scholarly journals The range of validity of cluster masses and ages derived from broad-band photometry

2009 ◽  
Vol 5 (S266) ◽  
pp. 100-105
Author(s):  
J. Maíz Apellániz
Keyword(s):  
Near Infrared ◽  
Classical Method ◽  
Broad Band ◽  
Mass Function ◽  
Initial Mass Function ◽  
Stellar Clusters ◽  
Stochastic Effects ◽  
Stellar Initial Mass Function ◽  
The Individual ◽  
Wavelength Filters

AbstractI analyze the stochastic effects introduced by sampling the stellar initial mass function (SIMF) in the derivation of the individual masses and the cluster mass function (CMF) from broad-band visible/near-infrared unresolved photometry. The classical method of using unweighted U BV photometry to simultaneously establish ages and extinctions of stellar clusters is found to be unreliable for clusters older than ≈30 Myr, even for relatively large cluster masses. On the other hand, augmenting the filter set to include longer-wavelength filters and using weights for each filter increases the range of masses and ages that can be measured accurately with unresolved photometry. Nevertheless, a relatively large range of masses and ages is found to be dominated by SIMF sampling effects that render the observed masses useless, even when using U BV RI JHK photometry.

scholarly journals The origin of very massive stars around NGC 3603

2019 ◽  
Vol 625 ◽  
pp. L2 ◽  
Author(s):  
V. M. Kalari ◽  
J. S. Vink ◽  
W. J. de Wit ◽  
N. J. Bastian ◽  
R. A. Méndez
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Massive Stars ◽  
Mass Function ◽  
Initial Mass Function ◽  
Future Data ◽  
Solar Type ◽  
Stellar Initial Mass Function ◽  
The Universe ◽  
Shed Light

The formation mechanism of the most massive stars in the Universe remains an unsolved problem. Are they able to form in relative isolation in a manner similar to the formation of solar-type stars, or do they necessarily require a clustered environment? In order to shed light on this important question, we study the origin of two very massive stars (VMS): the O2.5If*/WN6 star RFS7 (∼100 M⊙), and the O3.5If* star RFS8 (∼70 M⊙), found within ∼53 and 58 pc, respectively, of the Galactic massive young cluster NGC 3603, using Gaia data. The star RFS7 is found to exhibit motions resembling a runaway star from NGC 3603. This is now the most massive runaway star candidate known in the Milky Way. Although RFS8 also appears to move away from the cluster core, it has proper-motion values that appear inconsistent with being a runaway from NGC 3603 at the 3σ level (but with substantial uncertainties due to distance and age). Furthermore, no evidence for a bow-shock or a cluster was found surrounding RFS8 from available near-infrared photometry. In summary, whilst RFS7 is likely a runaway star from NGC 3603, making it the first VMS runaway in the Milky Way, RFS8 is an extremely young (∼2 Myr) VMS, which might also be a runaway, but this would need to be established from future spectroscopic and astrometric observations, as well as precise distances. If RFS 8 was still not found to meet the criteria for being a runaway from NGC 3603 from such future data, this would have important ramifications for current theories of massive star formation, as well as the way the stellar initial mass function is sampled.

The IMF-SFH connection in massive early-type galaxies

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
I. Ferreras ◽  
C. Weidner ◽  
A. Vazdekis ◽  
F. La Barbera
Keyword(s):  
Age Distribution ◽  
Stellar Populations ◽  
Mass Function ◽  
Initial Mass Function ◽  
Population Synthesis ◽  
Early Type ◽  
Massive Galaxies ◽  
Stellar Initial Mass Function ◽  
The Many ◽  
The Imf

The stellar initial mass function (IMF) is one of the fundamental pillars in studies of stellar populations. It is the mass distribution of stars at birth, and it is traditionally assumed to be universal, adopting generic functions constrained by resolved (i.e. nearby) stellar populations (e.g., Salpeter 1955; Kroupa 2001; Chabrier 2003). However, for the vast majority of cases, stars are not resolved in galaxies. Therefore, the interpretation of the photo-spectroscopic observables is complicated by the many degeneracies present between the properties of the unresolved stellar populations, including IMF, age distribution, and chemical composition. The overall good match of the photometric and spectroscopic observations of galaxies with population synthesis models, adopting standard IMF choices, made this issue a relatively unimportant one for a number of years. However, improved models and observations have opened the door to constraints on the IMF in unresolved stellar populations via gravity-sensitive spectral features. At present, there is significant evidence of a non-universal IMF in early-type galaxies (ETGs), with a trend towards a dwarf-enriched distribution in the most massive systems (see, e.g., van Dokkum & Conroy 2010; Ferreras et al. 2013; La Barbera et al. 2013). Dynamical and strong-lensing constraints of the stellar M/L in similar systems give similar results, with heavier M/L in the most massive ETGs (see, e.g., Cappellari et al. 2012; Posacki et al. 2015). Although the interpretation of the results is still open to discussion (e.g., Smith 2014; La Barbera 2015), one should consider the consequences of such a bottom-heavy IMF in massive galaxies.

scholarly journals Is the stellar initial mass function universal?

2016 ◽  
Vol 57 (2) ◽  
pp. 2.32-2.36 ◽  
Author(s):  
Ignacio Ferreras ◽  
Francesco La Barbera ◽  
Alexandre Vazdekis
Keyword(s):  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Stellar Initial Mass Function

scholarly journals Statistical Properties of Kerr BH Flywheel Model of QSOs/AGNs

2000 ◽  
Vol 195 ◽  
pp. 417-418
Author(s):  
S. Nitta
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Kerr Black Hole ◽  
Mass Function ◽  
Initial Mass Function ◽  
Number Density ◽  
Disk System ◽  
The Press ◽  
The Individual ◽  
Density Population

The aim of this work is to demonstrate the properties of the magnetospheric model around Kerr black holes, so-called the “flywheel” (rotation powered) model. The fly-wheel engine of the BH accretion disk system is applied to the statistics of QSOs/AGNs. Nitta, Takahashi, & Tomimatsu clarified the individual evolution of the Kerr black-hole fly-wheel engine, which is parameterized by black-hole mass, initial Kerr parameter, magnetic field near the horizon, and a dimensionless small parameter. We impose a statistical model for the initial mass function of an ensemble of black holes using the Press-Schechter formalism. With the help of additional assumptions, we can discuss the evolution of the luminosity function and the spatial number density (population) of QSOs/AGNs. The result explains well the decrease of very bright QSOs and decrease of population after z ~ 2.

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