Engineering topics

Cochran, Anita L.

Publications and source records attributed to Cochran, Anita L..

27 records · Page 2

NASA NTRS1991

Planetary astronomy

The authors profile the field of astronomy, identify some of the key scientific questions that can be addressed during the decade of the 1990's, and recommend several facilities that are critically important for answering these questions. Scientific opportunities for the 1990' are discussed. Areas discussed include protoplanetary disks, an inventory of the solar system, primitive material in the solar system, the dynamics of planetary atmospheres, planetary rings and ring dynamics, the composition and structure of the atmospheres of giant planets, the volcanoes of IO, and the mineralogy of the Martian surface. Critical technology developments, proposed projects and facilities, and recommendations for research and facilities are discussed.

Morrison, David↗

NASA NTRS1991

Status of the profession

The number of astronomers has grown by about 40 percent over the past decade. The number of astronomers with jobs in industry, or with long-term, non-tenured, jobs has increased dramatically compared with traditional faculty positions. The increase in the number of astronomers and the declining share of the NSF budget going to astronomy has led to extreme difficulties in the NSF grant program and in support of the National Observatories. In 1989, direct NASA support of astronomers through the grants program exceeds that of NSF, although the total of the NSF grants program over decade far exceeds that of NASA. Access to major new telescopes will be important issue for the 1990s. US astronomers, who once had a monopoly on telescopes larger than 3 meters, will, by the year 2000, have access to just half of the world's optical telescope area.

Boyce, Peter B.↗

NASA NTRS1990

A search for eclipses of HD 114762 by a low-mass companion

HD 114762 has an unseen companion with a dynamical mass that satisfies the constraint mass sin i = 2.5 x 10 to the 31st gm. The companion is a good candidate for a planetary-mass object, but the inclination of its orbit is unknown and its mass is indeterminate. Tests were conducted for the specific case of a nearly edge-on orbit by looking for eclipses of HD 114762 by the companion. Although the a priori probability of an eclipse is low, this is a crucial case because the companion has its minimum mass if the orbit is edge on. No eclipses were found with a depth greater than 0.01 mag and, therefore, the inclination of the orbit of HD 114762 is less than 89 deg.

Robinson, Edward L.↗

NASA NTRS1990

Observations of CH in comets P/Brorsen-Metcalf and P/Halley

A common feature in the visual spectra of comets is the A squared delta - chi squared pi transition of CH at 4314 A (delta v = 0). This feature is very weak and is easily lost in the continuum or noise. However, the oscillator strength is very small, so even a weak feature indicates a large amount of CH. Understanding the parent of the CH in the comae of comets is very important for understanding the chemistry of comets and, thus, the early solar nebula. Potential parents for the CH are CH4 or more complex hydrocarbons, including polyoxy methanes (POMs). The ratio of CH4 to H2O is indicative of possible sites of formation of the comets. Past observations of comets have shown that the CH is present in the coma. However, because of the intrinsic weakness of the feature and the ease of photodissociating CH, the distribution of the CH in the coma has only been traced in the inner coma, where the fall-off is still 1/p, where p is the impact parameter. The first data sets tracing the distribution of CH to large distances from the nucleus in two comets is presented. Some preliminary models are presented pertaining to the parent of the CH.

Cochran, Anita L.↗

NASA NTRS1990

The near ultraviolet spectra of comets P/Brorsen-Metcalf and Austin

Results are reported on spectrophotometric observations of comets P/Brorsen-Metcalf and Austin from 3000 to 3600 A at a spectral resolution of about 1.8 A. The strongest features are the OH(A-X) 0-0 and 1-1 bands, and the NH(A-X) 0-0 bands. For the first time, the OH(A-X) 0-1 band was clearly found. The existence of the CN(B-X) 2-1 and 3-2 bands were verified and measured. A feature at 3258 A that was first seen in uncalibrated spectra was detected, and was identified as the NH singlet (c-a) 0-0 transition. The CO2(+) features at 3378, 3504, and 3512 A were also firmly identified. This ion was reported as being present in the tail of Comet Bester (1984 I) by Swings and Page (1950). The identification of a weak feature at 3547 A was proposed as the fundamental transition of H2CO, which would make this the first optical cometary detection of this molecule which is very abundant in giant molecular clouds.

Cochran, William D.↗

NASA NTRS1989

Are low-activity comets intrinsically different from more active comets?

A group of comets defined as 'normal' by Cochran (1987) is compared with comets from which no C2 or C3 emissions have been detected and exhibit anomalously low activity. It is established that the low-activity comets are C2- and C3-depleted relative to CN, and that this depletion is not due to these comets' being low producers of all types of gases. A study of all the orbital parameters of the group of comets is conducted, but no parameter is found able to account for the observed difference between normal and low-activity types. Several alternative scenarios for the differences in question are proposed and discussed.

Cochran, Anita L.↗

NASA NTRS1987

Coordinated observations of asteroids 1219 Britta and 1972 Yi Xing

A coordinated observational program conducted for asteroids 1219 Britta and 1972 Yi Xing has yielded a sidereal rotation period of 5.57497 + or - 0.00013 h for the former, which has retrograde rotation and may be classified as an S-type asteroid on the basis of its spectra and albedo. The 1972 Yi Xing synodic period is found to be 14.183 + or - 0.003 h, with an observed light-curve amplitude amplitude of 0.18 mag; its five-color measurements also appear consistent with an S-type classification. A light-curve maximum absolute magnitude of 13.32 + or - 0.01 is also obtained.

Binzel, Richard P.↗

NASA NTRS1987

Another look at abundance correlations among comets

Abundance correlations among comets are examined using three different data sets. The C2 and C3 production rates prove to be well correlated with CN production rates, but large scatter exists. It is concluded that a 'normal' comet is one for which Q(C3)/Q(CN) = 0.19 + or - 0.13 and Q(C2)/Q(CN) = 1.46 + or 0.68.

Cochran, Anita L.↗

NASA NTRS1987

Comet Giacobini-Zinner - A normal comet?

Observations of Comet Giacobini-Zinner were obtained during its 1985 apparition using an IDS spectrograph at McDonald Observatory. Column densities and production rates were computed. The production rates were compared to observations of other 'normal' comets. Giacobini-Zinner is shown to be depleted in C2 and C3 relative to CN. These production rates are down by a factor of 5.

Cochran, Anita L.↗