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Bertrand Plez - One of the best experts on this subject based on the ideXlab platform.
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red supergiants as Cosmic Abundance probes massive star clusters in m83 and the mass metallicity relation of nearby galaxies
The Astrophysical Journal, 2017Co-Authors: Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, C Lardo, C J Evans, Emma R Beasor, N Bastian, L. R. PatrickAbstract:We present an Abundance analysis of seven super-star clusters in the disk of M83. The near-infrared spectra of these clusters are dominated by Red Supergiants, and the spectral similarity in the J-band of such stars at uniform metallicity means that the integrated light from the clusters may be analysed using the same tools as those applied to single stars. Using data from VLT/KMOS we estimate metallicities for each cluster in the sample. We find that the Abundance gradient in the inner regions of M83 is flat, with a central metallicity of [Z] = 0.21$\pm$0.11 relative to a Solar value of $Z_\odot$=0.014, which is in excellent agreement with the results from an analysis of luminous hot stars in the same regions. Compiling this latest study with our other recent work, we construct a mass-metallicity relation for nearby galaxies based entirely on the analysis of RSGs. We find excellent agreement with the other stellar-based technique, that of blue supergiants, as well as with temperature-sensitive (`auroral' or `direct') \hii-region studies. Of all the HII-region strong-line calibrations, those which are empirically calibrated to direct-method studies (N2 and O3N2) provide the most consistent results.
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red supergiants as Cosmic Abundance probes the first direct metallicity determination of ngc 4038 in the antennae
The Astrophysical Journal, 2015Co-Authors: C Lardo, Ben Davies, Rolf-peter Kudritzki, Maria Bergemann, L. R. Patrick, J. Zachary Gazak, C J Evans, Bertrand PlezAbstract:We present a direct determination of the stellar metallicity in the close pair galaxy NGC 4038 (D= 20 Mpc) based on the quantitative analysis of moderate resolution KMOS/VLT spectra of three super star clusters (SSCs). The method adopted in our analysis has been developed and optimised to measure accurate metallicities from atomic lines in the J-band of single red supergiant (RSG) or RSG-dominated star clusters. Hence, our metallicity measurements are not a_ected by the biases and poorly understood systematics inherent to strong line H II methods which are routinely applied to massive data sets of galaxies. We _nd [Z]= +0.07 _ 0.03 and compare our measurements to H II strong line calibrations. Our Abundances and literature data suggest the presence of a at metallicity gradient, which can be explained as redistribution of metal-rich gas following the strong interaction.
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RED SUPERGIANTS AS Cosmic Abundance PROBES: THE MAGELLANIC CLOUDS
The Astrophysical Journal, 2015Co-Authors: Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, Zach Gazak, Chris Evans, L. R. PatrickAbstract:Red Supergiants (RSGs) are cool (∼ 4000K), highly luminous stars (L ∼ 105L⊙), and are among the brightest near-infrared (NIR) sources in star-forming galaxies. This makes them powerful probes of the properties of their host galaxies, such as kinematics and chemical Abundances. We have developed a technique whereby metallicities of RSGs may be extracted from a narrow spectral window around 1μm from only moderate resolution data. The method is therefore extremely efficient, allowing stars at large distances to be studied, and so has tremendous potential for extragalactic Abundance work. Here, we present an Abundance study of the Large and Small Magellanic Clouds (LMC and SMC respectively) using samples of 9-10 RSGs in each. We find average Abundances for the two galaxies of [Z]LMC = −0.37±0.14 and [Z]SMC = −0.53±0.16 (with respect to a Solar metallicity of Z⊙=0.012). These values are consistent with other studies of young stars in these galaxies, and though our result for the SMC may appear high it is consistent with recent studies of hot stars which find 0.5-0.8dex below Solar. Our best-fit temperatures are on the whole consistent with those from fits to the optical-infrared spectral energy distributions, which is remarkable considering the narrow spectral range being studied. Combined with our recent study of RSGs in the Galactic cluster Per OB1, these results indicate that this technique performs well over a range of metallicities, paving the way for forthcoming studies of more distant galaxies beyond the Local Group.
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Red Supergiants as Cosmic Abundance Probes: The Sculptor Galaxy NGC 300
The Astrophysical Journal, 2015Co-Authors: J. Zachary Gazak, Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, Chris Evans, L. R. Patrick, Fabio Bresolin, Ralf Bender, Michael WegnerAbstract:We present a quantitative spectroscopic study of twenty-seven red supergiants in the Sculptor Galaxy NGC 300. J-band spectra were obtained using KMOS on the VLT and studied with state of the art synthetic spectra including NLTE corrections for the strongest diagnostic lines. We report a central metallicity of [Z]= -0.03 +/- 0.05 with a gradient of -0.083 +/- 0.014 [dex/kpc], in agreement with previous studies of blue supergiants and H II-region auroral line measurements. This result marks the first application of the J-band spectroscopic method to a population of individual red supergiant stars beyond the Local Group of galaxies and reveals the great potential of this technique.
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red supergiant stars as Cosmic Abundance probes iii nlte effects in j band magnesium lines
The Astrophysical Journal, 2015Co-Authors: Maria Bergemann, Ben Davies, Rolf-peter Kudritzki, Zach Gazak, Bertrand PlezAbstract:Non-local thermodynamic equilibrium (NLTE) calculations for Mg i in red supergiant stellar atmospheres are presented to investigate the importance of NLTE for the formation of Mg i lines in the NIR J-band. Recent work using medium resolution spectroscopy of atomic lines in the J-band of individual red supergiant stars has demonstrated this technique is a very promising tool for investigating the chemical composition of the young stellar population in star forming galaxies. As in previous work, where NLTE effects were studied for iron, titanium, and silicon, substantial effects are found resulting in significantly stronger Mg i absorption lines. For the quantitative spectral analysis the NLTE effects lead to magnesium Abundances significantly smaller than in local thermodynamic equilibrium with the NLTE Abundance corrections varying smoothly between −0.4 dex and −0.1 dex for effective temperatures between 3400 and 4400 K. We discuss the physical reasons of the NLTE effects and the consequences for extragalactic J-band Abundance studies using individual red supergiants in the young massive galactic double cluster h and χ Persei.
Maria Bergemann - One of the best experts on this subject based on the ideXlab platform.
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red supergiants as Cosmic Abundance probes massive star clusters in m83 and the mass metallicity relation of nearby galaxies
The Astrophysical Journal, 2017Co-Authors: Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, C Lardo, C J Evans, Emma R Beasor, N Bastian, L. R. PatrickAbstract:We present an Abundance analysis of seven super-star clusters in the disk of M83. The near-infrared spectra of these clusters are dominated by Red Supergiants, and the spectral similarity in the J-band of such stars at uniform metallicity means that the integrated light from the clusters may be analysed using the same tools as those applied to single stars. Using data from VLT/KMOS we estimate metallicities for each cluster in the sample. We find that the Abundance gradient in the inner regions of M83 is flat, with a central metallicity of [Z] = 0.21$\pm$0.11 relative to a Solar value of $Z_\odot$=0.014, which is in excellent agreement with the results from an analysis of luminous hot stars in the same regions. Compiling this latest study with our other recent work, we construct a mass-metallicity relation for nearby galaxies based entirely on the analysis of RSGs. We find excellent agreement with the other stellar-based technique, that of blue supergiants, as well as with temperature-sensitive (`auroral' or `direct') \hii-region studies. Of all the HII-region strong-line calibrations, those which are empirically calibrated to direct-method studies (N2 and O3N2) provide the most consistent results.
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red supergiants as Cosmic Abundance probes the first direct metallicity determination of ngc 4038 in the antennae
The Astrophysical Journal, 2015Co-Authors: C Lardo, Ben Davies, Rolf-peter Kudritzki, Maria Bergemann, L. R. Patrick, J. Zachary Gazak, C J Evans, Bertrand PlezAbstract:We present a direct determination of the stellar metallicity in the close pair galaxy NGC 4038 (D= 20 Mpc) based on the quantitative analysis of moderate resolution KMOS/VLT spectra of three super star clusters (SSCs). The method adopted in our analysis has been developed and optimised to measure accurate metallicities from atomic lines in the J-band of single red supergiant (RSG) or RSG-dominated star clusters. Hence, our metallicity measurements are not a_ected by the biases and poorly understood systematics inherent to strong line H II methods which are routinely applied to massive data sets of galaxies. We _nd [Z]= +0.07 _ 0.03 and compare our measurements to H II strong line calibrations. Our Abundances and literature data suggest the presence of a at metallicity gradient, which can be explained as redistribution of metal-rich gas following the strong interaction.
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RED SUPERGIANTS AS Cosmic Abundance PROBES: THE MAGELLANIC CLOUDS
The Astrophysical Journal, 2015Co-Authors: Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, Zach Gazak, Chris Evans, L. R. PatrickAbstract:Red Supergiants (RSGs) are cool (∼ 4000K), highly luminous stars (L ∼ 105L⊙), and are among the brightest near-infrared (NIR) sources in star-forming galaxies. This makes them powerful probes of the properties of their host galaxies, such as kinematics and chemical Abundances. We have developed a technique whereby metallicities of RSGs may be extracted from a narrow spectral window around 1μm from only moderate resolution data. The method is therefore extremely efficient, allowing stars at large distances to be studied, and so has tremendous potential for extragalactic Abundance work. Here, we present an Abundance study of the Large and Small Magellanic Clouds (LMC and SMC respectively) using samples of 9-10 RSGs in each. We find average Abundances for the two galaxies of [Z]LMC = −0.37±0.14 and [Z]SMC = −0.53±0.16 (with respect to a Solar metallicity of Z⊙=0.012). These values are consistent with other studies of young stars in these galaxies, and though our result for the SMC may appear high it is consistent with recent studies of hot stars which find 0.5-0.8dex below Solar. Our best-fit temperatures are on the whole consistent with those from fits to the optical-infrared spectral energy distributions, which is remarkable considering the narrow spectral range being studied. Combined with our recent study of RSGs in the Galactic cluster Per OB1, these results indicate that this technique performs well over a range of metallicities, paving the way for forthcoming studies of more distant galaxies beyond the Local Group.
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Red Supergiants as Cosmic Abundance Probes: The Sculptor Galaxy NGC 300
The Astrophysical Journal, 2015Co-Authors: J. Zachary Gazak, Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, Chris Evans, L. R. Patrick, Fabio Bresolin, Ralf Bender, Michael WegnerAbstract:We present a quantitative spectroscopic study of twenty-seven red supergiants in the Sculptor Galaxy NGC 300. J-band spectra were obtained using KMOS on the VLT and studied with state of the art synthetic spectra including NLTE corrections for the strongest diagnostic lines. We report a central metallicity of [Z]= -0.03 +/- 0.05 with a gradient of -0.083 +/- 0.014 [dex/kpc], in agreement with previous studies of blue supergiants and H II-region auroral line measurements. This result marks the first application of the J-band spectroscopic method to a population of individual red supergiant stars beyond the Local Group of galaxies and reveals the great potential of this technique.
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red supergiant stars as Cosmic Abundance probes iii nlte effects in j band magnesium lines
The Astrophysical Journal, 2015Co-Authors: Maria Bergemann, Ben Davies, Rolf-peter Kudritzki, Zach Gazak, Bertrand PlezAbstract:Non-local thermodynamic equilibrium (NLTE) calculations for Mg i in red supergiant stellar atmospheres are presented to investigate the importance of NLTE for the formation of Mg i lines in the NIR J-band. Recent work using medium resolution spectroscopy of atomic lines in the J-band of individual red supergiant stars has demonstrated this technique is a very promising tool for investigating the chemical composition of the young stellar population in star forming galaxies. As in previous work, where NLTE effects were studied for iron, titanium, and silicon, substantial effects are found resulting in significantly stronger Mg i absorption lines. For the quantitative spectral analysis the NLTE effects lead to magnesium Abundances significantly smaller than in local thermodynamic equilibrium with the NLTE Abundance corrections varying smoothly between −0.4 dex and −0.1 dex for effective temperatures between 3400 and 4400 K. We discuss the physical reasons of the NLTE effects and the consequences for extragalactic J-band Abundance studies using individual red supergiants in the young massive galactic double cluster h and χ Persei.
Ben Davies - One of the best experts on this subject based on the ideXlab platform.
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red supergiants as Cosmic Abundance probes massive star clusters in m83 and the mass metallicity relation of nearby galaxies
The Astrophysical Journal, 2017Co-Authors: Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, C Lardo, C J Evans, Emma R Beasor, N Bastian, L. R. PatrickAbstract:We present an Abundance analysis of seven super-star clusters in the disk of M83. The near-infrared spectra of these clusters are dominated by Red Supergiants, and the spectral similarity in the J-band of such stars at uniform metallicity means that the integrated light from the clusters may be analysed using the same tools as those applied to single stars. Using data from VLT/KMOS we estimate metallicities for each cluster in the sample. We find that the Abundance gradient in the inner regions of M83 is flat, with a central metallicity of [Z] = 0.21$\pm$0.11 relative to a Solar value of $Z_\odot$=0.014, which is in excellent agreement with the results from an analysis of luminous hot stars in the same regions. Compiling this latest study with our other recent work, we construct a mass-metallicity relation for nearby galaxies based entirely on the analysis of RSGs. We find excellent agreement with the other stellar-based technique, that of blue supergiants, as well as with temperature-sensitive (`auroral' or `direct') \hii-region studies. Of all the HII-region strong-line calibrations, those which are empirically calibrated to direct-method studies (N2 and O3N2) provide the most consistent results.
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red supergiants as Cosmic Abundance probes the first direct metallicity determination of ngc 4038 in the antennae
The Astrophysical Journal, 2015Co-Authors: C Lardo, Ben Davies, Rolf-peter Kudritzki, Maria Bergemann, L. R. Patrick, J. Zachary Gazak, C J Evans, Bertrand PlezAbstract:We present a direct determination of the stellar metallicity in the close pair galaxy NGC 4038 (D= 20 Mpc) based on the quantitative analysis of moderate resolution KMOS/VLT spectra of three super star clusters (SSCs). The method adopted in our analysis has been developed and optimised to measure accurate metallicities from atomic lines in the J-band of single red supergiant (RSG) or RSG-dominated star clusters. Hence, our metallicity measurements are not a_ected by the biases and poorly understood systematics inherent to strong line H II methods which are routinely applied to massive data sets of galaxies. We _nd [Z]= +0.07 _ 0.03 and compare our measurements to H II strong line calibrations. Our Abundances and literature data suggest the presence of a at metallicity gradient, which can be explained as redistribution of metal-rich gas following the strong interaction.
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RED SUPERGIANTS AS Cosmic Abundance PROBES: THE MAGELLANIC CLOUDS
The Astrophysical Journal, 2015Co-Authors: Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, Zach Gazak, Chris Evans, L. R. PatrickAbstract:Red Supergiants (RSGs) are cool (∼ 4000K), highly luminous stars (L ∼ 105L⊙), and are among the brightest near-infrared (NIR) sources in star-forming galaxies. This makes them powerful probes of the properties of their host galaxies, such as kinematics and chemical Abundances. We have developed a technique whereby metallicities of RSGs may be extracted from a narrow spectral window around 1μm from only moderate resolution data. The method is therefore extremely efficient, allowing stars at large distances to be studied, and so has tremendous potential for extragalactic Abundance work. Here, we present an Abundance study of the Large and Small Magellanic Clouds (LMC and SMC respectively) using samples of 9-10 RSGs in each. We find average Abundances for the two galaxies of [Z]LMC = −0.37±0.14 and [Z]SMC = −0.53±0.16 (with respect to a Solar metallicity of Z⊙=0.012). These values are consistent with other studies of young stars in these galaxies, and though our result for the SMC may appear high it is consistent with recent studies of hot stars which find 0.5-0.8dex below Solar. Our best-fit temperatures are on the whole consistent with those from fits to the optical-infrared spectral energy distributions, which is remarkable considering the narrow spectral range being studied. Combined with our recent study of RSGs in the Galactic cluster Per OB1, these results indicate that this technique performs well over a range of metallicities, paving the way for forthcoming studies of more distant galaxies beyond the Local Group.
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Red Supergiants as Cosmic Abundance Probes: The Sculptor Galaxy NGC 300
The Astrophysical Journal, 2015Co-Authors: J. Zachary Gazak, Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, Chris Evans, L. R. Patrick, Fabio Bresolin, Ralf Bender, Michael WegnerAbstract:We present a quantitative spectroscopic study of twenty-seven red supergiants in the Sculptor Galaxy NGC 300. J-band spectra were obtained using KMOS on the VLT and studied with state of the art synthetic spectra including NLTE corrections for the strongest diagnostic lines. We report a central metallicity of [Z]= -0.03 +/- 0.05 with a gradient of -0.083 +/- 0.014 [dex/kpc], in agreement with previous studies of blue supergiants and H II-region auroral line measurements. This result marks the first application of the J-band spectroscopic method to a population of individual red supergiant stars beyond the Local Group of galaxies and reveals the great potential of this technique.
-
red supergiant stars as Cosmic Abundance probes iii nlte effects in j band magnesium lines
The Astrophysical Journal, 2015Co-Authors: Maria Bergemann, Ben Davies, Rolf-peter Kudritzki, Zach Gazak, Bertrand PlezAbstract:Non-local thermodynamic equilibrium (NLTE) calculations for Mg i in red supergiant stellar atmospheres are presented to investigate the importance of NLTE for the formation of Mg i lines in the NIR J-band. Recent work using medium resolution spectroscopy of atomic lines in the J-band of individual red supergiant stars has demonstrated this technique is a very promising tool for investigating the chemical composition of the young stellar population in star forming galaxies. As in previous work, where NLTE effects were studied for iron, titanium, and silicon, substantial effects are found resulting in significantly stronger Mg i absorption lines. For the quantitative spectral analysis the NLTE effects lead to magnesium Abundances significantly smaller than in local thermodynamic equilibrium with the NLTE Abundance corrections varying smoothly between −0.4 dex and −0.1 dex for effective temperatures between 3400 and 4400 K. We discuss the physical reasons of the NLTE effects and the consequences for extragalactic J-band Abundance studies using individual red supergiants in the young massive galactic double cluster h and χ Persei.
Rolf-peter Kudritzki - One of the best experts on this subject based on the ideXlab platform.
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red supergiants as Cosmic Abundance probes massive star clusters in m83 and the mass metallicity relation of nearby galaxies
The Astrophysical Journal, 2017Co-Authors: Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, C Lardo, C J Evans, Emma R Beasor, N Bastian, L. R. PatrickAbstract:We present an Abundance analysis of seven super-star clusters in the disk of M83. The near-infrared spectra of these clusters are dominated by Red Supergiants, and the spectral similarity in the J-band of such stars at uniform metallicity means that the integrated light from the clusters may be analysed using the same tools as those applied to single stars. Using data from VLT/KMOS we estimate metallicities for each cluster in the sample. We find that the Abundance gradient in the inner regions of M83 is flat, with a central metallicity of [Z] = 0.21$\pm$0.11 relative to a Solar value of $Z_\odot$=0.014, which is in excellent agreement with the results from an analysis of luminous hot stars in the same regions. Compiling this latest study with our other recent work, we construct a mass-metallicity relation for nearby galaxies based entirely on the analysis of RSGs. We find excellent agreement with the other stellar-based technique, that of blue supergiants, as well as with temperature-sensitive (`auroral' or `direct') \hii-region studies. Of all the HII-region strong-line calibrations, those which are empirically calibrated to direct-method studies (N2 and O3N2) provide the most consistent results.
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red supergiants as Cosmic Abundance probes the first direct metallicity determination of ngc 4038 in the antennae
The Astrophysical Journal, 2015Co-Authors: C Lardo, Ben Davies, Rolf-peter Kudritzki, Maria Bergemann, L. R. Patrick, J. Zachary Gazak, C J Evans, Bertrand PlezAbstract:We present a direct determination of the stellar metallicity in the close pair galaxy NGC 4038 (D= 20 Mpc) based on the quantitative analysis of moderate resolution KMOS/VLT spectra of three super star clusters (SSCs). The method adopted in our analysis has been developed and optimised to measure accurate metallicities from atomic lines in the J-band of single red supergiant (RSG) or RSG-dominated star clusters. Hence, our metallicity measurements are not a_ected by the biases and poorly understood systematics inherent to strong line H II methods which are routinely applied to massive data sets of galaxies. We _nd [Z]= +0.07 _ 0.03 and compare our measurements to H II strong line calibrations. Our Abundances and literature data suggest the presence of a at metallicity gradient, which can be explained as redistribution of metal-rich gas following the strong interaction.
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RED SUPERGIANTS AS Cosmic Abundance PROBES: THE MAGELLANIC CLOUDS
The Astrophysical Journal, 2015Co-Authors: Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, Zach Gazak, Chris Evans, L. R. PatrickAbstract:Red Supergiants (RSGs) are cool (∼ 4000K), highly luminous stars (L ∼ 105L⊙), and are among the brightest near-infrared (NIR) sources in star-forming galaxies. This makes them powerful probes of the properties of their host galaxies, such as kinematics and chemical Abundances. We have developed a technique whereby metallicities of RSGs may be extracted from a narrow spectral window around 1μm from only moderate resolution data. The method is therefore extremely efficient, allowing stars at large distances to be studied, and so has tremendous potential for extragalactic Abundance work. Here, we present an Abundance study of the Large and Small Magellanic Clouds (LMC and SMC respectively) using samples of 9-10 RSGs in each. We find average Abundances for the two galaxies of [Z]LMC = −0.37±0.14 and [Z]SMC = −0.53±0.16 (with respect to a Solar metallicity of Z⊙=0.012). These values are consistent with other studies of young stars in these galaxies, and though our result for the SMC may appear high it is consistent with recent studies of hot stars which find 0.5-0.8dex below Solar. Our best-fit temperatures are on the whole consistent with those from fits to the optical-infrared spectral energy distributions, which is remarkable considering the narrow spectral range being studied. Combined with our recent study of RSGs in the Galactic cluster Per OB1, these results indicate that this technique performs well over a range of metallicities, paving the way for forthcoming studies of more distant galaxies beyond the Local Group.
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Red Supergiants as Cosmic Abundance Probes: The Sculptor Galaxy NGC 300
The Astrophysical Journal, 2015Co-Authors: J. Zachary Gazak, Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, Chris Evans, L. R. Patrick, Fabio Bresolin, Ralf Bender, Michael WegnerAbstract:We present a quantitative spectroscopic study of twenty-seven red supergiants in the Sculptor Galaxy NGC 300. J-band spectra were obtained using KMOS on the VLT and studied with state of the art synthetic spectra including NLTE corrections for the strongest diagnostic lines. We report a central metallicity of [Z]= -0.03 +/- 0.05 with a gradient of -0.083 +/- 0.014 [dex/kpc], in agreement with previous studies of blue supergiants and H II-region auroral line measurements. This result marks the first application of the J-band spectroscopic method to a population of individual red supergiant stars beyond the Local Group of galaxies and reveals the great potential of this technique.
-
red supergiant stars as Cosmic Abundance probes iii nlte effects in j band magnesium lines
The Astrophysical Journal, 2015Co-Authors: Maria Bergemann, Ben Davies, Rolf-peter Kudritzki, Zach Gazak, Bertrand PlezAbstract:Non-local thermodynamic equilibrium (NLTE) calculations for Mg i in red supergiant stellar atmospheres are presented to investigate the importance of NLTE for the formation of Mg i lines in the NIR J-band. Recent work using medium resolution spectroscopy of atomic lines in the J-band of individual red supergiant stars has demonstrated this technique is a very promising tool for investigating the chemical composition of the young stellar population in star forming galaxies. As in previous work, where NLTE effects were studied for iron, titanium, and silicon, substantial effects are found resulting in significantly stronger Mg i absorption lines. For the quantitative spectral analysis the NLTE effects lead to magnesium Abundances significantly smaller than in local thermodynamic equilibrium with the NLTE Abundance corrections varying smoothly between −0.4 dex and −0.1 dex for effective temperatures between 3400 and 4400 K. We discuss the physical reasons of the NLTE effects and the consequences for extragalactic J-band Abundance studies using individual red supergiants in the young massive galactic double cluster h and χ Persei.
Zach Gazak - One of the best experts on this subject based on the ideXlab platform.
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RED SUPERGIANTS AS Cosmic Abundance PROBES: THE MAGELLANIC CLOUDS
The Astrophysical Journal, 2015Co-Authors: Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, Zach Gazak, Chris Evans, L. R. PatrickAbstract:Red Supergiants (RSGs) are cool (∼ 4000K), highly luminous stars (L ∼ 105L⊙), and are among the brightest near-infrared (NIR) sources in star-forming galaxies. This makes them powerful probes of the properties of their host galaxies, such as kinematics and chemical Abundances. We have developed a technique whereby metallicities of RSGs may be extracted from a narrow spectral window around 1μm from only moderate resolution data. The method is therefore extremely efficient, allowing stars at large distances to be studied, and so has tremendous potential for extragalactic Abundance work. Here, we present an Abundance study of the Large and Small Magellanic Clouds (LMC and SMC respectively) using samples of 9-10 RSGs in each. We find average Abundances for the two galaxies of [Z]LMC = −0.37±0.14 and [Z]SMC = −0.53±0.16 (with respect to a Solar metallicity of Z⊙=0.012). These values are consistent with other studies of young stars in these galaxies, and though our result for the SMC may appear high it is consistent with recent studies of hot stars which find 0.5-0.8dex below Solar. Our best-fit temperatures are on the whole consistent with those from fits to the optical-infrared spectral energy distributions, which is remarkable considering the narrow spectral range being studied. Combined with our recent study of RSGs in the Galactic cluster Per OB1, these results indicate that this technique performs well over a range of metallicities, paving the way for forthcoming studies of more distant galaxies beyond the Local Group.
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red supergiant stars as Cosmic Abundance probes iii nlte effects in j band magnesium lines
The Astrophysical Journal, 2015Co-Authors: Maria Bergemann, Ben Davies, Rolf-peter Kudritzki, Zach Gazak, Bertrand PlezAbstract:Non-local thermodynamic equilibrium (NLTE) calculations for Mg i in red supergiant stellar atmospheres are presented to investigate the importance of NLTE for the formation of Mg i lines in the NIR J-band. Recent work using medium resolution spectroscopy of atomic lines in the J-band of individual red supergiant stars has demonstrated this technique is a very promising tool for investigating the chemical composition of the young stellar population in star forming galaxies. As in previous work, where NLTE effects were studied for iron, titanium, and silicon, substantial effects are found resulting in significantly stronger Mg i absorption lines. For the quantitative spectral analysis the NLTE effects lead to magnesium Abundances significantly smaller than in local thermodynamic equilibrium with the NLTE Abundance corrections varying smoothly between −0.4 dex and −0.1 dex for effective temperatures between 3400 and 4400 K. We discuss the physical reasons of the NLTE effects and the consequences for extragalactic J-band Abundance studies using individual red supergiants in the young massive galactic double cluster h and χ Persei.
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red supergiant stars as Cosmic Abundance probes iii nlte effects in j band magnesium lines
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: Maria Bergemann, Ben Davies, Rolf-peter Kudritzki, Zach Gazak, Bertrand PlezAbstract:Non-LTE calculations for Mg I in red supergiant stellar atmospheres are presented to investigate the importance of non-LTE for the formation of Mg I lines in the NIR J-band. Recent work using medium resolution spectroscopy of atomic lines in the J-band of individual red supergiant stars has demonstrated that technique is a very promising tool to investigate the chemical composition of the young stellar population in star forming galaxies. As in previous work, where non-LTE effects were studied for iron, titanium and silicon, substantial effects are found resulting in significantly stronger Mg I absorption lines. For the quantitative spectral analysis the non-LTE effects lead to magnesium Abundances significantly smaller than in LTE with the non-LTE Abundance corrections varying smoothly between -0.4 dex and -0.1 dex for effective temperatures between 3400 K and 4400 K. We discuss the physical reasons of the non-LTE effects and the consequences for extragalactic J-band Abundance studies using individual red supergiants in the young massive galactic double cluster h and chi Persei.
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Red supergiants as Cosmic Abundance probes
EAS Publications Series, 2013Co-Authors: Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Maria Bergemann, Zach Gazak, Chris EvansAbstract:The chemical Abundances of galaxies provide key constraints to models of their formation and evolution. Unfortunately, the standard method of determining Abundances, from the strong emission lines of Hii-regions, is well-known to be subject to large systematic errors, particularly at high metallicities. To address this problem we are currently working on a project to measure a galaxy’s chemical Abundances from spectral analysis of individual RSGs. By focussing on a spectral window in the J -band which contains few molecular lines, we are able to derive accurate chemical Abundances from relatively low resolution data. In fact, we show that this technique can operate at distances of 3–4 Mpc using the VLT, and a factor of 10 further if we target massive RSG-dominated star clusters. Furthermore, in the ELT-era, we show that we can perform Abundance analysis on individual stars out to 70 Mpc, and redshifts of 0.1 for star clusters.
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red supergiant stars as Cosmic Abundance probes ii nlte effects in j band silicon lines
The Astrophysical Journal, 2013Co-Authors: Maria Bergemann, Ben Davies, Rolf-peter Kudritzki, Bertrand Plez, Matthias Wurl, Zach GazakAbstract:Medium-resolution J-band spectroscopy of individual red supergiant stars is a promising tool to investigate the chemical composition of the young stellar population in star-forming galaxies. As a continuation of recent work on iron and titanium, detailed non-LTE (NLTE) calculations are presented to investigate the influence of NLTE on the formation of silicon lines in the J-band spectra of red supergiants. Substantial effects are found resulting in significantly stronger absorption lines of neutral silicon in NLTE. As a consequence, silicon Abundances determined in NLTE are significantly smaller than in local thermodynamic equilibrium (LTE) with the NLTE Abundance corrections varying smoothly between ?0.4 dex and ?0.1 dex for effective temperatures between 3400?K and 4400?K. The effects are largest at low metallicity. The physical reasons behind the NLTE effects and the consequences for extragalactic J-band Abundance studies are discussed.
