Saturday, May 12, 2012

5 Papers and others

(1) 0704.22532v1.pdf - A survey of debris trails from short-period comets. Reach, Kelley, Sykes
Mean anomaly (parameter relating position and time via Kepler's Law of sweeping out areas at equal rates)

Note: Beta is the ratio of radiation pressure to gravity (1 means they are equal) in terms of acceleration/force.
E.g. (from paper 2) Comet P/2005 U1 Read - particle size: 10-100 micro m, terminal ejection v = (0.2 -3) m/s, escape velocity = 0.2 m/s

(2) 0x810.1351v1.pdf - Physical Properties of Main-Belt Comet P/2005 U1 (Read). Hsieh, Jewitt, Ishiguro
Terminal velocity of particles ejected (then form tails). Jets are modeled like cones, with constant angles = 45 degrees. Reference ejection velocity = 24 m/s

After impact with another body, the particle ejaculation comes mainly from that side of the comet.

(3) 1105.0944v1.pdf Physical Properties of Main-Belt Comet 176P/LINEAR. Hsieh, Ishiguro, Lacerda, Jewitt

Comas can be modeled as ellipsoides, with c/a == b/a for simplicity. 0 < c/a < b/a < 1. Dust tail is assumed to be a jet-driven cone, with cone opening angle of 45 degrees, and its central axis points toward right ascension, and declination in the inertial frame. If rotation, the angle can be approximated about the axis. Assume that dust particles are released uniformly from a sphere and that emission occurs only from direct sunlight. Comet's obliquity can lead to significantly active dust ejection during "summer" time.

Tail size affected by amount of volatile ice in comet. Maybe some variable initially optionally manually hard-coded in ssystem.ini. Later implement in UI adjustable by slider? This would be a hopeful deliverable depending on how long it takes to model the tails and coma correctly.

(4) 1961ApJ./../.pdf On the study of comet tails and models of the interplanetary medium. Brandt

Getting the tail direction:

(5) 1968Apj./../.pdf Theory of dust comets. I. Model and equations. Finson, Probstein

Distinctive comet phenomena becomes visible at 1AU from the Sun. 10**5- 10**6 km is typical coma diameter. Light intensity decreases 1/r

Plasma tails are long (10**7-10**8)km and narrow (10**5-10**6), straight, lagging in the radial direction by 3-5 degrees. Solar wind = 500 km/s. Comet velocity tangent to orbit = 30-60 km/s.
Dust tails are shorter (10**7)km and broader and curved, lagging between the extended radius vector of the Sun and the orbit path. EM interaction on dust tails are negligible.

The presence or absence of tails can affect the tails' orientation. Comets some times only have 1 type of tail. When both are present, the ion tail can charge and affect the dust tail because of its high speed 10km/s.

More: Appendix B (pg24, 25) determines how the comet looks like to an observer on Earth by relating an vector to a point on the tail axis. This way, parallax error for the antitail can be determined.

Update (5/24/12)

Length of comet tail (From ProjectPluto)

The formula gives the tail length L, in millions of kilometers, as follows:
mhelio = H + K * log10(r)
log10(Lo) = -0.0075*mhelio2 - 0.19*mhelio + 2.10
L = Lo * (1 - 10-4r) * (1 - 10-2r)
where H and K are the usual magnitude parameters, and r is the comets' distance from the Sun in AU.

Drawbacks of formula:

- it does not distinguish between ion and dust tails
- it does not take into account the continuing heating for some
  time after perihelion, which results in a longer tail after
  perihelion than before for a given solar distance on average.
  Such an improvement, however, is on my project list...
  This shortcoming, however, can be partially compensated by using
  two different sets of brightness parameters, which many comets
  with q < 1 AU actually show (pre- and postperihelion).
- not a consequence of the formula but equally important:
  the assumption of a tail directed exactly in the anti-solar
  direction can affect the apparent tail length in a recognizable
  way in the case of deviating or bended (dust) tails.

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