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| en:praktikum:wrstern [2016/10/08 00:42] – [Observational data] rhainich | en:praktikum:wrstern [2024/10/09 08:09] (current) – Adjusts name of laboratory computer rhainich |
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| Find the [[http://www.astro.physik.uni-potsdam.de/PoWR.html|grid models]] at the main page of the [[http://www.astro.physik.uni-potsdam.de|Astrophysics Department of the Uni Potsdam]]. Get an impression of the parameters that enter into the models, e.g. the range of temperatures and the so called transformed radius $R_{\mathrm{t}}$. Learn the principles of line-driven winds. | Find the [[http://www.astro.physik.uni-potsdam.de/PoWR.html|grid models]] at the main page of the [[http://www.astro.physik.uni-potsdam.de|Astrophysics Department of the Uni Potsdam]]. Get an impression of the parameters that enter into the models, e.g. the range of temperatures and the so called transformed radius $R_{\mathrm{t}}$. Learn the principles of line-driven winds. |
| Then copy the WRplot script ''lmcstars.plot'' and the accompanying file for the line identifications ''ident.dat'' from the directory ''~/scripts/d3/'' into your working directory on the laboratory course computer ''a12''. | Then copy the //WRplot// script ''lmcstars.plot'' and the accompanying file for the line identifications ''ident.dat'' from the directory ''~/scripts/d3/'' into your working directory on the laboratory course computer ''columba''. |
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| ===== Realization ===== | ===== Realization ===== |
| Display all data tables by clicking on ''Table'' and then ''All''. Mark and delete unneeded datasets and export the remaining data as a text file (choose a descriptive filename) with fixed column width. Add the reference number of the selected observation as comment line (starting with an asterisk, *). Alternatively, search for the star directly in the [[https://archive.stsci.edu/iue/search.php|IUE database]]. On the results page, click on the ''Data ID'' to get to the preview window, where you can download the spectra as ASCII files. | Display all data tables by clicking on ''Table'' and then ''All''. Mark and delete unneeded datasets and export the remaining data as a text file (choose a descriptive filename) with fixed column width. Add the reference number of the selected observation as comment line (starting with an asterisk, *). Alternatively, search for the star directly in the [[https://archive.stsci.edu/iue/search.php|IUE database]]. On the results page, click on the ''Data ID'' to get to the preview window, where you can download the spectra as ASCII files. |
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| Furthermore, use //[[http://simbad.u-strasbg.fr/simbad/|Simbad]]// and //[[http://vizier.u-strasbg.fr/viz-bin/VizieR|VizieR]]// to obtain the photometry of the star. This means the u, b, and v small band magnitudes ([[http://adsabs.harvard.edu/abs/1968MNRAS.140..409S|Smith et al. 1968]]) as well as the 2MASS IR broad band magnitudes (J, K and H). Copy these values to the //WRplot// script. If needed look for photometry in the literature. | Furthermore, use //[[http://simbad.u-strasbg.fr/simbad/|Simbad]]// and //[[http://vizier.u-strasbg.fr/viz-bin/VizieR|VizieR]]// to obtain the photometry of the star. This means the u, b, and v small band magnitudes ([[http://adsabs.harvard.edu/abs/1968MNRAS.140..409S|Smith et al. 1968]]) as well as the 2MASS IR broad band magnitudes (J, K, and H). Copy these values to the //WRplot// script. If needed look for photometry in the literature. |
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| ==== Fit the spectrum ==== | ==== Fit the spectrum ==== |
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| In principle the WRplot script can be used right away, just some variables and parameters need to be set (so far they are seeded with "= ?"). Choose a model and the corresponding grid, copy the values for the photometry and enter the path of the observational data. | In principle the //WRplot// script can be used right away, just some variables and parameters (those that are seeded with q ''?'') need to be specified. Choose a model and the corresponding grid, copy the values for the photometry and enter the path of the observational data. Create the so-called masterplot by running the script |
| Create the so-called masterplot (as PDF file) by running the script | |
| wrpdf lmcstars.plot | wrpdf lmcstars.plot |
| which creates the file ''lmcstars.pdf''. It contains five panels and a headline with information on the model, its temperature, radius, velocity, abundances and the model number. | which creates the file ''lmcstars.pdf''. It contains five panels and a headline with information on the model, its temperature, radius, velocity, abundances, and the model number. The uppermost panel shows the spectral energy distribution (SED) in a double logarithmic plot (absolute flux over wavelength). The observation is in blue, the chosen model in red, the blue boxes mark the photometry. The other panels show the normalized line spectrum (flux over wavelength) in the same color coding. |
| The uppermost panel shows the spectral energy distribution (SED) in a double logarithmic plot (absolute flux over wavelength). The observation is in blue, the chosen model in red, the blue boxes mark the photometry. The other panels show the normalized line spectrum (flux over wavelength) in the same color coding. | |
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| The task is to select the model that shows the best possible accordance between the observed and model spectrum. Mainly pay attention to the identified spectral lines: Their form, height and width should be reproduced by the model spectrum. By changing the model number (variable ''MODEL'') change the temperature (the first part of the model number) and/or the transformed radius (the second part). First check if the hydrogen lines $\mathrm{H_{\alpha}}$, $\mathrm{H_{\beta}}$ and $\mathrm{H_{\gamma}}$ can (roughly) be reproduced; if the hydrogen lines are very different, change the grid. | |
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| | The task is to select the model that shows the best possible accordance with the observed spectrum. Pay attention to the identified spectral lines: Their form, height, and width should be reproduced by the model spectrum. By changing the model number (variable ''MODEL''), the temperature (the first two digits of the model number) and/or the transformed radius (the last two digits of the model number) can be changed. First check if the hydrogen lines $\mathrm{H_{\alpha}}$, $\mathrm{H_{\beta}}$, and $\mathrm{H_{\gamma}}$ can (roughly) be reproduced. If the hydrogen lines are very different, change the grid. |
| For the LMC there are three model grids available that differ in their hydrogen content (and their helium content, thus): 40, 20, 0% hydrogen mass fraction. Change between the model grids by setting the appropriate path (variable ''PATH''): | For the LMC there are three model grids available that differ in their hydrogen content (and their helium content, thus): 40, 20, 0% hydrogen mass fraction. Change between the model grids by setting the appropriate path (variable ''PATH''): |
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| |WNs with 40% H (WNL) | ''~/scripts/d3/models/wnl40/'' | | |WNs with 40% hydrogen (WNL) | ''~/scripts/d3/models/wnl40/'' | |
| |WNs with 20% H (WNL) | ''~/scripts/d3/models/wnl20/'' | | |WNs with 20% hydrogen (WNL) | ''~/scripts/d3/models/wnl20/'' | |
| |WNs without H (WNE) | ''~/scripts/d3/models/wne/'' | | |WNs without hydrogen (WNE) | ''~/scripts/d3/models/wne/'' | |
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| Some standard grid models have different versions with different wind velocities ($v_{\text{inf}}$) available. Once a model has been found that reproduces the normalized line spectrum start with the SED. To fit the SED change the reddening (variable ''EBVSMITH'') and shift in luminosity (variable ''shift''). Their starting values could be ''shift=0'' and ''EBVSMITH=0.1''. The line strength of the normalized emission spectrum depends on the temperature and the transformed radius, so the luminosity can be scaled up/down in a certain interval by help of the ''shift'' variable without changing the spectrum. The model SED should reproduce the general distribution of the observations while going through the center of the photometry boxes. This ensures the correct flux distribution for the model. | For some standard grid models, additional versions with different wind velocities ($v_{\text{inf}}$) are available. Once a model has been found that reproduces the normalized line spectrum continue with the SED fit. For this purpose, adjust the reddening (variable ''EBVSMITH'') and apply a shift to the luminosity (variable ''shift''). Their starting values could be ''shift=0'' and ''EBVSMITH=0.1''. The line strength of the normalized emission spectrum depends on the temperature and the transformed radius, so the luminosity can be scaled up/down in a certain interval by means of the ''shift'' variable without affecting the normalized spectrum. The model SED should reproduce the general trend of the observations, while going through the center of the photometry boxes. This ensures a correct model flux. |
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| ==== Determine the stellar parameters ==== | ==== Determine the stellar parameters ==== |
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| The stellar parameters can be obtained from the information of the selected model. These parameters are described on the PoWR homepage. Following the Stefan-Boltzmann law: | The stellar parameters can be obtained from the properties of the selected model. These parameters are described on the PoWR homepage. Following the Stefan-Boltzmann law: |
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| $L \propto R_{*}^2$ and $L \propto T^4$, | $L \propto R_{*}^2$ and $L \propto T^4$, |
| $L \propto R_{*}^2 \cdot T^4$. | $L \propto R_{*}^2 \cdot T^4$. |
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| The stellar radius (at constant luminosity) is proportional to $T^{−2}$. By adding the ''shift'' parameter to the luminosity the true luminosity can be customized for a star. | The stellar radius (at constant luminosity) is proportional to $T^{−2}$. By adding the ''shift'' parameter to the luminosity, the model luminosity can be adjusted to the true luminosity of a star. |
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| The mass loss rate is connected to the luminosity via the transformed radius: | The mass loss rate is connected to the luminosity via the transformed radius: |
| $\dot{M}^{\frac{2}{3}} \propto T^{−2} \cdot R_t$. | $\dot{M}^{\frac{2}{3}} \propto T^{−2} \cdot R_t$. |
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| ===== Protocol ===== | ===== Report ===== |
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| A usual laboratory course protocol is to be handed in. | A usual laboratory course report is to be handed in. |
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| [[en:praktikum:index|Overview: Laboratory Courses]] | [[en:praktikum:index|Overview: Laboratory Courses]] |