* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Variable and Binary Stars
History of Solar System formation and evolution hypotheses wikipedia , lookup
Dyson sphere wikipedia , lookup
Aries (constellation) wikipedia , lookup
Observational astronomy wikipedia , lookup
Corona Australis wikipedia , lookup
Canis Minor wikipedia , lookup
Star of Bethlehem wikipedia , lookup
Auriga (constellation) wikipedia , lookup
Star catalogue wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
Corona Borealis wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Canis Major wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Stellar evolution wikipedia , lookup
Stellar kinematics wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Star formation wikipedia , lookup
Cosmic distance ladder wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Variable and Binary Stars Not so Unusual All stars are variable to some extent – – – – Some over periods of days or weeks Others over centuries or millennia Often many modes of variability The Sun is variable +/- 0.07% By a small majority, all stars are binary or trinary – 53% of star systems are multiple – 75% of O-type stars seem to have a companion – If Jupiter had been ~100 times more massive, the Sun would have a companion star Variable When an Astrophysicist talks about variable stars, s/he usually means a dramatically variable star Some are variable even to the naked eye, once you know what you are looking for – Mira (o Ceti): T ~ 1 year AKA “Wonderful” in Latin – Algol (b Persei): T ~ 1 week AKA “The Demon” in Arabic – Suggests ancient peoples noticed these changes Intrinsic variability due to instability in the Hydrostatic Equilibrium Extrinsic variability due to shape, bright spots, rotation, neighbors (some) Categories of Variables Cepheid RR Lyrae T Tauri Explosive variables (novae, discussed elsewhere) Eclipsing binaries – A combination of our two subjects! – Also ellipsoidal binaries Cepheid The first Cepheid variable, Delta Cephei, is close enough for a parallax measurement Population I, giant yellow stars – F6-K2 – Young, metal rich – 103,104 Lsun T ~ days to months Henrietta Leavitt and Cepheid Variables One of Edward Pickering’s “harem” “a straight line can readily be drawn ... showing that there is a simple relation between the brightness of the variables and their periods...” Rosetta Stone Since Delta Cephei is close enough for a parallax measurement, and since the magnitude variation a la Leavitt gives a good measure of intrinsic brightness, distance to other Cepheids can be obtained Used to find the distance to the Small Magellenic Cloud, changing ideas about the scale of the Universe – hmmmmmm RR Lyrae Common in globular clusters – Spectral type F2-A2, yellow or white giant – Population II (as one would expect in a globular cluster) Periods of a day down to several hours Amplitude of 0.3-2 magnitudes Also a reliable distance indicator etacar.umn.edu T Tauri Very young low mass star: – > F, G, K, M – >10 Myr – > 3 Msun Still undergoing gravitational contraction Intermediate stage between a protostar and a main sequence star. Binary Systems and Variability If two stars coalesce out of a globule near enough to each other but with sufficient relative velocity, they will orbit about their common center AKA Barycenter Beta, not part of the system b a Alpha Centauri A Proxima Centauri, currently the closest star to the Sun Barnard’s star, not a binary but on its way. By 11,700 it’ll be the closest star Rho Ophiuchi Trinary System Binary stars M4 Antares Mizar, an eclipsing binary Spectral Red-Shift The shift in the spectrum can show the speeds in a binary pair also Also useful in finding extra-solar planets A new device called a laser comb produces a series of spectral lines at precisely spaced frequencies, allowing measuring star motions 60 times more precisely Light Curve, one more time Piper Reid, Dripping Springs High School, Austin TX Link to her paper Contributions to a Nova This binary system has a giant and a dwarf star The dotted line is the Roche lobe If the giant expands during the course of its demise beyond the Roche lobe, the dwarf can steal material and go nova Blue Stragglers: O-types merging gently But That Is Just One Possible Fate of a Star