209 research outputs found
The Remarkable Mid-Infrared Jet of Massive Young Stellar Object G35.20-0.74
The young massive stellar object G35.20-0.74 was observed in the mid-infrared
using T-ReCS on Gemini South. Previous observations have shown that the near
infrared emission has a fan-like morphology that is consistent with emission
from the northern lobe of a bipolar radio jet known to be associated with this
source. Mid-infrared observations presented in this paper show a monopolar
jet-like morphology as well, and it is argued that the mid-infrared emission
observed is dominated by thermal continuum emission from dust. The mid-infrared
emission nearest the central stellar source is believed to be directly heated
dust on the walls of the outflow cavity. The hydroxyl, water, and methanol
masers associated with G35.20-0.74 are spatially located along these
mid-infrared cavity walls. Narrow jet or outflow cavities such as this may also
be the locations of the linear distribution of methanol masers that are found
associated with massive young stellar objects. The fact that G35.20-0.74 has
mid-infrared emission that is dominated by the outflow, rather than disk
emission, is a caution to those that consider mid-infrared emission from young
stellar objects as only coming from circumstellar disks.Comment: Accepted for publication in ApJ Letters; 4 pages; 2 figures; a
version with full resolution images is available here:
http://www.ctio.noao.edu/~debuizer
A sub-arcsecond study of the hot molecular core in G023.01-00.41
(Abridged) METHODS: We performed SMA observations at 1.3 mm with both the
most extended and compact array configurations, providing sub-arcsecond and
high sensitivity maps of various molecular lines, including both hot-core and
outflow tracers. We also reconstruct the spectral energy distribution of the
region from millimeter to near infrared wavelengths, using the Herschel/Hi-GAL
maps, as well as archival data. RESULTS: From the spectral energy distribution,
we derive a bolometric luminosity of about 4x10^4 Lsun. Our interferometric
observations reveal that the distribution of dense gas and dust in the HMC is
significantly flattened and extends up to a radius of 8000 AU from the center
of radio continuum and maser emission in the region. The equatorial plane of
this HMC is strictly perpendicular to the elongation of the collimated bipolar
outflow, as imaged on scales of about 0.1-0.5 pc in the main CO isotopomers as
well as in the SiO(5-4) line. In the innermost HMC regions (ca. 1000 AU), the
velocity field traced by the CH3CN(12_K-11_K) line emission shows that
molecular gas is both expanding along the outflow direction following a
Hubble-law, and rotating about the outflow axis, in agreement with the (3-D)
velocity field traced by methanol masers. The velocity field associated with
rotation indicates a dynamical mass of 19 Msun at the center of the core. The
latter is likely to be concentrated in a single O9.5 ZAMS star, consistent with
the estimated bolometric luminosity of G023.01-00.41. The physical properties
of the CO(2-1) outflow emission, such as its momentum rate 6x10^-3 Msun km/s
/yr and its outflow rate 2x10^-4 Msun/yr, support our estimates of the
luminosity (and mass) of the embedded young stellar object.Comment: 24 pages, 11 figures, 6 tables, accepted by Astronomy & Astrophysic
Trigonometric Parallaxes of Massive Star Forming Regions: IV. G35.20-0.74 and G35.20-1.74
We report trigonometric parallaxes for the high-mass star forming regions
G35.20-0.74 and G35.20-1.74, corresponding to distances of 2.19 (+0.24 -0.20)
kpc and 3.27 (+0.56 -0.42) kpc, respectively. The distances to both sources are
close to their near kinematic distances and place them in the
Carina-Sagittarius spiral arm. Combining the distances and proper motions with
observed radial velocities gives the locations and full space motions of the
star forming regions. Assuming a standard model of the Galaxy, G35.20-0.74 and
G35.20-1.74 have peculiar motions of ~13 km/s and ~16 km/s counter to Galactic
rotation and ~9 km/s toward the North Galactic Pole.Comment: 16 pages, 8 figure
Mid-Infrared Imaging of the Bipolar Planetary Nebula M2-9 from SOFIA
We have imaged the bipolar planetary nebula M2-9 using SOFIA's FORCAST
instrument in six wavelength bands between 6.6 and 37.1 . A bright
central point source, unresolved with SOFIA's 4-to-5 beam,
is seen at each wavelength, and the extended bipolar lobes are clearly seen at
19.7 and beyond. The photometry between 10 and 25 is well fit
by the emission predicted from a stratified disk seen at large inclination, as
has been proposed for this source by Lykou et al and by Smith and Gehrz. The
principal new results in this paper relate to the distribution and properties
of the dust that emits the infrared radiation. In particular, a considerable
fraction of this material is spread uniformly through the lobes, although the
dust density does increase at the sharp outer edge seen in higher resolution
optical images of M2-9. The dust grain population in the lobes shows that small
( 1 ) particles appear to be present in
roughly equal amounts by mass. We suggest that collisional processing within
the bipolar outflow plays an important role in establishing the particle size
distribution.Comment: 40 pages, 9 figures, 2 table
Born Again Protoplanetary Disk Around Mira B
The Mira AB system is a nearby (~107 pc) example of a wind accreting binary
star system. In this class of system, the wind from a mass-losing red giant
star (Mira A) is accreted onto a companion (Mira B), as indicated by an
accretion shock signature in spectra at ultraviolet and X-ray wavelengths.
Using novel imaging techniques, we report the detection of emission at
mid-infrared wavelengths between 9.7 and 18.3 m from the vicinity of Mira
B but with a peak at a radial position about 10 AU closer to the primary Mira
A. We interpret the mid-infrared emission as the edge of an optically-thick
accretion disk heated by Mira A. The discovery of this new class of accretion
disk fed by M-giant mass loss implies a potential population of young planetary
systems in white-dwarf binaries which has been little explored, despite being
relatively common in the solar neighborhood.Comment: Accepted for Ap
Mid-Infrared Imaging of NGC 6334 I
We present high-resolution (<0.5") mid-infrared Keck II images of individual
sources in the central region of NGC 6334 I. We compare these images to images
at a variety of other wavelengths from the near infrared to cm radio continuum
and speculate on the nature of the NGC 6334 I sources. We assert that the
cometary shape of the UCHII region here, NGC 6334 F, is due to a champagne-like
flow from a source on the edge of a molecular clump and not a due to a bow
shock caused by the supersonic motion of the UCHII region through the
interstellar medium. The mid-infrared emission in concentrated into an arc of
dust that define the boundary between the UCHII region and the molecular clump.
This dust arc contains a majority of the masers in the region. We discuss the
nature of the four near-infrared sources associated with IRS-I 1, and suggest
that one of the sources, IRS1E, is responsible for the heating and ionizing of
the UCHII region and the mid-infrared dust arc. Infrared source IRS-I 2, which
has been thought to be a circumstellar disk associated with a linear
distribution of methanol masers, is found not to be directly coincident with
the masers and elongated at a much different position angle. IRS-I 3 is found
to be a extended source of mid-infrared emission coming from a cluster of young
dusty sources seen in the near-infrared.Comment: Accepted for publication by the Astrophysical Journal, 27 pages, 9
figure
SiO Outflow Signatures Toward Massive Young Stellar Objects with Linearly Distributed Methanol Masers
Methanol masers are often found in linear distributions, and it has been
hypothesized that these masers are tracing circumstellar accretion disks around
young massive stars. However, recent observations in H2 emission have shown
what appear to be outflows at similar angles to the maser distribution angles,
not perpendicular as expected in the maser-disk scenario. The main motivation
behind the observations presented here is to determine from the presence and
morphology of an independent outflow tracer, namely SiO, if there are indeed
outflows present in these regions and if they are consistent or inconsistent
with the maser-disk hypothesis. For ten sources with H2 emission we obtained
JCMT single dish SiO (6-5) observations to search for the presence of this
outflow indicator. We followed up those observations with ATCA interferometric
mapping of the SiO emission in the (2-1) line in six sources. The JCMT
observations yielded a detection in the SiO (6-5) line in nine of the ten
sources. All of the sources with bright SiO lines display broad line wings
indicative of outflow. A subset of the sources observed with the JCMT have
methanol maser velocities significantly offset from their parent cloud
velocities, supporting the idea that the masers in these sources are likely not
associated with circumstellar disks. The ATCA maps of the SiO emission show
five of the six sources do indeed have SiO outflows. The spatial orientations
of the outflows are not consistent with the methanol masers delineating disk
orientations. Overall, the observations presented here seem to provide further
evidence against the hypothesis that linearly distributed methanol masers
generally trace the orientations of circumstellar disks around massive young
stars.Comment: Accepted for publication in A&A; 36 pages, 8 figures; a version with
higher quality figures can be found at http://www.jim-debuizer.net/researc
Mid-Infrared Photometry and Spectra of Three High Mass Protostellar Candidates at IRAS 18151-1208 and IRAS 20343+4129
We present arcsecond-scale mid-ir photometry (in the 10.5 micron N band and
at 24.8 microns), and low resolution spectra in the N band (R~100) of a
candidate high mass protostellar object (HMPO) in IRAS 18151-1208 and of two
HMPO candidates in IRAS 20343+4129, IRS 1 and IRS 3. In addition we present
high resolution mid-ir spectra (R~80000) of the two HMPO candidates in IRAS
20343+4129. These data are fitted with simple models to estimate the masses of
gas and dust associated with the mid-ir emitting clumps, the column densities
of overlying absorbing dust and gas, the luminosities of the HMPO candidates,
and the likely spectral type of the HMPO candidate for which [Ne II] 12.8
micron emission was detected (IRAS 20343+4129 IRS 3). We suggest that IRAS
18151-1208 is a pre-ultracompact HII region HMPO, IRAS 20343+4129 IRS 1 is an
embedded young stellar object with the luminosity of a B3 star, and IRAS
20343+4129 IRS 3 is a B2 ZAMS star that has formed an ultracompact HII region
and disrupted its natal envelope.Comment: 40 pages, 8 figures, 3 tables. Accepted for publication in
Astrophysical Journal (Part 1
- …