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Boötes II (dwarf galaxy)

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Boötes II (dwarf galaxy)


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Bootes II Dwarf Galaxy[1]
Observation data (J2000 epoch)
Constellation Boötes
Right ascension 13h 58m 00s[1]
Declination +12° 51′ 00″[1]
Distance 136 ± 7 kly (42 ± 2 kpc)[2][3]

Apparent magnitude (V)
 15.8 ± 0.5[4]
Characteristics
Type dSph[4]

Apparent size (V)
 8.0+2.2
−2.8′[2]
Other designations
Boo II,[2] PGC 4713552
See also: Galaxy, List of galaxies

Bootes II or Boo II is a dwarf spheroidal galaxy situated in the Bootes constellation and discovered in 2007 in the data obtained by Sloan Digital Sky Survey.[4] The galaxy is located at the distance of about 42 kpc from the Sun and moves towards the Sun with the speed of 120 km/s.[4][5] It is classified as a dwarf spheroidal galaxy (dSph) meaning that it has an approximately round shape with the half-light radius of about 51 pc.[2][note 1]


Bootes II is one of the smallest and faintest satellites[note 2] of the Milky Way—its integrated luminosity is about 1,000 times that of the Sun (absolute visible magnitude of about −2.7), which is much lower than the luminosity of the majority of globular clusters.[2] However the mass of the galaxy is substantial corresponding to the mass to light ratio of more than 100.[3]


The stellar population of Bootes II consists mainly of moderately old stars formed 10–12 billion years ago.[5] The metallicity of these old stars is low at [Fe/H]=−1.8, which means that they contain 80 times less heavy elements than the Sun.[3][5] Currently there is no star formation in Bootes II. The measurements have so far failed to detect any neutral hydrogen in it—the upper limit is only 86 solar masses.[6]


Bootes II is located only 1.5 degrees (~1.6 kpc) away from another dwarf galaxy—Boötes I,[4] although they are unlikely to be physically associated because they move in opposite directions relative to the Milky Way. Their relative velocity—about 200 km/s is too high. It is more likely associated with the Sagittarius Stream and, therefore, with the Sagittarius Dwarf Elliptical Galaxy (SagDEG). Bootes II may be either a satellite galaxy of SagDEG or one of its star clusters torn from the main galaxy 4–7 billion years ago.[5]



Notes[edit]





  1. ^ Other sources give the half-light radius of about 36 pc.[3]


  2. ^ Only Segue 1, Segue 2 and Willman 1 are fainter.[2]




References[edit]





  1. ^ abc "NAME Bootes II". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2010-02-13..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""""'""'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}


  2. ^ abcdef Martin, Nicolas F.; de Jong, Jelte T. A.; Rix, Hans-Walter (September 2008). "A Comprehensive Maximum Likelihood Analysis of the Structural Properties of Faint Milky Way Satellites". The Astrophysical Journal. 684 (2): 1075. arXiv:0805.2945. Bibcode:2008ApJ...684.1075M. doi:10.1086/590336.


  3. ^ abcd Walsh, S.M.; Willman, B.; Sand, D.; et al. (2008). "Boötes II ReBoöted: An MMT/MegaCam Study of an Ultrafaint Milky Way Satellite". The Astrophysical Journal. 688 (1): 245–253. arXiv:0712.3054. Bibcode:2008ApJ...688..245W. doi:10.1086/592076.


  4. ^ abcde Walsh, S.M.; Jerjen, H.; Willman, B. (June 2007). "A Pair of Boötes: A New Milky Way Satellite". The Astrophysical Journal. 662 (2): L83–L86. arXiv:0705.1378. Bibcode:2007ApJ...662L..83W. doi:10.1086/519684.


  5. ^ abcd Koch, Andreas; Wilkinson, Mark I.; Kleyna, Jan T.; et al. (January 2009). "A Spectroscopic Confirmation of the Bootes II Dwarf Spheroidal". The Astrophysical Journal. 690 (1): 453–462. arXiv:0809.0700. Bibcode:2009ApJ...690..453K. doi:10.1088/0004-637X/690/1/453.


  6. ^ Grcevich, Jana; Putman, Mary E. (May 2009). "H I in Local Group Dwarf Galaxies and Stripping by the Galactic Halo". The Astrophysical Journal. 696 (1): 385. arXiv:0901.4975. Bibcode:2009ApJ...696..385G. doi:10.1088/0004-637X/696/1/385.












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