6.7 GHz variability characteristics of new periodic methanol maser sources

ABSTRACT Discovery of periodic maser emission was an unexpected result from monitoring observations of methanol transitions in high-mass young stellar objects. We report on the detection of five new periodic sources from a monitoring program with the Torun 32 m telescope. Variability with a period of 149 to 540 d and different patterns from sinusoidal-like to intermittent was displayed. Three-dimensional structure of G59.633−0.192 determined from the time delays of burst peaks of the spectral features and high angular resolution map implies that the emission traces a disc. For this source the 6.7 GHz light curve followed the infrared variability supporting a radiative scheme of pumping. An unusual time delay of ∼80 d occurred in G30.400−0.296 could not be explained by the light travel time and may suggest a strong differentiation of physical conditions and excitation in this deeply embedded source. Our observations suggest the intermittent variability may present a simple response of maser medium to the underlying variability induced by the accretion luminosity while other variability patterns may reflect more complex changes in the physical conditions.

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A wide survey for circumstellar disks in the Lupus complex

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936756 ◽

2020 ◽

Vol 642 ◽

pp. A86

Author(s):

P. S. Teixeira ◽

A. Scholz ◽

J. Alves

Keyword(s):

Three Dimensional ◽

Circumstellar Disks ◽

Young Stellar Objects ◽

Dimensional Structure ◽

Spectral Energy ◽

Mass Star ◽

Nearby Star ◽

Stellar Objects ◽

Star Forming ◽

Low Mass

Previous star formation studies have, out of necessity, often defined a population of young stars confined to the proximity of a molecular cloud. Gaia allows us to examine a wider, three-dimensional structure of nearby star forming regions, leading to a new understanding of their history. We present a wide-area survey covering 494 deg2 of the Lupus complex, a prototypical low-mass star forming region. Our survey includes all known molecular clouds in this region as well as parts of the Upper Scorpius and Upper Centaurus Lupus (UCL) groups of the Sco-Cen complex. We combine Gaia DR2 proper motions and parallaxes as well as ALLWISE mid-infrared photometry to select young stellar objects (YSOs) with disks. The YSO ages are inferred from Gaia color-magnitude diagrams, and their evolutionary stages from the slope of the spectral energy distributions. We find 98 new disk-bearing sources. Our new sample includes objects with ages ranging from 1 to 15 Myr and masses ranging from 0.05 to 0.5 M⊙, and consists of 56 sources with thick disks and 42 sources with anemic disks. While the youngest members are concentrated in the clouds and at distances of 160 pc, there is a distributed population of slightly older stars that overlap in proper motion, spatial distribution, distance, and age with the Lupus and UCL groups. The spatial and kinematic properties of the new disk-bearing YSOs indicate that Lupus and UCL are not distinct groups. Our new sample comprises some of the nearest disks to Earth at these ages, and thus provides an important target for follow-up studies of disks and accretion in very low mass stars, for example with ALMA and ESO-VLT X-shooter.

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NIR integral field spectroscopy of high mass young stellar objects

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313000343 ◽

2012 ◽

Vol 8 (S292) ◽

pp. 53-53

Author(s):

K. Murakawa ◽

S. L. Lumsden ◽

R. D. Oudmaijer ◽

B. Davies ◽

M. G. Hoare

Keyword(s):

Gas Phase ◽

Adaptive Optics ◽

Three Dimensional ◽

Young Stellar Objects ◽

High Mass ◽

Spectral Features ◽

Stellar Objects ◽

Integral Field Spectroscopy ◽

Field Spectroscopy ◽

Integral Field

AbstractWe present K-band Integral Field Spectroscopy of six high mass young stellar objects (IRAS~18151–1208, AFGL~2136, S106~IRS4, V645 Cyg, IRAS~19065+0526, and G082.5682+ 00.4040) obtained using the adaptive optics assisted NIFS instrument mounted on the Gemini North telescope. The targets are chosen from the Red MSX Source survey led by University of Leeds. The data show the spectral features of Brγ, H2, and gas phase CO emissions and absorptions with a spectral resolution of R ≈ 5500, which allow a three-dimensional spectro-astrometric analysis of the line emissions. We discuss the results of the ionized jets and winds, and rotating CO torus.

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A search for the OH 6035 MHz line in high-mass star-forming regions

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039009 ◽

2020 ◽

Vol 642 ◽

pp. A145

Author(s):

M. Szymczak ◽

P. Wolak ◽

A. Bartkiewicz ◽

M. Aramowicz ◽

M. Durjasz

Keyword(s):

Young Stellar Objects ◽

High Mass ◽

Mass Star ◽

General Increase ◽

Stellar Objects ◽

Star Forming ◽

Physical Conditions ◽

Star Forming Regions ◽

Maser Line ◽

Variability Index

Context. The excited states of OH masers detected in the environment of high-mass young stellar objects (HMYSOs) are important for improving our understanding of the physical conditions of these objects and also provide information about their magnetic fields. Aims. We aim to search for excited-state OH 6035 MHz maser emission in HMYSOs which might have escaped detection in previous surveys or were never searched for. Methods. A sample of HMYSOs derived from untargeted surveys of the 6668 MHz methanol maser line was observed at 6035 MHz OH transition with the Torun 32 m radio telescope. The 6035 MHz detections were observed in the OH 6031 MHz line. Two-thirds of the detections were observed at least three times over a two-year period. Results. Out of 445 targets, 37 were detected at 6035 MHz, including seven new discoveries. The 6031 MHz line was detected towards ten 6035 MHz sources, one of which was not previously reported. All the newly detected sources are faint with the peak flux density lower than 4 Jy and show significant or high variability on timescales of 4 to 20 months. Zeeman pair candidates identified in three new sources imply a magnetic field intensity of 2–11 mG. Comparison of our spectra with those obtained ~10 yr ago indicates different degrees of variability but there is a general increase in the variability index on an ~25 yr timescale, usually accompanied by significant changes in the profile shape.

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Principal component analysis tomography in near-infrared integral field spectroscopy of young stellar objects – I. Revisiting the high-mass protostar W33A

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab358 ◽

2021 ◽

Vol 503 (1) ◽

pp. 270-291

Author(s):

F Navarete ◽

A Damineli ◽

J E Steiner ◽

R D Blum

Keyword(s):

Large Scale ◽

Near Infrared ◽

Rotation Axis ◽

Principal Component ◽

Young Stellar Objects ◽

High Mass ◽

Continuum Emission ◽

Rotating Disc ◽

Stellar Objects ◽

K Band

ABSTRACT W33A is a well-known example of a high-mass young stellar object showing evidence of a circumstellar disc. We revisited the K-band NIFS/Gemini North observations of the W33A protostar using principal components analysis tomography and additional post-processing routines. Our results indicate the presence of a compact rotating disc based on the kinematics of the CO absorption features. The position–velocity diagram shows that the disc exhibits a rotation curve with velocities that rapidly decrease for radii larger than 0.1 arcsec (∼250 au) from the central source, suggesting a structure about four times more compact than previously reported. We derived a dynamical mass of 10.0$^{+4.1}_{-2.2}$ $\rm {M}_\odot$ for the ‘disc + protostar’ system, about ∼33 per cent smaller than previously reported, but still compatible with high-mass protostar status. A relatively compact H2 wind was identified at the base of the large-scale outflow of W33A, with a mean visual extinction of ∼63 mag. By taking advantage of supplementary near-infrared maps, we identified at least two other point-like objects driving extended structures in the vicinity of W33A, suggesting that multiple active protostars are located within the cloud. The closest object (Source B) was also identified in the NIFS field of view as a faint point-like object at a projected distance of ∼7000 au from W33A, powering extended K-band continuum emission detected in the same field. Another source (Source C) is driving a bipolar $\rm {H}_2$ jet aligned perpendicular to the rotation axis of W33A.

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High-Angular Resolution Near-Infrared Observations of the Circumstellar Environment of Young Stellar Objects

The Role of Dust in the Formation of Stars - ESO Astrophysics Symposia ◽

10.1007/978-3-540-68594-4_1 ◽

1996 ◽

pp. 3-6

Author(s):

N. Ageorges ◽

A. Eckart

Keyword(s):

Near Infrared ◽

Angular Resolution ◽

Young Stellar Objects ◽

High Angular Resolution ◽

Stellar Objects ◽

Infrared Observations ◽

Circumstellar Environment

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Modeling Outflows from Young Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900241776 ◽

2004 ◽

Vol 221 ◽

pp. 351-358

Author(s):

Hsien Shang

Keyword(s):

Real Data ◽

Young Stars ◽

Young Stellar Objects ◽

High Angular Resolution ◽

Stellar Objects ◽

High Resolution Data ◽

Radiative Processes ◽

Theoretical Predictions ◽

Consistent Manner ◽

Multi Wavelength

We have constructed the foundations to a series of diagnostics methods to probe the jet phenomena in young stars as observed at various optical forbidden lines and radio wavelengths. We calculate and model in a self-consistent manner the physical and radiative processes, which arise within an inner disk-wind driven magnetocentrifugally from the circumstellar accretion disk of a sun-like star. Comparing with real data taken at high angular resolution, our approach will provide the basis of systematic diagnostics for jets and their related young stellar objects, to attest the emission mechanisms of such phenomena. Such approach can help bring first-principle theoretical predictions to confront actual multi-wavelength observations, and will bridge the link between complex numerical simulations and observational data. Analysis methods discussed here are immediately applicable to new high-resolution data obtained with HST, Adaptic Optics, and radio interferometry.

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Water fountains: bipolar fast stellar jets traced by water vapor maser emission

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312019746 ◽

2012 ◽

Vol 8 (S290) ◽

pp. 227-228

Author(s):

Hiroshi Imai

Keyword(s):

Active Galactic Nuclei ◽

Galactic Nuclei ◽

Asymptotic Giant Branch ◽

Young Stellar Objects ◽

Agb Stars ◽

Stellar Objects ◽

Stellar Jets ◽

The Masses ◽

Host Stars ◽

Maser Sources

AbstractHighly collimated, bipolar fast jets are found in asymptotic giant branch (AGB) and post-AGB stars as well as in active galactic nuclei and young stellar objects. It is still unclear how to launch such jets from dying stars that were originally spherically symmetric. Exploration of the stellar jet evolution is also expected to probe its role in shaping a planetary nebula. Interestingly, some of stellar H2O maser sources — water fountains — exhibit stellar jets with spatially and kinematically high collimation in the earliest phase (<1000 years) of the jet evolution. Such water fountains have been identified in 14 sources to date. We have recently conducted interferometric (VLBA, EVN, VERA, VLA) maser and the single-dish (ASTE) CO J = 3 → 2 line observations of the water fountains. They have revealed a typical dynamical age (< 100 yr) and the detailed kinematical structures of the water fountains, possibility of the coexistence of “equatorial flows”, and their locations and kinematics in the Milky Way. Based on these results, the masses and evolutionary statuses of the host stars are also estimated.

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Protostellar Outflows at the EarliesT Stages (POETS)

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037472 ◽

2020 ◽

Vol 635 ◽

pp. A118

Author(s):

L. Moscadelli ◽

A. Sanna ◽

C. Goddi ◽

V. Krishnan ◽

F. Massi ◽

...

Keyword(s):

Thermal Emission ◽

Three Dimensional ◽

Radio Continuum ◽

Young Stellar Objects ◽

High Mass ◽

Proper Motions ◽

Long Baseline ◽

Protostellar Outflows ◽

Water Masers ◽

Water Maser

Context. 22 GHz water masers are the most intense and widespread masers in star-forming regions. They are commonly associated with protostellar winds and jets emerging from low- and high-mass young stellar objects (YSO). Aims. We wish to perform for the first time a statistical study of the location and motion of individual water maser cloudlets, characterized by typical sizes that are within a few au, with respect to the weak radio thermal emission from YSOs. Methods. For this purpose, we have been carrying out the Protostellar Outflows at the EarliesT Stages survey of a sample (38) of high-mass YSOs. The 22 GHz water maser positions and three-dimensional (3D) velocities were determined through multi-epoch Very Long Baseline Array observations with accuracies of a few milliarcsec (mas) and a few km s−1, respectively. The position of the ionized core of the protostellar wind, marking the YSO, was determined through sensitive radio continuum, multi-frequency Jansky Very Large Array observations with a typical error of ≈20 mas. Results. The statistic of the separation of the water masers from the radio continuum shows that 84% of the masers are found within 1000 au from the YSO and 45% of them are within 200 au. Therefore, we can conclude that the 22 GHz water masers are a reliable proxy for locating the position of the YSO. The distribution of maser luminosity is strongly peaked towards low values, indicating that about half of the maser population is still undetected with the current Very Long Baseline Interferometry detection thresholds of 50–100 mJy beam−1. Next-generation, sensitive (at the nJy level) radio interferometers will have the capability to exploit these weak masers for an improved sampling of the velocity and magnetic fields around the YSOs. The average direction of the water maser proper motions provides a statistically-significant estimate for the orientation of the jet emitted by the YSO: 55% of the maser proper motions are directed on the sky within an angle of 30° from the jet axis. Finally, we show that our measurements of 3D maser velocities statistically support models in which water maser emission arises from planar shocks with propagation direction close to the plane of the sky.

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Bipolar H II regions

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833015 ◽

2018 ◽

Vol 617 ◽

pp. A67 ◽

Cited By ~ 7

Author(s):

M. R. Samal ◽

L. Deharveng ◽

A. Zavagno ◽

L. D. Anderson ◽

S. Molinari ◽

...

Keyword(s):

Star Formation ◽

Molecular Cloud ◽

Galactic Plane ◽

Three Dimensional ◽

Young Stellar Objects ◽

Formation Processes ◽

Two Dimensional ◽

Stellar Objects ◽

Flat Structures ◽

Exciting Star

Aims. We aim to identify bipolar Galactic H II regions and to understand their parental cloud structures, morphologies, evolution, and impact on the formation of new generations of stars. Methods. We use the Spitzer-GLIMPSE, Spitzer-MIPSGAL, and Herschel-Hi-GAL surveys to identify bipolar H II regions and to examine their morphologies. We search for their exciting star(s) using NIR data from the 2MASS, UKIDSS, and VISTA surveys. Massive molecular clumps are detected near these bipolar nebulae, and we estimate their temperatures, column densities, masses, and densities. We locate Class 0/I young stellar objects (YSOs) in their vicinities using the Spitzer and Herschel-PACS emission. Results. Numerical simulations suggest bipolar H II regions form and evolve in a two-dimensional flat- or sheet-like molecular cloud. We identified 16 bipolar nebulae in a zone of the Galactic plane between ℓ ± 60° and |b| < 1°. This small number, when compared with the 1377 bubble H II regions in the same area, suggests that most H II regions form and evolve in a three-dimensional medium. We present the catalogue of the 16 bipolar nebulae and a detailed investigation for six of these. Our results suggest that these regions formed in dense and flat structures that contain filaments. We find that bipolar H II regions have massive clumps in their surroundings. The most compact and massive clumps are always located at the waist of the bipolar nebula, adjacent to the ionised gas. These massive clumps are dense, with a mean density in the range of 105 cm−3 to several 106 cm−3 in their centres. Luminous Class 0/I sources of several thousand solar luminosities, many of which have associated maser emission, are embedded inside these clumps. We suggest that most, if not all, massive 0/I YSO formation has probably been triggered by the expansion of the central bipolar nebula, but the processes involved are still unknown. Modelling of such nebula is needed to understand the star formation processes at play.

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