J/AJ/109/2480 VI photometry of late-type stars in M31. I. (Brewer+ 1995)
Late-type stars in M31. I.
Photometric study of AGB stars and metallicity gradients
Brewer J.P., Richer H.B., Crabtree D.R.
<Astron. J. 109, 2480 (1995)>
=1995AJ....109.2480B 1995AJ....109.2480B
ADC_Keywords: Stars, late-type ; Photometry
Abstract:
We have imaged five 7'x7' fields in M31 spanning galactocentric radii
from 4 to 32 kpc along the SW semi-major axis. The fields were
observed through two broadband (V and I) and two narrowband (CN and
TiO) ({DELTA}ν=+2.8100A and ({DELTA}ν=-1.7800A, respectively)
filters. The broadband data were used to construct I, (V-I)
color-magnitude diagrams (CMDs) and, in some of our fields, we found
significant numbers of stars in the Cepheid instability strip. A
distance modulus for the Cepheids in the middle field was found that
agreed well with other values in the literature. The width of the
giant branch (GB) in the I, (V-I) CMD of all five fields was
investigated, and we show that in four of the fields a likely
explanation for the GB width is a combination of both metallicity and
mass variations. Using the broadband data, the asymptotic giant branch
(AGB) luminosity functions (LFs) were measured in the five fields, and
we show that differences exist between these LFs. We speculate on how
the different star-forming histories in the fields may lead to the
observed AGB LFs and GB widths. Using the narrowband data along with
the broadband data we separated the AGB stars into carbon-rich (C) and
oxygen-rich (M) types. The carbon stars LFs were used to obtain an
estimate for the distance modulus of M31 which agrees with the value
derived from Cepheids. The ratio of C- to M-stars (C/M) is believed to
be an indicator of gaseous chemical abundance at the time of formation
of these stars. We show that the C/M ratio increases smoothly with
galactocentric distance, suggesting an inverse correlation with
metallicity. This is the first demonstration of this effect within a
single extragalactic system. We find that differences in the width of
the GB and the AGB LFs do not significantly affect the C/M ratio. We
consider the effect of the increasing C/M ratio on the ISM in M31, and
cite evidence in favor of a model where the grain composition in M31
is a function of galactocentric distance.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 33 111 Serendipity
table7.dat 52 243 Coordinates and photometry of candidate C stars
table8.dat 52 5256 Coordinates and photometry of candidate M stars
table2.tex 70 142 AASTeX version of table2.dat
table7.tex 66 265 AASTeX version of table7.dat
table8.tex 66 5278 AASTeX version of table8.dat
field1.fit 2880 2855 Field 1 I-band image, RA=0:41:41, DE=+40:59:00
field2.fit 2880 2855 Field 2 I-band image, RA=0:41:08, DE=+40:50:41
field3.fit 2880 2855 Field 3 I-band image, RA=0:40:22, DE=+40:36:24
field4.fit 2880 2855 Field 4 I-band image, RA=0:39:24, DE=+40:14:32
field5.fit 2880 2852 Field 5 I-band image, RA=0:35:42, DE=+39:29:03
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See also:
J/AJ/112/491: Late-Type Stars in M31. II. (Brewer+ 1996)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1 I1 --- Field Field in which star/cluster was identified
3- 7 I5 pix Xpos X coordinate on the I-band image
9- 12 I4 pix Ypos Y coordinate on the I-band image
15- 19 A5 --- Type Type of star/cluster (1)
22- 31 A10 --- ID Identification from the literature
33 A1 --- Ref Reference code for ID (2)
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Note (1): OC: Open cluster; GC: Globular cluster; GSC: Star from HST Guide
Star Catalog; Ceph: Cepheid variable; Irreg: Irregular variable;
Eclip: Eclipsing variable; Short: Short period variable
Note (2): 1 Hodge 1981, Atlas of the Andromeda Galaxy (University of Washington
Press, Seattle)
2 Hubble Space Telescope Guide Star Catalog
3 Baade & Swope (1965AJ.....70..212B 1965AJ.....70..212B)
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Byte-by-byte Description of file: table7.dat table8.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- ID ID for each star, ordered by magnitude
10- 13 I4 pix Xpos X coordinate on the I-band image
15- 18 I4 pix Ypos Y coordinate on the I-band image
20- 25 F6.2 mag Imag I magnitude
27- 30 F4.2 mag e_Imag ALLSTAR error in Imag
32- 36 F5.2 mag V-I V-I color
38- 41 F4.2 mag e_V-I Error in V-I (1)
43- 47 F5.2 mag CN-TiO CB-TiO color
49- 52 F4.2 mag e_CN-TiO Error in CN-TiO (1)
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Note (1): Error derived by adding ALLSTAR errors in quadrature.
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Origin: AAS CD-ROM series, Volume 5, 1995 Lee Brotzman [ADS] 26-Sep-1995
(End) [CDS] 09-Jan-1996