CDROM/APJS/V98/P595 OB Asociations in M31 (Hill+ 1995)
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Ultraviolet and Optical Observations of OB Associations in M31
Jesse K. Hill, Joan E. Isensee, Ralph C. Bohlin, K. P. Cheng,
P. M. N. Hintzen, Robert W. O'Connell, Morton S. Roberts,
Andrew M. Smith, Eric P. Smith, and Theodore P. Stecher
<1995, ApJS, 98, 595>
=1995ApJS...98..595H
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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 2490 A), and for 130 of these stars in the far-UV
B1 band (central wavelength 1520 A). 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. (1992, A&AS,
96, 379) 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. (1992, ApJS, 82, 197). Comparison
with evolutionary models suggests a maximum initial mass ~85 Msun.
Ultraviolet extinction within most M31 OB associations is found to
follow an extinction curve similar to that of Hutchings et al. (1992,
ApJ, 400, L35). 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.
Keywords: galaxies: individual (M31), galaxies: photometry,
galaxies: star clusters, ultraviolet: stars
Description:
The 'figures' directory contain finding charts for the observed
associations in Postscript format.
File Summary:
------------------------------------------------------------------------------File Name
Lrecl
Records
Explanations
------------------------------------------------------------------------------table2.dat
32
63
Positions of M31 associations and
numbers of
stars observed by UIT
table3.dat
61
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.dat
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
figures
.
.
Directory of Postscript figures
------------------------------------------------------------------------------Byte-by-byte Description of file: table2.dat
------------------------------------------------------------------------------Bytes Format Units
Label Explanations
------------------------------------------------------------------------------1- 3
I3
--vdB
van den Bergh association observed by
UIT
4- 6
I3
h
RAh
Right Ascension, equinox J2000
7- 9
I3
min
RAm
R.A.
10-14
F5.1
s
RAs
R.A.
15
1X
----Blank
16
A1
--DESign declination (always blank)
17-18
I2
deg
DEd
Declination, equinox J2000
19-21
I3
arcmin
DEm
Dec.
22-24
I3
arcsec
DEs
Dec.
25-28
I4
--N_NUV No. of stars observed in near-UV (2490
A)
29-32
I4
--N_FUV No. of stars observed in far-UV (1520 A)
------------------------------------------------------------------------------Byte-by-byte Description of file: table3.dat
------------------------------------------------------------------------------Bytes Format Units
Label
Explanations
------------------------------------------------------------------------------1- 3
I3
--vdB
van den Bergh association observed by
UIT
4- 9
F6.2
--E(B-V)
*[]? Value of E(B-V) within M31
10-15
F6.2
--Z249
[]? Normalized extinction Z249 =
A249/E(B-V)
16-21
F6.2
--Z152
[]? Normalized extinction Z152 =
A152/E(B-V)
22
1X
----Blank
23-24
A2
--l_f249
[>=] f249 limiting characters, '>='
25-28
F4.2
--f249
*Near-UV total flux above the sky
29-33
F5.2
--e_f249
*[]? fractional error in f249
34
1X
----Blank
35-36
A2
--l_f152
[>=] f152 limiting characters, '>='
37-40
F4.2
--f152
*Far-UV total flux above the sky
41-45
F5.2
--e_f152
*[]? Fractional error in f152
46-51
F6.2
mag
m152-m249 []? m152-m249 = -2.5xlogf152/f249
52-56
F5.2
--T249
*[]? Fraction of f249 by nonforeground
stars
57-61
F5.2
--T152
*[]? Fraction of f152 by nonforeground
stars
------------------------------------------------------------------------------Notes for file: table3.dat
------------------------------------------------------------------------------E(B-V):
Value of E(B-V) within M31 estimated by comparing association CMDs
with the library of Fanelli et al. (1992, ApJS, 82, 197).
f249, e_f249:
Total flux and fractional error above the sky in the near-UV A1
band (central wavelength 2490 A), in units of 10E-14 ergs/cm^2/A/s.
f152, e_f152:
Total flux and fractional error above the sky in the near-UV B1 band
(central wavelength 1520 A), in units of 10E-14 ergs/cm^2/A/s.
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.
------------------------------------------------------------------------------Byte-by-byte Description of file: table4.dat
------------------------------------------------------------------------------Bytes Format Units
Label
Explanations
-------------------------------------------------------------------------------
1- 3
I3
--vdB
*van den Bergh association observed by
UIT
4
1X
----Always '-', separating assoc. and seq.
nos.
5- 7
I3
--Seq
Sequential number of star within
association
8-14
F7.1
arcsec X
X offset E of N of fiducial pos. in
Table 2
15-21
F7.1
arcsec Y
Y offset E of N of fiducial pos. in
Table 2
22
1X
----Blank
23-28
F6.2
mag
m249
Near-UV magnitude
29-34
F6.2
mag
m152
[]? Far-UV magnitude
35-40
F6.2
mag
U
[]? U magnitude
41-46
F6.2
mag
B
[]? B magnitude
47-52
F6.2
mag
R
[]? R magnitude
53
1X
----Blank
54-69
A16
--ID
*Alternate identification
------------------------------------------------------------------------------Notes for file: table4.dat
------------------------------------------------------------------------------vdB:
No stars are measureable in the UIT bands in four faint associations.
ID:
Sources identified with open clusters (Hodge 1979, AJ, 84, 744) or
globular clusters (Bohlin et al. 1993, ApJ, 417, 127) are noted in
this field. Stars measured in A78 corresponding with stars in field
1 of Massey, Armandroff, & Conti (1986, AJ, 92, 1303) are also
noted. Stars identifiable with stars in the catalog of Magnier et
al. (1992, A&AS, 96, 379) 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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(End)
Lee Brotzman [ADS]
02-Aug-95