FUSE and RS CVns:Stellar Atmospheres, Magnetism, Binary Stars, and

High-Resolution Spectroscopy

Dr. Seth Redfield

• 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)

Outline

• 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.

I. RS CVn

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

The Doppler Effect shifts lines in the stellar spectrum as the stars alternate moving towards and away from us

QuickTime™ and aVideo decompressor

are needed to see this picture.

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

400 700500 600

R ~ 1

“Photometry”

I

400 700500 600

R ~ 1

R ~ 100

I

400 700500 600

R ~ 1

R ~ 100

R ~ 10000

(about resolution of human eye)

I

400 700500 600

R ~ 1

R ~ 100

R ~ 10000

R ~ 1000000

FUSE

R ~ 10000

392 395393 394

R ~ 1000000

R ~ 10000

392 395393 394

FUSE

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 DataBackground 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

The Doppler Effect shifts lines in the stellar spectrum as the stars alternate moving towards and away from us

QuickTime™ and aVideo decompressor

are needed to see this picture.

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

Our Solar System

Close-in Extrasolar Planets (CEGPs)

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.