Description of the REDDY VESTA ROTATIONALLY RESOLVED NEAR-INFRARED SPECTRA bundle V1.0 ==================================================== Bundle Generation Date: 2020-02-28 Peer Review: 2011 Asteroid Review, Tue May 31 00:00:00 MST 2011 Discipline node: Small Bodies Node Content description based on the data set catalog file description for the PDS3 version, EAR-A-I0046-3-REDDYVESTA-V1.0 ====================================================================================================================== Note: for PDS3 data sets migrated to PDS4, the following text is taken verbatim from the data set description and confidence level note of the PDS3 data set catalog file. In these cases, some details may not be correct as a description of the PDS4 bundle. All spectral observations were obtained using the SpeX instrument on NASA IRTF in low-resolution mode. Observations were made remotely and in classical mode on site. SpeX in low resolution mode (0.8 arcsecond slit) has resolving powers of R~100 across the wavelength region from 0.75 to 2.5 microns. An infrared guider is available to guide on calibration stars (sidereal rates) and near-Earth asteroids (non-sidereal rates). The main spectrograph uses a 1024x1024 Aladdin 3 InSb array and the guider uses a 512x512 Aladdin 2 InSb array [RAYNERETAL2004]. Low-resolution spectrographs like SpeX are ideal for resolving broad absorption features produced by abundant mafic minerals like olivine and pyroxene that make up many asteroid surface assemblages. The low resolution prism mode also helps in obtaining spectra with higher signal-to-noise-ratios (SNR) and asteroids as faint as Vmag~17.5 are routinely observed. Spectral observations for this data set were made by taking nodded spectral image pairs of the target asteroid, local standard star (for telluric correction), solar-analog stars, and calibration flat-field and argon arc-lamp images. The placement of these stellar observations, temporally and spatially on the sky, in relation to the asteroid is important for producing good quality spectra. If the atmosphere over Mauna Kea is stable throughout the observing run, then the log of the flux (apparent magnitude) of the object will decrease linearly with increasing air mass. Hence, all objects are typically observed at air masses less than 1.5, which corresponds to a zenith angle of less than 50 degrees. However, if the atmosphere is unstable over Mauna Kea, whether due to an orographic cap cloud or rapid variability of water vapor content, it often produces a non-linear magnitude-air mass relationship. Local (or extinction) standard stars close to the asteroid are observed to correct for the terrestrial atmospheric water vapor features. Generally, the greater the distance between the local standard star and the asteroid, the poorer is the monitoring of the sky conditions for the asteroid. During a typical observing run, a local standard star with spectral properties similar to our Sun (i.e., G-type, main sequence stars), is paired with an asteroid and is observed over a wide air mass range that bracket the air mass range of the asteroid observations. These standard star observations were used to create an atmospheric model that was then used to correct for the telluric water bands. Solar analog stars are observed to remove the solar continuum from the asteroid spectrum. The solar analog star we used is GSC04914-00950. The spectra were normalized to unity at 1.5 microns by dividing all the reflectance values with the reflectance at 1.5 microns. SpeX prism data was processed using IDL-based Spextool provided by the NASA IRTF [CUSHINGETAL2004]. Vesta has a rotation period of 5.342129760+/-0.00000096 [DRUMMONDETAL1998] and based on this the relative rotational phases are listed below assuming 0 rotation phase for the first observation. File Name Rot.Phase vesta01.tab 0.00 vesta02.tab 0.05 vesta03.tab 0.09 vesta04.tab 0.13 vesta05.tab 0.16 vesta06.tab 0.20 vesta07.tab 0.30 vesta08.tab 0.34 vesta09.tab 0.37 vesta10.tab 0.41 vesta11.tab 0.48 vesta12.tab 0.55 vesta13.tab 0.64 vesta14.tab 0.68 vesta15.tab 0.71 vesta16.tab 0.75 vesta17.tab 0.82 vesta18.tab 0.86 vesta19.tab 0.92 vesta20.tab 1.00 vesta21.tab 1.05 vesta22.tab 1.09 A pdf file with thumbnail plots of all the spectra is available in the document directory for browse purposes. For further information about these data, see REDDYETAL2011. Cited References Drummond, J.D., Fugate, R.Q., Christou, J.C., Hege, E.K., Full adaptive optics images of Asteroids Ceres and Vesta; Rotational poles and triaxial ellipsoid dimensions. Icarus 132 (1), 80-99, 1998. [DRUMMONDETAL1998] Cushing, M.C., W.D. Vacca, and J.T. Rayner, Spextool: A spectral extraction package for SpeX, a 0.8-5.5 micron cross-dispersed spectrograph, PASP 116, 362-376, 2004. [CUSHINGETAL2004] Rayner, J.T., P. M. Onaka, M. C. Cushing and W. D. Vacca, Four Years of Good SpeX, in Ground-based Instrumentation for Astronomy, A. F. M. Moorwood and M. Iye, Eds., Proceedings of the SPIE, vol. 5492, pp. 1498-1509, 2004. [RAYNERETAL2004] Reddy, V., J.A. Sanchez, J-Y. Li, K. Archer, R.A. Tucker, and 6 others, Photometric, Spectral Phase and Temperature Effects on Vesta and HED Meteorites: Implications for Dawn Mission, Icarus (Submitted), 2011. [REDDYETAL2011] Known issues or problems with the data ====================================== Uncertainties in spectral parameters for near-IR data are crucial for detecting and quantifying surface composition. No systematic variations either in reflectance or wavelength were found in the Spextool data sets. The average wavelength resolution of SpeX data reduced with Spextool is 0.016 microns using the 0.8 arcsecond slit. This is due to spectral resolution based on the wavelength calibration. The errors plotted with the data are standard errors of the mean. Uncertainties in the data arise primarily due to low SNR of the final average spectrum, incomplete correction of telluric absorption features, and variable sky/weather conditions. PDS3 Source =========== Version 1.0 of this bundle was migrated from version 1.0 of the PDS3 data set EAR-A-I0046-3-REDDYVESTA-V1.0.