Measuring copper abundances in the Galactic Bulge
(2024) ASTK03 20232Astrophysics
Department of Physics
- Abstract
- Context: The chemical evolution of Cu in the Galactic bulge have been studied in a few studies using red giant branch stars, but the ages of individual red giant stars are difficult to determine. In addition, the bulge has been a challenging region of the Milky Way galaxy to obtain high-resolution spectra of stars, except when observing through certain few small fields into the bulge that are known to have low extinction. Fortunately, a sample of dwarf and subgiant stars were observed during gravitational microlensing events, whose ages were easily determined for each individual star using isochrone fitting and are widely spread across the longitude of the bottom-half of the Galactic bulge. Previous studies that have analysed the sample of... (More)
- Context: The chemical evolution of Cu in the Galactic bulge have been studied in a few studies using red giant branch stars, but the ages of individual red giant stars are difficult to determine. In addition, the bulge has been a challenging region of the Milky Way galaxy to obtain high-resolution spectra of stars, except when observing through certain few small fields into the bulge that are known to have low extinction. Fortunately, a sample of dwarf and subgiant stars were observed during gravitational microlensing events, whose ages were easily determined for each individual star using isochrone fitting and are widely spread across the longitude of the bottom-half of the Galactic bulge. Previous studies that have analysed the sample of microlensed bulge dwarf stars were successful in measuring the abundances for a variety of elements, but have not made measurements for Cu. Therefore, this work has focused on measuring the abundance of Cu in the Galactic bulge using the sample of microlensed bulge dwarf stars.
Method: The Cu abundances for a sample of 71 microlensed dwarf and subgiant stars that are located in the Galactic bulge were analysed by generating a synthetic spectra with known stellar parameters and fitting it to the observed spectra with the best chosen Cu abundance value for the absorption line at 5782 Å.
Results: The Cu abundances for 31 microlensed bulge stars were reliably measured. It was found that Cu/Fe remained flat across metallicities Fe/H between 0.7 ≤ Fe/H ≤ 0.55. Comparing the Cu/Fe-Fe/H trend of the microlensed bulge stars with that of the Galactic chemical evolution model for the bulge did not agree well with each other, where the bulge model has an relative overproduction of Cu/Fe for higher metallicities Fe/H > 0.5. The results fit well with the observed Cu/Fe-Fe/H trend seen in the sample of thick disk dwarf stars for 0.7 ≤ Fe/H ≤ 0.0 and the ages for the microlensed bulge dwarfs agreed well with the ages of the thick disk dwarf stars. Finally, comparing the Cu abundances with the C and O abundances measured in the microlensed bulge dwarf star sample showed that Cu and C were in lockstep when plotting Cu/C vs. C/H and it was found that Cu/O rises for increasing O/H abundances.
Conclusion: From the results, the linear Cu/Fe-Fe/H trend showed a lockstep behaviour between Cu and Fe, which suggests a dependency between the production of Cu and metallicity. A few microlensed bulge dwarf stars show signs that the formation of the bulge and thick disk are similar. Finally, the rising trend for Cu/O for larger O/H implies that massive stars, which are believed to be the major producers of Cu, are not the only contributor of Cu and contribution from other sources need to be considered. (Less) - Popular Abstract
- Imagine an astronomer meeting an archaeologist in a bar. You might think that they have nothing in common between them. Their fields of study seem very independent from each other. So are their personalities, because one of them is more down to earth and keeps getting annoyed at the one who constantly has their head in the stars. Puns aside, there is one field of research, in particular, that combines both archaeology and astronomy. This is a field known as Galactic archaeology.
Stars are in a continuous cycle of creating and recycling heavy elements. Just like the child possessing the genes of their parents, the next generation of stars capture a portion of the elements that were made and ejected by the previous generation of stars in... (More) - Imagine an astronomer meeting an archaeologist in a bar. You might think that they have nothing in common between them. Their fields of study seem very independent from each other. So are their personalities, because one of them is more down to earth and keeps getting annoyed at the one who constantly has their head in the stars. Puns aside, there is one field of research, in particular, that combines both archaeology and astronomy. This is a field known as Galactic archaeology.
Stars are in a continuous cycle of creating and recycling heavy elements. Just like the child possessing the genes of their parents, the next generation of stars capture a portion of the elements that were made and ejected by the previous generation of stars in the local region of the Galaxy. Today, we can see stars in the Galaxy that range in ages between 1 billion to over 12 billion years old, which are as close to the time when the Galaxy was formed. These stars are the fossils for Galactic archaeologists to study how the abundance of a certain element has changed over the lifespan of the Galaxy.
In order to measure the abundance of an element in a star, astronomers need to collect light emitted from the star. More specifically, it is the light that has been absorbed by the elements that allow astronomers to measure its abundance in a star. This requires a good quality spectrum where lots of light is collected from the star. Unfortunately, this is challenging when observing stars in the core of the Milky Way galaxy, which is also known as the Galactic bulge. The solar system is located within the disc of the Galaxy and roughly 26 000 light years from its center. As a result, numerous layers of interstellar dust and gas clouds in the disc obscure our line of sight to the bulge and block the light from the stars. Just like trying to make out the details of something through a thick fog, light from the bulge stars are severely diminished and trying to measure the abundances of elements from faint stars is almost impossible. However, a unique sample of stars were observed during rare events known as gravitational microlensing events. Just like how a magnifying glass can start a fire during a sunny day, light from a faint star in the bulge can be magnified toward Earth, causing the brightness of the star to be amplified. During this phenomenon, astronomers can collect more light from a faint star in the bulge and obtain a good quality spectrum to measure the abundances of elements in these stars that were previously hidden deep behind layers of dust and gas in the Galactic bulge.
The goal of this project was to measure the abundance of copper in a sample of microlensed dwarf stars that were observed in the Galactic bulge. This was achieved by generating artificial-programmed spectra with the best copper abundances that best replicate the observed spectra of the stars in the sample. Previous studies have successfully measured the abundances of a variety of elements that commonly measured in stars, such as alpha elements (e.g. oxygen, magnesium). So far, copper has not been measured in the sample of microlensed bulge dwarf stars and has been studied in only a few studies using samples of bulge red-giant stars. Red giants are not good candidates to investigate how the abundance of copper found in stars have evolved over the lifetime of the Galaxy as the ages of individual red giants are dicult to determine, whereas the ages of individual microlensed dwarf star were easily determined and, thus, makes this an interesting sample to study. This is an opportunity to place copper under the magnifying glass and discover what it can reveal about the Galactic bulge behind its interstellar dusty curtains. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9147361
- author
- Höglinger, Nikolei LU
- supervisor
- organization
- course
- ASTK03 20232
- year
- 2024
- type
- M2 - Bachelor Degree
- subject
- keywords
- Copper, Galaxy: abundances, Galaxy: bulge, Chemical Evolution
- report number
- 2024–EXA220
- language
- English
- id
- 9147361
- date added to LUP
- 2024-01-31 15:48:27
- date last changed
- 2024-01-31 15:48:27
@misc{9147361,
abstract = {{Context: The chemical evolution of Cu in the Galactic bulge have been studied in a few studies using red giant branch stars, but the ages of individual red giant stars are difficult to determine. In addition, the bulge has been a challenging region of the Milky Way galaxy to obtain high-resolution spectra of stars, except when observing through certain few small fields into the bulge that are known to have low extinction. Fortunately, a sample of dwarf and subgiant stars were observed during gravitational microlensing events, whose ages were easily determined for each individual star using isochrone fitting and are widely spread across the longitude of the bottom-half of the Galactic bulge. Previous studies that have analysed the sample of microlensed bulge dwarf stars were successful in measuring the abundances for a variety of elements, but have not made measurements for Cu. Therefore, this work has focused on measuring the abundance of Cu in the Galactic bulge using the sample of microlensed bulge dwarf stars.
Method: The Cu abundances for a sample of 71 microlensed dwarf and subgiant stars that are located in the Galactic bulge were analysed by generating a synthetic spectra with known stellar parameters and fitting it to the observed spectra with the best chosen Cu abundance value for the absorption line at 5782 Å.
Results: The Cu abundances for 31 microlensed bulge stars were reliably measured. It was found that Cu/Fe remained flat across metallicities Fe/H between 0.7 ≤ Fe/H ≤ 0.55. Comparing the Cu/Fe-Fe/H trend of the microlensed bulge stars with that of the Galactic chemical evolution model for the bulge did not agree well with each other, where the bulge model has an relative overproduction of Cu/Fe for higher metallicities Fe/H > 0.5. The results fit well with the observed Cu/Fe-Fe/H trend seen in the sample of thick disk dwarf stars for 0.7 ≤ Fe/H ≤ 0.0 and the ages for the microlensed bulge dwarfs agreed well with the ages of the thick disk dwarf stars. Finally, comparing the Cu abundances with the C and O abundances measured in the microlensed bulge dwarf star sample showed that Cu and C were in lockstep when plotting Cu/C vs. C/H and it was found that Cu/O rises for increasing O/H abundances.
Conclusion: From the results, the linear Cu/Fe-Fe/H trend showed a lockstep behaviour between Cu and Fe, which suggests a dependency between the production of Cu and metallicity. A few microlensed bulge dwarf stars show signs that the formation of the bulge and thick disk are similar. Finally, the rising trend for Cu/O for larger O/H implies that massive stars, which are believed to be the major producers of Cu, are not the only contributor of Cu and contribution from other sources need to be considered.}},
author = {{Höglinger, Nikolei}},
language = {{eng}},
note = {{Student Paper}},
title = {{Measuring copper abundances in the Galactic Bulge}},
year = {{2024}},
}