Bruce Wilking - Academia.edu (original) (raw)

Papers by Bruce Wilking

Research paper thumbnail of Low-Luminosity Members of the R Coronae Australis Infrared Cluster

Astrophysics and Space Science Library, 1994

Research paper thumbnail of The Initial Mass Function and Disk Frequency of the rho Ophiuchi Cloud: An Extinction-limited Sample

Astronomical Journal, 2011

We have completed an optical spectroscopic survey of an unbiased, extinction-limited sample of ca... more We have completed an optical spectroscopic survey of an unbiased, extinction-limited sample of candidate young stars covering 1.3 deg2 of the rho Ophiuchi star-forming region. While infrared, X-ray, and optical surveys of the cloud have identified many young stellar objects (YSOs), these surveys are biased toward particular stages of stellar evolution and are not optimal for studies of the disk

Research paper thumbnail of Spectroscopy of Brown Dwarf Candidates in the NGC 1333 Molecular Cloud

Proceedings of The International Astronomical Union, 2003

We present an analysis of low-resolution infrared spectra for 25 brown dwarf candidates in the NG... more We present an analysis of low-resolution infrared spectra for 25 brown dwarf candidates in the NGC 1333 molecular cloud. Candidates were chosen on the basis of their association with the high column density cloud core, and near-infrared fluxes and colors. We compare the depths of water vapor absorption bands in our candidate objects with a grid of dwarf, subgiant, and

Research paper thumbnail of IRAS observations of the Rho Ophiuchi infrared cluster - Spectral energy distributions and luminosity function

The Astrophysical Journal, 1989

... These associations are regarded as uncertain, and these sources have not been included in sub... more ... These associations are regarded as uncertain, and these sources have not been included in subsequent discussions of the spectral energy distributions and luminosity function. ... iZIL ~ ~ 9LE ~iZ 91 ~ ~ 4 T~ (LI) (91) (cT) (i't) (~j) (Zr) (It) (ofl (6) (~) (L) (9) (c) (~) ( z) (I) 9g/9 c~/c ...

Research paper thumbnail of IRAS observations of young stellar objects in the Corona Australis dark cloud

The Astrophysical Journal, 1992

Research paper thumbnail of Infrared Properties of Weak Radio Sources in the ρ Ophiuchi Molecular Cloud

The Astrophysical Journal, 2001

Research paper thumbnail of Further mid-infrared study of the rho Ophiuchi cloud young stellar population: Luminosities and masses of pre-main-sequence stars

The Astrophysical Journal, 1994

... 191 Gif-sur-Yvette Cedex, France; andre@sapvxg.saclay.cea.fr ERICK T. YoUNG"2'3 Ste... more ... 191 Gif-sur-Yvette Cedex, France; andre@sapvxg.saclay.cea.fr ERICK T. YoUNG"2'3 Steward Observatory, University of Arizona, Tucson, AZ 85721; erick~sparky.as ... the IRTF 58 x 62 InSb array camera, while M, N, and Q (20 JLm) band data were acquired with the Bob 1 IRTF ...

Research paper thumbnail of Low-mass stars and substellar objects in the NGC 1333 molecular cloud

The Astronomical …, 2004

We present the results of near-infrared imaging and low-resolution near-infrared spectroscopy of ... more We present the results of near-infrared imaging and low-resolution near-infrared spectroscopy of low-mass objects in the NGC 1333 molecular cloud. A JHK survey of an 11A4 Â 11A7 area of the northern cluster was conducted to a sensitivity of K 16 mag. Using near-infrared magnitudes and colors from this and previously published surveys, 25 brown dwarf candidates were selected toward the high-extinction cloud core. Spectra in the K band were obtained and comparisons of the depths of water vapor absorption bands in our candidate objects with a grid of dwarf, subgiant, and giant standards were made to derive spectral types. These data were then used to derive effective temperatures and stellar luminosities that, when combined with theoretical tracks and isochrones for pre-main-sequence objects, resulted in estimates for their masses and ages. The models suggest a median age for the sample of less than 1 Myr with substellar masses for at least nine of the candidates, including the X-ray flare source ASR 24. Surface gravities have been estimated for the brown dwarf candidates and, for a given spectral type, are found to more closely resemble dwarfs than giants. Using the near-infrared imaging data and age estimates from the spectroscopic sample, an extinction-limited sample in the northern cluster was defined. Consistent with recent studies of other young clusters, this sample exhibits an accretion disk frequency of 0.75 AE 0.20 and a mass spectrum slope across the hydrogen-burning limit of 1:6, where dN/dM / M À .

Research paper thumbnail of Deep Infrared Imaging of the R Coronae Australis Cloud Core

The Astronomical Journal, 1997

Page 1. Deep Infrared Imaging of the R Corona Australis Cloud Core Bruce A. Wilking Department of... more Page 1. Deep Infrared Imaging of the R Corona Australis Cloud Core Bruce A. Wilking Department of Physics and Astronomy, University of Missouri-St. Louis 8001 Natural Bridge Road, St. Louis, MO 63121 brucew@newton.umsl.edu Mark J. McCaughrean ...

Research paper thumbnail of Structure and chemistry in the northwestern condensation of the Serpens molecular cloud core

The Astrophysical Journal, 1994

... C From Zhang et al. 1988, Fig. la and lb. d Central source only. 308 a (1950) 15~ 27m008 226 ... more ... C From Zhang et al. 1988, Fig. la and lb. d Central source only. 308 a (1950) 15~ 27m008 226 McMULLIN, MUNDY, WILKING, HEZEL, & BLAKE Vol. 424 were consistent withRodriguez et al. (1989) suggested that the lobe emission had varied. ...

Research paper thumbnail of Distribution and Motion of the Water Masers near IRAS 05413−0104

The Astrophysical Journal, 1998

We have used the NRAO Very Long Baseline Array to image water masers associated with the low-lumi... more We have used the NRAO Very Long Baseline Array to image water masers associated with the low-luminosity, young stellar object (YSO) IRAS 05413Ϫ0104 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 position angle of the ⅙ ⅙ 23 ‫ע‬ 2 maser spot distribution is in excellent agreement with measured position angles for the observed larger scale H and SiO emission distributions; radial velocities are in agreement with SiO measurements showing redshifted 2 gas to the southwest and blueshifted gas to the northeast. We have detected proper motions of numerous maser spots averaging mas yr , implying space velocities of km s for a source distance of 450

Research paper thumbnail of A Spectral Line Study of Serpens S68 FIRS1 Region

The Astrophysical Journal, 2000

A j \ 1 mm to 3 mm study of the Serpens molecular cloud core on scales of 10@ to 10A is presented... more A j \ 1 mm to 3 mm study of the Serpens molecular cloud core on scales of 10@ to 10A is presented, concentrating on the northwest condensation and the embedded sources, S68 FIRS1 and S68 N. We adopt temperatures of 25 K for the extended structure (several arcminute scale) and 35 K for the embedded sources. With these values, we use molecular line ratios and LVG statistical equilibrium calculations to derive physical properties in the region. We obtain densities between 0.4È1.2 ] 106 cm~3 and an overall mass of 250È300

Research paper thumbnail of Water masers associated with low-mass stars: A 13 month monitoring survey

The Astrophysical Journal, 1994

Research paper thumbnail of Time‐Resolved AU‐Scale Jets Traced by Masers in the IRAS 4A/B Regions of NGC 1333

The Astrophysical Journal, 2008

We present results of VLBI observations of the water masers associated with IRAS 4A and IRAS 4B i... more 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 associates 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 red-shifted. 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 blue-shifted and red-shifted 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.

Research paper thumbnail of IRAS 21391 + 5802 - A study in intermediate mass star formation

The Astronomical Journal, 1993

We present infrared and millimeter wavelength observations of the cold IRAS source 21391 + 5802 a... more We present infrared and millimeter wavelength observations of the cold IRAS source 21391 + 5802 and its associated molecular core. Infrared observations at lambda = 3.5 microns reveal a heavily obscured, central point source which is coincident with a compact lambda = 2.7 mm continuum and C18O emission region. The source radiates about 310 solar luminosities, primarily at FIR wavelengths,

Research paper thumbnail of Proper motion of water masers near NGC1333-SVS13

Arxiv preprint astro-ph/ …, 2001

VLBA observations of water masers toward the region of NGC1333 near SVS13, the driving source for... more VLBA observations of water masers toward the region of NGC1333 near SVS13, the driving source for the well-known Herbig-Haro objects HH7-11, are reported. Maser emission was observed over four epochs spaced by three weeks during late 1998. SVS13 is associated with the millimeter continuum SED Class I source SSV13A1. High resolution CO observations have secured the association of the flow with the continuum object on arc-second scales. A 1998 Aug 12 VLA observation places the blueshifted masers within 80 AU (0".2) of the 2.7 mm position for A1 reported from BIMA. We report observations of two groups of masers, one redshifted by about 6 km s −1 and one blueshifted by about 2-3 km s −1 , separated by about 100 AU in projected distance along position angle 21 degrees. Redshifted masers were present only in the latter two epochs. During all epochs, an arclike structure was present with similar morphology; over time this structure moved relative to the southernmost blue maser toward the southeast, roughly along the position angle defined by the Herbig-Haro objects, with a proper motion of about 13 km s −1 . Both redshifted and blueshifted masers are clearly part of the same lobe of the flow; their observed Doppler shifts are artifacts of the opening angle of the flow. Our data suggest that the opening angle is about 10 o . We measure lower expansion velocities and a wider opening angle than has been found in some other flows near Class 0 SED objects, perhaps indicating that the flows open and slow as they age.

Research paper thumbnail of Multiple Outflows in the Haro 6-10/GV Tau/IRAS04263+2426 T Tau/Infrared Companion Binary

Research paper thumbnail of A Monthly Survey of Water Masers Associated with Low-Mass Stars

The Astrophysical Journal Supplement Series, 1996

We have performed a multiepoch survey of water masers toward low-luminosity young stellar objects... more We have performed a multiepoch survey of water masers toward low-luminosity young stellar objects (YSOs). These objects were selected to be in an early phase of stellar evolution based on IRAS colors and association with molecular outflows or dense cores. The sample was restricted to YSOs in nearby clouds (d < 450 pc) with luminosities <120 Lsun. Seven new sources of maser emission have been found resulting in a total of 22 YSOs with L < 120 Lsun known to display maser activity. We present monitoring data (at least two epochs of observation) for 47 sources. Four objects were monitored on a semiregular basis for more than S years. Based on a coherent 13 month subset of this survey, we estimate that the maser phase in low-mass embedded sources occupies about one-third of the duration of the embedded phase of evolution. Some spectrally isolated water maser features are seen to appear and disappear on timescales less than about 2 months. This characteristic timescale is consistent with shock crossing times for reasonable values of the shock velocity and size and is thus suggestive that the masers originate in the shocked gas. Some embedded sources can have long periods of inactivity (˜5 yr) when no masers are seen to our detection limit. Sources with stronger masers and more complex spectra can maintain emission over this same time period. We determined threshold values of the CO mass-loss rate (4 × 10-5 Msun yr-1), 6 cm radio luminosity (0.25 kpc2 mJy), and the IRAS in-band luminosity (25 Lsun) above which water masers were always detected. The isotropic luminosity of the water masers in any given source can vary over more than 2 orders of magnitude in a period of several months. Thus, a single epoch measurement of this luminosity may provide a misleading result, especially if compared to other physical parameters such as the bolometric luminosity.

Research paper thumbnail of Water Masers in the Circumstellar Environments of Young Stellar Objects

Astronomical Journal, 1998

We present a high-resolution radio and millimeter-wavelength study of five low-mass young stellar... more We present a high-resolution radio and millimeter-wavelength study of five low-mass young stellar objects with known water maser emission: RNO 15 FIR, Orion A-W, L1157, B361, and L1251A. These objects are cold IRAS sources with far-infrared luminosities ranging from less than 6 to 40 L_&sun;. Radio continuum observations are used to locate precisely the young stellar object(s) responsible for the

Research paper thumbnail of Circularly Polarized Radio Emission from an X-Ray Protostar

The Astrophysical Journal, 1998

... Neuh auser, R. & Preibisch, T. 1997, A&A, 322, 37 Phillips, RB, Lonsdale, CJ & Fe... more ... Neuh auser, R. & Preibisch, T. 1997, A&A, 322, 37 Phillips, RB, Lonsdale, CJ & Feigelson, ED 1993, ApJ, 403, L43 Page 13. { 13 { ... B. Reipurth & C. Bertout (Dordrecht:Kluwer), p. 83 Saraceno, P., Andr e, P., Ceccarelli, C., Gri n, M. & Molinari, S. 1996, A&A, 309, 827 ...

Research paper thumbnail of Low-Luminosity Members of the R Coronae Australis Infrared Cluster

Astrophysics and Space Science Library, 1994

Research paper thumbnail of The Initial Mass Function and Disk Frequency of the rho Ophiuchi Cloud: An Extinction-limited Sample

Astronomical Journal, 2011

We have completed an optical spectroscopic survey of an unbiased, extinction-limited sample of ca... more We have completed an optical spectroscopic survey of an unbiased, extinction-limited sample of candidate young stars covering 1.3 deg2 of the rho Ophiuchi star-forming region. While infrared, X-ray, and optical surveys of the cloud have identified many young stellar objects (YSOs), these surveys are biased toward particular stages of stellar evolution and are not optimal for studies of the disk

Research paper thumbnail of Spectroscopy of Brown Dwarf Candidates in the NGC 1333 Molecular Cloud

Proceedings of The International Astronomical Union, 2003

We present an analysis of low-resolution infrared spectra for 25 brown dwarf candidates in the NG... more We present an analysis of low-resolution infrared spectra for 25 brown dwarf candidates in the NGC 1333 molecular cloud. Candidates were chosen on the basis of their association with the high column density cloud core, and near-infrared fluxes and colors. We compare the depths of water vapor absorption bands in our candidate objects with a grid of dwarf, subgiant, and

Research paper thumbnail of IRAS observations of the Rho Ophiuchi infrared cluster - Spectral energy distributions and luminosity function

The Astrophysical Journal, 1989

... These associations are regarded as uncertain, and these sources have not been included in sub... more ... These associations are regarded as uncertain, and these sources have not been included in subsequent discussions of the spectral energy distributions and luminosity function. ... iZIL ~ ~ 9LE ~iZ 91 ~ ~ 4 T~ (LI) (91) (cT) (i&#x27;t) (~j) (Zr) (It) (ofl (6) (~) (L) (9) (c) (~) ( z) (I) 9g/9 c~/c ...

Research paper thumbnail of IRAS observations of young stellar objects in the Corona Australis dark cloud

The Astrophysical Journal, 1992

Research paper thumbnail of Infrared Properties of Weak Radio Sources in the ρ Ophiuchi Molecular Cloud

The Astrophysical Journal, 2001

Research paper thumbnail of Further mid-infrared study of the rho Ophiuchi cloud young stellar population: Luminosities and masses of pre-main-sequence stars

The Astrophysical Journal, 1994

... 191 Gif-sur-Yvette Cedex, France; andre@sapvxg.saclay.cea.fr ERICK T. YoUNG"2'3 Ste... more ... 191 Gif-sur-Yvette Cedex, France; andre@sapvxg.saclay.cea.fr ERICK T. YoUNG"2'3 Steward Observatory, University of Arizona, Tucson, AZ 85721; erick~sparky.as ... the IRTF 58 x 62 InSb array camera, while M, N, and Q (20 JLm) band data were acquired with the Bob 1 IRTF ...

Research paper thumbnail of Low-mass stars and substellar objects in the NGC 1333 molecular cloud

The Astronomical …, 2004

We present the results of near-infrared imaging and low-resolution near-infrared spectroscopy of ... more We present the results of near-infrared imaging and low-resolution near-infrared spectroscopy of low-mass objects in the NGC 1333 molecular cloud. A JHK survey of an 11A4 Â 11A7 area of the northern cluster was conducted to a sensitivity of K 16 mag. Using near-infrared magnitudes and colors from this and previously published surveys, 25 brown dwarf candidates were selected toward the high-extinction cloud core. Spectra in the K band were obtained and comparisons of the depths of water vapor absorption bands in our candidate objects with a grid of dwarf, subgiant, and giant standards were made to derive spectral types. These data were then used to derive effective temperatures and stellar luminosities that, when combined with theoretical tracks and isochrones for pre-main-sequence objects, resulted in estimates for their masses and ages. The models suggest a median age for the sample of less than 1 Myr with substellar masses for at least nine of the candidates, including the X-ray flare source ASR 24. Surface gravities have been estimated for the brown dwarf candidates and, for a given spectral type, are found to more closely resemble dwarfs than giants. Using the near-infrared imaging data and age estimates from the spectroscopic sample, an extinction-limited sample in the northern cluster was defined. Consistent with recent studies of other young clusters, this sample exhibits an accretion disk frequency of 0.75 AE 0.20 and a mass spectrum slope across the hydrogen-burning limit of 1:6, where dN/dM / M À .

Research paper thumbnail of Deep Infrared Imaging of the R Coronae Australis Cloud Core

The Astronomical Journal, 1997

Page 1. Deep Infrared Imaging of the R Corona Australis Cloud Core Bruce A. Wilking Department of... more Page 1. Deep Infrared Imaging of the R Corona Australis Cloud Core Bruce A. Wilking Department of Physics and Astronomy, University of Missouri-St. Louis 8001 Natural Bridge Road, St. Louis, MO 63121 brucew@newton.umsl.edu Mark J. McCaughrean ...

Research paper thumbnail of Structure and chemistry in the northwestern condensation of the Serpens molecular cloud core

The Astrophysical Journal, 1994

... C From Zhang et al. 1988, Fig. la and lb. d Central source only. 308 a (1950) 15~ 27m008 226 ... more ... C From Zhang et al. 1988, Fig. la and lb. d Central source only. 308 a (1950) 15~ 27m008 226 McMULLIN, MUNDY, WILKING, HEZEL, &amp;amp; BLAKE Vol. 424 were consistent withRodriguez et al. (1989) suggested that the lobe emission had varied. ...

Research paper thumbnail of Distribution and Motion of the Water Masers near IRAS 05413−0104

The Astrophysical Journal, 1998

We have used the NRAO Very Long Baseline Array to image water masers associated with the low-lumi... more We have used the NRAO Very Long Baseline Array to image water masers associated with the low-luminosity, young stellar object (YSO) IRAS 05413Ϫ0104 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 position angle of the ⅙ ⅙ 23 ‫ע‬ 2 maser spot distribution is in excellent agreement with measured position angles for the observed larger scale H and SiO emission distributions; radial velocities are in agreement with SiO measurements showing redshifted 2 gas to the southwest and blueshifted gas to the northeast. We have detected proper motions of numerous maser spots averaging mas yr , implying space velocities of km s for a source distance of 450

Research paper thumbnail of A Spectral Line Study of Serpens S68 FIRS1 Region

The Astrophysical Journal, 2000

A j \ 1 mm to 3 mm study of the Serpens molecular cloud core on scales of 10@ to 10A is presented... more A j \ 1 mm to 3 mm study of the Serpens molecular cloud core on scales of 10@ to 10A is presented, concentrating on the northwest condensation and the embedded sources, S68 FIRS1 and S68 N. We adopt temperatures of 25 K for the extended structure (several arcminute scale) and 35 K for the embedded sources. With these values, we use molecular line ratios and LVG statistical equilibrium calculations to derive physical properties in the region. We obtain densities between 0.4È1.2 ] 106 cm~3 and an overall mass of 250È300

Research paper thumbnail of Water masers associated with low-mass stars: A 13 month monitoring survey

The Astrophysical Journal, 1994

Research paper thumbnail of Time‐Resolved AU‐Scale Jets Traced by Masers in the IRAS 4A/B Regions of NGC 1333

The Astrophysical Journal, 2008

We present results of VLBI observations of the water masers associated with IRAS 4A and IRAS 4B i... more 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 associates 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 red-shifted. 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 blue-shifted and red-shifted 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.

Research paper thumbnail of IRAS 21391 + 5802 - A study in intermediate mass star formation

The Astronomical Journal, 1993

We present infrared and millimeter wavelength observations of the cold IRAS source 21391 + 5802 a... more We present infrared and millimeter wavelength observations of the cold IRAS source 21391 + 5802 and its associated molecular core. Infrared observations at lambda = 3.5 microns reveal a heavily obscured, central point source which is coincident with a compact lambda = 2.7 mm continuum and C18O emission region. The source radiates about 310 solar luminosities, primarily at FIR wavelengths,

Research paper thumbnail of Proper motion of water masers near NGC1333-SVS13

Arxiv preprint astro-ph/ …, 2001

VLBA observations of water masers toward the region of NGC1333 near SVS13, the driving source for... more VLBA observations of water masers toward the region of NGC1333 near SVS13, the driving source for the well-known Herbig-Haro objects HH7-11, are reported. Maser emission was observed over four epochs spaced by three weeks during late 1998. SVS13 is associated with the millimeter continuum SED Class I source SSV13A1. High resolution CO observations have secured the association of the flow with the continuum object on arc-second scales. A 1998 Aug 12 VLA observation places the blueshifted masers within 80 AU (0".2) of the 2.7 mm position for A1 reported from BIMA. We report observations of two groups of masers, one redshifted by about 6 km s −1 and one blueshifted by about 2-3 km s −1 , separated by about 100 AU in projected distance along position angle 21 degrees. Redshifted masers were present only in the latter two epochs. During all epochs, an arclike structure was present with similar morphology; over time this structure moved relative to the southernmost blue maser toward the southeast, roughly along the position angle defined by the Herbig-Haro objects, with a proper motion of about 13 km s −1 . Both redshifted and blueshifted masers are clearly part of the same lobe of the flow; their observed Doppler shifts are artifacts of the opening angle of the flow. Our data suggest that the opening angle is about 10 o . We measure lower expansion velocities and a wider opening angle than has been found in some other flows near Class 0 SED objects, perhaps indicating that the flows open and slow as they age.

Research paper thumbnail of Multiple Outflows in the Haro 6-10/GV Tau/IRAS04263+2426 T Tau/Infrared Companion Binary

Research paper thumbnail of A Monthly Survey of Water Masers Associated with Low-Mass Stars

The Astrophysical Journal Supplement Series, 1996

We have performed a multiepoch survey of water masers toward low-luminosity young stellar objects... more We have performed a multiepoch survey of water masers toward low-luminosity young stellar objects (YSOs). These objects were selected to be in an early phase of stellar evolution based on IRAS colors and association with molecular outflows or dense cores. The sample was restricted to YSOs in nearby clouds (d < 450 pc) with luminosities <120 Lsun. Seven new sources of maser emission have been found resulting in a total of 22 YSOs with L < 120 Lsun known to display maser activity. We present monitoring data (at least two epochs of observation) for 47 sources. Four objects were monitored on a semiregular basis for more than S years. Based on a coherent 13 month subset of this survey, we estimate that the maser phase in low-mass embedded sources occupies about one-third of the duration of the embedded phase of evolution. Some spectrally isolated water maser features are seen to appear and disappear on timescales less than about 2 months. This characteristic timescale is consistent with shock crossing times for reasonable values of the shock velocity and size and is thus suggestive that the masers originate in the shocked gas. Some embedded sources can have long periods of inactivity (˜5 yr) when no masers are seen to our detection limit. Sources with stronger masers and more complex spectra can maintain emission over this same time period. We determined threshold values of the CO mass-loss rate (4 × 10-5 Msun yr-1), 6 cm radio luminosity (0.25 kpc2 mJy), and the IRAS in-band luminosity (25 Lsun) above which water masers were always detected. The isotropic luminosity of the water masers in any given source can vary over more than 2 orders of magnitude in a period of several months. Thus, a single epoch measurement of this luminosity may provide a misleading result, especially if compared to other physical parameters such as the bolometric luminosity.

Research paper thumbnail of Water Masers in the Circumstellar Environments of Young Stellar Objects

Astronomical Journal, 1998

We present a high-resolution radio and millimeter-wavelength study of five low-mass young stellar... more We present a high-resolution radio and millimeter-wavelength study of five low-mass young stellar objects with known water maser emission: RNO 15 FIR, Orion A-W, L1157, B361, and L1251A. These objects are cold IRAS sources with far-infrared luminosities ranging from less than 6 to 40 L_&sun;. Radio continuum observations are used to locate precisely the young stellar object(s) responsible for the

Research paper thumbnail of Circularly Polarized Radio Emission from an X-Ray Protostar

The Astrophysical Journal, 1998

... Neuh auser, R. & Preibisch, T. 1997, A&A, 322, 37 Phillips, RB, Lonsdale, CJ & Fe... more ... Neuh auser, R. & Preibisch, T. 1997, A&A, 322, 37 Phillips, RB, Lonsdale, CJ & Feigelson, ED 1993, ApJ, 403, L43 Page 13. { 13 { ... B. Reipurth & C. Bertout (Dordrecht:Kluwer), p. 83 Saraceno, P., Andr e, P., Ceccarelli, C., Gri n, M. & Molinari, S. 1996, A&A, 309, 827 ...