Andromeda II

Infobox Galaxy
name = Andromeda II
epoch = J2000
type = dSphcite web
title=NASA/IPAC Extragalactic Database
work=Results for Andromeda II
url=http://nedwww.ipac.caltech.edu/
accessdate=2006-11-29 ]
ra = RA|01|16|29.8
dec = DEC|+33|25|09
dist_ly = 2.22 ± 0.07 Mly (680 ± 20 kpc)cite journal
author=I. D. Karachentsev, V. E. Karachentseva, W. K. Hutchmeier, D. I. Makarov
title=A Catalog of Neighboring Galaxies
journal=Astronomical Journal
year=2004
volume=127
pages=2031–2068
url=http://adsabs.harvard.edu/abs/2004AJ....127.2031K
doi=10.1086/382905] cite journal
author=Karachentsev, I. D.; Kashibadze, O. G.
title=Masses of the local group and of the M81 group estimated from distortions in the local velocity field
journal=Astrophysics
year=2006
volume=49
issue=1
pages=3–18
url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006Ap.....49....3K
doi=10.1007/s10511-006-0002-6 ]
z = -188 ± 3 km/s
appmag_v = 13.5
size_v = 3′.6 × 2′.52
constellation name = Andromeda
notes = satellite galaxy of M31
names = Andromeda II Dwarf Spheroidal,
PGC 4601,cite web
title=SIMBAD Astronomical Database
work=Results for Andromeda II
url=http://simbad.u-strasbg.fr/Simbad
accessdate=2006-11-29] And II

Andromeda II (And II) is a dwarf spheroidal galaxy about 2.22 Mly away in the constellation Andromeda. It is part of the Local group of galaxies and is a satellite galaxy of the Andromeda Galaxy (M31) but it's also situated closely to the Triangulum Galaxy (M33), it is not quite clear if it is a satellite of the one or the other galaxy.Fact|date=January 2008

It was discovered by Sidney van den Berghcite journal
author=McConnachie, A. W.; Irwin, M. J.; Ferguson, A. M. N.; Ibata, R. A.; Lewis, G. F.; Tanvir, N.
title=Distances and metallicities for 17 Local Group galaxies
journal=Monthly Notices of the Royal Astronomical Society
year=2005
volume=356
issue=4
pages=979–997
url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005MNRAS.356..979M
doi=10.1111/j.1365-2966.2004.08514.x ] in a survey of photographic plates taken with the Palomar 48-inch (1.2-meter) Schmidt telescope in 1970 and 1971, together with Andromeda I, Andromeda III, and the presumable non- or background galaxy Andromeda IV (van den Bergh 1972).citation
last1 = van den Bergh
first1 = Sydney
authorlink1 = Sidney van den Bergh
journal = Astrophysical Journal
year = 1972
date = January 1972
title = Search for Faint Companions to M31
volume = 171
url = http://adsabs.harvard.edu/abs/1972ApJ...171L..31V
pages = L31
doi = 10.1086/180861]

pectra observations

Using the Keck telescope Côté et al 1999 observed spectra for seven stars inside Andromeda II. From this data, they found an average velocity V_r of -188 ± 3 km/sec and velocity dispersion of 9.2 ± 2.6 km/sec. This gives a mass to light ratio of M/L_v of ±|21|14|10 solar units which implies that And II contains a significant amount of dark matter. Also in 1999, Côté, Oke, & Cohen used the Keck to measure the spectra of 42 red giants. From this, they deduced an average metallicity of < [Fe/H] > = -1.47 ± 0.19 and a dispersion of 0.35 ± 0.10 dex. citation
last1 = van den Bergh
first1 = Sidney
authorlink1 = Sidney van den Bergh
title = Updated Information on the Local Group
year = 2000
date = April 2000
journal = The Publications of the Astronomical Society of the Pacific
volume = 112
issue = 770
url = http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000PASP..112..529V
pages = 533
doi = 10.1086/316548]

In 1999, Da Costa et al. studied the color-magnitude diagram of And II and discovered that most of stars in And II have ages between 6 and 9 Gyr. However, the observation of RR Lyrae variables and blue horizontal-branch stars demonstrates the existence of a population segment with an age greater than 10 Gyr. And II differs from And I in that it does not show a radial gradient in horizontal-branch morphology. Additionally, the dispersion in abundance is significantly larger in And II as compared to And I. This implies that these two dwarf spheroidal companions to the Andromeda galaxy have very different evolutionary histories. This raises the question of whether there is a correlationbetween a radial horizontal-branch gradient and the metallicity dispersion between dwarf spheroidal galaxies.

ee also

* Andromeda's satellite galaxies

External links

* [http://www.seds.org/~spider/spider/LG/and2.html SEDS: Dwarf Spheroidal Galaxy Andromeda II]

References