Molecular jet emission and a spectroscopic survey of S235AB
A&A
Astronomy & Astrophysics
R. A. Burns 2
T. Handa 2
T. Hirota 0 1
K. Motogi 3
H. Imai 2
T. Omodaka 2
0 Department of Astronomical Sciences, SOKENDAI (Graduate University for Advanced Studies) , Osawa 2-21-1, Mitaka, 181-8588 Tokyo , Japan
1 Mizusawa VLBI Observatory, National Astronomical Observatory of Japan , Osawa 2-21-1, Mitaka, 181-8588 Tokyo , Japan
2 Graduate School of Science and Engineering, Kagoshima University , 1-21-35 Kôrimoto, 890-0065 Kagoshima , Japan
3 Mizusawa VLBI Observatory, National Astronomical Observatory of Japan , 2-12 Hoshi-ga-oka, Mizusawa-ku, Oshu-shi, 023-0861 Iwate , Japan
Context. The S235AB star forming region houses a massive young stellar object which has recently been reported to exhibit possible evidence of jet rotation - an illusive yet crucial component of disk aided star formation theories. Aims. We confirm the presence of a molecular counterpart to the jet and we also study the molecular environment in S235AB. Methods. We search for velocity wings in the line emission of thermal SiO (J = 2-1, v = 0), a tracer of shocked gas, which would indicate the presence of jet activity. Utilising other lines detected in our survey we use the relative intensities of intra species transitions, isotopes, and hyperfine transitions to derive opacities, temperatures, column densities, and abundances of various molecular species in S235AB. Results. The SiO (J = 2-1, v = 0) emission exhibits velocity wings of up to 75 km s−1 above and below the velocity of the star, indicating the presence of a jet. The molecular environment describes an evolutionary stage resembling a hot molecular core.
stars; massive - ISM; jets and outflows
1. Introduction
The target of our study, S235AB, is a star forming region that
houses a massive young stellar object (MYSO) called
S235ABMIR, which was recently reported to exhibit fast (∼50 km s−1)
jet-tracing water masers with a signature of rotation
(Burns et al.
2015)
. The confirmation of a rotating jet in an MYSO would
have a great impact on the theories of star formation as it would
provide a method of removing angular momentum from the
inner disk of the system and enabling accretion, while also
corroborating a magneto-centrifugal launching mechanism for jets
from massive young stars
(see Konigl & Pudritz 2000)
.
S235AB-MIR is known to have slow molecular outflows
(Felli et al. 2004); however, aside from the fast water maser
velocities, there is no evidence in the literature of a fast molecular
jet in S235AB-MIR. In Felli et al. (2004) the authors claimed
to have found a continuum jet aligned with the water maser jet;
however, they later retracted the claim in Felli et al. (2006). As
a follow-up to the maser jet results of
Burns et al. (2015)
the
primary aim of our spectral line survey was to find the
molecular counterpart to the water maser jet in S235AB, which should
be readily identifiable from doppler broadened line “wings”
seen in the thermal gas jet tracer SiO (J = 2–1, v = 0) (e.g.
López-Sepulcre et al. 2011). The secondary aim of our
observations was to further investigate the physical gas conditions in
S235AB via basic astrochemical study using auxiliary spectral
lines.
S235AB is known to have a dense molecular core
centered on S235AB-MIR and molecular outflows mapped in
HCO+ (1–0) and C34S (5–4) (Felli et al. 2004), CS (7–6) (Wu
et al. 2010), and 13CO (Felli et al. 1997). The Spitzer colours
indicate that S235AB-MIR has a mass of 11 M , making it the
only MYSO in the region (Dewangan & Anandarao 2011), and
non-detection of centimetre emission in S235AB attests to its
youth (Tofani et al. 1995; Felli et al. 2006).
2. Observations and data reduction
We conducted molecular line observations of S235AB in March
and April of 2015 with the 45 m radio telescope of the
Nobeyama Radio Observatory (NRO), a branch of the National
Astronomical Observatory of Japan.
We observed in two-sideband mode using the TZ receiver
and we observed horizontal and vertical linear polarisations
simultaneously. The upper sideband (USB) and lower
sideband (LSB) central frequencies were 85.85 and 97.85 GHz,
respectively, with band widths of 4 GHz each. The beamsize was
about 18 . The SAM45 spectrometer provided 16 independent
frequency arrays (8 per polarisation), which we organised to
provide continuous coverage of a wide frequency range, and
to include lines of particular interest. The frequency resolution
was 244.14 kHz, providing a bandwidth of 1000 MHz per array.
Observing coordinates were centred on the position of
S235AB-MIR at (α, δ)J2000.0 = (05h40m53s.384 +35◦41 48. 447).
Sky-level subtraction was performed using a region of empty
sky at coordinates (α, δ)J2000.0 = (05h40m58s.30 +35◦41 48. 60).
Absolute flux calibration was performed using the chopper
wheel method, empty sky, and hot load. Pointing accuracy
was checked using a nearby SiO maser source, RU Aur,
every ∼1–2 h.
During the March observations the atmospheric conditions
were good with (...truncated)