3. Stars

2016 ◽  
pp. 22-49
Author(s):  
James Binney
Keyword(s):  
Star Formation ◽  
20Th Century ◽  
Binary Stars ◽  
Star Clusters ◽  
Solar Neutrinos ◽  
Interstellar Gas ◽  
Stellar Seismology ◽  
Stellar Masses ◽  
Century Science ◽  
The Universe

Most of what we know about the Universe has been gleaned from the study of stars, and a major achievement of 20th-century science was to understand how stars work and their lifecycles from birth to death. ‘Stars’ describes this lifecycle beginning with star formation when a cloud of interstellar gas suffers a runaway of its central density. It then considers nuclear fusion, key stellar masses, and life after the main sequence when the star burns its core helium. The surfaces of stars are described along with stellar coronae and exploding stars—both core-collapse and deflagration supernovae. Finally, globular star clusters, solar neutrinos, stellar seismology, and binary stars are discussed.

scholarly journals Modeling of Integrated Spectral Energy Distributions of Stellar Populations with Various Binary Fractions

2021 ◽  
Vol 2068 (1) ◽  
pp. 012048
Author(s):  
Zhongmu Li ◽  
Chen Yan
Keyword(s):  
Binary Stars ◽  
Star Clusters ◽  
Stellar Populations ◽  
Spectral Studies ◽  
Spectral Energy ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
Spectral Fitting ◽  
The Universe

Abstract Binary stars are common in the universe, but binary fractions are various in different star clusters and galaxies. Studies have shown that binary fraction affects the integrated spectral energy distributions obviously, in particular in the UV band. It affects spectral fitting of many star clusters and galaxies significantly. However, previous works usually take a fixed binary fraction, i.e., 0.5, and this is far from getting accurate results. Therefore, it is important to model the integrated spectral energy distributions of stellar populations with various binary fractions. This work presents a modeling of spectral energy distributions of simple stellar populations with binary fractions of 0.3, 0.7, and 1.0. The results are useful for different kinds of spectral studies.

scholarly journals Galaxies in the first billion years: implications for re-ionization and the star formation history at z>6

2006 ◽  
Vol 2 (14) ◽  
pp. 248-248
Author(s):  
Andrew J. Bunker ◽  
Elizabeth R. Stanway ◽  
Laurence P. Eyles ◽  
Richard S. Ellis ◽  
Richard G. McMahon ◽  
...  
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Stellar Populations ◽  
Star Formation History ◽  
Star Forming ◽  
Formation History ◽  
Stellar Masses ◽  
The Universe ◽  
Selection Of

AbstractWe discuss the selection of star-forming galaxies at z≃6 through the Lyman-break technique. Spitzer imaging implies many of these contain older stellar populations (>200Myr) which produce detectable Balmer breaks. The ages and stellar masses (∼1010M⊙) imply that the star formation rate density at earlier epochs may have been significantly higher than at z≃6, and might have played a key role in re-ionizing the universe.

scholarly journals A VLT/MUSE analysis of HeIIλ1640 emitters at z = 2 – 4

2019 ◽  
Vol 15 (S352) ◽  
pp. 78-78
Author(s):  
Themiya Nanayakkara
Keyword(s):  
Star Formation ◽  
Binary Stars ◽  
Stellar Population ◽  
Population Models ◽  
X Ray ◽  
Uv Emission ◽  
Low Metallicity ◽  
Star Formation Histories ◽  
X Ray Binaries ◽  
The Universe

AbstractIn the quest to study early star-formation physics in the universe, one of the most sought after tracers is HeIIλ1640, with its presence in the lack of other metal emission/absorption lines generally being interpreted as evidence for metal-poor stellar populations. HeII ionizing photons are produced via sources of hard ionizing radiation and requires photons with energies ⩾ 54.4eV, however, traditional stellar population models lack sufficient ionising photons to match with current observations. Our analysis of z = 2 – 4 HeIIλ1640 emitters from deep 10-30h pointings from MUSE has shown that ISM properties inferred from multiple rest-UV diagnostics are not compatible with requirements necessary to reproduce HeIIλ1640 equivalent-widths. Thus, we have used latest generation of single, rotational, and binary stellar population models with realistic dust physics to explore rest-UV emission line diagnostics and link with H and He+ ionisation photon production efficiencies (ξion (H,He+)) in a variety of stellar/gas metallicities and star-formation histories. I will discus our latest results and show that including ‘exotic’ stellar phenomena such as extreme low-metallicity binary stars, X-ray binaries, and dust dissociation physics may be necessary to lessen the tension between models and observations.

scholarly journals Size, shade, or shape? The contribution of galaxies of different types to the star formation history of the Universe from SDSS-IV MaNGA

2021 ◽  
Vol 502 (3) ◽  
pp. 3128-3143
Author(s):  
Thomas Peterken ◽  
Alfonso Aragón-Salamanca ◽  
Michael Merrifield ◽  
Vladimir Avila-Reese ◽  
Nicholas F Boardman ◽  
...  
Keyword(s):  
Star Formation ◽  
Sloan Digital Sky Survey ◽  
Star Formation History ◽  
Fourth Generation ◽  
Massive Galaxies ◽  
Formation History ◽  
Galaxy Sample ◽  
History Of ◽  
Stellar Masses ◽  
The Universe

ABSTRACT By fitting stellar populations to the fourth generation of the Sloan Digital Sky Survey (SDSS-IV) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey observations of ∼7000 suitably weighted individual galaxies, we reconstruct the star formation history of the Universe, which we find to be in reasonable agreement with previous studies. Dividing the galaxies by their present-day stellar mass, we demonstrate the downsizing phenomenon, whereby the more massive galaxies hosted the most star formation at earlier times. Further dividing the galaxy sample by colour and morphology, we find that a galaxy’s present-day colour tells us more about its historical contribution to the cosmic star formation history than its current morphology. We show that downsizing effects are greatest among galaxies currently in the blue cloud, but that the level of downsizing in galaxies of different morphologies depends quite sensitively on the morphological classification used, due largely to the difficulty in classifying the smaller low-mass galaxies from their ground-based images. Nevertheless, we find agreement that among galaxies with stellar masses $M_{\star } \gt 6\times 10^{9}\, \mathrm{ M}_{\odot }$, downsizing is most significant in spirals. However, there are complicating factors. For example, for more massive galaxies, we find that colour and morphology are predictors of the past star formation over a longer time-scale than in less massive systems. Presumably this effect is reflecting the longer period of evolution required to alter these larger galaxies’ physical properties, but shows that conclusions based on any single property do not tell the full story.

scholarly journals The VIMOS VLT Deep Survey: A census of active and passive galaxies to redshift 1.3

2006 ◽  
Vol 2 (S235) ◽  
pp. 400-400
Author(s):  
D. Vergani
Keyword(s):  
Star Formation ◽  
Cosmic Time ◽  
Late Type ◽  
Limited Sample ◽  
Active Star ◽  
Star Forming ◽  
Star Formation Activity ◽  
Deep Survey ◽  
Stellar Masses ◽  
The Universe

AbstractWe are studying how stellar masses assemble through cosmic time since the Universe had only 30% of its present age. We are conducting a census of galaxies which covers the end of the most active star-forming phase, using a mass-limited sample of approximately 5,000 objects selected from the VIMOS VLT Deep Survey (VVDS) in the redshift range 0.45 < z < 1.3. With a criterion based on the direct spectral measurement of the 4000Å Balmer break, Dn(4000), we have classified our sample in spectroscopically early and late-type galaxies. The trends existing between stellar mass, spectroscopic classification, and star formation activity are clearly shown in our analysis.

scholarly journals Exhausted gas reservoirs drive massive galaxy quenching in the early universe

2020 ◽  
Author(s):  
Katherine Whitaker ◽  
Christina Williams ◽  
Lamiya Mowla ◽  
Justin Spilker ◽  
Sune Toft ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Gas ◽  
Dark Matter Halos ◽  
Gas Reservoirs ◽  
Massive Galaxies ◽  
Star Forming ◽  
Early Galaxies ◽  
Stellar Masses ◽  
Cold Dust ◽  
The Universe

Abstract When the Universe was merely three billion years old, about half of massive galaxies had already formed the bulk of their stars and new star formation plummeted [1]. How galaxies quench at such early times remains a puzzle, as their dark matter halos contain large gas reservoirs [2-4]. This gas should cool efficiently, sustaining star formation over long periods [5,6]. Here we present sensitive 1.3mm wavelength observations of cold dust in six quenched galaxies in the redshift range z=1.6 to z=3.2 with stellar masses ranging from 2.5x1010M⊙ to 5x1011M⊙, which are magnified by foreground galaxy clusters. Even with factors of up to 30 in magnification, four of the six galaxies are undetected at this wavelength. We show that these quenched galaxies have extremely little dust at early times, and by proxy very little cold molecular gas. The median dust mass is <0.01% of the stellar mass (molecular gas mass <1%), more than two orders of magnitude less than star-forming galaxies at this epoch [4]. The implication is that most early galaxies shut off star formation because their reservoir of molecular gas was rapidly depleted or removed, and is not being replenished.

scholarly journals The effects of a background potential in star cluster evolution

2020 ◽  
Vol 639 ◽  
pp. A92 ◽  
Author(s):  
B. Reinoso ◽  
D. R. G. Schleicher ◽  
M. Fellhauer ◽  
N. W. C. Leigh ◽  
R. S. Klessen
Keyword(s):  
Binary Stars ◽  
Gravitational Force ◽  
Massive Star ◽  
Star Clusters ◽  
Star Cluster ◽  
Early Evolution ◽  
Relaxation Processes ◽  
Blue Stragglers ◽  
Stellar Collisions ◽  
The Universe

Runaway stellar collisions in dense star clusters are invoked to explain the presence of very massive stars or blue stragglers in the center of those systems. This process has also been explored for the first star clusters in the Universe and shown to yield stars that may collapse at some points into an intermediate mass black hole. Although the early evolution of star clusters requires the explicit modeling of the gas out of which the stars form, these calculations would be extremely time-consuming and often the effects of the gas can be accurately treated by including a background potential to account for the extra gravitational force. We apply this approximation to model the early evolution of the first dense star clusters formed in the Universe by performing N-body simulations, our goal is to understand how the additional gravitational force affects the growth of a very massive star through stellar mergers in the central parts of the star cluster. Our results show that the background potential increases the velocities of the stars, causing an overall delay in the evolution of the clusters and in the runaway growth of a massive star at the center. The population of binary stars is lower due to the increased kinetic energy of the stars, initially reducing the number of stellar collisions, and we show that relaxation processes are also affected. Despite these effects, the external potential enhances the mass of the merger product by a factor ∼2 if the collisions are maintained for long times.

scholarly journals Ultra Massive Passive Galaxies at z~1.7

2015 ◽  
Vol 11 (S319) ◽  
pp. 111-111
Author(s):  
Liz Arcila-Osejo ◽  
Marcin Sawicki ◽  
Anneya Golob ◽  
Stephane Arnouts ◽  
Thibaud Moutard
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Effective Area ◽  
Dark Matter Halos ◽  
Quenching Mechanism ◽  
Massive Galaxies ◽  
Star Formation Activity ◽  
Stellar Masses ◽  
The Universe ◽  
Very High

AbstractAt redshift z~1.7 the Universe was at the peak of its star-formation activity. It is thus a puzzle why some galaxies, many of them very massive (M* ⩾ 1011 M⊙), had already chosen to stop forming stars. These ultra-massive galaxies, guaranteed to be the central galaxies of their host dark matter halos, must have attained very high rates of star formation to assemble their stellar masses in such a short amount of time. Using the largest (to date) K-selected gzKs survey of passive galaxies (in an effective area of ~ 27.5 deg2) we study the demographics of these dead monsters, hoping to help understand the quenching mechanism that shut them down.

scholarly journals Concluding Remarks

1977 ◽  
Vol 33 ◽  
pp. 211-214
Author(s):  
Ivan R. Kino
Keyword(s):  
Star Formation ◽  
Celestial Mechanics ◽  
Star Clusters ◽  
Hard Core ◽  
Stellar Dynamics ◽  
Stellar Spectroscopy ◽  
Multiple Stars ◽  
Double And Multiple Stars ◽  
Impossible Task ◽  
The Universe

It is a great honor to be asked to summarize a conference such as this one, but it is also an impossible task. For a summary I refer you to the table of contents; what I will do here instead is to offer some personal impressions of what we have been doing.My initial feeling was that of an outsider; I have never worked in the field of double and multiple stars, to which many of you have devoted your careers. Yet this meeting has impressed me with the interrelationship of our areas. In this room, are astronomers who represent and have discussed celestial mechanics, stellar dynamics, stellar spectroscopy, and the astrophysics of star formation. I have not counted heads, but we outsiders might even outnumber you hard-core binary-fanciers. And this is, in some sense, a measure of the value of this meeting, and, even more pointedly, of the value of your work: how much does it matter to the rest of us? Every astronomer should ask himself—particularly when the technicalities get thickest— “What am I doing this for?” The answer is emphatically not merely that this particular work is interesting to do. The appeal of astronomy is not in the bricks and mortar that each of us prepares, but rather in the architecture of the structure that we build with those materials. The questions that we really pursue are not the orbits of binaries, nor the structure of star clusters, but rather the basic problems of the universe: how and why are stars made, and why do they develop as they do?

scholarly journals The Universe at z > 10: predictions for JWST from the universemachine DR1

2020 ◽  
Vol 499 (4) ◽  
pp. 5702-5718
Author(s):  
Peter Behroozi ◽  
Charlie Conroy ◽  
Risa H Wechsler ◽  
Andrew Hearin ◽  
Christina C Williams ◽  
...  
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Formation Rate ◽  
Mass Function ◽  
Model Parameters ◽  
James Webb Space Telescope ◽  
Luminosity Functions ◽  
Galaxy Halo ◽  
Stellar Masses ◽  
The Universe

ABSTRACT The James Webb Space Telescope (JWST) is expected to observe galaxies at z &gt; 10 that are presently inaccessible. Here, we use a self-consistent empirical model, the universemachine, to generate mock galaxy catalogues and light-cones over the redshift range z = 0−15. These data include realistic galaxy properties (stellar masses, star formation rates, and UV luminosities), galaxy–halo relationships, and galaxy–galaxy clustering. Mock observables are also provided for different model parameters spanning observational uncertainties at z &lt; 10. We predict that Cycle 1 JWST surveys will very likely detect galaxies with M* &gt; 107 M⊙ and/or M1500 &lt; −17 out to at least z ∼ 13.5. Number density uncertainties at z &gt; 12 expand dramatically, so efforts to detect z &gt; 12 galaxies will provide the most valuable constraints on galaxy formation models. The faint-end slopes of the stellar mass/luminosity functions at a given mass/luminosity threshold steepen as redshift increases. This is because observable galaxies are hosted by haloes in the exponentially falling regime of the halo mass function at high redshifts. Hence, these faint-end slopes are robustly predicted to become shallower below current observable limits (M* &lt; 107 M⊙ or M1500 &gt; −17). For reionization models, extrapolating luminosity functions with a constant faint-end slope from M1500 = −17 down to M1500 = −12 gives the most reasonable upper limit for the total UV luminosity and cosmic star formation rate up to z ∼ 12. We compare to three other empirical models and one semi-analytic model, showing that the range of predicted observables from our approach encompasses predictions from other techniques. Public catalogues and light-cones for common fields are available online.

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