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FUSE and RS CVns:
Stellar Atmospheres, Magnetism, Binary Stars, and
High-Resolution Spectroscopy
Dr. Seth Redfield
Outline
• What are RS CVns?
– Introduce our subject.
• What physical processes will we be investigating?
– Place the characteristics of our subject into the larger astrophysical
context. (Stellar Atmospheres, Magnetic Fields, Binary Stars)
• How do we study RS CVns and their properties?
– Use our observers toolbox. (Spectroscopy and FUSE)
• How can we apply this to other systems?
– Look at an interesting analogy. (CEGPs)
I. RS CVn
•
A class of stars based on the prototypical star: RS CVn, or the 11th variable star
in the constellation Canum Venatici, “the hunting dogs”, (between Bootis and
the Big Dipper).
•
Comprised of 2 stars in a close orbit around each other (i.e., a binary system).
They are tidally locked (i.e., rotation period equals orbital period, of only days).
•
Both stars are solar-like stars, and therefore have similar stellar structures as
our sun (e.g., a corona, and strong magnetic fields at the surface).
•
Due to the close proximity of two such similar stars, they interact strongly, and
amplify the magnitude and frequency of solar-type events (e.g., flares, and
starspots).
•
There are currently 100s known, mostly nearby systems, but due to their
violent outbursts, some can be seen in globular clusters and even nearby
galaxies.
IIa. Stellar Atmospheres
IIa. Stellar Atmospheres
Optical Continuum
IIa. Stellar Atmospheres
Ca II (near-UV/optical)
IIa. Stellar Atmospheres
O VI (far-UV)
IIa. Stellar Atmospheres
Fe XVIII (X-ray)
IIb. Visualizing Magnetic Fields
Simple drawing of magnetic field lines
IIb. Visualizing Magnetic Fields
Demonstration using
magnet and iron filings
IIb. Visualizing Magnetic Fields
An astrophysical example: Our Sun
IIb. Visualizing Magnetic Fields
An astrophysical example: Our Sun
IIc. Binary Stars
Close binaries will share
magnetic field lines, which
may in turn influence
atmospheric features (e.g,
starspots, flares)
IIc. Binary Stars
QuickTime™ and a
Video decompressor
are needed to see this picture.
The Doppler Effect shifts
lines in the stellar
spectrum as the stars
alternate moving towards
and away from us
IIIa. How can we measure the properties
of RS CVn stars?
• Need high resolution spectroscopy in order to see spectral
features from both stars in the binary.
• Need to observe wavelengths that are sensitive to the
magnetically active region between the chromosphere and the
corona (i.e., the transition region).
IIIa. How can we measure the properties
of RS CVn stars?
• Need high resolution spectroscopy in order to see spectral
features from both stars in the binary.
• Need to observe wavelengths that are sensitive to the
magnetically active region between the chromosphere and the
corona (i.e., the transition region).
SOLUTION: Use the Far Ultraviolet
Spectroscopic Explorer (FUSE)
Spectral Resolution (R) = /
“How well can we divide up light into
its individual wavelengths”
I
R~1
400
500

600
“Photometry”
700
I
R~1
R ~ 100
400
500

600
700
I
R~1
R ~ 100
R ~ 10000
400
500

600
(about resolution of human eye)
700
R~1
I
R ~ 100
R ~ 10000
FUSE
R ~ 1000000
400
500

600
700
R ~ 10000
392
393

394
395
R ~ 10000
FUSE
R ~ 1000000
392
393

394
395
IIIa. FUSE: Far-Ultraviolet
Spectroscopic Explorer
Launched June 24th, 1999
IIIa. FUSE
Effective diameter: only 10 cm!
Spectral range:
900-1200 Angstroms
(90-120 nanometers).
Nominal lifetime: 3 years.
IIIa. FUSE
IIIa. FUSE: Raw Data
Background
Contamination
Our Star
IIIa. FUSE: Reduced Data
IIIa. FUSE: Observing Plan
• Observe RS CVn systems multiple times over the course of
their orbital period.
• Use FUSE and far-UV transition region spectral emission lines
to observe the 2 solar-type stars in the RS CVn system.
• Look for other phenomena, such as flares, starspots, etc.
IIIa. FUSE
IIc. Binary Stars
QuickTime™ and a
Video decompressor
are needed to see this picture.
The Doppler Effect shifts
lines in the stellar
spectrum as the stars
alternate moving towards
and away from us
IIIa. FUSE
IIIa. FUSE
• This RS CVn survey is an ongoing program. Have monitored
5 systems and expect to do a few more.
• Will continue to track transition region emission lines to
measure the strength and variability of the atmospheres of both
stars in the binary. Search for material in between the stars,
trapped in the magnetic field lines connecting the two
atmospheres.
• Monitor emission for flares.
IV. The CEGP analogy
• Are there other tidally locked, magnetically interacting pairs of
astronomical objects out there that our expertise from the RS
CVn survey can be applied?
Earth and Jupiter have magnetic fields
Close-in Extrasolar
Planets (CEGPs)
Our Solar System
Does the same interaction occur
between a CEGP and its host star?
• Take high-resolution spectra
of stars with CEGPs.
• Monitor the variability of
the atmospheric lines.
• Find out if the magnetic
variability that we detect is
correlated with the orbital
period of the CEGP.