Lunar and Planetary Science XXX 2034.pdf

PROGRESS REPORT ON SPECTROSCOPIC SEARCH FOR AQUEOUS ALTERATION ON SURFACES INVOLVING THE NASA/JOVE AND NSF/REU PROGRAMS. M. Leake, Valdota State University (Department of Physics, Astronomy and Geosciences, Valdosta State University, Valdosta, GA 31698, [email protected]).

Introduction: Progress is being made on a survey of for long term study of solar system objects. The prog- primitive C-class for the presence of water ress on a spectroscopic survey of primitive C-class of hydration in clay-type minerals to understand the asteroids for the presence of water of hydration in extent of aqueous alteration in the early solar system. clay-type minerals, in order to understand the extent Correlation of a spectral feature at 0.7 microns due to of aqueous alteration in the early solar system, is here the Fe2+ to Fe3+ transition in iron oxides in phyllosili- reviewed. cates with a feature at 3.0 microns associated with adsorbed OH [1, 2] leads us to concentrate our search Aqueous Alteration is defined as alteration of mate- around the 0.7 micron region, using both low resolu- rial by interaction of that material with liquid water tion spectroscopy and intermediate filter . formed by melting of incorporated ice [1]. Narrow- Over two observing runs in June 1997 and May band reflectance spectrophotometry of these asteroids 1998, sixteen asteroids have been observed from fa- reveals subtle features at 0.7 microns which are cor- cilities at Kitt Peak and Valdosta State University related with stronger bands in the infrared 3.0 micron (VSU), involving nearly 10 students. region. Both features are associated with water of hydration in clay minerals known as phyllosilicates, Student Involvement: The program is funded by a the 0.7 micron band being associated with transitions NASA/University Joint Venture in Space Science in iron oxides from the ferrous (Fe2+) to ferric (Fe3+) Research (JOVE). The JOVE program was devised state, and the 3.0 micron feature linked to OH, to give faculty members opportunities to embark on interlayer and adsorbed water. The evidence for and research projects under the mentoring of NASA sci- location of hydrated minerals on primitive C asteroids entists at major research laboratories. In addition to of the outer belt may delineate the extent of aqueous equipment funding, the NASA/JOVE program at alteration on and of solar system objects [6], including VSU provides funds for student involvement in all such processes as impact heating of icy asteroids or aspects of the research process, and funds for educa- ground water percolation near magma chambers. tional outreach and curriculum development. Valdo- However, questions arise about the uniqueness of this sta State University is a predominantly undergradu- set of signatures with phyllosilicates, especially when, ate, regional university within the University System because of lack of IR detectors, one focuses only on of Georgia, offers the System’s only Bachelor of Sci- the 0.7 micron feature to flag the purported water of ence degree in Astronomy, and is a member of the hydration[7]. Study of the 0.7 micron feature should Southeastern Association for Research in Astronomy therefore be made in addition to or in conjunction (SARA). The SARA consortium conducts an active with detection of complementary IR absorption fea- NSF/Research Experience for Undergraduates pro- tures. gram in astronomy during the summer, allowing at least one of the 10-12 REU students to participate in Selection Criteria: Asteroids were selected this solar system research. Over the first two years within the following parameters: semi-major axis of the program, students have made over seven pres- from 2.5 - 3.4 AU; apparent 11-14; taxo- entations and three publications [3, 4, 5]. nomic class C and subgroups B, G, and F, group P and D (Trojans and outer belt); diameter 200 km and Goals: Under the JOVE program, the author had the below; position on meridian on observing date; Decli- opportunity to investigate aqueous alteration of nations above -23 degrees; low air ; periods, primitive asteroid surfaces using CCD spectroscopy varied. Asteroids observed in May 1998 include 48 with JSC colleague and mentor, Dr. Faith Vilas. In Doris, 49 Pales, 53 Kalypso, 58 Concordia, 59 Elpis, addition to the pedagogic goals of exposing students 194 Prokne, 334 Chicago, 511 Davida, 747 Winches- to research at all levels, and giving them opportuni- ter, 772 Taneta, and 1021 Flammerio. Scheduling ties to present their findings at national conferences, challenges included the presence of a waxing Moon JOVE has helped the author to obtain both the neces- on our last nights and short nights so close to summer sary equipment and knowledge to build a data base solstice. Lunar and Planetary Science XXX 2034.pdf

Spectroscopic Search for Aqueous Alterations: M. A. Leake

Other Preparations and Reductions: Before the ob- Future Plans: The primary upgrade in equipment will serving runs, ephemerides and finder charts were pre- be the use of a Microluminetics Cryocam CCD ther- pared through the SAO Skyview web site and the moelectrically cooled to -70 degrees C and mounted to ASTFINDER program on the Asteroid Data Base of the spectroscope. Signal to noise will be greatly im- Lowell Observatory (http://asteroid.lowell.edu/). proved. . Alternatively, the project will be continued Hourly motions and tracking corrections were com- with CCD photometry using filters that are 0.03-0.04 puted. Finder charts were nine arc minutes square, the microns in width, centered on 0.55, 0.70, 0.85, 0.90 same dimensions as the field of view of the Axiom and 1.0 microns. Of special interest are detection of CCD 2048 x 2048 camera on the 0.9-m SARA tele- compositional heterogeneities on these objects, espe- scope. Spectra are being reduced using the IRAF util- cially with regard to presence of water-altered miner- ity operating with Sun stations and UNIX. Solar als. Continuous photometric and spectral monitoring analog stars [8,9] and comparison HgNe spectra en- of rotating primitive asteroids may reveal these able us to determine the included wavelengths and changes, and enable us to determine the location of relative spectrum. regions of aqueous alteration remotely. If rotational information is not available (, pole ori- Observing Techniques: Observing runs with the entation, shape parameters), photometry will enable student research assistants were made on June 19-24, one to establish the and (possibly) pole 1997 and May 25-30, 1998 at the SARA 0.9-m tele- positions. Student majors and those in the JOVE and scope at Kitt Peak National Observatory, Arizona. REU programs will participate in data collection, data New equipment and observing techniques made data analysis and presentation of the results of the several collection more efficient in the latest run [3,4]. The aspects of this study. Optomechanics 10C Spectroscope was used with its 150 grooves/mm grating, blazed at 7500 A, providing References: [1] Vilas, Jarvis, and Gaffey (1994) approximately 120A/mm resolution at the first order, Icarus 109, 274. [2] Vilas F. (1994) Icarus 111, through the 100 micron slit. The SBIG ST-6 CCD 456. [3] Alpert A.J. et al. (1997) BAAS 29(5) 1317. camera collecting the primary spectra was thermo- [4] Alpert A.J. et al. (1998) I.A.P.P.P. Comm. 71,87- electrically cooled to -20.0 degrees C. We found the 91. [5] Watkins L. et al. (1998) BAAS 29 (5) 1213. larger slit and lower dispersion grating helpful in de- [6] Vilas F. and Gaffey M. (1989) Science 246, 790. creasing exposure times and increasing signal to [7] King T. and Clark R. (1997) LPS XXVIII, 727. [8] noise. Comparison spectra were provided by HgNe Hardorp J. (1978) A.&A. 63, 383-390. [9] Hardorp J. source within the spectroscope. Typical asteroid ex- (1980) A&A. 120, 529-59. posures for the spectroscope with ST-6 were 15 min- utes. Asteroid magnitudes of 13.9 were reached. So- Acknowledgments: VSU students and I would like to lar analog stars [8,9] were observed throughout the acknowledge JOVE/NASA Grant NAG8-1264, Jove night. We used a SBIG ST-4 CCD camera mounted at Augmentation Grant; and two Equipment, Technology the slit-viewing optics to guide on the asteroid. De- and Construction Trust Fund grants from the Univer- spite the one-arcsecond field of view of the ST-4, once sity System of Georgia. REU student Adina Alpert the asteroid was properly identified and “placed” in and I acknowledge funding from the SARA REU Pro- the slit, we could successfully guide for up to 60 min- gram, NSF grant AST - 9619939. ute exposures. Used for asteroid identification and probably underutilized, the SARA Axiom CCD cam- era, 2048x2048 pixels, was thermoelectrically cooled to -15.0 C. The ST-6 was controlled by a 486 PC us- ing the ST6OPS software, while the ST-4 was con- trolled by a Compaq Pentium laptop using ST-4 soft- ware.