- ID:
- ivo://CDS.VizieR/J/A+A/325/255
- Title:
- 5cm OH masers survey
- Short Name:
- J/A+A/325/255
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have undertaken a comprehensive search for 5 cm OH masers in regions visible from Effelsberg with the 100-m telescope (i.e., those with declinations above -29^o^). Our sample is based on bright sources taken from the IRAS Point Source Catalog and/or from previous 18cm OH and H_ 2_O surveys. Among the 165 sources observed, 16 are new (15 exhibit emission and one source shows both absorption and emission). Two new absorption line sources have been tentatively detected. The general properties of the 5cm OH sources are presented and discussed. The 6035MHz line is more often detected than the 6031MHz line. Nevertheless, the latter line is frequently present, a fact that is not explained by present OH excitation models. Simple calculations tend to show that there are enough FIR photons to pump the 6035 and 6031MHz masers, and we found that the statistics of the ratio S_ radio_/S_ IR_ at 18, 5 and 6cm suggest that the maser pumping efficiency decreases with increasing OH excitation. Variability on short (months) or long (years) time-scales is a common feature in many 5 cm OH sources. We also present observations of the 6 GHz satellite lines and report, besides W3(OH), on two certain and perhaps two newly detected weak sources. Some implications on the excitation of OH are briefly discussed.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/463/205
- Title:
- CS and NH3 Survey of H2O Maser Emission
- Short Name:
- J/ApJ/463/205
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- CS J=1-0 and NH(J,K)=(1,1) observations toward a large sample of H2O maser regions are reported. A total of 172 sources were observed. 107 were observed in CS and 164 in NH_3_. The main purpose of this work was to study the relationship between the parameters that characterize the high velocity H2O maser emission, which originates in very small (about 10 AU) and very dense (10^7-10^9/cm^3^) regions, and those that characterize the molecular emission coming from quiescent, more extended (0.1-1.0 pc) high density (10^4-10^5/cm^3^) regions, traced by the CS and NH_3_ emissions. The observations were carried out between 1986 and 1990 with the 37 m radio telescope at Haystack Observatory The emission of the (J,K)=(1,1) inversion transition of the NH_3_ molecule at 23.694496 GHz, and the emission of the J=1->0 rotational transition of the CS molecule at 48.990968 GHz were observed.
- ID:
- ivo://CDS.VizieR/J/A+A/582/A68
- Title:
- Database of circumstellar OH masers
- Short Name:
- J/A+A/582/A68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new database of circumstellar OH masers at 1612, 1665, and 1667MHz in the Milky Way galaxy. The database (version 2.4) contains 13655 observations and 2341 different stars detected in at least one transition. Detections at 1612MHz are considered to be complete until the end of 2014 as long as they were published in refereed papers. Detections of the main lines (1665 and 1667MHz) and non-detections in all transitions are included only if published after 1983. The database contains flux densities and velocities of the two strongest maser peaks, the expansion velocity of the shell, and the radial velocity of the star. Links are provided for about 100 stars (<5% of all stars with OH masers) to interferometric observations and monitoring programs of the maser emission published since their beginnings in the 1970s. Access to the database is possible over the Web (www.hs.uni-hamburg.de/maserdb), allowing cone searches for individual sources and lists of sources. A general search is possible in selected regions of the sky and by defining ranges of flux densities and/or velocities. Alternative ways to access the data are via the German Virtual Observatory and the CDS.
- ID:
- ivo://CDS.VizieR/J/A+AS/124/385
- Title:
- Dense molecular cores. V.
- Short Name:
- J/A+AS/124/385
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of the observations of 17 molecular clouds associated with bright FIR sources in the NH_3_ (1, 1) and (2, 2) lines with the 100-m radio telescope in Effelsberg. The lines were detected in 11 clouds and 10 of them have been mapped in these lines. The kinetic temperatures, sizes, masses and mean densities of the ammonia cores have been derived. For most of the detected clouds the masses derived under the assumption of a relative ammonia abundance of {chi}(NH_3_)=3x10^-8^ are close to virial masses. However, in S 88 B the ratio M/M_vir_ is only ~0.1 and in a few other cases this ratio is significantly lower than unity which may indicate ammonia underabundance. Almost all objects with the signs of underabundance are among the most luminous IR sources in our sample. Most of the mapped cores are elongated with noticeable velocity gradients along the major axis. The most prominent example is S 255. S 87 has a two-component structure with 2 distinct velocity components which overlap partly spatially. In about half of the mapped sources the NH_3_ line widths increase near the peaks of the ammonia emission. The kinetic temperatures are centrally peaked. They reach 20-28K in the centre and drop to 15-20K at the edges of the ammonia emitting regions. In S 76 E a weak extended emission in the (1, 1) line at the velocity blue-shifted by ~5km/s relative to the core emission was detected. Hyperfine intensity anomalies in the (1, 1) transition were found in S 199 in addition to the known case of these anomalies in S 87.
- ID:
- ivo://CDS.VizieR/J/A+AS/133/337
- Title:
- Dense molecular cores. VII.
- Short Name:
- J/A+AS/133/337
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We searched the IRAS point source catalogue (Cat. <II/125>) for possible associations with our targets. In table 2, we list the sources from this catalogue located within 5' from the maser positions. They are present in all cases except G 145.39+4.00.
- ID:
- ivo://CDS.VizieR/J/A+A/486/191
- Title:
- Distances towards 6.7GHz methanol masers
- Short Name:
- J/A+A/486/191
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Distances to most star forming regions are determined using kinematics, through the assumption that the observed radial velocity arises from the motion of the source with respect to the Sun resulting from the differential rotation of Galaxy. The primary challenge associated with the application of this technique in the inner Galaxy is the kinematic distance ambiguity. In this work, we aim to resolve the kinematic distance ambiguity towards a sample of 6.7GHz methanol masers, which are signposts of the early stages of massive star formation. We measured 21cm HI absorption spectra using the Very Large Array in C and CnB configurations. A comparison of the maximum velocity of HI absorption with the source velocity and tangent point velocity was used to resolve the kinematic distance ambiguity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/451/74
- Title:
- Excited-state hydroxyl maser polarimetry
- Short Name:
- J/MNRAS/451/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present polarimetric maser observations with the Australia Telescope Compact Array of excited-state hydroxyl (OH) masers. We observed 30 fields of OH masers in full Stokes polarization with the Compact Array Broadband Backend at both the 6030 and 6035 MHz excited-state OH transitions, and the 6668 MHz methanol maser transition, detecting 70 sites of maser emission. Amongst the OH we found 112 Zeeman pairs, of which 18 exhibited candidate {pi} components. This is the largest single full polarimetric study of multiple sites of star formation for these frequencies, and the rate of 16 percent {pi} components clearly indicates that the {pi} component exists, and is comparable to the percentage recently found for ground-state transitions. This significant percentage of {pi} components, with consistent proportions at both ground- and excited-state transitions, argues against Faraday rotation suppressing the {pi} component emission. Our simultaneous observations of methanol found the expected low level of polarization, with no circular detected, and linear only found at the =<10 percent level for the brightest sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/678/96
- Title:
- Extragalactic H2O masers
- Short Name:
- J/ApJ/678/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Green Bank Telescope, we conducted a "snapshot" survey for water maser emission toward the nuclei of 611 galaxies and detected eight new sources. The sample consisted of nearby (v<5000km/s) and luminous (M_B_<-19.5) galaxies, some with known nuclear activity but most not previously known to host AGNs. Our detections include both megamasers associated with AGNs and relatively low luminosity masers probably associated with star formation. The detection in UGC 3789 is particularly intriguing because the spectrum shows both systemic and high-velocity lines indicative of emission from an AGN accretion disk seen edge-on. Based on 6 months of monitoring, we detected accelerations among the systemic features ranging from 2 to 8km/s/yr, the larger values belonging to the most redshifted systemic components. High-velocity maser lines in UGC 3789 show no detectable drift over the same period. Although UGC 3789 was not known to be an AGN prior to this survey, the presence of a disk maser is strong evidence for nuclear activity, and an optical spectrum obtained later has confirmed it. With follow-up observations, it may be possible to measure a geometric distance to UGC 3789.
- ID:
- ivo://CDS.VizieR/J/ApJS/160/220
- Title:
- Full-polarization observations of OH masers
- Short Name:
- J/ApJS/160/220
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present full-polarization VLBA maps of the ground-state, main-line, ^2^{Pi}_3/2_, J=3/2 OH masers in 18 Galactic massive star-forming regions. This is the first large polarization survey of interstellar hydroxyl masers at VLBI resolution. A total of 184 Zeeman pairs are identified, and the corresponding magnetic field strengths are indicated. We also present spectra of the NH_3_ emission or absorption in these star-forming regions.
- ID:
- ivo://CDS.VizieR/J/A+A/650/A142
- Title:
- G24.78+0.08 A1 ALMA images and datacubes
- Short Name:
- J/A+A/650/A142
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Hyper-compact (HC) or ultra-compact HII regions are the first manifestations of the radiation feedback from a newly born massive star. Therefore, their study is fundamental to understanding the process of massive (>=8M_{sun}_) star formation. We employed Atacama Large Millimeter/submillimeter Array (ALMA) 1.4mm Cycle 6 observations to investigate at high angular resolution (~0.050, corresponding to 330au) the HC HII region inside molecular core A1 of the high-mass star-forming cluster G24.78+0.08. We used the H30{alpha} emission and different molecular lines of CH_3_CN and ^13^CH_3_CN to study the kinematics of the ionized and molecular gas, respectively. At the center of the HC HII region, at radii <~500au, we observe two mutually perpendicular velocity gradients, which are directed along the axes at PA=39{deg} and PA=133{deg}, respectively. The velocity gradient directed along the axis at PA=39{deg} has an amplitude of 22km/s/mpc, which is much larger than the other;s, 3km/s/mpc. We interpret these velocity gradients as rotation around, and expansion along, the axis at PA=39{deg}. We propose a scenario where the H30{alpha} line traces the ionized heart of a disk-jet system that drives the formation of the massive star (~20M_{sun}_) responsible for the HC HII region. Such a scenario is also supported by the position-velocity plots of the CH_3_CN and ^13^CH_3_CN lines along the axis at PA=133{deg}, which are consistent with Keplerian rotation around a 20M_{sun}_ star. Toward the HC HII region in G24.78+0.08, the coexistence of mass infall (at radii of ~5000au), an outer molecular disk (from <~4000 au to >~500au), and an inner ionized disk (<~500au) indicates that the massive ionizing star is still actively accreting from its parental molecular core. To our knowledge, this is the first example of a molecular disk around a high-mass forming star that, while becoming internally ionized after the onset of the HII region, continues to accrete mass onto the ionizing star.
