26 research outputs found
The rich molecular environment of the luminous blue variable star AFGL 2298
We investigated the molecular environment of AFGL 2298, an obscured Galactic
Luminous blue variable (LBV) star which hosts a highly structured circumstellar
environment with hints of multiple mass-loss events in the last few a.
We present spectral line observations of AFGL 2298 at 1 and 3 mm performed with
the IRAM 30m radio telescope. Furthermore, we report the detection of several
carbon- and nitrogen- bearing species (CO, CO, CO, CO,
HCO, HCN, HNC, HCO, CN, NH, and CH) in the
surroundings of AFGL 2298. In addition, we identified three velocity components
that clearly stand out from the Galactic background. The morphology,
kinematics, masses and isotopic ratios, together with a comparative study of
the fractional abundances, lead us to suggest that two of these components (36
and 70 km/s) have a stellar origin. The other component (46 km/s) most likely
traces swept-up interstellar material, probably harbouring also a
photon-dominated region. The first inventory of the circumstellar molecular gas
around AFGL 2298 is provided. The results are compatible with the hypothesis of
former mass-loss events, produced before the one that created the infrared
nebula. There are chemical hints of the presence of ejected stellar material,
and also swept up gas. These findings will help to better understand the
mass-loss history of this class of evolved massive stars, which heavily
influence the overall chemical evolution of the Galaxy.Comment: Accepted to Astronomy and Astrophysics. 15 pages, 4 tables, 11
figure
A warm molecular ring in AG Car: composing the mass-loss puzzle
We present APEX observations of CO J=3-2 and ALMA observations of CO J=2-1,
13CO J=2-1 and continuum toward the galactic luminous blue variable AG Car.
These new observations reveal the presence of a ring-like molecular structure
surrounding the star. Morphology and kinematics of the gas are consistent with
a slowly expanding torus located near the equatorial plane of AG Car. Using
non-LTE line modelling, we derived the physical parameters of the gas, which is
warm (50 K) and moderately dense (10 cm. The total mass of molecular
gas in the ring is 2.70.9 solar masses. We analysed the radio continuum
map, which depicts a point-like source surrounded by a shallow nebula. From the
flux of the point-like source, we derived a current mass-loss date of
solar masses / yr. Finally, to better understand the
complex circumstellar environment of AG Car, we put the newly detected ring in
relation to the main nebula of dust and ionised gas. We discuss possible
formation scenarios for the ring, namely, the accumulation of interstellar
material due to the action of the stellar wind, the remnant of a close binary
interaction or merger, and an equatorially enhanced mass-loss episode. If
molecular gas formed in situ as a result of a mass eruption, it would account
for at least a 30 of the total mass ejected by AG Car. This detection adds
a new piece to the puzzle of the complex mass-loss history of AG Car, providing
new clues about the interplay between LBV stars and their surroundings.Comment: 16 pages, 13 figures. Accepted for publication in MNRA
Classification of compact radio sources in the Galactic plane with supervised machine learning
Generation of science-ready data from processed data products is one of the
major challenges in next-generation radio continuum surveys with the Square
Kilometre Array (SKA) and its precursors, due to the expected data volume and
the need to achieve a high degree of automated processing. Source extraction,
characterization, and classification are the major stages involved in this
process. In this work we focus on the classification of compact radio sources
in the Galactic plane using both radio and infrared images as inputs. To this
aim, we produced a curated dataset of ~20,000 images of compact sources of
different astronomical classes, obtained from past radio and infrared surveys,
and novel radio data from pilot surveys carried out with the Australian SKA
Pathfinder (ASKAP). Radio spectral index information was also obtained for a
subset of the data. We then trained two different classifiers on the produced
dataset. The first model uses gradient-boosted decision trees and is trained on
a set of pre-computed features derived from the data, which include
radio-infrared colour indices and the radio spectral index. The second model is
trained directly on multi-channel images, employing convolutional neural
networks. Using a completely supervised procedure, we obtained a high
classification accuracy (F1-score>90%) for separating Galactic objects from the
extragalactic background. Individual class discrimination performances, ranging
from 60% to 75%, increased by 10% when adding far-infrared and spectral index
information, with extragalactic objects, PNe and HII regions identified with
higher accuracies. The implemented tools and trained models were publicly
released, and made available to the radioastronomical community for future
application on new radio data.Comment: 27 pages, 15 figures, 9 table
First Detection of Silicon-bearing Molecules in η Car
We present ALMA band 6 observations of the luminous blue variable η Car obtained within the ALMAGAL program. We report SiO J = 5 → 4, SiS J = 12 → 11, and SiN N = 5 → 4 emission in the equatorial region of the Homunculus nebula, constituting the first detection of silicon- and sulfur-bearing molecules in the outskirts of a highly evolved, early-type massive star. The SiO, SiS, and SiN trace a clumpy equatorial ring that surrounds the central binary at a projected distance of ∼2″, delineating the inner rims of the butterfly-shaped dusty region. The formation of silicon-bearing compounds is presumably related to the continuous recycling of dust due to the variable wind regime of η Car, which destroys grains and releases silicon back to the gas phase. We discuss possible formation routes for the observed species, contextualizing them within the current molecular inventory of η Car. We find that the SiO and SiS fractional abundances in localized clumps of the ring, 6.7 × 10−9 and 1.2 × 10−8, respectively, are exceptionally lower than those measured in C- and O-rich AGB stars and cool supergiants, while the higher SiN abundance, 3.6 × 10−8, evidences the nitrogen-rich chemistry of the ejecta. These abundances must be regarded as strict upper limits, since the distribution of H2 in the Homunculus is unknown. In any case, these findings shed new light on the peculiar molecular ecosystem of η Car and establish its surroundings as a new laboratory to investigate the life cycle of silicate dust in extreme astrophysical conditions
Evolutionary Map of the Universe (EMU): 18-cm OH-maser discovery in ASKAP continuum images of the SCORPIO field
Abstract Low- and intermediate-mass stars end their life dispersing their outer layers into the circumstellar medium, during the asymptotic and post-asymptotic giant branch phases. OH masers at 18 cm offer an effective way to probe their circumstellar environment. In this work we present the discovery of seven OH maser sources likely associated with such evolved stars from the visual inspection of ASKAP continuum images. These seven sources do not emit real continuum emission, but the high sensitivity of our images allows us to detect their maser emission, resembling continuum sources. To confirm their nature, we carried out spectral-line observations with ATCA. All the sources showed the double-peaked spectra at 1612 MHz, typical of evolved stars. The detection of maser emission in continuum images can be a complementary and easy-to-use method to discover new maser sources with the large-area deep surveys conducted with the SKA precursors. The implication for radio stars studies are remarkable since pure OH maser sources (i.e. with no continuum associated) represent, at a sensitivity of , about 4 percent of all Galactic sources and by far the most numerous stellar population.</jats:p
A first glimpse at the Galactic plane with the ASKAP: the SCORPIO field
In the broad context of the Australian Square Kilometer Array Pathfinder (ASKAP) early-science phase and preparation for the related surveys, we report the first radio observations towards the Galactic plane. The targeted field was chosen to encompass the entire SCORPIO survey, one of the several pathfinder projects for the Evolutionary Map of the Universe survey planned with the ASKAP. The observations were carried out in 2018 January at a central frequency of 912 MHz, with 15 operational antennas, and covered a total area of about 40 square degrees in three different pointings. The final image has a resolution of 24.1 × 21.1 arcsec2 and a median rms of 541 μJy beam−1. We were able to extract 3545 candidate sources, 75 per cent of them point sources. For a preliminary validation, a comparison with the 843 MHz Molonglo Galactic Plane Survey is presented. Although the present observations were obtained with the ASKAP only partially deployed, its unique capability to map complex sources, such as those inhabiting the Galactic plane, at different angular scales, is highlighted. Within the SCORPIO field all the previously classified H II regions, Planetary Nebulae (PNe), and supernovae remnants (SNRs), previously known to be radio sources, were detected. We also report new radio detections from several H II regions previously classified as ‘candidates’ or ‘radio quiet’ and from half of all the PNe in the SCORPIO field with robust classification. Most notably, we find numerous unclassified, extended sources which constitute a promising sample of candidates H II regions and SNRs
Discovery and origin of the radio emission from the multiple stellar system KQ Vel
KQVel is a binary system composed of a slowly rotating magnetic Ap star with
a companion of unknown nature. In this paper, we report the detection of its
radio emission. We conducted a multi-frequency radio campaign using the ATCA
interferometer (band-names: 16cm, 4cm, and 15mm). The target was detected in
all bands. The most obvious explanation for the radio emission is that it
originates in the magnetosphere of the Ap star, but this is shown unfeasible.
The known stellar parameters of the Ap star enable us to exploit the scaling
relationship for non-thermal gyro-synchrotron emission from early-type magnetic
stars. This is a general relation demonstrating how radio emission from stars
with centrifugal magnetospheres is supported by rotation. Using KQVel's
parameters the predicted radio luminosity is more than five orders of
magnitudes lower than the measured one. The extremely long rotation period
rules out the Ap star as the source of the observed radio emission. Other
possible explanations for the radio emission from KQVel, involving its unknown
companion, have been explored. A scenario that matches the observed features
(i.e. radio luminosity and spectrum, correlation to X-rays) is a hierarchical
stellar system, where the possible companion of the magnetic star is a close
binary (possibly of RSCVn type) with at least one magnetically active late-type
star. To be compatible with the total mass of the system, the last scenario
places strong constraints on the orbital inclination of the KQVel stellar
system
The SARAO MeerKAT 1.3 GHz Galactic Plane Survey
We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half of the Galactic Plane (251\deg 358\deg and 2\deg 61\deg at ). SMGPS is the largest, most sensitive and highest angular resolution 1 GHz survey of the Plane yet carried out, with an angular resolution of 8" and a broadband RMS sensitivity of 10--20 Jy/beam. Here we describe the first publicly available data release from SMGPS which comprises data cubes of frequency-resolved images over 908--1656 MHz, power law fits to the images, and broadband zeroth moment integrated intensity images. A thorough assessment of the data quality and guidance for future usage of the data products are given. Finally, we discuss the tremendous potential of SMGPS by showcasing highlights of the Galactic and extragalactic science that it permits. These highlights include the discovery of a new population of non-thermal radio filaments; identification of new candidate supernova remnants, pulsar wind nebulae and planetary nebulae; improved radio/mid-IR classification of rare Luminous Blue Variables and discovery of associated extended radio nebulae; new radio stars identified by Bayesian cross-matching techniques; the realisation that many of the largest radio-quiet WISE HII region candidates are not true HII regions; and a large sample of previously undiscovered background HI galaxies in the Zone of Avoidance
The SARAO MeerKAT 1.3 GHz Galactic Plane Survey
We present the SARAO MeerKAT Galactic Plane Survey (SMGPS), a 1.3 GHz continuum survey of almost half of the Galactic Plane (251○ ≤l ≤ 358○ and 2○ ≤l ≤ 61○ at |b| ≤ 1
5). SMGPS is the largest, most sensitive and highest angular resolution 1 GHz survey of the Plane yet carried out, with an angular resolution of 8″ and a broadband RMS sensitivity of ∼10–20 μJy beam−1. Here we describe the first publicly available data release from SMGPS which comprises data cubes of frequency-resolved images over 908–1656 MHz, power law fits to the images, and broadband zeroth moment integrated intensity images. A thorough assessment of the data quality and guidance for future usage of the data products are given. Finally, we discuss the tremendous potential of SMGPS by showcasing highlights of the Galactic and extragalactic science that it permits. These highlights include the discovery of a new population of non-thermal radio filaments; identification of new candidate supernova remnants, pulsar wind nebulae and planetary nebulae; improved radio/mid-IR classification of rare Luminous Blue Variables and discovery of associated extended radio nebulae; new radio stars identified by Bayesian cross-matching techniques; the realisation that many of the largest radio-quiet WISE H II region candidates are not true H II regions; and a large sample of previously undiscovered background H I galaxies in the Zone of Avoidance