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During 1944, Walter Baade categorized groups of stars within the Milky Way into stellar populations. In the abstract of the article by Baade, he recognizes that Jan Oort originally conceived this type of classification in 1926:
The two types of stellar populations had been recognized among the stars of our own galaxy by Oort as early as 1926.
A subdwarf, sometimes denoted by "sd", is a star with luminosity class VI under the Yerkes spectral classification system. They are defined as stars with luminosity 1.5 to 2 magnitudes lower than that of main-sequence stars of the same spectral type. On a Hertzsprung–Russell diagram subdwarfs appear to lie below the main sequence.
In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word "metals" as a convenient short term for "all elements except hydrogen and helium". This word-use is distinct from the conventional chemical or physical definition of a metal as an electrically conducting solid. Stars and nebulae with relatively high abundances of heavier elements are called "metal-rich" in astrophysical terms, even though many of those elements are nonmetals in chemistry.
The red clump is a clustering of red giants in the Hertzsprung–Russell diagram at around 5,000 K and absolute magnitude (MV) +0.5, slightly hotter than most red-giant-branch stars of the same luminosity. It is visible as a denser region of the red-giant branch or a bulge towards hotter temperatures. It is prominent in many galactic open clusters, and it is also noticeable in many intermediate-age globular clusters and in nearby field stars.
Kappa Capricorni is a solitary star in the constellation Capricornus. It is visible to the naked eye with an apparent visual magnitude of +4.73. Based upon an annual parallax shift of 11.09 mas as seen from the Earth, the star is located about 294 light years from the Sun.
In astronomy, the intracluster medium (ICM) is the superheated plasma that permeates a galaxy cluster. The gas consists mainly of ionized hydrogen and helium and accounts for most of the baryonic material in galaxy clusters. The ICM is heated to temperatures on the order of 10 to 100 megakelvins, emitting strong X-ray radiation.
Canes Venatici I or CVn I is a dwarf spheroidal galaxy situated in the Canes Venatici constellation and discovered in 2006 in the data obtained by Sloan Digital Sky Survey. It is one of the most distant known satellites of the Milky Way as of 2011 together with Leo I and Leo II. The galaxy is located at a distance of about 220 kpc from the Sun and is moving away from the Sun at a velocity of about 31 km/s. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an elliptical shape with the half-light radius of about 550 pc.
Ursa Major II Dwarf is a dwarf spheroidal galaxy situated in the Ursa Major constellation and discovered in 2006 in the data obtained by the Sloan Digital Sky Survey. The galaxy is located approximately 30 kpc from the Sun and moves towards the Sun with the velocity of about 116 km/s. It has an elliptical shape with the half-light radius of about 140 pc.
Segue 1 is a dwarf spheroidal galaxy or globular cluster situated in the Leo constellation and discovered in 2006 by Sloan Digital Sky Survey. It is located at a distance of about 23 kpc from the Sun and moves away from the Sun with the velocity of about 206 km/s. Segue 1 has a noticeably elongated shape with the half-light radius of about 30 pc. This elongation may be caused by the tidal forces acting from the Milky Way galaxy if Segue 1 is being tidally disrupted now.
Canes Venatici II or CVn II is a dwarf spheroidal galaxy situated in the Canes Venatici constellation and discovered in 2006 in the data obtained by Sloan Digital Sky Survey. The galaxy is located at the distance of about 150 kpc from the Sun and moves towards the Sun with the velocity of about 130 km/s. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an elliptical shape with the half-light radius of about 74+14
−10 pc.
Coma Berenices or Com is a dwarf spheroidal galaxy situated in the Coma Berenices constellation and discovered in 2006 in data obtained by the Sloan Digital Sky Survey. The galaxy is located at the distance of about 44 kpc from the Sun and moves away from the Sun with the velocity of about 98 km/s. It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an elliptical shape with the half-light radius of about 70 pc.
Hercules, or Her, is a dwarf spheroidal galaxy situated in the Hercules constellation and discovered in 2006 in data obtained by the Sloan Digital Sky Survey. The galaxy is located at a distance of about 140 kpc from the Sun and moves away from the Sun with a velocity of about 45 km/s. It is classified as a dwarf spheroidal galaxy (dSph). It has a noticeably elongated shape with a half-light radius of about 350 pc. This elongation may be caused by tidal forces acting from the Milky Way galaxy, meaning that Her is being tidally disrupted now. Her also shows some gradient of velocities across the galaxy's body and is embedded into a faint stellar stream, which also points towards its ongoing tidal disruption.
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Rosemary F. G. Wyse is a Scottish astrophysicist and professor in the physics and astronomy department at Johns Hopkins University.
The thick disk is one of the structural components of about 2/3 of all disk galaxies, including the Milky Way. It was discovered first in external edge-on galaxies. Soon after, it was proposed as a unique galactic structure in the Milky Way, different from the thin disk and the halo in the 1983 article by Gilmore & Reid. It is supposed to dominate the stellar number density between 1 and 5 kiloparsecs above the galactic plane and, in the solar neighborhood, is composed almost exclusively of older stars. Its stellar chemistry and stellar kinematics are also said to set it apart from the thin disk. Compared to the thin disk, thick disk stars typically have significantly lower levels of metals—that is, the abundance of elements other than hydrogen and helium.
HD 193664 a star in the northern constellation of Draco. HD 193664 is its Henry Draper Catalogue designation. With an apparent magnitude of 5.93, according to the Bortle Scale it is visible to the naked eye from suburban skies. Parallax measurements yield an estimated distance of 57 light years. It has a relatively large proper motion of 0.558 arc seconds per year across the sky, and is drifting closer to the Sun with a radial velocity of −4.7 km/s.
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References
- ↑ Fenner, Yeshe; Gibson, Brad K. (5 March 2013). "Deriving the Metallicity Distribution Function of Galactic Systems" (PDF). Publications of the Astronomical Society of Australia. 20 (2): 189–195. arXiv: astro-ph/0304320 . Bibcode:2003PASA...20..189F. doi:10.1071/AS02047. S2CID 9965955.
- ↑ Casagrande, L.; Schönrich, R.; Asplund, M.; Cassisi, S.; Ramírez, I.; Meléndez, J.; Bensby, T.; Feltzing, S. (26 May 2011). "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s)" (PDF). Astronomy & Astrophysics. 530: A138. arXiv: 1103.4651 . Bibcode:2011A&A...530A.138C. doi:10.1051/0004-6361/201016276. S2CID 56118016.
- ↑ Frinchaboy, P. M.; Rhee, J.; Ostheimer, J. C.; Majewski, S. R.; Patterson, R. J.; Johnson, W. Y.; Dinescu, D. I.; Palma, C.; Westfall, K. B. (2002). "The Metallicity Distribution Function of omega Centauri". Omega Centauri. 265: 143. arXiv: astro-ph/0112169 . Bibcode:2002ASPC..265..143F.
- ↑ Beers, Timothy C; Christlieb, Norbert; Norris, John E; Bessell, Michael S; Wilhelm, Ronald; Carlos Allende Prieto; Yanny, Brian; Rockosi, Constance; Heidi Jo Newberg; Rossi, Silvia; Young Sun Lee (2005). "The Metallicity Distribution Function of the Halo of the Milky Way". Proceedings of the International Astronomical Union. 1: 175–183. arXiv: astro-ph/0508423 . Bibcode:2005IAUS..228..175B. doi:10.1017/S1743921305005521. S2CID 18380786.
- ↑ Sarajedini, Ata; Jablonka, Pascale (2005). "The Metallicity Distribution Function of Field Stars in M31's Bulge". The Astronomical Journal. 130 (4): 1627–1634. arXiv: astro-ph/0506653 . Bibcode:2005AJ....130.1627S. doi:10.1086/433171. S2CID 17051527.
- ↑ Schlesinger, Katharine J; Johnson, Jennifer A; Rockosi, Constance M; Young Sun Lee; Morrison, Heather L; Schoenrich, Ralph; Carlos Allende Prieto; Beers, Timothy C; Yanny, Brian; Harding, Paul; Schneider, Donald P; Chiappini, Cristina; da Costa, Luiz N; Maia, Marcio A. G; Minchev, Ivan; Rocha-Pinto, Helio; Santiago, Basilio X (2011). "The Metallicity Distribution Functions of SEGUE G and K dwarfs: Constraints for Disk Chemical Evolution and Formation". The Astrophysical Journal. 761 (2): 160. arXiv: 1112.2214 . Bibcode:2012ApJ...761..160S. doi:10.1088/0004-637X/761/2/160. S2CID 119205318.
- ↑ Yong, David; Norris, John E.; Bessell, M. S.; Christlieb, N.; Asplund, M.; Beers, Timothy C.; Barklem, P. S.; Frebel, Anna; Ryan, S. G. (1 January 2013). "The Most Metal-Poor Stars. III. The Metallicity Distribution Function and CEMP Fraction". The Astrophysical Journal. 762 (1): 27. arXiv: 1208.3016 . Bibcode:2013ApJ...762...27Y. doi:10.1088/0004-637X/762/1/27. S2CID 16930550.
- ↑ "Chemical evolution models". bas.bg. Retrieved 3 March 2017.
- ↑ Lai, David K.; Young Sun Lee; Bolte, Michael; Lucatello, Sara; Beers, Timothy C.; Johnson, Jennifer A.; Sivarani, Thirupathi; Rockosi, Constance M. (2011). "The [Fe/H], [C/Fe], and [alpha/Fe] distributions of the Bootes I Dwarf Spheroidal Galaxy". The Astrophysical Journal. 738 (1): 51. arXiv: 1106.2168 . Bibcode:2011ApJ...738...51L. doi:10.1088/0004-637X/738/1/51. S2CID 118627008.
