Transcript Slide 1
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.