Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.mrao.cam.ac.uk/yerac/testi/testi.ps Äàòà èçìåíåíèÿ: Thu Feb 23 01:36:06 1995 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 01:03:05 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: jet

Exploring the engines of molecular outflows
By L eon a r d o T e s t i
e­mail: testi@arcetri.astro.it
Dipartimento di Astronomia e Scienza dello Spazio, Universit`a degli Studi di Firenze, Largo
E. Fermi 5, I--50125, Firenze, ITALY
Water vapour masers and CO outflows are well known to be associated with the youngest
phases of evolution of massive stellar objects. Nevertheless, up to now there is a lack of high
resolution multiwavelength study of the regions containing these objects. Using the VLA, the
CSO and the TIRGO equipped with the new Near­Infrared (NIR) camera ARNICA, we have
begun a systematic study of water maser/CO outflow regions. These new high resolution and
high sensitivity data have proved to be very useful in probing the star formation activity and
the connection between infrared and radio sources. Here we report the results obtained in
a preliminary sub­sample of objects. The NIR data showed that both the maser spots and
the large­scale outflows tend to be associated to the most embedded and probably younger
sources of the infrared clusters. Infrared emission lines observed with narrow band filters show
the presence of jet­like structures in most of the sources observed. Water masers, jet­like and
Herbig­Haro­like infrared structures, and CO outflows enable to probe ejection phenomena at
all spacial scales ranging from 0.01 to 1 parsec.
1. Introduction
H 2 O masers and CO outflows are well known to be signposts of star formation, see
also the contribution of Codella & Palla, this volume. Recent surveys have shown that
the two events are usually associated (Felli et al. (1992)), a nd are related to the same
Young Stellar Objects (YSO). On the other hand, these phenomena trace widely different
physical scales, ranging from ¸ 0:01 to 1 parsec. Which relationship exists between
the two events and in which evolutionary stage of a YSO they are produced are key
questions to address in order to understand the physical processes occurring during the
star formation process. Only high sensitivity and high resolution line and continuum
observations in the radio, submillimeter and infrared windows can hopefully address
such questions.
Using the VLA in its most extended (A) configuration for H 2 O maser line and 8:4 GHz
continuum high resolution mapping, the CSO for submillimeter molecular line emission
observations, and the TIRGO for NIR imaging, we are carrying out a detailed study
of a sample of regions with known H 2 O masers and broad­wing CO lines. In this pa­
per we will present the preliminary results obtained on two of the observed objects:
BD+40 ffi 4124 (Palla et al. (1995)) and AFGL 5142 (Hunter et al. (1994)).
The first field (BD+40 ffi 4124) is centered on a well known Herbig Ae/Be star, and the
H 2 O maser was discovered during a survey carried out by Palla & Prusti (1993) using
the Medicina radio telescope for water vapour observations toward Herbig Ae/Be stars.
AFGL 5142 is a well known dense molecular core (Verdes­Montenegro et al. (1989)),
with no optically visible young stars detected. In spite of the supposed difference between
the two regions our data reveal that the source powering the H 2 O masers and the CO
outflows is indeed very similar in the two cases and has the same infrared characteristics
of sources detected toward a larger sample of H 2 O masers (Testi et al. (1994)).
1

2 Leonardo Testi: Exploring the engines of molecular outflows
2. Observations
The observations will be described briefly in the following sections. For a complete
description of the observations and data reduction see Palla et al. (1995) and Hunter et
al. (1994). In particular, more information on ARNICA and on the NIR techniques used
with TIRGO can be obtained here.
2.1. NIR observations
Near infrared images in the J(1:2 ¯m), H(1:6 ¯m), and K(2:2 ¯m) broad bands were
obtained at TIRGO, with the NIR imaging camera ARNICA, using a mosaicing tech­
nique. The observed fields cover roughly 7 0 \Theta 7 0 , with a scale of ¸ 0:95 00 =pixel, and a
measured Point Spread Function of ¸ 3 00 (Full Width at Half Maximum). In addition,
for the AFGL 5142 field, narrow band images were obtained in the H 2 (2:122 ¯m) and
in the Brackett fl (2:166 ¯m) filters.
Photometric calibration was achieved by observing a set of UKIRT faint standard
stars before and after the broad band observations. The narrow band images have been
calibrated with the broad band ones, assuming that a set of stars does not have detectable
line emission. The limiting magnitudes (3oe in 5 00 aperture) achieved in J, H, and K were
¸ 17:3, ¸ 16:2, and ¸ 16:0 respectively, in both fields.
2.2. VLA observations
The VLA H 2 O line and 8:4 GHz continuum observations have been performed with
the array in its most extended (A) configuration. The synthesized beam obtained were
¸ 0:11 00 at 22 GHz and ¸ 0:27 00 at 8:4 GHz. The data were calibrated and reduced using
the AIPS software.
2.3. CSO observations
The sources were mapped using the on­the­fly technique in various transitions of CO and
CS, the beam was between 20 00 and 30 00 , depending on the transition. All the data have
been reduced and analyzed using the CLASS software. The calibration is expected to be
accurate within 20% and the pointing within 4 00 .
3. Results
3.1. BD+40 ffi 4124
In Figure 1 a NIR ``true­color'' image of the BD+40 ffi 4124 field is presented, the J­band
image has been coded in blue, the H­band in green, and the K­band in red. In this kind
of figure a Main­Sequence (MS) star should appear white­blue, all the orange and red
sources are either suffer heavily from extinction or have a strong NIR excess. Sources
with strong NIR excess have a Spectral Energy Distribution (SED) that falls toward
longer wavelengths less rapidly than that of MS stars; in some extreme case the SED
could rise toward longer wavelengths. Following Lada & Adams (1992) this kind of
SED is characteristic of YSOs in which the young star is still embedded in an hot dusty
envelope.
The VLA radio continuum map of these region contains only a faint pointlike object
at the position of BD+40 ffi 4124, while the line maps show only one maser spot roughly
30 00 to the south­east. The maser spot is coincident with the star V 1318S, which has a
large NIR excess (see also Aspin et al. (1994)).
Our CSO observations were able to resolve the bipolar structure of the CO outflow
in the region, whose presence had been inferred by the broad wings of the CO lines

Leonardo Testi: Exploring the engines of molecular outflows 3
Figure 1. NIR ``true­colour'' image of the BD+40 ffi 4124 field. The J­image is coded in blue,
H­ in green, and K­ in red. See text for details.
Figure 2. On the left an overlay of the CO outflow map (blue wing, solid line; red wing,
dashed line) on the K­band image greyscale, the position of the maser spot is marked with a
triangle, the radio continuum source is coincident with BD+40 ffi 4124 (the saturated star to the
north­west). On the right, (J--H,H--K) colour­colour diagram of the NIR sources the position of
V 1318S is marked.
observed with poorer angular resolution. The outflow is very compact, the actual length
is estimated to be less than 30 00 , which correspond to ¸ 0:15 pc. The dunamical center of
the outflow is coincident with the maser spot, indicating that the very young embedded
source V 1318S is probably the source powering both these phenomena.
In Figure 2 an overlay of the CSO CO 2 ! 1 outflow map on the central region of
the K­band image is presented; also shown in the figure are the locations of the H 2 O
maser spot and of the radio continuum source. On the right a (J--H, H--K) colour­colour
diagram of the sources detected in the field is shown, the position of V 1318S is marked.

4 Leonardo Testi: Exploring the engines of molecular outflows
Figure 3. Same as Figure 1 but for AFGL 5142.
The colours of MS stars are shown with the continuum line, reddened MS stars should
lie in the band in the ``reddening belt'' defined by the long­dashed lines. V 1318S lies
well on the right with respect to MS stars, indicating that it has a strong NIR excess.
3.2. AFGL 5142
In Figure 3 a NIR­true­colour image of the AFGL 5142 field is shown. A cluster of
very red sources is detected at the center of the image, and the overlay with the CSO
CO data (Figure 4) on the K­band map show that the NIR cluster is located at the
dynamical center of the large outflow. A detailed look at Figure 3 shows that the red
and the blue lobe centers do not coincide. We interpret this as the presence of two
outflows in the region: a large­scale one (¸ 2 0 ) and a small scale one (¸ 0:5 0 ), oriented
almost perpendicularly. We identified a possible powering candidate for the large one in
an infrared source designed IRS2, while the small­scale one is associated with a deeply
embedded NIR source designed as IRS1. This picture is by our VLA and H 2 molecular
line observations. In the radio continuum a faint and compact source is detected at the
location of IRS1 (most probably the free­free emission of a ionized stellar wind). The
H 2 O line observations reveal five maser spots, two of them roughly coincident with the
continuum source, and the others aligned with the compact outflow axis. Comparing our
results with that of Torrelles et al. (1992) a proper motion along this axis was marginally
detected in the two most distant spots from the continuum source. In the H 2 line a jet­
like feature and several HH­like knots have been detected, the jet is pointing outward
from IRS1 in the same direction of the red­lobe of the compact outflow. In Figure 5
an overlay of the VLA and the H 2 data on the central region of the K­band image is
presented.
The source IRS1 has been detected at 850 ¯m with the JCMT (see the contribution
of Jenness, indicating that is indeed a very young and deeply embedded YSO.

Leonardo Testi: Exploring the engines of molecular outflows 5
Figure 4. Same as Figure 2 but for AFGL 5142. On the colour­colour diagram the positions
of the NIR sources IRS1 and IRS2 are marked.
Figure 5. Overlay on the central region of the K­band image (greyscale) of the H2 data (after
continuum subtraction, green contours), the VLA radio continuum peak (yellow concentric
circles), and the VLA positions of the maser spots (violet crosses). The VLA position are
determined much better than the dimensions of the markers. In red is the IRAS PSC error box.
4. Conclusions
The source powering the H 2 O masers and the compact molecular outflows shows very
similar NIR properties, and appears to be YSO in the very preliminary stages of their
lives. As discussed in Testi et al. (1994) the infrared properties of the objects appear
to be those of young luminous stars deeply embedded in hot dust cocoons, responsible
for the high extinction and for the NIR excess. In order to better understand the nature
and evolutionary status of the sources, high sensitivity and high resolution mid­ and far­
infrared observations are needed. For this purposes the new ground­based mid­infrared
instrumentation (like the new generation of TIRGO instruments: TIRCAM and TC­
MIRC) as well as spacecraft mission (like ISO) are expected to produce new and very
important results.
Partly based on observations collected at TIRGO (Gornergrat, Switzerland), VLA

6 Leonardo Testi: Exploring the engines of molecular outflows
(Socorro, New Mexico, USA), CSO (Hawaii, USA). TIRGO is operated by CAISMI--
CNR Arcetri, Firenze, Italy. This work has been done in collaboration with many people,
among them I would like to acknowledge Marcello Felli, Gianni Tofani and Francesco
Palla from the Arcetri Astrophysical Observatory and Todd Hunter and Greg Taylor
from Caltech. I would like to thank the staff of the TIRGO, VLA, and CSO for help and
hospitality. I would expecially thank Enrico Brunetti and Roberto Baglioni for helping
with many technical problems.
REFERENCES
Aspin C., Sandell G. & Weintraub D.A., 1994, A&A, 282, L25.
Felli M., Palagi F. & Tofani G., 1992, A&A, 255, 293.
Hunter T.R., Testi L., Taylor G.B., Tofani G., Felli M., & Phillips T.G., 1994, A&A, submitted.
Lada C. & Adams F.C., 1992, AJ, 393, 278.
Palla F. & Prusti T., 1993, A&A, 272, 249.
Palla F., Testi L., Hunter T.R., Taylor G.B., Prusti T., Felli M., Natta A. & Stanga R.M., 1995,
A&A, 293, 521.
Testi L., Felli M., Persi P. & Roth M., 1994,, A&A, 288, 634.
Torrelles J.M., G'omez J.F., Anglada G., et al., 1992, AJ, 392, 616.
Verdes­Montenegro L., Torrelles J.M., Rodriguez L.F., et al., 1989, AJ, 346, 193.