Effective Temperature Of Uranus

NASA NGR 09-015-047, NGR 22-007-270, NGR 44-012-152Astronom

Test results of Spacelab 2 infrared telescope focal plane

The small helium cooled infrared telescope for Spacelab 2 is designed for sensitive mapping of extended, low-surface-brightness celestial sources as well as highly sensitive investigations of the shuttle contamination environment (FPA) for this mission is described as well as the design for a thermally isolated, self-heated J-FET transimpedance amplifier. This amplifier is Johnson noise limited for feedback resistances from less than 10 to the 8th power Omega to greater than 2 x 10 to the 10th power Omega at T = 4.2K. Work on the focal plane array is complete. Performance testing for qualification of the flight hardware is discussed, and results are presented. All infrared data channels are measured to be background limited by the expected level of zodiacal emission

Phase Determination from Mostly One-sided Interferograms

We show how to detect and correct for non-linear phase shifts in a mainly one-sided interferogram of an emission-line source. We simultaneously detect and correct for an out-of-phase emission background from the spectrometer. The method requires two auxiliary spectra, one of a strong continuum source, and one of an emission-line source with little or no continuum

Imaging the spotty surface of Betelgeuse in the H band

This paper reports on H-band interferometric observations of Betelgeuse made at the three-telescope interferometer IOTA. We image Betelgeuse and its asymmetries to understand the spatial variation of the photosphere, including its diameter, limb darkening, effective temperature, surrounding brightness, and bright (or dark) star spots. We used different theoretical simulations of the photosphere and dusty environment to model the visibility data. We made images with parametric modeling and two image reconstruction algorithms: MIRA and WISARD. We measure an average limb-darkened diameter of 44.28 +/- 0.15 mas with linear and quadratic models and a Rosseland diameter of 45.03 +/- 0.12 mas with a MARCS model. These measurements lead us to derive an updated effective temperature of 3600 +/- 66 K. We detect a fully-resolved environment to which the silicate dust shell is likely to contribute. By using two imaging reconstruction algorithms, we unveiled two bright spots on the surface of Betelgeuse. One spot has a diameter of about 11 mas and accounts for about 8.5% of the total flux. The second one is unresolved (diameter < 9 mas) with 4.5% of the total flux. Resolved images of Betelgeuse in the H band are asymmetric at the level of a few percent. The MOLsphere is not detected in this wavelength range. The amount of measured limb-darkening is in good agreement with model predictions. The two spots imaged at the surface of the star are potential signatures of convective cells.Comment: 10 pages, 10 figures, accepted for publication in A&A, references adde

Balloon measurements of stratospheric HCl and HF by far infrared emission spectroscopy

We have analyzed atmospheric thermal emission spectra obtained with the balloon-borne FIRS-2 far infrared Fourier transform spectrometer during balloon flights from Palestine, Texas on May 12-13, 1988 and from Fort Sumner, New Mexico on September 26-27, 1989 and on July 4-5, 1990. Seven and two pure rotational transition lines in 100-205 cm(exp -1) range are analyzed for deriving vertical profiles of stratospheric HCl and HF, respectively. We obtain both the daytime and nighttime average vertical profiles from 15 to 50 km. We compare these profiles with the ones obtained in June, 1983 with the first version of FIRS spectrometer during the Balloon Intercomparison Campaign (BIC-2). BIC-2 results were revised to be consistent with the present analysis which uses the latest spectral parameters. According to our comparison results no increase is recognized for HCl but about 3 percent per year increase for HF from 1983 to 1990, assuming a linear trend. These annual increase rates are smaller than those reported by other groups. Recently Rinsland et al. (1991) and Wallace and Livingston (1991) reported long term behavior of total HCl and HF observed on Kit Peak between 1977 and 1990. As Kit Peak is located near both balloon launching sites, Palestine and Fort Sumner, we think our results are favorably comparable with theirs. Comparison results with ours and ground-based measurements will be presented and discussed

Measurement of HO2 and other trace gases in the stratosphere using a high resolution far-infrared spectrometer at 28 km

This report covers the time period 1 January 1993 to 30 June 1993. During this reporting period we had our third Upper Atmosphere Research Satellite (UARS) correlative balloon flight and submitted the results from this flight to the Central Data Handling Facility (CDHF). We made a number of improvements in our data processing software in preparation for a new analysis of our old balloon data sets. Finally, we continue to analyze the data obtained during the second Airborne Arctic Stratospheric Expedition (AASE 2)

LLiST - a new star tracker camera for tip-tilt correction at IOTA

The tip-tilt correction system at the Infrared Optical Telescope Array (IOTA) has been upgraded with a new star tracker camera. The camera features a backside-illuminated CCD chip offering doubled overall quantum efficiency and a four times higher system gain compared to the previous system. Tests carried out to characterize the new system showed a higher system gain with a lower read-out noise electron level. Shorter read-out cycle times now allow to compensate tip-tilt fluctuations so that their error imposed on visibility measurements becomes comparable to, and even smaller than, that of higher-order aberrations.Comment: To be published in "New Frontiers in Stellar Interferometry", W. A. Traub, ed., SPIE Proceedings Series, Vol. 5491, paper [5491-126]; 10 pages, 6 figures, 1 table; Latex spie class, uses packages graphicx and url; bib style spiebib; keywords: interferometry, tip-tilt correctio

Study of molecular layers in the atmosphere of the supergiant star µ Cep by interferometry in the K band

Infrared interferometry of supergiant and Mira stars has recently been reinterpreted as revealing the presence of deep molecular layers. Empirical models for a photosphere surrounded by a simple molecular layer or envelope have led to a consistent interpretation of previously inconsistent data. The stellar photospheres are found to be smaller than previously understood, and the molecular layer is much higher and denser than predicted by hydrostatic equilibrium. However, the analysis was based on spatial observations with medium-band optical filters, which mixed the visibilities of different spatial structures. This paper reports spatial interferometry with narrow spectral bands, isolating near-continuum and strong molecular features, obtained for the supergiant µ Cep. The measurements confirm strong variation of apparent diameter across the K-band. A layer model shows that a stellar photosphere of angular diameter 14.11±0.60 mas is surrounded by a molecular layer of diameter 18.56±0.26 mas, with an optical thickness varying from nearly zero at 2.15 µm to >1 at 2.39 µm. Although µ Cep and α Ori have a similar spectral type, interferometry shows that they differ in their radiative properties. Comparison with previous broad-band measurements shows the importance of narrow spectral bands. The molecular layer or envelope appears to be a common feature of cool supergiants

Observations of Mira stars with the IOTA/FLUOR interferometer and comparison with Mira star models

We present K'-band observations of five Mira stars with the IOTA interferometer. The interferograms were obtained with the FLUOR fiber optics beam combiner, which provides high-accuracy visibility measurements in spite of time-variable atmospheric conditions. For the M-type Miras X Oph, R Aql, RU Her, R Ser, and the C-type Mira V CrB we derived the uniform-disk diameters 11.7mas, 10.9mas, 8.4mas, 8.1mas, and 7.9mas (+/- 0.3mas), respectively. Simultaneous photometric observations yielded the bolometric fluxes. The derived angular Rosseland radii and the bolometric fluxes allowed the determination of effective temperatures. For instance, the effective temperature of R Aql was determined to be 2970 +/- 110 K. A linear Rosseland radius for R Aql of (250 +100/-60) Rsun was derived from the angular Rosseland radius of 5.5mas +/- 0.2mas and the HIPPARCOS parallax of 4.73mas +/- 1.19mas. The observations were compared with theoretical Mira star models of Bessel et al. (1996) and Hofmann et al. (1998). The effective temperatures of the M-type Miras and the linear radius of R Aql indicate fundamental mode pulsation.Comment: 12 pages, 4 postscript figure