J/AJ/90/2221 UMi dwarf galaxy BV photometry (Olszewski+, 1985)
The Ursa Minor dwarf galaxy : still an old stellar system.
Olszewski E.W., Aaronson M.
<Astron. J. 90, 2221 (1985)>
=1985AJ.....90.2221O 1985AJ.....90.2221O
ADC_Keywords: Galaxies, photometry ; Photometry, CCD ; Photometry, UBV
Abstract:
We have constructed a color-magnitude diagram of the Ursa Minor dwarf
spheroidal to mV=24.8mag from charged-coupled device (CCD)
observations with the Kitt Peak 4 m telescope. The main-sequence
turnoff is easily visible. Fits to evolutionary isochrones and the
globular M92 indicate that Ursa Minor has an age and metal abundance
very similar to that of the latter cluster. No evidence for stars
younger than about 16 billion years is seen, with the possible
exception of approximately 20 stars believed to be blue stragglers.
Ursa Minor is therefore an extreme-age galaxy, unlike superficially
similar objects such as the Carina dwarf. Indeed, Ursa Minor may be
the only outer-halo spheroidal whose stellar content lives up to the
classical ideals of a Population II system. A distance modulus of
(m-M)0=19.0mag is derived from a sliding fit to the M92 ridge lines.
However, this modulus is uncertain by ∼0.1mag, for the horizontal
branch in our color-magnitude diagram is poorly populated. The ratio
of blue stragglers to anomalous Cepheids in Ursa Minor is estimated to
be ∼100, a number that may provide an important constraint on binary
models for the origin of these stars. A surprising result of our study
is the discovery of clumpiness in the distribution of stars. This
finding may give more weight to the idea that dwarf spheroidal
galaxies were previously dwarf irregular galaxies, although clearly,
if so, Ursa Minor must have lost its gaseous content very soon after
formation.
Objects:
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RA (2000) DE Designation(s)
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15 09 11.4 +67 12 52 UMi dwarf galaxy = UGC 9749
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 58 1486 Coordinates, magnitudes, and derived errors
for Ursa Minor stars.
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See also:
J/AJ/110/2131 : M/L for Draco and UMi. I. (Armandroff+ 1995)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- [OA85] [1/1486]+ Sequential number
6- 11 F6.2 pix Xpos X position
13- 18 F6.2 pix Ypos Y position (1)
20- 25 F6.3 mag Vmag V magnitude
27- 32 F6.3 mag B-V B-V colour index
34- 38 F5.3 mag e_Vmag rms uncertainty on Vmag
40- 44 F5.3 mag e_B-V rms uncertainty on B-V
46 I1 --- Flag [0/1] Note about existence on Fig.4 (2)
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Note (1): Typos in the original table were corrected from the finding chart:
740: Ypos = 26.51 transformed in 226.51
741: Ypos = 226.7p transformed in 226.7
1007: Xpos = aF1.04 transformed in 201.04
1017: Ypos = 316.T? transformed in 316.2
Note (2): the flag is
0 if star only appears in fig. 3
1 if star appears in both fig. 3 and 4.
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History:
Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 05-Aug-2000