Andromeda I

{{Short description|Dwarf galaxy in the constellation Andromeda}}

{{about|the galaxy|the stars|1 Andromedae|and|Iota Andromedae|other uses|And 1 (disambiguation)}}

{{Infobox Galaxy

| name = Andromeda I

| image = Andromeda I Hubble WikiSky.jpg

| caption = Andromeda I by the HST

| epoch = J2000

| type = dSph

| ra = {{RA|00|45|39.8}}{{cite web

| title = NASA/IPAC Extragalactic Database

| work = Results for Andromeda I

| url = http://nedwww.ipac.caltech.edu/

| access-date = 2008-01-21 }}

| dec = {{DEC|+38|02|28}}

| dist_ly = 2.40 ± 0.08 Mly (735 ± 23 kpc){{citation

| author = I. D. Karachentsev| author2 = V. E. Karachentseva| author3 = W. K. Hutchmeier| author4 = D. I. Makarov

| title = A Catalog of Neighboring Galaxies

| journal = Astronomical Journal

| date = 2004

| volume = 127

| issue = 4

| pages = 2031–2068

| bibcode = 2004AJ....127.2031K

| doi = 10.1086/382905

| doi-access = free

}}{{citation

| author = Karachentsev, I. D.| author2 = Kashibadze, O. G.

| title = Masses of the local group and of the M81 group estimated from distortions in the local velocity field

| journal = Astrophysics

| date = 2006

| volume = 49

| issue = 1

| pages = 3–18

| bibcode = 2006Ap.....49....3K

| doi = 10.1007/s10511-006-0002-6

| s2cid = 120973010

}}

| z = -368 ± 11 km/s

| appmag_v = 13.6

| size_v = 2.5{{prime}} × 2.5{{prime}}

| constellation name = Andromeda

| notes = satellite galaxy of M31

| names = And I, Anon 0043+37, PGC 2666

}}

Andromeda I is a dwarf spheroidal galaxy (dSph){{citation

| last1 = van den Bergh

| first1 = Sydney

| author-link1 = Sidney van den Bergh

| journal = Astrophysical Journal

| date = January 1972

| title = Search for Faint Companions to M31

| volume = 171

| bibcode = 1972ApJ...171L..31V

| pages = L31

| doi = 10.1086/180861

| doi-access = free

}} about 2.40 million light-years away in the constellation Andromeda. Andromeda I is part of the local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It is roughly 3.5 degrees south and slightly east of M31.{{citation

|publisher = Students for the Exploration and Development of Space (SEDS)

|title = Andromeda I

|date = July 25, 2001

|url = http://spider.seds.org/spider/LG/and1.html

}} As of 2005, it is the closest known dSph companion to M31{{citation

| bibcode = 2005AJ....129.2232P

| title = The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda I and Andromeda III

| date = May 2005

| journal = The Astronomical Journal

| volume = 129

| issue = 5

| pages = 2232–2256

| doi = 10.1086/428372

| author = Pritzl, Barton J.

| author2 = Armandroff, Taft E.

| author3 = Jacoby, George H.

| author4 = Da Costa, G. S.

|arxiv = astro-ph/0501083 |s2cid = 9749493}} at an estimated projected distance of ~40{{citation

| bibcode = 2004MNRAS.350..243M

| title = Determining the location of the tip of the red giant branch in old stellar populations: M33, Andromeda I and II

| date = May 2004

| journal = Monthly Notices of the Royal Astronomical Society

| volume = 350

| issue = 1

| pages = 250

| doi = 10.1111/j.1365-2966.2004.07637.x

| display-authors = 4

| author = McConnachie, A. W.

| author2 = Irwin, M. J.

| author3 = Ferguson, A. M. N.

| author4 = Ibata, R. A.

| author5 = Lewis, G. F.

| author6 = Tanvir, N.

| doi-access = free

|arxiv = astro-ph/0401453 |s2cid = 18742035}} kpc or ~150,000 light-years.

Andromeda I was discovered by Sidney van den Bergh{{Citation

| title=Distances and metallicities for 17 Local Group galaxies

| journal=Monthly Notices of the Royal Astronomical Society

| date=2005

| volume=356

| issue=4

| pages=979–997

| bibcode=2005MNRAS.356..979M | doi=10.1111/j.1365-2966.2004.08514.x

| doi-access=free| postscript=.

|arxiv = astro-ph/0410489 }} in 1970 with the Mount Palomar Observatory 48-inch telescope. Further study of Andromeda I was done by the WFPC2 camera of the Hubble Space Telescope. This found that the horizontal branch stars, like other dwarf spheroidal galaxies were predominantly red.{{citation

| title = The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda I

| date = December 1996

| bibcode = 1996AJ....112.2576D

| journal = Astronomical Journal

| volume = 112

| pages = 2576

| doi = 10.1086/118204

| author = Da Costa, G. S.

| author2 = Armandroff, T. E.

| author3 = Caldwell, Nelson

| author4 = Seitzer, Patrick

|arxiv = astro-ph/9610083 | s2cid = 119431084

}} From this, and the abundance of blue horizontal branch stars, along with 99 RR Lyrae stars detected in 2005, lead to the conclusion there was an extended epoch of star formation. The estimated age is approximately 10 Gyr. The Hubble Space Telescope also found a globular cluster in Andromeda I, being the least luminous galaxy where such a cluster was found.{{Cite book| chapter = Discovery of a Globular Cluster in M31's Dwarf Spheroidal Companion Andromeda I

| bibcode = 2000AGM....17..P61G

| series = Astronomische Gesellschaft Abstract Series

| title = Abstracts of Contributed Talks and Posters presented at the Annual Scientific Meeting of the Astronomische Gesellschaft

| place = Bremen

| date = September 18–23, 2000

| volume = 17

| author = Grebel, E. K.

| author2 = Dolphin, A. E.

| author3 = Guhathakurta, P.

| journal = Astronomische Gesellschaft Meeting Abstracts

}}