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Journal articles on the topic 'Stars – Initial mass function'

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Published: 10 December 2022

Last updated: 29 January 2023

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1

Larson, Richard B. "Fragmentation and the Initial Mass Function." International Astronomical Union Colloquium 120 (1989): 44–55. http://dx.doi.org/10.1017/s0252921100023472.

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A central problem in the theory of star formation is to understand the spectrum of masses, or Initial Mass Function, with which stars are formed. The fundamental role of the IMF in galactic evolution has been described by Tinsley (1980), and an extensive review of evidence concerning the IMF and its possible variability has been presented by Scalo (1986). Although the IMF derived from the observations is subject to many uncertainties, two basic features seem reasonably well established. One is that the typical stellar mass, defined such that equal amounts of matter condense into stars above and below this mass, is within a factor of 3 of one solar mass. A theory of star formation should therefore be able to explain why most stars are formed with masses of order one solar mass. The second apparently universal feature is that the IMF for relatively massive stars can be approximated by a power law with a slope not greatly different from that originally proposed by Salpeter (1955). Thus we also need to understand why the IMF always has a similar power-law tail toward higher masses.

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2

Leitherer, Claus. "The Stellar Initial Mass Function in Starburst Galaxies." Symposium - International Astronomical Union 186 (1999): 243–50. http://dx.doi.org/10.1017/s0074180900112707.

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Starburst galaxies are currently forming massive stars at prodigious rates. I discuss the star-formation histories and the shape of the initial mass function, with particular emphasis on the high- and on the low-mass end. The classical Salpeter IMF is consistent with constraints from observations of the most massive stars, irrespective of environmental properties. The situation at the low-mass end is less clear: direct star counts in nearby giant H II regions show stars down to ~1 M⊙, whereas dynamical arguments in some starburst galaxies suggest a deficit of such stars.

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3

Yoshii, Y., and H. Saio. "Initial mass function for zero-metal stars." Astrophysical Journal 301 (February 1986): 587. http://dx.doi.org/10.1086/163925.

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4

Zorec, J., R. Levenhagen, J. Chauville, Y. Frémat, D. Ballereau, A. M. Hubert, M. Floquet, and N. V. Leister. "The Initial Mass Function of Be Stars." Symposium - International Astronomical Union 215 (2004): 83–84. http://dx.doi.org/10.1017/s0074180900195270.

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Allowing for systematic differences in the counting of Be Stars due to their overluminosity, changes produced by their fast rotation on spectral types and time spent in the main sequence, a difference between the IMF (Be) and IMF(B) appears, which indicates that the appearance of the Be phenomenon may relay on differences in the initial star formation conditions.

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5

Larson, Richard B. "Some processes influencing the stellar initial mass function." Symposium - International Astronomical Union 147 (1991): 261–73. http://dx.doi.org/10.1017/s0074180900239600.

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Current evidence suggests that the stellar initial mass function has the same basic form everywhere, and that its fundamental features are (1) the existence of a characteristic stellar mass of order one solar mass, and (2) the existence of an apparently universal power-law form for the mass spectrum of the more massive stars. The characteristic stellar mass may be determined in part by the typical mass scale for the fragmentation of star forming clouds, which is predicted to be of the order of one solar mass. The power-law extension of the mass spectrum toward higher masses may result from the continuing accretional growth of some stars to much larger masses; the fact that the most massive stars appear to form preferentially in cluster cores suggests that such continuing accretion may be particularly important at the centers of clusters. Numerical simulations suggest that forming systems of stars may tend to develop a hierarchical structure, possibly self-similar in nature. If most stars form in such hierarchically structured systems, and if the mass of the most massive star that forms in each subcluster increases as a power of the mass of the subcluster, then a mass spectrum of power-law form is predicted. Some possible physical effects that could lead to such a relation are briefly discussed, and some observational tests of the ideas discussed here are proposed.

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6

Larson, Richard B. "Some processes influencing the stellar initial mass function." Symposium - International Astronomical Union 147 (1991): 261–73. http://dx.doi.org/10.1017/s0074180900198985.

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Current evidence suggests that the stellar initial mass function has the same basic form everywhere, and that its fundamental features are (1) the existence of a characteristic stellar mass of order one solar mass, and (2) the existence of an apparently universal power-law form for the mass spectrum of the more massive stars. The characteristic stellar mass may be determined in part by the typical mass scale for the fragmentation of star forming clouds, which is predicted to be of the order of one solar mass. The power-law extension of the mass spectrum toward higher masses may result from the continuing accretional growth of some stars to much larger masses; the fact that the most massive stars appear to form preferentially in cluster cores suggests that such continuing accretion may be particularly important at the centers of clusters. Numerical simulations suggest that forming systems of stars may tend to develop a hierarchical structure, possibly self-similar in nature. If most stars form in such hierarchically structured systems, and if the mass of the most massive star that forms in each subcluster increases as a power of the mass of the subcluster, then a mass spectrum of power-law form is predicted. Some possible physical effects that could lead to such a relation are briefly discussed, and some observational tests of the ideas discussed here are proposed.

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7

Federrath, Christoph, Mark Krumholz, and Philip F. Hopkins. "Converging on the Initial Mass Function of Stars." Journal of Physics: Conference Series 837 (May 30, 2017): 012007. http://dx.doi.org/10.1088/1742-6596/837/1/012007.

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8

Malkov, O., and H. Zinnecker. "Binary stars and the fundamental initial mass function." Monthly Notices of the Royal Astronomical Society 321, no. 1 (February 11, 2001): 149–54. http://dx.doi.org/10.1046/j.1365-8711.2001.04015.x.

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9

Hopkins, Andrew. "Measuring the stellar initial mass function." Proceedings of the International Astronomical Union 15, S352 (June 2019): 98. http://dx.doi.org/10.1017/s1743921320001155.

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AbstractThe birth of stars and the formation of galaxies are cornerstones of modern astrophysics. While much is known about how galaxies globally and their stars individually form and evolve, one fundamental property that affects both remains elusive. This is problematic because this key property, the stellar initial mass function (IMF), is a key tracer of the physics of star formation that underpins almost all of the unknowns in galaxy and stellar evolution. It is perhaps the greatest source of systematic uncertainty in star and galaxy evolution. The past decade has seen a growing number and variety of methods for measuring or inferring the shape of the IMF, along with progressively more detailed simulations, paralleled by refinements in the way the concept of the IMF is applied or conceptualised on different physical scales. This range of approaches and evolving definitions of the quantity being measured has in turn led to conflicting conclusions regarding whether or not the IMF is universal. Here I summarise the growing wealth of approaches to our understanding of this fundamental property that defines so much of astrophysics, and highlight the importance of considering potential IMF variations, reinforcing the need for measurements to quantify their scope and uncertainties carefully. I present a new framework to aid the discussion of the IMF and promote clarity in the further development of this fundamental field.

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10

De Marchi, Guido, and Francesco Paresce. "The Initial Mass Function of Low-Mass Stars in Globular Clusters." Astrophysical Journal 476, no. 1 (February 10, 1997): L19—L22. http://dx.doi.org/10.1086/310490.

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11

Goswami, S., A. Slemer, P. Marigo, A. Bressan, L. Silva, M. Spera, L. Boco, V. Grisoni, L. Pantoni, and A. Lapi. "The effects of the initial mass function on Galactic chemical enrichment." Astronomy & Astrophysics 650 (June 2021): A203. http://dx.doi.org/10.1051/0004-6361/202039842.

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Context. We have been seeing mounting evidence that the stellar initial mass function (IMF) might extend far beyond the canonical Mi ∼ 100 M⊙ limit, but the impact of such a hypothesis on the chemical enrichment of galaxies is yet to be clarified. Aims. We aim to address this question by analysing the observed abundances of thin- and thick-disc stars in the Milky Way with chemical evolution models that account for the contribution of very massive stars dying as pair instability supernovae. Methods. We built new sets of chemical yields from massive and very massive stars up to Mi ∼ 350 M⊙ by combining the wind ejecta extracted from our hydrostatic stellar evolution models with explosion ejecta from the literature. Using a simple chemical evolution code, we analysed the effects of adopting different yield tables by comparing predictions against observations of stars in the solar vicinity. Results. After several tests, we set our focus on the [O/Fe] ratio that best separates the chemical patterns of the two Milky Way components. We find that with a standard IMF, truncated at Mi ∼ 100 M⊙, we can reproduce various observational constraints for thin-disc stars; however, the same IMF fails to account for the [O/Fe] ratios of thick-disc stars. The best results are obtained by extending the IMF up to Mi = 350 M⊙, while including the chemical ejecta of very massive stars in the form of winds and pair instability supernova (PISN) explosions. Conclusions. Our study indicates that PISN may have played a significant role in shaping the chemical evolution of the thick disc of the Milky Way. Including their chemical yields makes it easier to reproduce not only the level of the α-enhancement, but also the observed slope of thick-disc stars in the [O/Fe] vs. [Fe/H] diagram. The bottom line is that the contribution of very massive stars to the chemical enrichment of galaxies is potentially quite important and should not be neglected in models of chemical evolution.

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12

Nakamura, Fumitaka, and Masayuki Umemura. "On the Initial Mass Function of Population III Stars." Astrophysical Journal 548, no. 1 (February 10, 2001): 19–32. http://dx.doi.org/10.1086/318663.

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13

Schaerer, Daniel. "The massive star Initial Mass function." Symposium - International Astronomical Union 212 (2003): 642–51. http://dx.doi.org/10.1017/s007418090021303x.

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We review our current knowledge on the IMF in nearby environments, massive star forming regions, super star clusters, starbursts and alike objects from studies of integrated light, and discuss the various techniques used to constrain the IMF. In most cases, including UV-optical studies of stellar features and optical-IR analysis of nebular emission, the data is found to be compatible with a ‘universal’ Salpeter-like IMF with a high upper mass cut-off over a large metallicity range. In contrast, near-IR observations of nuclear starbursts and LIRG show indications of a lowerMupand/or a steeper IMF slope, for which no alternate explanation has yet been found. Also, dynamical mass measurements of seven super star clusters provide so far no simple picture of the IMF. Finally, we present recent results of a direct stellar probe of the upper end of the IMF in metal-rich H ii regions, showing no deficiency of massive stars at high metallicity, and determining a lower limit ofMup≳ 60 – 90 M⊙.

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14

Luhman, K. L. "The Variation of the Initial Mass Function in Clusters." Symposium - International Astronomical Union 221 (2004): 237–46. http://dx.doi.org/10.1017/s0074180900241648.

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I review recent measurements of the initial mass function of stars and brown dwarfs in star-forming regions and open clusters and summarize the implications of these data for theories of star formation.

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15

Hubbard, W. B., Adam Burrows, and Jonathan I. Lunine. "The initial mass function for very low mass stars in the Hyades." Astrophysical Journal 358 (August 1990): L53. http://dx.doi.org/10.1086/185778.

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16

Jeffries, R. D. "Measuring the Initial Mass Function of Low Mass Stars and Brown Dwarfs." EAS Publications Series 57 (2012): 45–89. http://dx.doi.org/10.1051/eas/1257002.

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17

Schneider, Raffaella, Ruben Salvaterra, Andrea Ferrara, and Benedetta Ciardi. "Constraints on the initial mass function of the first stars." Monthly Notices of the Royal Astronomical Society 369, no. 2 (May 3, 2006): 825–34. http://dx.doi.org/10.1111/j.1365-2966.2006.10331.x.

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18

Bruzzese, S. M., David A. Thilker, G. R. Meurer, Luciana Bianchi, A. B. Watts, A. M. N. Ferguson, A. Gil de Paz, B. Madore, D. Christopher Martin, and R. Michael Rich. "The initial mass function in the extended ultraviolet disc of M83." Monthly Notices of the Royal Astronomical Society 491, no. 2 (November 22, 2019): 2366–90. http://dx.doi.org/10.1093/mnras/stz3151.

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ABSTRACT Using Hubble Space Telescope ACS/WFC data we present the photometry and spatial distribution of resolved stellar populations of four fields within the extended ultraviolet disc (XUV disc) of M83. These observations show a clumpy distribution of main-sequence stars and a mostly smooth distribution of red giant branch stars. We constrain the upper end of the initial mass function (IMF) in the outer disc using the detected population of main-sequence stars and an assumed constant star formation rate (SFR) over the last 300 Myr. By comparing the observed main-sequence luminosity function to simulations, we determine the best-fitting IMF to have a power-law slope α = −2.35 ± 0.3 and an upper mass limit $M_{\rm u}=25_{-3}^{+17} \, \mathrm{M}_\odot$. This IMF is consistent with the observed H $\rm \alpha$ emission, which we use to provide additional constraints on the IMF. We explore the influence of deviations from the constant SFR assumption, finding that our IMF conclusions are robust against all but strong recent variations in SFR, but these are excluded by causality arguments. These results, along with our similar studies of other nearby galaxies, indicate that some XUV discs are deficient in high-mass stars compared to a Kroupa IMF. There are over one hundred galaxies within 5 Mpc, many already observed with HST, thus allowing a more comprehensive investigation of the IMF, and how it varies, using the techniques developed here.

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19

Singh, Mahendra. "Initial mass functions of Wolf-Rayet stars." Astrophysics and Space Science 124, no. 1 (1986): 101–4. http://dx.doi.org/10.1007/bf00649752.

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20

Parravano, Antonio, Christopher F. McKee, and David J. Hollenbach. "AN INITIAL MASS FUNCTION FOR INDIVIDUAL STARS IN GALACTIC DISKS. I. CONSTRAINING THE SHAPE OF THE INITIAL MASS FUNCTION." Astrophysical Journal 726, no. 1 (December 10, 2010): 27. http://dx.doi.org/10.1088/0004-637x/726/1/27.

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21

Nam, Donghee G., Christoph Federrath, and Mark R. Krumholz. "Testing the turbulent origin of the stellar initial mass function." Monthly Notices of the Royal Astronomical Society 503, no. 1 (February 26, 2021): 1138–48. http://dx.doi.org/10.1093/mnras/stab505.

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ABSTRACT Supersonic turbulence in the interstellar medium (ISM) is closely linked to the formation of stars; hence, many theories connect the stellar initial mass function (IMF) with the turbulent properties of molecular clouds. Here, we test three turbulence-based IMF models (by Padoan and Nordlund, Hennebelle and Chabrier, and Hopkins) that predict the relation between the high-mass slope (Γ) of the IMF, dN/d log M ∝ MΓ, and the exponent n of the velocity power spectrum of turbulence, Ev(k) ∝ k−n, where n ≈ 2 corresponds to typical ISM turbulence. Using hydrodynamic simulations, we drive turbulence with an unusual index of n ≈ 1, measure Γ, and compare the results with n ≈ 2. We find that reducing n from 2 to 1 primarily changes the high-mass region of the IMF (beyond the median mass), where we measure high-mass slopes within the 95 per cent confidence interval of −1.5 < Γ < −1 for n ≈ 1 and −3.7 < Γ < −2.4 for n ≈ 2, respectively. Thus, we find that n = 1 results in a significantly flatter high-mass slope of the IMF, with more massive stars formed than for n ≈ 2. We compare these simulations with the predictions of the three IMF theories. We find that while the theory by Padoan and Nordlund matches our simulations with fair accuracy, the other theories either fail to reproduce the main qualitative outcome of the simulations or require some modifications. We conclude that turbulence plays a key role in shaping the IMF, with a shallower turbulence power spectrum producing a shallower high-mass IMF, and hence more massive stars.

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22

Ishigaki, Miho N., Nozomu Tominaga, Chiaki Kobayashi, and Ken’ichi Nomoto. "The Initial Mass Function of the First Stars Inferred from Extremely Metal-poor Stars." Astrophysical Journal 857, no. 1 (April 11, 2018): 46. http://dx.doi.org/10.3847/1538-4357/aab3de.

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23

Luhman, K. L. "The Initial Mass Function of Low‐Mass Stars and Brown Dwarfs in Taurus." Astrophysical Journal 544, no. 2 (December 2000): 1044–55. http://dx.doi.org/10.1086/317232.

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24

Latif, Muhammad A., Daniel Whalen, and Sadegh Khochfar. "The Birth Mass Function of Population III Stars." Astrophysical Journal 925, no. 1 (January 1, 2022): 28. http://dx.doi.org/10.3847/1538-4357/ac3916.

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Abstract Population III stars ended the cosmic dark ages and began early cosmological reionization and chemical enrichment. However, in spite of their importance to the evolution of the early universe, their properties remain uncertain because of the limitations on previous numerical simulations and the lack of any observational constraints. Here, we investigate Population III star formation in five primordial halos using 3D radiation-hydrodynamical cosmological simulations. We find that multiple stars form in each minihalo and that their numbers increase over time, with up to 23 stars forming in one of the halos. Radiative feedback from the stars generates strong outflows, deforms the surrounding protostellar disk, and delays star formation for a few thousand years. Star formation rates vary with halo, and depend on the mass accretion onto the disk, the halo spin number, and the fraction of massive stars in the halo. The stellar masses in our models range from 0.1–37 M ⊙, and of the 55 stars that form in our models, 12 are >10 M ⊙ and most of the others are 1–10 M ⊙. Our simulations thus suggest that Population III stars have characteristic masses of 1–10 M ⊙ and top-heavy initial mass functions with dN/dM ∝ M * − 1.18 . Up to 70% of the stars are ejected from their disks by three-body interactions that, along with ionizing UV feedback, limit their final masses.

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25

Parmentier, G., and G. Gilmore. "The Origin of the Universal Globular Cluster Mass Function." Proceedings of the International Astronomical Union 3, S246 (September 2007): 413–17. http://dx.doi.org/10.1017/s1743921308016062.

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AbstractEvidence favouring a Gaussian initial mass function for systems of old globular clusters has accumulated over recent years. We show that a bell-shaped mass function may be the imprint of expulsion from protoclusters of the leftover star forming gas due to supernova activity. Owing to the corresponding weakening of its gravitational potential, a protocluster retains a fraction only of its newly formed stars. The mass fraction of bound stars extends from zero to unity depending on the star formation efficiency achieved by the protoglobular cloud. We investigate how such wide variations affect the mapping of the protoglobular cloud mass function to the initial globular cluster mass function. We conclusively demonstrate that the universality of the globular cluster mass function originates from a common protoglobular cloud mass-scale of about 106 M⊙ among galaxies. Moreover, gas removal during star formation in massive gas clouds is highlighted as the likely prime cause of the predominance of field stars in the Galactic Halo.

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26

Lazar, Alexandres, and Volker Bromm. "Probing the initial mass function of the first stars with transients." Monthly Notices of the Royal Astronomical Society 511, no. 2 (January 28, 2022): 2505–14. http://dx.doi.org/10.1093/mnras/stac176.

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ABSTRACT The emergence of the first, so-called Population III (Pop III), stars shaped early cosmic history in ways that crucially depends on their initial mass function (IMF). However, because of the absence of direct observational constraints, the detailed IMF remains elusive. Nevertheless, numerical simulations agree in broad terms that the first stars were typically massive and should often end their lives in violent, explosive deaths. These fates include extremely luminous pair-instability supernovae (PISNe) and bright gamma-ray bursts (GRBs), the latter arising from the collapse of rapidly rotating progenitor stars into black holes. These high-redshift transients are expected to be within the detection limits of upcoming space telescope missions, allowing to place effective constraints on the shape of the primordial IMF that is not easily accessible with other probes. This paper presents a framework to probe the Pop III IMF, utilizing the cosmological source densities of high-redshift PISNe and GRBs. Considering these transients separately could provide useful constraints on the Pop III IMF, but tighter bounds are obtainable by combining PISN and GRB counts. This combined diagnostic is more robust as it is independent of the underlying Pop III star formation rate density, an unknown prior. Future surveys promise to capture most high-redshift GRBs across the entire sky, but high-redshift PISN searches with future telescopes, e.g. Roman Space Telescope, will likely be substantially incomplete. Nevertheless, we demonstrate that even such lower bounds on the PISN count will be able to provide key constraints on the primordial IMF, in particular, if it is top-heavy or not.

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27

Riaz, R., D. R. G. Schleicher, S. Vanaverbeke, and R. S. Klessen. "Do fragmentation and accretion affect the stellar initial mass function?" Monthly Notices of the Royal Astronomical Society 494, no. 2 (March 20, 2020): 1647–57. http://dx.doi.org/10.1093/mnras/staa787.

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ABSTRACT While the stellar initial mass function (IMF) appears to be close to universal within the Milky Way galaxy, it is strongly suspected to be different in the primordial universe, where molecular hydrogen cooling is less efficient and the gas temperature can be higher by a factor of 30. In between these extreme cases, the gas temperature varies depending on the environment, metallicity, and radiation background. In this paper we explore if changes of the gas temperature affect the IMF of the stars considering fragmentation and accretion. The fragmentation behaviour depends mostly on the Jeans mass at the turning point in the equation of state (EOS) where a transition occurs from an approximately isothermal to an adiabatic regime due to dust opacities. The Jeans mass at this transition in the EOS is always very similar, independent of the initial temperature, and therefore the initial mass of the fragments is very similar. Accretion on the other hand is strongly temperature dependent. We argue that the latter becomes the dominant process for star formation efficiencies above 5–7 per cent, increasing the average mass of the stars.

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28

Scalo, John M. "The Initial Mass Function of Massive Stars in Galaxies: Empirical Evidence." Symposium - International Astronomical Union 116 (1986): 451–66. http://dx.doi.org/10.1017/s0074180900149411.

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Observational constraints on the form of the high-mass stellar IMF are reviewed. The evidence includes star counts in the solar neighborhood, individual and composite star clusters, and nearby galaxies, and arguments based on integrated light and chemical evolution modeling. There is no convincing evidence for any systematic variations of the shape of the high-mass IMF. However, the various determinations are very uncertain, and do not allow any firm estimate of the logarithmic slope of the upper IMF; the appropriate value is somewhere between −1.3 and −2.3, with region-to-region variations smaller than about ±0.5. A number of lines of evidence suggest that the lower mass limit or mode mass of the IMF increases with increasing star formation rate, reaching perhaps 10–15 m⊙ in some starburst galaxies. It is also possible that the upper mass limit depends on metallicity, based on variations in excitation conditions of HII regions.

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29

Sekiguchi, Kazuhiro, and Kurt S. Anderson. "The initial mass function for early-type stars in starburst galaxies." Astronomical Journal 94 (September 1987): 644. http://dx.doi.org/10.1086/114500.

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30

Lada, Charles J. "Stellar Multiplicity and the Initial Mass Function: Most Stars Are Single." Astrophysical Journal 640, no. 1 (February 23, 2006): L63—L66. http://dx.doi.org/10.1086/503158.

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31

Löckmann, U., H. Baumgardt, and P. Kroupa. "Constraining the initial mass function of stars in the Galactic Centre." Monthly Notices of the Royal Astronomical Society 402, no. 1 (December 11, 2009): 519–25. http://dx.doi.org/10.1111/j.1365-2966.2009.15906.x.

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32

Sharda, Piyush, Christoph Federrath, and Mark R. Krumholz. "The importance of magnetic fields for the initial mass function of the first stars." Monthly Notices of the Royal Astronomical Society 497, no. 1 (July 6, 2020): 336–51. http://dx.doi.org/10.1093/mnras/staa1926.

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ABSTRACT Magnetic fields play an important role for the formation of stars in both local and high-redshift galaxies. Recent studies of dynamo amplification in the first dark matter haloes suggest that significant magnetic fields were likely present during the formation of the first stars in the Universe at redshifts of 15 and above. In this work, we study how these magnetic fields potentially impact the initial mass function (IMF) of the first stars. We perform 200 high-resolution, three-dimensional (3D), magnetohydrodynamic (MHD) simulations of the collapse of primordial clouds with different initial turbulent magnetic field strengths as predicted from turbulent dynamo theory in the early Universe, forming more than 1100 first stars in total. We detect a strong statistical signature of suppressed fragmentation in the presence of strong magnetic fields, leading to a dramatic reduction in the number of first stars with masses low enough that they might be expected to survive to the present-day. Additionally, strong fields shift the transition point where stars go from being mostly single to mostly multiple to higher masses. However, irrespective of the field strength, individual simulations are highly chaotic, show different levels of fragmentation and clustering, and the outcome depends on the exact realization of the turbulence in the primordial clouds. While these are still idealized simulations that do not start from cosmological initial conditions, our work shows that magnetic fields play a key role for the primordial IMF, potentially even more so than for the present-day IMF.

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33

Frantsman, Yu L. "The Evolution of Stars on the AGB: The Mass Loss Intensity and the Formation of Carbon Stars." International Astronomical Union Colloquium 106 (1989): 224. http://dx.doi.org/10.1017/s0252921100062941.

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Simulated populations of white dwarfs and N type carbon stars were generated for a Salpeter initial mass function and constant stellar birth rate history. The effect of very strong mass loss on the mass distribution of white dwarfs and the luminosity distribution of carbon stars is discussed and the results are compared with observations. A significant mass loss by stars on the TP-AGB occurs besides regular stellar wind and planetary nebulae ejection. Thus it is possible to explain the luminosity functions of carbon and M stars in the Magellanic Clouds (with very few stars brighter than Mbol = -6.0), the very narrow mass distribution of white dwarfs, and the very small number of white dwarfs with M > 1.0 MΘ. The luminosity of some AGB stars in the SMC is so high that they may be supernova of type 1 1/2 precursors. There are no such stars in the LMC. Comparison of the theoretical and observed luminosity distributions of high-luminosity AGB stars in the Magellanic Clouds shows that the mass-loss rate of these stars in the LMC is about an order of magnitude larger than in the SMC. In the Galaxy carbon stars may form only from stars with initial mass less than 1.5 MΘ due to the relatively small initial heavy element abundance in these stars; this is perhaps the main reason for the absence of carbon stars in open clusters in the Galaxy.

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34

Hénault-Brunet, V., M. Gieles, J. Strader, M. Peuten, E. Balbinot, and K. E. K. Douglas. "On the black hole content and initial mass function of 47 Tuc." Monthly Notices of the Royal Astronomical Society 491, no. 1 (October 24, 2019): 113–28. http://dx.doi.org/10.1093/mnras/stz2995.

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ABSTRACT The globular cluster (GC) 47 Tuc has recently been proposed to host an intermediate-mass black hole (IMBH) or a population of stellar mass black holes (BHs). To shed light on its dark content, we present an application of self-consistent multimass models with a varying mass function and content of stellar remnants, which we fit to various observational constraints. Our best-fitting model successfully matches the observables and correctly predicts the radial distribution of millisecond pulsars and their gravitational accelerations inferred from long-term timing observations. The data favours a population of BHs with a total mass of $430^{+386}_{-301}$ M⊙, but the most likely model has very few BHs. Since our models do not include a central IMBH and accurately reproduce the observations, we conclude that there is currently no need to invoke the presence of an IMBH in 47 Tuc. The global present-day mass function inferred is significantly depleted in low-mass stars (power-law slope $\alpha =-0.52^{+0.17}_{-0.16}$). Given the orbit and predicted mass-loss history of this massive GC, the dearth of low-mass stars is difficult to explain with a standard initial mass function (IMF) followed by long-term preferential escape of low-mass stars driven by two-body relaxation, and instead suggests that 47 Tuc may have formed with a bottom-light IMF. We discuss alternative evolutionary origins for the flat mass function and ways to reconcile this with the low BH retention fraction. Finally, by capturing the effect of dark remnants, our method offers a new way to probe the IMF in a GC above the current main-sequence turn-off mass, for which we find a slope of −2.49 ± 0.08.

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Caballero-Nieves, Saida M., and P. A. Crowther. "The Young and the Massive: Stars at the upper end of the Initial Mass Function." Proceedings of the International Astronomical Union 12, S329 (November 2016): 104–9. http://dx.doi.org/10.1017/s174392131700326x.

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AbstractThe upper mass limit of stars remains an open question in astrophysics. Here we discuss observations of the most massive stars (greater than 100 solar masses) in the local universe and how the observations fit in with theoretical predictions. In particular, the Large Magellanic Cloud plays host to numerous very massive stars, making it an ideal template to study the roles that environment, metallicity, and multiplicity play in the formation and evolution of the most massive stars. We will discuss the work that is instrumental in laying the groundwork for interpreting future observations by James Webb of starburst regions in the high redshift universe.

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Murphy, Laura J., Jose H. Groh, Eoin Farrell, Georges Meynet, Sylvia Ekström, Sophie Tsiatsiou, Alexander Hackett, and Söbastien Martinet. "Ionizing photon production of Population III stars: effects of rotation, convection, and initial mass function." Monthly Notices of the Royal Astronomical Society 506, no. 4 (July 20, 2021): 5731–49. http://dx.doi.org/10.1093/mnras/stab2073.

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ABSTRACT The first stars are thought to be one of the dominant sources of hydrogen reionization in the early Universe, with their high luminosities and surface temperatures expected to drive high ionizing photon production rates. In this work, we take our Geneva stellar evolution models of zero-metallicity stars and predict their production rates of photons capable to ionize H, He i, and He ii, based on a blackbody approximation. We present analytical fits in the range 1.7–500 $\, \mathrm{M}_{\odot }$. We then explore the impact of stellar initial mass, rotation, and convective overshooting for individual stars. We have found that ionizing photon production rates increase with increasing initial mass. For the rotational velocities considered we see changes of up to 25 per cent to ionizing photons produced. This varies with initial mass and ionizing photon species and reflects changes to surface properties due to rotation. We have also found that higher convective overshooting increases ionizing photon production by approximately 20 per cent for the change in overshooting considered here. For stellar populations, we explore how the production of ionizing photons varies as a function of the initial mass function (IMF) slope, and minimum and maximum initial masses. For a fixed population mass we have found changes of the order of 20–30 per cent through varying the nature of the IMF. This work presents ionizing photon production predictions for the most up to date Geneva stellar evolution models of Population III stars, and provides insight into how key evolutionary parameters impact the contribution of the first stars to reionization.

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Kroupa, Pavel, and Carsten Weidner. "Galactic‐Field Initial Mass Functions of Massive Stars." Astrophysical Journal 598, no. 2 (December 2003): 1076–78. http://dx.doi.org/10.1086/379105.

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Luhman, K. L., G. H. Rieke, Erick T. Young, Angela S. Cotera, H. Chen, Marcia J. Rieke, Glenn Schneider, and Rodger I. Thompson. "The Initial Mass Function of Low‐Mass Stars and Brown Dwarfs in Young Clusters." Astrophysical Journal 540, no. 2 (September 10, 2000): 1016–40. http://dx.doi.org/10.1086/309365.

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Essex, Christopher, Shantanu Basu, Janett Prehl, and Karl Heinz Hoffmann. "A multiple power-law distribution for initial mass functions." Monthly Notices of the Royal Astronomical Society 494, no. 2 (April 11, 2020): 1579–86. http://dx.doi.org/10.1093/mnras/staa755.

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ABSTRACT We introduce a new multi-power-law distribution for the initial mass function (IMF) to explore its potential properties. It follows on prior work that introduced mechanisms accounting for mass accretion in star formation, developed within the framework of general evolution equations for the mass distribution of accreting and non-accreting (proto)stars. This paper uses the same fundamental framework to demonstrate that the interplay between a mass-dependent and a time-dependent step-like dropout rate from accretion leads to IMFs that exhibit multiple power laws for an exponential mass growth. While the mass-dependent accretion and its dropout is intrinsic to each star, the time-dependent dropout might be tied to a specific history such as the rapid consumption of nebular material by nearby stars or the sweeping away of some material by shock waves. The time-dependent dropout folded into the mass-dependent process of star formation is shown to have a significant influence on the IMFs.

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Komiya, Yutaka, Takuma Suda, Asao Habe, and Masayuki Y. Fujimoto. "EMP stars with high mass IMF and hierarchical galaxy formation." Proceedings of the International Astronomical Union 5, S265 (August 2009): 128–29. http://dx.doi.org/10.1017/s1743921310000384.

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AbstractExtremely metal-poor (EMP) stars in the Galactic halo are stars formed in the very early stage of the chemical evolution of the Galaxy. In previous study, we proposed that typical mass of EMP stars are massive, based on observations of carbon-enhanced EMP stars. In this study, we build a merger tree of the Galaxy semi-analytically and follow the chemical evolution along the merger tree. We also consider the effect of binary and high-mass initial mass function(IMF). Resultant theoretical metallicity distribution function (MDF) and abundance distribution are compared with observed metal-poor halo stars.

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Komiya, Yutaka, Shimako Yamada, Takuma Suda, and Masayuki Y. Fujimoto. "The stellar initial mass function in the early universe revealed from old stellar populations in our neighbourhood." Proceedings of the International Astronomical Union 8, S295 (August 2012): 322. http://dx.doi.org/10.1017/s1743921313005243.

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AbstractWe present a new method to investigate the IMF in the early universe from observations of extremely metal-poor (EMP) stars. EMP stars are the low-mass survivors of stars which are formed in the early universe. We can give constraints on the IMF from statistics of the elemental abundances of the EMP stars in the Galactic halo.

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Vesperini, Enrico, Jongsuk Hong, Jeremy J. Webb, Franca D’Antona, and Annibale D’Ercole. "Dynamical effects on the stellar mass function of multiple stellar populations in globular clusters." Proceedings of the International Astronomical Union 14, S351 (May 2019): 346–49. http://dx.doi.org/10.1017/s1743921319007683.

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AbstractWe present a brief summary of the results of a study of the effects of dynamical evolution on the stellar mass function of multiple-population globular clusters. Theoretical studies have predicted that the process of multiple-population cluster formation results in a system in which second-generation (2G) stars are initially more centrally concentrated than first-generation (1G) stars. In the study presented here, we have explored the implications of the initial differences between the 2G and 1G structural properties for the evolution of the local (measured at different distances from a cluster center) and global mass function. We have studied both systems in which 1G and 2G stars start with the same initial mass function (IMF) and systems in which 1G and 2G stars have different IMFs. Finally we have explored the evolution of the spatial mixing and found that the multiscale nature of the clusters studied leads to a dependence of the mixing rate on the stellar mass.

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Chulkov, Dmitry. "Pairing function of visual binary stars." Monthly Notices of the Royal Astronomical Society 501, no. 1 (November 20, 2020): 769–83. http://dx.doi.org/10.1093/mnras/staa3601.

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ABSTRACT An all-sky sample of 1227 visual binaries based on Washington Double Star catalogue is constructed to infer the initial mass function (IMF), mass ratio, and projected distance distribution with a dedicated population synthesis model. Parallaxes from Gaia DR2 and Hipparcos are used to verify the distance distribution. The model is validated on the single-star Tycho-2 sample and successfully reproduces the observed magnitudes and angular separations. The projected separation distribution follows f(s) ∼ s−1.2 in 102–2 × 103 au range for 1–4.5 m⊙ primary stars. Several algorithms are explored as pairing functions. Random pairing is confidently rejected. Primary-constrained pairing (PCP) and split-core pairing (SCP), the scenarios adopting primary component’s or total system’s mass as fundamental, are considered. The preferred IMF slope is α ∼ 2.8 either way. A simple power-law mass ratio distribution is unlikely, but the introduction of a twin excess provides a favourable result. PCP with f(q) ∼ q−1 is preferred with a tiny twin fraction, models with f(q) ∼ q−1.5 are acceptable when a larger twin excess is allowed. SCP is similar to PCP when a larger slope of the power law is adopted: f(q) ∼ qβ + 0.7.

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Farrell, Eoin, Adam S. Jermyn, Matteo Cantiello, and Daniel Foreman-Mackey. "The Initial Magnetic Field Distribution in AB Stars." Astrophysical Journal 938, no. 1 (October 1, 2022): 10. http://dx.doi.org/10.3847/1538-4357/ac8423.

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Abstract Stars are born with magnetic fields, but the distribution of their initial field strengths remains uncertain. We combine observations with theoretical models of magnetic field evolution to infer the initial distribution of magnetic fields for AB stars in the mass range of 1.6–3.4 M ⊙. We tested a variety of distributions with different shapes and found that a distribution with a mean of ∼800 G and a full width of ∼600 G is most consistent with the observed fraction of strongly magnetized stars as a function of mass. Our most-favored distribution is a Gaussian with a mean of μ = 770 G and standard deviation of σ = 146 G. Independent approaches to measure the typical field strength suggest values closer to 2–3 kG, a discrepancy that could suggest a mass-dependent and bimodal initial field distribution, or an alternative theoretical picture for the origin of these magnetic fields.

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Rubin, Douglas, and Abraham Loeb. "Constraining the Stellar Mass Function in the Galactic Center via Mass Loss from Stellar Collisions." Advances in Astronomy 2011 (2011): 1–19. http://dx.doi.org/10.1155/2011/174105.

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The dense concentration of stars and high-velocity dispersions in the Galactic center imply that stellar collisions frequently occur. Stellar collisions could therefore result in significant mass loss rates. We calculate the amount of stellar mass lost due to indirect and direct stellar collisions and find its dependence on the present-day mass function of stars. We find that the total mass loss rate in the Galactic center due to stellar collisions is sensitive to the present-day mass function adopted. We use the observed diffuse X-ray luminosity in the Galactic center to preclude any present-day mass functions that result in mass loss rates>10-5M⨀yr−1in the vicinity of~1″. For present-day mass functions of the form,dN/dM∝M-α, we constrain the present-day mass function to have a minimum stellar mass≲7M⨀and a power-law slope≳1.25. We also use this result to constrain the initial mass function in the Galactic center by considering different star formation scenarios.

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Nakano, Takenori. "Star Formation: Can There BE a Break in the IMF Near 0.1Mʘ?" Highlights of Astronomy 11, no. 1 (1998): 425–26. http://dx.doi.org/10.1017/s1539299600021638.

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The initial mass function of stars (IMF) at small masses depends on several factors. First, it depends on the mass function of cloud cores in which stars form. Second, there must be a lower limit to the core mass for contraction; very small mass cores may not contract even if they exist. This must affect greatly the IMF near its lower end. Third, not all core matter may become stars; we must determine the stellar mass M*, or the star formation efficiency M*/Mcc, as a function of the mass of the cloud core, Mcc. In this paper we discuss the second and third points.

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Park, Byeong-Gon, Hwankyung Sung, Michael S. Bessell, and Yong Hee Kang. "The Pre–Main-Sequence Stars and Initial Mass Function of NGC 2264." Astronomical Journal 120, no. 2 (August 2000): 894–908. http://dx.doi.org/10.1086/301459.

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48

Kroupa, P. "The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems." Science 295, no. 5552 (January 4, 2002): 82–91. http://dx.doi.org/10.1126/science.1067524.

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Haas, M. R., and P. Anders. "Population synthesis from clustered star formation." Proceedings of the International Astronomical Union 5, S262 (August 2009): 347–48. http://dx.doi.org/10.1017/s1743921310003170.

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In recent years, a series of papers (Kroupa & Weidner 2003, Weidner & Kroupa 2004, Weidner & Kroupa 2005 and Weidner & Kroupa 2006, WK06 from now on) have proposed that the stellar content of an entire galaxy may not be well described by the same initial mass function (IMF) that describes the distribution of stellar masses in the star clusters, where these stars form. The reason is that star clusters also form with a cluster mass function (CMF), which is a power law with a power law index of ~−2. If the lowest mass clusters are of masses smaller than the physical upper mass limit for stars they will be deficient in high mass stars. Therefore, if the stellar content of all clusters is added together, making up the Integrated Galactic Initial Mass Function (IGIMF), the distribution of stellar masses may be steeper at the high mass end, depending on the exact shape of the CMF.

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Haas, M. R., and P. Anders. "Galactic consequences of clustered star formation." Proceedings of the International Astronomical Union 5, S266 (August 2009): 417–20. http://dx.doi.org/10.1017/s1743921309991566.

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AbstractIf all stars form in clusters and both stars and clusters follow a power-law distribution which favours the creation of low-mass objects, the numerous low-mass clusters will be deficient in high-mass stars. Therefore, the stellar mass function integrated over the entire galaxy (the integrated galactic initial mass function; IGIMF) will be steeper at the high-mass end than the underlying stellar IMF. We show how the steepness of the IGIMF depends on the sampling method and on the assumptions made regarding the star cluster mass function. We also investigate the O-star content, integrated photometry and chemical enrichment of galaxies that result from several IGIMFs compared to more standard IMFs.

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