scholarly journals KVN Single-dish Water and Methanol Maser Line Surveys of Galactic YSOs

2012 ◽  
Vol 8 (S287) ◽  
pp. 488-491
Author(s):  
Kee-Tae Kim ◽  
Do-Young Byun ◽  
Jae-Han Bae ◽  
Won-Ju Kim ◽  
Hyun-Woo Kang ◽  
...  
Keyword(s):  
Class I ◽  
High Mass ◽  
Evolutionary Stage ◽  
Intermediate Mass ◽  
Detection Rates ◽  
Methanol Maser ◽  
Dense Cores ◽  
The Galaxy ◽  
Maser Line ◽  
Circumstellar Environments

AbstractWe have carried out simultaneous 22 GHz H2O and 44 GHz Class I CH3OH maser line surveys of more than 1500 intermediate- and high-mass YSOs in the Galaxy using newly-constructed KVN 21-m telescopes. As the central (proto)stars evolve, the detection rates of the two masers rapidly decrease for intermediate-mass YSOs while the rates increase for high-mass YSOs. These results suggest that the occurrence of the two masers is closely related both to the evolutionary stage of the central objects and to the circumstellar environments. CH3OH masers always have very similar velocities (<10 km s−1) to the natal dense cores, whereas H2O masers often have significantly different velocities. The isotropic luminosities of both masers are well correlated with the bolometric luminosities of the central (proto)stars.

scholarly journals Nitrogen and hydrogen fractionation in high-mass star-forming cores from observations of HCN and HNC

2018 ◽  
Vol 609 ◽  
pp. A129 ◽  
Author(s):  
L. Colzi ◽  
F. Fontani ◽  
P. Caselli ◽  
C. Ceccarelli ◽  
P. Hily-Blant ◽  
...  
Keyword(s):  
Solar System ◽  
Solar Nebula ◽  
Rotational Transition ◽  
High Mass ◽  
Evolutionary Stage ◽  
Mass Star ◽  
Stellar Cluster ◽  
Star Forming ◽  
Star Forming Regions ◽  
Dense Cores

The ratio between the two stable isotopes of nitrogen, 14N and 15N, is well measured in the terrestrial atmosphere (~272), and for the pre-solar nebula (~441, deduced from the solar wind). Interestingly, some pristine solar system materials show enrichments in 15N with respect to the pre-solar nebula value. However, it is not yet clear if and how these enrichments are linked to the past chemical history because we have only a limited number of measurements in dense star-forming regions. In this respect, dense cores, which are believed to be the precursors of clusters and also contain intermediate- and high-mass stars, are important targets because the solar system was probably born within a rich stellar cluster, and such clusters are formed in high-mass star-forming regions. The number of observations in such high-mass dense cores has remained limited so far. In this work, we show the results of IRAM-30 m observations of the J = 1−0 rotational transition of the molecules HCN and HNC and their 15N-bearing counterparts towards 27 intermediate- and high-mass dense cores that are divided almost equally into three evolutionary categories: high-mass starless cores, high-mass protostellar objects, and ultra-compact Hii regions. We have also observed the DNC(2–1) rotational transition in order to search for a relation between the isotopic ratios D/H and 14N/15N. We derive average 14N/15N ratios of 359 ± 16 in HCN and of 438 ± 21 in HNC, with a dispersion of about 150–200. We find no trend of the 14N/15N ratio with evolutionary stage. This result agrees with what has been found for N2H+ and its isotopologues in the same sources, although the 14N/15N ratios from N2H+ show a higher dispersion than in HCN/HNC, and on average, their uncertainties are larger as well. Moreover, we have found no correlation between D/H and 14N/15N in HNC. These findings indicate that (1) the chemical evolution does not seem to play a role in the fractionation of nitrogen, and that (2) the fractionation of hydrogen and nitrogen in these objects is not related.

Zeeman Effect Observations in Class I Methanol Masers

2018 ◽  
Vol 14 (A30) ◽  
pp. 140-140
Author(s):  
Emmanuel Momjian ◽  
Anuj P. Sarma
Keyword(s):  
Zeeman Effect ◽  
Linear Structure ◽  
Class I ◽  
Star Forming ◽  
Methanol Maser ◽  
Star Forming Regions ◽  
Splitting Factor ◽  
Maser Line ◽  
Methanol Masers ◽  
Expected Values

AbstractWe report the detection of the Zeeman effect in the 44 GHz Class I methanol maser line toward the star forming region DR21W. The 44 GHz methanol masers in this source occur in a ∼3” linear structure that runs from northwest to southeast, with the two dominant components at each end, and several weaker maser components in between. Toward a 93 Jy maser in the dominant northwestern component, we find a significant Zeeman detection of −23.4 ± 3.2 Hz. If we use the recently published result of Lankhaar et al. (2018) that the F=5-4 hyperfine transition is responsible for the 44 GHz methanol maser line, then their value of z = −0.92 Hz mG−1 yields a line-of-sight magnetic field of Blos =25.4 ± 3.5 mG. If Class I methanol masers are pumped in high density regions with n∼107–8 cm−3, then magnetic fields in these maser regions should be a few to several tens of mG. Therefore, our result in DR21W is certainly consistent with the expected values.Using the above noted splitting factor in past Zeeman effect detections in Class I methanol masers reported by Sarma & Momjian (2011) and Momjian & Sarma (2017) in the star forming regions OMC-2 and DR21(OH) result in Blos values of 20.0 ± 1.2 mG and 58.2 ± 2.9 mG, respectively. These are also consistent with the expected values.

scholarly journals Deuterium Fractionation and Ionization Degree in Massive Protostellar/cluster Cores

2012 ◽  
Vol 8 (S292) ◽  
pp. 40-40
Author(s):  
Huei-Ru Chen ◽  
Sheng-Yuan Liu ◽  
Yu-Nung Su
Keyword(s):  
High Mass ◽  
Evolutionary Stage ◽  
Gas Temperature ◽  
Ionization Degree ◽  
Dark Clouds ◽  
Dense Cores ◽  
General Chemical ◽  
Upper Limits ◽  
Cluster Cores ◽  
Infrared Extinction

AbstractWe have conducted a survey of deuterium fractionation of N2H+, RD(N2H+) ≡ N(N2D+)/N(N2H+), with the Arizona Radio Observatory (ARO) Submillimeter Telescope (SMT) to assess the use of RD(N2H+) as an evolutionary tracer among massive protostellar/cluster cores in early stages. Our sample includes 32 dense cores in various evolutionary stages, from high-mass starless cores (HMSCs), high-mass protostellar objects (HMPOs), to ultra-compact (UC) HII regions, in infrared dark clouds (IRDCs) and high infrared extinction clouds. The results show a decreasing trend in deuterium fractionation with evolutionary stage traced by gas temperature and line width (Fig. 1). A moderate increasing trend of deuterium fractionation with the CO depletion factor is also found among cores in IRDCs and HMSCs. These suggest a general chemical behavior of deuterated species in low- and high-mass protostellar candidates. Upper limits to the ionization degree are also estimated to be in the range of 4 × 10−8 − 5 × 10−6.

scholarly journals 44 GHz Methanol Maser Surveys

2012 ◽  
Vol 8 (S287) ◽  
pp. 133-140
Author(s):  
S. E. Kurtz
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Class Ii ◽  
Class I ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Methanol Maser ◽  
Star Forming Regions ◽  
Methanol Masers

AbstractClass I 44 GHz methanol masers are not as well-known, as common, or as bright as their more famous Class II cousins at 6.7 and 12.2 GHz. Nevertheless, the 44 GHz masers are commonly found in high-mass star forming regions. At times they appear to trace dynamically important phenomena; at other times they show no obvious link to the star formation process. Here, we summarize the major observational efforts to date, including both dedicated surveys and collateral observations. The principal results are presented, some that were expected, and others that were unexpected.

scholarly journals An evolutionary sequence for high-mass star formation

2012 ◽  
Vol 8 (S292) ◽  
pp. 39-39
Author(s):  
S. L. Breen ◽  
S. P. Ellingsen
Keyword(s):  
Star Formation ◽  
Strong Evidence ◽  
High Mass ◽  
Evolutionary Stage ◽  
Mass Star ◽  
Evolutionary Sequence ◽  
Subsequent Work ◽  
Star Forming ◽  
Methanol Maser ◽  
Methanol Masers

AbstractDetermining an evolutionary clock for high-mass star formation is an important step towards realizing a unified theory of star formation, as it will enable qualitative studies of the associated high-mass stars to be executed. Our recent studies have shown that masers have great potential to accurately trace the evolution of these regions. We have investigated the relative evolutionary phases associated with the presence of combinations of water, methanol and hydroxyl masers. Comparison between the characteristics of coincident sources has revealed strong evidence for an evolutionary sequence for the different maser species, a result that we now aim to corroborate through comparisons with chemical clocks.Using our new, large samples of methanol masers at 6.7 GHz (MMB survey; Green et al. (2009)) and 12.2 GHz (Breen et al. 2012), 22 GHz water masers (Breen & Ellingsen 2012), OH masers together with complementary data, we find strong evidence that it is not only the presence or absence of the different maser species that indicates the evolutionary stage of the associated high-mass star formation region (see e.g. Breen et al. (2010)), but that the properties of those masers can give even finer evolutionary details. Most notably, the intensity and velocity range of detected maser emission increases as the star forming region evolves (Breen et al. 2011).Subsequent work we have undertaken (Ellingsen et al. 2011) has shown that the presence of rare 37.7 GHz methanol masers may signal the end of the methanol maser phase. They show that 37.7 GHz methanol masers are associated only with the most luminous 6.7 and 12.2 GHz methanol masers, which combined with the rarity of these objects is consistent with them being a short lived phase towards the end of the 6.7 GHz methanol maser lifetime.An independent confirmation of our maser evolutionary timeline can be gained through comparisons with chemical clocks. MALT90 is a legacy survey of 1000s of dense star forming cores at 90GHz, simultaneously observing 16 molecular lines with the Mopra radio telescope (see e.g. Foster et al. 2011). It provides the perfect dataset to test the maser evolutionary timeline due to the targeted lines and the fact that at least one-quarter of the MALT90 sources correspond to maser sites, providing a large enough sample for meaningful analysis. From our preliminary analysis, we find that star formation regions showing similar maser properties also show similar thermal line properties; as would be expected if our evolutionary scenario were accurate.

scholarly journals New class I methanol masers

2012 ◽  
Vol 8 (S287) ◽  
pp. 433-440 ◽  
Author(s):  
M. A. Voronkov ◽  
J. L. Caswell ◽  
S. P. Ellingsen ◽  
S. L. Breen ◽  
T. R. Britton ◽  
...  
Keyword(s):  
Class I ◽  
High Mass ◽  
Mass Star ◽  
Star Forming ◽  
Methanol Maser ◽  
New Class ◽  
Star Forming Regions ◽  
Rare Class ◽  
New Type ◽  
Methanol Masers

AbstractWe review properties of all known collisionally pumped (class I) methanol maser series based on observations with the Australia Telescope Compact Array (ATCA) and the Mopra radio telescope. Masers at 36, 84, 44 and 95 GHz are most widespread, while 9.9, 25, 23.4 and 104 GHz masers are much rarer, tracing the most energetic shocks. A survey of many southern masers at 36 and 44 GHz suggests that these two transitions are highly complementary. The 23.4 GHz maser is a new type of rare class I methanol maser, detected only in two high-mass star-forming regions, G357.97-0.16 and G343.12-0.06, and showing a behaviour similar to 9.9, 25 and 104 GHz masers. Interferometric positions suggest that shocks responsible for class I masers could arise from a range of phenomena, not merely an outflow scenario. For example, some masers might be caused by interaction of an expanding Hii region with its surrounding molecular cloud. This has implications for evolutionary sequences incorporating class I methanol masers if they appear more than once during the evolution of the star-forming region. We also make predictions for candidate maser transitions in the ALMA frequency range.

scholarly journals The Methanol Multibeam Survey: a unique window on high-mass star formation in our Galaxy

2012 ◽  
Vol 8 (S292) ◽  
pp. 79-82
Author(s):  
J. L. Caswell
Keyword(s):  
Mass Range ◽  
High Mass ◽  
Galactic Rotation ◽  
Evolutionary Stage ◽  
Mass Star ◽  
Methanol Maser ◽  
Model Free ◽  
Radio Measurements ◽  
The Many

AbstractThe Methanol Multibeam (MMB) survey has yielded over 1000 masers at the 6668-MHz methanol transition: a near-complete census throughout the Galactic disc, as evident from the discovery statistics, and corroborated by preliminary distance determinations. Each maser pinpoints a massive star in a brief early evolutionary phase. Follow-up comparisons reveal in most cases a matching IR source in the GLIMPSE survey. The methanol masers effectively distinguish the genuine high mass proto-stars from the many thousand IR mimics of similar color. Longer IR wavelength follow-ups by Herschel instruments, and in the radio mm-continuum, will refine the mass-range encompassed by the masers; and, complemented by radio measurements at short cm-wavelengths, will define the evolutionary stage of each site, distinguishing hyper-compact HII regions from an earlier phase. Follow-up studies of key molecular gas tracers, including closely associated masers (other methanol transitions, water and OH), reveal the extent of homogeneity in the population and environments of high mass stars.Distance estimates based on the maser velocities have already allowed useful exploration of Galactic structure. Future astrometric parallax measurements extended to the full maser sample will precisely define the geometry of Galactic spiral arms of our Galaxy and independently define the velocity field, allowing a model-free study of Galactic rotation and dynamics. Associated OH masers (present at about half of the methanol sites) are being exploited to provide the first Galaxy-wide grid of ‘in situ’ magnetic field estimates.Our detailed characterization of the Galactic methanol maser population provides a yardstick for extragalactic comparisons with M31 and the LMC. Notably, our survey of the LMC has shown its methanol maser population to be remarkably small relative to our Galaxy - a likely consequence of low LMC metallicity.

Class II 6.7 GHz Methanol Maser Association with Young Massive Cores Revealed by ALMA

2017 ◽  
Vol 13 (S336) ◽  
pp. 247-250
Author(s):  
James O. Chibueze ◽  
Timea Csengeri ◽  
Ken’ichi Tatematsu ◽  
Tetsuo Hasegawa ◽  
Satoru Iguchi ◽  
...  
Keyword(s):  
Class Ii ◽  
High Mass ◽  
Evolutionary Sequence ◽  
Maser Emission ◽  
Methanol Maser ◽  
Promising Tool ◽  
Dense Cores ◽  
Show Evidence ◽  
Statistical Viewpoint ◽  
Compact Array

AbstractThe association of 6.7 GHz class II methanol (CH3OH) masers with ATLASGAL/ ALMA 0.9 mm massive dense cores is presented in this work from a statistical viewpoint. 42 of the 112 cores (37.5%) detected with the Atacama Compact Array (ACA) excite 6.7 GHz CH3OH masers. ACA cores have offsets 0\rlap.″17 to 4\rlap.″79 from the methanol multibeam survey (MMB), with a median of 2.″19. Approximately 90% of the MMB-associated cores are of masses > 40 M⊙. Because all the cores show evidence of outflow activity, and only a fraction of the cores excited CH3OH masers, we suggest that outflows precede the emergence of maser emission. This first ALMA survey of massive dense cores combined with the MMB survey along with other maser specie surveys is a promising tool to trace the evolutionary sequence of high-mass stars.

scholarly journals Methanol masers in the Herschel era Putting them in the star formation context

2012 ◽  
Vol 8 (S287) ◽  
pp. 492-496
Author(s):  
Michele Pestalozzi
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Galactic Plane ◽  
High Mass ◽  
Space Observatory ◽  
Methanol Maser ◽  
Open Time ◽  
The Galaxy ◽  
Methanol Masers ◽  
Using Data

AbstractMethanol masers are known to be among the most reliable tracers of high-mass stars in early stages of evolution. A number of searches across the Galaxy has yielded to date, a complete census of those masers in two thirds of the Milky Way, providing a catalogue of some 800 sources to be studied in depth. In particular, it is important to characterise the physical properties of the objects hosting methanol masers, and this is possible today using data from the Herschel Space Observatory (HSO). The exceptional spatial resolution of HSO and its wavelength coverage are perfectly tuned to put the methanol maser phase into its star formation context. This paper presents results on the characterisation of methanol maser hosts using Herschel data from the Hi-GAL project, an Open Time Key Project to survey the inner Galactic plane at 5 wavelengths between 70 and 500 μm.

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