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An Infrared Stellar Thermometer

Puspure, Ieva LU (2021) In Lund Observatory Examensarbeten ASTK02 20211
Lund Observatory
Abstract (Swedish)
Infrared (IR) spectroscopy has many advantages over optical, one of which is allowing us
to see through intergalactic dust, letting us probe deeper into space and dust-dense regions
such as galactic centers. However the investigating the IR spectral range is a relatively
new field, owing to recent developments in detector technology, and stellar parameter
determination in IR is not well researched. This thesis aims to explore stellar temperature
determination in this spectral range.
Temperature can be considered as one of the most important stellar parameters, as it
is crucial to know when determining chemical abundances, and it allows us to classify stars
from which we may then analyse individual bodies and stellar populations. A... (More)
Infrared (IR) spectroscopy has many advantages over optical, one of which is allowing us
to see through intergalactic dust, letting us probe deeper into space and dust-dense regions
such as galactic centers. However the investigating the IR spectral range is a relatively
new field, owing to recent developments in detector technology, and stellar parameter
determination in IR is not well researched. This thesis aims to explore stellar temperature
determination in this spectral range.
Temperature can be considered as one of the most important stellar parameters, as it
is crucial to know when determining chemical abundances, and it allows us to classify stars
from which we may then analyse individual bodies and stellar populations. A variety of
methods exist for determination, however in this thesis we use spectral synthesis.
We determine the effective temperature through spectral synthesis done with high resolution and high signal-to-noise ratio H-band (1.5{1.8 microns) spectra taken by the IGRINS
spectrometer of 12 K-giants, with a range of temperatures between 4100{5200 K and metallicites between -0.80{0.30 dex. We use stellar parameters from J¨onnson et. al. (in prep)
determined in the optical range for modelling stellar atmospheres, and as a benchmark for
stellar temperatures.
We find that only using Fe I absorption lines for spectral synthesis produces poor results
in comparison, and choose to additionally look at CO molecular lines, using carbon and
oxygen abundances found in J¨onnson et. al. (in prep.). While these produce temperatures
closer to the benchmark, the best results are found from a combination of Fe I and CO
lines which give temperatures on average 40 K higher with σ = 24 K. (Less)
Popular Abstract
Millions of stars litter the night sky, and our understanding of how they were born is still
developing. These burning orbs of gas are so far away that even the light they give off takes
years to arrive to us on Earth. So how are we to measure anything about them if sending
any equipment to their distant locations is unimaginable? Since the days of Newton, the
only way we have been able to say anything about stars has been by looking at the colour
of their light.
While stars appear to glow in a single colour to us, they are a mixture of many colours.
By dispersing the light of stars, we can see that certain colours that make up the light
are not as bright as others; each of the elements that make up a star will absorb certain
... (More)
Millions of stars litter the night sky, and our understanding of how they were born is still
developing. These burning orbs of gas are so far away that even the light they give off takes
years to arrive to us on Earth. So how are we to measure anything about them if sending
any equipment to their distant locations is unimaginable? Since the days of Newton, the
only way we have been able to say anything about stars has been by looking at the colour
of their light.
While stars appear to glow in a single colour to us, they are a mixture of many colours.
By dispersing the light of stars, we can see that certain colours that make up the light
are not as bright as others; each of the elements that make up a star will absorb certain
colours of light more than other colours. How much light is absorbed will depend on how
hot the star is, and by finding patterns in the light absorption we can determine the exact
temperature, creating somewhat of a long-distance thermometer.
Equipment both in space and on Earth, such as the famous Hubble Telescope, measure
how brightly stars glow through different colour filters. We have researched this extensively
in visible light, however the light stars emit goes beyond what we can see with our naked
eye, such as infrared.
We have developed computer programs that can find out star temperatures from light
measurements, but we are not exactly sure which element patterns are best to look at in
infrared for finding temperature; studying this will allow us to use upcoming instruments,
such as the James Webb Space Telescope, to their full potential.
By understanding how best to utilise infrared measurements, we also increase how much
of space we can see, as light visible to the naked eye can often be blocked by clouds of
dust that litter space. This is not as large of a problem for infrared light, as it can travel
through dust much better than visible light. Because of this we can use thermal cameras
to see people through smoke for example, as anything with heat will also release infrared
light. Deepening our understanding of the infrared range will allow us to broaden our
horizons in our understanding of even the most distant stars. (Less)
Please use this url to cite or link to this publication:
author
Puspure, Ieva LU
supervisor
organization
course
ASTK02 20211
year
type
M2 - Bachelor Degree
subject
keywords
Infrared Spectroscopy, Infrared, Red giants, Stellar Temperature, Spectroscopy
publication/series
Lund Observatory Examensarbeten
report number
2021-EXA178
language
English
id
9066412
date added to LUP
2021-10-07 13:46:56
date last changed
2021-10-07 13:46:56
@misc{9066412,
  abstract     = {{Infrared (IR) spectroscopy has many advantages over optical, one of which is allowing us
to see through intergalactic dust, letting us probe deeper into space and dust-dense regions
such as galactic centers. However the investigating the IR spectral range is a relatively
new field, owing to recent developments in detector technology, and stellar parameter
determination in IR is not well researched. This thesis aims to explore stellar temperature
determination in this spectral range.
Temperature can be considered as one of the most important stellar parameters, as it
is crucial to know when determining chemical abundances, and it allows us to classify stars
from which we may then analyse individual bodies and stellar populations. A variety of
methods exist for determination, however in this thesis we use spectral synthesis.
We determine the effective temperature through spectral synthesis done with high resolution and high signal-to-noise ratio H-band (1.5{1.8 microns) spectra taken by the IGRINS
spectrometer of 12 K-giants, with a range of temperatures between 4100{5200 K and metallicites between -0.80{0.30 dex. We use stellar parameters from J¨onnson et. al. (in prep)
determined in the optical range for modelling stellar atmospheres, and as a benchmark for
stellar temperatures.
We find that only using Fe I absorption lines for spectral synthesis produces poor results
in comparison, and choose to additionally look at CO molecular lines, using carbon and
oxygen abundances found in J¨onnson et. al. (in prep.). While these produce temperatures
closer to the benchmark, the best results are found from a combination of Fe I and CO
lines which give temperatures on average 40 K higher with σ = 24 K.}},
  author       = {{Puspure, Ieva}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Lund Observatory Examensarbeten}},
  title        = {{An Infrared Stellar Thermometer}},
  year         = {{2021}},
}