| 1. |
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| 2. |
- Biver, N., et al.
(author)
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Radio observations of Comet 9P/Tempel 1 before and after Deep Impact
- 2007
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In: Icarus. - : Elsevier BV. - 1090-2643 .- 0019-1035. ; 191:2, s. 494-512
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Journal article (peer-reviewed)abstract
- Comet 9P/Tempel 1 was the target of a multi-wavelength worldwide investigation in 2005. The NASA Deep Impact mission reached the comet on 4.24 July 2005, delivering a 370-kg impactor which hit the comet at 10.3 km s -1 . Following this impact, a cloud of gas and dust was excavated from the comet nucleus. The comet was observed in 2005 prior to and after the impact, at 18-cm wavelength with the Nançay radio telescope, in the millimeter range with the IRAM and CSO radio telescopes, and at 557 GHz with the Odin satellite. OH observations at Nançay provided a 4-month monitoring of the outgassing of the comet from March to June, followed by the observation of H 2 O with Odin from June to August 2005. The peak of outgassing was found to be around 1 × 10 28 molec. s -1 between May and July. Observations conducted with the IRAM 30-m radio telescope in May and July 2005 resulted in detections of HCN, CH 3 OH and H 2 S with classical abundances relative to water (0.12, 2.7 and 0.5%, respectively). In addition, a variation of the HCN production rate with a period of 1.73 ± 0.10 days was observed in May 2005, consistent with the 1.7-day rotation period of the nucleus. The phase of these variations, as well as those of CN seen in July by Jehin et al. [Jehin, E., Manfroid, J., Hutsemékers, D., Cochran, A.L., Arpigny, C., Jackson, W.M., Rauer, H., Schulz, R., Zucconi, J.-M., 2006. Astrophys. J. 641, L145-L148], is consistent with a rotation period of the nucleus of 1.715 days and a strong variation of the outgassing activity by a factor 3 from minimum to maximum. This also implies that the impact took place on the rising phase of the "natural" outgassing which reached its maximum ≈4 h after the impact. Post-impact observations at IRAM and CSO did not reveal a significant change of the outgassing rates and relative abundances, with the exception of CH 3 OH which may have been more abundant by up to one order of magnitude in the ejecta. Most other variations are linked to the intrinsic variability of the comet. The Odin satellite monitored nearly continuously the H 2 O line at 557 GHz during the 38 h following the impact on the 4th of July, in addition to weekly monitoring. Once the periodic variations related to the nucleus rotation are removed, a small increase of outgassing related to the impact is present, which corresponds to the release of ≈ 5000 ± 2000 tons of water. Two other bursts of activity, also observed at other wavelengths, were seen on 23 June and 7 July; they correspond to even larger releases of gas. © 2006 Elsevier Inc. All rights reserved.
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| 3. |
- Biver, N., et al.
(author)
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Radio observations of Comet 9P/Tempel 1 before and after Deep Impact
- 2007
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In: Icarus. - : Elsevier BV. - 1090-2643 .- 0019-1035. ; 187:1, s. 253-271
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Journal article (peer-reviewed)abstract
- Comet 9P/Tempel 1 was the target of a multi-wavelength worldwide investigation in 2005. The NASA Deep Impact mission reached the comet on 4.24 July 2005, delivering a 370-kg impactor which hit the comet at 10.3 km s -1 . Following this impact, a cloud of gas and dust was excavated from the comet nucleus. The comet was observed in 2005 prior to and after the impact, at 18-cm wavelength with the Nançay radio telescope, in the millimeter range with the IRAM and CSO radio telescopes, and at 557 GHz with the Odin satellite. OH observations at Nançay provided a 4-month monitoring of the outgassing of the comet from March to June, followed by the observation of H 2 O with Odin from June to August 2005. The peak of outgassing was found to be around 1 × 10 28 molec. s -1 between May and July. Observations conducted with the IRAM 30-m radio telescope in May and July 2005 resulted in detections of HCN, CH 3 OH and H 2 S with classical abundances relative to water (0.12, 2.7 and 0.5%, respectively). In addition, a variation of the HCN production rate with a period of 1.73 ± 0.10 days was observed in May 2005, consistent with the 1.7-day rotation period of the nucleus. The phase of these variations, as well as those of CN seen in July by Jehin et al. [Jehin, E., Manfroid, J., Hutsemékers, D., Cochran, A.L., Arpigny, C., Jackson, W.M., Rauer, H., Schulz, R., Zucconi, J.-M., 2006. Astrophys. J. 641, L145-L148], is consistent with a rotation period of the nucleus of 1.715 days and a strong variation of the outgassing activity by a factor 3 from minimum to maximum. This also implies that the impact took place on the rising phase of the "natural" outgassing which reached its maximum ≈4 h after the impact. Post-impact observations at IRAM and CSO did not reveal a significant change of the outgassing rates and relative abundances, with the exception of CH 3 OH which may have been more abundant by up to one order of magnitude in the ejecta. Most other variations are linked to the intrinsic variability of the comet. The Odin satellite monitored nearly continuously the H 2 O line at 557 GHz during the 38 h following the impact on the 4th of July, in addition to weekly monitoring. Once the periodic variations related to the nucleus rotation are removed, a small increase of outgassing related to the impact is present, which corresponds to the release of ≈ 5000 ± 2000 tons of water. Two other bursts of activity, also observed at other wavelengths, were seen on 23 June and 7 July; they correspond to even larger releases of gas. © 2006 Elsevier Inc. All rights reserved.
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| 4. |
- Brand, J., et al.
(author)
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Patterns in water maser emission of evolved stars on the timescale of decades
- 2022
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In: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 18, s. 319-323
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Conference paper (peer-reviewed)abstract
- We present our past and current long-term monitoring program of water masers in the circumstellar envelopes of evolved stars, augmented by occasional interferometric observations. Using as example the Mira-variable U Her, we identify three types of variability: periodic (following the optical variation), long-term (years-decades) and short-term irregular (weeks-months). We show there are regions in the maser shell where excitation conditions are favourable, which remain stable for many years. Lifetimes of maser clouds in the wind-acceleration zone are of the order of up to a few years. Much longer lifetimes are found for the peculiar case of a maser cloud outside that zone (as in RT Vir), or in some cases where the motion of spectral features can be followed for the entire 2 decade monitoring period (as in red supergiant VX Sgr).
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| 5. |
- Brand, J., et al.
(author)
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Water vapour masers in long-period variable stars: II. The semi-regular variables R Crt and RT Vir
- 2020
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 644
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Journal article (peer-reviewed)abstract
- Context. Water masers emitting at a radiofrequency of 22 GHz are often found in the circumstellar envelopes of evolved stars. We monitored the H2O maser emission of a larger sample of evolved stars of different types to study the maser properties as a function of stellar type. Aims. We wish to understand the origin and evolution of the H2O masers in circumstellar envelopes. In this paper, we take a closer look at R Crt and RT Vir, two nearby (
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| 6. |
- Crovisier, J., et al.
(author)
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The chemical composition of 9P/tempel 1 from radio observations
- 2009
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In: ESO Astrophysics Symposia. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1431-2433 .- 1611-6143. - 9783540769583 ; 2009, s. 243-248
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Conference paper (peer-reviewed)abstract
- In 2005, as part of a world-wide multi-wavelength investigation of comet 9P/Tempel 1 in support to the Deep Impact mission, we conducted radio spectroscopic observations with the Nançay radio telescope, the Odin satellite, the CSO 10-m and the IRAM 30-m telescopes. We report here our results concerning the chemical composition of the comet. The relative abundances of the detected species (H2O, CH3OH, H2S, HCN) or their upper limits (CO, H2CO, CS) are comparable to the mean values observed in other comets. No significant changes of the outgassing rates (except possibly for CH3OH) or of the molecular abundances were observed following the impact.
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| 7. |
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| 8. |
- Engels, D., et al.
(author)
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Variability of masers in circumstellar shells on timescales of decades
- 2007
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In: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 3:S242, s. 318-319
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Conference paper (peer-reviewed)abstract
- Based on a 15-20 year long monitoring program of H2O masers and new observations of OH masers discovered 35 years ago, we studied the variability of maser emission in AGB stars over timescales of decades. The H2O maser features in the semi-regular variable stars RX Boo and SV Peg, and of the Mira stars U Her and R Cas, showed strong fluctuations superposed in case of the Mira stars on regular variations due to the pulsation of the stars. The spatial distribution of the emission regions in RX Boo and U Her showed deviations from spherical symmetry, which remained unchanged over >10 years. We conclude that the spatial asymmetry is determined by the underlying asymmetry of the mass loss process. There is no evidence that mass loss rates or the wind geometry in these stars have varied over the last 20 years. In 2005 we re-detected at 1612 MHz the 114 OH/IR stars discovered before 1978, implying an OH maser lifetime of >2800 years (1). © 2008 International Astronomical Union.
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| 9. |
- Forkman, Peter, 1959, et al.
(author)
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Longest continous ground-based measurements of mesospheric CO
- 2003
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In: Geophysical Research Letters. - 1944-8007 .- 0094-8276. ; 30:10
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Journal article (peer-reviewed)abstract
- The longest continuous series of ground-based measurements of mesospheric CO is presented. The continuous data cover the period September 2000 to September 2002. Sporadic measurements from 1988 and 1989 are also reported. The results show a large CO accumulation in the winter mesosphere, which is consistent with generally accepted ideas about the seasonally-varying mean meridional circulation. Comparison of the observations with simulations by the Whole Atmosphere Community Climate Model (WACCM) indicate that the model can reproduce the observed seasonal cycle as well as much of its variability, although calculated columns amounts are smaller than the largest values seen in the data.
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| 10. |
- Forkman, Peter, 1959, et al.
(author)
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The 22 GHz radio-aeronomy receiver at Onsala Space Observatory
- 2003
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In: Journal of Quantitative Spectroscopy and Radiative Transfer. - 0022-4073. ; 77:1, s. 23-42
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Journal article (peer-reviewed)abstract
- We present a radiometer system for regular long-term measurements of water vapour in the middle atmosphere. To be able to do continuous and long-term measurements a simple, robust, reliable and automatic system is needed. Our system therefore is based on a stable, uncooled, HEMT amplifier frontend and on a digital spectrometer backend. In order to minimise reflections in the frontend transmission line, which distort the signal due to standing waves, we have designed a corrugated receiver horn, which combines good characteristics (low return loss and sidelobes) and narrow beamwidth to simplify the receiver optics. In order to make the radiometer system as simple as possible, we use the sky as the calibration cold load. This is possible since we use the observed brightness temperatures of an already existing broadband dual-channel 21.0/31.4-GHz radiometer, at the observation site, to estimate the brightness temperature of the sky at . However, we have developed a calibration method, which makes it possible to estimate the sky brightness temperature even if we cannot use the dual-channel radiometer. Despite new measurements, which became available in recent years, the determination of middle atmospheric water vapour distribution still remains a challenge due to the fact that there is a large dispersion among the different measurement methods and data sets, which are obtained on a sparse and sporadic basis. This is the reason why several instruments similar to ours currently are developed in Europe.
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| 11. |
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| 12. |
- Kalenskii, S.V., et al.
(author)
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Class I methanol masers in regions of low-mass star formation
- 2007
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In: Proceedings of "Millimeter wave astronomy and star formation", ed. I. Zinchenko, Nizhny Novgorod, Russia, August 2007, Inst. of Applied Physics RAS. ; , s. 10-14
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Conference paper (other academic/artistic)
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| 13. |
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| 14. |
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| 15. |
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- Karlsson, R., et al.
(author)
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Hydroxyl, water, ammonia, carbon monoxide and neutral carbon towards the Sgr A complex: VLA, Odin and SEST observations
- 2013
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 554
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Journal article (peer-reviewed)abstract
- Aims. The Sagittarius A complex in the Galactic centre comprises an ensemble of molecular clouds of different species with a variety of geometrical and kinematic properties. This work aims to study molecular abundances, morphology, and kinematics by comparing hydroxyl, water, carbon monoxide, ammonia, and atomic carbon and some of their isotopologues, in the +50 km s-1 cloud, the circumnuclear disk (CND), the +20 km s-1 cloud, the expanding molecular ring and the line-of-sight spiral arm features, including the Local/Sgr arm, the −30 km s-1 arm, and the 3-kpc arm.Methods. We observed the +50 km s-1 cloud, the CND and the +20 km s-1 cloud, and other selected positions at the Galactic centre with the VLA, and the Odin satellite. The VLA was used to map the 1665 and 1667 MHz OH lambda doublet main lines of the (2Π3/2) state, and the Odin satellite was used to map the 557 GHz H2O (110 − 101) line as well as to observe the 548 GHz H218O (110-101) line, the 572 GHz NH3 (10 − 00) line, the 576 GHz CO J = 5 − 4 line and the 492 GHz C i (3P1–3P0) line. Furthermore, the SEST was used to map a region of the Sgr A complex in the 220 GHz C18O J = 2−1 line.Results. Strong OH absorption, H2O emission and absorption lines were seen at all observed positions, and the H218O line was detected in absorption towards the +50 km s-1 cloud, the CND, the +20 km s-1cloud, the expanding molecular ring, and the 3-kpc arm. Strong CO J = 5−4, C18O J = 2−1, and neutral carbon C i emissions were seen towards the +50 and +20 km s-1 clouds. NH3 was only detected in weak absorption originating in the line-of-sight spiral arm features. The abundances of OH and H2O in the +50 and +20 km s-1 clouds reflect the different physical environments in the clouds, where shocks and star formation prevail in the +50 km s-1 cloud and giving rise to a higher rate of H2O production there than in the +20 km s-1 cloud. In the CND, cloud collisions and shocks are frequent, and the CND is also subject to intense UV-radiation emanating from the supermassive black hole and the central star cluster. The CND is rich in H2O and OH, and these abundances are considerably higher than in the +50 and +20 km s-1 clouds. We compare our estimated abundances of OH, H2O, and NH3 with similar and differing results for some other sources available in the literature. As compared to the quiescent cloud values of a few × 10-9, or lower, the H2O abundance is markedly enhanced in the front sides of the Sgr A molecular cloud cores, (2−7) × 10-8, as observed in absorption, and highest in the CND. A similar abundance enhancement is seen in OH. The likely explanation is PDR chemistry including grain surface reactions, and perhaps also the influence of shocks. In the redward high-velocity line wings of the +50 and +20 km s-1 clouds and the CND, the H2O abundances are estimated to be (1−6) × 10-6 or higher, i.e., similar to the water abundances in outflows of the Orion KL and DR21 molecular clouds, which are said to be caused by the combined action of shock desorption from icy grain mantles and high-temperature, gas-phase shock chemistry.
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| 20. |
- Larsson, Bengt, et al.
(author)
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Molecular oxygen in the rho Ophiuchi cloud
- 2007
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In: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 466:3, s. 5-
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Journal article (peer-reviewed)abstract
- Context: Molecular oxygen, O2, has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission.Aims: The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. Methods: The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core ρ Oph A was observed with Odin for 34 days during several observing runs.Results: We detect a spectral line at v_LSR =+3.5 km s-1 with Δ v_FWHM=1.5 km s-1, parameters which are also common to other species associated with ρ Oph A. This feature is identified as the O2 (NJ = 11 - 1_0) transition at 118 750.343 MHz.Conclusions: The abundance of molecular oxygen, relative to H{2} , is 5 × 10-8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits.Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Étude Spatiale (CNES). The Swedish Space Corporation has been the industrial prime contractor and also is operating the satellite. Appendix A is only available in electronic form at http://www.aanda.org
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| 21. |
- Olofsson, Henrik, 1972, et al.
(author)
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CO line observations of OH/IR stars in the inner Galactic Bulge: Characteristics of stars at the tip of the AGB
- 2022
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 665
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Journal article (peer-reviewed)abstract
- Context. OH/IR stars are examples of late stellar evolution on the asymptotic giant branch (AGB), and they are, as such, important objects to study. They are also excellent probes of stellar populations, in particular in regions of high interstellar extinction such as the central regions of our Galaxy. Aims. Our goal is to characterise the stellar and circumstellar properties of high-mass-loss-rate OH/IR stars in the inner Galactic Bulge using the Atacama Large Millimeter/submillimeter Interferometer (ALMA). Methods. Rotational lines of (CO)-C-12 and (CO)-C-13, as well as a millimetre-wave continuum, have been observed for a sample of 22 OH/IR stars in directions within 2 degrees of the Galactic Centre. Photometry data (approximate to 1-30 mu m) have been gathered from the literature to construct spectral energy distributions (SEDs) and to determine pulsational variability. Radiative transfer models have been used to interpret the line and photometry data. Results. All stars in the sample were detected in at least one CO line, and eight objects were detected in 324 GHz continuum. Based on luminosity criteria, the sample is divided into 17 objects that most likely lie within the inner Galactic Bulge, and five objects that are most likely foreground objects. The median luminosity of the inner-Galactic-Bulge sub-sample, 5600 L-circle dot, corresponds to an initial mass in the range 1.2-1.6 M-circle dot, indicating that these inner-Galactic-Bulge OH/IR stars descend from solar-type stars. The objects in this sub-sample are further divided into two classes based on their SED characteristics: Eleven objects have SEDs that are well matched by models invoking dust envelopes extending from a few stellar radii and outwards, while six objects are better modelled as having detached dust envelopes with inner radii in the range 200-600 au and warmer central stars. The former objects have periodic variability, while the latter objects are predominantly non-periodic. The median gas-mass-loss rate, gas terminal expansion velocity, gas-to-dust mass ratio, and circumstellar (CO)-C-12/(CO)-C-13 abundance ratio have been estimated to be 2 x 10(-5) M-circle dot yr(-1), 18 km s(-1), 200 (excluding the sources with detached dust envelopes, which show markedly lower gas-to-dust ratios), and 5, respectively, for the inner-Galactic-Bulge sub-sample. All line brightness distributions are resolved at an angular scale of approximate to 0 ''.15, but only two objects show a structure in their circumstellar envelopes at our resolution and sensitivity. In both cases, this structure takes the form of a cavity and a bipolar morphology. Conclusions. The inner-Galactic-Bulge sub-sample consists of high mass-loss-rate stars that descend from solar-type progenitors and that lie near the tip of the AGB. Some of the sample stars may have recently ceased mass loss and, hence, have begun to evolve beyond the AGB, as evidenced by a change in circumstellar characteristics and indications of warmer central stars. The inferred very low stellar C-12/C-13 isotope ratios are indicative of CNO-cycle nuclear processing, and they are most likely established at the surfaces of the stars during the first dredge-up on the red giant branch since these stars are not expected to experience hot-bottom burning. The inner-Galactic-Bulge OH/IR stars studied here constitute an excellent sample of equidistant objects for the purpose of understanding the evolution of the mass-loss-rate characteristics at the tip of the AGB.
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| 22. |
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| 23. |
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| 24. |
- Winnberg, Anders, 1937
(author)
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How does the Galactic Bulge rotate?
- 2003
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In: Mass-losing pulsating stars and their circumstellar matter; eds. Y. Nakada, M. Honma and M. Seki. ; Astrophysics and Space Science Library, Vol. 283, s. 367-371
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Journal article (other academic/artistic)
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| 25. |
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| 26. |
- Winnberg, Anders, 1937, et al.
(author)
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Water vapour masers in long-period variable stars: III. Mira variables U Her and RR Aql
- 2024
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 686
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Journal article (peer-reviewed)abstract
- Context. Water maser emission is often found in the circumstellar envelopes of evolved stars, that is, asymptotic giant branch stars and red supergiants with oxygen-rich chemistry. The H2O emission shows strong variability in evolved stars of both of these types. Aims. We wish to understand the reasons for the strong variability of water masers emitted at 22 GHz. In this paper, we study U Her and RR Aql as representatives of Mira variable stars. Methods. We monitored UHer and RRAql in the 22 GHz maser line of water vapour with single-dish telescopes. The monitoring period covered about two decades between 1990 and 2011, with a gap between 1997 and 2000 in the case of RRAql. Observations were also made in 1987 and 2015 before and after the period of contiguous monitoring. In addition, maps of UHer were obtained in the period 1990-1992 with the Very Large Array. Results. We find that the strongest emission in UHer is located in a shell with boundaries of 11-25 AU. The gas-crossing time is 8.5 yr. We derive lifetimes for individual maser clouds of ≤4 yr based on the absence of detectable line-of-sight velocity drifts of the maser emission. The shell is not evenly filled, and its structure is maintained over much longer timescales than those of individual maser clouds. Both stars show brightness variability on several timescales. The prevalent variation is periodic, following the optical variability of the stars with a lag of 2-3 months. Superposed are irregular fluctuations of a few months in duration, with increased or decreased excitation at particular locations, and long-Term systematic variations on timescales of a decade or more. Conclusions. The properties of the maser emission are governed by those of the stellar wind while traversing the H2O maser shell. Inhomogeneities in the wind affecting the excitation conditions and prevalent beaming directions likely cause the variations seen on timescales of longer than the stellar pulsation period. We propose the existence of long-living regions in the shells, which maintain favourable excitation conditions on timescales of the wind-crossing times through the shells or orbital periods of (sub)stellar companions. The H2O maser properties in these two Mira variables are remarkably similar to those in the semiregular variables studied in our previous papers regarding shell location, outflow velocity, and lifetime. The only difference is the regular brightness variations of the Mira variables caused by the periodic pulsation of the stars.
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| 27. |
- Winnberg, Anders, 1937, et al.
(author)
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Water Vapour Masers in the Mira Variable U Herculis
- 2011
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In: Proceedings from conference Why Galaxies Care about AGB stars II, in Vienna 16 - 20 August 2010; published in Astronomical Society of the Pacific conf series, vol 445. ; 445, s. 375-376
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Conference paper (other academic/artistic)
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