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J/ApJS/98/595 OB associations in M31 (Hill+ 1995)
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Ultraviolet and optical observations of OB associations in M31
Hill J.K., Isensee J.E., Bohlin R.C., Cheng K.P., Hintzen P.M.N.,
OConnell R.W., Roberts M.S., Smith A.M.,Smith E.P.,Stecher T.P.
<Astrophys. J. Suppl. Ser. 98, 595 (1995)>
=1995ApJS...98..595H
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ADC_Keywords: Galaxies, photometry ; Photometry, ultraviolet
Keywords: galaxies: individual (M31) - galaxies: photometry -
galaxies: star clusters - ultraviolet: stars
Abstract:
Images of the central and southern parts of the local group Sb spiral
galaxy M31 were obtained by the Ultraviolet Imaging Telescope during
the Astro-1 Spacelab mission. Stellar photometry is obtained for 611
stars in 59 van den Bergh associations in the near-UV A1 band
(central wavelength 2490A), and for 130 of these stars in the far-UV
B1 band (central wavelength 1520A). In addition, B-band magnitudes
for 456 of the stars in ~30 associations, together with U- and R-band
photometry for ~290 stars in ~15 associations are determined from CCD
images. B-magnitudes from the catalog of
Magnier et al. (1992A&AS...96..379M) are given for 137 stars and
R-magnitudes for 233 stars. Stellar positions are obtained from the
ground-based CCD images and from UIT images. Total fluxes in the UV
bands are measured for 63 associations. Finding charts are presented
in the NUV and FUV bands, as well as one optical band. Tables give the
images utilized in this investigation, the associations observed, with
positions, total UV fluxes, extinctions estimated from color-magnitude
diagrams, and stellar positions with photometry in up to five bands.
UV color magnitude diagrams are presented with extinctions estimated
by comparing the observed association color magnitude diagrams with
colors and magnitudes of early-type stars computed from the IUE
spectral atlas of Fanelli et al. (1992ApJS...82..197F). Comparison
with evolutionary models suggests a maximum initial mass
~85M_{sun}_. Ultraviolet extinction within most M31 OB associations is
found to follow an extinction curve similar to that of
Hutchings et al. (1992ApJ...400L..35H). The variation in the fraction
of near-UV stars also measured in the far-UV among the associations is
probably caused by variations in age, extinction, and the degree of
foreground contamination.
Description:
The 'figures' directory contain finding charts for the observed
associations in Postscript format.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 32 63 Positions of M31 associations and numbers of
stars observed by UIT
table3 63 63 Extinction and ultraviolet surface photometry
of M31 associations
table4.dat 69 611 Source identifications, positions and
magnitudes
table2.tex 78 139 LaTeX version of table2.dat
table3.tex 73 132 LaTeX version of table3
table4.tex 81 703 LaTeX version of table4.dat
aastab.sty 72 115 Modified AAS table style file
environ.tex 77 125 Custom LaTeX environments and related macros
fig/* . 91 Maps in PostScript Format
(only on the AAS CD-ROM Volume 5, 1995,
directory /volume5/apjs/v98/p595/figures )
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- vdB van den Bergh association observed by UIT
5- 6 I2 h RAh Right Ascension, equinox J2000
8- 9 I2 min RAm Right Ascension, equinox J2000
11- 14 F4.1 s RAs Right Ascension, equinox J2000
16 A1 --- DE- Sign declination (always blank)
17- 18 I2 deg DEd Declination, equinox J2000
20- 21 I2 arcmin DEm Declination, equinox J2000
23- 24 I2 arcsec DEs Declination, equinox J2000
26- 28 I3 --- N(NUV) No. of stars observed in near-UV (2490 A)
30- 32 I3 --- N(FUV) No. of stars observed in far-UV (1520 A)
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Byte-by-byte Description of file: table3
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Bytes Format Units Label Explanations
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1- 3 I3 --- vdB van den Bergh association observed by UIT
5- 9 F5.2 --- E(B-V) *[]? Value of E(B-V) within M31
11- 15 F5.2 --- Z249 []? Normalized extinction Z249 = A249/E(B-V)
17- 21 F5.2 --- Z152 []? Normalized extinction Z152 = A152/E(B-V)
23- 24 A2 --- l_f249 [>=] f249 limiting characters, '>='
25- 29 F5.2 --- f249 *Near-UV total flux above the sky
31- 34 F4.2 --- e_f249 *[]? fractional error in f249
36- 37 A2 --- l_f152 [>=] f152 limiting characters, '>='
38- 42 F5.2 --- f152 *Far-UV total flux above the sky
44- 47 F4.2 --- e_f152 *[]? Fractional error in f152
49- 53 F5.2 mag m152-m249 []? m152-m249 = -2.5xlogf152/f249
55- 58 F4.2 --- T249 *[]? Fraction of f249 by nonforeground stars
60- 63 F4.2 --- T152 *[]? Fraction of f152 by nonforeground stars
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Note on E(B-V):
Value of E(B-V) within M31 estimated by comparing association CMDs
with the library of Fanelli et al. (1992ApJS...82..197F).
Note on f249, e_f249:
Total flux and fractional error above the sky in the near-UV A1
band (central wavelength 2490A), in units of 10E-14ergs/cm^2/A/s.
Note on f152, e_f152:
Total flux and fractional error above the sky in the near-UV B1 band
(central wavelength 1520A), in units of 10E-14ergs/cm^2/A/s.
Note on T249, T152:
The flux contributed in the near-UV by stars thought to be galactic
foreground stars has been subtracted from the total near-UV flux for
the association. Foreground stars are generally not measurable in
the far-UV. Total fluxes of the associations in the UIT bands are
computed from the areas outlined on the charts. Sky values are
estimated from the average of several nearby approximately circular
areas of ~10" diameter. The fractions of the total flux in the UIT
bands contributed by the measured nonforeground stars are given.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- vdB *van den Bergh association observed by UIT
4 A1 --- n_vdB Always '-', separating assoc. and seq. nos.
5- 7 I3 --- Seq Sequential number of star within association
9- 14 F6.1 arcsec Xpos X offset E of N of fiducial pos. in Table 2
16- 21 F6.1 arcsec Ypos Y offset E of N of fiducial pos. in Table 2
24- 28 F5.2 mag m249 Near-UV magnitude
30- 34 F5.2 mag m152 []? Far-UV magnitude
36- 40 F5.2 mag Umag []? U magnitude
42- 46 F5.2 mag Bmag []? B magnitude
48- 52 F5.2 mag Rmag []? R magnitude
54- 69 A16 --- ID *Alternate identification
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Note on vdB:
No stars are measurable in the UIT bands in four faint associations.
Note on ID:
Sources identified with open clusters (Hodge 1979AJ.....84..744H) or
globular clusters (Bohlin et al. 1993ApJ...417..127B) are noted in
this field. Stars measured in A78 corresponding with stars in field
1 of Massey, Armandroff, & Conti (1986AJ.....92.1303M) are also
noted. Stars identifiable with stars in the catalog of Magnier et
al. (1992A&AS...96..379M) are noted by Mn, where n is the Magnier
identification number. Where possible, table 4 contains magnitudes
obtained from the authors' B and R images. When a star has a
Magnier number, but the B (or R) magnitude is from the author's
data, as asterisk (or plus sign) appears after the Magnier number in
Table 4. Probable foreground stars are designated by an "F".
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Origin: AAS CD-ROM series, Volume 5, 1995 Lee Brotzman [ADS] 02-Aug-95
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(End) [CDS] 01-Feb-1996