the area of the OB association Sco OB1 covering about 1 deg2. UBVI photometry is employed in tandem with Gaia DR2 data to investigate the three-dimensional structure and the star formation history of the region. By combining parallaxes and proper motions, we identify seven physical groups located between the young open cluster NGC 6231 and the bright nebula IC 4628. The most prominent group coincides with the sparse open cluster Trumpler 24. We confirm the presence of the intermediate-age star cluster VdB-Hagen 202, which is unexpected in this environment, and provide for the first time estimates of its fundamental parameters. After assessing individual groups membership, we derive mean proper motion components, distances, and ages. The seven groups belong to two different families. To the younger family (family I) belong several pre-main-sequence (PMS) stars as well. These are evenly spread across the field, and also in front of VdB-Hagen 202. VdB-Hagen 202, and two smaller, slightly detached, groups of similar properties form family II, which do not belong to the association, but are caught in the act of passing through it. As for the younger population, this forms an arc-like structure from the bright nebula IC 4628 down to NGC 6231, as previously found. Moreover, the PMS stars density seems to increase from NGC 6231 northward to Trumpler 24.

scholarly journals Stochastic model of lignocellulosic material saccharification

2021 ◽  
Vol 17 (9) ◽  
pp. e1009262
Author(s):  
Eric Behle ◽  
Adélaïde Raguin
Keyword(s):  
Lignin Content ◽  
Three Dimensional ◽  
Enzymatic Saccharification ◽  
Biofuel Production ◽  
Dimensional Structure ◽  
Gillespie Algorithm ◽  
Promising Alternative ◽  
Fitting Procedure ◽  
Time Courses ◽  
Pre Treatment

The processing of agricultural wastes towards extraction of renewable resources is recently being considered as a promising alternative to conventional biofuel production. The degradation of agricultural residues is a complex chemical process that is currently time intensive and costly. Various pre-treatment methods are being investigated to determine the subsequent modification of the material and the main obstacles in increasing the enzymatic saccharification. In this study, we present a computational model that complements the experimental approaches. We decipher how the three-dimensional structure of the substrate impacts the saccharification dynamics. We model a cell wall microfibril composed of cellulose and surrounded by hemicellulose and lignin, with various relative abundances and arrangements. This substrate is subjected to digestion by different cocktails of well characterized enzymes. The saccharification dynamics is simulated in silico using a stochastic procedure based on a Gillespie algorithm. As we additionally implement a fitting procedure that optimizes the parameters of the simulation runs, we are able to reproduce experimental saccharification time courses for corn stover. Our model highlights the synergistic action of enzymes, and confirms the linear decrease of sugar conversion when either lignin content or crystallinity of the substrate increases. Importantly, we show that considering the crystallinity of cellulose in addition to the substrate composition is essential to interpret experimental saccharification data. Finally, our findings support the hypothesis of xylan being partially crystalline.

scholarly journals FIGS: spectral fitting constraints on the star formation history of massive galaxies since the cosmic noon

2019 ◽  
Vol 486 (1) ◽  
pp. 1358-1376 ◽  
Author(s):  
Ignacio Ferreras ◽  
Anna Pasquali ◽  
Nor Pirzkal ◽  
John Pharo ◽  
Sangeeta Malhotra ◽  
...  
Keyword(s):  
Star Formation ◽  
Near Infrared ◽  
Age Distribution ◽  
Principal Component ◽  
Stellar Mass ◽  
Star Formation History ◽  
Population Parameters ◽  
Massive Galaxies ◽  
Star Forming ◽  
Spectral Fitting

Abstract We constrain the stellar population properties of a sample of 52 massive galaxies – with stellar mass log (Ms/M⊙) ≳ 10.5 – over the redshift range 0.5 &lt; z &lt; 2 by use of observer-frame optical and near-infrared slitless spectra from Hubble Space Telescope’s ACS and WFC3 grisms. The deep exposures (∼100 ks) allow us to target individual spectra of massive galaxies to F160W = 22.5 AB. Our spectral fitting approach uses a set of six base models adapted to the redshift and spectral resolution of each observation, and fits the weights of the base models, including potential dust attenuation, via a Markov Chain Monte Carlo method. Our sample comprises a mixed distribution of quiescent (19) and star-forming galaxies (33). We quantify the width of the age distribution (Δt) that is found to dominate the variance of the retrieved parameters according to principal component analysis. The population parameters follow the expected trend towards older ages with increasing mass, and Δt appears to weakly anticorrelate with stellar mass, suggesting a more efficient star formation at the massive end. As expected, the redshift dependence of the relative stellar age (measured in units of the age of the Universe at the source) in the quiescent sample rejects the hypothesis of a single burst (aka monolithic collapse). Radial colour gradients within each galaxy are also explored, finding a wider scatter in the star-forming subsample, but no conclusive trend with respect to the population parameters.

Periodic motion embedded in plane Couette turbulence: regeneration cycle and burst

2001 ◽  
Vol 449 ◽  
pp. 291-300 ◽  
Author(s):  
GENTA KAWAHARA ◽  
SHIGEO KIDA
Keyword(s):  
Periodic Motion ◽  
Temporal Structure ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Navier Stokes ◽  
Low Velocity ◽  
Mean Velocity ◽  
Navier Stokes Equation ◽  
Time Periodic Solutions ◽  
Regeneration Cycle

Two time-periodic solutions with genuine three-dimensional structure are numerically discovered for the incompressible Navier–Stokes equation of a constrained plane Couette flow. One solution with strong variation in spatial and temporal structure exhibits a full regeneration cycle, which consists of the formation and breakdown of streamwise vortices and low-velocity streaks; the other one, of gentle variation, represents a spanwise standing-wave motion of low-velocity streaks. These two solutions are unstable and the corresponding periodic orbits in the phase space are connected with each other. A turbulent state wanders around the strong one for most of the time except for occasional escapes from it. As a result, the mean velocity profile and the root-mean-squares of velocity fluctuations of the plane Couette turbulence agree very well with the temporal averages of those of this periodic motion. After an occasional escape from the strong solution, the turbulent state reaches the gentle periodic solution and returns. On the way back, it experiences an overshoot accompanied by strong turbulence activity like an intermittent bursting phenomenon.

scholarly journals Environmental Effects on LRGs as Cosmic Chronometers

2015 ◽  
Vol 11 (S319) ◽  
pp. 140-140
Author(s):  
Gaochao Liu ◽  
Youjun Lu ◽  
Lizhi Xie ◽  
Xuelei Chen ◽  
Yongheng Zhao
Keyword(s):  
Star Formation ◽  
Age Distribution ◽  
Hubble Constant ◽  
Star Formation History ◽  
Mass Dependence ◽  
Population Synthesis ◽  
Luminous Red Galaxies ◽  
Formation History ◽  
The Mean ◽  
Red Galaxies

AbstractMassive luminous red galaxies (LRGs) are believed to be evolving passively and can be used as cosmic chronometers to estimate the Hubble constant (the differential age method). However, different LRGs may be located in different environments. We investigate the environmental and mass dependence of the formation of ‘quiescent’ LRGs by using the population synthesis software STARLIGHT. We derive the stellar populations in each LRG, and obtain the mean age distribution and the mean star formation history (SFH) of those LRGs. We find that there is no apparent dependence of the mean age and the SFH of quiescent LRGs on their environment, while the ages of these quiescent LRGs depend weakly on their mass. We also evaluate the possible uncertainties in estimating the Hubble constant by the differential age method when using LRGs as cosmic chronometers.

scholarly journals Young Magellanic Cloud Clusters (< 1 Gyr): Census, Properties, Star Formation History

1999 ◽  
Vol 190 ◽  
pp. 405-409 ◽  
Author(s):  
Eva K. Grebel ◽  
Dennis Zaritsky ◽  
Jason Harris ◽  
Ian Thompson
Keyword(s):  
Star Formation ◽  
Age Distribution ◽  
Magellanic Clouds ◽  
Star Formation History ◽  
Stellar Content ◽  
Preliminary Results ◽  
Cloud Clusters ◽  
Formation History ◽  
Cluster Properties ◽  
Cluster Age

We report preliminary results from an automated cluster survey of the Magellanic Clouds aimed at improving the cluster census and at deriving cluster properties from their resolved stellar content. The survey is tripling the number of known clusters. The cluster age distribution shows similar peaks at 100–200 Myr in LMC and SMC, coincident with the closest encounter of the Clouds and perigalacticon.

scholarly journals The Gaia DR2 halo white dwarf population: the luminosity function, mass distribution, and its star formation history

2021 ◽  
Vol 502 (2) ◽  
pp. 1753-1767
Author(s):  
Santiago Torres ◽  
Alberto Rebassa-Mansergas ◽  
María E Camisassa ◽  
Roberto Raddi
Keyword(s):  
Star Formation ◽  
Mass Distribution ◽  
White Dwarf ◽  
High Speed ◽  
White Dwarfs ◽  
Luminosity Function ◽  
Age Distribution ◽  
Star Formation History ◽  
Formation History ◽  
The Individual

ABSTRACT We analyse the volume-limited nearly complete 100 pc sample of 95 halo white dwarf candidates identified by the second data release of Gaia. Based on a detailed population synthesis model, we apply a method that relies on Gaia astrometry and photometry to accurately derive the individual white dwarf parameters. This method is tested with 25 white dwarfs of our sample for which we took optical spectra and performed spectroscopic analysis. We build and analyse the halo white dwarf luminosity function, for which we find for the first time possible evidences of the cut-off, leading to an age estimate of ${\simeq}12\pm 0.5$ Gyr. The mass distribution of the sample peaks at $0.589\, \mathrm{ M}_{\odot }$, with $71{{\ \rm per\ cent}}$ of the white dwarf masses below $0.6\, \mathrm{ M}_{\odot }$ and just two massive white dwarfs of more than $0.8\, \mathrm{ M}_{\odot }$. From the age distribution, we find three white dwarfs with total ages above 12 Gyr, of which J1312−4728 is the oldest white dwarf known with an age of $12.41\pm 0.22\,$ Gyr. We prove that the star formation history is mainly characterized by a burst of star formation that occurred from 10 to 12 Gyr in the past, but extended up to 8 Gyr. We also find that the peak of the star formation history is centred at around 11 Gyr, which is compatible with the current age of the Gaia-Enceladus encounter. Finally, $13{{\ \rm per\ cent}}$ of our halo sample is contaminated by high-speed young objects (total age &lt;7 Gyr). The origin of these white dwarfs is unclear but their age distribution may be compatible with the encounter with the Sagittarius galaxy.

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