scholarly journals Astrometry Missions: Probing the Galaxy and Beyond

2001 ◽  
Vol 205 ◽  
pp. 469-474
Author(s):  
F. Mignard
Keyword(s):  
Star Formation ◽  
Age Determination ◽  
Deep Impact ◽  
The Core ◽  
The Galaxy ◽  
Formation And Evolution ◽  
Space Astrometry ◽  
Summary Data

In the wake of the HIPPARCOS success four highly accurate space astrometry missions are now approved for launch within the next ten years. Stellar physics and galactic physics constitute the core science of these missions with deep impact on star formation and evolution, cosmic distance scales and age determination of the oldest stars. Summary data are provided in this paper to compare the goals and capabilities of these missions.

scholarly journals Microarcsec Astrometry: The Gaia Mission

1998 ◽  
Vol 11 (1) ◽  
pp. 581-582
Author(s):  
L. Lindegren ◽  
M.A.C. Perryman
Keyword(s):  
Accurate Determination ◽  
Distance Measurements ◽  
Profound Impact ◽  
Individual Stars ◽  
The Galaxy ◽  
Direct Distance ◽  
Scientific Potential ◽  
Space Astrometry ◽  
Small Instrument

The Hipparcos mission demonstrated the efficiency of space astrometry (in terms of number of objects, accuracy, and uniformity of results) and the fact that a relatively small instrument can have a very large scientific potential in the area of astrometry. However, Hipparcos could probe less than 0.1 per cent of the volume of the Galaxy by direct distance measurements. Using a larger instrument and more efficient detectors, it is now technically feasible to increase the efficiency of a space astrometry mission by several orders of magnitude, thus encompassing a large part of the Galaxy within its horizon for accurate determination of parallaxes and transverse velocities. Such a mission will have immediate and profound impact in the areas of the physics and evolution of individual stars and of the Galaxy as a whole.

scholarly journals CCD Photometry in the Core of the Fornax Dwarf Galaxy

1988 ◽  
Vol 126 ◽  
pp. 583-584
Author(s):  
Robert M. Light ◽  
P. Seitzer
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Dwarf Galaxy ◽  
Field Population ◽  
Ccd Photometry ◽  
The Core ◽  
The Galaxy ◽  
Good Determination ◽  
Giant Branch Stars

The present study is concerned with the examination of properties of stars in the core of the Fornax dwarf spheroidal galaxy. Previous studies have shown that Fornax has a very diverse stellar population. Four of the globular clusters associated with Fornax were found to have metallicities significantly lower than the mean metallicity of the field population of the galaxy (Buonanno et al. 1985); these clusters point out an older, metal-poor population. Also, there are a number of luminous carbon stars, which are indicative of a much younger population (see Mould and Aaronson 1986). Studies of the field population of Fornax (Demers, Kunkel, and Hardy, 1979; Buonanno et al., 1985) have shown a dispersion in metallicity. We have measured a large sample of giant branch stars, enabling a good determination of mean properties of the Fornax stellar population, as well as allowing a comparison of stars as a function of distance from the center of Fornax.

scholarly journals The Next Generation Fornax Survey (NGFS): VII. A MUSE view of the nuclear star clusters in Fornax dwarf galaxies

2020 ◽  
Vol 495 (2) ◽  
pp. 2247-2264
Author(s):  
Evelyn J Johnston ◽  
Thomas H Puzia ◽  
Giuseppe D’Ago ◽  
Paul Eigenthaler ◽  
Gaspar Galaz ◽  
...  
Keyword(s):  
Star Formation ◽  
Globular Clusters ◽  
Dwarf Galaxies ◽  
Star Clusters ◽  
Stellar Populations ◽  
Host Galaxy ◽  
Wide Field ◽  
The Core ◽  
The Galaxy

ABSTRACT Clues to the formation and evolution of nuclear star clusters (NSCs) lie in their stellar populations. However, these structures are often very faint compared to their host galaxy, and spectroscopic analysis of NSCs is hampered by contamination of light from the rest of the system. With the introduction of wide-field integral field unit (IFU) spectrographs, new techniques have been developed to model the light from different components within galaxies, making it possible to cleanly extract the spectra of the NSCs and study their properties with minimal contamination from the light of the rest of the galaxy. This work presents the analysis of the NSCs in a sample of 12 dwarf galaxies in the Fornax Cluster observed with the Multi-Unit Spectroscopic Explorer (MUSE). Analysis of the stellar populations and star formation histories reveal that all the NSCs show evidence of multiple episodes of star formation, indicating that they have built up their mass further since their initial formation. The NSCs were found to have systematically lower metallicities than their host galaxies, which is consistent with a scenario for mass assembly through mergers with infalling globular clusters, whilst the presence of younger stellar populations and gas emission in the core of two galaxies is indicative of in-situ star formation. We conclude that the NSCs in these dwarf galaxies likely originated as globular clusters that migrated to the core of the galaxy that have built up their mass mainly through mergers with other infalling clusters, with gas-inflow leading to in-situ star formation playing a secondary role.

scholarly journals Star formation history of the galaxy merger Mrk848 with SDSS-IV MaNGA

2016 ◽  
Vol 11 (S321) ◽  
pp. 304-304
Author(s):  
Fang-Ting Yuan ◽  
Shiyin Shen ◽  
Lei Hao ◽  
Maria Argudo Fernandez
Keyword(s):  
Star Formation ◽  
Star Formation History ◽  
Galaxy Mergers ◽  
The Core ◽  
Integral Field Spectroscopy ◽  
3D Data ◽  
The Galaxy ◽  
Multi Wavelength ◽  
History Of ◽  
Star Formation Histories

AbstractWith the 3D data of SDSS-IV MaNGA (Bundy et al. 2015) spectra and multi-wavelength SED modeling, we expect to have a better understanding of the distribution of dust, gas and star formation of galaxy mergers. For a case study of the merging galaxy Mrk848, we use both UV-to-IR broadband SED and the MaNGA integral field spectroscopy to obtain its star formation histories at the tail and core regions. From the SED fitting and full spectral fitting, we find that the star formation in the tail regions are affected by the interaction earlier than the core regions. The core regions show apparently two times of star formation and a strong burst within 500Myr, indicating the recent star formation is triggered by the interaction. The star formation histories derived from these two methods are basically consistent.

scholarly journals ChandraObservations of the Galaxy Cluster A478: The Interaction of Hot Gas and Radio Plasma in the Core, and an Improved Determination of the Comptony‐Parameter

2003 ◽  
Vol 587 (2) ◽  
pp. 619-624 ◽  
Author(s):  
M. Sun ◽  
C. Jones ◽  
S. S. Murray ◽  
S. W. Allen ◽  
A. C. Fabian ◽  
...  
Keyword(s):  
Galaxy Cluster ◽  
Hot Gas ◽  
The Core ◽  
The Galaxy

The star formation history of the M31 galaxy derived from Long-Period-Variable star counts

2018 ◽  
Vol 14 (S343) ◽  
pp. 512-513
Author(s):  
Maryam Torki ◽  
Atefeh Javadi ◽  
Jacco Th. van Loon ◽  
Hossein Safari
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Variable Stars ◽  
Star Formation History ◽  
Long Period ◽  
Formation History ◽  
The Galaxy ◽  
History Of ◽  
Period Variable ◽  
Formation And Evolution

AbstractThe determination of the star formation history is a key goal for understanding galaxies. In this regard, nearby galaxies in the Local Group offer us a complete suite of galactic environment that is perfect for studying the connection between stellar populations and galaxy evolution. In this paper, we present the star formation history of M31 using long period variable stars that are prime targets for studying the galaxy formation and evolution because of their evolutionary phase. In this method, at first, we convert the near-infrared K-band magnitude of evolved stars to mass and age and from this we reconstruct the star formation and evolution of the galaxy.

scholarly journals Evolutionary Models of Nucleosynthesis in the Galaxy

1971 ◽  
Vol 10 ◽  
pp. 179-222
Author(s):  
J. W. Truran ◽  
A.G.W. Cameron
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Massive Star ◽  
Massive Stars ◽  
Cosmic Ray ◽  
Heavy Elements ◽  
Core Material ◽  
Massive Star Formation ◽  
The Core ◽  
The Galaxy

AbstractA model of the galaxy is constructed and evolved in which the integrated influence of stellar and supernova nucleosynthesis on the composition of the interstellar gas is traced numerically. Our detailed assumptions concerning the character of the matter released from evolving stars and supernovae are guided by the results of recent stellar evolutionary calculations and hydrodynamic studies of supernova events. Stars of main sequence mass in the range 4 ≤ M ≤ 8 M⊙ are assumed to give rise to supernova events, leaving remnants we identify with neutron stars and pulsars and forming both the carbon-to-iron nuclei and the r-process heavy elements in the explosive ejection of the core material. For more massive stars, we assume the core implosion will result in the formation of a Schwarzschild singularity, that is, a black hole or ‘collapsar’. The straightforward assumptions (1) that the gas content of the galaxy decreases exponentially with time to its present level of ~ 5 % and (2) that the luminosity function characteristic of young clusters and the solar neighborhood is appropriate throughout galactic history, lead to the prediction that ≈ 20% of the unevolved stars of approximately one solar mass (M⊙) in the galaxy today should have metal compositions Z ≲ 0.1 Z⊙. As Schmidt has argued from similar reasoning, this is quite inconsistent with current observations; an early generation dominated by more massive stars – which would by now have evolved – is suggested by this difficulty. Many of these massive stars, according to our assumptions, will end their lives as collapsed black hole remnants. It is difficult to visualize an epoch of massive star formation in the collapsing gas cloud which formed our galaxy which would enrich the gas rapidly enough to account for the level of heavy element abundances in halo population stars; we have therefore proposed a stage of star formation which is entirely pregalactic in character. We suggest that the Jeans’ length-sized initial condensations in the expanding universe discussed by Peebles and Dicke may provide the appropriate setting for this first generation of stars. Guided by these considerations, and by the need for a substantial quantity of ‘unseen’ mass to bind our local group of galaxies, we have constructed a model of the galaxy in which this violent early phase of massive star formation produces both (1) approximately 25 % of the level of heavy elements observed in the solar system and (2) an enormous unseen mass in the form of black holes. The implications of our model for other features of the galaxy, including supernova nucleosynthesis, the cosmic ray production of the light elements, and cosmochronology, are discussed in detail.

scholarly journals Are globular clusters the natural outcome of regular high-redshift star formation?

2014 ◽  
Vol 10 (S312) ◽  
pp. 147-154
Author(s):  
J. M. Diederik Kruijssen
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Globular Clusters ◽  
High Redshift ◽  
Cluster Formation ◽  
Dark Matter Halo ◽  
Host Galaxy ◽  
The Galaxy ◽  
Natural Outcome ◽  
Formation And Evolution

AbstractWe summarise the recent progress in understanding the formation and evolution of globular clusters (GCs) in the context of galaxy formation and evolution. It is discussed that an end-to-end model for GC formation and evolution should capture four different phases: (1) star and cluster formation in the high-pressure interstellar medium of high-redshift galaxies, (2) cluster disruption by tidal shocks in the gas-rich host galaxy disc, (3) cluster migration into the galaxy halo, and (4) the final evaporation-dominated evolution of GCs until the present day. Previous models have mainly focussed on phase 4. We present and discuss a simple model that includes each of these four steps – its key difference with respect to previous work is the simultaneous addition of the high-redshift formation and early evolution of young GCs, as well as their migration into galaxy haloes. The new model provides an excellent match to the observed GC mass spectrum and specific frequency, as well as the relations of GCs to the host dark matter halo mass and supermassive black hole mass. These results show (1) that the properties of present-day GCs are reproduced by assuming that they are the natural outcome of regular high-redshift star formation (i.e. they form according to same physical processes that govern massive cluster formation in the local Universe), and (2) that models only including GC evaporation strongly underestimate their integrated mass loss over a Hubble time.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

Imaging of ribosomal RNA-protein interactions by dark-field STEM

1989 ◽  
Vol 47 ◽  
pp. 250-251
Author(s):  
M. Boublik ◽  
V. Mandiyan ◽  
S. Tumminia ◽  
J.F. Hainfeld ◽  
J.S. Wall
Keyword(s):  
Nucleic Acid ◽  
16S Rrna ◽  
Dark Field ◽  
Radius Of Gyration ◽  
Central Domain ◽  
The Core ◽  
16S Rna ◽  
30S Subunit ◽  
Core Particles

Success in protein-free deposition of native nucleic acid molecules from solutions of selected ionic conditions prompted attempts for high resolution imaging of nucleic acid interactions with proteins, not attainable by conventional EM. Since the nucleic acid molecules can be visualized in the dark-field STEM mode without contrasting by heavy atoms, the established linearity between scattering cross-section and molecular weight can be applied to the determination of their molecular mass (M) linear density (M/L), mass distribution and radius of gyration (RG). Determination of these parameters promotes electron microscopic imaging of biological macromolecules by STEM to a quantitative analytical level. This technique is applied to study the mechanism of 16S rRNA folding during the assembly process of the 30S ribosomal subunit of E. coli. The sequential addition of protein S4 which binds to the 5'end of the 16S rRNA and S8 and S15 which bind to the central domain of the molecule leads to a corresponding increase of mass and increased coiling of the 16S rRNA in the core particles. This increased compactness is evident from the decrease in RG values from 114Å to 91Å (in “ribosomal” buffer consisting of 10 mM Hepes pH 7.6, 60 mM KCl, 2 m Mg(OAc)2, 1 mM DTT). The binding of S20, S17 and S7 which interact with the 5'domain, the central domain and the 3'domain, respectively, continues the trend of mass increase. However, the RG values of the core particles exhibit a reverse trend, an increase to 108Å. In addition, the binding of S7 leads to the formation of a globular mass cluster with a diameter of about 115Å and a mass of ∽300 kDa. The rest of the mass, about 330 kDa, remains loosely coiled giving the particle a “medusa-like” appearance. These results provide direct evidence that 16S RNA undergoes significant structural reorganization during the 30S subunit assembly and show that its interactions with the six primary binding proteins are not sufficient for 16S rRNA coiling into particles resembling the native 30S subunit, contrary to what has been reported in the literature.

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