J/AJ/105/894 Star formation in DDO 210 and NGC 3109 (Greggio+ 1993)
Star formation in dwarf irregular galaxies: DDO 210 and NGC 3109
GREGGIO L., MARCONI G., TOSI M., FOCARDI P.
<Astron. J. 105, 894 (1993)>
=1993AJ....105..894G 1993AJ....105..894G
ADC_Keywords: Galaxies, optical; Photometry, CCD; Positional data
Abstract:
The method proposed in Paper I [Tosi et al., AJ, 102, 951 (1991)] to study
the star formation histories in nearby irregulars is here applied to the
galaxies DDO 210 and NGC 3109. To this purpose we have obtained deep CCD
photometry of two regions in DDO 210 and three regions in NGC 3109,
reaching V = 24 with the required accuracy of Sigma(V) ≤ 0.1 mag.
Major information on the stellar populations, star formation rates, and
initial mass functions of these regions in the last 1 Gyr are derived from
the comparison of the observational color-magnitude diagrams and luminosity
functions, with the corresponding synthetic diagrams and luminosity
functions generated by a numerical simulation code based on stellar
evolutionary tracks. In general, for both galaxies we find that in the
last 1 Gyr the star formation activity has been rather continuous, possibly
occurring in long episodes of moderate activity separated by short
quiescent periods. According to our models the metallicity should be fairly
low (in the range 0.05 ≤ Z/Zsun ≤ 0.5) and the initial mass function
exponent in the vicinity of Salpeter's value, i.e., slightly flatter than
in the solar neighborhood. The studied regions of NGC 3109 appear to
contain different stellar populations (i.e., with slightly different
metallicity and star formation histories), whereas those of DDO 210 seem to
have fairly similar stellar contents, although for this galaxy the
interpretation is more uncertain. As a by-product of our method we find
that the distance modulus to DDO 210 should be (m-M)0 approx. 28, which
places this galaxy beyond the edge of the Local Group.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2a.dat 45 435 Principal parameters from the selected stars in
DDO 210 region A
table2b.dat 45 148 Principal parameters from the selected stars in
DDO 210 region B
table3a.dat 56 1020 Principal parameters from the selected stars in
NGC 3109 region A
table3b.dat 56 653 Principal parameters from the selected stars in
NGC 3109 region B
table3c.dat 56 933 Principal parameters from the selected stars in
NGC 3109 region C
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Byte-by-byte Description of file: table2a.dat table2b.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- N Star number
4- 14 F11.6 pix X X pixel coordinate, referred to the bottom
left corner of each frame
15- 25 F11.6 pix Y Y pixel coordinate
26- 35 F10.6 mag V V magnitude
36- 45 F10.6 mag B-V B-V color
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Byte-by-byte Description of file: table3a.dat table3b.dat table3c.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- N Star number
5- 15 F11.6 pix X X pixel coordinate, referred to the bottom
left corner of each frame
16- 26 F11.6 pix Y Y pixel coordinate
27- 36 F10.6 mag Vmag V magnitude
37- 46 F10.6 mag B-V B-V color
47- 56 F10.6 mag V-R V-R color
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Note: The tables contains the data for all the objects detected with photometric
error smaller than 0.1 mag.
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Origin: AAS CD-ROM series, Volume 1, 1993
(End) Patricia Bauer [CDS] 20-Jun-1994