A&A 389, 572-576 (2002)
DOI: 10.1051/0004-6361:20020619
L. F. Rodríguez 1 - G. Anglada 2,3 - J. M. Torrelles 4 - J. E. Mendoza-Torres 5 - A. D. Haschick 6 - P. T. P. Ho 3
1 - Instituto de Astronomía,
UNAM, Campus Morelia,
Apdo. Postal 3-72, Morelia, Michoacán 58089, México
2 -
Instituto de Astrofísica de Andalucía, CSIC,
Camino Bajo de Huétor 24, 18008 Granada, Spain
3 -
Harvard-Smithsonian Center for Astrophysics, 60 Garden St.,
Cambridge, MA 02138, USA
4 -
Institut d'Estudis Espacials de Catalunya (IEEC/CSIC)
and
Instituto de Ciencias del Espacio (CSIC), Edifici Nexus, c/ Gran Capità
2-4, 08034 Barcelona, Spain
5 -
Instituto Nacional de Astrofísica, Optica y Electrónica, Luis
Enrique Erro No. 1, Apdo. Postal 51 y 216, 72840
Tonantzintla, Puebla, México
6 -
MIT Haystack Observatory, Westford, MA 01886, USA
Received 24 October 2001 / Accepted 16 April 2002
Abstract
The young stellar object SVS 13 is believed to power the
chain formed by the HH 7-11 objects. Recent observations
have revealed that in the radio
continuum (3.6-cm) the source is a binary with
components separated by
about 0
3 in the east-west direction.
The members of the binary are named VLA 4A (western component)
and VLA 4B (eastern component).
In an attempt to ascertain which of the two
components of the binary is the most likely candidate to drive the
outflow, we obtained accurate positions for the H2O maser spots toward this
source, also known as H2O(A), derived from Very Large Array observations
in its highest angular resolution A configuration.
We detected a total of eleven spots
over four observational sessions (made in the
years 1983, 1985, 1988, and 1989).
The spots are segregated in two velocity
groups: a velocity group with
similar to
that of the ambient cloud
(
km s-1),
for which we detected five
features (with
in the range of 6.5 to 12.2 km s-1)
and a blueshifted velocity group (six features with
in the range of
-25.4 to -5.6 km s-1). Remarkably, all the spots in the first
velocity group are associated with
VLA 4A, while all the spots in the blueshifted velocity group
are associated with VLA 4B. We discuss the possible implications
of this observation. We also present accurate positions of the H2O
maser HH 7(B) and of the masers associated with IRAS4B (VLA 28) and
IRAS7 (VLA 27, the exciting source of HH 6).
Key words: ISM: Herbig-Haro objects - ISM: jets and outflows - masers - stars: pre-main sequence
NGC 1333 is a reflection nebula associated with a region of recent, very active star formation in the Perseus molecular cloud. A cluster of about 150 low- to intermediate-mass YSOs have been identified in near-infrared images (Aspin et al. 1994). The region also contains about 20 groups of Herbig-Haro (HH) objects, some with highly collimated jets (Bally et al. 1996). Rodríguez et al. (1999) found a total of 44 sources at centimeter wavelengths, most of which are associated or believed to be associated with young objects in the region.
The best studied HH group in this region is
HH 7-11, a classical system of bright HH objects, first
reported by Herbig (1974) and by Strom et al. (1974). Strom et al. (1976) discovered a 2.2 m source, SVS 13, roughly
aligned with the chain of HH objects, that was proposed as their exciting
source. Rodríguez et al. (1997), through a high angular
resolution VLA map of the region detected SVS 13 as a radio cm source
(VLA 4), but also detected a new object, VLA 3, located 6'' to the SW,
and argued that this new object was a better candidate to drive the
outflow. Bachiller et al. (2000) find extremely high velocity molecular gas
in association with SVS 13 and high velocity gas in the vicinity
of both SVS 13 and VLA 3, favoring the former object as the
exciting source of the HH 7-11 outflow.
Deep radio maps with subarcsecond angular resolution obtained by
Anglada et al. (2000) revealed that
the radio source associated with SVS 13 (VLA 4) is
actually a binary (VLA 4A and 4B),
separated by 0
,
corresponding to a projected separation of 65 AU for a distance of 220 pc
(Cernis 1990).
The source SVS 13 presents a number of peculiar properties. It was detected initially as a near-IR source (Strom et al. 1976). Later, Goodrich (1986) detected a faint visible counterpart. The source exhibited a large increase of its brightness in the optical and near-IR in 1988-1990 (Eislöffel et al. 1991). Since then, the flux remained almost steady (Aspin & Sandell 1994). In addition, despite being optically visible, SVS13 is a strong mm source (Grossman et al. 1987; Chini et al. 1997; Bachiller et al. 1998; Looney et al. 2000). Anglada et al. (2000) have argued that the two components of this binary system could be in different evolutionary stages and/or suffer from different extinction, with the more extincted object (proposed to be VLA 4B by Anglada et al.) being associated with the previously reported mm source, while the other component (VLA 4A) would correspond to the visible star SVS 13.
In order to further investigate SVS13, we have analyzed archive Very Large Array (VLA) observations of the H2O maser emission at 1.3 cm toward SVS 13 made with subarcsec angular resolution along several epochs. Our goals were to establish accurately the position of the H2O masers with respect to the components of the radio binary and to study if this relative location could shed light on the evolutionary stage of the stars. We were also interested in trying to understand from which of the stars of this binary system is the outflow originating, since high velocity H2O masers are indicators of outflow activity and can be observed with very high angular resolution. We also studied water masers in three other locations in NGC 1333.
The H2O maser observations were made with the
VLA of NRAO
in the A configuration
during 1983 October 21, 1985 February 18, 1988 October 31,
and 1989 February 5.
The phase calibrator was 0333+321, for which we assumed a
flux density of 1 Jy at 1.3 cm.
The observations were taken with a total bandwidth of
3.1 MHz and 64 channels with a width of 49 kHz each (equivalent to
0.7 km s-1).
The data were calibrated, edited, and imaged using the software
AIPS of NRAO. The synthesized beam had typical HPFW of
,
for maps made with natural weighting.
In order to accurately
compare the H2O maser positions with the 3.6 cm continuum
positions of Anglada et al. (2000), that also used
0333+321 as phase calibrator, we shifted the
maser positions by
and
to account for a recent refinement
of the position of 0333+321.
This maser was first detected by Dickinson et al.
(1974) and monitored extensively by Haschick et al. (1980),
who called it H2O(A) to distinguish it from other masers
in the region.
We detected a total of eleven H2O spots associated
with SVS 13 over the
four epochs (one in 1983, four in 1985, four in 1988, and two in 1989).
Both in 1985 and in 1988 two spots at different radial
velocity (with LSR radial velocities of
-20.1 and -15.5 km s-1 for 1985 and
with LSR radial velocities of -14.8 and -5.6 km s-1
for 1988, see Fig. 1)
appeared to coincide spatially within our
positional uncertainty of
and were considered as arising from the same position
(that was taken to be the average of the two nearby positions).
Furthermore, the two spots detected in 1989
coincide within
with spots reported
in 1988 (see Table 1), and they were taken to be the same
source.
![]() |
Figure 1: H2O spectrum of SVS 13 in 1988 October 31. |
Open with DEXTER |
We did not detect H2O emission in association with VLA 3, the source proposed by Rodríguez et al. (1997) as an alternative candidate to drive the HH 7-11 objects.
In Fig. 2 we show the maser spots overlapped on the
3.6 cm contour map of Anglada et al. (2000). As can be seen,
the spots appear to be segregated in two velocity
groups: a velocity group with
similar to
that of the ambient cloud
(
km s-1),
for which we detected five
features with
in the range of 6.5 to 12.2 km s-1and a blueshifted velocity group,
for which we detected six features with
in the range of
-25.4 to -5.6 km s-1. Remarkably, all the spots in the ambient
velocity group are associated with
VLA 4A, while all the spots in the blueshifted velocity group
are associated with VLA 4B.
![]() |
Figure 2:
Positions of the H2O spots associated
with SVS 13, overlapped on the
3.6 cm continuum image of Anglada et al. (2000). The LSR velocity
of the spots is given in the figure. The contours of
the continuum emission are -3, 3, 4, 5, and 6 times 14 ![]() ![]() |
Open with DEXTER |
We have tried to put this result in a more quantitative manner, plotting the difference of the angular separation of the spots to the continuum sources A and B, d(A)-d(B), as a function of LSR velocity. This plot is shown in Fig. 3. It appears to us to be very significant statistically that d(A)-d(B), in the vertical axis, is always positive for blueshifted spots (indicating that these spots are always closer to VLA4B than to VLA4A) and always negative for spots with systemic velocity (indicating that these spots are always closer to VLA4A than to VLA4B).
![]() |
Figure 3:
Difference of the angular separation of the spots
to the continuum sources VLA 4A and VLA 4B, d(A)-d(B), as a function of
LSR velocity. Note that d(A)-d(B) is always positive for blueshifted spots
and always negative for spots at the systemic velocity
of ![]() |
Open with DEXTER |
We believe that this result supports the suggestion of Anglada et al.
(2000) that there are at least two stars,
VLA 4A and VLA 4B, in association with SVS 13.
If the mean radial velocity of the maser groups were indicative of the
radial velocity of the stars, one could argue that VLA 4A is the more
massive of the two (since its velocity is closer to the ambient
cloud velocity) and that the blueshifted velocity seen in VLA 4B
indicates orbital motion for this star.
However, at a distance of 220 pc (Cernis 1990), the angular
separation between VLA 4A and VLA 4B corresponds to 65 AU,
and a mass
would be required for VLA 4A.
The modest bolometric luminosity of the source
(
;
Jennings et al. 1987) seems to rule out such a massive star.
We then tentatively propose that the radial velocity of both
stars is most probably close to that of the ambient cloud,
and that the blueshifted velocities observed in the H2O masers
associated with VLA 4B are produced by outflow motions
that are not present or are not as important in VLA 4A.
A puzzling feature of the blueshifted masers associated with
VLA 4B is that they appear to the NW of the source, while
the geometry of the large scale CO outflow (Bachiller et al. 2000)
would imply that they should appear to the SE.
We also note as an
alternative explanation that the blueshifted
masers could be part of an outflow from VLA 4A.
VLBA monitoring of these masers, such as that reported
by Wootten et al. (2000) should help
clarify their nature.
The millimeter observations of Looney et al. (2000) do not resolve
the two components of SVS 13. However, their peak position coincides,
within
,
with the mean position of the components VLA 4A and VLA 4B,
as given by Anglada et al. (2000).
![]() |
Flux Density | |||
Epoch | ![]() |
![]() |
(km s-1) | (Jy) |
1983 | 03 25 58.179 | +31 05 45.50 | +7.3 | 0.9 |
1985 | 03 25 58.194 | +31 05 45.49 | -25.4 | 1.9 |
1985 | 03 25 58.196 | +31 05 45.58 | -20.1, -15.5 | 0.5, 1.9 |
1985 | 03 25 58.179 | +31 05 45.46 | +9.5 | 0.6 |
1988 | 03 25 58.195 | +31 05 45.52 | -14.8, -5.6 | 2.8, 0.2 |
1988 | 03 25 58.178 | +31 05 45.43 | +7.6 | 0.2 |
1988 | 03 25 58.179 | +31 05 45.64 | +12.2 | 1.6 |
1989 | 03 25 58.194 | +31 05 45.51 | -19.8 | 13.0 |
1989 | 03 25 58.178 | +31 05 45.65 | +6.5 | 2.2 |
In the same field of SVS 13 (at an angular distance
of
to the SW) we also observed the maser
called H2O(B) by Haschick et al. (1980). This maser
was detected in 1985, 1988, and 1989 and its parameters are
given in Table 2.
It is associated with a radio source reported
by Haschick et al. (1980). It has a millimeter
counterpart, MMS3 (Chini et al. 1997; Looney et al. 2000). This relatively
bright radio source (
2.1 mJy at 3.6 cm) has been
recently studied by Rodríguez et al. (1997, 1999),
who name it VLA 2. These authors find that the
radio source is a double with angular
separation of
in the NS direction,
and constituted by the components
VLA 2(a) and VLA 2(b) (see Fig. 1 of
Rodríguez et al. 1997). The water masers are,
within
,
clearly associated
with VLA 2(a), the brightest of the two components.
This result is relevant because new observations
by Reipurth et al. (2002) indicate that
VLA 2(a) is the source
actually associated with a star and that VLA 2(b) is most probably just a
moving Herbig-Haro knot.
The position of VLA 2(a) coincides within
with that of its millimeter counterpart, MMS3 (SVS 13C in the
nomenclature of Looney et al. 2000).
![]() |
Flux Density | |||
Epoch | ![]() |
![]() |
(km s-1) | (Jy) |
1985 | 03 25 56.406 | +31 05 19.68 | +8.8, +13.4 | 0.8, 1.1 |
1988 | 03 25 56.409 | +31 05 19.64 | +3.0, +14.1 | 3.6, 0.5 |
1989 | 03 25 56.410 | +31 05 19.65 | +1.2 | 7.5 |
1989 | 03 25 56.403 | +31 05 19.62 | -2.0 | 9.7 |
It is unclear if this maser is the one previously identified
as H2O(C) by Haschick et al. (1980).
Its parameters are given in Table 3.
Our accurate position and that given for H2O(C) by Haschick et al. (1980)
suggest that there is no positional coincidence
and that this is a new maser.
Within
,
all maser spots
coincide spatially with the radio source VLA 28
(Mundy et al. 1993; Rodríguez et al. 1999). This source is the centimeter
counterpart to the source IRAS4B
(Sandell et al. 1991)
and is believed to drive a molecular outflow
(Blake et al. 1995). The centimeter position of VLA 28
coincides within
with that of its millimeter counterpart
(Looney et al. 2000).
Marvel et al. (2000) have recently reported water maser
emission associated with the relatively nearby source
IRAS4A. We do not detect water emission at the position
of this source, which is located at
from
our phase center.
![]() |
Flux Density | |||
Epoch | ![]() |
![]() |
(km s-1) | (Jy) |
1983 | 03 26 06.491 | +31 02 50.06 | -0.9 | 28.2 |
1983 | 03 26 06.477 | +31 02 50.39 | +9.7 | 1.3 |
1985 | 03 26 06.488 | +31 02 50.12 | -0.2 | 1.5 |
1985 | 03 26 06.475 | +31 02 50.45 | +14.9 | 6.2 |
1988 | 03 26 06.498 | +31 02 49.92 | +13.1 | 1.2 |
1988 | 03 26 06.488 | +31 02 50.06 | +13.8 | 2.2 |
1989 | 03 26 06.496 | +31 02 49.95 | +9.8 | 1.5 |
1989 | 03 26 06.491 | +31 02 50.07 | +10.5 | 0.5 |
![]() |
Flux Density | |||
Epoch | ![]() |
![]() |
(km s-1) | (Jy) |
1983 | 03 26 05.483 | +31 08 11.19 | +6.0 | 0.7 |
1983 | 03 26 05.487 | +31 08 11.26 | +8.0 | 6.2 |
1985 | 03 26 05.613 | +31 08 12.80 | +8.0 | 4.6 |
1988 | 03 26 05.040 | +31 08 02.31 | +17.8 | 0.8 |
1988 | 03 26 05.048 | +31 07 50.14 | +20.4 | 0.2 |
The two maser spots detected in 1988 appear to be significantly redshifted in velocity with respect to the 1983 and 1985 detections. These two spots are also significantly displaced to the SW of the continuum source and may be tracing the red lobe of this outflow.
We presented high angular resolution VLA observations of water masers toward three regions in NGC 1333. Our main results are the following.
Acknowledgements
We thank Mark Claussen for his comments. LFR acknowledges the support from DGAPA, UNAM and CONACyT, México. GA and JMT acknowledge support from DGESIC grant PB98-0670-C02 and from Junta de Andalucía (Spain). GA also acknowledges support from MEC, Spain, and from SAO, USA.