530 research outputs found
PO and PN in the wind of the oxygen-rich AGB star IK Tau
Phosphorus-bearing compounds have only been studied in the circumstellar
environments (CSEs) of the asymptotic giant branch (AGB) star IRC +10216 and
the protoplanetary nebula CRL 2688, both C-rich objects, and the O-rich red
supergiant VY CMa. The current chemical models cannot reproduce the high
abundances of PO and PN derived from observations of VY CMa. No observations
have been reported of phosphorus in the CSEs of O-rich AGB stars. We aim to set
observational constraints on the phosphorous chemistry in the CSEs of O-rich
AGB stars, by focussing on the Mira-type variable star IK Tau. Using the IRAM
30m telescope and the Submillimeter Array (SMA), we observed four rotational
transitions of PN (J=2-1,3-2,6-5,7-6) and four of PO
(J=5/2-3/2,7/2-5/2,13/2-11/2,15/2-13/2). The IRAM 30m observations were
dedicated line observations, while the SMA data come from an unbiased spectral
survey in the frequency range 279-355 GHz.
We present the first detections of PN and PO in an O-rich AGB star and
estimate abundances X(PN/H2) of about 3x10^-7 and X(PO/H2) in the range
0.5-6.0x10^-7. This is several orders of magnitude higher than what is found
for the C-rich AGB star IRC +10216. The diameter (<=0.7") of the PN and PO
emission distributions measured in the interferometric data corresponds to a
maximum radial extent of about 40 stellar radii. The abundances and the spatial
occurrence of the molecules are in very good agreement with the results
reported for VY CMa. We did not detect PS or PH3 in the survey. We suggest that
PN and PO are the main carriers of phosphorus in the gas phase, with abundances
possibly up to several 10^-7. The current chemical models cannot account for
this, underlining the strong need for updated chemical models that include
phosphorous compounds.Comment: Accepted for publication in Astronomy & Astrophysics, 10 pages, 8
figure
Search for aluminium monoxide in the winds of oxygen-rich AGB stars
Aluminium monoxide, AlO, is likely efficiently depleted from the gas around
oxygen-rich evolved stars to form alumina clusters and dust seeds. Its presence
in the extended atmospheres of evolved stars has been derived from optical
spectroscopy. More recently, AlO gas was also detected at long wavelengths
around the supergiant VY CMa and the oxygen-rich asymptotic giant branch (AGB)
star o Cet (Mira A). In search of AlO, we mined data obtained with APEX, the
IRAM 30m telescope, Herschel/HIFI, SMA, and ALMA, which were primarily aimed at
studying other molecular species. We report here on observations of AlO towards
a sample of eight oxygen-rich AGB stars in different rotational transitions, up
to seven for some stars. We present definite detections of one rotational
transition of AlO for o Cet and R Aqr, and tentative detections of one
transition for R Dor and o Cet, and two for IK Tau and W Hya. The presented
spectra of WX Psc, R Cas, and TX Cam show no signature of AlO. For o Cet, R
Aqr, and IK Tau, we find that the AlO(N=9-8) emission likely traces the inner
parts of the wind, out to only a few tens of AU, where the gas has not yet
reached its terminal velocity. The conclusive detections of AlO emission in the
case of o Cet and R Aqr confirm the presence of AlO gas in outflows of AGB
stars. The tentative detections further support this. Since most of the
observations presented in this study were obtained with stronger emission from
other species than AlO in mind, observations with higher sensitivity in
combination with high angular resolution will improve our understanding of the
presence and behaviour of AlO. From the current data sets we cannot firmly
conclude whether there is a direct correlation between the wind properties and
the detection rate of AlO emission. We hope that this study can serve as a
stimulus to perform sample studies in search of AlO in oxygen-rich outflows.Comment: 9 pages, 9 figures, Accepted for publication in Astronomy &
Astrophysic
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: II. Cep A & NGC 7538
We report trigonometric parallaxes for the sources NGC 7538 and Cep A,
corresponding to distances of 2.65 [+0.12/-0.11] kpc and 0.70 [+0.04/-0.04]
kpc, respectively. The distance to NGC 7538 is considerably smaller than its
kinematic distance and places it in the Perseus spiral arm. The distance to Cep
A is also smaller than its kinematic distance and places it in the Local arm or
spur. Combining the distance and proper motions with observed radial velocities
gives the location and full space motion of the star forming regions. We find
significant deviations from circular Galactic orbits for these sources: both
sources show large peculiar motions (> 10 km/s) counter to Galactic rotation
and NGC 7538 has a comparable peculiar motion toward the Galactic center.Comment: 21 pages, 8 figures; to appear in the Astrophysical Journa
Orion KL: The hot core that is not a "Hot Core"
We present sensitive high angular resolution submillimeter and millimeter
observations of torsionally/vibrationally highly excited lines of the CHOH,
HCN, SO, and CHCN molecules and of the continuum emission at 870
and 1300 m from the Orion KL region, made with the Submillimeter Array
(SMA). These observations plus recent SMA CO J=3-2 and J=2-1 imaging of the
explosive flow originating in this region, which is related to the
non-hierarchical disintegration of a massive young stellar system, suggest that
the molecular Orion "Hot Core" is a pre-existing density enhancement heated
from the outside by the explosive event -- unlike in other hot cores we do not
find any self-luminous submillimeter, radio or infrared source embedded in the
hot molecular gas. Indeed, we do not observe filamentary CO flow structures or
"fingers" in the shadow of the hot core pointing away from the explosion
center. The low-excitation CHCN emission shows the typical molecular
heart-shaped structure, traditionally named the Hot Core, and is centered close
to the dynamical origin of the explosion. The highest excitation CHCN lines
are all arising from the northeast lobe of the heart-shaped structure, {\it i.
e.} from the densest and most highly obscured parts of the Extended Ridge. The
torsionally excited CHOH and vibrationally excited HCN lines appear to
form a shell around the strongest submillimeter continuum source. Surprisingly
the kinematics of the Hot Core and Compact Ridge regions as traced by CHCN
and HCN also reveal filament-like structures that emerge from the dynamical
origin. All of these observations suggest the southeast and southwest sectors
of the explosive flow to have impinged on a pre-existing very dense part of the
Extended Ridge, thus creating the bright Orion KL Hot Core.Comment: Submitted to A&
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
Simulation of saltwater intrusion in the Minho river estuary under sea level rise scenarios
Estuaries are areas that are vulnerable to the impacts of climate change. Understanding how these impacts affect these complex environments and their uses is essential. This paper presents a work based on an analytical solution and 2DH and 3D versions of the Delft3D numerical model to simulate the Minho River estuary and its saline wedge length under climate change projections. Temperature observations at several locations in the estuary region were selected to determine which model better simulated the temperature patterns. Specific simulations were performed for the observation periods. Sixteen numerical model scenarios were proposed, considering a varying tide, different river flows, and several SLR projections based on the RCP4.5 and RCP8.5 for 2050 and 2100. The analytical solution was also calibrated using the numerical model solutions. The results show that although there is no relevant stratification, there was a difference in both models in which in the worst climate change scenario, the length of the saline intrusion increased up to 28 km in the 2DH model and 30 km in the 3D model. It was concluded that the 3D model results were more precise, but both configurations can provide insights into how the saline intrusion will be affected. Additionally, the excellent agreement between the analytical solution and the results of the numerical models allowed us to consider the analytical solution a helpful tool for practical applications. It was demonstrated that freshwater discharges and bed slopes are the most critical drivers for the saline intrusion length in the Minho River estuary as they have more impact than the increase in sea level. Therefore, flow regulation can be an excellent way to control saline intrusion in the future.NNI -Nortel Networks Inc(2022.07420
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