1,722,624 research outputs found
Methanol observation of IRAS 19312+1950: A possible new type of class I methanol maser
Get PDFWe report the result of a systematic methanol observation toward IRAS 19312+1950. The properties of the SiO, H2O, and OH masers of this object are consistent with those of mass-losing evolved stars, but some other properties are difficult to explain in the standard scheme of stellar evolution in its late stage. Interestingly, a tentative detection of radio methanol lines was suggested toward this object by a previous observation. To date, there are no confirmed detections of methanol emission towards evolved stars, so investigation of this possible detection is important to better understand the circumstellar physical/chemical environment of IRAS 19312+1950. In this study, we systematically observed multiple methanol lines of IRAS 19312+1950 in the λ = 3 mm, 7 mm, and 13 mm bands, and detected six lines including four thermal lines and two class I maser lines. We derived basic physical parameters, including kinetic temperature and relative abundances, by fitting a radiative transfer model. According to the derived excitation temperature and line profiles, a spherically expanding outflow lying at the center of the nebulosity is excluded from the possibilities for methanol emission regions. The detection of class I methanol maser emission suggests that a shock region is involved in the system of IRAS 19312+1950. If the central star of IRAS 19312+1950 is an evolved star as suggested in the past, the class I maser detected in the present observation is the first case detected in an interaction region between an evolved star outflow and ambient molecular gas. © The Author 2015. Published by Oxford University Press on behalf of the Astronomical Society of Japan
Molecules in the peculiar age-defying source IRAS 19312+1950
Get PDFContext. IRAS 19312+1950 is an isolated infrared source that exhibits a
characteristic quasi-point-symmetric morphology in the near- and mid-infrared
images and is also very bright in molecular radio lines. Because of its unique
observational characteristics, various observational studies have been
conducted and several hypotheses have been proposed regarding its origin, which
is still unclear. So far, it has been suggested that it could be a peculiar
evolved star, a young stellar object, or even a red nova remnant. Regardless of
which type of object it is ultimately classified as, IRAS 19312+1950 is
exceptionally bright in the infrared and molecular radio lines and therefore
will undoubtedly be crucial as a prototype of this kind of object having a
peculiar nature or unusual evolutionary phase.
Aims. This study aims to reveal the molecular composition of the central part
of IRAS 19312+1950 by performing an unbiased molecular radio line survey and
discussing the origin of the object from a molecular chemical point of view.
Methods. We carried out a spectral line survey with the IRAM 30 m telescope
towards the center of IRAS 19312+1950 in the 3 and 1.3 mm windows.
Results. In total, 28 transition lines of 22 molecular species and those
isotopologues are detected towards IRAS 19312+1950, some of which exhibit a
broad and a narrow components. Seventeen thermal lines and 1 maser line are
newly detected. The molecular species of CO, SiO, HNC,
HCO, HCO, and -CH are detected for the first
time in this object.
Conclusions. Our results, in combination with previous studies, favor the
hypothesis that IRAS 19312+1950 might be a red nova remnant, in which the
progenitors that merged to become a red nova may have contained at least two
evolved stars with oxygen-rich and carbon-rich chemistry, respectively.Comment: 30 pages, 24 figures, accepted for publication in A&
Maser properties of the enigmatic IRAS source 19312+1950
No full textThe IRAS source, 19312+1950, exhibits SiO maser emission, which is predominantly detected in evolved stars enshrouded by a cold molecular envelope. In fact, the majority of the observational properties of IRAS 19312+1950 are consistent with the nature of an asymptotic giant branch (AGB) star or post-AGB star. Interestingly, however, some of the observational properties cannot be readily explained within the standard scheme of stellar evolution, and those are rather reminiscent of young stellar objects. In the present research, we considered the evolutionary status of IRAS 19312+1950 as revealed by the very long baseline interferometry and MERLIN observations in SiO, H 2O, and OH maser lines. The double-peaked profile of the 22 GHz H 2O maser line is clearly detected, with the emission regions of its redshifted and blueshifted components separately located, leaving a space of about 10.9 mas between them. The kinematic properties of the H 2O maser emission region appear to be more consistent with a bipolar flow rather than other interpretations such as the Keplerian rotation of a disk. The redshifted component of the SiO maser emission, which exhibits a double-peak profile in previous single-dish observations, is clearly detected in the present interferometry, while the 1612 MHz OH maser line exhibits a complicated line profile consisting of a single strong peak and many weak, high-velocity spikes. The structure of the OH maser emission region is partially resolved, and the kinematic properties of the OH maser emission region are observations reminiscent of a spherically expanding shell, even though the evidence is scant. Collectively, the maser observations described here provide additional support for the evolved star hypothesis for IRAS 19312+1950. © 2011. The American Astronomical Society.link_to_subscribed_fulltex
Molecular line observations of the SiO maser source IRAS 19312+1950
No full textIRAS 19312+1950 is a unique SiO maser source, exhibiting a rich set of molecular radio lines, although SiO maser sources are usually identified as oxygen-rich evolved stars, in which chemistry is relatively simple comparing with carbon-rich environments. The rich chemistry of IRAS 19312+1950 has raised a problem in circumstellar chemistry if this object is really an oxygen-rich evolved star, but its evolutional status is still controversial. In this paper, we briefly review the previous observations of IRAS 19312+1950, as well as presenting preliminary results of recent VLBI observations in maser lines. PDF file of the poster is available from http://www.geocities.jp/nakashima_junichi/. © 2008 International Astronomical Union.link_to_subscribed_fulltex
Near-infrared polarimetric study of the bipolar nebula IRAS 19312+1950
No full textAims. We have investigated the properties of the central star and dust in the bipolar nebula IRAS 19312+1950, which is an unusual object showing the characteristics of a supergiant, a young stellar object, and an asymptotic giant branch (AGB) star. Methods. We obtained H-band Polarimetric data of IRAS 19312+1950 using the near-infrared camera (CIAO) on the 8 m Subaru telescope. In order to investigate the physical properties of the central star and the nebula, we performed radiative transfer modeling and compared the model results with the observed spectral energy distributions (SEDs), the radial profiles of the total intensity image, and the fraction of linear polarization map. Results. The total intensity image shows a nearly spherical core with ∼3″ radius, an S-shaped arm extending ∼10″ in the northwest to southeast direction, and an extended lobe towards the southwest. The polarization map shows a centro-symmetric vector alignment in almost the entire nebula and low polarizations along the S-shaped arm. These results suggest that the nebula is accompanied by a central star, and the S-shaped arm has a physically ring-like structure. From our radiative transfer modeling, we estimated the stellar temperature, the bolometric luminosity, and the current mass-loss rate to be 2800 K, 7000 L⊙, and 5.3 × 10-6 M ⊙ yr-1, respectively. Conclusions. Taking into account previous observational results, such as the detection of SiO maser emissions and silicate absorption feature in the 10 μm spectrum, our dust radiative transfer analysis based on our near-infrared imaging polarimetry suggests that (1) the central star of IRAS 19312+1950 is likely to be an oxygen-rich, dust-enshrouded AGB star and (2) most of the circumstellar material originates from other sources (e.g. ambient dark clouds) rather than being a result of mass loss from the central star. © ESO 2007.link_to_subscribed_fulltex
The magnetically-active, low-mass, triple system WDS 19312+3607
Get PDFAims. We investigated in detail the system WDS 19312+3607, whose primary is an active M4.5Ve star previously inferred to be young (τ ~ 300–500 Ma) based on
its high X-ray luminosity.
Methods. We collected intermediate- and low-resolution optical spectra taken with
2 m-class telescopes, photometric data from the B to 8 μm bands, and
data for eleven astrometric epochs with a time baseline of over 56 years for
the two components in the system, G 125–15 and G 125–14.
Results. We derived the M4.5V spectral types of both stars, confirmed their common
proper motion, estimated their heliocentric distance and projected physical
separation, determined their Galactocentric space velocities, and deduced a
most-probable age of older than 600 Ma.
We discovered that the primary, G 125–15, is an inflated, double-lined,
spectroscopic binary with a short period of photometric variability of
1.6 d, which we associated with orbital synchronisation.
The observed X-ray and Hα emissions, photometric variability, and
abnormal radius and effective temperature of G 125–15 AB are indicative of
strong magnetic activity, possibly because of the rapid rotation.
In addition, the estimated projected physical separation between G 125–15 AB
and G 125–14 of about 1200 AU ensures that WDS 19312+3607 is one of the widest
systems with intermediate M-type primaries.
Conclusions. G 125–15 AB is a nearby (d ≈ 26 pc), bright (J ≈ 9.6 mag), active spectroscopic binary with a single proper-motion companion of the same spectral type at a wide separation.
They are thus ideal targets for specific follow-ups to investigate wide and close multiplicity or stellar expansion and surface cooling because of the lower convective efficiency
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
On the Nature of the Enigmatic Object IRAS 19312+1950: A Rare Phase of Massive Star Formation?
Get PDFIRAS 19312+1950 is a peculiar object that has eluded firm characterization since its discovery, with combined maser properties similar to an evolved star and a young stellar object (YSO). To help determine its true nature, we obtained infrared spectra of IRAS 19312+1950 in the range 5–550 μm using the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a compact, slightly asymmetric continuum source at 170 μm, indicative of a large, dusty circumstellar envelope. The far-IR CO emission line spectrum reveals two gas temperature components: ≈0.22 solar masses of material at 280 ± 18 K, and ≈1.6 solar masses of material at 157 ± 3 K. The O i 63 μm line is detected on-source but no significant emission from atomic ions was found. The HIFI observations display shocked, high-velocity gas with outflow speeds up to 90 km/s along the line of sight. From Spitzer spectroscopy, we identify ice absorption bands due to H2O at 5.8 μm and CO2 at 15 μm. The spectral energy distribution is consistent with a massive, luminous (~2 × 10^4 solar luminosities) central source surrounded by a dense, warm circumstellar disk and envelope of total mass ~500–700 solar masses, with large bipolar outflow cavities. The combination of distinctive far-IR spectral features suggest that IRAS 19312+1950 should be classified as an accreting, high-mass YSO rather than an evolved star. In light of this reclassification, IRAS 19312+1950 becomes only the fifth high-mass protostar known to exhibit SiO maser activity, and demonstrates that 18 cm OH maser line ratios may not be reliable observational discriminators between evolved stars and YSOs
- …
