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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
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:
FileName Lrecl Records Explanations
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 2880 2855 Field 1 I-band image, RA=0:41:41, DE=+40:59:00 2880 2855 Field 2 I-band image, RA=0:41:08, DE=+40:50:41 2880 2855 Field 3 I-band image, RA=0:40:22, DE=+40:36:24 2880 2855 Field 4 I-band image, RA=0:39:24, DE=+40:14:32 2880 2852 Field 5 I-band image, RA=0:35:42, DE=+39:29:03
See also: <J/AJ/112/491:> Late-Type Stars in M31. II. (Brewer+ 1996) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
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)
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)
Byte-by-byte Description of file: table7.dat table8.dat
Bytes Format Units Label Explanations
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)
Note (1): Error derived by adding ALLSTAR errors in quadrature.
Origin: AAS CD-ROM series, Volume 5, 1995 Lee Brotzman [ADS] 26-Sep-1995
(End) [CDS] 09-Jan-1996
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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