Antonio Aparicio - Academia.edu (original) (raw)
Papers by Antonio Aparicio
Astronomical Journal, 1999
Our solution for the SFH of Leo I defines a minimum of chi-square in a well defined position of t... more Our solution for the SFH of Leo I defines a minimum of chi-square in a well defined position of the parameter space, and the derived SFR(t) is robust, in the sense that its main characteristics are unchanged for different combinations of the remaining parameters. However, only a narrow range of assumptions for Z(t), IMF and beta(f,q)\beta(f,q)beta(f,q) result in a good agreement between the data and the models, namely: Z=0.0004, a Kroupa et al. (1993) IMF or slightly steeper, and a relatively large fraction of binary stars. Most star formation activity (70% to 80%) occurred between 7 and 1 Gyr ago. At 1 Gyr ago, it abruptly dropped to a negligible value, but seems to have been active until at least ~ 300 Myr ago. Our results don't unambiguously answer the question of whether Leo I began forming stars around 15 Gyr ago, but it appears that the amount of this star formation, if existing at all, would be small.
The interpretation of globular cluster horizontal branch (HB) morphology is a classical problem t... more The interpretation of globular cluster horizontal branch (HB) morphology is a classical problem that can significantly blur our understanding of stellar populations. In this paper, we present a new multivariate analysis connecting the effective temperature extent of the HB with other cluster parameters. The work is based on Hubble Space Telescope photometry of 54 Galactic globular clusters. The present study reveals an important role of the total mass of the globular cluster on its HB morphology. More massive clusters tend to have HBs more extended to higher temperatures. For a set of three input variables including the temperature extension of the HB, [Fe/H] and M_V, the first two eigenvectors account for the 90% of the total sample variance. Possible effects of cluster self-pollution on HB morphology, eventually stronger in more massive clusters, could explain the results here derived.
Astronomical Journal, 2008
The ACS Survey of Globular Clusters has used HST's Wide-Field Channel to obtain uniform imaging o... more The ACS Survey of Globular Clusters has used HST's Wide-Field Channel to obtain uniform imaging of 65 of the nearest globular clusters to provide an extensive homogeneous dataset for a broad range of scientific investigations. The survey goals required not only a uniform observing strategy, but also a uniform reduction strategy. To this end, we designed a sophisticated software program to process the cluster data in an automated way. The program identifies stars simultaneously in the multiple dithered exposures for each cluster and measures them using the best available PSF models. We describe here in detail the program's rationale, algorithms, and output. The routine was also designed to perform artificial-star tests, and we run a standard set of ∼10 5 tests for each cluster in the survey. The catalog described here will be exploited in a number of upcoming papers and will eventually be made available to the public via the world-wide web.
Astronomical Journal, 1995
The stellar content and stellar age distribution of the Pegasus Dwarf Irregular Galaxy are discus... more The stellar content and stellar age distribution of the Pegasus Dwarf Irregular Galaxy are discussed in the light of deep CM diagrams for (V - R) and (V - I) color indices, complemented by Hα data. The CM diagrams of Pegasus show two structures-red tail and red tangle-which denote the presence of intermediate-age and old stars in the galaxy. After NGC 6822, Pegasus is the second dwarf irregular galaxy in which these structures are clearly detected, suggesting that the CM diagram of most dwarf irregulars could show these structures if photometry is deep enough. The youngest star in Pegasus is some 10 Myr old, but the galaxy shows little star forming activity over the last 100 Myr. However the CM diagram is populated by a large number of older stars which can be up to 10 Gyr old or more. These stars mainly concentrate in the red tangle. From the maximum extension to the red of the red tail, we estimate that the maximum metallicity of Pegasus' stars could be as large as Z=0.008. By means of a further development of the technique of artificial stars, we carried out a careful, deep study of the effects of crowding on the measured colors and magnitudes of stars. This is a necessary step, previous to the experiments with synthetic diagrams on which we are currently working to analyze the full star formation history of this galaxy. Data for 40000 artificial stars, with injected colors and magnitudes spread over a wide range, were added to the observed frames in several steps, and used to derive the most important crowding effects, namely the fraction of missing stars-or crowding factors-magnitude and color shifts, and external photometric errors, each as a function of magnitude and (V - R) and (V - I) color indices. The main effects detected from our tests can be summarized as follows: (l) Crowding factors, color and magnitude shifts, and external errors are a function not only of magnitude but also of color index. (2) In general, crowding produces a shift of blue stars to the red and of red stars to the blue. (3) There is no significant relation between external and internal errors; external errors are larger by a factor which varies from 1 to 7. Furthermore, we have tested a widely used, abbreviated alternative procedure which does not consider injected color indices, but only magnitudes of the artificial stars. It is much faster, but its results are inadequate for the synthetic diagrams tests. The weakness of the method lies in the fact that it overlooks the dependency of crowding effects on the color indices of stars. This dependency is large, especially for external errors.
Astronomical Journal, 2001
The stellar population of Draco is mainly old. Although some intermediate-age population is prese... more The stellar population of Draco is mainly old. Although some intermediate-age population is present in Draco, most of the star formation (up to 90%) took place before ~10 Gyr ago. No significant star formation activity is detected in the last ~2 Gyr. Two methods ("partial model" and "subgiant") have been used to investigate the star formation history of Draco.
Astronomical Journal, 2007
Ata Sarajedini 1, Luigi R. Bedin 2, Brian Chaboyer 3, Aaron Dotter 3, Michael Siegel 4, Jay Ander... more Ata Sarajedini 1, Luigi R. Bedin 2, Brian Chaboyer 3, Aaron Dotter 3, Michael Siegel 4, Jay Anderson 5, Antonio Aparicio 6, Ivan King 7, Steven Majewski 8, A. Marín-Franch 9, Giampaolo Piotto 10, I. Neill Reid 11 and Alfred Rosenberg 12
Astrophysical Journal, 2008
Photometry with HST's ACS reveals that the subgiant branch (SGB) of the globular cluster NGC 1851... more Photometry with HST's ACS reveals that the subgiant branch (SGB) of the globular cluster NGC 1851 splits into two well-defined branches. If the split is due only to an age effect, the two SGBs would imply two star formation episodes separated by sim\simsim 1 Gyr. We discuss other anomalies in NGC 1851 which could be interpreted in terms of a double stellar population. Finally, we compare the case of NGC 1851 with the other two globulars known to host multiple stellar populations, and show that all three clusters differ in several important respects.
Astrophysical Journal, 2007
As part of a major program to use isolated Local Group dwarf galaxies as near-field probes of cos... more As part of a major program to use isolated Local Group dwarf galaxies as near-field probes of cosmology, we have obtained deep images of the dwarf irregular galaxy Leo A with the Advanced Camera for Surveys aboard the Hubble Space Telescope. From these images we have constructed a color-magnitude diagram (CMD) reaching apparent [absolute] magnitudes of (M475, M814) > (29.0 [+4.4], 27.9 [+3.4]), the deepest ever achieved for any irregular galaxy beyond the Magellanic Clouds. We derive the star-formation rate (SFR) as a function of time over the entire history of the galaxy. We find that over 90% of all the star formation that ever occurred in Leo A happened more recently than 8 Gyr ago. The CMD shows only a very small amount of star formation in the first few billion years after the Big Bang; a possible burst at the oldest ages cannot be claimed with high confidence. The peak SFR occurred ~1.5-4 Gyr ago, at a level 5-10 times the current value. Our modelling indicates that Leo A has experienced very little metallicity evolution; the mean inferred metallicity is consistent with measurements of the present-day gas-phase oxygen abundance. We cannot exclude a scenario in which ALL of the ancient star formation occurred prior to the end of the era of reionization, but it seems unlikely that the lack of star formation prior to ~8 Gyr ago was due to early loss or exhaustion of the in situ gas reservoir.
Astronomy & Astrophysics, 2005
We present distance modulus and reddening determinations for 72 Galactic globular clusters from t... more We present distance modulus and reddening determinations for 72 Galactic globular clusters from the homogeneous photometric database of Piotto et al. ([CITE]), calibrated to the HST flight F439W and F555W bands. The distances have been determined by comparison with theoretical absolute magnitudes of the ZAHB. For low and intermediate metallicity clusters, we have estimated the apparent Zero Age Horizontal Branch (ZAHB) magnitude from the RR Lyrae level. For metal rich clusters, the ZAHB magnitude was obtained from the fainter envelope of the red HB. Reddenings have been estimated by comparison of the HST colour-magnitude diagrams (CMD) with ground CMDs of template clusters with low reddening. The homogeneity of both the photometric data and the adopted methodological approach allowed us to obtain highly accurate relative cluster distances and reddenings. Our results are also compared with recent compilations in the literature. Based on observations with the Hubble Space Telescope. Tables 3 and 4 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/432/851
Annual Review of Astronomy and Astrophysics, 2005
▪ Abstract Most of what we know about the stellar population of nearby, resolved galaxies comes f... more ▪ Abstract Most of what we know about the stellar population of nearby, resolved galaxies comes from the interpretation of their color-magnitude diagrams, by comparison with stellar evolutionary models. We review how well current stellar evolution models reproduce the properties of ...
Astronomical Journal, 2008
We present stellar metallicities derived from Ca II triplet spectroscopy in over 350 red giant br... more We present stellar metallicities derived from Ca II triplet spectroscopy in over 350 red giant branch stars in 13 fields distributed in different positions in the SMC, ranging from sim\simsim1\arcdeg\@ to sim\simsim4\arcdeg\@ from its center. In the innermost fields the average metallicity is [Fe/H] sim−1\sim -1sim−1. This value decreases when we move away towards outermost regions. This is the first detection of a metallicity gradient in this galaxy. We show that the metallicity gradient is related to an age gradient, in the sense that more metal-rich stars, which are also younger, are concentrated in the central regions of the galaxy.
Astronomical Journal, 2004
We present the results of a search for variable stars in the Local Group dwarf galaxy Phoenix. Ni... more We present the results of a search for variable stars in the Local Group dwarf galaxy Phoenix. Nineteen Cepheids, six candidate long-period variables, one candidate eclipsing binary and a large number of candidate RR Lyrae stars have been identified. Periods and light curves have been obtained for all the Cepheid variables. Their distribution in the period-luminosity diagram reveals that both Anomalous Cepheids (AC) and short-period Classical Cepheids s-pCC are found in our sample. This is the first time that both types of variable star are identified in the same system even though they likely coexist, but have gone unnoticed so far, in other low-metallicity galaxies like Leo A and Sextans A. We argue that the conditions for the existence of both types of variable star in the same galaxy are a low metallicity at all ages, and the presence of both young and intermediate-age (or old, depending on the nature of AC) stars. The RR Lyrae candidates trace, together with the well developed horizontal branch, the existence of an important old population in Phoenix. The different spatial distributions of s-pCC, AC and RR Lyrae variables in the Phoenix field are consistent with the stellar population gradients found in Phoenix, in the sense that the younger population is concentrated in the central part of the galaxy. The gradients in the distribution of the young population within the central part of Phoenix, which seem to indicate a propagation of the recent star formation, are also reflected in the spatial distribution of the s-pCC.
Astronomical Journal, 2008
Ca ii triplet spectroscopy has been used to derive stellar metallicities for individual stars in ... more Ca ii triplet spectroscopy has been used to derive stellar metallicities for individual stars in four Large Magellanic Cloud fields situated at galactocentric distances of 3 • , 5 • , 6 • , and 8 • to the north of the bar. Observed metallicity distributions show a well-defined peak, with a tail toward low metallicities. The mean metallicity remains constant until 6 • ([Fe/H] ∼ −0.5 dex), while for the outermost field, at 8 • , the mean metallicity is substantially lower than in the rest of the disk ([Fe/H] ∼ −0.8 dex). The combination of spectroscopy with deep CCD photometry has allowed us to break the RGB age-metallicity degeneracy and compute the ages for the objects observed spectroscopically. The obtained age-metallicity relationships (AMRs) for our four fields are statistically indistinguishable. We conclude that the lower mean metallicity in the outermost field is a consequence of it having a lower fraction of intermediate-age stars, which are more metal-rich than the older stars. The disk AMR is similar to that for clusters. However, the lack of objects with ages between 3 and 10 Gyr is not observed in the field population. Finally, we used data from the literature to derive consistently the AMR of the bar. Simple chemical evolution models have been used to reproduce the observed AMRs with the purpose of investigating which mechanism has participated in the evolution of the disk and bar. We find that while the disk AMR is well reproduced by close-box models or models with a small degree of outflow, that of the bar is only reproduced by models with combination of infall and outflow.
Astronomical Journal, 2004
}, with the only requirement of referencing this paper and crediting as indicated in the site.
Astronomical Journal, 1999
Our solution for the SFH of Leo I defines a minimum of chi-square in a well defined position of t... more Our solution for the SFH of Leo I defines a minimum of chi-square in a well defined position of the parameter space, and the derived SFR(t) is robust, in the sense that its main characteristics are unchanged for different combinations of the remaining parameters. However, only a narrow range of assumptions for Z(t), IMF and beta(f,q)\beta(f,q)beta(f,q) result in a good agreement between the data and the models, namely: Z=0.0004, a Kroupa et al. (1993) IMF or slightly steeper, and a relatively large fraction of binary stars. Most star formation activity (70% to 80%) occurred between 7 and 1 Gyr ago. At 1 Gyr ago, it abruptly dropped to a negligible value, but seems to have been active until at least ~ 300 Myr ago. Our results don't unambiguously answer the question of whether Leo I began forming stars around 15 Gyr ago, but it appears that the amount of this star formation, if existing at all, would be small.
The interpretation of globular cluster horizontal branch (HB) morphology is a classical problem t... more The interpretation of globular cluster horizontal branch (HB) morphology is a classical problem that can significantly blur our understanding of stellar populations. In this paper, we present a new multivariate analysis connecting the effective temperature extent of the HB with other cluster parameters. The work is based on Hubble Space Telescope photometry of 54 Galactic globular clusters. The present study reveals an important role of the total mass of the globular cluster on its HB morphology. More massive clusters tend to have HBs more extended to higher temperatures. For a set of three input variables including the temperature extension of the HB, [Fe/H] and M_V, the first two eigenvectors account for the 90% of the total sample variance. Possible effects of cluster self-pollution on HB morphology, eventually stronger in more massive clusters, could explain the results here derived.
Astronomical Journal, 2008
The ACS Survey of Globular Clusters has used HST's Wide-Field Channel to obtain uniform imaging o... more The ACS Survey of Globular Clusters has used HST's Wide-Field Channel to obtain uniform imaging of 65 of the nearest globular clusters to provide an extensive homogeneous dataset for a broad range of scientific investigations. The survey goals required not only a uniform observing strategy, but also a uniform reduction strategy. To this end, we designed a sophisticated software program to process the cluster data in an automated way. The program identifies stars simultaneously in the multiple dithered exposures for each cluster and measures them using the best available PSF models. We describe here in detail the program's rationale, algorithms, and output. The routine was also designed to perform artificial-star tests, and we run a standard set of ∼10 5 tests for each cluster in the survey. The catalog described here will be exploited in a number of upcoming papers and will eventually be made available to the public via the world-wide web.
Astronomical Journal, 1995
The stellar content and stellar age distribution of the Pegasus Dwarf Irregular Galaxy are discus... more The stellar content and stellar age distribution of the Pegasus Dwarf Irregular Galaxy are discussed in the light of deep CM diagrams for (V - R) and (V - I) color indices, complemented by Hα data. The CM diagrams of Pegasus show two structures-red tail and red tangle-which denote the presence of intermediate-age and old stars in the galaxy. After NGC 6822, Pegasus is the second dwarf irregular galaxy in which these structures are clearly detected, suggesting that the CM diagram of most dwarf irregulars could show these structures if photometry is deep enough. The youngest star in Pegasus is some 10 Myr old, but the galaxy shows little star forming activity over the last 100 Myr. However the CM diagram is populated by a large number of older stars which can be up to 10 Gyr old or more. These stars mainly concentrate in the red tangle. From the maximum extension to the red of the red tail, we estimate that the maximum metallicity of Pegasus' stars could be as large as Z=0.008. By means of a further development of the technique of artificial stars, we carried out a careful, deep study of the effects of crowding on the measured colors and magnitudes of stars. This is a necessary step, previous to the experiments with synthetic diagrams on which we are currently working to analyze the full star formation history of this galaxy. Data for 40000 artificial stars, with injected colors and magnitudes spread over a wide range, were added to the observed frames in several steps, and used to derive the most important crowding effects, namely the fraction of missing stars-or crowding factors-magnitude and color shifts, and external photometric errors, each as a function of magnitude and (V - R) and (V - I) color indices. The main effects detected from our tests can be summarized as follows: (l) Crowding factors, color and magnitude shifts, and external errors are a function not only of magnitude but also of color index. (2) In general, crowding produces a shift of blue stars to the red and of red stars to the blue. (3) There is no significant relation between external and internal errors; external errors are larger by a factor which varies from 1 to 7. Furthermore, we have tested a widely used, abbreviated alternative procedure which does not consider injected color indices, but only magnitudes of the artificial stars. It is much faster, but its results are inadequate for the synthetic diagrams tests. The weakness of the method lies in the fact that it overlooks the dependency of crowding effects on the color indices of stars. This dependency is large, especially for external errors.
Astronomical Journal, 2001
The stellar population of Draco is mainly old. Although some intermediate-age population is prese... more The stellar population of Draco is mainly old. Although some intermediate-age population is present in Draco, most of the star formation (up to 90%) took place before ~10 Gyr ago. No significant star formation activity is detected in the last ~2 Gyr. Two methods ("partial model" and "subgiant") have been used to investigate the star formation history of Draco.
Astronomical Journal, 2007
Ata Sarajedini 1, Luigi R. Bedin 2, Brian Chaboyer 3, Aaron Dotter 3, Michael Siegel 4, Jay Ander... more Ata Sarajedini 1, Luigi R. Bedin 2, Brian Chaboyer 3, Aaron Dotter 3, Michael Siegel 4, Jay Anderson 5, Antonio Aparicio 6, Ivan King 7, Steven Majewski 8, A. Marín-Franch 9, Giampaolo Piotto 10, I. Neill Reid 11 and Alfred Rosenberg 12
Astrophysical Journal, 2008
Photometry with HST's ACS reveals that the subgiant branch (SGB) of the globular cluster NGC 1851... more Photometry with HST's ACS reveals that the subgiant branch (SGB) of the globular cluster NGC 1851 splits into two well-defined branches. If the split is due only to an age effect, the two SGBs would imply two star formation episodes separated by sim\simsim 1 Gyr. We discuss other anomalies in NGC 1851 which could be interpreted in terms of a double stellar population. Finally, we compare the case of NGC 1851 with the other two globulars known to host multiple stellar populations, and show that all three clusters differ in several important respects.
Astrophysical Journal, 2007
As part of a major program to use isolated Local Group dwarf galaxies as near-field probes of cos... more As part of a major program to use isolated Local Group dwarf galaxies as near-field probes of cosmology, we have obtained deep images of the dwarf irregular galaxy Leo A with the Advanced Camera for Surveys aboard the Hubble Space Telescope. From these images we have constructed a color-magnitude diagram (CMD) reaching apparent [absolute] magnitudes of (M475, M814) > (29.0 [+4.4], 27.9 [+3.4]), the deepest ever achieved for any irregular galaxy beyond the Magellanic Clouds. We derive the star-formation rate (SFR) as a function of time over the entire history of the galaxy. We find that over 90% of all the star formation that ever occurred in Leo A happened more recently than 8 Gyr ago. The CMD shows only a very small amount of star formation in the first few billion years after the Big Bang; a possible burst at the oldest ages cannot be claimed with high confidence. The peak SFR occurred ~1.5-4 Gyr ago, at a level 5-10 times the current value. Our modelling indicates that Leo A has experienced very little metallicity evolution; the mean inferred metallicity is consistent with measurements of the present-day gas-phase oxygen abundance. We cannot exclude a scenario in which ALL of the ancient star formation occurred prior to the end of the era of reionization, but it seems unlikely that the lack of star formation prior to ~8 Gyr ago was due to early loss or exhaustion of the in situ gas reservoir.
Astronomy & Astrophysics, 2005
We present distance modulus and reddening determinations for 72 Galactic globular clusters from t... more We present distance modulus and reddening determinations for 72 Galactic globular clusters from the homogeneous photometric database of Piotto et al. ([CITE]), calibrated to the HST flight F439W and F555W bands. The distances have been determined by comparison with theoretical absolute magnitudes of the ZAHB. For low and intermediate metallicity clusters, we have estimated the apparent Zero Age Horizontal Branch (ZAHB) magnitude from the RR Lyrae level. For metal rich clusters, the ZAHB magnitude was obtained from the fainter envelope of the red HB. Reddenings have been estimated by comparison of the HST colour-magnitude diagrams (CMD) with ground CMDs of template clusters with low reddening. The homogeneity of both the photometric data and the adopted methodological approach allowed us to obtain highly accurate relative cluster distances and reddenings. Our results are also compared with recent compilations in the literature. Based on observations with the Hubble Space Telescope. Tables 3 and 4 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/432/851
Annual Review of Astronomy and Astrophysics, 2005
▪ Abstract Most of what we know about the stellar population of nearby, resolved galaxies comes f... more ▪ Abstract Most of what we know about the stellar population of nearby, resolved galaxies comes from the interpretation of their color-magnitude diagrams, by comparison with stellar evolutionary models. We review how well current stellar evolution models reproduce the properties of ...
Astronomical Journal, 2008
We present stellar metallicities derived from Ca II triplet spectroscopy in over 350 red giant br... more We present stellar metallicities derived from Ca II triplet spectroscopy in over 350 red giant branch stars in 13 fields distributed in different positions in the SMC, ranging from sim\simsim1\arcdeg\@ to sim\simsim4\arcdeg\@ from its center. In the innermost fields the average metallicity is [Fe/H] sim−1\sim -1sim−1. This value decreases when we move away towards outermost regions. This is the first detection of a metallicity gradient in this galaxy. We show that the metallicity gradient is related to an age gradient, in the sense that more metal-rich stars, which are also younger, are concentrated in the central regions of the galaxy.
Astronomical Journal, 2004
We present the results of a search for variable stars in the Local Group dwarf galaxy Phoenix. Ni... more We present the results of a search for variable stars in the Local Group dwarf galaxy Phoenix. Nineteen Cepheids, six candidate long-period variables, one candidate eclipsing binary and a large number of candidate RR Lyrae stars have been identified. Periods and light curves have been obtained for all the Cepheid variables. Their distribution in the period-luminosity diagram reveals that both Anomalous Cepheids (AC) and short-period Classical Cepheids s-pCC are found in our sample. This is the first time that both types of variable star are identified in the same system even though they likely coexist, but have gone unnoticed so far, in other low-metallicity galaxies like Leo A and Sextans A. We argue that the conditions for the existence of both types of variable star in the same galaxy are a low metallicity at all ages, and the presence of both young and intermediate-age (or old, depending on the nature of AC) stars. The RR Lyrae candidates trace, together with the well developed horizontal branch, the existence of an important old population in Phoenix. The different spatial distributions of s-pCC, AC and RR Lyrae variables in the Phoenix field are consistent with the stellar population gradients found in Phoenix, in the sense that the younger population is concentrated in the central part of the galaxy. The gradients in the distribution of the young population within the central part of Phoenix, which seem to indicate a propagation of the recent star formation, are also reflected in the spatial distribution of the s-pCC.
Astronomical Journal, 2008
Ca ii triplet spectroscopy has been used to derive stellar metallicities for individual stars in ... more Ca ii triplet spectroscopy has been used to derive stellar metallicities for individual stars in four Large Magellanic Cloud fields situated at galactocentric distances of 3 • , 5 • , 6 • , and 8 • to the north of the bar. Observed metallicity distributions show a well-defined peak, with a tail toward low metallicities. The mean metallicity remains constant until 6 • ([Fe/H] ∼ −0.5 dex), while for the outermost field, at 8 • , the mean metallicity is substantially lower than in the rest of the disk ([Fe/H] ∼ −0.8 dex). The combination of spectroscopy with deep CCD photometry has allowed us to break the RGB age-metallicity degeneracy and compute the ages for the objects observed spectroscopically. The obtained age-metallicity relationships (AMRs) for our four fields are statistically indistinguishable. We conclude that the lower mean metallicity in the outermost field is a consequence of it having a lower fraction of intermediate-age stars, which are more metal-rich than the older stars. The disk AMR is similar to that for clusters. However, the lack of objects with ages between 3 and 10 Gyr is not observed in the field population. Finally, we used data from the literature to derive consistently the AMR of the bar. Simple chemical evolution models have been used to reproduce the observed AMRs with the purpose of investigating which mechanism has participated in the evolution of the disk and bar. We find that while the disk AMR is well reproduced by close-box models or models with a small degree of outflow, that of the bar is only reproduced by models with combination of infall and outflow.
Astronomical Journal, 2004
}, with the only requirement of referencing this paper and crediting as indicated in the site.