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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
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: -------------------------------------------------- RA (2000) DE Designation(s) -------------------------------------------------- 15 09 11.4 +67 12 52 UMi dwarf galaxy = UGC 9749 -------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table4.dat 58 1486 Coordinates, magnitudes, and derived errors for Ursa Minor stars.
See also: J/AJ/110/2131 : M/L for Draco and UMi. I. (Armandroff+ 1995) Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
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)
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.
History: Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 05-Aug-2000
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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