- ID:
- ivo://CDS.VizieR/J/MNRAS/377/571
- Title:
- GLIMPSE 6.7GHz methanol masers non-detections
- Short Name:
- J/MNRAS/377/571
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The University of Tasmania Mt Pleasant 26-m and Ceduna 30-m radio telescopes have been used to search for 6.7-GHz class II methanol masers towards 200 GLIMPSE (The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) sources. The target regions were selected on the basis of their mid-infrared colours as being likely to be young high-mass star formation regions and are either bright at 8.0{mu}m, or have extreme [3.6]-[4.5] colour. Methanol masers were detected towards 38 sites, nine of these being new detections. The prediction was that approximately 20 new 6.7-GHz methanol masers would be detected within 3.5-arcmin of the target GLIMPSE sources, but this is the case for only six of the new detections. A number of possible reasons for the discrepancy between the predicted and actual number of new detections have been investigated. It was not possible to draw any firm conclusions as to the cause, but it may be because many of the target sources are at an evolutionary phase prior to that associated with 6.7-GHz methanol masers. Through comparison of the spectra collected as part of this search with those in the literature, the average lifetime of individual 6.7-GHz methanol maser spectral features is estimated to be around 150yr, much longer than is observed for 22-GHz water masers.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/634/A41
- Title:
- G107.298+5.639 multi-frequency maser light curves
- Short Name:
- J/A+A/634/A41
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Periodic flares of maser emission are thought to be induced either by variations of the seed photon flux in young binary systems or the pump rate regulated by stellar and accretion luminosities. We seek to study the variability of four maser transitions of three different species in G107.298+5.639 to constrain the dominant mechanism of periodic flares. Light curves of the 6.7GHz methanol and 22.2GHz water vapour maser were obtained with the Torun 32m radio telescope over 39 and 34 cycles, respectively. The target was also monitored at the 1.6GHz hydroxyl transitions with the Nancay radio telescope over 13 cycles. All these maser lines were imaged using VLBI arrays. The study confirms alternating flares of the methanol and water masers with a period of 34.4d and reveals the synchronised behaviour of the methanol and hydroxyl masers in this source. The observed spatial distribution of the methanol maser cloudlets and the measured time delays of the flares of individual features imply a ring-like structure of radius 240au and thickness 30au. Internal proper motions indicate that the velocity of methanol cloudlets is dominated by a disc-wind component of about 5km/s. The methanol emission detected during only one VLBI observation is located in a region about 550 au from a central star, which also exhibits OH maser flares. The erratic appearance of methanol features can be related to a powering object of relatively low luminosity which, during some variability cycles, can excite molecules only in the nearest part of the disc. A careful analysis of the maser and infrared light curves reveal a strong correlation between the 6.7GHz line and the infrared flux densities supporting a radiative pumping of the maser. The synchronised behaviour of the hydroxyl 1665/1667MHz and 6.7GHz methanol transitions indicates a common pumping mechanism for the periodic flares of G107.298+5.639.
- ID:
- ivo://CDS.VizieR/J/ApJ/647/418
- Title:
- Ground-state OH masers in W3(OH) study
- Short Name:
- J/ApJ/647/418
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present VLBA observations of the ground-state hydroxyl masers in W3(OH) at 0.02km/s spectral resolution. Over 250 masers are detected, including 56 Zeeman pairs. Line shapes are predominantly Gaussian or combinations of several Gaussians, with normalized deviations typically of the same magnitude as in masers in other species.
- ID:
- ivo://CDS.VizieR/J/A+A/469/207
- Title:
- High-resolution images in Cep-A HW2 region
- Short Name:
- J/A+A/469/207
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Due to its relatively small distance (725pc), the Cepheus A East star-forming region is an ideal laboratory to study massive star formation processes. Based on its morphology, it has been suggested that the flattened molecular gas distribution around the YSO HW2 may be a 350-AU-radius massive protostellar disk. The goal of our work is to ascertain the nature of this structure. We have employed the Plateau de Bure Interferometer to acquire (sub-)arcsecond-resolution imaging of high-density and shock tracers, such as methyl cyanide (CH3CN) and silicon monoxide (SiO), towards the HW2 position. On the 1" scale, the flattened distribution of molecular gas around HW2 appears to be due to the projected superposition, on the plane of the sky, of at least three protostellar objects, of which at least one is powering a molecular outflow at a small angle with respect to the line of sight. The presence of a protostellar disk around HW2 is not ruled out.
- ID:
- ivo://CDS.VizieR/J/ApJS/209/25
- Title:
- H_2_O + CH_3_OH maser survey of Orion protostars
- Short Name:
- J/ApJS/209/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a maser survey toward 99 protostars in the Orion molecular cloud complex are presented. The target sources are low-mass protostars identified from infrared observations. Single-dish observations were carried out in the water maser line at 22GHz and the methanol class I maser lines at 44, 95, and 133GHz. Most of the detected sources were mapped to determine the source positions. Five water maser sources were detected, and they are excited by HH 1-2 VLA 3, HH 1-2 VLA 1, L1641N MM1/3, NGC 2071 IRS 1/3, and an object in the OMC 3 region. The water masers showed significant variability in intensity and velocity with time scales of 1 month or shorter. Four methanol emission sources were detected, and those in the OMC 2 FIR 3/4 and L1641N MM1/3 regions are probably masers. The methanol emission from the other two sources in the NGC 2071 IRS 1-3 and V380 Ori NE regions are probably thermal. For the water masers, the number of detections per protostar in the survey region is about 2%, which suggests that the water masers of low-mass protostars are rarely detectable. The methanol class I maser of low-mass protostars is an even rarer phenomenon, with a detection rate much smaller than 1%.
- ID:
- ivo://CDS.VizieR/J/ApJ/658/1096
- Title:
- H2O maser classification
- Short Name:
- J/ApJ/658/1096
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of 22GHz H2O maser observations of a sample of 85 post-asymptotic giant branch (post-AGB) candidate stars, selected on the basis of their OH 1612MHz maser and far-infrared properties. All sources were observed with the Tidbinbilla 70m radio telescope, and 21 detections were made; 86GHz SiO Mopra observations of a subset of the sample are also presented.
- ID:
- ivo://CDS.VizieR/J/ApJ/669/424
- Title:
- H2O maser emissions of IRAS 19134+2131
- Short Name:
- J/ApJ/669/424
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Very Long Baseline Array at six epochs, we have observed H_2_O maser emission in the preplanetary nebula IRAS 19134+2131 (I19134), in which the H_2_O maser spectrum has two groups of emission features separated in radial velocity by ~100km/s. We also obtained optical images of I19134 with the Hubble Space Telescope to locate the bipolar reflection nebula in this source for the first time.
- ID:
- ivo://CDS.VizieR/J/MNRAS/430/1309
- Title:
- H_2_O masers in AFGL 2591 VLA 3-N
- Short Name:
- J/MNRAS/430/1309
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we analyse multi-epoch very long baseline interferometry water maser observations carried out with the Very Long Baseline Array towards the high-mass star-forming region AFGL 2591. We detected maser emission associated with the radio continuum sources VLA 2 and VLA 3. In addition, a water maser cluster, VLA 3-N, was detected ~0.5arcsec north of VLA 3. We concentrate the discussion of this paper on the spatio-kinematical distribution of the water masers towards VLA 3-N. The water maser emission towards the region VLA 3-N shows two bow-shock-like structures, northern and southern, separated from each other by ~100mas (~330AU). The spatial distribution and kinematics of the water masers in this cluster have persisted over a time span of 7yr. The northern bow shock has a somewhat irregular morphology, while the southern one has a remarkably smooth morphology. We measured the proper motions of 33 water maser features, which have an average proper motion velocity of ~1.3mas/yr (~20km/s). The morphology and the proper motions of this cluster of water masers show systematic expanding motions that could imply one or two different centres of star formation activity. We made a detailed model for the southern structure, proposing two different kinematic models to explain the three-dimensional spatio-kinematical distribution of the water masers: (1) a static central source driving the two bow-shock structures and (2) two independent driving sources, one of them exciting the northern bow-shock structure, and the other one, a young runaway star moving in the local molecular medium exciting and moulding the remarkably smoother southern bow-shock structure. Future observations will be necessary to discriminate between the two scenarios, in particular by identifying the still unseen driving source(s).
- ID:
- ivo://CDS.VizieR/J/A+A/291/261
- Title:
- H2O masers in HII regions
- Short Name:
- J/A+A/291/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a survey of 22.2GHz H2O maser emission towards a large sample of HII regions (427) detected in hydrogen recombination lines (Lockman) are presented. The sample favours classical HII regions with large excitation parameter. We found 68 water maser sources, 17 of which are new detections. Adding the detections found in the literature, the total number of masers associated with the sample is 80. The overall maser percentage is low (19%), much less than what found in samples of ultracompact (UC) HII regions. The percentage changes if we divide our sample into two sub-classes: HII regions known to have ultracompact components (i.e. where a younger generation of star formation is also present) and the rest. In the first sub-class the maser percentage is 28%, in the second 15%. The total number of masers in HII regions where no UC component has been (so far) reported is 43. This value is greater than that expected from the ratio between the lifetime of the HII region (10^6^yr) and that of the maser phase, even assuming a maser lifetime as long as 10^5^yr. This implies that maser excitation (and star formation) occurs several times in the lifetime of the same star forming complex. From 410 positions observed, 230 can be associated with a high degree of confidence to an IRAS Point Source. We expect that most of the HII regions not associated with IRAS PS are diffuse regions in the last phases of their evolution. The percentage of water masers in this sub-class is very low: 8%. The number of masers with no counterpart in the Lockman sample (and above Dec=-30{deg}) is very large: 334. This number most probably reflects the extreme high density conditions known to exist in the earliest phases of an HII region, which strongly reduce its radio continuum and line emission. The analysis of a homogeneous sample of classical HII regions allows to confirm in a quantitative fashion the well known result that the maser phenomenon occurs during the earliest phase of the evolution of a massive star and that it fades away as the HII region evolves into the diffuse stage.
- ID:
- ivo://CDS.VizieR/J/ApJ/805/53
- Title:
- H2O masers in W43A monitored with VLBA
- Short Name:
- J/ApJ/805/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the distribution patterns of H_2_O maser features in the "water fountain" source (WF) W43A and show that they are closely related to the early morphological changes in a planetary nebula (PN). Using the Very Long Baseline Array, we have detected detected H_2_O maser features in W43A in 13 epochs across >10yr. W43A is the only WF that has been observed for over a decade. We introduce a new cavity model scenario --a halo with a bipolar evacuated volume that has a partially enhanced wall-- and compare it with the "traditional" precessing jet model particularly in terms of explaining the bow-shaped distribution patterns of H_2_O maser features in the most recent epochs and their temporal evolution. Long-term observations show that the distribution patterns require more than a single jet to form. Moreover, we have identified six groups of H_2_O maser features at both the redshifted and blueshifted sides with point symmetry. The six groups are believed to correspond to periodic mass profiles in the envelope and have recorded the mass-loss history. Together with a geometric similarity to the mid-infrared morphology of W43A, the results suggest that H_2_O masers can be used to trace the inner morphology and rapid temporal changes in evolved stars, especially where the PN shaping has just started.
