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Unformatted text preview: Observations of 6cm OH Maser Emission in MonR2 and LDN 1084 Laura Zschaechner, Nguyen Phan May 11, 2009 Abstract MonR2 and LDN 1084, both regions of massive star formation, are known sources of excited state OH maser emission at the 4765 MHz transition. Both of these sources have been studied over the past 20-25 years and have displayed variability over time. In this paper, we give a brief overview of the phenomenon of astrophysical masers and discuss additional observations made with the VLA at 4765 MHz which could be used to better characterize variability of these two sources. We report a detection of approximately 6.65 Jy in MonR2, but due to a pointing error, no detection was made for LDN 1084. Our observed flux density for MonR2 suggests that it might be undergoing another flaring event. However, frequent observations are needed to better characterize the variability of this maser 1 Introduction 1.1 Background on Masers The discovery of the first astrophysical maser dates back to 1965 when Weaver et al. de- tected 1665 MHz emission emanating from a re- gion of star formation (Gray). The initial dis- covery caused bewilderment and the molecule re- sponsible for the emission was labeled ’mysterium’ (Gray). However, polarization measurements con- ducted by Weinre et al. (1965) identified the 1665 MHz emission as the result of molecular transi- tions in OH, the hydroxyl molecule (Elitzur). The invention of the laboratory maser about a decade earlier provided an understanding of the physics of light amplification by stimulated emission and was eventually used to explain mechanism behind astrophysical masers (Letokhov and Johansson). Although the mechanism powering astrophysical masers are similar to that of laboratory masers, astrophysical masers are simpler because of the absence of resonant cavities and reflecting mirrors (Elitzur). Today, over one hundred maser species have been discovered in interstellar space among these are OH , CO 2 , NH 3 , H 2 O , SiO , HCN , CH , CH 3 OH (methanol), and H 2 CO (Gray). Table 1 gives a brief overview of several species that have been detected from the radio to the opti- cal regimes and the corresponding year of discov- ery (Letokohov and Johansson). Maser emission has been found in a wide variety of astrophysi- cal environments. Galactic masers are typically found in comets, molecular clouds, star-forming regions, the circumstellar envelopes of late-type stars, supernovae remnants expanding into adja- cent molecular region, and even in planetary at- mospheres (Letokhov and Johansson). Their ex- tragalactic counterparts, referred to as megam- ersars because of their high luminosities, are found near the jets and nuclei of active galaxies (Letokhov and Johansson)....
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This note was uploaded on 12/13/2011 for the course ASTRO 423 taught by Professor Gregtaylor during the Fall '11 term at New Mexico.
- Fall '11