AST case studies
AST · Put your knowledge to work in context.
The Astronomy Subject Test (AST) is a standardized, multiple-choice examination that assesses a candidate's grasp of astronomy at the undergraduate level, spanning astrophysics and cosmology, stellar structure and evolution, galaxies, planetary science, instrumentation, celestial mechanics, the interstellar medium, and the underlying physics. It is typically taken by students preparing for graduate study or by candidates who need an external, comparable measure of their astronomy knowledge. The AST case studies are 5 cases and about 2,327 words.
1Radial Velocity Signal or Stellar Rotation?
A G-type main-sequence star (mass 1.0 M sun, radius 1.0 R sun, v sin i = 4.5 km/s, rotation period 24 d) is monitored with a high-resolution spectrograph for 120 nights. The team reports a periodic radial-velocity signal with P = 24.0 d and semi-amplitude K = 8 m/s.
469 words, about 2 min2Turnoff Age of a Metal-Poor Globular Cluster
A globular cluster has [Fe/H] = -2.0, an apparent turnoff magnitude of V = 19.2, and a horizontal-branch magnitude of V = 15.8. The reddening is E(B-V) = 0.04 and the distance modulus from the HB is (m-M) V = 15.6.
511 words, about 3 min3Flat Rotation Curve Without Dark Matter?
A spiral galaxy at inclination i = 60 deg has an observed HI rotation curve that is flat at v obs = 180 km/s from R = 5 kpc to R = 25 kpc. The stellar disk has a scale length of 3 kpc and a central surface brightness corresponding to a stellar mass of 5 x 10^10 M sun.
512 words, about 3 min4Europa Clipper Flyby Geometry and Communication Window
A spacecraft in a highly elliptical orbit around Jupiter has a perijove of 5 R J (R J = 71,492 km) and an apojove of 200 R J. During a Europa flyby at 25,000 km altitude, the spacecraft passes behind Europa as seen from Earth for a predicted 18 minutes.
394 words, about 2 min5Pulsar Timing Residuals and a Suspected Companion
A millisecond pulsar with a spin period of 3.2 ms has timing residuals that show a sinusoid with a 60-day period and an amplitude of 12 microseconds. The pulsar's dispersion measure is 15 pc/cm^3, and the timing baseline is 3 years with 200 observations.
441 words, about 2 min