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J/AJ/115/130 NGC 925 & NGC 1637 supergiants VRI CCD photometry (Sohn+ 1998)
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VRI CCD photometry of supergiant stars in the barred galaxies
NGC 925 and NGC 1637
Sohn Y.-J., Davidge T.J.
<Astron. J. 115, 130 (1998)>
=1998AJ....115..130S (SIMBAD/NED BibCode)
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ADC_Keywords: Stars, supergiant ; Photometry, VRI ; Photometry, CCD
Keywords: galaxies: individual (NGC 925, NGC 1637) - galaxies: stellar content
Abstract:
V, R, and I CCD images obtained with the Canada-France-Hawaii
Telescope are used to investigate the bright stellar content of the
barred spiral galaxies NGC 925 and NGC 1637. Not counting objects
located in H II regions, we detect 295 supergiants in NGC 925 and 266
in NGC 1637. Comparisons with theoretical isochrones indicate that
massive star formation in NGC 925 has been ongoing for at least a few
tens of millions of years. Most of the supergiants in NGC 925 are
younger than 20Myr and have masses between 10 and 60M_{sun}_. The
majority of supergiants in NGC 1637 appear to be younger than 40Myr
and have initial masses between 8 and 60 M_{sun}_. The luminosity
functions of supergiants in both galaxies follow power laws with
exponents d(logn)/d(logV)=0.50+/-0.05 for NGC 925 and 0.62+/-0.04 for
NGC 1637. These values are shallower than what is seen in most spiral
galaxies, although there are some exceptions. Archival Hubble Space
Telescope images of NGC 925 are used to assess the effects of blending
on our photometric measurements. We conclude that crowding could cause
a flattening of the luminosity function and bias the brightnesses of
the most luminous stars. The brightest red supergiants are used to
estimate the distance moduli of these galaxies. After applying
corrections for blending, we find that {mu}_0_=29.67 for NGC 925 and
{mu}_0_=29.47 for NGC 1637, corresponding to linear distances of
8.6^+1.1^_-1.0_ and 7.8^+1.0^_-0.9_Mpc, respectively. The distance
computed for NGC 925 is in good agreement with that recently derived
from Cepheids.
Objects:
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RA (2000) DE Designation(s)
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02 27 16.5 +33 34 14 NGC 925
04 41 28.1 -02 51 53 NGC 1637
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 60 437 Positions, magnitudes and colors of NGC 925 stars
table4.dat 53 435 Positions, magnitudes and colors of NGC 1637 stars
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See also:
J/AJ/112/2559 : Supergiants in NGC 672 (Sohn+ 1996)
J/AJ/109/517 : Photoelectric types of bright galaxies (Buta+ 1995)
Byte-by-byte Description of file: table3.dat table4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- [SD98] Identification number (1)
5- 12 F8.3 pix Xc X coordinate (2)
14- 20 F7.3 pix Yc Y coordinate (2)
22- 26 F5.2 mag Vmag V magnitude
28- 31 F4.2 mag e_Vmag rms uncertainty on Vmag
33- 37 F5.2 mag V-I V-I colour index
39- 42 F4.2 mag e_V-I rms uncertainty on V-I
44- 48 F5.2 mag R-I R-I colour index
50- 53 F4.2 mag e_R-I rms uncertainty on R-I
55- 56 I2 --- HK1 ? HII region identification (3)
57 A1 --- --- [,] Dash
59- 60 I2 --- HK2 ? HII region identification (3)
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Note (1): In Simbad, [SD98] NGC 925 NNN for table3.dat
[SD98] NGC 1637 NNN for table4.dat
Note (2): The field centers are
2h 24m 16.5s +33deg 20' 48" (1950) for NGC 925
4h 38m 57.6s -02deg 57' 35" (1950) for NGC 1637
1 pix = 1.13".
Note (3): Hodge & Kennicutt (1983AJ.....88..296H) HII region identification
<HK NGC 925 NNN> in Simbad. Only in table3.dat
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History: Copied from the electronic version of AJ
References:
Sohn & Davidge Paper I. 1996AJ....111.2280S
Sohn & Davidge Paper II. 1996AJ....112.2559S, Cat. <J/AJ/112/2559>
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(End) Patricia Bauer [CDS] 09-Mar-1998