Water maser emission in Bok globulesWater maser emission in Bok globules

Bok GlobulesBok Globules Bok globules are small (<1 pc), isolated, and simple molecular clouds, where low- and intermediate-mass star formation can take place (Bok & Reilly 1947,,Yun & Clemens 1992). Since they are identified from optical images (e.g., Clemens & Barvainis 1988), without any selection

Bok globules are small (<1 pc), isolated, and simple molecular clouds, where low- and intermediate-mass star formation can take place (Bok & Reilly 1947,,Yun & Clemens 1992). Since they are identified from optical images (e.g., Clemens & Barvainis 1988), without any selection

I. de Gregorio-Monsalvo1, J. F. Gómez2, O. Suárez3, T.B.H. Kuiper4, G. Anglada2, N.A. Patel5, J.M. Torrelles6 I. de Gregorio-Monsalvo1, J. F. Gómez2, O. Suárez3, T.B.H. Kuiper4, G. Anglada2, N.A. Patel5, J.M. Torrelles6

(1) ESO/ALMA (Chile), (2) CSIC-IAA (Spain), (3) LAEFF- INTA (Spain), (4) JPL, CALTECH (USA), (5) CfA (USA), (6) CSIC-IEEC (Spain)(1) ESO/ALMA (Chile), (2) CSIC-IAA (Spain), (3) LAEFF- INTA (Spain), (4) JPL, CALTECH (USA), (5) CfA (USA), (6) CSIC-IEEC (Spain)

Single-dish Water Masers Survey Towards Bok GlobulesSingle-dish Water Masers Survey Towards Bok Globules

Interferometric Observations of Water Masers in Bok GlobulesInterferometric Observations of Water Masers in Bok Globules

CB 3CB 3

CB 232CB 232CB 101CB 101

Pictures of Bok globules. Pictures of Bok globules.

Robledo 70 m antenna.Robledo 70 m antenna.

Robledo 70 m surveyRobledo 70 m surveyWe searched for water maser emission towards the positions within the globules with the highest probability of harboring a YSO:

- Radio continuum sources (from submillimeter to centimeter wavelengths).- Center of molecular outflows.- Peak of high-density molecular tracers.- IRAS sources.

This survey was performed with the NASA’s 70 m antenna in Robledo de Chavela, near Madrid, Spain. Out of the 207 observed targets positions, we obtained seven detections (six new) towards CB 3, CB 34, CB 54, CB 65, CB 101, CB 199, and CB 232. We increased from three (CB 3, CB 39, and CB 205, which water maser emission was known) to nine the known Bok globules associated to this kind of emission.

All our selection criteria have the same weight as predictors of the presence of water masers, except the IRAS sources, which are worse predictor (Gómez et al. 2006).

We searched for water maser emission towards the positions within the globules with the highest probability of harboring a YSO:- Radio continuum sources (from submillimeter to centimeter wavelengths).- Center of molecular outflows.- Peak of high-density molecular tracers.- IRAS sources.

This survey was performed with the NASA’s 70 m antenna in Robledo de Chavela, near Madrid, Spain. Out of the 207 observed targets positions, we obtained seven detections (six new) towards CB 3, CB 34, CB 54, CB 65, CB 101, CB 199, and CB 232. We increased from three (CB 3, CB 39, and CB 205, which water maser emission was known) to nine the known Bok globules associated to this kind of emission.

All our selection criteria have the same weight as predictors of the presence of water masers, except the IRAS sources, which are worse predictor (Gómez et al. 2006).

Contours represent near-IR emission.The cross marks the maser positionContours represent near-IR emission.The cross marks the maser position

Contours represent near-IR emission.The cross marks the maser positionContours represent near-IR emission.The cross marks the maser position

Proposed modelProposed model

Left: Model of a decelerating and precessing jet. Circles represent parcels of gas moving in the direction of the arrow. Right: Position-velocity distribution for the proposed model along the projected main axis of the jet.

Left: Model of a decelerating and precessing jet. Circles represent parcels of gas moving in the direction of the arrow. Right: Position-velocity distribution for the proposed model along the projected main axis of the jet.

This globule contains a CO outflow centered near the IRAS source (ellipsoid). The water maser position is associated to the near-IR source CB 232 YC1-I, and supports it as the engine of the maser emission and the outflow.

This globule contains a CO outflow centered near the IRAS source (ellipsoid). The water maser position is associated to the near-IR source CB 232 YC1-I, and supports it as the engine of the maser emission and the outflow.

CB 54CB 54

Left: Contours represent near-IR emission. The cross marks the maser position. Right: Contours represent radio continuum emission . Crosses are water masers.

Left: Contours represent near-IR emission. The cross marks the maser position. Right: Contours represent radio continuum emission . Crosses are water masers.

CB 54 contains a multiple stellar system located near the center of the CO bipolar outflow that exists in the region. The masers are located at an elongated feature (brighter in H2, proposed to be shocked material). We proposed that feature (named CB 54 YC1-SW) as the powering source of the masers. We have just confirmed this result with recent VLA-A observations that shows a faint radio continuum source at that position.

CB 54 contains a multiple stellar system located near the center of the CO bipolar outflow that exists in the region. The masers are located at an elongated feature (brighter in H2, proposed to be shocked material). We proposed that feature (named CB 54 YC1-SW) as the powering source of the masers. We have just confirmed this result with recent VLA-A observations that shows a faint radio continuum source at that position.

.The masers are associated with a point near-IR source, counterpart of IRAS 17503-0833. There are no signs of star formation activity, since there is no CO molecular outflow, nor high-density gas emission at that position. The SED and the location of this object in a IR color-color diagram suggest that it is an evolved Mira star.

.The masers are associated with a point near-IR source, counterpart of IRAS 17503-0833. There are no signs of star formation activity, since there is no CO molecular outflow, nor high-density gas emission at that position. The SED and the location of this object in a IR color-color diagram suggest that it is an evolved Mira star.

The maser emission is located close to the Class 0 object CB 3-mm, the best candidate to power the water masers and the outflow. Water masers are distributed in an elongated structure of ~0’’.1 along the direction of the molecular outflow that exists in the region, and seems to be tracing the inner part of a collimated jet (see right Fig). The position-velocity distribution (see bottom-left Fig) of the masers shows a wave-like structure consistent with a precessing jet at scales of ~250 AU. We can reproduce that pattern considering a model where we approximate the jet to a narrow cone on which surface discrete ejections of decelerated material are located (see bottom-right Fig). We also consider the changes in velocity due to precession as negligible (de Gregorio-Monsalvo et al.).

The maser emission is located close to the Class 0 object CB 3-mm, the best candidate to power the water masers and the outflow. Water masers are distributed in an elongated structure of ~0’’.1 along the direction of the molecular outflow that exists in the region, and seems to be tracing the inner part of a collimated jet (see right Fig). The position-velocity distribution (see bottom-left Fig) of the masers shows a wave-like structure consistent with a precessing jet at scales of ~250 AU. We can reproduce that pattern considering a model where we approximate the jet to a narrow cone on which surface discrete ejections of decelerated material are located (see bottom-right Fig). We also consider the changes in velocity due to precession as negligible (de Gregorio-Monsalvo et al.).

Left: The cross marks the maser emission. Contours represent near-IR H2 emission. Top right: Spatial distribution of the independent maser spectral features. Bottom right: Water maser spectrum

Left: The cross marks the maser emission. Contours represent near-IR H2 emission. Top right: Spatial distribution of the independent maser spectral features. Bottom right: Water maser spectrum

P-V diagramP-V diagram

Position-velocity distribution of the centroids of the water masers at different velocity channels.

Position-velocity distribution of the centroids of the water masers at different velocity channels.

REFERENCES:Bok & Reilly 1947, ApJ, 105, 225 Furuya et al. 2001, ApJ, 559, L143Claussen et al. 1998, ApJ, 507, L79 Gómez et al. 2006, AJ, 132, 1322Clemens & Barvainis 1988, ApJS, 68, 257 Yun & Clemens 1992, ApJ, 385, L21de Gregorio-Monsalvo et al. 2006, astro-ph/0608667

CB 68 IC2944

Systematic studies of Bok globules are interesting laboratories in the study of the star-formation processes and its evolution with a lower chance of contamination from multiple generations of young stellar objects (YSOs) within the same region. Water maser emission is a powerful tool for characterizing the physical conditions of the gas surrounding the youngest YSOs at high resolution (≤1 mas; Furuya et al. 2001), and they tend to be located within several hundred AU from their powering source in low-mass YSOs (Claussen et al .1998). We have performed a sensitive single-dish survey in water maser emission at 22 GHz towards Bok globules, complemented with VLA interferometric observations, with the next aims:

- Search for the best predictors for the presence of water maser emission. - Study the physical conditions kinematics and chemistry of the innermost areas.

- Use the accurate positions of water masers to derive information about their powering source. - Determine whether the maser emission tends to trace collimated jets or circumstellar disks.

Systematic studies of Bok globules are interesting laboratories in the study of the star-formation processes and its evolution with a lower chance of contamination from multiple generations of young stellar objects (YSOs) within the same region. Water maser emission is a powerful tool for characterizing the physical conditions of the gas surrounding the youngest YSOs at high resolution (≤1 mas; Furuya et al. 2001), and they tend to be located within several hundred AU from their powering source in low-mass YSOs (Claussen et al .1998). We have performed a sensitive single-dish survey in water maser emission at 22 GHz towards Bok globules, complemented with VLA interferometric observations, with the next aims:

- Search for the best predictors for the presence of water maser emission. - Study the physical conditions kinematics and chemistry of the innermost areas.

- Use the accurate positions of water masers to derive information about their powering source. - Determine whether the maser emission tends to trace collimated jets or circumstellar disks.

Future Studies with ALMA : Submillimeter Water MasersFuture Studies with ALMA : Submillimeter Water Masers

MotivationMotivation

criterion related to possible star-forming activity, catalogs of Bok globules may span a wide range of evolutionary stages.criterion related to possible star-forming activity, catalogs of Bok globules may span a wide range of evolutionary stages.

We plan to continue our search for water masers in Bok globules at millimeter and submillimeter frequencies. Upcoming millimeter and submillimeter telescopes, like ALMA, will allow a detailed study of the processes involved in star formation, and water maser emission at those frequencies could become a powerful tool to study: - The physics, chemistry, and kinematics of the innermost areas of star-forming regions. - The excitation mechanism of water molecule, providing constrains on the models of pumping mechanism and on the physical conditions of the emitting regions. - The application of these masers lines for future self-calibration and cross-calibration techniques of data from millimeter/submillimeter interferometers.

We plan to continue our search for water masers in Bok globules at millimeter and submillimeter frequencies. Upcoming millimeter and submillimeter telescopes, like ALMA, will allow a detailed study of the processes involved in star formation, and water maser emission at those frequencies could become a powerful tool to study: - The physics, chemistry, and kinematics of the innermost areas of star-forming regions. - The excitation mechanism of water molecule, providing constrains on the models of pumping mechanism and on the physical conditions of the emitting regions. - The application of these masers lines for future self-calibration and cross-calibration techniques of data from millimeter/submillimeter interferometers.

More information at idegrego@eso.org