Comet LINEAR 1999 S4
Narrowband Photometry Results

Photometry of comet LINEAR was performed using narrowband filters to isolate the light emitted from several different gas species (OH, NH, CN, C3, C2). These measurements can be used to determine how much of each gas is being released from the nucleus. In addition, the sunlight reflected from dust particles is measured at several different wavelengths to get an estimate of the amount of dust that is being emitted.

We have photometry measurements, obtained at Lowell Observatory, on 11 nights between the comet's discovery and the time that it broke up. We also have measurements on three nights following the breakup.

Gas and Dust Production

The results from these measurements show that the gas production in Comet LINEAR was not unusual, with different species increasing at the same rate as the comet approached the sun. One aspect that was unusual was that the emission peaked in early June and then dropped through June and July. Though we do not have any measurements immediately after the breakup, our data from about a week later show that the gas production had plummeted rapidly.

Dust "production" on the other hand stayed almost constant as the comet approached the sun. This probably indicates that an outburst early in the apparition produced a lot of dust, which remained in the coma due to slow emission velocities.

Size of the Nucleus

It is a straightforward calculation to determine how much water ice will vaporize from a given area of a comet's surface when a known amount of sunlight hits it. Using this calculation, combined with our photometry measurements, we determined that the amount of surface area that must be active is 2.4 km2 (about 1 square mile). This translates to a minimum effective diameter of 0.88 kilometers (about half a mile) for comet LINEAR. This is a lower limit, because the entire surface area may not be active.

Chemical Composition and Classification

The chemical composition of comets from the Oort cloud all have essentially the same relative amounts of the different gas species that we measure. This type of composition is classified as "typical". About half of short-period comets (from the Kuiper Belt) also fit this "typical" composition, but the other half are depleted in carbon-chain molecules (C2, C3) with respect to the other gases.

Our measurements indicate that LINEAR is depleted of the carbon chain molecules. This is very unusual, because LINEAR is an Oort cloud comet. In fact, this is the first Oort cloud comet that we have measured that can be classified as depleted.

Other astronomers have found that LINEAR is depleted in other carbon-based molecules such as CO, methane, ethane and ethanol.

Go to the Imaging Results from Before Breakup.

Return to the LINEAR 1999 S4 Home Page.