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Cochran, W. D.

Publications and source records attributed to Cochran, W. D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

TOI-220 b : a warm sub-Neptune discovered by TESS

ABSTRACT In this paper, we report the discovery of TOI-220 b, a new sub-Neptune detected by the Transiting Exoplanet Survey Satellite (TESS) and confirmed by radial velocity follow-up observations with the HARPS spectrograph. Based on the combined analysis of TESS transit photometry and high precision radial velocity measurements, we estimate a planetary mass of 13.8 ± 1.0 M⊕ and radius of 3.03 ± 0.15 R⊕, implying a bulk density of 2.73 ± 0.47 $\rm {g\,cm}^{-3}$. TOI-220 b orbits a relative bright (V= 10.4) and old (10.1 ± 1.4 Gyr) K dwarf star with a period of ∼10.69 d. Thus, TOI-220 b is a new warm sub-Neptune with very precise mass and radius determinations. A Bayesian analysis of the TOI-220 b internal structure indicates that due to the strong irradiation it receives, the low density of this planet could be explained with a steam atmosphere in radiative–convective equilibrium and a supercritical water layer on top of a differentiated interior made of a silicate mantle and a small iron core.

Hoyer, S.↗
NASA NTRS1987

Spectrophotometry of Pluto-Charon mutual events - Individual spectra of Pluto and Charon

Time-resolved spectra of the March 3 and April 4, 1987 mutual events of Pluto and Charon, obtained with spectral coverage from 5500 to 10,000 A with 25-A spectral resolution, are discussed. Charon has a featureless reflectance spectrum, with no evidence of methane absorption. Charon's reflectance appears neutral in color and corresponds to a geometric albedo of about 0.37 at 6000 A. The Pluto reflectance spectrum displays methane absorption bands at 7300, 7900, 8400, 8600, and 8900 A and is red in color, with a geometric albedo of about 0.56 at 6000 A.

Sawyer, S. R.↗
NASA NTRS1986

High resolutions spectroscopy of P/Halley

High resolution spectra of the coma of P/Halley were obtained on 25 April, 2 May, and 3 May 1986. The self-scanned Digicon detector of the 2.7 m telescope coude spectrograph was used to obtain spectra at a resolution of 0.6A. Results of the observation of the NH (A 3 Pi i yields X 3 Sigma (-)) band near 3360 A are presented. The summed NH spectrum represents the results of 190 min of integration centered on the nucleus of the comet. Eight rotational lines from the P and R branches of the band are detected. The lines from the Q branch are especially weak, and are not obviously resolved in the spectrum. The data are compared with the theoretical emission spectrum of Litvak and Kuiper (1982) and substantial discrepancies are found. These discrepancies are explained through a consideration of the relative timescales for collisions, resonance fluorescence, and radiative decays of the NH molecules in the coma.

Cochran, W. D.↗
NASA NTRS1986

A continued program of planetary study at the University of Texas McDonald Observatory

The beginning of eclipses of the Pluto-Charon system was detected. The onset of coma formation of P/Halley at 5.4 au was detected and evidence of sublimation at 4.8 au when CN emission was detected. Extensive spatial maps of the gas in the comae of comets Halley and Giacobini-Zinner were obtained in fall 1985. Halley was time variable, and Giacobini-Zinner was depleted in C2 and C3 relative to CN. Comet Kopff was shown to have a pre-perihelion brightness maximum of its gas, consistent with mantle development if the comet is a high obliquity object. New Haser model scale lengths for CN, C3, and C2 were determined using results from the Faint Comet Survey. Spectra of 12 asteroids in unusual orbits showed no evidence of any comet-like emission features. In particular, 3200 Phaethon (1983 TB) has no gas or dust coma, in spite of the similarity of its orbit with the Geminid meteor stream. Data were analyzed on Saturn's H2 and CH4 bands for the recent southern summer using a Tomasko-Doose type of haze distribution. This haze model fits the data moderately well, giving a CH4 mixing ratio of (4.2 + or 0.4)x003. Simple functions were found to approximate the collision-induced rotation-translation thermal opacity of H2.

Smith, H. J.↗
NASA NTRS1986

Spectroscopy of asteroids in unusual orbits

Medium-resolution spectroscopy of a collection of nonmain-belt asteroids has been obtained in order to search for possible cometlike spectral features. The asteroids include nine earth approachers, two Trojans, and the unusual object 2060 Chiron. All spectra were obtained and reduced in the same manner as comet data in the McDonald Observatory Faint Comet Survey. No indication of cometary activity was found in any of the asteroids observed.

Cochran, W. D.↗
NASA NTRS1984

High Precision Measurement of Stellar Radial Velocity Variations

A prototype instrument for measurement of stellar radial velocity variations to a precision of a few meters per second is discussed. The instrument will be used to study low amplitude stellar non-radial oscillations, to search for binary systems with large mass ratios, and ultimately to search for extrasolar planetary systems. The instrument uses a stable Fabry-Perot etalon, in reflection, to impose a set of fixed reference absorption lines on the stellar spectrum before it enters the coude spectrograph of the McDonald Observatory 2.7-m telescope. The spectrum is recorded on the Octicon detector, which consists of eight Reticon arrays placed end to end. Radial velocity variations of the star are detected by measuring the shift of the stellar lines with respect the artificial Fabry-Perot lines, and correcting for the known motions in the solar system.

Cochran, W. D.↗
NASA NTRS1984

Absolute spectrophotometry of Titan, Uranus, and Neptune 3500-10,500 A

The present absolute measurements of Titan, Uranus and Neptune geometric albedo spectra in the 3500-10,500 A range have a resolution of about 7 A, together with high SNR, in virtue of the exceptional effeciency of the spectrograph and Reticon detector employed. The high precision and spectral resolution of the data, which are in excellent agreement with the Uranus albedo measurements of Lockwood et al. (1983), make possible quantitative measurements of the effects of Raman scattering by H2 in the Uranus and Neptune atmospheres.

Neff, J. S.↗
NASA NTRS1984

Spectral characteristics of two types of low latitude aurorae

Attention is given to two types of aurorae whose low altitude emissions seem to be due to energy loss from trapped ring current ions or electrons whose energy is of the order of 1 eV. The spectral characteristics which predominate in the first type of aurora indicate direct precipitation of ring current particles as ions, and/or indirect precipitation as energetic neutrals, following charge transfer with exospheric H or O neutrals. The spectral characteristics of the second type indicate excitation by electrons and can yield brighter displays. The time variations of the emissions are found to be closely related to fluctuations of periods shorter than an hour in the magnetograms from nearby observatories.

Tinsley, B. A.↗
NASA NTRS1984

Detection of forbidden O I 1S-1D in comet IRAS-Araki-Alcock

Spectra of the forbidden O I 1D-3P 'red' doublet and the 1S-1D 'green' line in Comet IRAS-Araki-Alcock (1983d) were obtained during its close approach to the earth. This is the first unequivocal photoelectric detection of the green line in a cometary spectrum. The population ratio of the O (1S) state to the O (1D) state in the inner coma is not greater than 0.03. This ratio eliminates CO or CO2 and points strongly to H2O as the primary parent for excited oxygen atoms.

Cochran, W. D.↗
NASA NTRS1983

Longitudinal variability of methane and ammonia bands on Jupiter. II - Temporal variations

A set of spectra has been obtained of the Jovian equatorial zone central meridian 6190 A CH4 and 6450 A NH3 bands on the nights of February 26, 27, and 28, 1980, a year after the data reported by Cochran and Cochran (1980), in order to check the previous results and search for possible temporal variations. The new data confirm the results of the previous study. A correlation of the NH3 and CH4 equivalent widths, as well as a lack of any strong correlation of red continuum reflectivity with equivalent width, are found. Longitude regions of larger or smaller than average equivalent width still seem to exist a year later, with some slight drift in longitude. An increase in the average CH4 and NH3 equivalent width over the entire planet was detected during the one year interval. This is easily understood as the result of a global decrease in the mean altitude of the NH3 cloud.

Cochran, W. D.↗
NASA NTRS1983

Desaturation of H2 quadrupole lines in the atmospheres of the outer planets

The vibrational dependence of self-broadening of molecular hydrogen lines results in a desaturation of quadrupole absorption lines long thought to be highly saturated in planetary atmospheres. This desaturation significantly alters H2 abundances in the atmospheres of Uranus and Neptune. Baseline models are presented to illustrate the effects of the revision of this fundamental H2 parameter.

Cochran, W. D.↗
NASA NTRS1983

Observations of optical emissions from precipitation of energetic neutral atoms and ions from the ring current

In the present investigation, results obtained at three different locations are compared, taking into account the McDonald Observatory (latitude 30.7 deg N, longitude 101.0 deg W, altitude 2050 m), Mt. Haleakala (latitude 20.7 deg N, longitude 156.6 deg W, altitude 3050 m), and Cachoeira Paulista (latitude 22.7 deg S, longitude 45.0 deg W, altitude 500 m). The intercomparison of results from the three well-separated sites makes it possible to make evaluations of the local time, storm time, and latitude variation of the ring current precipitation.

Rohrbaugh, R. P.↗
NASA NTRS1982

Copernicus measurement of the Jovian Lyman-alpha emission and its aeronomical significance

It is pointed out that the intensity of the Lyman-alpha emission is a good indicator of the principal aeronomical processes on the major planets. The high-resolution ultraviolet spectrometer aboard the Orbiting Astronomical Observatory Copernicus was used in 1980 April and May to detect the Jovian Lyman-alpha emission by spectroscopically discriminating it from other Doppler shifted Lyman-alpha emissions such as those of the geocorona, and the interplanetary medium. Taking into consideration the reported emission data, it appears that an unusually large energy input due to the particle precipitation in the auroral region must have been responsible for the large observed Lyman-alpha intensity during the Voyager encounter. At most other times, the observed Jovian Lyman-alpha intensity can be explained, within the range of statistical uncertainty, by a model that takes into consideration the solar EUV flux, the solar Lyman-alpha flux, the high exospheric temperature, and the eddy diffusion coefficient without energy input from the auroral sources.

Atreya, S. K.↗
NASA NTRS1982

Doppler line profiles measurement of the Jovian Lyman Alpha emission with OAO-C

Observation of Jupiter made with the high resolution ultraviolet spectrometer of the Orbiting Astronomical Observatory copernicus in April and May, 1980, yield a Jovian Lyman alpha emission intensity of 7 + or 2.5 RR. This indicates a decrease by about a factor of two since the Voyager ultraviolet spectrometer measurements, nearly a year earlier. An unusually high column abundance of hydrogen atoms above the methane homopause at the Voyager epoch is indicated. Since the auroral charged particle bombardment of molecular hydrogen is expected to contribute significantly to the global population of the hydrogen atoms, it is suggested that at the time of the Voyager Jupiter encounter unusually high auroral activity existed, perhaps d to the high concentration of the Io plasma torus. The temporal variation of the Saturn lyman alpha emission, when contrasted with the Jovian data, reveals that the auroral processes are not nearly as important in determining the Saturn Lyman alpha intensity in the nonauroral region.

Barker, E. S.↗
NASA NTRS1982

Rayleigh, Raman and particulate scattering

Analysis of the visible and near infrared spectra of planetary atmospheres and the multiple scattering of photons within the atmosphere are discussed. Photons detected within the spectral region are solar photons which were scattered by the gas and particles in the planetary atmosphere. An example is given for the incident and emitted fluxes for a hypothetical planet with an effective temperature of 100 K. The absorption spectrum of the planetary atmosphere is discussed in terms of the various scattering processes photons undergo within the atmosphere. Three different physical processes are considered. Rayleigh scattering and Raman scattering by the gas molecules, and scattering by any cloud or dust aerosol particles in the atmosphere. The physics of each of these processes is examined.

Cochran, W. D.↗
NASA NTRS1982

Spatially resolved reflectivities of Saturn - 3000-6000 A

Absolute reflectivity reductions are presented for spectrophotometric observations of seven spatially-resolved regions on the disk of Saturn in the 3000-6000 A region. An asymmetry is found between northern and southern hemisphere data, in the equivalent width of the CH4, 5430-A band and in the continuum reflectivity. In addition, the spectra are found not to include the 4700 A reflectivity peak found by Bergstralh et al (1981), and to exhibit general agreement with the Podolack and Danielson (1977) model. The blue and visual spectral region continuum reflectivity of a planetary atmosphere provides constraints for determining aerosol particle single-scattering albedo and vertical distribution, which are in turn important to an understanding of planetary energy balance, atmospheric dynamics, and planetary molecular absorption spectrum interpretation.

Cochran, W. D.↗
NASA NTRS1982

Polarimetry of Pluto

The polarization of Pluto has been measured for a range of solar phase angles from 0.8 to 1.8 deg. A mean linear polarization of 0.29 + or - 0.01% (error of the mean) was found. No dependence of both the amount of polarization and position angles with rotational phase or solar phase angle could be detected. The positional angles of polarization agree with calculated position angles of the defect of illumination and are therefore parallel to the scattering plane. The observed polarization cannot be explained as resulting purely from a surface material which is similar to asteroidal surfaces. A hypothesis of polarization from a thin atmosphere, in addition to the surface polarization, is advanced.

Breger, M.↗