Publications (9)6.02 Total impact
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Conference Proceeding: Twenty-Plus Years of Water Maser Spectra and Component Positions in IRAS16293-2422
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ABSTRACT: We present the results of a VLA archival study of the water masers near the solar analogue young stellar object IRAS16293-2422, going back to 1985, as well as the results of monitoring these masers with the GBT in 2003 and 2004. We present both spectra (from both the VLA and the GBT), and component positions from the VLA data. We compare the spectra from the VLA and the GBT with published spectra in 1991 and 1992 from the Haystack 37-m (Claussen et al. 1996, ApJS, 106, 111), and also with published spectra from the Nobeyama 45-m (Furuya et al. 2003, ApJS, 144, 71). We further present component positions going back to 1985, using VLA archival data; the positions are accurate to at least the 100 mas level, and in many cases to the 10 mas level. We use the positions and spectra to draw conclusions about the proper motions of the maser sources, and compare this to the motion and evolution of the radio continuum sources as shown by Loinard et al. (2007, ApJ, 670, 1353) and Chandler et al. (2005, ApJ, 632, 371), in order to understand the evolution of this source over the past twenty-plus years. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.Bulletin of the American Astronomical Society; 01/2009 -
Article: Time-Resolved AU-Scale Jets Traced by Masers in the IRAS 4A/B Regions of NGC 1333
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ABSTRACT: We present results of VLBI observations of the water masers associated with IRAS 4A and IRAS 4B in the NGC 1333 star-forming region taken in four epochs over a two month period. Both objects have been classified as extremely young sources, and each source is known to be a multiple system. Using the Very Long Baseline Array, we detected 35 masers in epoch I, 40 masers in epoch II, 35 in epoch III, and 24 in epoch IV. Only one identified source in each system is associated with these masers. These data are used to calculate proper motions for the masers and trace the jet outflows within 100 AU of IRAS 4A2 and IRAS 4BW. In IRAS 4A2 there are two groups of masers, one near the systemic cloud velocity and one redshifted. They expand linearly away from each other at velocities of 53 km s^-1. In IRAS 4BW, masers are observed in two groups that are blueshifted and redshifted relative to the cloud velocity. They form complex linear structures with a thickness of 3 mas (1 AU at a distance of 320 pc) that expand linearly away from each other at velocities of 78 km s^-1. Neither of the jet outflows traced by the maser groups align with the larger scale outflows. We suggest the presence of unresolved companions to both IRAS 4A2 and 4BW.apj. 09/2008; 685:285-297. -
Conference Proceeding: A High Time Resolution Study of Water Masers Near Young Stellar Objects
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ABSTRACT: From April 2003 to March 2004, we monitored the water maser emission from a sample of approximately 30 low-to-intermediate mass young stellar objects (YSOs) in different environments approximately every two weeks (excluding the summer months), using the 100-meter NRAO Green Bank Telescope. In this poster we present the spectra from this monitoring project, and address the questions of variation timescales, the underlying causes of the maser excitation and variations, and the role of YSO evolution in the water maser phenomenon. We report the results of a search for high-velocity (+/- 350 km/s) water maser emission toward these objects, obtained as a byproduct of this monitoring project. Finally, we will report on a detailed case study: the very strong and highly variable water masers in the low-mass YSO IRAS 16293-2422 in the rho Ophiuchi star-forming region.The NRAO is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. Part of this research was carried out under the auspices of the National Science Foundation's Research Experience for Teachers (RET) program at the NRAO, and we gratefully acknowledge the funding for this program.Bulletin of the American Astronomical Society; 06/2006 -
Conference Proceeding: Motions of Water Masers toward Class I Protostar YLW16A
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ABSTRACT: We present three epochs of phase referenced VLBA observations of water masers toward Class I protostar YLW16A, which is located in the $rho$ Ophiuchus cloud. We determine absolute positions of the strongest maser and show that the absolute motion is due to the parallax, global motion of the cloud, and the proper motion of the maser itself. Assuming that the $rho$ Ophiuchus cloud is 150 pc distant, and estimating the global motion of the cloud via Hipparcos stellar proper motions, we estimate the proper motion of the strong maser reference feature to be 6.2+/-3.5 kms^-1. Combined with the radial velocity of this feature, we find the space motion to be 14.8+/-3.5 kms^-1 and the angle of inclination to the plane of the sky to be 65+/-12 degrees. We also track the motion of a weaker maser between epochs. The NRAO is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. Part of this research was carried out under the auspices of the National Science Foundation's Research Experience for Undergraduates (REU) program at the NRAO, and we gratefully acknowledge the funding for this program.Bulletin of the American Astronomical Society; 12/2004 -
Article: Distribution and Motion of the Water Masers near IRAS 05413-0104
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ABSTRACT: We have used the NRAO Very Long Baseline Array to image water masers associated with the low-luminosity, young stellar object (YSO) IRAS 05413-0104 at four epochs over a period of 10 weeks. The maser images show the detail of a symmetric, jetlike structure about 300 mas in extent. The 23^deg+/-2^deg position angle of the maser spot distribution is in excellent agreement with measured position angles for the observed larger scale H_2 and SiO emission distributions; radial velocities are in agreement with SiO measurements showing redshifted gas to the southwest and blueshifted gas to the northeast. We have detected proper motions of numerous maser spots averaging 30+/-12 mas yr^-1, implying space velocities of 64+/-27 km s^-1 for a source distance of 450 pc. Some masers are located within a projected distance of 40 AU of the origin of expansion, the assumed position of the central source, suggesting that jet formation and acceleration takes place within this radius of the YSO. We compute an inclination of the outflow system to the plane of the sky of 4 deg, based on the relative magnitude of the proper motions and radial velocities of the masers. VLBI observations of water masers in YSOs are clearly demonstrated to be interesting and competitive probes of the kinematics of the gas in YSO jets.apjl. 11/1998; 507:L79-L82. -
Conference Proceeding: Water Masers toward the Low-Luminosity YSO IRAS 05413-0104
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ABSTRACT: We report on water maser proper motion in the jet of the YSO IRAS 05413-0104.IAU Colloq. 164: Radio Emission from Galactic and Extragalactic Compact Sources; 01/1998 -
Conference Proceeding: Water Masers Toward Low-Luminosity Young Stellar Objects
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ABSTRACT: A review of the importance of water maser observations toward young stellar objects (YSOs) is presented. Also, we present recent, differing types of observations of water masers near YSOs. Single antenna observations, taken regularly, characterize the variability of the masers and allow estimates of time and spatial scales. High resolution ($$backslash$sim$ 1 mas) multi-epoch observations allow proper motions to be studied. Detailed analysis of such proper motions will allow the placement of the masers in the circumstellar (a disk) or near-stellar environment at the base of the outflow. Radio interferometric techniques are the best method of making estimates of the kinematics of the gas in these regions.Herbig-Haro Flows and the Birth of Stars; 01/1997 -
Article: The Environment and Gas Kinematics of Low-Luminosity YSOs
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ABSTRACT: We report on observations of H_2O masers toward several low luminosity, embedded far-infrared objects. Water maser monitoring with the Haystack 37m telescope and the NRAO 43m telescope shows dramatic variations of H_2O maser emission toward several sources on timescales of one month or less. Observations of these masers with very high angular resolution, using the NRAO VLA, allow us to pinpoint their positions with respect to cm and mm continuum emission, near-infrared sources, and high-velocity molecular gas. These embedded, low-luminosity sources are perhaps the youngest prestellar objects known. Associating the water masers directly with such objects allows us to establish that maser emission occurs early in the stellar evolution cycle. The velocities of the masers can be used as probes of the kinematics of the gas at higher angular resolution than is possible with other tracers, and their variability can give constraints upon the pumping mechanisms which can be related to physical conditions in the maser cloud. We will highlight several sources including the protobinary sources IRAS 16293-2422 and IRAS 4 in NGC1333, the very low luminosity mm continuum source VLA 16234-2417, and the exciting source for HH7-11, SSV13.11/1992; 24:1287. -
Article: Water masers associated with low-mass stars - A survey of the Rho Ophiuchi infrared cluster
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ABSTRACT: The authors report the detection of H2O masers toward two extremely young pre-main-sequence objects embedded in the nearby Rho Ophiuchi molecular cloud complex. These embedded sources (YLW 16 and IRAS 16293-2422) are among the lowest luminosity objects known to be associated with maser emission (16 and 27 L_sun;). The masers exhibit multiple velocity components which varied substantially in intensity over a period of 9 months and which are spatially unresolved (<70 A.U.). The authors suggest a model whereby the maser activity in both sources arises from the interaction of a strong stellar wind with circumstellar material.The Astrophysical Journal 08/1987; 320:L133-L137. · 6.02 Impact Factor
