scholarly journals Star Formation as Seen by Low Mass Stars

2014 ◽  
Vol 1 (1) ◽  
pp. 113-117
Author(s):  
Nino Panagia ◽  
Guido De Marchi
Keyword(s):  
Star Formation ◽  
Physical Properties ◽  
Main Sequence ◽  
Hubble Space Telescope ◽  
Ongoing Study ◽  
Low Mass Stars ◽  
Homogeneous Sample ◽  
Wide Range ◽  
Low Mass ◽  
Pms Stars

Using the Hubble Space Telescope (HST) we have characterised and compared the physical properties of a large sample of pre-main sequence (PMS) stars spanning a wide range of masses (0:5 - 4M<sub>ʘ</sub>), metallicities (0:1 - 1 Z<sub>ʘ</sub>) and ages (0:5 - 30 Myr). This is presently the largest and most homogeneous sample of PMS objects with known physical properties. The main results of this ongoing study are briefly summarised here.

scholarly journals Measurements of the Ca ii infrared triplet emission lines of pre-main-sequence stars

2020 ◽  
Vol 72 (5) ◽  
Author(s):  
Mai Yamashita ◽  
Yoichi Itoh ◽  
Yuhei Takagi
Keyword(s):  
Main Sequence ◽  
Open Clusters ◽  
Emission Lines ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Chromospheric Activity ◽  
Low Mass ◽  
Pms Stars ◽  
Infrared Triplet ◽  
Narrow Emission

Abstract We investigated the chromospheric activity of 60 pre-main-sequence (PMS) stars in four molecular clouds and five moving groups. It is considered that strong chromospheric activity is driven by the dynamo processes generated by stellar rotation. In contrast, several researchers have pointed out that the chromospheres of PMS stars are activated by mass accretion from their protoplanetary disks. In this study, the Ca ii infrared triplet (IRT) emission lines were investigated utilizing medium- and high-resolution spectroscopy. The observations were conducted with Nayuta/MALLS and Subaru/HDS. Additionally, archive data obtained by Keck/HIRES, VLT/UVES, and VLT/X-Shooter were used. The small ratios of the equivalent widths indicate that Ca ii IRT emission lines arise primarily in dense chromospheric regions. Seven PMS stars show broad emission lines. Among them, four PMS stars have more than one order of magnitude brighter emission line fluxes compared to the low-mass stars in young open clusters. The four PMS stars have a high mass accretion rate, which indicates that the broad and strong emission results from a large mass accretion. However, most PMS stars exhibit narrow emission lines. No significant correlation was found between the accretion rate and flux of the emission line. The ratios of the surface flux of the Ca ii IRT lines to the stellar bolometric luminosity, $R^{\prime }_{\rm IRT}$, of the PMS stars with narrow emission lines are as large as the largest $R^{\prime }_{\rm IRT}$ of the low-mass stars in the young open clusters. This result indicates that most PMS stars, even in the classical T Tauri star stage, have chromospheric activity similar to zero-age main-sequence stars.

scholarly journals A Relative Age Test of Pre-Main Sequence Evolutionary Models Based on the Young Quadruple System GG Tauri

2001 ◽  
Vol 200 ◽  
pp. 464-467
Author(s):  
Russel J. White
Keyword(s):  
Spectral Type ◽  
Temperature Scale ◽  
Main Sequence ◽  
Evolutionary Models ◽  
Low Mass Stars ◽  
Relative Age ◽  
Wide Range ◽  
Quadruple System ◽  
Low Mass

The components of the young hierarchical quadruple GG Tau, which span a wide range in spectral type (K7 – M7.5), are used to test both evolutionary models and the temperature scale for very young, low mass stars under the assumption of coeval formation. Of the evolutionary models tested which extend into the substellar regime, those of Baraffe et al. yield the most consistent ages when combined with a temperature scale intermediate between that of dwarfs and giants. The Palla & Stahler and Siess et al. models are also capable of yielding a coeval age down to their lowest mass (0.1 M⊙). These latter two models, which extend to much higher masses than the Baraffe et al. models, agree reasonably well with the Baraffe et al. models at 1.0 M⊙ and thus could be combined to construct a set evolutionary models that extends from Substellar to several solar masses.

scholarly journals Clustered Star Formation in the Magellanic Clouds

2007 ◽  
Vol 3 (S246) ◽  
pp. 61-62
Author(s):  
Dimitrios A. Gouliermis
Keyword(s):  
Star Formation ◽  
Hubble Space Telescope ◽  
Magellanic Clouds ◽  
Initial Mass Function ◽  
Star Formation History ◽  
Wide Field ◽  
Space Telescope ◽  
Low Mass ◽  
Pms Stars ◽  
The Impact

AbstractThe Large and Small Magellanic Cloud (LMC, SMC) offer an outstanding variety of young stellar associations, in which large samples of low-mass stars (withM≤ 1 M⊙) currently in the act of formation can be resolved and explored sufficiently with theHubble Space Telescope. Previous observations with theWide-Field Planetary Camera 2(WFPC2) provided the first evidence of the existence of low-mass pre-main sequence (PMS) stars in the vicinity of star forming associations in the Magellanic Clouds (MCs) (Gouliermiset al. 2006a), and recent results from deeper observations with theAdvanced Camera for Surveys(ACS) enhanced dramatically the picture of these systems with the discovery of large numbers of PMS stars. The associations LH 95 (Gouliermiset al. 2002, 2007a) in the LMC, and NGC 346 (Gouliermiset al. 2006b) and NGC 602 (Gouliermiset al. 2007b) in the SMC, are currently under investigation with the use of observations from bothHubbleandSpitzer Space Telescope. I present the impact of our recent results in terms of the star formation history and Initial Mass Function (IMF) of these interesting systems, using as example the case of NGC 602.

scholarly journals X-ray Emission from Young Stars in Suburban Orion

2004 ◽  
Vol 219 ◽  
pp. 228-232
Author(s):  
K. Briggs ◽  
M. Güdel ◽  
M. Audard ◽  
K. Smith ◽  
R. Mewe ◽  
...  
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Young Stars ◽  
Rossby Number ◽  
Low Mass Stars ◽  
X Ray ◽  
Star Forming ◽  
Low Mass ◽  
Pms Stars

X-ray emission from > 100 pre-main sequence (PMS) stars in the Orion star-forming complex is studied in a 20-ks observation by XMM-Newton. No relation between the ratio of X-ray and bolometric luminosities, LX/Lbol, and rotation period or Rossby number is exhibited, though the action of a solar-like dynamo is not excluded because all stars would appear to be in the “saturated regime” of such a dynamo. Low-mass stars showing a strong U — V excess have lower median X-ray luminosity, suggesting that accretion suppresses magnetic activity.

scholarly journals The naked T Tauri stars: The low mass pre-main sequence unveiled

1987 ◽  
Vol 122 ◽  
pp. 107-108
Author(s):  
Frederick M. Walter
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
T Tauri Stars ◽  
Low Mass Stars ◽  
X Ray ◽  
T Tauri ◽  
Low Mass ◽  
The Impact ◽  
Circumstellar Environment

I discuss a survey of X-ray sources in regions of star formation. The survey has revealed at least 30 low mass PMS, naked T Tauri stars (NTTS) in Tau-Aur, and a comparable number in Oph. I summarize the properties of these stars, and argue that the spectra of the classical T Tauri stars are due to the interaction of an underlying NTTS with a dominant circumstellar environment. I discuss the impact the NTTS are likely to have on our understanding of the PMS evolution of low mass stars.

scholarly journals The HST/ACS star formation history of the Tucana dwarf spheroidal galaxy: clues from the horizontal branch

2019 ◽  
Vol 630 ◽  
pp. A116 ◽  
Author(s):  
A. Savino ◽  
E. Tolstoy ◽  
M. Salaris ◽  
M. Monelli ◽  
T. J. L. de Boer
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Star Formation History ◽  
Horizontal Branch ◽  
Low Mass Stars ◽  
Formation History ◽  
History Of ◽  
Low Mass ◽  
Ancient Times ◽  
Red Giant

We report a new star formation history for the Tucana dwarf spheroidal galaxy, obtained from a new look at a deep HST/ACS colour-magnitude diagram. We combined information from the main sequence turn-off and the horizontal branch to resolve the ancient star formation rates on a finer temporal scale than previously possible. We show that Tucana experienced three major phases of star formation, two very close together at ancient times and the last one ending between 6 and 8 Gyr ago. We show that the three discrete clumps of stars on the horizontal branch are linked to the distinct episodes of star formation in Tucana. The spatial distribution of the clumps reveals that each generation of stars presents a higher concentration than the previous one. The simultaneous modelling of the horizontal branch and the main sequence turn-off also allows us to measure the amount of mass lost by red giant branch stars in Tucana with unprecedented precision, confirming dwarf spheroidals to be excellent laboratories to study the advanced evolution of low-mass stars.

scholarly journals Hα photometry of low mass stars in 47 Tucanae: chromospheric activity and exotica

2012 ◽  
Vol 8 (S290) ◽  
pp. 187-188
Author(s):  
Giacomo Beccari ◽  
Guido De Marchi ◽  
Nino Panagia ◽  
Luca Pasquini
Keyword(s):  
Globular Cluster ◽  
Main Sequence ◽  
High Efficiency ◽  
Hubble Space Telescope ◽  
Cataclysmic Variables ◽  
Low Mass Stars ◽  
Theoretical Predictions ◽  
Hα Emission ◽  
Low Mass ◽  
Advanced Camera For Surveys

AbstractWe have used archival Hubble Space Telescope (HST) observations obtained with the Advanced Camera for Surveys (ACS) to study the Hα emission properties of main sequence (MS) stars in the globular cluster 47 Tucanae. An accurate photometric measurement of their Hα equivalent width, allows us to identify objects with large Hα emission. We demonstrate that this method allows us to identify and characterise candidate cataclysmic variables (CVs) with high efficiency, reconciling observations with theoretical predictions on the number of dynamically formed CVs expected in a 47 Tucanae-like globular cluster.

scholarly journals The effect of photoionizing feedback on the shaping of hierarchically-forming stellar clusters

2020 ◽  
Vol 499 (1) ◽  
pp. 668-680
Author(s):  
Alejandro González-Samaniego ◽  
Enrique Vazquez-Semadeni
Keyword(s):  
Star Formation ◽  
Early Stage ◽  
Stellar Clusters ◽  
Low Mass Stars ◽  
Transfer Scheme ◽  
Star Forming ◽  
Secondary Star ◽  
Low Mass ◽  
Hydrodynamical Simulations ◽  
Formation Efficiency

ABSTRACT We use two hydrodynamical simulations (with and without photoionizing feedback) of the self-consistent evolution of molecular clouds (MCs) undergoing global hierarchical collapse (GHC), to study the effect of the feedback on the structural and kinematic properties of the gas and the stellar clusters formed in the clouds. During this early stage, the evolution of the two simulations is very similar (implying that the feedback from low-mass stars does not affect the cloud-scale evolution significantly) and the star-forming region accretes faster than it can convert gas into stars, causing the instantaneous measured star formation efficiency (SFE) to remain low even in the absence of significant feedback. Afterwards, the ionizing feedback first destroys the filamentary supply to star-forming hubs and ultimately removes the gas from it, thus first reducing the star formation (SF) and finally halting it. The ionizing feedback also affects the initial kinematics and spatial distribution of the forming stars because the gas being dispersed continues to form stars, which inherit its motion. In the non-feedback simulation, the groups remain highly compact and do not mix, while in the run with feedback, the gas dispersal causes each group to expand, and the cluster expansion thus consists of the combined expansion of the groups. Most secondary star-forming sites around the main hub are also present in the non-feedback run, implying a primordial rather than triggered nature. We do find one example of a peripheral star-forming site that appears only in the feedback run, thus having a triggered origin. However, this appears to be the exception rather than the rule, although this may be an artefact of our simplified radiative transfer scheme.

scholarly journals Globular clusters and the evolution of their multiple stellar populations

2015 ◽  
Vol 12 (S316) ◽  
pp. 328-333
Author(s):  
W. Chantereau ◽  
C. Charbonnel ◽  
G. Meynet
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Chemical Properties ◽  
Stellar Populations ◽  
Chemical Compositions ◽  
Low Mass Stars ◽  
Sequence Band ◽  
Low Mass ◽  
Chemical Distribution ◽  
Host Stars

AbstractOur knowledge of the formation and early evolution of globular clusters (GCs) has been totally shaken with the discovery of the peculiar chemical properties of their long-lived host stars. Therefore, the interpretation of the observed Colour Magnitude Diagrams (CMD) and of the properties of the GC stellar populations requires the use of new stellar models computed with relevant chemical compositions. In this paper we use the grid of evolution models for low-mass stars computed by Chantereau et al. (2015) with the initial compositions of second-generation stars as predicted by the fast rotating massive stars scenario to build synthesis models of GCs. We discuss the implications of the assumed initial chemical distribution on 13 Gyr isochrones. We build population synthesis models to predict the fraction of stars born with various helium abundances in present day globular clusters (assuming an age of 13 Gyr). With the current assumptions, 61 % of stars on the main sequence are predicted to be born with a helium abundance in mass fraction, Yini, smaller than 0.3 and only 11 % have a Yini larger than 0.4. Along the horizontal branch, the fraction of stars with Yini inferior to 0.3 is similar to that obtained along the main sequence band (63 %), while the fraction of very He-enriched stars is significantly decreased (only 3 % with Yini larger than 0.38).

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