Multiple Outflows in the LkHα 234 Region

Miguel A. Trinidad

Instituto Nacional de Astrofısica, Optica y Electronica (INAOE), Luis Enrique Erro 1,

Tonantzintla, Puebla 72840, Mexico

Instituto de Astronomıa, (UNAM), Apdo. Postal 70-264, D.F. 04510, Mexico

trinidad@inaoep.mx

Salvador Curiel

Instituto de Astronomıa, (UNAM), Apdo. Postal 70-264, D.F. 04510, Mexico

Jose M. Torrelles

Instituto de Ciencias del Espacio (CSIC) and Institut d’Estudis Espacials de Catalunya,

Edifici Nexus, Gran Capita, 2-4, E-08034 Barcelona, Spain

Luis F. Rodrıguez

Centro de Radioastronomıa y Astrofısica, (UNAM), Apdo. Postal 3-72 (Xangari) 58089

Morelia, Michoacan, Mexico

Jorge Canto

Instituto de Astronomıa, (UNAM), Apdo. Postal 70-264, D.F. 04510, Mexico

Jose F. Gomez

Laboratorio de Astrofısica Espacial y Fısica Fundamental (INTA), Apdo. Correos 50727,

E-28080 Madrid, Spain

Nimesh Patel and Paul T.P. Ho

Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138,

USA

ABSTRACT

We report results of radio continuum (1.3 and 3.6 cm) and H2O maser line

observations, carried out with the Very Large Array (VLA) in its A configuration,

toward the star-forming region LkHα 234. We detected five radio continuum

– 2 –

sources (VLA 1, VLA 2, VLA 3A, VLA 3B, and LkHα 234) in a region of

' 5′′ (' 5000 AU), of which three were previously unknown (VLA 1, VLA 2

and VLA 3B). VLA 3A and VLA 3B seem to form a close (' 220 AU) binary

system. Their elongated morphologies and positive spectral indices suggest that

both, VLA 3A and VLA 3B, could be thermal radio jets. In addition, we detected

three clusters of water masers, which are spatially associated with VLA 1, VLA 2

and VLA 3B. Based on the analysis of the distribution of the water masers and

the characteristics of the continuum emission, we favor the new radio continuum

source VLA 2 as the exciting source of the large-scale CO/[SII] outflow observed

in the region. Moreover, we find that the multiple outflows observed in the region

share a similar orientation. Finally, our data confirm that there is no evidence

indicating that the Herbig Be star LkHα 234 is driving any of the outflows in the

region.

Subject headings: ISM: individual (LkH Alpha 234) — ISM: jets and outflows —

masers — stars: formation — stars: pre-main sequence

1. Introduction

It is well known that water masers are usually found in star forming regions. These

masers are strong and variable (e.g., Reid & Moran 1981, Brand et al. 2003), and sometimes

they are associated with both expanding and rotating motions, namely outflows (in most

of the cases) and disks around young stellar objects (YSOs). In this sense, high angular

resolution observations of water masers have revealed to be a very powerful tool to probe

the small-scale environment of the central engine responsible for the phenomena associated

with YSOs (Chandler 2004, Claussen 2002, Claussen et al. 1998, Fiebig et al. 1996, Furuya

et al. 1999, 2000, Imai et al. 2002, Menten & van der Tak 2004, Patel et al. 2000, Seth et

al. 2002, Torrelles et al. 1996, 2001, 2003, Trinidad et al. 2003).

LkHα 234 is one of the brightest sources in the NGC 7129 molecular cloud, located at a

distance of 1 kpc (Racine 1968). It has a bolometric luminosity ' 1.3×103 L� (Bechis et al.

1978), and is classified as a Herbig Be star (Herbig 1960) of spectral type B5e-B7e (Strom

et al. 1972). This young star of intermediate luminosity is associated with an extended

reflection nebula (Bechis et al. 1978). It is also associated with a large-scale CO outflow,

which appears to be aligned with the [SII] optical jet observed in the region (Edwards &

Snell 1983; Mitchell & Matthews 1994; Ray et al. 1990). The CO outflow is asymmetric,

with its much more prominent redshifted lobe located to the northeast of LkHα 234, whereas

the [SII] optical jet is blueshifted and is located to the southwest of LkHα 234 (PA = 252◦).

– 3 –

Cabrit et al. (1997) have also observed bright H2 emission in the region, which appears to be

a jet with complex structure. This H2 emission has an inner part at PA = 226◦, which is not

coincident either with the [SII] optical jet or with the optical star LkHα 234. In addition,

mid-infrared observations show that LkHα 234 has a companion at 2.′′7 to the northwest

(IRS 6; Cabrit et al. 1997).

LkHα 234 was thought to be one of the few Herbig Be stars to drive outflow activity

(Edwards & Snell, 1983). However, recent observations show that LkHα 234 is not spatially

associated either with the CO outflow or with the H2/optical jets observed in the region

(Cabrit et al. 1997; Fuente et al. 2001), which rules out that LkHα 234 is the exciting

source of this outflow phenomena. In this sense, Fuente et al. (2001) have proposed that the

CO/[SII] outflow is driven by IRS 6, while a millimeter source (MM1) is the driving energy

source of the H2 jet.

In addition to the infrared and millimeter sources, a 3.6 cm continuum source is detected

in the region (Skinner et al. 1993, Tofani et al. 1995), which does not coincide spatially

with the LkHα 234 optical star (the objects are displaced by ∼ 2.′′5). The radio continuum

emission has been interpreted as an ionized stellar wind (Wilking et al. 1986, Skinner et al.

1993), but it has not been thought to be associated with the outflow activity observed in

the region. In addition, H2O maser emission has also been detected around LkHα 234. In

particular, Rodrıguez & Canto (1983) detected two water masers while Tofani et al. (1995)

detected three, one of them coinciding with the 3.6 cm radio continuum source.

In this paper we present high angular resolution observations (' 0.′′1-0.′′3) of radio con-

tinuum and water maser emission toward the LkHα 234 region. We will refer to the group

of infrared, millimeter and radio continuum sources around the LkHα 234 optical star as

the “LkHα 234 region”. In the present study we use the radio continuum emission and the

water maser distribution to study the nature of the sources, proposing a new candidate for

the exciting source of the large scale CO/[SII] outflow. This paper is organized as follows:

in section §2 we describe the radio continuum and H2O observations, in §3 we present the

results, a general discussion is offered in §4, and we summarize our main conclusions in §5.

– 4 –

2. Observations

The observations were carried out with the VLA of the National Radio Astronomy

Observatory (NRAO)1 in its A configuration during 2000 December 23. We observed si-

multaneously 1.3 cm continuum and H2O maser emission during 3 hours. A bandwidth of

25 MHz with seven channels of 3.125 MHz each, and another of 3.125 MHz with 63 channels

of 48.8 KHz each were used for the continuum and line observations, respectively. Both

the right and left circular polarizations were sampled in the two different bandwidths. The

narrow bandwidth used for the line observations was centered at the frequency of the H2O

616 → 523 maser line (rest frequency 22235.080 MHz) at the velocity of VLSR = −9.3 km s−1

covering the velocity range from −29 to +11 km s−1. The broad bandwidth was centered at

the frequency of 22285.08 MHz. The sources B1331+305 and B2022+616 were used as the

absolute amplitude and the phase calibrator, respectively, with an adopted flux density of

2.52 Jy for B1331+305 and a bootstrapped flux density of 1.76±0.08 Jy for B2022+616. The

data were reduced with standard techniques using the software package Astronomical Image

Processing System (AIPS) of NRAO. Once the strongest H2O maser component was identi-

fied in a particular spectral channel of the narrow bandwidth, its signal was self-calibrated

in phase and amplitude. The phase and amplitude corrections were then applied (cross-

calibration) to both the narrow and the broad bandwidth data, removing both atmospheric

and instrumental errors (see for details Reid & Menten 1990; Torrelles et al. 1996).

Observations at 3.6 cm (15 minutes on source) were also carried out with the VLA

during the 1.3 cm observations. An effective bandwidth of 100 MHz with two circular

polarizations was used. The absolute amplitude and phase calibrators were also B1331+305

and B2022+616, respectively, being 5.18 Jy the adopted flux density of B1331+305 and

3.25± 0.01 Jy the bootstrapped flux density of B2022+616. The data were also edited and

calibrated following standard procedures with AIPS. The phase center of the observations

at both 1.3 and 3.6 cm wavelengths was set at the same position; α(2000) = 21h43m06.s483

and δ(2000) = 66◦06′55.′′12.

1The NRAO is operated by Associated Universities, Inc., under cooperative agreement with the NationalScience Foundation.

– 5 –

3. Results

3.1. Continuum emission at 3.6 cm and 1.3 cm

Figure 1a shows a contour map of the continuum emission of the LkHα 234 region at

3.6 cm. In order to study the continuum emission at maximum sensitivity, this map was

made with natural weighting, resulting in an angular resolution of ' 0.′′33 and an rms noise

of the image of 25 µJy beam−1. At this wavelength, two sources are clearly detected in the

field (VLA 1 and VLA 3). In addition, there is evidence of a weak source (VLA 2) at a level

of 4-σ (0.1 mJy beam−1). There is also weak emission (4-σ) spatially coinciding with the

star LkHα 234. The main parameters of the sources detected at this wavelength are listed

in Table 1.

Figure 1b shows a contour map of the continuum emission at 1.3 cm with a beam size

of ' 0.′′20. At this wavelength, VLA 3 is clearly detected and looks like a compact source

plus extended emission toward the northwest. In addition, the 1.3 cm continuum image

reveals weak features at the 3-σ level coinciding spatially with VLA 1 and VLA 2. The peak

position of VLA 3 at both wavelengths (1.3 and 3.6 cm) coincides with the radio continuum

source detected by Skinner et al. (1993) and Tofani et al. (1995) at 3.6 cm. Cabrit et al.

(1997) suggested that the infrared source IRS 6 could be associated with the radio continuum

source at 3.6 cm, however our data do not seem to confirm this result. Although our data

suggest that both sources (IRS 6 and VLA 3) do not spatially coincide (see Figures 1 and

2), given the large positional uncertainty for IRS 6 and that different astrometry was used

for the VLA map and the near infrared image, we cannot rule out the possibility that they

both are associated to the same source.

Higher angular resolution contour maps (uniform weighting of the [u,v]) of VLA 3 at 3.6

(' 0.′′21) and 1.3 cm (' 0.′′11) are shown in Figures 2a and b, respectively. At 1.3 cm, VLA 3

clearly splits into two components that we name as VLA 3A and VLA 3B (see Table 1).

These two sources, separated in the sky by ' 0.′′22 (220 AU), have peak flux densities of 1.4

and 0.6 mJy beam−1 (λ = 1.3 cm), respectively. We have been able to obtain a deconvolved

size of 0.′′09 × 0.′′05 (PA ∼ 55◦) for VLA 3A at 1.3 cm. However, VLA 3B is compact and

appears unresolved at this wavelength. On the other hand, at 3.6 cm VLA 3A is unresolved

while VLA 3B seems to be elongated in the northeast-southwest direction. To investigate

the nature of VLA 3B, we subtracted VLA 3A (a point source) from the (u,v) data at 3.6 cm

using the task UVSUB in AIPS. The resulting image (see Figure 2c) shows that VLA 3A is

indeed unresolved whereas VLA 3B has a jet-like morphology with a deconvolved size of '0.′′29×≤0.′′17 (PA = 57◦).

– 6 –

3.2. Water masers

We detected 21 H2O maser spots in the LkHα 234 region with a beam size of ' 0.′′08.

The maser spots are spatially concentrated in three clusters coinciding with VLA 1 (2 spots),

VLA 2 (16 spots) and VLA 3 (3 spots) (see Table 2 and Figs. 1-5). The position, velocity,

and flux density of the H2O maser spots are listed in Table 2. The water maser emission

is observed in the velocity range from −4 to −18.5 km s−1. The strongest component is

detected at VLSR = −9.3 km s−1 with an intensity Sν = 84.5 Jy, which is associated with

VLA 2. We do not find water maser emission near the position of the optical star LkHα 234.

4. Discussion: Radio Continuum and Water Maser Emission

4.1. VLA 1

VLA 1 is clearly detected at 3.6 cm, showing an elongated structure (0.′′56× ≤ 0.′′30,

PA = 45◦), but it is marginally detected at 1.3 cm (3-σ level; Table 1, Figs. 1 and 3). This

source was not detected by either Skinner et al. (1993) or Tofani et al. (1995) at 3.6 cm. On

the other hand, two maser spots are spatially associated with VLA 1 (Fig. 3 and Table 2).

The elongated structure of VLA 1 at 3.6 cm could indicate that it is a radio jet contributing

to the outflow activity in the region. However, we think that more sensitive 1.3 cm continuum

observations together with simultaneous 3.6 cm continuum observations are necessary before

we can ascertain the nature of this source by measuring a reliable spectral index.

4.2. VLA 2

The source VLA 2 is marginally detected (Figures 1 and 4, Table 1). Although VLA 2

is detected only at a 4-σ level at 3.6 cm, there are two additional arguments to support

that VLA 2 is a genuine source. First, a weak (3-σ) feature at 1.3 cm is observed at that

position, and second, it is spatially coincident with a cluster of water maser spots, containing

the strongest maser spot in the LkHα 234 region. Furthermore, the geometrical center of

the water masers is at α(2000) = 21h43m06.s330; δ(2000) = 66◦06′55.′′93, which is nearly

coincident with the nominal VLA 2 position (Table 1). It is interesting to note that in the

high-mass star forming regions of Cepheus A, W75N(B), and AFGL 2591, where different

radio continuum sources and water masers are distributed within small regions of a few

arcseconds (a few thousand of AUs), thus probably sharing the same molecular environment,

brighter masers are associated with weaker radio continuum sources (Torrelles et al. 2001,

– 7 –

2003, Trinidad et al. 2003). In order to establish whether this is a real general tendency

in star forming regions or not, further simultaneous observations of continuum and water

maser emission at 1.3 cm toward a larger sample of embedded YSOs clusters are necessary.

An important result in VLA 2 comes from the spatial distribution of the associated

16 water maser spots (Table 2 and Figure 4). These masers are distributed in two main

groups separated by ' 0.′′3 (300 AU), one of them to the northeast (8 spots; hereafter the

NE group) and the other one to the west and southwest (2+5 spots; hereafter the SW

group) from VLA 2. The spectra of these two groups of masers are shown in Figure 5. The

mean velocity of the maser spots associated with VLA 2 is VLSR = −10.6 km s−1 (with a

standard deviation of 3.3 km s−1), which is similar to the ambient molecular cloud velocity

(−10.3 km s−1; e.g. Font et al. 2001). On the other hand, the mean velocity of the maser

spots located to the NE is −9.1 km s−1 (redshifted) while the mean velocity of the SW

masers is −12.2 km s−1 (blueshifted). This spatial-velocity segregation of the water masers

is also seen in Figure 6, where we present the position-velocity distribution of the masers

along the axes with PA = 67◦ and −23◦. These diagrams show that the NE maser group is

mainly redshifted, while the SW one is mainly blueshifted with respect to the cloud velocity.

The spatio-kinematical distribution of the water masers around VLA 2 is similar to

that found towards the protostars IRAS 05413-0104 by Claussen et al. (1998) and S106

FIR by Furuya et al. (1999, 2000). In these sources, based on the spatial distribution and

relative proper motions of the maser components, these authors concluded that the water

masers are associated with a highly collimated compact jet-like flow that could originate

from a presumed protostar located in between two groups of masers. The similarity we find

between VLA 2 and the YSOs IRAS 05413-0104 and S106 FIR leads us to suggest that the

water masers in VLA 2 are associated with a collimated outflow, with VLA 2 as the central

source. Furthermore, since the redshifted CO lobe of the LkHα 234 region is detected toward

the NE, while the blueshifted optical S[II] jet is detected toward the SW, with a position

angle similar to that of the major axis of the maser distribution (PA≈ 247◦), we suggest

that the masers in VLA 2 are tracing the base of this large-scale outflow seen in CO/[SII].

4.3. VLA 3

VLA 3 is the strongest radio continuum source in the field at both wavelengths (1.3 and

3.6 cm). It was previously detected at 3 mm, 1.3 and 2 cm by Wilking et al. (1986). They

estimated a spectral index (Sν ∝ να) of 1.6, which was interpreted as a partially ionized

stellar wind. In addition, VLA 3 has also been detected at 2, 3.6 and 6 cm by Skinner et al.

(1993), who calculated spectral indices α6−3.6cm = 0.6, α6−2cm = 0.27, and α3.6−2cm = 0.43,

– 8 –

and interpreted these values as due to an ionized wind.

In order to estimate the spectral index for VLA 3 between 1.3 and 3.6 cm, we convolved

the 1.3 cm data with an elliptical Gaussian to give an angular resolution similar to that

obtained at 3.6 cm (' 0.′′3). We estimate a spectral index α3.6−1.3cm = 1.2, similar to

that obtained by Wilking et al. (1986), but different from those found by Skinner et al.

(1993). However, we note that the flux densities of VLA 3 obtained at different epochs

and wavelengths (Table 3) show that VLA 3 is a highly variable source. This fact could

explain the different measurements of the spectral index. On the other hand, as mentioned

before (§3.1), VLA 3 is a binary system where their components, VLA 3A and VLA 3B,

are separated by 0.′′22. Therefore, such flux density variations of VLA 3 could be produced

by individual flux density variations of VLA 3A and/or VLA 3B. Other thermal jet sources

have been found to exhibit variability on timescales of months to years (Porras et al. 2002,

Galvan-Madrid, Avila, and Rodrıguez, 2004).

To know the nature of VLA 3A and VLA 3B, we have calculated their spectral indices

using their flux densities at 1.3 and 3.6 cm (although VLA 3 is variable, the observations at

1.3 and 3.6 cm were carried out at the same date). In the following sections (§§4.3.1,4.3.2),

we discuss the nature of these two sources.

4.3.1. VLA 3A

VLA 3A has a spectral index α3.6−1.3cm ' 1.1 and a deconvolved size of 0.′′09×0.′′05 (PA

∼ 55◦) at 1.3 cm, which implies that its centimeter continuum emission is due to free-free

thermal emission from ionized gas. This spectral index could be consistent with VLA 3A

being an ultracompact partially optically thick H II region, or alternatively a thermal radio

jet. We discuss both scenarios below.

i) H II region. Assuming that VLA 3A is a homogeneous, isothermal (T = 104K) and

compact (0.′′09 × 0.′′05) H II region, and that it is at a distance of 1 kpc, we can calculate

some of its physical parameters (see e.g. Rodrıguez et al. 1980). First, we estimate an

opacity of τ1.3 cm ' 0.55 and τ3.6 cm ' 4.2, being consistent with a partially optically thick

H II region. In addition, we obtain an electron density Ne = 1.8×106 cm−3, an ionized mass

MH II = 9.3× 10−7 M�, and a rate of ionizing photons to maintain ionized the H II region

Ni = 6.1× 1044 s−1. This number of ionizing photons can be provided by a zero-age main-

sequence (ZAMS) B2 star, which is expected to have a luminosity of ∼ 2.8×103 L� (Panagia

1973). However, this luminosity is higher than that observed for the whole LkHα 234 region

(1.3× 103 L�, Bechis et al. 1978). This implies another ionizing mechanism to maintain the

– 9 –

estimated rate of ionizing photons.

ii) Thermal radio jet. An alternative possible scenario to explain the origin of the radio

continuum emission of VLA 3A is a radio jet. The spectral index that we estimate for

this source is consistent with that expected for an optically partially thick thermal jet (e.g.

Reynolds 1986; Anglada et al. 1998). In addition, a limit for the dependence of the angular

size of its major axis with frequency (θmaj ∝ ν−β) can also be estimated by using the angular

size at 1.3 cm and the upper limit at 3.6 cm. In this case, we obtain that β . 0.9, which

would be consistent with the value expected for thermal radio jets (β = 0.6). On the other

hand, the opening angle of VLA 3A is approximately estimated as

θo = 2 tan−1(θmin/θmaj), (1)

where θmin and θmaj are the angular sizes of the minor and major axes of the jet. For VLA 3A

we estimate θo ≈ 58◦.

We can also estimate the ionized mass-loss rate (Mion) for VLA 3A. According to

Reynolds (1986), for a pure hydrogen jet with constant velocity and ionization fraction,

we have(Mion

10−6M�yr−1

)= 0.54

[(2− α)(0.1 + α)

1.3− α

]3/4 [(SνmJy

)( ν

10GHz

)−α]3/4(V

103kms−1

)

×( νm

10GHz

)0.75α−0.45(θorad

)3/4

(sin i)−1/4

(d

kpc

)3/2(T

104K

)−0.075

, (2)

where α is the spectral index, Sν is the observed flux density at frequency ν, V is the terminal

velocity of the jet, νm is the turnover frequency, θo is the opening angle, i is the jet axis

inclination, d is the distance to the source and T is the electron temperature. Assuming

that the jet axis is nearly perpendicular to the line of sight (sin i = 1), a distance of 1 kpc,

an electron temperature of 104 K, and a lower limit for νm (= 22.2 GHz), we obtain Mion =

2.2V (Mion and V in units given in equation 2). For high-luminosity objects, velocities

of ∼ 500 − 103 km s−1 are usually adopted (e.g. Rodrıguez, 1998), then for intermediate

luminosity objects we can assume a velocity ∼ 500 km s−1. Under this assumption, we

derive a mass-loss rate of ∼ 10−6 M� yr−1, and a momentum rate deposited by the jet into

the ambient medium of ∼ 5× 10−4 M� yr−1 km s−1. These values are very similar to those

found for Cep A HW2 (Rodrıguez et al. 1994) and for HH 80-81 IRS (Martı et al. 1999),

which are thermal radio jets powered by a massive star.

– 10 –

4.3.2. VLA 3B

VLA 3B has a spectral index α3.6−1.3cm ' 0.7 and a deconvolved size of ' 0.′′29× ≤ 0.′′17

(PA = 57◦) at 3.6 cm, which also implies that the continuum emission is due to free-free

thermal emission from ionized gas. As in VLA 3A (§4.3.1), this spectral index could be

consistent with a partially optically thick H II region or an ionized jet. We discuss both

possibilities below.

i) H II region. Using the flux densities at 1.3 and 3.6 cm, we estimate an opacity of

τ1.3 cm ' 0.3 and τ3.6 cm ' 2.2 for VLA 3B, which is consistent with partially optically thick

emission. In addition, under the same assumptions made for VLA 3A and using a size of

. 0.′′1 at 1.3 cm, we estimate for VLA 3B an electron density Ne = 107 cm−3, an ionized

mass MHII = 1.6× 10−4 M�, and a rate of ionizing photons Ni = 6.6× 1044 s−1, which can

be supplied by a ZAMS B2 star. However, as mentioned in §4.3.1, the observed luminosity

in the LkHα 234 region is lower than that expected for these type of stars.

ii) Thermal radio jet. The spectral index obtained for VLA 3A is very similar to that

found for the thermal radio jet Cepheus A HW2 (α20−0.7cm ' 0.7; Rodrıguez et al. 1994).

Since VLA 3B is unresolved at 1.3 cm, a limit for its size dependence with frequency can be

estimated as θmaj ∝ ν−β, with β & 0.9. This value is larger than that expected for a conical

jet (β = 0.7) and could indicate that VLA 3B is a highly confined jet (Reynolds 1986).

Using the same assumptions as in VLA 3A, its observed flux density at 1.3 cm, an

opening angle of θo = 1 rad, and equation 2 (§4.3.1), we estimate Mion ' 0.6V (Mion and V

in units given in equation 2). Then, assuming a terminal velocity of ' 500 km s−1, we find

Mion ' 3 × 10−7 M� yr−1. In addition, the momentum rate deposited by the jet into the

ambient medium is P ' 1.5× 10−5 M� yr−1 km s−1. These values are consistent with those

found for low-mass YSOs (e.g., Anglada et al. 1998), which could suggest that VLA 3B is a

low-mass YSO.

On the other hand, although the jet-like radio sources VLA 3A and VLA 3B and the

infrared H2 jet (Cabrit et al. 1997) have similar position angles we think that they are not

spatially associated given the spatial displacement of MM1 (the energy source of the H2 jet,

Fuente et al. 2001) with respect to VLA 3 by 2.′′4 (see Fig. 1).

Finally, there are three maser spots spatially associated with the binary VLA 3 (Figure

2), two of them associated with VLA 3B and another one located between VLA 3A and

VLA 3B. One of the water masers associated with VLA 3B is blueshifted (−12.5 km s−1) and

the other one is redshifted (−6.0 km s−1) with respect to the cloud velocity (−10.3 km s−1).

The line connecting the two water masers does not seem to be aligned along the major axis

of the jet-like structure, but rather perpendicular to it.

– 11 –

4.4. LkHα 234 star

The LkHα 234 star is detected marginally at 3.6 cm (Figure 1 and Table 1). In addition,

we do not find any water maser around the LkHα 234 star. From these results, we cannot

provide evidence that the Herbig Be star LkHα 234 is associated with any of the observed

outflows in the region.

4.5. Parallel Outflows in the LkHα 234 Region

We identify at least two different thermal radio jets (VLA 3A and VLA 3B) and a

CO/[SII]/H2O outflow (VLA 2) in a region of ' 5′′×5′′ (' 5000×5000 UA). It is remarkable

that the axes of both thermal radio jets are parallel, and the axes of the outflows are sharing

a similar orientation (see §§4.2 and 4.3). Moreover, two infrared H2 jets, with similar position

angles to the jets and the outflow, were observed in this region (Cabrit et al. 1997). Outflows

sharing a similar orientation have been also observed in other star-forming regions (e.g.

IC 1396-N, Nisini et al. 2001; ρ Oph A, Kamazaki et al. 2003; IC 1396-W, Froebrich

& Scholz 2003), and different mechanisms have been invoked to explain the alignment of

the outflows: magnetic field, density gradient or initial angular momentum of the molecular

cloud. We think that all sources observed in this region (∼ 5′′) form a cluster of YSOs, which

were possibly born inside the same core in the NGC 7129 molecular cloud. This fact could

explain that the major axes of the outflows (∼ 45◦ − 70◦) have nearly the same orientation.

5. Conclusions

Our VLA observations of water masers and radio continuum emission at 1.3 and 3.6 cm

show that the LkHα 234 region contains a cluster of YSOs. In a field of ' 5′′ we have detected

five radio continuum sources (VLA 1, VLA 2, VLA 3A, VLA 3B, and LkHα 234) and 21

water maser spots. These water masers are mainly distributed in three clusters associated

with VLA 1, VLA 2, and VLA 3B. Our main conclusions can be summarized as follows:

1. The spatio-kinematical distribution of the water maser spots around the radio contin-

uum source VLA 2 suggests that they are tracing the base of the large-scale CO/[SII]

outflow. We favor VLA 2 as its energy source.

2. VLA 3A and VLA 3B seem to form a binary system separated by 220 AUs. From

their elongated emission and spectral indices we suggest that each star of this binary

energizes a thermal radio jet parallel between them.

– 12 –

3. It seems that there are at least four independent outflows in the LkHα 234 region: the

CO/S[II]/H2O outflow, the H2 jet, and the radio jets VLA 3A and VLA 3B. Moreover,

all outflows have similar orientation.

4. We confirm that the Herbig Be star LkHα 234 is not powering any of the outflows in

the region, which suggests that it is more evolved and less embedded than the other

sources in the region.

5. Finally, the LkHα 234 region can be considered as a ridge with several sites of low-

and intermediate-mass star formation at different evolutionary stages, but without a

clear relation between position and evolutionary stage (as it is predicted by theories

of sequential star formation). The formation of stars in this region appears random,

rather than sequentially triggered.

SC and MAT acknowledge support from CONACyT grant 33933−E. JFG and JMT

acknowledge support from MCYT grant AYA2002-00376 (including FEDER funds). We

thank E. Brinks for valuable comments. We also thank an anonymous referee for a careful

and thoughtful review.

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This preprint was prepared with the AAS LATEX macros v5.2.

– 15 –

LkH 234α

DE

CL

INA

TIO

N (

J200

0)

RIGHT ASCENSION (J2000)21 43 06.8 06.7 06.6 06.5 06.4 06.3 06.2 06.1 06.0

66 06 59

58

57

56

55

54

VLA 1

VLA 2

VLA 3

IRS6

MM1

A1

A2

a)

LkH 234α

DE

CL

INA

TIO

N (

J200

0)

RIGHT ASCENSION (J2000)21 43 06.8 06.7 06.6 06.5 06.4 06.3 06.2 06.1 06.0

66 06 59

58

57

56

55

54

VLA 1

VLA 2

VLA 3

IRS6

MM1

A2

A1

b)

Fig. 1.— a (top panel): Contour map of the continuum emission from the LkHα 234 region at 3.6 cm with natural weighting.

Contours are −5,−4,−3, 3, 4, 5, 7, 10, 14, 21 and 30 times 25 µJy beam−1, the rms noise of the map. The beam (0.′′37× 0.′′30)

is shown in the lower right-hand corner. b (bottom panel): Contour map of the LkHα 234 region at 1.3 cm. Contours are

−4,−3, 3, 4, 5, 6, 7, 9, 11 and 14 times 0.11 mJy beam−1, the rms noise of the map. The beam (0.′′20 × 0.′′19) is shown

in the lower right-hand corner. The small crosses indicate the position of the H2O maser spots detected in the region. The

sources LkHα 234 and FIRS1–MM1 are indicated by a star and a diamond, respectively. The large cross shows the position

of IRS 6 and its size represents the positional error. The straight line A1 indicates the direction of the CO/[SII] outflow with

VLA 2 proposed to be its energy source (this paper). The line labelled A2 shows the direction of the infrared H2 jet, with MM1

proposed to be its energy source (Cabrit et al. 1997, Fuente et al. 2001; see text).

– 16 –D

EC

LIN

AT

ION

(J2

000)

RIGHT ASCENSION (J2000)21 43 06.55 06.50 06.45 06.40

66 06 55.6

55.4

55.2

55.0

54.8

54.6

54.4

VLA 3B

VLA 3A

IRS6

DE

CL

INA

TIO

N (

J200

0)

RIGHT ASCENSION (J2000)21 43 06.55 06.50 06.45 06.40

66 06 55.6

55.4

55.2

55.0

54.8

54.6

54.4

VLA 3B

VLA 3A

IRS6

DE

CL

INA

TIO

N (

J200

0)

RIGHT ASCENSION (J2000)21 43 06.55 06.50 06.45 06.40

66 06 55.6

55.4

55.2

55.0

54.8

54.6

54.4

VLA 3B

IRS6

a)

b)

c)

Fig. 2.— a (top): Contour map of the continuum emission of VLA 3 at 3.6 cm using

uniform weighting and the Briggs “robustness” parameter set to −5 (see Briggs 1995 for

more details). Contours are −4,−3, 3, 4, 5, 6, 7, 8, 9, 10 and 12 times 47 µJy beam−1,

the rms of the map. The beam (0.′′26× 0.′′17) is shown in the lower left-hand corner. From

this figure we see that VLA 3 is in fact a binary system, which is formed by VLA 3A and

VLA 3B. b (middle): Contour map of VLA 3 at 1.3 cm using uniform weighting and the

Briggs “robustness” parameter set to 0. Contours are −4,−3, 3, 4, 5, 7, 9, 11 and 13 times

0.11 mJy beam−1, the rms of the map. The beam (0.′′12× .′′10) is shown in the lower left-hand

corner. At this frequency, the two sources are completely separated. c (bottom): We have

subtracted the source VLA 3A from the (u,v) data at 3.6 cm. Contours are −4,−3, 3, 4, 5,

6, 7 and 8 times 45 µJy beam−1, the rms of the map. In this panel, only VLA 3B remains

and its morphology is elongated, suggesting a jet-like appearance. In the three panels the

small crosses indicate the position of the H2O maser spots associated with VLA 3 and the

large cross indicates the position of IRS6 (its size represents the error in its position).

– 17 –D

EC

LIN

AT

ION

(J2

000)

RIGHT ASCENSION (J2000)21 43 06.25 06.20 06.15 06.10 06.05 06.00

66 06 59.2

59.0

58.8

58.6

58.4

58.2

58.0

57.8

57.6

57.4

VLA 1

Fig. 3.— VLA-A continuum map of the radio source VLA 1 in the LkHα 234 region at

3.6 cm. Contours are −4,−3, 3, 4, 5, 6 and 7 times 25 µJy beam−1, the rms of the map.

The beam (0.′′37 × 0.′′30) is shown in the lower left-hand corner. The crosses indicate the

position of the H2O maser spots spatially associated with VLA 1.

– 18 –D

EC

LIN

AT

ION

(J2

000)

RIGHT ASCENSION (J2000)21 43 06.40 06.38 06.36 06.34 06.32 06.30 06.28 06.26

66 06 56.4

56.3

56.2

56.1

56.0

55.9

55.8

55.7

55.6

55.5

Fig. 4.— VLA-A continuum map of the radio source VLA 2 in the LkHα 234 region at

1.3 cm. The continuum source is barely detected and only one contour is shown (3-σ). A

cluster of 16 H2O maser spots (circles) is spatially associated with VLA 2.

– 19 –

-20 -15 -10 -5 0

0

20

40

60

80

100

Velocity (km/s)

S-W Masers

Cloud Velocity

N-E Masers

Fig. 5.— Spectra of the water maser spots located to the northeast (dotted line) and

southwest (solid line) from the radio continuum source VLA 2.

– 20 –

Fig. 6.— Position-velocity distribution of the H2O maser spots associated with VLA 2. Left

panel: Along the major axis with PA = 67◦ of the maser spot distribution, which is nearly

parallel to the axis of CO/[SII] outflow. Right panel: Same as left panel but in the direction

of the minor axis (PA = −23◦). The vertical axis corresponds to the velocity of the maser

spots after subtracting their mean velocity (−10.6 km s−1). The horizontal axis corresponds

to the relative position of the maser spots along the major and minor axis of the maser

distribution with respect to their geometrical center. Relative position errors are typically

∼ 1 mas.

– 21 –

Table 1. Parameters of the Sources in the LkHα 234 Region

Position a Deconvolved

size

Source α(2000) δ(2000) Sν(3.6 cm) Sν(1.3 cm) (λ = 3.6 cm) Spectral

21h 43m 66◦ 06′ (mJy) (mJy) (arcsec) Index

VLA 1 06.093 58.13 0.32± 0.09 ≤ 0.33b 0.56× ≤ 0.30 (45◦) ≤ 0.03

VLA 2 06.321 55.95 0.1c ≤ 0.33b ≤ 0.3 ...

VLA 3A 06.479 55.02 0.67± 0.08 1.96± 0.21 0.09× 0.05 (55◦)d 1.11± 0.16

VLA 3B 06.462 55.22 0.61± 0.10 1.19± 0.26 0.29× ≤ 0.17 (57◦) 0.69± 0.29

IRS6e 06.41 54.8 ... ... ... ...

MM1f 06.3 57.4 ... ... ... ...

LkHα 234 06.816 54.26 0.1c ... ≤ 0.3 ...

aUnits of right ascension are hours, minutes, and seconds, and units of declination are

degrees, arcminutes, and arcseconds.

b3-σ upper limit.

c4-σ level.

dsize at 1.3 cm

ePosition taken from Cabrit et al. (1997).

fPosition taken from Fuente et al. (2001).

– 22 –

Table 2. H2O Masers in LkHα 234 Region

Position e

VLSR Sν Associated

α(2000) δ(2000) (km s−1) (Jy) Continuum Source

21h 43m 66◦ 06′

06.1018 58.196 -11.2 0.13 VLA 1

06.1034 58.202 -15.2 2.58 VLA 1

06.3003 55.936 -16.5 0.74 VLA 2

06.3005 55.940 -17.8 3.79 VLA 2

06.3013 55.835 -11.9 0.69 VLA 2

06.3028 55.832 -8.6 1.61 VLA 2

06.3048 55.823 -11.2 2.69 VLA 2

06.3075 55.821 -9.3 8.15 VLA 2

06.3085 55.819 -9.9 15.07 VLA 2

06.3217 55.949 -11.2 0.98 VLA 2

06.3516 55.968 -7.3 37.30 VLA 2

06.3517 55.971 -9.3 84.52 VLA 2

06.3521 55.974 -5.3 1.73 VLA 2

06.3521 55.981 -10.6 11.73 VLA 2

06.3531 55.991 -11.2 5.25 VLA 2

06.3533 55.985 -4.6 0.14 VLA 2

06.3552 56.016 -11.9 2.33 VLA 2

06.3555 56.027 -12.5 1.41 VLA 2

06.4650 55.241 -12.5 0.13 VLA 3B

06.4669 55.216 -6.0 3.03 VLA 3B

06.4906 55.194 -13.9 0.20 VLA 3

eUnits of right ascension are hours, minutes, and seconds,

and units of declination are degrees, arcminutes, and arcsec-

onds. Relative position errors are typically ∼ 1 mas.

– 23 –

Table 3. Summary of the Observations of VLA 3

λ Date Flux Density Reference

(cm) (mJy)

6.0 1983 Jan 0.9± 0.3 1

1991 Jun 1.65± 0.18 2

3.6 1990 Feb 1.34± 0.12 2

1991 Jun 2.29± 0.18 2

2000 Dec 1.27± 0.10 3

2.0 1985 Dec 3.29± 0.35 4

1991 Jun 2.67± 0.45 2

1.3 1985 Dec 6.68± 0.95 4

2000 Dec 3.21± 0.21 3

0.3 1985 Jun 93± 23 4

0.26 1998 Nov 91± 6 5

References. — (1) Snell & Bally (1986), (2)

Skinner et al. (1993), (3) This work, (4) Wilk-

ing et al. (1986), and (5) Fuente et al. (2001).