J/AJ/109/173 BVR photometry of NGC 6822 (Marconi+ 1995)
Star formation in dwarf irregular galaxies: NGC 6822.
Marconi G., Tosi M., Greggio L., Focardi P.
<Astron. J. 109, 173 (1995)>
=1995AJ....109..173M 1995AJ....109..173M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, photometry ; Photometry, CCD
Abstract:
Our proposed method to study the star-formation histories in nearby
irregulars is here applied to NGC 6822. To this purpose we have
obtained accurate CCD photometry of three regions in the galaxy,
reaching V=23.5 with the required accuracy of σBVR≤0.1mag.
Major information on the stellar populations, star-formation rates,
and initial mass functions of these regions in the last 1Gyr 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. We find that in the last
1Gyr the star-formation activity has been rather continuous, possibly
occurring in long episodes of moderate activity separated by short
quiescent periods, and that the initial mass function exponent a is in
the vicinity of Salpeter's value, i.e., slightly flatter than in the
solar neighborhood. The studied regions of NGC 6822 appear to contain
different stellar populations. The preferred star formation regime for
region A is a continuous activity coupled with a moderately flat
α. For region C, instead, our best models suggest a
discontinuous star formation and a moderately steep α. NGC 6822
is the last object of our original sample of five nearby irregulars.
We can then draw the scenario resulting from this sample: most of the
observed fields appear to have experienced a gasping regime of star
formation, with average exponent α=2.35 for the initial mass
function. Despite their small sizes, the majority of the sample
galaxies contain different stellar populations in different regions.
Objects:
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RA (2000) DE Designation(s)
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19 44 56.0 -14 48 06 NGC 6822
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3 38 1772 Principal parameters of the selected stars of NGC 6822
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See also:
J/AJ/105/894 : Star formation in DDO 210 and NGC 3109 (Greggio+ 1993)
Byte-by-byte Description of file: table3
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Bytes Format Units Label Explanations
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1 A1 --- Region [ABC] NGC 6822 region
2- 4 I3 --- Star Star number in the region
6- 10 F5.1 pix Xpos X position (1)
12- 17 F6.1 pix Ypos Y position (1)
20- 24 F5.2 mag Vmag V magnitude
26- 30 F5.2 mag B-V B-V colour index
32- 36 F5.2 mag V-R ? V-R colour index
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Note (1): The field are centered at:
RA(1950)=19h42m07s, DE(1950)=-14°58'24" for field A
RA(1950)=19h42m15s, DE(1950)=-14°55'54" for field B
RA(1950)=19h42m07s, DE(1950)=-14°53'23" for field C
North is down, East is right, 1 pix = 0.17"
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History: Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 16-Sep-1997